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Ⅰ IntroductionThe energy storage units of several devices we come across every day are batteries; they are available in various shapes, sizes, parameters, and shapes. They can usually be found in vehicles, emergency power sources, mobile devices, tablets, iPads, and many other portable electronic devices. But not all devices will use the same type of battery; each device has its own specifications and power supply requirements, and to choose the right battery for your application, you will need a battery selection guide. So, the considerations to consider when choosing a battery for your next electronic product design will be investigated in this post. If you are completely new to batteries, then it is recommended that you read this article on battery types and their applications before continuing further to understand the fundamentals of batteries selection.CatalogⅠ IntroductionⅡ Some Factors to ConsiderⅢ Rechargeable / Non-Rechargeable BatteriesⅣ Availability of SpaceⅤ System Operating VoltageⅥ Operating TemperatureⅦ Capacity-Power & EnergyⅧ ChemistryⅨ CostⅩ Shelf LifeⅪ How to Choose a BatteryⅫ FAQⅡ Some Factors to ConsiderYou must be aware of the important parameters involved in its activity when selecting a battery for your application. The truth of the battery is that, because no battery is ideal, there is no common form of battery for all applications. You should be able to manage the exhaustion of other parameters when you choose to use one parameter of the battery.  For example, if you want your battery to provide a lot of energy for your application, the internal resistance of the cell should be reduced, which can only be accomplished by increasing the surface area of the electrode. Inactive components such as current collectors and conductive aid are also improved by this because energy density is traded off to gain power. You must give up anything to get the other in a battery in order to get exactly what you want in your application. In the following picture, the important battery parameters are given.Now, to understand its significance and effect on battery efficiency during service, let's briefly look at each battery parameter.Ⅲ Rechargeable / Non-Rechargeable BatteriesIn deciding between a main and secondary battery, there might not be much uncertainty, you only have to decide whether you want the battery to be used once or several times. The primary (non-rechargeable) battery can be used for occasional applications such as toys, flashlights, smoke detectors, etc. They are also used in products such as pacemakers, wristwatches and hearing aids where charging is not feasible. The secondary (rechargeable) batteries can be used in applications where a standard power source such as cell phones, computers, cars, etc. is needed. Compared to primary batteries, secondary batteries often have a higher self-discharge rate because of their ability to recharge, which is an ignorant fact.Ⅳ Availability of SpaceThe batteries, including button cells, cylindrical cells, pouch cells and prismatic cells, are available in different shapes and sizes. In order to make your computer comfortably portable, the battery size really matters. AA, AAA and 9V batteries suitable for portable devices are the standard sizes available. In applications where there is less room but more power needed, lithium batteries (pouch type) are widely preferred. If the power demand is lower since they are very lightweight and the smallest of battery types, coin cells may also be considered.Ⅴ System Operating VoltageOne of the most significant characteristics of the battery, which is calculated based on the electrode & electrolyte used, is the battery voltage (Chemical Reaction). There is a common misconception that in any device, it is not the case that a fully discharged battery would have 0V. In fact, if the battery reads 0V, it's probably dead. A battery's output voltage should always be read from its nominal voltage level. Water is used as an electrolyte by the zinc-carbon battery and nickel-metal hydride battery and provides a nominal voltage of 1.2V to 2V, while the lithium-based batteries use organic electrolytes that can provide a nominal voltage of 3.2 to 4V. Most of the equipment's electronic parts run in the 3V voltage range. A single cell battery would be enough to power the equipment if you use a lithium-based battery. Note that the battery voltage will not be constant and will differ between the minimum value and the maximum value, depending on the battery power available. This is the minimum and maximum value shown below for each battery. Your nominal voltage would only be 3.2V to 4V if your circuit is running at 5V and you are charging it with a lithium battery. Boost converter circuits are used in these cases to convert the battery voltage required for the circuit to 5V. If your operating voltage is very high, like 24V or 12V, you can either use a 12V lead-acid battery or combine more than one lithium cell in series to increase the resulting output voltage if you need high power density.Ⅵ Operating TemperatureFor example, the battery operating with aqueous electrolytes can not be used in temperature conditions below 0 ° C as the aqueous electrolyte could be frozen below 0 ° C, in the same way,  the lithium-based batteries could work up to -40 ° C, but the efficiency could be reduced. The battery performance can be drastically modified by the temperature. The optimum charging rate for the lithium-ion batteries is between the temperature ranges of 20 ° C to 45 ° C. If you want to use a lower current/voltage outside this temperature range, this will result in a longer charge time. Lithium dendrite plating can be produced in the electrolyte if the temperature drops below 5 ° C or 10 ° C, which must be avoided by trickle charging.Ⅶ Capacity-Power & EnergyThe battery's strength determines the battery's runtime. Battery power/capacity is expressed in watt-hours (Wh). By multiplying the battery voltage (V) by the amount of current a battery can produce over a given amount of time, the watt-hour is determined. The battery voltage is almost set and the current that can be supplied by a battery is written on the battery, expressed in the Ampere-hour rating (Ah or mAh). Consider a 5V battery with a capacity of 2 amp-hours (Ah), so it has a power of 10Wh. The 2Ah battery will produce 2 Amps for 1 hour or 0.2A for 10 hours or 0.02A (20mA) for 100 hours. At a given discharge rate, temperature, and cut-off voltage, battery manufacturers often specify the power, where the capacity always depends on all three variables. A battery's capacity can tell us how much energy it can supply to an application. For instance, consider a 12V, 10Ah car battery, the battery's actual capacity is 120Wh (12V x 10Ah), but it will have a capacity of 36Wh in a 3.6V laptop battery that has the same 10Ah dissipation (3.6Vx 10Ah). You can see from the example that the amount of power a car battery can hold is three times higher than a laptop battery, even though they have the same Ah.High-power batteries always have quick discharge capabilities at high drain speeds, such as power tools or applications for vehicle starter batteries, with poor energy capacity for most high-power batteries.Ⅷ ChemistryYou would have learned by this time that all the characteristics of a battery are often dependent on the chemistry involved in the battery, so when selecting the type of battery, you should be more conscious. Batteries are known as Lead Acid Batteries, Alkaline Batteries, Ni-Cad Batteries (Nickel Cadmium), Ni- MH Batteries (Nickel Metal Hydride), Li-Ion (Lithium-Ion) and LiPoly (Lithium Polymer) Batteries based on the chemistry used in the process.Ⅸ CostThe battery will be one of the costly things in the Bill of Materials (BOM) for most portable electronic devices, so it will impact the total cost of your electronic applications most of the time. Therefore, you should know your product specifications and budget and then pick the right battery for your product.Ⅹ Shelf LifeNot all batteries are used directly after development, but they remain on the shelf for a long time before they are used. A battery's shelf life informs you how long it is possible to keep a battery unused. In primary batteries, the shelf life is largely known as a reality only because the secondary batteries can be recharged once they are used. The battery could sit idle there for years, for example, in a fire alarm siren device, until it detects a fire and activates the alarm. The battery maintains its output even if it is left unused for a long time, so care should be taken.Ⅺ How to Choose a BatteryNow that we've looked at the criteria that you should consider before selecting the battery for a portable electronic application, let's look at the common battery selection cases. Bear in mind that these are just tips and not difficult written guidelines.• You can use lead-acid batteries for items that consume more electricity, including projectors, large sound systems, and motorized projects. You can go for 'Sea deep cycle' batteries if you're going to have heavy battery use.• You can go for the lithium coin cells or small lithium polymer cells if your electronics need to be very small, about an inch on either side.• If you are going to manufacture the part, use inexpensive alkaline batteries of common sizes in large quantities. So the client considers it easy to replace them.• If you want the product to be user-serviceable, the battery can be adjusted by the customers themselves for batteries of 9V or AA capacity.• Use 3 Alkaline (4.5V) or 4NiMH (4.8V) cells if the circuit needs an input of approximately 5V.• Use a battery holder from your local shop to build a rechargeable battery pack and stick it with NiMH batteries and then begin recharging your battery.• If you want to replace any of the rechargeable batteries with your alkaline battery, test your system to make sure it will work at a lower voltage without any problems.• Always use a high-quality charger with sensors to ensure proper charging and trickle charging if you want your battery to have a longer life span since using a cheap charger would destroy your cells in the battery pack.How To Buy the Right Battery for Your CarⅫ FAQ1. How do I choose a battery?Factors to be considered while choosing a BatteryRechargeable / Non-Rechargeable batteriesAvailability of SpaceSystem Operating VoltageOperating TemperatureCapacity of the battery - Power & EnergyBattery ChemistryCost of Battery 2. What size battery does my car take?Your car's battery group size can be found in the battery section of the owner's manual. If you no longer have access to your original owner's manual, you may also consult the reference guides provided by battery retailers to determine the appropriate battery group size for your car. 3. How many Ah battery do I need for home?The battery you need will have to be powerful enough to provide the required power for at least 2 hours. As battery voltage is generally taken at 12 Volts, here is how you calculate the battery capacity. So, a battery with capacity equal to or higher than 140 Ah will suffice for your home. 4. How do I choose the right battery?To get the right battery power for your vehicle, you need to consider the cold cranking amps (CCA) and reserve capacity (RC). Cranking amps is the measure of your battery's starting power and should always match the standard requirements of your vehicle. Check the owner's manual for these specifications. 5. What brand of car battery lasts the longest?Best Rated Car Batteries for Long Lasting Performance 2020Optima RedTopExide Edge AGM Sealed BatteryOdyssey PC680ACDelco 94RAGM Professional

IntroductionIn electronics, current sense amplifiers are special-purpose amplifiers that output a voltage proportional to the current flowing in a power rail. They are often referred to as current shunt amplifiers because they use a shunt resistor in the power rail that provides a small voltage drop when current flows through the resistor. These devices are designed to handle common-mode voltages that can exceed their own supply voltage. The working principle of a current sensing amplifier is based on Ohm's law (V = I × R), where the voltage drop across the sense resistor is converted and amplified to a measurable output voltage by the current sense amplifier.Ⅰ Current Sense Amplifier Overview1.1 What is a Current Sense Amplifier?Current sense amplifiers are designed for the specific purpose of amplifying very small sensed voltages across a shunt resistor, typically within a range of 10 to 100 mV. These amplifiers are optimized for DC precision (e.g., low input offset voltage, typically less than 50 µV) and high common-mode rejection ratio (CMRR). Current sensing amplifiers can measure current flowing in a single direction (unidirectional) or in both directions through the sensing resistor. When an amplifier is capable of detecting current flow in both directions, it is called a bidirectional current sensing amplifier. Modern current sense amplifiers also feature enhanced bandwidth (up to several MHz), low quiescent current (as low as 50 µA), and integrated protection features such as overcurrent detection and alert outputs.1.2 Common-Mode Voltage and CMRRCommon-mode voltage is critical for both standard amplifiers and current sense amplifiers. The common-mode voltage refers to the average voltage applied to the inputs of the amplifier. This parameter is crucial because the amplifier has a limited ability to distinguish and differentiate signals depending on the common-mode voltage level. A standard op-amp's input range is typically insufficient for precision current sensing operations. In current sense amplifiers, the common-mode voltage range often extends well beyond the actual supply voltage of the amplifier. For example, modern current sense amplifiers can achieve supply operating voltage ranges from -4 V to +80 V, with some specialized devices supporting ranges up to +120 V or even higher for automotive and industrial applications.Op-Amp CMRR (Common Mode Rejection Ratio) ExplainedThe CMRR (common-mode rejection ratio) is the ratio of differential gain to common-mode gain, typically expressed in decibels (dB). For an ideal op-amp, the CMRR is infinite, but in real circuits, it typically ranges from 80 to 120 dB for high-performance current sense amplifiers. A high CMRR means that the amplifier can effectively reject common-mode signals while accurately amplifying the differential signal. For a current sense amplifier, high CMRR is essential because it determines how well the amplifier can measure small differential voltages in the presence of large common-mode voltages. Modern current sense amplifiers achieve CMRR values exceeding 100 dB, enabling them to sense tiny voltage drops across shunt resistors even when the common-mode voltage is several orders of magnitude larger. The high CMRR also helps eliminate noise on the current sense lines, improving measurement accuracy and system reliability.1.3 Main Types of Current Sense AmplifiersHigh-side AmplifiersThe current is measured between the supply rail and the load. The DC voltage applied to the input pins can be much higher than the amplifier's power supply voltage. High-side sensing is preferred in applications requiring ground fault detection and load diagnostics.Low-side AmplifiersThe current is measured between the load and ground. The voltage applied to the input pins is close to ground potential. Low-side sensing is simpler to implement but can interfere with ground reference integrity.Bidirectional AmplifiersThese amplifiers can measure current flow in both directions, making them ideal for battery monitoring, motor control, and applications with regenerative braking.Integrated Current Sense Amplifiers with ADCModern devices integrate analog-to-digital converters (ADC) and digital interfaces (I²C, SPI) for direct microcontroller communication, simplifying system design.Figure 1. High-side Current Sensing AmplifierⅡ Current Sense Amplifiers vs Common AmplifiersCurrent sense amplifiers and common operational amplifiers have different specifications and are designed for specific purposes. Standard operational amplifiers typically cannot amplify very small differential voltages in the presence of large common-mode voltages and have relatively low CMRR (typically 80-90 dB). In contrast, precision current sense amplifiers can detect and amplify very small voltage drops (as low as a few millivolts) while maintaining high CMRR (100-120 dB or higher).For normal operational amplifiers, the input voltage must remain between the power supply rails (VCC and VEE), and the amplifiers can only operate on input signals within this range. In a standard amplifier, applying an external voltage beyond the power rails to the input pins will activate internal ESD protection diodes, potentially causing large currents to flow and damaging the device.However, current sense amplifiers are designed to handle input voltages that far exceed their supply voltage. For example, an amplifier powered by 3.3V or 5V can safely measure voltages on power rails operating at 12V, 24V, 48V, or even higher. These amplifiers use specialized input architectures and protection circuits that allow them to operate with high common-mode voltages. When the common-mode input voltage exceeds VCC, the amplifier employs advanced circuit techniques to maintain accurate measurements without damage. Some modern current sense amplifiers also feature integrated overcurrent detection, alert outputs, and enhanced EMI/RFI rejection for robust performance in noisy industrial and automotive environments. Ⅲ How to Design a Circuit Using Current Sense AmplifiersConsider a design example with a 12V, 1A power rail where high-precision current sensing is required. Current sense amplifiers provide an ideal solution for this application. However, proper component selection is critical for optimal performance.For this application, select a current sense amplifier rated for at least 12V common-mode voltage with sufficient bandwidth for the application (typically 100 kHz to 1 MHz for DC and low-frequency AC measurements). Choose between high-side and low-side sensing based on system requirements. High-side current sensing is preferred for detecting fault or short-circuit conditions while maintaining ground integrity. Low-side current sensing offers simpler implementation but disrupts the ground reference path.The LT6108 (now part of Analog Devices) is an excellent choice for this application. This amplifier features a wide input common-mode voltage range (-0.3V to +60V), high gain accuracy, and low offset voltage. The device can operate with supply voltages from 2.9V to 60V, making it suitable for both 12V and lower voltage control circuits. Key specifications include: input offset voltage of 50 µV (typical), CMRR of 125 dB (minimum), and bandwidth of 500 kHz.Figure 2. LT6108 Circuit for Fault Protection with Fast Latching Load DisconnectThe circuit above demonstrates a practical implementation using the LT6108. A 1-ohm sense resistor creates a voltage drop proportional to the load current (1V drop at 1A). The IRF9640 P-channel MOSFET serves as the switching element, while the 2N2222 NPN transistor (note: 2N2700 in the original text appears to be a typo) provides the control function. The amplifier output can trigger the switching MOSFET to disconnect the load when current exceeds a preset threshold. In this configuration, the trip point is set at 250 mA. The circuit will open when current exceeds this limit, providing overcurrent protection. For different current thresholds (e.g., 1A), adjust the voltage divider network at the comparator input. The VOUT pin provides a voltage proportional to the sensed current, enabling real-time current monitoring. This circuit topology can be adapted using other current sense amplifiers with appropriate input voltage ranges. For higher voltage applications (24V, 48V), select amplifiers with extended common-mode voltage ranges, such as the INA240 (up to 80V) or MAX40080 (up to 60V).Design Considerations:Sense Resistor Selection: Choose a value that provides adequate voltage drop (typically 50-100 mV at full scale) while minimizing power dissipation. For 1A measurement, resistor values between 0.05Ω and 0.1Ω are common.PCB Layout: Use Kelvin connections to the sense resistor to eliminate errors from trace resistance. Keep traces short and symmetric to minimize offset errors.Filtering: Add input filtering capacitors (typically 0.1 µF ceramic) close to the amplifier inputs to reduce noise and improve stability.Gain Setting: Many current sense amplifiers offer programmable gain through external resistors, allowing optimization for specific current ranges. Ⅳ Common Applications of Current Sensing ICs4.1 Low-side Current Sense ICLow-side current sensing places the shunt resistor between the load and ground. This configuration measures current by monitoring the voltage drop across the sense resistor in the ground return path. The diagrams below demonstrate low-side measurement circuits.Practical implementations include using the INA181 current sense amplifier with its output connected to an ADC (Analog-to-Digital Converter) for digital processing. Another approach employs the AD8202 current sense amplifier from Analog Devices for sensing current through inductive loads. Modern alternatives include the INA190 series and MAX9938, which offer enhanced precision and lower power consumption.1) AdvantagesLow-side current measurement offers several benefits. The configuration is straightforward to implement because the common-mode voltage remains close to ground potential. Standard operational amplifiers or simple differential amplifiers can be used since high common-mode rejection is not critical. The low common-mode voltage simplifies circuit design and reduces component costs. Additionally, low-side sensing typically provides better noise immunity in the measurement path.2) DisadvantagesThe primary limitation of low-side current measurement is the disruption of the ground reference. Placing the shunt resistor in series with the ground path means the load no longer has a direct connection to system ground. This can cause ground bounce issues, interfere with proper operation of the load, and make it impossible to detect ground faults or short circuits to ground. Additionally, low-side sensing cannot detect leakage currents or faults that bypass the sense resistor. For these reasons, high-side sensing is often preferred in safety-critical applications.4.2 High-side Current Sense ICUnlike low-side current sensing, high-side current sensing places the shunt resistor between the positive power supply and the load. This configuration preserves ground integrity while enabling current measurement. The circuits shown below illustrate high-side current sensing implementations.Practical examples include the TI INA240, which provides analog output or integrated comparators for overcurrent detection. Some variants offer digital output via I²C interface for direct microcontroller communication. The Linear Technology LT6100 (now Analog Devices) demonstrates high-side current sensing with a fused load for enhanced protection. Modern alternatives include the INA226 (with integrated 16-bit ADC and I²C interface), MAX40080 (with integrated 12-bit ADC), and INA3221 (triple-channel monitor for multi-rail systems).Figure 3. TI INA240 in Circuit1) AdvantagesHigh-side current measurement offers significant advantages over low-side sensing. First, it maintains ground integrity, ensuring the load has a solid ground reference. This prevents ground bounce and interference issues. Second, it enables detection of all fault conditions, including short circuits to ground, since all current must flow through the sense resistor. Third, high-side sensing allows accurate measurement of the actual load current without ground path interference. Fourth, it provides better system diagnostics and fault isolation capabilities. Finally, high-side sensing is essential for battery monitoring applications where the negative terminal is grounded.2) DisadvantagesThe primary challenge of high-side current sensing is the requirement for high common-mode rejection. The small differential voltage (typically 50-100 mV) across the shunt resistor sits on top of a large common-mode voltage equal to the supply rail voltage. This requires specialized amplifiers with high CMRR (>100 dB) and wide common-mode input ranges. Additionally, high-side sensing circuits are typically more complex and expensive than low-side alternatives. However, advances in integrated circuit technology have made high-side current sense amplifiers increasingly affordable and easy to implement.4.3 Bidirectional Current Sense ICBidirectional current sense circuits use a single shunt resistor but require amplifiers capable of detecting current flow in both directions. These circuits are essential for applications such as battery charge/discharge monitoring, motor control with regenerative braking, and power management systems with bidirectional power flow.Several architectures enable bidirectional current sensing. One approach uses two current sense amplifiers (such as the INA300) connected in a configuration where each amplifier detects current flow in one direction. The circuit requires reverse polarity protection and switching logic to select the appropriate amplifier output based on current direction.A more elegant solution uses integrated bidirectional current sense amplifiers such as the INA240, INA180, or MAX40080. These devices use a reference voltage (typically mid-supply or an external reference) as the zero-current point. When current flows in one direction, the output voltage rises above the reference; when current reverses, the output falls below the reference. The differential output voltage is proportional to current magnitude, while the polarity indicates current direction.Modern bidirectional amplifiers like the INA226 and INA3221 integrate ADCs and digital interfaces, providing signed current measurements directly to microcontrollers. These devices simplify system design by eliminating external ADCs and reference voltage circuits. For high-precision applications, devices like the MAX40080 offer 12-bit resolution with ±0.1% accuracy across the full bidirectional range.4.4 Isolated Current Sense ICIsolated current sensing techniques provide galvanic isolation between the current measurement circuit and the control electronics. This is essential for high-voltage applications, safety-critical systems, and situations requiring ground loop elimination. Several isolation methods are available:Current Transformer (CT) Isolation: Uses magnetic coupling through a transformer core. The primary winding carries the measured current, inducing a proportional voltage in the secondary winding. This method is limited to AC current measurement and provides excellent isolation (typically >4 kV).Hall Effect Sensors: Measure the magnetic field generated by current flow through a conductor. Hall effect sensors can measure both DC and AC currents and provide good isolation. Examples include the ACS712, ACS724, and TMCS1100 series.Isolated Amplifiers: Use capacitive or magnetic isolation to transmit the measurement signal across an isolation barrier. Examples include the AMC1200 (capacitive isolation), Si8920 (magnetic isolation), and ACPL-C87A (optical isolation). These devices typically provide 3-5 kV isolation and can measure both DC and AC currents.Rogowski Coils: Air-core coils that measure the rate of change of current (di/dt). These are ideal for high-frequency AC current measurement and provide inherent isolation.Isolated current sensing is mandatory in applications such as motor drives, solar inverters, electric vehicle charging systems, and industrial power monitoring where high voltages and safety requirements necessitate galvanic isolation between measurement and control circuits.Figure 4. Low-side Current Sensing CircuitⅤ Key Specifications and Selection CriteriaWhen selecting a current sense amplifier, consider the following critical specifications:Common-Mode Voltage Range: Must exceed the maximum voltage on the power rail being monitored. Include margin for transients and voltage spikes.Input Offset Voltage: Determines minimum detectable current. Lower offset voltage (typically <50 µV) enables accurate measurement of small currents.CMRR: Higher values (>100 dB) provide better rejection of common-mode noise and more accurate differential measurements.Bandwidth: Must be sufficient for the application. DC to 100 kHz for most power monitoring; 1 MHz or higher for motor control and fast transient detection.Gain Options: Fixed or programmable gain allows optimization for specific current ranges.Supply Voltage: Must be compatible with system power rails. Many devices operate from 2.7V to 5.5V for easy integration with digital systems.Quiescent Current: Important for battery-powered applications. Modern devices offer quiescent currents as low as 50 µA.Package and Size: SOT-23, SOIC, and DFN packages are common. Smaller packages reduce PCB footprint but may have thermal limitations.Integrated Features: Some devices include comparators, ADCs, digital interfaces (I²C, SPI), alert outputs, and overcurrent protection.Temperature Range and Accuracy: Industrial (-40°C to +125°C) and automotive (-40°C to +150°C) grades are available. Temperature drift should be <2 µV/°C for precision applications.Ⅵ Emerging Trends and Future DevelopmentsThe current sense amplifier market continues to evolve with several notable trends:Higher Integration: Modern devices integrate ADCs, digital interfaces, voltage monitors, and power calculation engines on a single chip, reducing component count and system cost.Wider Voltage Ranges: New amplifiers support common-mode voltages up to 120V or higher, enabling direct monitoring of high-voltage rails without external attenuation.Lower Power Consumption: Shutdown modes and ultra-low quiescent current (<50 µA) enable use in battery-powered IoT devices and energy harvesting applications.Enhanced Accuracy: Improved manufacturing processes deliver offset voltages below 25 µV and gain errors below 0.1%, enabling precision measurements with smaller sense resistors and lower power loss.Automotive Qualification: AEC-Q100 qualified devices for electric vehicles, battery management systems, and 48V automotive systems.Digital Configurability: Software-programmable gain, filtering, and alert thresholds enable flexible, adaptive current monitoring systems.Multi-Channel Integration: Devices like the INA3221 integrate multiple current sense channels for simultaneous monitoring of multiple power rails.Ⅶ ConclusionAs an essential component of modern electronics, current sense amplifiers provide high-precision, flexible solutions for a wide array of applications including automotive systems, power management, battery monitoring, motor control, and industrial automation. Devices like the INA280, INA226, MAX40080, and LT6108 offer high-precision current measurement capabilities by accurately sensing voltage drops across shunt resistors. With diverse circuit requirements, a broad range of current sense amplifiers are available, including high-voltage, high-resolution, bidirectional, and isolated variants. The continued evolution of current sense amplifier technology—featuring higher integration, wider voltage ranges, lower power consumption, and enhanced digital connectivity—ensures these devices will remain critical components in next-generation power management and monitoring systems. When selecting a current sense amplifier, carefully consider application requirements including voltage range, accuracy, bandwidth, power consumption, and integration features to ensure optimal performance and system reliability. Frequently Asked Questions about Current Sense Amplifier Circuits1. What is a current sense amplifier?Current sense amplifiers (also called current shunt amplifiers) are special-purpose amplifiers that output a voltage proportional to the current flowing in a power rail. They utilize a "current-sense resistor" (shunt resistor) to convert the load current in the power rail to a small voltage, which is then amplified by the current sense amplifier. The currents in the power rail can range from milliamps to 20 A or more, requiring the current-sense resistor to be typically in the range of 1 mΩ to 100 mΩ. These amplifiers are specifically designed to handle high common-mode voltages while accurately measuring small differential voltages. 2. How does a current sense amplifier work?Current sense amplifiers work by measuring the small voltage drop across a shunt resistor placed in series with the load current. According to Ohm's law (V = I × R), the voltage drop is directly proportional to the current. The amplifier's differential inputs measure this voltage drop while rejecting the large common-mode voltage present on the power rail. The amplifier then amplifies the differential signal to produce an output voltage that can be easily measured by ADCs or comparators. Unlike normal differential amplifiers that are powered between two power supply rails (VCC and VEE) and can only handle signals between these rails, current sense amplifiers use specialized input stages that can tolerate input voltages far exceeding their supply voltage without activating ESD protection diodes or causing damage. 3. What are the main types of current sense amplifiers?The main types of current sense amplifiers include:High-Side Current Sense: Measures current between the power supply and load, maintaining ground integrity.Low-Side Current Sense: Measures current between the load and ground, offering simpler implementation.Bidirectional Current Sense: Measures current flow in both directions, essential for battery monitoring and regenerative systems.Isolated Current Sense: Provides galvanic isolation using magnetic, capacitive, or optical coupling for high-voltage and safety-critical applications. 4. What is the main purpose of a current sense amplifier?The main purpose of a current sense amplifier is to accurately measure current flow in power rails by amplifying the small voltage drop across a shunt resistor. These amplifiers can detect and amplify very small voltages, typically in the 10 to 100 mV range, while rejecting large common-mode voltages. Applications include power management, battery monitoring, motor control, overcurrent protection, system diagnostics, and energy measurement. Current sense amplifiers enable precise current monitoring for efficiency optimization, fault detection, and system protection. They can measure current flowing in a single direction (unidirectional) or in both directions (bidirectional) through the sense resistor, depending on the application requirements. 5. What is the difference between a voltage amplifier and a current sense amplifier?While both are amplifiers, they serve different purposes and have distinct specifications. Standard voltage amplifiers (operational amplifiers) are general-purpose devices designed to amplify signals within their power supply rails. They typically have moderate CMRR (80-90 dB), input voltage ranges limited to their supply voltages, and are not optimized for measuring very small differential voltages in the presence of large common-mode voltages.Current sense amplifiers, in contrast, are specialized devices optimized for measuring small voltage drops across shunt resistors. They feature very high CMRR (100-120 dB or higher), ultra-low input offset voltage (<50 µV), and the ability to handle common-mode voltages far exceeding their supply voltage. For example, a current sense amplifier powered by 3.3V can safely measure voltages on a 48V power rail. Current sense amplifiers use specialized input architectures that prevent ESD protection diodes from conducting when input voltages exceed supply rails, enabling them to operate in high-voltage environments. They are specifically designed for DC precision, high common-mode rejection, and wide common-mode voltage ranges—characteristics essential for accurate current measurement in power management applications. 6. How do I select the right shunt resistor value?Shunt resistor selection involves balancing several factors: voltage drop, power dissipation, and measurement accuracy. The voltage drop should be large enough for accurate measurement (typically 50-100 mV at full-scale current) but small enough to minimize power loss. Use the formula R = V / I, where V is the desired voltage drop and I is the maximum current. For example, for 1A measurement with 50 mV drop: R = 0.05V / 1A = 0.05Ω (50 mΩ). Power dissipation is calculated as P = I² × R. For 1A through 50 mΩ: P = 1² × 0.05 = 0.05W (50 mW). Select a resistor with adequate power rating (typically 2-4× calculated power) and low temperature coefficient (<50 ppm/°C) for stable measurements. Consider resistor tolerance (typically 1% or better) as it directly affects measurement accuracy. 7. What are the key advantages of high-side vs. low-side current sensing?High-side sensing places the shunt resistor between the power supply and load, maintaining ground integrity and enabling detection of all fault conditions including ground shorts. It provides better system diagnostics but requires amplifiers with high CMRR and wide common-mode voltage range. Low-side sensing places the shunt resistor between load and ground, offering simpler implementation and lower cost since common-mode voltage is near ground. However, it disrupts ground reference and cannot detect ground faults. High-side sensing is preferred for safety-critical applications, battery monitoring, and systems requiring fault detection, while low-side sensing is suitable for cost-sensitive applications where ground disruption is acceptable. 8. Can current sense amplifiers measure AC current?Yes, many current sense amplifiers can measure AC current, provided their bandwidth is sufficient for the frequency of interest. The amplifier's bandwidth must be at least 10× the highest frequency component of the AC signal for accurate measurement. For example, measuring 60 Hz AC requires minimum 600 Hz bandwidth. Most modern current sense amplifiers offer bandwidths from 100 kHz to several MHz. For AC-only measurements (where DC component is not needed), current transformers or Rogowski coils provide better performance. For combined DC and AC measurement (such as motor current with PWM ripple), use a current sense amplifier with adequate bandwidth and consider adding filtering to reduce high-frequency noise while preserving the signals of interest.

IntroductionSeries Circuits and Parallel Circuits are main circuit connections, also a third type of circuit involves the dual use of series and parallel connections in a circuit. Circuit connection is a kind of principle for layout diagram that shows the relationship between components drawn by physical and electrical standardized symbols for research and engineering planning. As we all know, there are two types of circuit we can make, called series and parallel. They provide solutions for analyzing performance, installing electronic and electrical products.CatalogIntroductionⅠ Series Circuits and Parallel CircuitsⅡ Series Circuits and Parallel Circuits Calculation2.1 Resistors2.2 Capacitors2.3 Inductor2.4 Switch2.5 Power Supply2.6 Series and Parallel Circuits RulesⅢ Six Circuit Design Software Tools Introduction3.1 Protel PCB Design Platform3.2 Altium Designer3.3 Quartus II3.4 Electronics Workbench (EWB)3.5 NI Multisim3.6 Allegro PCBⅣ Frequently Asked Questions about Series and Parallel CircuitsⅠ Series Circuits and Parallel CircuitsWhat is the difference between series and parallel circuits? Just have a look of the following video and words description about series circuits and parallel circuits to get the basics and differences of them.Series vs Parallel CircuitsSeries connection is one of the basic ways to connect circuit elements. The circuit formed by connecting various electrical parts in series. In the series circuit, the current through each part is equal.Parallel connection is another connection method between electrical components. Components connected in parallel are connected in multiple paths so that the current can split up, and the same voltage is applied to each component.Ⅱ Series Circuits and Parallel Circuits Calculation👉 Resistors in Series and Parallel Circuits2.1 ResistorsResistors in SeriesAs shown in the figure, n resistors connect in series. Now connect the power supply to both ends of this series circuit. According to Kirchhoff’s current law, the current given from the power supply is equal to the current through each resistor, so .According to Ohm’s law, the voltage across the k-th resistor is equal to the current through multiplied by its resistance .According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the algebraic sum of the voltage across all resistors.Therefore, the equivalent resistance Req of n resistors in series is .According to Ohm’s law, the voltage across the power source is equal to the given current times the equivalent resistance .Pay attention to the voltage shared by the resistors of the series circuit is proportional.Conductance G is the reciprocal of resistance R, so the equivalent conductance of n resistors in series is Among them, Gn is the conductance of the n-th resistor.For the simple case of two resistors in series, the equivalent conductance is .Resistors in ParallelWhen linear resistors connect in parallel, the conductance (the reciprocal of resistance) is equal to the sum of the conductances of the parallel resistors, which is called the equivalent conductance, and the reciprocal is called the equivalent resistance. For example, the resistances of R1, R2, and R3, their conductances are G1, G2, and G3, respectively. The total resistance R and total conductance G of the parallel circuit are calculated according to the formula .Note: Calculate the total series and parallel resistance of a circuit using Apogeeweb's Parallel and Series Resistor Calculator. 👉 Capacitors in Series and Parallel Circuits2.2 CapacitorsCapacitors in SeriesAs shown in the figure, n capacitors are connected in series. From the definition of capacitor, it can be obtained that the current passing through the k-th capacitor is equal to its capacitance multiplied by the voltage change rate across it:According to Kirchhoff’s current law, the current i given from the power source (ac or dc) is equal to the current passing through each capacitor, so According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the algebraic sum of the voltage across all capacitors:The voltage change rate of the power supply end is .Therefore, the equivalent capacitance Ceq of n capacitors in series is Each capacitor has a “voltage rating” set by its manufacturer. Assuming that the working voltage exceeds the voltage rating of the capacitor, it may cause capacitor failure. In order to avoid it, several similar capacitors can be connected in series to make the algebraic sum of the voltage rating greater than the operating voltage. However, this will also reduce the equivalent capacitance of the circuit.Capacitors in ParallelAs shown in the figure, n capacitors are connected in parallel. From the definition of capacitor, it can be obtained that the current ik through the k-th capacitor is equal to its capacitance Ck multiplied by the voltage change rate across it:According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the voltage across each capacitor:According to Kirchhoff’s current law, the current given from the power source (dc or ac) is equal to the algebraic sum of the current through each capacitor: Therefore, the equivalent capacitance Ceq of n capacitors in parallel is .Note: Calculate the total series and parallel capacitance of a circuit using Apogeeweb's Series and Parallel Capacitance Calculator. 👉 Inductors in Series and Parallel Circuits2.3 InductorInductor in SeriesAs shown in the figure, n inductors are connected in series. According to the method described above, the equivalent inductance can be calculated as .Among them, Ln is the inductance of the n-th inductor.The magnetic field generated by the inductor will be coupled with the winding coil of the adjacent inductor. So it is difficult to avoid the mutual influence of the adjacent inductors. The mutual inductance M of physical quantities can give a measure of this influence.A series circuit composed of two inductors L1 and L2, and the mutual inductance Ms.1) Assuming that the magnetic fields or fluxes generated by two inductors are in the same direction, the equivalent mutual inductance Leq is expressed by the equation: 2) Assuming that the magnetic fields or fluxes generated by two inductors are in opposite directions, Leq is expressed by the equation:For a parallel circuit with three or more inductors, it is necessary to consider the self-inductance of each inductor and the mutual inductance among the inductors, which makes the calculation more complicated. The equivalent inductance is the algebraic sum of all self-inductance and mutual inductance.For example, a series circuit composed of three inductors will involve three self-inductances and six mutual inductances. The self-inductances of the three inductors are M11, M22, and M33, and the mutual inductances are M12, M13, M21, M23, M31, and M32.Equivalent inductance is .Since the mutual inductance between any two inductors is equal to each other, the latter two sets of mutual inductance can be combined:Inductors in ParallelN ideal inductors without mutual inductance are connected in parallel. Similar to the method described above, the equivalent inductance Leq can be calculated as .Among them, Li is the inductance of the i-th inductor.The above equation describes an ideal case where n inductors are connected in parallel without mutual inductance.A parallel circuit composed of two inductors with inductances L1 and L2 and mutual inductance M:1) Assuming that the magnetic fields or fluxes generated by two inductors are in the same direction, the equivalent mutual inductance Leq is expressed by the equation: 2) Assuming that the magnetic fields or fluxes generated by two inductors are in opposite directions, Leq is expressed by the equation:For a parallel circuit with three or more inductors, it is necessary to consider the self-inductance of each inductor and the mutual inductance among the inductors, which makes the calculation more complicated. 👉 Switch in Series and Parallel Circuits2.4 SwitchSwitch in SeriesTwo or more switches are connected in series to form an or gate circuit. Assuming a power supply is connected to both ends of the circuit, current will only flow when all switches are closed.Switch in ParallelTwo or more switches are connected in parallel to form an or gate circuit. Assuming that a power supply is connected to both ends of this circuit, even though any one of the switches is closed, current will flow. 👉 Power Supply in Series and Parallel Circuits2.5 Power SupplyPower Supply in SeriesFor example, assuming that several cells in the battery pack are connected in series to form a power source, the voltage across the power source is the algebraic sum of the voltages across all cells.Power Supply in ParallelFor example, assuming that a battery pack uses several single batteries with the same voltage connected in parallel as a power source, the voltage across the power source is equal to the voltage across the single battery.Note: Get more info from Switching Power Supply Circuit Diagram with Explanation. 2.6 Series and Parallel Circuits RulesHow to judge whether the electrical circuits are connected in series or in parallel? Series and parallel are the two most basic forms of circuit connection, and there are certain differences between them. So get to know their basic characteristics well according to the following specific methods.(1) Visual CheckLook at the connection form of electrical parts in the circuit. The one by one in sequence is series; the one paralleled between two points of the circuit is parallel.(2) Current FlowWhen the current flowing from the positive pole of the power supply to each element in turn shows that the circuit is in series; when the current flows to two branches and get together at a certain place finally, it indicates that the circuit is in parallel.(3) Removing ComponentsRemove one electrical part at will to see whether other electrical components are working normally. If the circuit can continue to work, then the connection relationship of this circuit is in parallel, otherwise, it is in series. Ⅲ Six Circuit Design Software Tools Introduction3.1 Protel PCB Design PlatformProtel PCB is a CAD software for the circuit industry launched by Protel Systems Pty Ltd in 1985, and has rebranded to Altium Designer. It has many advantages compared with many EDA software for circuit designers. Almost all circuit companies use it. The early Protel PCB was mainly used as a printed board automatic wiring tool. It ran in DOS and had fewer hardware requirements. It can run under the 1M memory of a 286 machine without a hard disk. However, it’s less functional, only electrical schematic drawing and printed board design functions, and the PCB layout rate of automatic wiring is also low.It is a professional circuit board drawing tool. It includes electrical schematic drawing, analog circuit and digital circuit mixed signal simulation, multilayer PCB design, programmable logic device design, chart generation, circuit table generation, and supports macro operations, etc. And it has a client/server architecture. PROTEL is also compatible with some other design software file formats, such as ORCAD, PSPICE, EXCEL, etc. Using automatic routing of multi-layer can achieve 100% layout rate of high-density PCBs.3.2 Altium DesignerAltium Designer is one of the most popular of the high end PCB design software packages on the market today. It provides a single, unified application that incorporates all the technologies and capabilities necessary for complete electronic products, which mainly runs on the Windows operating system. This software provides designers with brand-new design solutions through the perfect integration of schematic design, circuit simulation, PCB drawing editing, topology logic automatic routing, signal integrity analysis and design output, etc. When using this software, the quality and efficiency of circuit design can be greatly improved.Fully inheriting the functions and advantages of the previous series of versions of Protel 99SE and Protel DXP, Altium Designer has many improvements and many high-end features. The platform broadens the traditional interface of board-level design and fully integrates FPGA design functions and SOPC design implementation functions, allowing engineers to integrate FPGA in system design with PCB design and embedded design. With these advantages, Altium Designer requires higher computer system performance than the previous version. 3.3 Quartus IIThe Altera Quartus II design software is a multiplatform design environment that easily adapts to your specific needs in all phases of FPGA and CPLD design. In other words, Quartus II software delivers the highest productivity and performance for Altera FPGAs, CPLDs, and HardCopy ASICs. It is a comprehensive CPLD/FPGA development software, and supports schematics, VHDL, VerilogHDL and AHDL (Altera Hardware supports Description Language) and other design input forms. Quartus II embedded with its own synthesizer and simulator, can complete the process of design input to the hardware configuration. It can run in Windows, Linux and Unix. Use Tcl scripts to complete the design process, and it also provides a complete user graphical interface design method. Quartus II has the characteristics of fast running speed, unified interface, centralized function, easy to learn and easy to use.Quartus II provides a fully integrated development which independent of circuit structure, with all the features of digital logic design, including:1. You can use the schematic diagram, structural block diagram, VerilogHDL, AHDL and VHDL to complete the circuit description, and save it as a design entity file.2. Chip (circuit) plane layout wiring editing3. With LogicLock region, users can build and optimize the system, and add subsequent modules that have little or no impact on the performance of the original system.4. Powerful logic synthesis tool5. Complete circuit function simulation and sequential logic simulation6. Timing analysis and critical path delay analysis7. Signaltap ii logic analyzer can be used for embedded logic analysis.8. Support the addition and creation of software source files, and link them to generate programming files.9. Use the combined compilation method to complete the overall design process at one time.10. Automatically locate compilation errors.11. Efficient period programming and verification12. Read into standard EDIF, VHDL and Verilog netlist files.13. It can generate VHDL and Verilog netlist files used by third-party EDA software.3.4 Electronics Workbench (EWB)EWB is is a mixed-mode SPICE-based electronics design and simulation tool, launched by Interactive Image Technology Co., Ltd. in the early 1990s. It is used for mixed simulation of analog circuits and digital circuits. With this powerful software, you can directly see the output of various circuits on the screen.Compared with other EDA software, EWB is a smaller software, and its function is relatively single. However. its simulation function is very powerful, almost 100% simulation results of real circuits. It provides parts such as multimeters, oscilloscopes, signal generators, frequency sweepers, logic analyzers, digital signal generators, logic converters, etc., and its device library contains many transistor components, integrated circuits and digital gate circuit chips from large companies.  In addition, components that are not in the device library can also be imported externally. Among many circuit simulation software, EWB is the easiest to use. Its working interface is very intuitive. The schematic diagram and various tools are in the same window. People who have never touched it can use the software proficiently with a short-time learning. For electronic designers, it is an excellent EDA tool. For many circuits, you can know its results without using a soldering iron. If you want to change components or change parameters, you only need to click the mouse. It can also be used as an auxiliary teaching software for electrical knowledge.3.5 NI MultisimMultisim is a Windows-based simulation tool launched by National Instruments (NI) Co., Ltd.. It is industry standard SPICE simulation and circuit design software for analog, digital, and power electronics in education and research. It includes graphical input of circuit schematics, circuit hardware description language input, and has rich simulation analysis capabilities. Engineers can use it to interactively build circuit schematics and simulate the circuit.With SPICE simulation, designers can quickly capture, simulate and analyze new designs without knowing SPICE deeply, which also makes it more suitable for electronics education. Through Multisim and virtual instrument technology, PCB designers and electronics educators can complete a complete integrated design process from theory to schematic capture and simulation to prototype design and testing.NI Multisim software is an EDA tool software specially used for electronic circuit simulation and design. As a personal desktop electronic design tool running in Windows, NI Multisim is a complete integrated design environment. Its computer simulation and virtual instrument technology can solve the problem of disconnection between theoretical teaching and actual reality experiment. Students can easily reproduce the theoretical knowledge they have learned through computer simulation, and can use virtual instrument technology to create their own instruments. It has an intuitive graphical interface, abundant components, powerful simulation capabilities, abundant testing instruments and complete analysis methods. NI Multisim software is a not bad teaching tool.3.6 Allegro PCBAllegro PCB is an advanced PCB design routing tool introduced by Cadence. It provides a good and interactive working interface, and powerful and complete functions. Provide the most perfect solution for the current high-speed, high-density, multi-layer complex PCB design and wiring, with the combination of its front-end products Cadence, OrCAD, and Capture. Allegro has a complete constraint setting. Users only need to set the wiring rules as required. The wiring design requirements can be met without violating DRC, thus saving tedious manual inspection time and improving work efficiency. It can also define parameters such as minimum line width or line length to meet the various requirements of today's high-speed circuit board wiring. Allegro PCB enables you to do high-speed design, RF antenna, flex-circuitry, and design for manufacturing (DFM) technology.For the drawing and modification functions of copper foil that the industry attaches great importance to, Allegro provides a simple and convenient inner layer division function, as well as the ability to review the inner layer of the positive and negative film. For copper paving, it can also be divided into dynamic copper or static copper, which can be used for different applications. Dynamic copper parameters can be divided into different levels of settings for all copper, single copper or single object, so as to meet the requirements of different connection effects or spacing values to match the special settings due to design requirements. Ⅳ Frequently Asked Questions about Series and Parallel Circuits1. What is the difference between parallel and series circuits?In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents flowing through each component. ... In a series circuit, every device must function for the circuit to be complete. If one bulb burns out in a series circuit, the entire circuit is broken. 2. What are the rules for series and parallel circuits?Rules regarding Series and Parallel CircuitsVoltage drops add to equal total voltage.All components share the same (equal) current.Resistances add to equal total resistance. 3. What are the similarities and differences between series and parallel circuits?Series circuits are designed so that the current through each component is the same, whereas parallel circuits are designed so that the voltage through each component is the same. 4. Why is resistance different in series and parallel?In a series circuit, the output current of the first resistor flows into the input of the second resistor; therefore, the current is the same in each resistor. In a parallel circuit, all of the resistor leads on one side of the resistors are connected together and all the leads on the other side are connected together. 5. Which software is best for circuit design?Based on Proto-Electronics client preferences, we have drawn up the top 10 best electronics CAD software programmes.EagleAltiumProteusKiCadCadence OrCAD PCB DesignerDesignSparkProtelCadstar

IntroductionAlarm Circuits and Control Circuits are pretty common in daily life. A control circuit is a special type of circuit used to control the operation of a completely separate power circuit. Alarm circuit is a security circuit to reduce life loss and poverty under the excepted prevailing conditions. Both are quite famous and you probably could have seen plenty of different versions of them. Here, we will introduce several available home/office hobby circuits for smoking alarm, temperature controlling and timing, with their design principles, and component selection. They will provide more convenience for your daily life.A Simple Guide to Electronic Components in CircuitsCatalogIntroductionⅠ Indoor Monitoring Circuit DesignⅡ Smoke Alarm Circuit DesignⅢ Temperature Controlled Circuit Using NE555Ⅳ Temperature Sensor Circuit for Temp MeasuringⅤ Water Tank Temperature Controlled ProjectⅥ Cyclic Timing Circuit DiagramⅦ Indoor Overvoltage Protection Circuit DesignⅧ Temperature Fan Controller DiagramⅨ Water Boiling Alarm Circuit DesignⅩ FAQEvery alarm circuit and control circuit is composed of a number of basic components connected together to achieve the desired performance. The following lists some common and simple alarm and control circuits diagrams to share different ideas for protecting your home/office and making your life more easier.Ⅰ Indoor Monitoring Circuit DesignThe monitor can detect infrared rays emitted by the human body, and when a person enters the monitoring area, it can sound for alarm. It is suitable for homes, offices, warehouses, laboratories and other important occasions.👍 Circuit Working ModelFigure 1. Infrared Detection Alarm CircuitThe device consists of an infrared sensor, a signal amplifier circuit, a voltage comparator, a delay circuit and an audio alarm circuit. When the sensor IC1 detects the infrared signal radiated by the human body in front, it outputs a weak electrical signal from the pin②. It is amplified by the first-stage amplifying circuit formed by the transistor VT1, and then input to the operational amplifier IC2 through C2 with high gain and low-noise amplification. IC3 acts as a voltage comparator. Its pin⑤ reference voltage is provided by R10 and VD1. When the signal voltage output by IC2 pin① pass to the IC3 pin⑥, the voltages of the two input terminals are compared. At this time, IC3 pin⑦ changes from the high level to the low level. IC4 is an alarm delay circuit, formed by R14 and C6. Its continuous time is about 1 minute.When IC3 pin⑦ becomes low level, C6 discharges through VD2, IC4 pin② becomes low level,  which is compared with IC4 pin③ reference voltage. When it is lower than its reference voltage, IC4 pin① changes to high level, VT2 is turned on, and the buzzer BL is powered on and emits an alarm sound. After the infrared signal of the humans disappears, IC3 pin⑦ outputs to high level, and VD2 is cut off at this time. Since the voltage at both ends of C6 cannot change suddenly, charge C6 slowly through R14. When the voltage at both ends of C6 is higher than its reference voltages, IC4 pin① becomes low level for about 1 minute. That is, the alarm time lasts for 1 minute.The power-on delay circuit is composed of VT3, R20, and C8. It is mainly to prevent alarming immediately when powering on, so that the user has enough time to leave the monitoring site, and at the same time can prevent a false alarm occurred during a power cut. The device uses 9-12V DC power supply, with T step-down, full-bridge rectification, and C10 filtering. The detection circuit uses IC5 for power supply, and automatic non-stop conversion with AC and DC. 👉 Components SelectionIC1 adopts imported device Q74, the wavelength is 9~10um. IC2 uses op-amp LM358, which has high gain and low power consumption. IC3 and IC4 are dual voltage comparators LM393 with low power consumption and low offset voltage. Among them, C2 and C5 must use tantalum capacitors with small drain electrodes, otherwise the debugging will be affected. R12 is the key element to adjust sensitivity, and linear high-precision sealed type should be selected. Other components can be selected as shown in the circuit diagram. 👉 DIY and AdjustmentWhen making, a Fresnel lens is installed in front of the IC1 sensor. Since the frequency range of the human body is 0.1~10Hz, it is necessary to use the Fresnel lens to multiply the frequency of the human body. After installation finished, connect the power supply for debugging. Let a person walk about 7-10m in front of the detector, adjust R12 in the circuit, and make the buzzer alarm. As long as the other parts are of good quality and welded correctly, they can work normally without debugging. The static working current of this machine is about 10mA. It will enter the waiting state about 1 minute after the power is turned on. As long as someone enters the monitoring area, it will alarm, and stops in 1 minute. In addition, if the buzzer is changed to a relay to drive other devices, it will be used for other controls. Ⅱ Smoke Alarm Circuit DesignThis smoke alarmer can be used in family rooms or various places where smoking is forbidden (such as hospitals, conference rooms, etc.). When someone smokes, the no-smoking warning device will emit a warning sound of "No Smoking!" to remind the smoker to stop smoking consciously.👍 Circuit Working ModelFigure 2. Smoke Alarm CircuitThe no-smoking warning circuit is composed of a smoke detector, a monostable trigger, a voice generator and a power amplifier circuit. The smoke detector consists of potentiometer RP1, resistor R1 and gas sensor. The monostable trigger has time-base integrated circuit IC1, resistor R2, capacitor C1, and potentiometer RP2. The voice generator circuit is composed of voice integrated circuit IC2, resistors R3-R5, capacitor C2 and Zener diode VS. The audio power amplifier circuit includes transistor V, boost power amplifier module IC3, resistors R6 and R7, capacitors C3 and C4, and speaker BL.When the gas sensor doesn’t detect smoke, the resistance value between A and B is relatively large. IC1 pin2 is high level (higher than 2VCC/3), pin3 outputs low level, while voice generator circuit and the audio power amplifier circuit does not work. When someone smokes and the gas sensor detects the smoke, the resistance value between the A and B becomes smaller, causing the voltage of IC1 pin2 to drop. When the voltage of this pin drops to VCC/3, IC1 pin3 changes from low level to high level. Pass through current limiter R3, filter C2 and Zener diode VS, the high level will generate 4.2V DC voltage, which is supplied to voice IC2 and crystal arm. After IC2 energizes and works, it outputs a voice electrical signal. After the signal is amplified by V and IC3, it makes BL to emit a voice warning sound of "No Smoking!" 👉 Components SelectionRl~R7 selects 1/4W carbon film resistor or metal film resistor for use. RP1 and RP2 can choose small linear potentiometer or variable resistor. C1, C2 and C4 all use aluminum electrolytic capacitors with a withstand voltage of 16V; C3 uses monolithic capacitors. VS selects the silicon Zener diode of 1/2W, 4.2V for use. V uses S9013 or C8050 silicon NPN transistors. IC1 uses the NE555 timer IC; IC2 uses the voice integrated circuit; lC3 uses the WVH68 boost power amplifier thick-mode IC. BL selects 8Ω, 1~3W electrodynamic speakers. The gas sensor is MQK-2 type sensor. 👉 DIY and AdjustmentThis no-smoking warning device can be used as a smoke alarm to detect fires or harmful gases, and combustible gases. Adjusting the RP1 resistance can change the heating current of the gas sensor (usually about 130mA). And adjusting the RP2 resistance can change the sensitivity of the monostable trigger circuit. Ⅲ Temperature Controlled Circuit Using NE555This circuit is an automatic temperature controller composed of a 555 timer IC and a few peripheral components. Because the voltage at each point in the circuit comes from the same DC power supply, it does not need a high-performance regulated one. Using the capacitor step-down method can work reliably. The circuit components are low in price, small in size, and easy to self-made under amateur conditions. The automatic temperature controller made by this circuit can be used for electric heating control in industrial production and household use, with good effect.👍 Circuit Working ModelFigure 3. 555 Timer Based Circuit for Temperature ControlWhen the temperature is low, the resistance of the thermistor Rt with a negative temperature coefficient is large, the potential of pin2 of the 555 timer IC is lower than 1/3 of the voltage of Ec (about 4V), and its pin3 output high level. At this time, V conducts, the heater RL is heating, and the timing cycle starts. When the temperature of the thermistor Rt is higher than the set value and the timing cycle has not been completed, the heater RL will cut off after the timing cycle stops. When the Rt temperature drops below the set value, V will conduct again and turn on the heater RL for heating. In this way, automatic temperature control can be achieved. 👉 Components SelectionIn this circuit, the thermistor Rt can be a negative temperature coefficient type MF12 or MF53, or other types of negative temperature coefficient thermistors with different resistance values, as long as Rt＋VR1= 2R4 is satisfied under the temperature condition to be controlled. A larger potentiometer VR1 can have a larger adjustment range, but its sensitivity will decrease. The bidirectional thyristor V can also be selected according to the size of the load current. There are no special requirements for other components. Choose according to the parameters given in the circuit diagram. 👉 DIY and AdjustmentThe whole circuit can be installed on PCB. Generally, debugging is not required. The time interval is 1... .1R2×C3, which should be smaller than the thermal time constant of the heating system, but not too small, otherwise it will cause excessive radio frequency interference due to the thyristor V turns on or off rapidly. After installation and debugging, it can be put into a small plastic box, and the thermistor Rt can be led to the required place. Ⅳ Temperature Sensor Circuit for Temp MeasuringThis circuit is a thermometer made by AD590 special integrated temperature sensor, which has the characteristics of simple structure, reliable use and high precision.👍 Circuit Working ModelFigure 4. Digital Thermometer CircuitAfter the 100V AC voltage passes through the transformer T1, the rectifier bridge stack UR and the capacitor C1, the DC voltage is obtained, and then the adjustable voltage regulator circuit μA723C provides a stable working voltage for the temperature sensor AD590. AD590 is a new type of current output temperature sensor, composed of multiple transistors and resistors with the same parameters. When a specific DC working voltage is applied to both ends of the sensor, if the sensor temperature is 1 degree Celsius, the output current of the sensor changes by 1 μA. The changing current of the sensor is converted into a voltage signal through the resistor R5 and the variable resistor RP2, and then output to the digital meter, which displays the temperature change. 👉 Components SelectionThe IC selects AD590-series temperature sensor. There are no special requirements for other components of this circuit, and can be selected according to the parameters given in the circuit diagram. 👉 DIY and AdjustmentBy adjusting the value of resistor R5 and variable resistor RP2, the sensitivity of the circuit output can be improved. Ⅴ Water Tank Temperature Controlled ProjectAn automatic fish tank water temperature controller uses a negative temperature coefficient thermistor as a temperature sensor to automatically heat the fish tank through heating gas. The transient time of this circuit is small, which is beneficial to the accuracy of temperature control. And it is suitable for various sizes of fish tanks.👍 Circuit Working ModelFigure 5. Automatic Control of Fishbowl Water TemperatureAfter being rectified by diodes VD2~VD5 and filtered by capacitor C2, a voltage of about 12V is provided to the control part of the circuit. 555 timer is connected as a monostable flip-flop, the transient state is 11s. Set the control temperature to 25ºC, adjust the potentiometer RP, to get RP + Rt = 2R1 ( Rt is the thermistor with negative temperature coefficient). When the temperature is lower than 25ºC, the Rt resistance value increases, and the pin2 of the 555 timer is low level, then the pin3 output changes from low level to high level. The relay K is turned on, and its contact is closed. The heating tube starts to heat until the temperature returns to 25ºC, the Rt resistance value becomes smaller, the pin2 of the 555 timer is at high level, and the pin3 outputs low level. The relay K loses power, its contact is open, and the heating stops. 👉 Components SelectionIC uses NE555, NA555, SL555 and other 555 timer ICs; VD1 uses IN4148 silicon switching diodes; LED uses common light-emitting diodes; VD2~VD5 uses IN4001 silicon rectifier diodes; Rt uses 470Ω MF51-type negative temperature coefficient thermistors at room temperature; RP uses WSW organic solid trimming potentiometer; R1and R2 uses RXT-1/8W carbon film resistors; C1 and C3 uses CD11-16V electrolytic capacitors; C2 uses CT1 ceramic dielectric capacitors; K uses 12V JZC-22F electromagnetic relay. 👉 DIY and AdjustmentThe temperature sensor probe connects the thermistor Rt with wires, and then seals the solder joint with epoxy glue, to avoid water erosion. As long as the circuit is correct in the DIY process, this circuit is easy to operate. If the component performance is good, it can be used without debugging after installation. Ⅵ Cyclic Timing Circuit DiagramThe circuit can set the cycle time of the equipment and each time it works, allowing the equipment to work continuously according to the set time. This circuit can be applied to control occasions such as timing pumping, timing ventilation, and timing cut off.👍 Circuit Working ModelFgiure 6. Cycle Timing CircuitAfter the circuit is stepped down through the capacitor C2 and the bleeder resistor R3, and then rectified by the bridge stack IC2, and stabilized by VD2, a DC voltage of about 12V is obtained to supply power to IC1 and other circuits. IC1 is a 14-bit binary counter/frequency divider integrated circuit. A clock oscillator with a certain frequency is formed by the internal circuits of R1, R2, C1 and IC1 to provide clock pulses for timing IC1. When the circuit is powered on, it first enters the working gap waiting time of the device. IC1 internally realizes the delay by counting and dividing the clock pulse.  When the timing is up (according to the parameters in the figure, about 3 hours), the Q14 terminal of IC1 outputs high level, making the transistor V conducts. The relay KA gets to work, and drives the controlled equipment to start working. At this time, IC1 starts to count the working time of the device again. When the timing expires (according to the parameters in the figure, about 20 minutes), the Q14 terminal outputs low level. So that V is cut off and the device stops working. And meanwhile, IC1 automatically resets and starts the next timing. So that the device can perform timing cycle according to requirements. In the figure, VL is a working indicator. 👉 Components SelectionIntegrated circuit IC1 chooses 14-bit binary counter/frequency divider CD4066, or CC4066 or other digital circuit integrated blocks with the same function. IC2 selects a 1A, 50V bridge stack, or can be connected with four 1N4007 diodes. Transistor V uses NPN-type transistor 8050, and other transistors such as 9013 or 3DG12 can also be used. VD1 selects rectifier diode 1N4007; VD1 selects 1W, 12V silicon regulator tube, such as 1N4742; VD3 ~VD5 use switching diodes 1N4148; VL selects ordinary light-emitting diodes. Resistors R1, R2, R4, R6 and R7 use 1/4W metal film resistors; R3 and R5 use 1/2W carbon film resistors. C1 selects polyester or monolithic capacitors; C2 selects polypropylene capacitors with a withstand voltage of 450V and above; C3 selects aluminum electrolytic capacitors with a withstand voltage of 16V. Relay KA chooses a miniature relay with a coil voltage of 12V, and the contacts capacity is determined according to the power of the controlled device. 👉 DIY and AdjustmentAfter the circuit is installed, it can work normally without debugging. When you need to adjust the control time, you can adjust the parameters of R1, and C1. Also you can change the position of the IC1 output control terminal (Q4 ~Q14). Ⅶ Indoor Overvoltage Protection Circuit DesignBecause the instability of the mains, the household appliances often affected, their service life may reduce. In serious cases, it is easy to burn out due to voltage surge. The circuit described in this example can solve this problem well.👍 Circuit Working ModelFigure 7. Overvoltage Protection Circuit for AppliancesThe mains supply provides a stable 12V working voltage for the switch integrated circuit via C1, VD1, and DW1. VD3, R2 and RP1 form a voltage divider sampling circuit. When the mains voltage is normal, DW2 cannot be turned on, the working voltage of TWH8778 pin⑤ is lower than 1.6V. The relay J does not pull in, and the mains supplies the CZ socket through the J-1 normally closed contact. When the mains voltage is high than the normal setting, DW2 breaks down, the potential of TWH8778 pin⑤ rises to 1.6V, causing the IC to flip, pin ③ outputs high level. At this time, the relay is pulled in, and the electrical power supply is immediately cut off, avoiding the overvoltage affects electrical appliances. 👉 Components SelectionC1 uses 0.47µ/400V electrolytic capacitor, relay J uses 6V DC contactor; RP uses ordinary trimming potentiometer, chip IC can be TWH8778-type electronic switch or TWH8752-type electronic switch. 👉 DIY and AdjustmentAfter the device is welded correctly, connect the mains power to the input end of the voltage regulator, cooperate with the voltage regulator and carefully adjust RP1, so that the relay J is closed when the voltage is 250V, and then the circuit is connected to the mains power grid. Ⅷ Temperature Fan Controller DiagramThis is an automatic fan temperature controlled governor, which can automatically adjust the speed according to the temperature change. The circuit can be adjusted, so it can be used for the control of other electrical equipment.👍 Circuit Working ModelFigure 8. Automatic Temperature Control and Speed Regulation in Fan CircuitThe IC in the picture is a 555 timer IC, which forms a multivibrator with components of R2, R3 and C2. It can send out a rectangular wave signal with an adjustable duty cycle. When the temperature changes, the resistance value of the thermistor changes, so the duty cycle of the square wave output by the multivibrator changes. Adjusting the conduction angle of the bidirectional thyristor VT changes the voltage across the fan electrodes, which automatically adjusts the speed of the electric fan. 👉 Components SelectionThe integrated circuit IC selects NE555 timer, and models such as LM555 and TLC555 can also be used. VT is a bidirectional thyristor, its withstand voltage should be above 400V, and the rated current should be reasonably selected according to the capacity of the electric fan to be controlled. Resistor R1～R5 can choose ordinary 1/8 or 1/4W carbon film resistors; Rt is a negative temperature coefficient thermistor, and can choose a thermistor with a resistance of about 10KΩ at room temperature. Capacitor C1 uses ordinary aluminum electrolytic capacitors; Capacitors C2 and C3 are polyester capacitors. VD is a Zener diode with a steady voltage of 9.1V. 👉 DIY and AdjustmentYou can make your own PCB, or use a universal one. After the circuit is installed, the temperature of the thermistor Rt can be artificially changed to observe the speed of the fan motor. If the temperature control effect is not ideal, the resistance value or temperature change range of the thermistor can be adjusted appropriately. Ⅸ Water Boiling Alarm Circuit DesignOnce the water boils in the kitchen, if it is not turned gas off in time, the boiling water will overflow and extinguish the flame. The gas may spill, which is very unsafe. This problem can be solved by using the water alarm.👍 Circuit Working ModelFigure 9. Boiling Water Alarm CircuitThis circuit uses thermistor as the temperature sensing element. When the water temperature rises, the resistance of the thermistor decreases and the potential at point A increases. When the potential at point A is higher than the conversion voltage of the IC-1 inverter, the IC -1 will output low level, IC-2 will output high level. Making the audio oscillator composed of IC-3 and IC-4 work, and the piezoelectric ceramic sheet makes sound. When IC-2 outputs low level, the audio oscillator doesn’t work, and the piezoelectric ceramic chip is silent. 👉 Components SelectionIC uses C066 two input terminal four NAND gate, working voltage 3V~18V, power supply is 3V~6V; RT thermistor selection resistance value is about 1kΩ; piezoelectric ceramic chip diameter is 27mm; resistor selection is ordinary 1/8 or 1/4W metal film resistors. 👉 DIY and AdjustmentFind two starter shells of waste fluorescent lamps, use iron sheet as a clip, close the tops of the two starters, and fasten them with screws. One of the starters can be set on the mouth of the kettle to obtain the temperature of the water. The two pins of the thermistor are welded on the cover of the other starter and put into the shell. Note that the thermistor must be close to the inner shell wall to facilitate heat transfer. Solder the outer lead of the thermistor and the temperature sensor. After all the components are welded and checked, you can turn on the power for debugging. Put the temperature sensor on the mouth of the kettle, and adjust the RP when the water boils to make the piezoelectric ceramic sheet sound. Repeat it several times before this circuit can be used normally. If you want to change the sound frequency, you can change the C2 capacity. If you feel that the sound is light, you can connect an external transistor to the IC-4 output terminal to amplify the sound.  Ⅹ FAQ1. How do you make a security alarm circuit?The cathode of the photodiode is connected to the supply while the anode is connected to a 10KΩ resistor. Another end of the resistor is connected to the ground. The anode terminal of the photodiode is also connected to pin 5 of the LM358 op-amp, which is the non-inverting terminal. 2. What is the technique of alarm circuits?In a closed-circuit system, the electric circuit is closed when the door is shut. This means that as long as the door is closed, electricity can flow from one end of the circuit to the other. But if somebody opens the door, the circuit is opened, and electricity can't flow. This triggers an alarm. 3. What is a security alarm circuit?This circuit will help you to guard your precious documents as well as jewelry from intruders or theft. All you need is just to place this circuit in front of the locker or below the mat so when any unknown person comes and walks over the switch, the circuit will trigger and the sound of an alarm comes. 4. What type of circuits are security alarms made of?The simplest type of contact-operated security circuit consists of an alarm bell (or a buzzer or electronic 'siren sound' generator, etc.), wired in series with a normally-open (n.o.) close-to-operate switch; the combination being wired across a suitable battery supply, as shown in the basic 'door-bell' alarm circuit ... 5. What are the three basic parts of an alarm system?The main components of an alarm system would be a sensor, a camera, a motion detector, a buzzer a flash light and batteries. It is a component that is usually used to detect noise or movement. Sensors are usually connected to the circuit. 

IntroductionPCB exists in every electronic device. A fully functional PCB is mainly used to create connections between components, such as resistors, capacitors, inductors, diodes, transistors, integrated chips, etc. It is the carrier of the entire logic circuit. Sound PCB design can save production costs, and achieve good circuit performance and heat dissipation effect. PCB designs vary in complexity according to product needs. This article mainly talks about wiring, one of the basics of PCB design.PCB Design: From Idea to Schematic to PCBCatalogIntroductionⅠ PCB Basics: Wiring RulesⅡ Three PCB Wiring MethodsⅢ PCB Design: Wire InspectionⅣ Complete PCB Design Projects Inspection4.1 General PCB Design Inspection Projects4.2 PCB Electrical Characteristics Checking Projects4.3 PCB Physical Characteristics Checking Projects4.4 PCB Mechanical Design Factors4.5 PCB Installation Requirements4.6 PCB Pull-out Requirements4.7 PCB Mechanical Considerations4.8 PCB Electrical Considerations4.9 Electronics Inspection Before Into A PCBⅤ ConclusionⅠ PCB Basics: Wiring Rules1. The area within 1mm from the edge of the PCB board and within 1mm around the mounting hole will not take wiring.2. The power line width should not be less than 18mil; the signal line width should not be less than 12mil; the cpu input and output lines should not be less than 10mil (or 8mil); the line spacing should not be less than 10mil.3. It is necessary noted that the power line and the ground line should be as radial as possible, and the signal line must not be looped.4. Ground circuit rulesThe loop area formed by the signal line should be as small as possible. The smaller the loop area, the less external radiation and the less interference from the outside. An example is shown in the figure below:5. Crosstalk controlHere crosstalk refers to the mutual interference caused by long parallel wiring between different networks on the PCB, which caused by the distributed capacitance and inductance between the parallel lines. The main measures to overcome it are:a. Increase the spacing of parallel wiring and follow the 3W rule. To ensure that the distance between the lines is large enough, when the distance between the line and the center of the line is not less than 3 times the line width (as shown in the figure below). If the line center distance is not less than 3 times the line width, 70% of the line electric fields will not interfere with each other, which is called 3W rule.b. Insert a grounded isolation wire between the parallel wires. Reduce the distance between the wiring layer and the ground plane.6. The direction control rules of routing:The routing directions of adjacent layers are orthogonal. Different signal lines in the same direction on adjacent layers should be avoided to reduce unnecessary interlayer crosstalk. When the signal rate is high, use a ground plane to isolate each wiring layer, in other words, isolate each signal line with ground line. The neighbouring wires used in the input and output end of the circuit shouldn’t be parallel to prevent the feedback, and it is best to add a ground wire between these wires.7. Open loop inspection rules for wiring:Generally, it is not allowed to have a floating wiring at one end, because of the "antenna effect" and unnecessary interference radiation and reception, which may bring unpredictable results.8. Impedance matching inspection rulesThe wiring width of the same network should be kept the same. Line width variations will bring uneven line characteristic impedance, and reflection will occur when the transmission speed is high. This situation should be avoided in the design. Under certain conditions, such as the lead wires of the connector and the similar structure of the lead wires of the BGA package, the change of the line width may not be avoided, so that the length of the middle inconsistent part should be minimized.9. Wiring closed loop inspection rules:Prevent signal lines from forming self-loops between different layers. Such problems are prone to occur in multilayer board design, and it will cause radiation interference. As shown below:10. The branch length control rule of wiring:Try to control the length of branches, and the general requirement is Tdelay≤Trise/20.11. Resonance rules of wiring:For high-frequency signal design, the wiring length must not be an integer multiple of its wavelength to avoid resonance.12. Line length control rules:In fact, it refers to the short-circuit rule. When designing, you should keep the wiring length as short as possible to reduce interference problems caused by unnecessary lines. Especially for some important signal lines, such as clock lines, be sure to place oscillators close to the device. In the case of driving multiple devices, the network topology should be decided according to the specific situation.13. Parallel input and output wires on the PCB board should be avoided as far as possible to avoid parallel. It is best to place a ground wire between the two wires to avoid circuit feedback coupling.14. Digital ground and analog ground should be separated. For low-frequency circuits, single-point parallel grounding should be used. High-frequency circuits should be grounded in series with multiple points. For digital circuits, the ground wire should be closed into a loop to improve anti-noise capability.15. The wiring and via distribution of the whole circuit board should be uniformity. When the outer signal of the circuit board has a large blank area, auxiliary lines should be added to make the lines distribution on the board basically balanced.16. The low-frequency circuit can be grounded at a single point in parallel, and the actual wiring can be connected in series and then grounded in parallel. The high-frequency circuit can be grounded in series with multiple points. The ground wire should be short and thick. For high-frequency components, a large area ground foil can be used. The ground wire should be as thick as possible. If the ground wire is a very thin, the ground potential will change with the current, which reduces the noise resistance.17. Multilayer boards should be as symmetrical as possible when designing the laminated structure, as well as the wiring density and copper layout of each layer to reduce warpage and reduce EMI during soldering.18. The signal line should not cross the power supply and ground. The signal reference plane should be as complete as possible.19. Impedance controlThe signal lines that need impedance control must be wired in strict accordance with the calculated data, in addition, it is necessary to tell manufacturers it. For signal lines that do not require it, the impedance should be calculated to prevent unnecessary interference.20. Grid copper should be used less in low frequency circuits. Although it can effectively reduce the problem of large area copper skin blistering. When using grid copper, you need to consider the electrical length of the grid line and the working frequency of the circuit board. If using grid copper, the power supply should also be coated with solid copper as much as possible.21. A group of buses with the same attribute should be wired side by side as much as possible, and the length should be as equal as possible. Ⅱ Three PCB Wiring MethodsThe wires should take the shortest route between components according to the specified wiring rules. Limit the coupling between parallel wires as much as possible. Good PCB design requires the minimum number of wiring layers, and also requires fair use of the widest wire and the largest pad size corresponding to packaging density. For example, rounded corners and smooth inner corners design may avoid some electrical and mechanical problems, therefore, sharp corners and sharp corners in the wire should be avoided. Here introduces three main PCB routing methods; right-angle wiring, differential wiring, and serpentine wiring to illustrate PCB layout:A. The influence of right-angle wiring on the signal is mainly reflected in three aspects:1. The corner can be equivalent to the capacitive load on the transmission line to slow down the rise time.2. Discontinuous impedance will cause signal reflection.3. The EMI generated by the right-angle tip reaches the RF field above 10GHz. Such a right-angle is likely to develop into the source of high-speed problems. B. To figure out what is differential wiring, you must first understand what is differential signal. In a word, the driving end sends two equal and inverted signals, and the receiving end judges the logic state "0" or "1" by comparing the difference between the two voltages. The pair of traces carrying differential signals is called differential traces. Compared with ordinary single-ended signal traces, differential signals have the most obvious advantages in the following three aspects:1. Have Strong anti-interference ability. Because the coupling between the two differential traces occurs, when there is noise interference from the outside, they are almost coupled to the two lines at the same time. However, the receiving end only cares about the difference between the two signals. Therefore, the external common mode noise can be completely canceled.2. It can effectively suppress EMI. Due to the opposite polarity of the two signals, the electromagnetic fields radiated by them can cancel each other out. What’s more, the tighter the coupling, the less the electromagnetic energy leaked to the outside world.3. The timing positioning is accurate. Because the switch change of the differential signal is located at the intersection of the two signals. Unlike ordinary single-ended signals, which rely on the high and low threshold voltages to judge. Timing positioning is less affected by the process and temperature, and also more suitable for circuits with low amplitude signals. The current popular LVDS (low voltage differential signaling) refers to this small amplitude differential signaling technology. C. Serpentine line is a type of wiring method often used in PCB layout. Its main purpose is to adjust the delay to meet the system timing design requirements. The two most critical parameters are the parallel coupling length (Lp) and the coupling distance (S). Obviously, when a signal is transmitted on a serpentine trace, the parallel line segments will be coupled in a differential mode. The smaller the S, the greater the Lp, the greater the coupling. It may cause the transmission delay to be reduced, also the signal quality is greatly reduced due to crosstalk. The mechanism can refer to the analysis of common mode and differential mode crosstalk. The following are some suggestions when dealing with serpentine wring:1. Try to increase the distance (S) of parallel lines, at least more than 3H(H refers to the distance from the signal trace to the reference plane). As long as S is large enough, the mutual coupling effect can be almost completely avoided.2. Reduce the coupling length Lp. When the double Lp delay approaches or exceeds the signal rise time, the crosstalk generated will reach saturation.3. The signal transmission delay caused by the strip-line or embedded micro-strip line is less than that of the micro-strip. Theoretically, the strip-line will not affect the transmission rate due to differential mode crosstalk.4. For signal lines with high-speed and strict timing requirements, try not to take serpentine lines, especially in a small area.5. You can often use s-shaped routing at any angle, which can effectively reduce the mutual coupling.6. In high speed, the serpentine line has no ability so-called filtering or anti-interference, and can only reduce the signal quality, so it is better to use for timing matching.7. Sometimes you can consider the spiral routing method for winding. Simulation shows that its effect is better than normal serpentine routing.Ⅲ PCB Design: Wire Inspection1.Wire SpacingThe minimum spacing of wires must be determined to eliminate voltage breakdown or arcing between adjacent wires. The spacing is variable, it mainly depends on the following factors:1) Peak voltage between adjacent wires2) Atmospheric pressure (maximum working altitude)3) Coating layer4) Capacitive coupling parametersComponents with critical impedance or high-frequency components should be placed very close to reduce the critical stage delay. There is something need to pay attention to. Transformers and inductive components should be isolated to prevent coupling. Inductive signal wires should be laid orthogonally at right angles. Components that generate any electrical noise due to magnetic field movement should be isolated or rigidly installed to prevent excessive vibration.2. Whether the wire is short and straight without sacrificing function.3. Whether the restrictions on the wire width are complied with.4. There must be a minimum distance between wires, wires and mounting holes, wires and pads.5. Whether to avoid all the wires (including component leads) closer to parallel wiring.6. Whether sharp corners (≤90℃) are avoided in the wire pattern. Ⅳ Complete PCB Design Projects Inspection4.1 General PCB Design Inspection Projects1) Has the circuit been analyzed? Is the circuit divided into basic units to smooth the signal?2) Does the circuit allow short or isolated key leads?3) Where must be shielded, are they effectively shielded?4) Have you made full use of the basic grid graphics?5) Is the best size of the printed circuit board?6) Do you use the available wire width and spacing as much as possible?7) Has the preferred pad size and hole size been used?8) Are the base plate and the sketch consistent?9) Is less cross-wiring used? Do cross wires pass through components and accessories?10) Are the letters visible after assembly? Are their size and model correct?11) In order to prevent blistering, is there any window on the large area of copper foil?12) Are there tool positioning holes?4.2 PCB Electrical Characteristics Checking Projects1) Have you analyzed the influence of wire resistance, inductance, and capacitance, as well as the critical voltage drop on the ground?2) Does the wire spacing and shape meet the insulation requirements?3) Has the insulation resistance value been controlled and specified in key areas?4) Is the polarity fully recognized?5) According to geometric view, has the effect of wire spacing on leakage resistance and voltage been measured?6) Has the medium for changing the surface coating been identified?4.3 PCB Physical Characteristics Checking Projects1) Are all pads and their positions suitable for final assembly?2) Can the assembled PCB meet the shock and vibration conditions?3) What is the required spacing of standard components?4) Are the components that are not firmly installed or the heavier parts fixed?5) Is the heating element heat dissipation and cooling normally? Or is it isolated from the printed circuit board and other heat-sensitive elements?6) Are the voltage divider and other multi-lead components placed correctly?7) Is the arrangement and orientation of components easy to check?8) Has it eliminated all possible interference on the printed circuit board?9) Is the size of the positioning hole correct?10) Are the tolerances complete and reasonable?11) Have you controlled and signed the physical properties of all coatings?12) Is the ratio of via hole and lead diameter within an acceptable range?4.4 PCB Mechanical Design FactorsThe printed circuit board adopts mechanical methods to support the components, however, it cannot be used as an unique structural part of the entire device. On the edge of the printing plate, at least every 5 inches for a certain support. The factors that must be considered when selecting and designing printed circuit boards are as follows:1) The size and shape of the printed circuit board.2) The type of mechanical accessories and plug (seat) required.3) The environmental adaptability of circuits.4) According to some factors, such as heat and dust, install the printed circuit board vertically or horizontally.5) Some environmental factors that require special attention, such as heat dissipation, ventilation, shock, vibration, and humidity, dust, and radiation, etc.6) Physical support7) Install and fix.8) Disassemble4.5 PCB Installation RequirementsAccording to practical experience, the distance between the supporting points of a printed circuit board with a thickness of 0.031-0.062 inches should be at least 4 inches. For a printed circuit board with a thickness greater than 0.093 inches, the distance between the supporting points should be at least 5 inches. Taking this measure can improve the rigidity of the printed circuit board and avoid possible resonance. The following factors should be considered before deciding which mounting technology they use.1) PCB structure.2) Input and output terminals.3) Available equipment space.4) Convenience of loading and unloading.5) Type of attachments.6) Required heat dissipation.7) Required shieldability.8) The type of circuit and its relationship with other circuits.4.6 PCB Pull-out Requirements1) The influence of plugging tools on the installation distance between two printed circuit boards.2) When the plug-in tool used in the equipment, its size should be considered.3) A plug-in device is required, which is usually fixed to the printed circuit board assembly with rivets.4) As for the mounting frame of the printed circuit board, special design such as load bearing flange is required.5) The adaptability of the plug-in tool used and the size, shape and thickness of the printed circuit board.4.7 PCB Mechanical ConsiderationsThe characteristics of the board substrate that have an important influence on the printed circuit assembly are: water absorption, thermal expansion coefficient, heat resistance, flexural strength, impact strength, tensile strength, shear strength and hardness. All these characteristics affect the function and the production efficiency of the printed circuit board structure. For most applications, the dielectric substrate materials of the printed circuit board are as following:1) Phenolic impregnated paper2) Acrylic-polyester impregnated randomly arranged glass mat3) Epoxy impregnated paper4) Epoxy impregnated glass clothEach substrate can be flame retardant or combustible. The first 3 types mentioned above can be processed. The most common used material for printed circuit boards with metalized holes is epoxy-glass cloth. Its dimensional stability is suitable for high-density circuits and can minimize the occurrence of cracks in the metalized holes. One disadvantage of epoxy-glass cloth laminate is that it is difficult to punch in the usual thickness range of printed circuit boards. For this, all holes are usually drilled and copied and milled to form a print shape of the circuit board.4.8 PCB Electrical ConsiderationsIn DC or low-frequency AC applications, the most important electrical characteristics of insulating substrates are: insulation resistance, anti-isolation, printed wire resistance, and breakdown strength. In high frequency and microwave applications, include: dielectric constant, capacitance, and dissipation factors. In all applications, the current carrying capacity of printed wires is important.4.9 Electronics Inspection Before Into A PCB1) Check the rationality and correctness of the schematic diagram.2) Check the correctness of the component packaging of the schematic.3) The distance between strong and weak current lines, and the distance between isolation areas.4) Check the schematic diagram and PCB diagram to prevent the loss of the network table.5) Whether the package of the component matches the physical object.6) Whether the placement of the components is appropriate.7) Whether the components are easy to install and disassemble.8) Whether the temperature sensitive element is too close to the heating element.9) Whether the distance and direction of the mutual inductance components are appropriate.10) Whether the placement between the connectors is smooth.11) Easy to plug in and plug out12) Input and output13) Strong current and weak current14) digital and analog should be interlaced.15) Arrangement of elements on the upside and downside16) Check whether the directional component has been wrong flipped instead of rotated.17) Check whether the mounting holes of the component pins are suitable and whether it is easy to insert.18) Check whether the empty pin of each component is normal and whether it is a missing line.19) Check whether there are vias between the upper and lower wiring of the same net table. And the pads are connected through the holes, to prevent disconnection and ensure the integrity of the circuit.20) Silk screen printing should be clear, so that the operation of welding or maintenance can be easy.21) The arrangement of power and signal lines in the socket should ensure signal integrity and anti-interference.22) Pay attention to the proper ratio of pads and solder holes.23) Each plug should be placed on the edge of the PCB board as much as possible and easy to operate.24) Whether the size and distribution of the mounting holes on the PCB are appropriate to reduce the PCB bending stress.25) Pay attention to the height distribution of the components on the PCB to ensure easy assembly.Ⅴ ConclusionBased on the above mentioned rules, drawing the PCB schematics you need becomes easier. Decide what PCB you want to and install a PCB design software. PCB software is really helpful and powerful. Also a software can check your design to make sure the design does not contain errors such as traces that incorrectly touch, traces too skinny, or drill holes that are too small. For example, run the Electrical Rules Checker (ERC) to see if you’ve made any typical errors. There is less thing stopping you from making your first PCB, right? Frequently Asked Questions about PCB Design Diagram1. Which side of PCB is correct for soldering?The bottom side of the PCB is usually the side without components and the side that touches the solder wave during assembly. That is why sometimes it is also called SOLDER side. However more often, PCB are populated on both sides and the assembly process does not require wave soldering. 2. Which soldering method is suitable for soldering printed circuit board?Soldering Iron – Used to melt solder and connect component pins to board pads. A cheap soldering pencil may be sufficient, but a temperature-controlled solder station is best for high performance boards. Solder – An alloy of tin and lead with a low melting point. 3. What is PCB diagram?A PCB schematic is a simple two-dimensional circuit design showing the functionality and connectivity between different components. ... Once the blueprint has been completed, the PCB design comes next. The design is the layout, or physical representation of the PCB schematic and includes the copper track and hole layout. 4. Why we use PCB in soldering?PCB soldering is another term for the process of soldering electrical circuit boards. ... As the soldering iron melts this metal, it is then used a bit like glue to stick to pieces together. As the solder metal cools, it will re-harden into one large shape that connects the two parts. 5. How do you read a PCB board?Start with an easy analog circuit, such as a guitar distortion pedal, and work your way up to more complicated versions. Make a drawing of the top of the circuit board. Show the positions of the capacitors, integrated circuits, resistors, transistors and other components. Review it to make sure everything is included.

IntroductionIn electronics, operational amplifiers are generally dual/quadruple configurations. So users can consider using the extra amplifier as a comparator. Electrical symbols of the comparator and the operational amplifier are very similar. They are devices with one input inverting terminal and one non-inverting terminal, and one output terminal. In addition, the output voltage range of the output terminal is generally between the rail-to-rail power supply. Meanwhile, they have same features of low bias voltage, high gain and high common-mode rejection ratio. When an op amp is used as a comparator, its own gain bandwidth product, group delay, slew rate and other parameters are likely to be changed due to internal frequency compensation and saturation effects. For an optimized single device, this change can be seen as an economical solution. This article discusses the specifications and characteristics to consider when using op-amps as comparators and provides design advice. How operational amplifier be a comparator and what the difference between them.Op Amp vs ComparatorCatalogIntroductionⅠ Operational Amplifier and Comparator1.1 Electronic Op Amp1.2 Electrical ComparatorⅡ Circuit Structure Comparison2.1 Op Amp2.2 ComparatorⅢ Difference between Amplifier and Comparator3.1 Total Difference Summary3.2 Distinctions between Op-amp and ComparatorⅣ Basic Use of Comparators and Op AmpsⅤ Op-amp Comparator5.1 Technique5.2 Op Amp Comparators DisadvantagesⅥ Using Op Amps as Comparators NotesⅦ ConclusionⅠ Operational Amplifier and Comparator1.1 Electronic Op AmpThe operational amplifier is a kind of differential amplifiers with high input resistance, low output resistance, high open gain (open-loop gain), and has the function of amplifying the voltage difference between the active input pin and the negative input pin. Operational amplifiers and voltage comparators are indeed the same in principle and diagram symbol. That said, they have 5 pins: two of which are power supply (+) and supply power (-), another two pins are non-inverting input (+) and non-inverting input terminal (-), and the last pin is the output terminal.Figure 1. Op Amp Symbol1.2 Electrical ComparatorComparing two or more data items to determine whether they are equal, or determining the  relationship and arrangement order between them is called comparison. A circuit or device that can realize this is called a comparator. Specifically, it is a circuit that compares an analog voltage signal with a reference voltage. The two inputs of the comparator are analog signals, and the output is a binary signal 0 or 1. When the difference of the input voltage increases or decreases and the sign of the positive and negative remains unchanged, the output remains constant. Comparing the voltages of the two input terminals, if the voltage at the positive input terminal is a and the voltage at the negative input terminal is b, when a>b, the output is high level(logic 1); when a<b, the output is low level(logic 0). The schematic diagram is shown below (the voltage at the input terminals of the comparator is IN1 and IN2, the power supply is VCC/GND, the pull-up resistor is 1K, and the pull-up voltage is VCC.).Figure 2. Volatge ComparatorWhen output voltage IN1＞IN2, positive input is in high level with high voltage.When output voltage IN2＞IN1, negative input is in low level with high voltage.A reference voltage is usually applied to an input terminal. Then the output will indicate the  signal applied to the other input. Comparators are often used to determine whether a signal is above or below the reference level. And meawhile, the comparator can form a non-sinusoidal waveform conversion circuit and be used in fields such as analog and digital signal conversion.When the reference voltage is zero, the comparator is called a zero-crossing detector. It uses to convert a sine wave into a square wave. Two comparators can form a "window" circuit, which is used to determine whether a signal is between two limited values. In an output state of the comparator changes as quickly as possible, and sometimes the output of the comparator is required to have a certain logical relationship with the input, a dedicated strobe pulse is required. At this time, the op amp comparator only has an output during operation. In general, a dedicated comparator IC has better performance. And it replaces the operational amplifier in some applications. The most common advantage is that the comparator IC operates with a single power supply.The comparator has a wide range of uses, and can be used for discrete control of voltage signals such as thermistors and photosensitive sensors. For example, the voltage value of the photoresistor is collected by a comparator to determine whether it is day or night. What’s more, the comparator can also be used for voltage adjustment in an analog negative feedback circuit.Figure 3. TLC311 ComparatorIt can be seen from the diagram that the difference between the operational amplifier and the comparator lies in the output circuit. The operational amplifier uses a dual-transistor push-pull output. While the comparator uses only one transistor, the collector is connected to the output terminal, and the emitter is grounded. In addition, the comparator requires an external pull-up resistor from the positive power supply terminal to the output terminal, which is equivalent to the collector resistance of the transistor. Op amp can be used for linear amplifying circuit (negative feedback), as well as the non-linear signal voltage comparison (open-loop or positive feedback). The comparator can only be used for signal voltage comparison, not for linear amplifier circuits (because it has no frequency compensation). Both can be used for signal voltage comparison, but the comparator is designed as a high-speed switch, which has a faster conversion rate and a shorter delay than an operational amplifier. Ⅱ Circuit Structure Comparison2.1 Op AmpFigure 4. Op Amp CircuitOp amp circuit generally consists of input segment, gain segment, and output segment. The input  is composed of a differential amplifier section for amplifying the voltage difference between two pins. In addition, the in-phase signal component (the state where there is no potential difference between the pins and the input voltage is some) is not amplified to take a cancellation effect. If only relying on the differential amplifier circuit, the gain is insufficient, so the gain section is used to further increase the open gain of the operational amplifier.The anti-vibration phase compensation capacitor is connected between the gain section of the ordinary operational amplifier. In order to avoid changes in the characteristics of the operational amplifier due to loads such as resistors connected to the output pins, a compensation capacitor is connected with the output as a buffer.The change (distortion, voltage drop, etc.) in output characteristics caused by the load is mainly determined by the circuit structure and current capability of the output section.Generally, types of output circuit stages are A, B, C, and AB type, which are classified according to the amount of drive current flowing in the output (the difference in bias voltage). Depending on the amount of drive current, the level of distortion coefficient in the output section will change. The order of general circuit distortion from small to large is type A, type AB, type B, and type C. 2.2 ComparatorFigure 5. Comparator CircuitThe comparator circuit structure is basically the same as that of an operational amplifier. Because a negative feedback circuit is not used, there is no built-in phase compensation capacitor for vibration isolation. Owing to it can limit the operating speed between the input and output, the response time is significantly improved compared with the operational amplifier.The output circuit form of the comparator is mainly divided into open collector (open drain) type and push-pull output type. The figure shows the internal equivalent circuit of BA10393, it is also an open collector output circuit. Ⅲ Difference between Amplifier and Comparator3.1 Total Difference Summary(1) The main difference between amplifier and comparator is the closed-loop characteristic. Most of the amplifiers work in a closed loop state, so it is required that they cannot be self-excited after the closed loop. Most of the comparators work in an open loop state and pursue speed. For the case of relatively low frequencies, the amplifier can completely replace the comparator (the output level should be considered), but in most cases, the comparator cannot be used as an amplifier.In order to increase the speed, the comparator optimization will reduce the range of closed-loop stability. While the op amp is optimized for the closed-loop stable range, so the speed is reduced. If an amplifier used as a comparator, as for performance, you may pay more than an amplifier price for its closed-loop stability.In other words, whether an op amp is used as a comparator or not is to see the negative feedback depth of the circuit. Therefore, a shallow closed-loop comparator may work in the amplifier state and will not have self-excited state. However, a lot of experiments must be done to ensure that the op amp is stable under all working conditions.(2) In general speaking, the comparator is an open-loop application of the op amp, but the comparator is designed for voltage threshold comparison. The required comparison threshold must be accurate, and the rise or fall time of output edge after comparison should be short. It conforms to TTL/CMOS level/or OC, etc., does not require the accuracy of the intermediate links, in addition, the driving capability is also different. In short, using op amps as comparators cannot achieve full-scale output in most cases, or the edge time after comparison is too long. So it is better to use special comparators in the design.Figure 6. Op Amp and Comparator Symbol3.2 Distinctions between Op-amp and ComparatorAlthough the electrical symbols of the comparator and the op amp are the same on the circuit diagram, the two devices have big differences and are generally not interchangeable. The differences are as following:1. The flipping speed of the comparator is fast, on the level of ns, while the flipping speed of the op amp is generally us level(except for special high-speed op amps).2. The op amp can be connected to the negative feedback circuit, but the comparator cannot use negative feedback. Although the comparator also has two input terminals of the inverting and non-inverting phase, when connecting negative feedback, the circuit cannot work stably without phase compensation circuit inside. But it is the main reason why the comparator is much faster than the op amp.3. The output stage of the operational amplifier generally adopts a push-pull circuit and a bipolar output. The output stage of most comparators is an open collector structure, so pull-up resistors and unipolar output are needed, which are easy to connect to digital circuits.4. Based on input, many operational amplifiers have built-in protection circuits to prevent large voltages from damaging the chip. When a large differential voltage is input, the input work will become abnormal, because the differential input voltage range of the op amp is usually limited. In addition, the common-mode input voltage range of non-rail-to-rail op amps cannot reach the positive power rail, but the comparator supports the positive power rail. Op amps and comparators have many similar parameters. It is more convenient to choose op amps instead of comparators in applications that require low offset voltage, low offset current, and high common mode rejection. Ⅳ Basic Use of Comparators and Op AmpsFigure 7. Operational Amplifier and ComparatorThe comparator is an open-loop circuit. Its function is to compare the voltage of the output terminal. When the voltage at the positive input terminal is large (IN2>IN1), the output is in high level (note: The comparator is an OC output, and the output terminal needs a pull-up resistor. A few volts will be pulled up to output a few volts, otherwise, the output will be an open circuit). When the negative input terminal voltage is large (IN1>IN2), the output will be in low level (GND). The voltage comparator input signal is an analog voltage, and the output signal generally only has two steady-state voltages of high level and low level. The voltage comparator can convert various periodic signals into rectangular waves.Operational amplifier can be used in linear amplifying circuit, and can also be used in non-linear circuit (used as comparator). It is widely used in electrical circuits, such as non-inverting amplification, inverse proportional amplification, difference, addition circuit, subtraction circuit, integral and differential circuit.  Ⅴ Op-amp Comparator5.1 TechniqueThe functions of the operational amplifier are more complicated, but the comparator is relatively simple. When the frequency requirement is not high, the operational amplifier can also be used as a low-performance comparator in practical applications.In theory, an operational amplifier with an open-loop configuration (no negative feedback) can function as a low-end comparator. When the voltage of the non-inverting input terminal (V+) is higher than the inverting input terminal (V-), due to the higher open-loop gain, a positive saturation voltage +U is output. When the voltage of the inverting input terminal (V-) is higher than the positive input terminal (V+), a reverse saturation voltage -U is output. For an op amp that works in a linear negative feedback configuration and is powered by a separate voltage (±V), is different from a non-linear comparator without negative feedback. 5.2 Op Amp Comparators DisadvantagesIn practice, the use of op amp comparators has the following disadvantages compared with the use of dedicated comparators:1) The op amp is designed to work in a linear segment with negative feedback, so saturated op amps generally have a slower flip speed. Most op amps have a compensation capacitor used to limit the slew rate of high-frequency signals. This makes the op amp comparator generally have a propagation delay on the level of microseconds, but a dedicated comparator is on the level of nanoseconds.2) The op amp does not have a built-in hysteresis circuit and requires a special external network to delay the input signal. 3) The static operating current of the op amp is stable only under negative feedback conditions. When the input voltage is not equal, there will be a DC offset.   4) The function of the comparator is to generate the input signal for the digital circuit. When using the op amp comparator, it is necessary to consider the compatibility with the digital circuit interface.5) Interference may occur between different frequencies of multiple op amps.6) Many op amps have diodes connected in reverse series at the input. The input of the two poles of the op amp is generally the same, which will not cause operational problems. But the two poles of the comparator need to be connected to different voltages, which may cause unexpected breakdown of the diode.7) Integrated circuits of dedicated comparator, which better combine the characteristics of analog and digital. It provides an output representing the logic state related to two analog voltages, one of which is a fixed reference quantity. When another voltage exceeds the reference value, is less than the reference value, or is in a specified range, the comparator can send a signal. It has an optimized combination of high gain, wide bandwidth and large flip rate to quickly change the output state. And the conversion time of digital signals is usually very fast. Ⅵ Using Op Amps as Comparators NotesThere are many points should remember when using op amps as comparators in circuits. You must consider five main op-amp characteristics to ensure expected performance:1) Power SupplyIf the logic and operational amplifier share the same power supply, the rail-to-rail operational amplifier can drive CMOS and TTL logic. but if they do not share the same power supply, an additional interface circuit is required.2) Input impedance and Bias CurrentWhen the operational amplifier is used as a comparator, it must meet the high input impedance condition. The input impedance of the CMOS voltage feedback operational amplifier is in the megohm level, which meets the requirement. As for current feedback (transconductance) operational amplifiers, the inverting input terminal has extremely low impedance, which cannot be used as a comparator.3) Differential Input CharacteristicsThe original intention of operational amplifier design is to cooperate with negative feedback to reduce the differential input as much as possible. In specific applications, the actual differential input voltage and the maximum differential input voltage that the op amp can actually provide should be considered.4) Common-mode Input CharacteristicsFor the old FET-type input operational amplifier, when the input exceeds the common-mode voltage range allowed by the device, a phase reversal will occur. At present, the op amps produced by various manufacturers use various methods to prevent the op amps from phase inversion. If the actual common-mode voltage range exceeds the allowable input common-mode voltage range of the op amp, you need to actually verify whether it is working properly.5) StabilityBecause there is no negative feedback externally, the open loop gain of the op amp used as a comparator is very high. Therefore, parasitic capacitance of the PCB and ground impedance of the non-inverting input terminal may cause the output to oscillate.Figure 8. Window Comparator CircuitⅦ ConclusionAlthough op amps are not designed to be used as comparators, nevertheless, many applications where the use of an op amp as a comparator is an economical engineering decision. It is important to make an reasonable decision to ensure that the op amp chosen performs as expected.That said, it is necessary to read the data sheets carefully and to consider the effects of op amp parameters on the application. Because the op amp is being used in a nonstandard manner, it may not reflect actual behavior, and some circuit experiment is advisable. Furthermore, because not all devices are typical in their behavior, some pessimism is warranted when interpreting the experimental results. Frequently Asked Questions about Operational Amplifier as Comparator1. Can an op amp be used as a comparator?However, op amps can also be used as comparators, which causes them to operate non-linearly. The inputs are driven hard and the output voltage slams to the power supply rail. 2. How does a comparator op amp work?A comparator circuit compares two voltages and outputs either a 1 (the voltage at the plus side; VDD in the illustration) or a 0 (the voltage at the negative side) to indicate which is larger. Comparators are often used, for example, to check whether an input has reached some predetermined value. 3. How op amp can be used as comparator in open loop configuration?Thus, an op-amp operating in open loop configuration will have an output that goes to positive saturation or negative saturation level or switch between positive and negative saturation levels and thus clips the output above these levels. This principle is used in a comparator circuit with two inputs and an output. 4. What is the difference between a comparator and an amplifier?Unlike operational amplifiers that usually operate with the input voltages at the same level, comparators typically see large differential voltage swings at their inputs. But some comparators without rail-to-rail inputs are specified to have a limited common mode input voltage range. 5. What is the difference between op amp and comparator?The difference between an op-amp comparator and a voltage comparator is in the output stage as a standard op-amp has an output stage that is optimized for linear operation, while the output stage of a voltage comparator is optimized for continuous saturated operation as it is always intended to be close to one supply.