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IntroductionA three-phase circuit consists of a three-phase source, a three-phase load, and a three-phase transmission line. The most basic characteristic of this circuit is that it has one or more groups of power supplies. Each group consists of three sinusoidal power supplies with the same amplitude, the same frequency, 120° phase difference, and the power supply and the load are connected in a specific way. Three-phase circuits are widely used in power systems such as power generation, transmission, distribution, and high-power electrical equipment.What does 3 phase mean?CatalogIntroductionⅠ Three-phase Circuit Basics1.1 Three-phase Circuit Characterized1.2 Three-phase Circuit Terms1.3 Three-phase Voltage & Current1.4 Three-phase Circuit AdvantagesⅡ Symmetrical vs Asymmetrical2.1 Symmetrical Three-phase Circuit2.2 Three-phase AsymmetryⅢ Power in Three Phase Circuit FormulasⅣ Frequently Asked Questions about Three-phase CircuitⅠ Three-phase Circuit BasicsThe three phases could be supplied over six wires, with two wires reserved for the exclusive use of each phase. However, they are generally supplied over only three wires, and the phase or line voltages are the voltages between the three possible pairs of wires. The phase or line currents are the currents in each wire. Voltages and currents are usually expressed as rms or effective values, as in single-phase analysis.1.1 Three-phase Circuit CharacterizedSpecial power supplySpecial loadSpecial connectionSpecial solution1.2 Three-phase Circuit Terms1) End wire (fire wire)2) Neutral line3) Line current4) Line voltage5) Phase current6) Phase voltage7) Three-phase three-wire system and three-phase four-wire system1.3 Three-phase Voltage & CurrentStar ConnectionSummery: Line Voltage vs Phase Voltage1) The line current is equal to the corresponding phase current.2) If the phase voltage is symmetrical, the line voltage is also symmetrical.3) The line voltage is equal to √3 times the phase voltage.4) The phase of the line voltage leads the corresponding phase voltage by 30°. Delta ConnectionSummery: Line Current vs Phase Current1) The line voltage is equal to the corresponding phase voltage.2) If the phase currents are symmetrical, the line currents are also symmetrical.3) The line current is equal to √3 times the phase voltage.4) The phase of the line current lags behind the corresponding phase voltage by 30°.1.4 Three-phase Circuit AdvantagesPower generation: Three-phase power is increased by 50% compared to single-phase power.Transmission: 25% less material than single-phase circuit transmission. That is, under certain conditions, transmitting a certain amount of power by three-phase only requires 75% of the copper of single-phase transmission.Power distribution: More economical than single-phase transformers and easier to connect to the load.Transportation: simple structure, low cost, reliable operation, convenient maintenance.In addition, three wires are usually seen in high-voltage transmission lines, whether on towers or poles, with pin or suspension insulators. Some high-voltage lines are now DC, since solid state devices make it easier to convert to and from AC. The DC lines are free of the problems created by phase, as well as eliminating the skin effect that reduces the effective area of the conductors. It is not nearly as easy to manage long-distance electrical transmission as might be thought.Ⅱ Symmetrical vs Asymmetrical2.1 Symmetrical Three-phase CircuitA symmetrical three-phase power source is usually generated by a three-phase synchronous generator, as shown in Figure (a). Among them, the three-phase windings differ by 120° in space. When the rotor rotates at a uniform angular velocity ω, an induced voltage is generated in the three-phase winding, thereby forming a symmetrical three-phase power supply as shown in Figure (b). Among them, the three ends of A, B, and C are called the start end, and the three ends of X, Y, and Z are called the end. When you connect a load to the three wires, it should be done in such a way that it does not destroy the symmetry.Instantaneous Voltage Calculation of Three-phase PowerIn the formula, take the phase A voltage uA as the reference sine quantity. The three-phase voltage waveform diagram is shown in Figure (a).The key to understanding three-phase is to understand the phasor diagram for the voltages or currents. The phasor of the three-phase power supply can be represented by the Figure (b).The characteristics of the symmetrical three-phase power supply can be derived from the above formula:From the above formula, the sum of the instantaneous value of the three-phase power supply and the sum of the phasor are always zero.The sequence in which each phase of the three-phase power passes through the same value (such as the maximum value) is called the phase sequence of the three-phase power, and the phase sequence of the above-mentioned three-phase voltage is called the positive sequence. Conversely, if phase B exceeds 120° of phase A and phase C exceeds 120° of phase B, this phase sequence is called reverse sequence. If there is no special instructions, it will generally default to positive order.2.2 Three-phase Asymmetry1) In a three-phase circuit, as long as there is asymmetrical part, it is called a three-phase asymmetry.2) The complex power absorbed by the three-phase load is equal to the sum of various complex powers.3) The instantaneous power of a three-phase circuit is the sum of the instantaneous power of each phase load.4) In a three-phase three-wire circuit, whether symmetrical or not, two power meters can be used to measure three-phase power.When the power supply voltage in the three-phase circuit is asymmetrical or the parameters in the circuit are asymmetrical, the current in the circuit is generally asymmetrical. This kind of circuit is called three-phase asymmetry. There are a lot of asymmetry parts in three-phase circuits, and the causes are different. For example, there are many low-power single-phase loads in a three-phase circuit, it is difficult to make them into a completely symmetrical circuit. When a three-phase circuit is broken or short-circuited, it is also a three-phase asymmetry circuit. In addition, some electrical equipment and instruments formally use three-phase asymmetry to work.For example, the most common low-voltage three-phase four-wire system. Due to the large number of single-phase loads in the low-voltage system, the equivalent impedances ZA, ZB, and ZC of the three phases circuit are generally different from each other, and the power supply voltage can generally be considered symmetrical. In this way, a symmetrical three-phase power supply converts to an asymmetrical three-phase load.The circuit shown in the figure has two nodes, and the voltage between the two nodes can be directly calculated according to the node voltage method.Although the power supply voltage in the above formula is symmetrical, the voltage between the neutral point of the power supply and the neutral point of load is not zero due to the load asymmetry, that is, UNN≠0. According to Kirchhoff's voltage law, the phase voltage of the load can be obtained as:The phasor diagram of each voltage corresponding to the above formula is as follows:Ⅲ Power in Three Phase Circuit Formulas1. Average PowerSuppose the power absorbed by a phase load in a symmetrical three-phase circuit is equal to Pp=UpIpcosφ, where Up is the phase voltage and Ip is the phase current of the load. Then the total three-phase power is: P=3UpIpcosφPay Attention To1) φ in the above formula is the phase difference angle (impedance angle) of phase voltage and phase current.2) cosφ is the power factor of each phase, in a symmetrical three-phase system:cosφA=cosφB=cosφC=cosφ3) The formula calculates the circuit power (or the power absorbed by the load).When the load is in a star connection, the line voltage  and line current  at the load end are substituted into the above formula:When the load is in a delta connection, the line voltage  and line current  at the load end are substituted into the above formula:2. Reactive powerThe reactive power absorbed by the load in a symmetrical three-phase circuit is equal to the sum of the reactive power of each phase:3. Apparent Power4. Instantaneous PowerSuppose the voltage and current of phase A of the three-phase load are:Then the instantaneous power of each phase is:It can be proved that their sum isThe above formula shows that the instantaneous power of a symmetrical three-phase circuit is a constant, and is equal to the average power. This is one of the advantages of a symmetrical circuit. For example, on a three-phase motor, a balanced electromagnetic torque is obtained and mechanical vibration is avoided, which is not available in single-phase motors. Ⅳ Frequently Asked Questions about Three-phase Circuit1. What is a 3 phase circuit?Three-phase power is a three-wire ac power circuit with each phase ac signal 120 electrical degrees apart. ... three-phase is that a three-phase power supply better accommodates higher loads. Single-phase power supplies are most commonly used when typical loads are lighting or heating, rather than large electric motors. 2. How many wires are in a 3 phase?four wiresThe three-phase system has four wires. Three are conductors and one is neutral. 3. What is the 3 phase power formula?3-Phase Calculations. For 3-phase systems, we use the following equation: kW = (V × I × PF × 1.732) ÷ 1,000. 4. What is the advantage of three-phase system?A three-phase circuit provides greater power density than a one-phase circuit at the same amperage, keeping wiring size and costs lower. In addition, three-phase power makes it easier to balance loads, minimizing harmonic currents and the need for large neutral wires. 5. What is meant by 3 phase balanced load?A balanced three-phase voltage or current is one in which the size of each phase is the same, and the phase angles of the three phases differ from each other by 120 degrees. ... With such a balanced load, if a balanced three-phase supply is applied, the currents will also be balanced.

IntroductionWhat is a triac? TRIAC (Triode for Alternating Current) is an electronic component that is widely used in alternating current power control. It is a three terminal electronic component that conducts current in either direction when triggered. TRIAC is able to switch high voltages and high levels of current, and over both parts of an AC waveform. This makes triac circuits ideal for use in a variety of applications where power switching is needed. You can find its applications in switching, phase control, chopper designs, brilliance control in lamps, speed control in fans, motors etc.TRIAC Characteristics, TRIAC Structure and TRIAC WorkingCatalogIntroductionⅠ TRIAC vs Silicon Controlled Rectifiers (SCR)Ⅱ TRIAC Structure and SymbolⅢ How Do You Use a TRIACⅣ How Does a TRIAC Work?4.1 TRIAC Leakage Current4.2 SolutionsⅠ TRIAC vs Silicon Controlled Rectifiers (SCR)Thyristor also called SCR stands for silicon controlled rectifier while TRIAC stands for triode for alternating current. The TRIAC has on and off state characteristics similar to SCR. The main difference between SCR and TRIAC is that thyristor is a unidirectional device while in TRIAC as a bidirectional device. A TRIAC is defined as a three terminal AC switch which is different from the other silicon controlled rectifiers (SCR) in the sense. They can turn and regulate both parts of the AC waveform easily. This makes this component appropriate for a variety of applications where control of AC power is needed. A dimmer circuit will be an example application, and we use it domestically as a ceiling fan regulator circuit. Also it can be used to regulate a motor or electric heater's input power. This is why TRIAC is used for applications of low to medium power, leaving SCR with high-power applications. While this is a very interesting system, a problem known as "leakage current" is present. And we'll talk more about this leakage current, its adverse effects, and some well-known ways to solve these problems in this article. But let's clear out the basics of TRIAC before that. Ⅱ TRIAC Structure and SymbolAs for triac symbol, like any other electronic component, it consists of two SCRs linked in an antiparallel configuration, and if we look very closely at its symbol, it clearly reflects the TRIAC's bidirectional properties. Which you observe from the picture below.The upgraded variant of the thyristor is the TRIAC. A thyristor can only control current in one direction, as you already know, but a TRIAC can control current in both negative and positive directions. TRIAC turns in each sine wave loop because of the existence of the sine wave, which means we can use the entire cycle, unlike SCRs. Like thyristor, a TRIAC has three terminals, but it becomes a little difficult to assign names to these terminals since they are related simply to the cathode and the anode of two SCRs. Two SCRs are also connected to the gate terminal, which is why it was called Anode 1 and Anode 2 or Main Terminal 1 and Main Terminal 2 (MT1 and MT2).A multimeter can be used to test the health of a triac. First put the multimeter selector switch in a high resistance mode (100K), then connect the positive lead of multimeter to the MT1 terminal of triac and negative lead to the MT2 terminal of triac (there is no problem if you reverse the connection). Ⅲ How Do You Use a TRIACTriacs are semiconductor devices that are widely used for switching medium power AC. Let's acquire a little knowledge of  TRIAC functions before going further. As the following figure shows you.Two-thyristor AnalogyWe have previously said that as a configuration of two SCRs, a TRIAC can be realized. The above image provides a little bit more clarity on the subject, but it is much more complex to work at the semiconductor level. A TRIAC can be activated in many ways, unlike SCR, regardless of the polarity of the terminals. Regardless of the polarity of the initiating pulse, it may also be activated. When working with TRIAC, one thing to remember is that when the MT2 and gate current are at the same polarity, the sensitivity of the trigger current is much greater. We can now move on to cleaning out our key issue of leakage current with the simple cleared out.Triac Switching Circuit ExampleⅣ How Does a TRIAC Work?4.1 TRIAC Leakage CurrentThere is structural leakage current in the off state of thyristor, TRIAC, or any other solid-state AC switches, which is why a small amount of current flows through the load, this circuit is sufficient in some cases to charge a load circuit (Inductive) and causes it to flash spontaneously. We need to take careful care of the specifics and design the circuit accordingly to avoid this, and we will talk more about it in this section of this article.If the voltage of MT2 reaches a certain rated threshold voltage (which can occur due to the transient state of high voltage), the leakage current between the two terminals may enter the point at which the TRIAC breaks into conduction mode. In this state, a sudden localized heat will be produced when a sudden increase in current flows through the TRIAC, so that the TRIAC can be destroyed. Incandescent lamps are most likely the source of strong inrush currents, with capacitive loads.4.2 SolutionsBy applying one or more of the following methods, this condition can be avoided:1) Maximum Temperature Ratings Tj max. ensure that the temperature is not surpassed. As temperature rises, the current of leakage through the system increases, we can eliminate/reduce this issue by integrating specific TRIAC brands for specific requirements.2) By placing a broad value resistor from the gate to the cathode, we can reduce the TRIAC's sensitivity. This decreases the gate current, thereby reducing the current of leakage. It, on the other hand, increases the TRIAC turn-on time.3) If it is not possible to implement the methods described above, we can use a TRIAC with a less sensitive gate during the off time and apply a small degree of reverse bias to the gate. In this process, we have to minimize the dissipation of power through the gate.4) Depending on the form of load, another strategy for reducing leakage current is to fully eliminate the snubber circuit. The capacitor leakage also becomes the main source of leakage current, so we can decrease the current flow through the snubber and decrease the leakage current by removing the snubber network.If you want to know more TRIAC info, you can check its Triac I-V Characteristics curves with more examples. Before try these methods to reduce current leakage, please remember safety first! Frequently Asked Questions about TRIAC Basic and Its Applications1. What is a triac used for?The Triac is most commonly used semiconductor device for switching and power control of AC systems as the triac can be switched “ON” by either a positive or negative Gate pulse, regardless of the polarity of the AC supply at that time. 2. Which is an example of Triac?TRIAC ApplicationsTRIAC is very commonly used in places where AC power has to be controlled for example, it is used in the speed regulators of ceiling fans, AC bulb dimmer circuits etc. Let us look into a simple TRIAC switching circuit to understand how it works practically. 3. What is triac and its characteristics?A Triac is defined as a three terminal AC switch which is different from the other silicon controlled rectifiers in the sense that it can conduct in both the directions that is whether the applied gate signal is positive or negative, it will conduct. Thus, this device can be used for AC systems as a switch. 4. What is a triac switch?A Triac is a high-speed solid-state device that can switch and control AC power in both directions of a sinusoidal waveform. Being a solid state device, thyristors can be used to control lamps, motors, or heaters etc. 5. What is the working principle of Triac?The triac is another three-terminal ac switch that is triggered into conduction when a low-energy signal is applied to its gate terminal. Unlike the SCR, the triac conducts in either direction when turned on.

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

IntroductionOver voltage protection is necessary to prevent damage as a result of electrical transients. It is a power supply feature which shuts down the supply, or clamps the output, when the voltage exceeds a preset level. Most power supplies use an over-voltage protection circuit to prevent damage to the electronic components. They offer some form of overvoltage-protect (OVP) circuit to detect and then quickly pull down the overvoltage. When the voltage exceed the rated maximum breakdown voltage, do you know using Zener diode to make overvoltage protection circuit? Here introduces the Zener diode overvoltage protection circuit, which is the most common way.CatalogIntroductionⅠ Over Voltage BackgroundⅡ Zener Diode Input Protection BasicsⅢ Simple Overvoltage Protection Circuit Using Zener DiodeⅣ How Do You Choose a Zener Diode to Protect a Circuit?Ⅴ Zener Overvoltage Protection OverviewⅠ Over Voltage BackgroundEvery circuit design operates at various voltage levels, with 3.3V, 5V, and 12V being the most common voltage levels for a digital circuit. But every design is special, and having more than one operating voltage is also normal for a circuit. For example, a standard computer SMPS system will work at six different levels of voltage, namely ±3.3V, ±5V, and ±12V. In these cases, if a low-power device is operated by a high voltage, the component will be permanently impaired if various voltage levels are used to power different types of components. Therefore, to avoid over-voltage harm, the designer should always concentrate on implementing an over-voltage security circuit in his designs.There will be three different voltage ratings for any part or circuit, namely the minimum operating voltage, the suggested or normal operating voltage and the maximum operating voltage. For any circuits or parts, any value over the maximum operating voltage can be fatal. Using a Zener diode over voltage protection circuit is a very common and cost-effective solution. Ⅱ Zener Diode Input Protection BasicsIn order to protect the circuit from overvoltage conditions, Zener diodes are often the first option. A Zener diode follows the same diode theory, which blocks the current flow in the reverse direction. However, there is a drawback that the Zener diode blocks the flow of current in the reverse direction only for a restricted voltage defined by the voltage rating of the Zener diode. A 5.1V Zener diode blocks current to flow in the opposite direction up to 5.1V If the voltage is greater than 5.1V through the Zener diode, it allows the current to pass through it. This Zener diode function makes it an excellent over-voltage security component.Over-Voltage Protection Circuit using Zener DiodesⅢ Simple Overvoltage Protection Circuit Using Zener DiodeConsider a circuit, where need microcontroller over-voltage protection. Anything that has a maximum rating of 5V across the microcontroller IO pins. So voltage more than 5V will damage the microcontroller.Figure 1. Overvoltage Protection for MicrocontrollerThe diode used in the circuit above is a Zener diode of 5.1V. During an over-voltage case, it will work perfectly. It can transfer the current and regulate the voltage up to 5.1V if the voltage is more than 5.1V. In practice, however, it will behave as a regular diode and block less than 5.1V The image below is a simulation of the spice circuit of Zener diode protection. For the full simulation description, you can make it based on your need.Figure 2. Simulating Overvoltage Protection CircuitThere is an input voltage in the schematic above, which is dc supply. The R1 and D1 are two components that protect the output from protection from over-voltage. The D1, 1N4099, in this case, is a Zener diode. When the V1 reaches 6.8V, the output will be protected. The output would remain at a maximum of 6.8V as a reference voltage of 1N4099.Let's see how the above circuit works as the protection circuit of the Zener diode input and protects the output from more than 6.8V voltage.Using pspice cadence, the above circuit is simulated. The output remains constant at 5.99V at the 6V input voltage across the V1 (Which is 6.0V).The input voltage in the above simulation is 6.8V. The performance, therefore, is 6.78V, which is similar to 6.8V. Let's further raise the input voltage and create a situation of overvoltage.Now, 7.5V, which is more than 6.8V, is the input voltage. The performance is now now at 6.88V. This is how a Zener diode is successful in saving the connected circuit from a situation of overvoltage, even when the voltage returns to less than 6.8V, as shown in the previous stage, the circuit will operate normally again. In other words, a Zener diode does not get fried even during an overvoltage state, unlike a fuse.To pick different overvoltage margins in the above circuit, any other Zener diodes with different values such as 3.3V, 5.1V, 9.1V, 10.2V can be used. Ⅳ How Do You Choose a Zener Diode to Protect a Circuit?The next critical part is choosing the value of the Zener Diode. The points below will assist you in selecting the correct Zener Diode value and part number.1) Choose the voltage of the Zener diode first. It is the voltage value that will serve as a close circuit for the Zener diode and protect the load from overvoltage. The Zener voltage is 6.8V in Pspice, for the above example.There will be some cases where there is no usable targeted Zener diode voltage. In such instances, it is possible to choose a near value of the Zener diode. For example, for overvoltage security up to 7V, a near value is a 6.8V Zener diode.2) Calculate the load current that is linked across the circuit of overvoltage safety. This is 50mA for our example discussed above. Other than the load current, biasing current is required by Zener diodes. Therefore, the total current, plus the Zener diode biasing current, should be equal to the load current. For the above mentioned example, it can be total current=50mA+10mA=60mA.3) There is a power ranking for Zener diodes. Therefore, for proper heat dissipation, the correct Zener diode power rating is required. Based on the measured total current in Phase - 2, which is 60mA, the power rating can be calculated. Therefore, the power rating of the Zener diode would be equal to the voltage of the Zener diode, which connects the total current flowing through the diode.4) Calculate the value of the resistor by differentiating the voltage of the source and the general voltage. The limit which can be applied to the circuit would be the source voltage. For example, it can be 13V to maximize overvoltage that can occur or can be added as a supply voltage.The voltage drop through the resistor will then be = 13V-6.8V = 6.2V According to the law of the ohm, the resistor value will be = 6.2V / 0.060 A = 103R It is possible to choose the standard value 100R resistor.5) Zener diode typical values are 5.1V, 5.6V, 6.2V, 12V and 15V -most common; they are also have 3V, 5V, 12V, 18V, 24V.Ⅴ Zener Overvoltage Protection OverviewZener diode as a voltage regulator, it is suitable for overvoltage protection circuit. Because the easiest and simplest process to protect devices from overvoltage is overvoltage-protect circuit using Zener diodes. The voltage remains regulated in this technique and the cost of this circuit is much lower compared to other techniques.Although, surely, there are disadvantages to this sort of circuit. Power dissipation is the main downside of this type of circuit. It still dissipates heat due to the linked series resistor and results in energy wastage. Frequently Asked Questions about Zener Diode Overvoltage Protection Circuit Design1. What is overvoltage protection?Over voltage protection is a power supply feature which shuts down the supply, or clamps the output, when the voltage exceeds a preset level. Most power supplies use an over-voltage protection circuit to prevent damage to the electronic components. 2. Which is most common circuit protection device?The SPD(surge protection device) device is allied in parallel in the power supply circuit, which can be used on all stages of the power supply system. The surge protection device is the most frequently used and also well-organized kind of over-voltage protective devices. 3. What can cause overvoltage?The main causes include insulation failure, arcing ground and resonance etc. 4. How does a Zener diode regulate voltage?Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. When connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage.

CatalogⅠ IntroductionⅡ The Layout of the Car MarketⅢ The Layout in the Industrial FieldⅣ The Layout on the Internet of ThingsⅤ ConclusionⅠ IntroductionON Semiconductor: In 2021, it will focus on the automotive, industrial and cloud power, and the Internet of Things marketThe end of the year and the beginning of the year is often a time for companies to make summaries and outlook, and the semiconductor industry is no exception. Not long ago, ON Semiconductor also made a year-end review of 2020 and revealed to the media what ON Semiconductor plans to do in 2021. "The year 2020 is a year of surprises for everyone. People around the world are experiencing the worst epidemic in a century. The good news is that the epidemic has eased in some parts of the world. Looking forward to 2021, we hope to get out of the epidemic as soon as possible and have a more favorable business environment." DavidSomo, senior vice president of strategy, marketing and solution engineering at ON Semiconductor, said in his opening remarks at the press conference.Due to the epidemic, the global economic situation in 2020 is not optimistic. According to Bloomberg data, GDP growth in 2020 is expected to drop from 2.8 percent in 2019 to minus 3.7 percent. China will be the only major economy in the world with positive growth by 2020, while all other economies are expected to suffer single-digit declines. Fortunately, in the second half of 2020, the global economy began to recover. As indicated by the PMI (Purchasing Managers' Index), manufacturing activity in all major economies resumed growth in the second half of the year, with the only exception being Japan, which also showed a positive trend. DavidSomo expressed an optimistic outlook for the global economy in 2021. "We expect that the economic outlook for next year will be positive, significantly better than this year, and there is a consensus for overall GDP growth of around 5% in 2021," he said. He also stressed that, for its part, ON Semiconductor wants to be a reliable supplier of power, analog, sensor and connection solutions, enabling innovation in energy-efficient electronics. It will focus on providing comprehensive solutions to global customers in the automotive, industrial and cloud power markets, as well as the Internet of Things market. Ⅱ The Layout of the Car MarketIn the automotive sector, ON Semiconductor implements a comprehensive sensor product and solution layout, including image sensors, radar, lidar, ultrasonic sensors and other products and solutions. In additon to sensors, R&D resources continue to be invested in silicon and silicon carbide power semiconductors, as well as LED lighting and automotive power management products. Those investments have also paid off handsomely, accounting for 33% of ON Semiconductor's $5.5 billion in 2019 revenue. DavidSomo pointed out that in the future, ON Semiconductor will continue to develop new products in the automotive market and increase investment in research and development. "On the automotive side, we will push forward research and development around sensors, autonomous driving-related applications, new energy vehicles, and the electrification of vehicles." He revealed. ON Semiconductor is one of the top 10 semiconductor suppliers in the automotive industry. DavidSomo proudly states, "Since entering the automotive market in 2010, ON Semiconductor has shipped 130 billion chips to automotive customers by 2019. In 2019, there were more than 230 ON Semiconductor devices used in every vehicle produced worldwide."The company has set the industry standard for automotive image sensors, with more than 120 million of them shipped to Advanced Driver Assistance System (ADAS) applications. Over the past 13 years, more than 400 million ON Semiconductor automotive image sensors have been used in vehicles on the road. ON Semiconductor has developed a complete portfolio of product solutions and sensor modes to support L4 and L5 autonomous vehicles, including ultrasonic sensor interfaces, image sensors, solid-state LIDAR and millimeter-wave radar technologies. DavidSomo said that ON Semiconductor's MMW technology, acquired from IBM Research Group in Sea Law (IBM), has been used in communications and fiber optics, and plans to use the technology in the automotive sector. It is currently being tested with customers for prototypes but has not yet been used in commercial automotive production. In the case of LiDAR, the technology came from the acquisition of sensL to acquire technology on solid-state LiDAR. According to DavidSomo, sensL was originally designed for use in the medical market but is now being developed for use in the automotive market. "Multiple customers have incorporated our Silicon Photomultiplier (SiPM) and Single-Photon Avalanche Diode (SPAD) technologies into solid-state lidar systems, enabling commercial lidar applications in the automotive industry for L2+ and L3 level autonomous driving safety applications." He went on to point it out. On the cost side, DavidSomo says that because ON Semiconductor's lidar solution is a solid-state solution, it has been able to bring the cost of lidar down from more than $1,000 for mechanical rotation in the past to the current $500 range for solid-state solutions. In terms of image sensors, over the years, ON Semiconductor has made three acquisitions, including Aptina, Cypress's image sensor technology and TrueSense, to enrich its image sensor portfolio.Ⅲ The Layout in the Industrial FieldDavidSomo said that ON Semiconductor offers a wide range of power and automation solutions in the industrial and cloud power markets that support different application scenarios. In terms of power semiconductors, in 2018, ON Semiconductor ranked second behind Infineon with a market share of about 9 percent, according to IHS. As an example, he pointed out that powering the cloud requires several processes, including generation, power supply and power demand management. "In these processes, we have a complete silicon and silicon carbide technology portfolio that supports power generation, transmission and distribution, as well as power and demand management for data centers and 5G base stations." He points it out. In terms of energy efficiency improvement, the use of ON Semiconductor's cloud power solution increased energy efficiency by about 0.5%. In a typical VL data center, the savings over the life of the system are estimated at approximately $38 million. The energy efficiency improvement is only 0.5%, which may not sound like much, but when measured at the system-wide level of deployment, the savings over the lifetime of the system are significant. The development of energy infrastructure is also unstoppable, as a society and the government further promote the development of new energy sources and shift more from coal-fired power generation to renewable energy sources such as wind and solar power. In order to save energy and reduce emissions, reduce air pollution, from fuel vehicles to new energy vehicles, which has generated the demand for electric vehicle charging pile, and ON Semiconductor silicon and silicon carbide power discrete devices and modules, can support the construction of electric vehicle charging pile. Similarly, its power technologies, such as solar inverters used in solar panels, enable clean energy generation, and "ON Semiconductor is fortunate to partner with customers in China to develop applications in these areas." DavidSomo said. Manufacturing is also one of the biggest users of energy. In the United States, our power solutions are used in plant motor drive systems, resulting in savings of more than $350 million per year. If applied globally, the potential savings could reach approximately $5.8 billion per year, resulting in energy efficiency improvements in manufacturing motor drive systems.Ⅳ The Layout on the Internet of ThingsIn the Internet of Things (IoT) area, ON Semiconductor has a complete set of key components and modules that enable devices to be connected, intelligent, aware and actuated in their operating environment."Of course, we recognize that our semiconductor components are not sufficient to build the end-to-end connected Internet of Things (IoT) systems that our customers need, so we are investing more to accelerate development and provide our customers with a number of development tools to enable faster application development and market deployment." DavidSomo admits. While ON Semiconductor can provide many of the key building blocks, DavidSomo believes it is important to work with partners in the Internet of Things (IoT) ecosystem to build IoT solutions for secure end-to-end connectivity. As shown in the figure below, ON Semiconductor works with a number of technology partners to enhance the performance of IoT devices developed by clients, as well as with infrastructure providers such as cloud service providers to enable edge devices to connect securely and stably to the cloud. He also revealed that the company is focusing on three vertical areas in the Internet of Things, namely asset tracking and monitoring, connected lighting, and smart homes and building automation.Ⅴ ConclusionIn conclusion, DavidSomo said that in the process of semiconductor device manufacturing, ON Semiconductor also recognizes the growing need to provide its customers with complete system solutions that add value. As a result, ON Semiconductor offers modular products for power components and built-in controls, as well as reference design kits to speed up customer product development. ON Semiconductor also provides software and design tools to help customers complete designs faster and get their equipment to market faster. He also stressed that ON Semiconductor will focus on research and development, and is committed to developing innovative products and solutions including power, simulation, sensors and connectivity solutions. "Through both endogenous growth and exogenous acquistions, we are further enhancing our capabilities to support the applications our customers are developing, while also building our professional application capabilities to help them develop products better and faster to market."

IntroductionLED lights cannot directly use the conventional mains grid voltage, because of the characteristics of LED lighting. In order to meet the special voltage and current requirements of LEDs, a specially designed voltage conversion device must be used to make LEDs work normally. This device is an LED driver. LED drivers are usually switching mode devices that convert the input voltage (Typically 120-220 VAC or 12 VDC) into a voltage at which the current drawn by the LED's is equal to its drive current. The drive current is regulated for optimum brightness, led service life, and battery life. A drive current lower than the maximum drive current of an LED can greatly prolong service life. As a key part of LED lighting, the quality of LED drivers directly affects the performance of LED lighting.Choose the Correct LED Drivers For LED LightsNo matter how good the quality of the LED driver is, failure and maintenance are inevitable. This article will analyze the 10 failures in LED lighting design and its application based on the relevant technology and practical experience of the LED driver.CatalogIntroductionⅠ LED Driver Failure Analysis1.1 Forward Voltage Drop (Vf) Range1.2 Power Margin and Derating Requirements1.3 LED Working Characteristics1.4 Test Session1.5 Different Load with Different Test Results1.6 LED Driver Circuit Problem1.7 Wrong Phase Wring1.8 Grid Fluctuation1.9 Frequent Line Trips1.10 Drive CoolingⅡ LED Driver Maintenance2.1 Multimeter to Detect LED Driver2.2 Identify LED Power SupplyⅢ LED Driver Circuit Modulation3.1 Pulse Width Modulation (PWM)3.2 Pulse Frequency Modulation (PFM)3.3 Sliding-Mode ModulationⅣ One Question Related to LED DriverⅠ LED Driver Failure AnalysisThe LED driver is measuring current passing through LEDs using sense resistor and then increase or decrease the voltage to maintain constant current continuously. LEDs are kind of diode so they need DC voltage to operate so most of the LED drivers are boost and can vary output supply in wide range (example, 16V to 38V). They also have dimming control by PWM signal from microcontroller OR by having a manual potentiometer to change sense resistor. According to them, LED driver failures are complex, but we can follow the steps below to analyse.1.1 Forward Voltage Drop (Vf) RangeLED lamp load end is generally composed of a number of LEDs connected in series, and its working voltage Vo=Vf×Ns, where Ns represents the number of LEDs. And the Vf of an LED varies with temperature. Generally, at a constant current, Vf becomes lower at high temperatures and becomes higher at low temperatures. The LED lamp load working voltage is VoL at high temperature, and VoH represents a value at low temperature. When selecting an LED driver, consider that the driver output voltage range is greater than VoL～VoH.If the maximum output voltage of the LED driver is lower than VoH, the maximum power of the lamp may not reach the actual power required at low temperature. If the minimum voltage of the selected LED driver is higher than VoL, the output of the driver may exceed the working range at high temperature. And LED driver will work unstable, making the lights flicker.Considering the overall cost and lamp efficiency, don’t blindly pursue the ultra-wide output voltage range of the LED driver. Because the driver voltage is only in a certain range, its efficiency is the highest. When the range is exceeded, the efficiency and power factor (PF) will deteriorate. In addition, if the design of the driver output voltage range is too wide, high costs and unoptimized efficiency will be made. 1.2 Power Margin and Derating RequirementsIn general, the nominal power of the LED driver refers to the data measured under the rated environment and rated voltage. Taking into account different applications, most LED driver suppliers will provide power derating curves in their product specifications (common load vs. ambient temperature derating curves and load vs. input voltage derating curves).As shown in Figure 1, the red curve represents the power derating curve when the input is 120Vac, and its load varies with the ambient temperature. When the ambient temperature is lower than 50℃, the LED driver is allowed to be 100% full load. When the ambient temperature is as high as 70℃, the LED driver can only be derated to 60% of the load. When the ambient temperature changes between 50℃~70℃, the driver load varies with the temperature linearly.Figure 1. Power Derating Curve (Load vs Ambient Temperature)The blue curve represents the power derating curve when the input is 230Vac or 277Vac, and its load varies with the ambient temperature. The principle is similar to the above mentioning.As shown in Figure 2, the blue curve represents the derating curve of the LED driver when the ambient temperature is 55°C, its output power varies with the input voltage. When the input voltage is 140Vac, the load of the driver is allowed to be 100%, and the input voltage will be adjusted downward. If the output power remains the same, the input current will rise, resulting in input terminal loss and lower efficiency. When the device temperature rises, exceeding the rated temperature, which may cause the device to fail.Figure 2. Power Derating Curve (Load vs Input Voltage)Therefore, when the input voltage is less than 140Vac, the output load of the LED driver is required to linearly decrease as the input voltage decreases. According to the above derating curve and corresponding requirements, when choosing a LED driver, actual applying needs are important, as well as the derating margin. 1.3 LED Working CharacteristicsWhen the required input power is a fixed value, such as a fixed error of 5%, the output current can only be adjusted to the specified power for each lamp. Due to different working ambient temperature and different lighting time, the power of each lamp will vary greatly.Although there are considerations for marketing and business factors. However, the volt-ampere characteristic of the LED lamp determines that the LED driver is a constant current source, and its output voltage varies with the series voltage Vo of the LED load. When the efficiency of the driver is basically unchanged, its input power changes with Vo. And meanwhile, the overall efficiency of the LED driver will increase after thermal equilibrium. Under the same output power, the input power will decrease compared to the boot time.Therefore, when formulating requirements, LED driver users should first understand the operating characteristics of LEDs. Avoid suggesting indicators that do not meet the principles of operating characteristics, and indicators that far exceed actual requirements, resulting in excess quality and cost waste. 1.4 Test SessionSample test problems, for example, multi-brand LED driver samples all failed during the test. The reason is that a self-dual voltage regulator is used to directly power the LED driver for testing. After power on, the voltage regulator is gradually adjusted from 0Vac to the rated operating voltage of the LED driver. This kind of test operation can easily make the LED driver start and work with the load when the input voltage is very small, but this situation will cause the input current to be far greater than the rated value. And the internal input terminal related components, such as fuses, rectifier bridges, thermistors, etc. will fail due to excessive current or overheating, damaging the LED driver.The correct test method is to adjust the voltage regulator to the rated operating voltage range of the LED driver, and then connect the driver to power-on test. Of course, technically improving the design can also avoid the failure caused by this kind of test misoperation. That is, a starting voltage limit circuit and an input undervoltage protection circuit are set at the input of the driver. When the input does not reach the start-up voltage set by the driver, the driver does not work. When the input voltage drops to the input undervoltage protection point, the driver enters the protection state. Although the driver has a self-protection function and will not fail, you must carefully understand whether the purchased LED driver product has this protection before testing (considering the actual application environment of the LED driver, most LED drivers currently do not have this set). 1.5 Different Load with Different Test ResultsOn the one hand, when the LED driver is tested with LED lights, the result is normal; on the other hand, when driver tested with an electronic load, the result may be abnormal. Usually this phenomenon has the following reasons:1) The output instantaneous voltage or power of the driver exceeds the working range of the electronic load instrument. (Especially in CV mode, the maximum test power should not exceed 70% of the maximum power of the load. Otherwise, the load may instantaneously have overpower protection when loading, causing the driver to fail to work.)2) The characteristics of the electronic load instrument used are not suitable for measuring constant-current device. And the load voltage gear jumping, result in the drive to fail to work.3) Because there is a large capacitor inside the input of the electronic load meter. The test is equivalent to connecting a large capacitor in parallel with the driver output, which may cause the driver's current sampling work to be unstable. As we all known, the LED driver is designed to meet the working characteristics of LED lamps. The most practical test method is to use the LED lamp as a load, and connects an ammeter and a voltmeter in series to test. 1.6 LED Driver Circuit ProblemThe following conditions often cause damage to the LED driver:Connect AC to the DC output terminal of the driver, causing the driver to fail.Connect AC to the DC/DC output or input of the driver, causing the driver to fail.Connect the output terminal of the constant current to the dimming light, causing the driver to fail.Connect the phase wire to the ground wire causing the driver has no output and the housing is charged. 1.7 Wrong Phase WringTake an international example: the rated working voltage between each phase line and the neutral line is 220V, and the voltage between the phase line and the phase line is 380V. If the driver is connected to two phase wires, after power on, the LED driver input voltage exceeds the rated range, which cause the product to fail.As shown in Figure 3, V1 represents the first phase voltage, V2 represents the second phase voltage, and R1 and R2 respectively represent the drivers normally installed on the line. When the neutral line (N) on the circuit is disconnected, the drivers R1 and R2 on the two branches are connected to the 380V voltage after being connected in series. Because of the difference in input internal resistance, when one of the drivers is charged to start, the internal resistance becomes smaller. Most of the voltage may be applied to another driver, causing the overvoltage damage. Therefore, it is recommended that switches or short-circuiters on the same distribution branch should be disconnected together, not just cut off the neutral line. What’s more, do not put the power distribution fuse on the neutral line to avoid bad effect of the neutral line on the circuit.Figure 3. Neutral Line Open Circuit Diagram 1.8 Grid FluctuationWhen wires of a transformer grid branch is too long and there is large power equipment on the branch, the grid voltage will fluctuate sharply when the large equipment starts and stops. It even causes the grid to be unstable. When the grid voltage exceeds 310V, the drive may be damaged (even if there is an LED lightning protection device, it is useless. Because the lightning protection device is to deal with pulse spikes of tens of uS level, and the fluctuation of the grid may reach tens of mS, or even hundreds of mS) . Therefore, special attention should be paid when there is large electric machinery on the street lighting branch power grid. It is best to monitor the fluctuation range of the power grid or to supply power to the grid transformer separately. 1.9 Frequent Line TripsToo many lights are connected on the same branch, which leads to overload on a certain phase and uneven power distribution among the phases, resulting in frequent line trips. 1.10 Drive CoolingAlthough the LED has high luminous efficiency, only a small part of the energy flowing through the LED is radiated in the form of visible light. And most of the remaining energy is consumed in the LED in the form of heat, so the LED generates more serious heat. When the driver is installed in a non-ventilated environment, the driver housing should be in contact with the lamp housing as much as possible. If possible, apply thermal glue or a thermal pad on the contact surface between the housing and the lamp housing to improve the heat dissipation of the LED driver and ensure the reliability of the driver.Ⅱ LED Driver Maintenance2.1 Multimeter to Detect LED DriverMeasuring the output voltage of the no-load LED driver with a multimeter, if the output voltage is not detected, does it mean that the driver is broken? Look at the following steps:1) The voltage of the non-isolated LED power supply in the no-load state is about 300V tested with a multimeter, and it is about 220V with a PFC.2) Isolating the LED power supply, the voltage in the no-load state, tested with a multimeter, is about 3-5V more than the total voltage of the rated LED series. However, although the output voltage can be tested under no load, it does not mean that it can be normal under load. At this time, it is necessary to connect the corresponding LED light board to see the performance of the LED lighting. If there is no flicker, the output voltage is also equal to the total voltage of LED lights in series connection. This situation can be considered normal, otherwise it fails. If there is no output voltage at no load, the power supply must be broken. 2.2 Identify LED Power SupplyThe LED power supply is widely used in many applications. So how to distinguish the quality of LED power supply is particularly important. A few methods are briefly introduced below. LED Driver ICThe power of IC drive, the quality of IC directly affects the whole power supply. The lighting manufacturer should understand the IC design solution and calculate the cost of the driver, so as to purchase power products at a reasonable price. TransformersThe control chip can be regarded as the brain center of the power supply, while the transformers determine the power and temperature resistance. The transformer is responsible for the transfer of "AC to DC". However, the energy overload will damage the device. The core of the transformer is the magnetic core and the wire package. Electrolytic Capacitors and Ceramic CapacitorsThe quality and life requirements of input electrolytic capacitors are important. However, people tend to ignore the quality requirements of the output capacitor. In fact, the life of the output capacitor also has a great impact on the life of the power supply. The output end has a switching frequency of up to 60,000 times per second, which causes the parasitic resistance of the capacitor to heat up and produce substances similar to scale. Finally, the electrolyte heats up and bursts. Ceramic capacitors: The materials are divided into X7R, X5R and Y5V, and the actual capacitance value of Y5V can only reach 1/10 of the actual value. In addition, the nominal capacitance value only refers to when a capacitor works at 0V. Therefore, this tiny chip with poor options will also lead to a price difference in cost and greatly shorten the life of the power supply. Circuit Design and Welding ProcessJudgment of the pros and cons of the design: Aside from the professional point of view, it can be distinguished by some intuitive methods, such as the neat layout of the components, and soldering points. As for flying leads and manually adding components, it is a serious lack of techniques and efficiency. As we all know, the quality of mechanized production of wave soldering process is definitely better than manual welding. Because the machining process is more neat and uniform. Identification method: whether there is red glue on the back board.The flashing phenomenon of the lamp after a period of use is basically caused by the power supply or the weak welding of the lamp beads. However, it is extremely difficult to detect the virtual welding of products through aging, so AOI must be used to detect the quality of the power supply. Batch Inspection of Aging Racks and High Temperature Aging RoomsNo matter how good the power products are controlled by materials and production processes, they still need to be tested for aging. Because the incoming inspection of electronic components and transformers is difficult to control. Only through the aging of the entire batch of power supplies and the high temperature sampling inspection of the high temperature room. This is a wide-ranging screening to determine whether the materials have safety hazards. Ⅲ LED Driver Circuit ModulationThe LED driver circuit is divided into constant-voltage type and constant-current type according to the power supply to the LED. Constant-current switch type LED driver circuit samples the current flowing through the LED lamp, and gives the output control signal to control the on and off of the switching power tube, which aims to adjust the output current as the set value. The dimming control circuit mainly includes SCR dimming circuit, pulse width modulation (PWM), pulse frequency modulation (PFM), sliding mode control, PWM_PFM, PSM, etc. Let's take pulse width modulation (PWM), pulse frequency modulation (PFM), and sliding mode modulation to introduce in detail below. 3.1 Pulse Width Modulation (PWM)Pulse width modulation, shown in the figure below, refers to the stability of the output voltage by changing the on-time of the switching power tube in each cycle at a specific frequency. That is adjusting the duty cycle to obtain stable output voltage. When the output voltage changes due to the working environment, noise and other factors, the error amplifier samples the voltage change and sends the signal to the control circuit. The control circuit adjusts the duty cycle of the switching power tube signal to maintain the stability of the output voltage.Figure 4. PWM Modulation Based on BUCK StructureFigure 4 (a). Voltage ModeFigure 4 (b). Peak Current ModeFigure 4 (c). Average Current Mode3.1.1 Advantages of PWM(1) The PWM modulation method has high efficiency under heavy load, and has a good dynamic response to load changes.(2) The output ripple voltage is small and the linearity is high.(3) The frequency is stable, the duty cycle adjustment is not restricted, the control is simple, and both the current control mode and the voltage control mode are applicable.3.1.2 Disadvantages of PWM(1) The efficiency of PWM modulation method decreases at light load.(2) The transient response is slow during constant-voltage driving, and a more complicated compensation circuit is required.(3) Accurate current detection circuit is required for constant-current driving. 3.2 Pulse Frequency Modulation (PFM)The pulse frequency modulation is shown in the figure below. Under the condition of a certain on-time of the switching power tube, the output voltage can be controlled by adjusting the off time. When the output voltage changes, the error amplifier samples the feedback signal and sends the output signal compared with the reference signal to the control circuit. The control circuit analyzes the error signal and generates a square wave signal with constant pulse width and varying frequency to control the switch power tube to maintain the stability of the output voltage.Figure 5. Pulse Frequency Modulation Based on BUCK Structure3.2.1 Advantages of PFM(1) The PFM modulation has very high efficiency, better frequency characteristics and higher voltage regulation rate at light load.(2) The PFM modulation has a relatively high transmission signal-to-noise ratio and a good anti-interference ability.(3) The output voltage has a large adjustable range and low power consumption.3.2.2 Disadvantages of PFM(1) The efficiency of the PFM modulation will decrease under heavy load.(2) The frequency spectrum of the output ripple is scattered and irregular.(3) The load adjustment range is very small, resulting in high filtering costs. 3.3 Sliding-Mode ModulationSliding-mode modulation mode, the full name is sliding mode variable structure control,  is a discontinuous control. As shown in Figure 6, the sliding mode makes the system structure change purposefully according to its current state, which force the system to make small amplitude and high frequency up and down movements along the designed trajectory under response conditions. That is, sliding mode movement. Reduce the system's sensitivity to disturbances and load jumps.Figure 6. Sliding Mode Control Based on BUCK Structure3.3.1 Advantages and Disadvantage of Sliding ModeIt has the advantages of fast dynamic response, strong robustness and wide stability range, but it also has a problem that the operating frequency is not fixed. Ⅳ One Question Related to LED Driver4.1 QuestionHow long do LED drivers last?4.2 AnswerWhile the light function of an LED may last for years, drivers can give out much sooner. This is why we recommend name brand LED bulbs for the home, especially those with 25,000 hour rated lives. In general, high power white LEDs use much more current, and need of more complicated drivers. Frequently Asked Questions about LED Drivers Failure Analysis and Maintenance1. What is a LED driver IC?They are configured as either inductorless (charge pump) or switching regulator-based LED drivers that support driving white LEDs in series, parallel or combination. ... Topologies include boost regulator, buck regulator, buck/boost, SEPIC topology LED drivers, and more. 2. What is a LED driver used for?LED drivers are electrical devices that prevent damage to LEDs by regulating the forward voltage (VF) of the LED that changes with temperature, avoiding thermal runaway while delivering a constant current to the LED. LED drivers also aid efforts to meet new energy requirements (e.g., Energy Star). 3. How do I choose an LED driver?Use an LED driver with at least the same value as your LED(s). The driver must have a higher output power than your LEDs require for extra safety. If the output is equivalent to the LED power requirements, it is running at full power. Running at full power may cause the driver to have a shorter life span. 4. Why do LED drivers fail?LED FailureThe LEDs usually fail, because they have been connected to a constant LED driver in parallel. If the LEDs have failed you may want to also replace the LED driver. We usually recommend using a model with an adjustable output, and trimming down the output voltage slightly, to avoid over powering the LEDs. 5. How long do LED drivers last?Namely, the life of the driving circuit expires prior to when the LED stops emitting light or has its brightness dropped. The typical nominal lifetime of these elements is often times less than 25,000 hours, while the lifetime of LED itself could be as long as 50,000-100,000 hours. 6. Why do my LED drivers get hot?If the LED driver is trying to draw DC (not a balanced load circuit) then that can also cause the transformer to overheat.7. What is the difference between a transformer and an LED driver?LED drivers and electronic transformers for retrofit LED lighting are not interchangeable. They differ in output and load compatibility i.e. which LED lights they will work with. The fundamental difference between the two is that LED drivers output DC while electronic halogen transformers output 12VAC.