The Kynix Blog

I IntroductionThe LC circuit is a circuit composed of capacitors, inductors, resistors and other components and electronic devices that can generate oscillating current or have a filtering effect, and is also called a resonant circuit, tank circuit, or tuned circuit. The LC circuit formed by connecting the inductor L and the capacitor C is the simplest type of LC circuit. LC circuits are widely used in radio technology and radio and television technology. The LC circuit is indispensable in various radio devices, equipment, measuring instruments, etc. This article will introduce what is the LC circuit, including its basic concepts, basic principles, working process and application circuit diagram. CatalogI IntroductionII The Concept of LC Circuit and ResonanceIII Introduction of Electromagnetic Principle of LC CircuitIV The Operation of LC CircuitV Comparison of Two Types of LC circuits 5.1 Capacitive Feedback Oscillation Circuit 5.2 Inductive Feedback Oscillation CircuitVI Series LC circuit and parallel LC circuit 6.1 Series LC Circuit 6.2 Parallel LC CircuitVII Application of LC Circuit 7.1 Application Note of LC Circuit 7.2 LC Application Circuit DiagramVIII One Quiz Related to LC Oscillator 8.1 Question 8.2 AnswerⅨ FAQII The Concept of LC Circuit and ResonanceIn an AC circuit with a resistor R, an inductor L, and a capacitor C, the phase of the voltage across the circuit and the current in it are generally different. If you adjust the parameters of the circuit components (L or C) or the power frequency, you can make them in the same phase, and the entire circuit appears purely resistive. When the circuit reaches this state, it is called resonance. In the resonant state, the total impedance of the circuit reaches or reaches the extreme value. According to different circuit connections, there are series LC circuit and parallel LC circuit. The essence of resonance is that the electric field energy in the capacitor and the magnetic field energy in the inductance can be converted into each other. The sum of the electric field energy and the magnetic field energy remains constant at all times. The power supply does not need to convert energy back and forth with the capacitor or inductor, but only supplies the energy consumed by the resistance in the circuit.Figure1. What is ResonanceThe LC circuit is used to generate signals of a specific frequency, or to extract signals of a specific frequency only from more complex signals. It is suitable for important components such as oscillation circuits, filter circuits, tuners, and mixers. LC circuit is an ideal model, it ignores the energy dissipation caused by resistance.Figure2. Energy Stored by a CapacitorThe LC circuit uses the energy storage characteristics of capacitors and inductors to alternately transform the two types of electromagnetic energy, that is to say, electrical energy and magnetic energy will have a maximum and minimum value, and there will be oscillation.  However, this is only an ideal situation. In fact, all electronic components will have losses. Energy will either be lost or leak out of the process of conversion between the capacitor and the inductor. The energy will continue to decrease, so the actual LC circuit needs An amplifying element that is either a triode or an integrated op amp and other electrical LC. Using this amplifying element, the continuously consumed oscillation signal is feedback amplified by various signal feedback methods, so as to finally output a signal with stable amplitude and frequency.The frequency calculation formula is f = 1 / [2π√ (LC)],Where f is the frequency and the unit is Hertz (Hz); L is the inductance and the unit is Henry (H); C is the capacitor and the unit is Farad (F).Figure3. Energy Stored by an InductorIII Introduction of Electromagnetic Principle of LC CircuitThe concept of the electromagnetic field is highly generalized. This is a very rich concept. Although it includes the magnetic field of electrostatic field and electric current, the electromagnetic field is not a simple addition of electric field and magnetic field. (1) Several possible situations about the time-varying electric field generated by the magnetic field①A constant magnetic field does not generate an electric field: for example, the original coil of the transformer is always connected to the current power supply. Because the constant current generates a constant magnetic field, no induced current is generated in the secondary coil loop-no electric field that drives charge. ②The changing magnetic field generates an electric field: According to the knowledge of electromagnetic induction, when the magnetic field changes in the closed-loop, an induced current is generated in the loop. Maxwell has a deep insight that the conductor loop is only a tool to reflect the existence of an induced electric field. In essence, as long as there is a magnetic field that changes in space, an electric field will be generated-it is not an electric field generated by a charge. ③ A uniformly changing magnetic field produces a constant electric field: According to Faraday's law of electromagnetic induction, ε = Δф / Δt can be the same as above, and the conclusion can be drawn from Faraday's law of electromagnetic induction.Figure4. Faraday’s Laws of Electromagnetic Induction(2) Regarding the generation of a magnetic field by an electric field, the following will be described in layers according to several possibilities of the time-varying electric field. ①A constant electric field does not generate a magnetic field, for example, the space around a static charge has only an electrostatic field and no magnetic field-a constant electric field does not generate a magnetic field. ②The changing electric field generates a magnetic field. With his extraordinary genius, Maxwell believes that when the capacitor is charged and discharged, the conduction current is interrupted by the capacitor in another way-continuous, he pointed out that the change in the electric field in the capacitor is equivalent to the current-like the conduction current, it can Generate a magnetic field (but does not generate human Joule heat), that is, a changing electric field generates a magnetic field. Connect the parallel-plate capacitor used for large-scale demonstration to the induction coil, and place a free small magnetic needle between the capacitor plates. The deflection of the free small magnetic needle shows that the changing electric field generates a magnetic field. A uniformly changing electric field produces a constant magnetic field: if the charge on the capacitor changes uniformly, the conduction current I = ΔQ / Δt is a steady current, which generates a constant magnetic field in space. When the charge on the capacitor changes uniformly with time, it is necessary to cause a uniform change in the electric field between the plates. The uniformly changed electric field, like a steady conduction current, must generate a constant magnetic field in space.Unevenly changing electric field produces a changing magnetic field using a similar narrative method to draw conclusions.Figure5. Magnetic Field Produced by Electric Current(3) Electromagnetic field According to the reasoning of the above two aspects, the extension points out: In general, the magnetic field generated by an unevenly changing electric field (such as an oscillating current) also changes unevenly, and this magnetic field must also produce an unevenly changing electric field. It can be seen that the changing electric field and magnetic field are always related to each other, forming an inseparable unity, which is the electromagnetic field. Conditions for generating electromagnetic fields:Generated by static charge.Generated by a uniformly changing magnetic field.Produced by steady current.Generated by a uniformly changing electric field. Interdependent non-uniformly changing electric and magnetic fields.Figure6. Electromagnetic FieldsIV The Operation of LC Circuit（1）Charging completed (discharge start): the electric field can reach the maximum, the magnetic field energy is zero, and the induced current i = 0 in the loop. （2）Discharge completed (charging started): the electric field energy is zero, the magnetic field can reach the maximum, and the induced current in the loop reaches the maximum. （3）Charging process: the electric field energy is increasing, the magnetic field energy is decreasing, the current in the loop is decreasing, and the electric capacity on the capacitor is increasing. From the perspective of energy: the magnetic field can be transformed into the electric field. （4）Discharge process: the electric field energy is decreasing, the magnetic field energy is increasing, the current in the loop is increasing, and the amount of electricity on the capacitor is decreasing. From the energy point of view: the electric field can be transformed into the magnetic field. In the process of generating an oscillating current in an oscillating circuit, the charge on the plate of the capacitor, the current through the coil, and the magnetic field and electric field associated with the current and charge all periodically change. This phenomenon is called electromagnetic oscillation.Figure7. Tuned CircuitV Comparison of Two Types of LC Circuits5.1 Capacitive Feedback Oscillation Circuit5.1.1 Circuit CompositionFigure8. Capacitive Feedback Oscillation CircuitIn order to obtain a better output voltage waveform, if the capacitor in the inductive feedback oscillation circuit is replaced with an inductor, the inductor is replaced with a capacitor, and after the conversion, the common terminal of the two capacitors is grounded, and the collector resistance Rc is increased, The capacitor feedback oscillation circuit is obtained, as shown on the right. Because the three terminals of the two capacitors are respectively connected to the three poles of the transistor, it is also called a capacitor three-point circuit. 5.1.2 Working Principle(1) According to the judgment method of the sine wave oscillation circuit, observe the circuit shown in the above figure, which includes four parts: the amplifier circuit, the frequency selection network, the feedback network and the nonlinear element (transistor);(2) The amplifier circuit can work normally;(3) Disconnect the feedback, add the input voltage with frequency f0, and given its polarity, determine the polarity of the feedback voltage obtained from C2 is the same as the input voltage. The polarity is as shown.(4) As long as the circuit parameters are properly selected, the circuit can meet the amplitude condition and produce a sine wave oscillation. 5.1.3 Oscillation Frequency and Starting ConditionsOscillation frequencyFeedback coefficientVibration conditions 5.1.4 Advantages and DisadvantagesThe output voltage waveform of the capacitive feedback oscillation circuit is good, but if the oscillation frequency is adjusted by changing the capacitance method, it will affect the feedback coefficient and the starting condition of the circuit; and if the oscillation frequency is adjusted by changing the inductance method, it is more difficult; Commonly used in the occasion of fixed oscillation frequency. When the adjustable range of the oscillation frequency is not large, the circuit shown in the figure on the right can be used as the frequency selection network.Figure9. Frequency Selective Network with Adjustable Frequency 5.1.5 Measures to Stabilize the Oscillation FrequencyTo increase the frequency of the capacitive feedback oscillation circuit, the capacitance of C1 and C2 and the inductance of L must be reduced. In fact, when C1 and C2 are reduced to a certain degree, the interelectrode capacitance of the transistor and the stray capacitance in the circuit will be included in C1 and C2, thus affecting the oscillation frequency. These capacitors are equivalent to the input capacitance Ci and output capacitance Co of the amplifier circuit. The improved circuit and equivalent appliances are shown in the figure below. Because the inter-electrode capacitance is affected by temperature, the stray capacitance is difficult to determine. In order to stabilize the oscillation frequency, a small-capacity capacitor C3 is connected in series with the inductor branch, and C3 <Oscillation frequencyAlmost has nothing to do with C1 and C2, so does Ci and Co, so the frequency stability is high.Figure10. Improvement of Capacitive Feedback Oscillation Circuit and Equivalent Circuit5.2 Inductive Feedback Oscillation Circuit5.2.1 Circuit CompositionIn order to overcome the disadvantage that the primary coil and the secondary coil of the transformer are not tightly coupled in the feedback oscillation circuit of the transformer, N1 and N2 of the transformer feedback oscillation circuit can be combined into one coil. As shown in the figure, in order to strengthen the resonance effect, the capacitor C is connected across the entire coil to obtain an inductive feedback oscillation circuit.Figure11. Inductive Feedback Oscillation Circuit5.2.2 Working PrincipleObserve the circuit, it contains four parts of the amplifier circuit, frequency selection network, feedback network and nonlinear components (transistors), and the amplifier circuit can work normally.Use the instantaneous polarity method to judge whether the circuit meets the sine wave oscillation phase conditions: ① Disconnect the feedback, add the input voltage with frequency f0, and give its polarity②It is judged that the polarity of the feedback voltage obtained from N2 is the same as the input voltage③ Therefore, the circuit satisfies the phase condition of sine wave oscillation, and the instantaneous polarity of each point is as shown in the above figure.As long as the circuit parameters are properly selected, the circuit can satisfy the amplitude condition and produce a sine wave oscillation.The following figure shows the AC path of the inductive feedback oscillation circuit. The three ends of the primary coil are connected to the three poles of the transistor, so the inductive feedback oscillation circuit is called an inductive three-point circuit.Figure12. AC Path of Inductive Feedback Oscillation Circuit 5.2.3 Oscillation Frequency and Starting ConditionsOscillation frequencyFeedback coefficientVibration conditions 5.2.4 Advantages and DisadvantagesIn the inductive feedback oscillation circuit, the coupling between N2 and N1 is tight, the amplitude is large, and it is easy to oscillate; when C uses a variable capacitor, the oscillation frequency with a wide adjustment range can be obtained, and the highest oscillation frequency can reach tens of MHz. Because the feedback voltage is taken from the inductance, it has a large reactance to high-frequency signals. The feedback signal contains more harmonic components, and the output voltage waveform is not good.VI Series LC Circuit and Parallel LC Circuit6.1 Series LC Circuit6.1.1 ConceptIn the LC circuit, the corresponding frequency value when the inductive reactance and capacitive reactance are equal is called the resonance frequency, that is, XC = XL. As shown in the figure below, the voltage u and the current i in the circuit are in the same phase, and the circuit is resistive. This phenomenon is called series resonance. When the circuit has series resonance, the impedance of the circuit Z = √R ^ 2 + (XC-XL) ^ 2 = R, the total impedance in the circuit is the smallest, and the current will reach the maximum value.Figure13. Series Resonance Frequency 6.1.2 Characteristics of Series LC CircuitWhen the input signal passes through the series LC circuit, according to the characteristics of the inductor and the capacitor, the higher the signal frequency, the larger the impedance of the inductor, and the smaller the impedance of the capacitor. The larger the impedance, the greater the attenuation of the signal. The signal with a higher frequency will be greatly attenuated by the inductor, while the DC signal cannot pass through the capacitor. When the frequency of the input signal bow is equal to the frequency of the LC resonance, the impedance of the LC series circuit is minimum. Signals at this frequency easily output through capacitors and inductors. At this time, the LC series resonant circuit plays the role of frequency selection.Figure14. The Frequency Characteristic for LC Series Resonant Circuits 6.1.3 FormulaWhen series resonance occurs:Inductive reactance XL = capacitive reactance XCSource voltage U = resistance voltage URInductor voltage UL = capacitance voltage UCInductive reactive power QL = capacitive reactive power QCThe total impedance of the circuit ∣Z∣ = resistance RApparent power S = resistance power P6.2 Parallel LC Circuit6.2.1 ConceptThe parallel LC resonance circuit is formed by connecting an inductor and a capacitor in parallel. In a parallel resonant circuit, if the current in the coil is equal to the current in the capacitor, the circuit reaches the state of parallel resonance. In this circuit, except for the LC parallel part, the impedance change of other parts has almost no effect on energy consumption. Therefore, the stability of this circuit is good, and it is used more than series resonance circuits. Parallel resonance is a complete compensation. The power supply does not need to provide reactive power, only the active power required by the resistor. At resonance, the total current of the circuit is the smallest, and the current of the branch is often greater than the total current of the circuit. Therefore, parallel resonance is also called current resonance. When parallel resonance occurs, a large current flows in the inductance and capacitance components, which may cause an accident that the circuit fuse blows or burns electrical equipment; but it is often used to select signals and eliminate interference in radio engineering.Figure15. Parallel LC Circuit6.2.2 Characteristics of Parallel LC Circuit(1) The current and voltage phases are the same, and the circuit is resistive. (2) The series impedance is the smallest and the current is the largest: Z = R, then I = U / R. (3) The voltage at the inductor end and the voltage at the capacitor end are equal in magnitude, opposite in phase, and compensate each other. The voltage at the resistor end is equal to the power supply voltage. (4) The ratio of the inductance (capacitance) terminal voltage to the power supply voltage at resonance is called the quality factor Q, which is also equal to the ratio of inductive reactance (or capacitive reactance) and resistance. When Q >> 1, the voltages on L and C are much larger than the power supply voltage (similar to resonance). This is called series resonance and is often used to amplify the signal voltage; however, series resonance should be avoided in the power supply circuit. VII Application of LC Circuit7.1 Application Note of LC CircuitIn amplifier circuits and other forms of signal processing circuits, parallel LC resonance circuits and series LC resonance circuits are used very frequently.(1) Frequency selection circuit or frequency selection amplifierThe LC circuit can form a frequency selection circuit or a frequency selection amplifier circuit, which is used to select a signal of a desired frequency among a large number of signals for amplification. This circuit is widely used in radio, television and other circuits, as well as in sine wave oscillator circuits.(2) Absorption circuitThe LC circuit can constitute an absorption circuit, which absorbs a signal of a certain frequency among signals of many frequencies, that is, performs attenuation, and removes signals of this frequency from signals of many frequencies.(3) Wave blocking circuitThe LC circuit can form a wave blocking circuit, which prevents signals of a certain frequency from passing through amplifier circuits or other circuits from signals of many frequencies.(4) Phase shift circuitAn LC parallel circuit is used to form a phase shift circuit, and the signal is phase shifted.7.2 LC Application Circuit DiagramLC parallel and series resonant circuits have many changes in application, which is a difficult point in circuit analysis.(1) LC free resonance circuitThe figure below shows the LC free resonance circuit. L in the circuit is an inductor, C is a capacitor, and L and C form a parallel circuit.Figure16. LC Free Resonance Circuit(2) LC parallel resonance phase shift circuitThe following figure shows the phase shift circuit composed of LC parallel resonance circuit. VT1 in the circuit constitutes a primary amplifier; R1 is its base bias resistor; R3 is its emitter resistor; C4 is the emitter bypass capacitor; L1 and C3 constitute an LC parallel resonance circuit, and R2 is the damping resistor of this resonant circuit.Figure17. LC Parallel Resonance Phase Shift CircuitBy adjusting the inductance of L1, the phase of the output signal voltage can be changed to achieve the purpose of phase shift. (3) LC series resonance absorption circuitThe function of the absorption circuit is to remove the signal of a certain frequency in the input signal. The following figure shows the absorption circuit composed of LC series resonant circuit. VT1 in the circuit constitutes a primary amplifier. L1 and C1 form the LC series resonance absorption circuit, and the resonance frequency is connected between the input terminal of VT1 and the ground.Figure18. LC Series Resonance Absorption Circuit (4) Series resonance high-frequency boost circuitThe figure below shows a high-frequency boost circuit composed of LC series circuits. VT1 in the circuit constitutes a first-stage common-emitter amplifier, and L1 and C4 constitute an LC series resonance circuit, which is used to boost high-frequency signals. The resonant frequency of the series resonant circuit of L1 and C4 is higher than the highest frequency of the working signal of this amplifier.Figure19. Series Resonance High Frequency Boost CircuitSince the impedance of the L1 and C4 circuits at resonance is the smallest, and the negative feedback resistance is the smallest after paralleling with the emitter negative feedback resistance R4, the amplification factor at this time is the largest. In this way, the high-frequency signal close to the resonance frequency is improved.For input signals with a frequency much lower than the resonant frequency, the L1 and C4 circuits have no boost effect on them, because the L1 and C4 circuits are in a detuned state and their impedance is very large, and the negative feedback resistance at this time is R4. (5) Input tuning circuitThe radio selects the required radio stations from many radio stations by input tuning circuit. The input tuning circuit is also called antenna tuning circuit, because there is a cash register antenna in this tuning circuit.The following figure shows a typical input tuning circuit. L1 in the circuit is the primary winding of the magnetic rod antenna, L2 is the secondary winding of the magnetic rod antenna; C1-1 is a connection of the double variable capacitor, which is the antenna connection, and C2 is the high-frequency compensation capacitor, which is the trimming capacitor. It is usually attached to a double variable capacitor.Figure20. Input Tuning CircuitThe working principle of input tuned circuit:The primary winding L1 of the magnetic rod antenna, variable capacitor c1-1, and trimmer capacitor C2 constitute LC series resonance circuit. When resonance occurs in the circuit, the energy in L1 is the largest, that is, the voltage amplitude of the signal of the resonant frequency at both ends of L1 is much larger than that of the signal of the non-resonant frequency. In this way, the amplitude of the resonant frequency signal output from the secondary winding L2 through magnetic coupling is the maximum. The following figure shows the practical input tuning circuit.Figure21. Pratical Input Tuning CircuitVIII One Quiz Related to LC Oscillator 8.1 QuestionThe output of a LC oscillator is often fed into a common collector amplifier stage. The reason for this is:a) To provide extra voltage gain.b) To provide negative feedback.c) To reduce loading on the tank circuit.d) To convert the sine wave output to a square wave.8.2 AnswerC Ⅸ FAQ1. What does an LC circuit do?LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal; this function is called a bandpass filter. 2. How do you solve an LC circuit?Begin with Kirchhoff's circuit rule. Take the derivative of each term. The voltage of the battery is constant, so that derivative vanishes. The derivative of charge is current, so that gives us a second-order differential equation. 3. What makes an ideal LC circuit?An LC circuit is an electronic circuit made up of an inductor and a capacitor. ... An ideal LC circuit does not have resistance. At the LC circuit energy saves in the capacitor's electric field. U is energy and q is electric charge. 4. Why do LC circuits resonate?Resonance of a circuit involving capacitors and inductors occurs because the collapsing magnetic field of the inductor generates an electric current in its windings that charges the capacitor, and then the discharging capacitor provides an electric current that builds the magnetic field in the inductor. 5. What is the difference between RC and LC circuits?RC - a resistor and capacitor in series. Exhibits charging behavior with a characteristic time constant with DC voltage source. ... LC (and RLC) - an inductor and capacitor (and resistor) in series. If initially charged, has oscillatory behavior (damped if also has a resistor). 6. What are the different properties of the LC circuit?An LC circuit is a closed loop with just two elements: a capacitor and an inductor. It has a resonance property like mechanical systems such as a pendulum or a mass on a spring: there is a special frequency that it likes to oscillate at, and therefore responds strongly to. 7. Is an LC circuit first order?In electronics, the classic second-order system is the LC circuit. The LC circuit is one of the last two circuits we will solve with the full differential equation treatment. 8. Where is energy stored in the LC circuit?The oscillations of an LC circuit can, thus, be understood as a cyclic interchange between electric energy stored in the capacitor, and magnetic energy stored in the inductor. 9. What is the natural frequency of the LC circuit?The natural frequency of an LC - circuit is 1,25000 cycles per second. 10. What is a parallel LC circuit?Parallel LC Circuit. The Voltage across each terminal of different elements in a parallel circuit is the same. Hence the voltage across the terminals is equal to the voltage across the inductor and the voltage across the capacitor. 

2026 Executive Summary: Resistors remain the fundamental components of modern circuitry, from consumer electronics to electric vehicle (EV) power management. This guide classifies resistors by material (Film, Composition, Alloy) and application (Precision, High-Power, Sensitive), providing engineers and hobbyists with critical selection criteria for voltage, power rating, and tolerance in 2026.I. Introduction: The Role of Resistors in 2026Resistors are passive electrical components that restrict current flow to adjust signal levels and voltage. In the 2026 electronics landscape, the variety of resistors continues to expand with the rise of IoT devices and high-voltage EV architectures. Resistors are generally divided into two primary categories: fixed resistors and variable resistors. Fixed resistors are categorized by material into wire-wound and non-wire-wound types. Non-wire-wound resistors split further into film and composite types. Structurally, they appear as tubular, disc, or planar (SMD) components. Depending on protection needs, they can be painted, plastic-pressed, or vacuum-sealed. This guide details the classification, characteristics, and pros/cons of resistor types, updated for 2026 standards. It serves as an essential resource for selecting the right component for modern circuit design.Video: Understanding Types of ResistorsII. How are Resistors Classified by Material?Material composition determines a resistor's noise, tolerance, and stability. In 2026, film-based resistors dominate consumer electronics, while wire-wound types are preferred for high-power applications.2.1 Film Resistors(1) Carbon Film ResistorsCarbon film resistors consist of a ceramic core coated with a crystalline carbon layer, thermally decomposed in a high-temperature vacuum. The resistance is precisely calibrated by cutting a helical groove into the carbon film. These resistors offer a balance of cost and performance. They feature good stability, a low negative temperature coefficient, and stable pulse load handling. Due to their low production cost, they remain widely used in general-purpose consumer electronics where ultra-high precision is not critical.Figure 1. The Appearance and Structure of Carbon Film Resistor(2) Metal Film ResistorsMetal film resistors are manufactured by vacuum-depositing a nickel-chromium (NiCr) or similar alloy onto a ceramic substrate. This technology allows for tighter tolerances than carbon types.Known for superior stability, heat resistance, and low noise electromotive force, metal film resistors are the standard for 2026 precision circuits, including audio equipment and measuring instruments.Figure 2. Metal Film Resistor(3) Metal Oxide Film ResistorsThese are created by spraying metal salt solutions (like tin tetrachloride) onto a heated ceramic skeleton at approximately 550°C. The resulting conductive film is fused firmly to the substrate. Metal oxide variants excel in harsh environments, offering stronger oxidation, acid, and salt resistance than standard metal films. While their resistance range is narrower (typically 1Ω ~ 200 kΩ), they handle power ratings from 1/8 W up to 50 kW in industrial applications.Figure 3. Metal Oxide Film Resistor2.2 Composition ResistorsComposition resistors mix conductive granules with a binder. While less common in modern high-precision tech, they are prized for their high surge energy handling. The distinct advantage of solid core resistors is reliability—often 5 to 10 times higher than film types in pulse-heavy applications. Despite drawbacks like higher noise and poor linearity, they are utilized in aerospace and submarine cabling where component failure is not an option. Solid Core Resistor (Model S): Common model RS11. Range: 4.7Ω – 22MΩ. Accuracy: ±5% to ±20%.High Voltage Composite Film: Models like RHY-10 (10kV) and RHY-35 (35kV) handle extreme voltages with resistance up to 1000MΩ.Carbon Film Composition: High resistance range (up to 106 MΩ) and 35kV working voltage. Used in vacuum megohm resistors for micro-current testing, despite poor moisture resistance.Organic Solid Composition: Pressed mixtures of graphite and organic binder. Compact and robust against overload, but with poor temperature stability. Common in older automotive instrument clusters.Glass Glaze Resistor: A sintered mix of metal oxides (ruthenium) and glass glaze. Features high-temperature resistance and high voltage handling (up to 15kV). Power ratings can reach 500W in specialized units.Figure 4. Different Types of Resistors2.3 Alloy Resistors(1) Precision Wire Wound Resistors (Model RX)Used in measurement instruments requiring stability. Tolerances can be as fine as ±0.005%. However, due to the coil structure, they act as inductors, making them unsuitable for high-frequency circuits.Figure 5. Precision Wire Wound Resistor(2) Power Type Wire Wound ResistorsDesigned for dissipation, these handle 2W to 200W+. They are often ceramic-encased and used in power supplies. Adjustable versions allow for manual resistance tuning during machine calibration. (3) Precision Alloy Foil ResistorsThe gold standard for stability in 2026. These resistors automatically compensate for temperature coefficients, maintaining accuracy across wide temperature ranges. Accuracy reaches ±0.001%, with stability around ±5 × 10-5%/year, making them vital for high-speed response circuits.III. What are the Main Classifications Based on Purpose?Beyond material, resistors are categorized by their specific function in a circuit topology.General Type: Standard components for consumer tech. Power: 1/20W ~ 2W. Tolerance: ±5% ~ ±20%.Precision Type: High stability for medical and audio devices. Tolerance: 2% down to 0.001%.High Frequency Type: Non-inductive designs (often film or solid) essential for RF and 5G communication circuits. Can handle up to 100W.High Voltage Type: Engineered for 1kV ~ 100kV applications, such as X-ray power supplies.High Resistance Type: Specialized for detecting weak currents, with values exceeding 10 MΩ (up to 1014Ω).Integrated Resistance (Resistor Networks): Multiple matched resistors on a single substrate (SIP/DIP packages). Critical for saving space in computer interfaces.Insurance (Fusible) Type: A dual-function safety component. Acts as a resistor under normal load but fuses open like a circuit breaker within seconds (7s to 120s) during overloads (12x-30x rated power).Figure 6. Different ResistorsIV. What are Sensitive Resistors (Sensors)?Sensitive resistors change their resistance in response to environmental stimuli, acting as the "senses" of modern IoT devices.(1) ThermistorTemperature-dependent resistors used for measurement and protection.NTC (Negative Temperature Coefficient): Resistance drops as heat rises. Used in temperature sensors.PTC (Positive Temperature Coefficient): Resistance spikes with heat. Used as self-resetting fuses.Figure 7. Thermistor(2) Photoresistor (LDR)Made from semiconductors like Cadmium Sulfide (CdS). High resistance in dark (>1.5MΩ) drops drastically (<1kΩ) when illuminated. Used in automatic streetlights and photoelectric controls.Figure 8. Photoresistor(3) Varistor (MOV)Voltage-dependent resistors, typically Zinc Oxide. They act as open circuits normally but short-circuit dangerous voltage spikes to ground. Essential for surge protection in power strips and automotive electronics.Figure 9. Metal Oxide Varistor(4) Magneto-resistorUtilizes the magnetoresistive effect (e.g., Indium Antimonide). Resistance rises with magnetic flux. Used in speed sensors, magnetic card readers, and brushless motor control.Figure 10. Magneto Resistor(5) Force Sensitive Resistor (FSR)Converts physical pressure/stress into electrical signals. Found in electronic drums, robotics touch sensors, and industrial scales.Figure 11. Force Sensitive Resistor(6) Gas-sensitive ResistorUtilizes metal oxides (like Tin Dioxide) that change resistance when gas molecules adsorb onto the surface. Standard in 2026 smart home air quality monitors and breathalyzers.Figure 12. Gas-sensitive Resistor(7) Humidity ResistorDetects relative humidity changes. Critical for HVAC systems and weather stations.Figure 13. Humidity ResistorV. Types of Potentiometers (Variable Resistors)5.1 What is a Potentiometer?A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. It is the manual interface for many electronic devices (volume knobs, dimmer switches) and a calibration tool for circuits (trimpots).5.2 How are Potentiometers Classified?By Material: Carbon Film (standard), Cermet (Ceramic/Metal mix for long life), Wirewound (high power).By Structure: Single-turn (general use), Multi-turn (high precision), Slide/Linear faders (audio mixers).By Resistance Scale:Linear (Type B): Resistance changes evenly. Used in brightness controls.Logarithmic (Type A): Resistance changes exponentially. Used in audio volume controls to match human hearing.Figure 14. PotentiometerVI. Comparison: Advantages and DisadvantagesChoosing the right resistor in 2026 requires balancing precision, power, and cost.6.1 Mind Map of Resistor ClassificationFigure 15. Mind Map of Types of Resistor6.2 Resistor Comparison TableResistor TypeKey CharacteristicsPrimary ApplicationsAdvantagesDisadvantagesCarbon Film (RT)Hydrocarbon deposit on ceramic. Tolerance ±5% to ±20%.General consumer electronics, toys, basic logic.Low cost, widely available.Poor thermal stability, higher noise.Metal Film (RJ)Vacuum evaporated alloy. Tolerance ±0.1% to ±1%.Audio equipment, precision instruments.Low noise, excellent stability, compact.Higher cost than carbon.Metal Oxide (RY)Tin/Antimony salt spray.Industrial power supplies, high temp zones.Resists oxidation, acids, and heat.Limited resistance range.Wire Wound (RX)Resistive wire wrapped around core.Power supplies, load testing, shunts.High power handling, thermal stability.Inductive (unsuitable for HF), bulky.Organic Solid (RS)Granular conductive mix, hot pressed.High-surge audio outputs.Robust overload capacity, reliable.Low precision, unstable with temp.Cement ResistorWire-wound encased in ceramic fireproof shell.Power adapters, current limiting.Explosion-proof, heat resistant.Large physical size, runs hot.0-ohm Resistor"Jumper" resistor (~0Ω).PCB bridges, configuration toggles.Simplifies PCB routing.N/A6.3 Comparison MatrixA quick reference guide for selecting resistors based on application (vertical) and material (horizontal).Classify by Use Classify by MaterialWire WoundFilm TypeCompositeCarbon FilmMetal FilmMetal OxideGlass GlazeComp. CarbonMetal FoilOrganic SolidInorganic SolidGeneral●●●●●  ●●Precision●●●   ●  High-Resistance  ● ●●   Power●●●      High-Voltage    ●●   High-Frequency   ●     VII. Quick Quiz: Resistor ClassificationQuestionWhat are the two primary macro-classifications of resistors?Answer1. Fixed Resistors (Value remains constant)2. Variable Resistors (Value is adjustable, e.g., potentiometers)VIII. Common Resistor Questions1. What is the main function of a resistor?A resistor opposes current flow to prevent short circuits and manage signal levels. It acts as a gatekeeper, ensuring downstream components receive the correct voltage and current.2. How does a resistor work?Resistors work by restricting the flow of electrons, similar to kinking a garden hose to reduce water flow. They dissipate the excess energy as heat.3. Why are resistors important for Arduino/IoT?They are essential for voltage division (converting 5V logic to 3.3V) and current limiting for LEDs to prevent burnout.4. What is a 0-ohm resistor used for?It acts as a bridge or jumper on a printed circuit board (PCB), allowing designers to route traces over other tracks without using a multi-layer board.5. What is the difference between resistance and a resistor?Resistance is a physical property (measured in Ohms). A resistor is the physical component manufactured to provide a specific amount of that resistance.Frequently Asked Questions (2026 Update)What is the difference between thin-film and thick-film resistors?Thin-film resistors (sputtered metal) offer high precision (0.1% tolerance) and low noise for audio/medical tech. Thick-film resistors (printed paste) are cheaper and handle higher power surges but have lower precision (5% tolerance), suitable for general electronics.Why are shunt resistors critical for EV battery management?Shunt resistors with ultra-low resistance measure high currents in Electric Vehicles (EVs) with extreme accuracy. They enable the Battery Management System (BMS) to calculate state-of-charge and prevent over-current scenarios efficiently.How do I choose the right resistor power rating for PCB design?Calculate the power dissipation ($P = I^2 \times R$) and choose a resistor with a rated power at least 50% higher than your calculation (derating). For enclosed 2026 IoT devices, a 2x safety margin is recommended to minimize heat.{ "@context": "https://schema.org", "@type": "Article", "headline": "Resistor Types and Classifications: The 2026 Engineering Guide", "datePublished": "2020-04-18", "dateModified": "2026-01-20", "author": { "@type": "Organization", "name": "ApogeeWeb" }, "mainEntity": { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What is the difference between thin-film and thick-film resistors?", "acceptedAnswer": { "@type": "Answer", "text": "Thin-film resistors (sputtered metal) offer high precision (0.1% tolerance) and low noise for audio/medical tech. Thick-film resistors (printed paste) are cheaper and handle higher power surges but have lower precision (5% tolerance)." } }, { "@type": "Question", "name": "Why are shunt resistors critical for EV battery management?", "acceptedAnswer": { "@type": "Answer", "text": "Shunt resistors with ultra-low resistance measure high currents in Electric Vehicles (EVs) with extreme accuracy. They enable the Battery Management System (BMS) to calculate state-of-charge and prevent over-current scenarios." } }, { "@type": "Question", "name": "How do I choose the right resistor power rating for PCB design?", "acceptedAnswer": { "@type": "Answer", "text": "Calculate the power dissipation (P = I^2 * R) and choose a resistor with a rated power at least 50% higher than your calculation (derating). For enclosed IoT devices, a 2x safety margin is recommended." } }, { "@type": "Question", "name": "What is the main function of a resistor?", "acceptedAnswer": { "@type": "Answer", "text": "A resistor opposes current flow to prevent short circuits and manage signal levels. It acts as a gatekeeper, ensuring downstream components receive the correct voltage and current." } } ] }}

CatalogI IntroductionII What is Infrared?III Theoretical Principle of Infrared Temperature MeasurementIV The Principle of Infrared ThermometerV Differences in Accuracy of Different Types of Infrared Thermometers  5.1 Three Categories of Infrared Thermometers  5.2 Differences Between Mainstream Infrared Thermometers  5.3 Infrared Temperature GunVI Infrared Thermometer Accuracy And Factors Affecting Accuracy  6.1 Precision of Infrared Thermometer  6.2 Factors Affecting The Accuracy of The Infrared Thermometer MeasurementVII Factors to Consider When Choosing An Infrared ThermometerVIII How To Make Infrared Thermometers More AccurateIX One Question Related to Infrared Thermometers  9.1 Question  9.2 AnswerX FAQI IntroductionIn the past two months, due to the outbreak of Coronavirus Disease 2019 (COVID-19), output of infrared thermometers exceeded the whole year of last year, driving the shipments and demand for chips such as sensors, MCUs, and operational amplifiers. Infrared thermometer is a non-contact diagnostic technology that can scan and image the thermal radiation of objects and display data. It has the advantages of wide measurement range, fast temperature measurement, high accuracy and high sensitivity. With the widespread use of infrared thermometers, some users have doubts about its working principle and accuracy. This article will introduce how the infrared thermometer works, and explain its accuracy and the factors that affect it.Figure1. Infrared ThermometerII What is Infrared?Infrared is an electromagnetic wave with a wavelength between microwave and visible light. The wavelength is between 1mm and 760 nanometers (nm), which is invisible light longer than red light. Anything above absolute zero (-273.15°C) can generate infrared rays. Modern physics calls it heat rays. Medical infrared can be divided into 2 categories: near infrared and far infrared. Containing thermal energy, the sun's heat is mainly transmitted to the earth through infrared rays. Infrared is a part of the many invisible rays of the sun's rays. It was discovered by British scientist Herschel in 1800 and is also called infrared thermal radiation. It has a strong thermal effect. He split the sunlight with a prism, and placed thermometers on the ribbons of various colors in an attempt to measure the heating effect of light of various colors. It was found that the thermometer located outside the red light warmed the fastest.  Therefore, it is concluded that in the solar spectrum, there must be invisible light outside the red light, which is infrared. Can also serve as a medium of transmission. The wavelength of infrared light in the solar spectrum is greater than visible light, with a wavelength of 0.75 to 1000 μm. Infrared can be divided into three parts, namely near infrared, with a wavelength between (0.75-1) to (2.5-3) μm; mid-infrared, with a wavelength between (2.5-3) to (25-40) μm; far infrared , The wavelength is between (25-40) ~ l500μm.Figure2. InfraredIII Theoretical Principle of Infrared Temperature MeasurementIn nature, when the temperature of an object is higher than absolute zero, due to the existence of internal thermal movement, it will continuously radiate electromagnetic waves to the surroundings, including infrared rays with a wavelength range of 0.75µm ~ 100µm. Its biggest feature is that at a given temperature and wavelength, the radiant energy emitted by an object has a maximum value.  This substance is called a black body, and its reflection coefficient is set to 1; the reflection coefficient of other substances is less than 1, and is called gray body. Because the black body's spectral radiant power P (λT) meets Planck's law between the absolute temperature T, it shows that at the absolute temperature T, the radiant power of the black body per unit area at the wavelength λ is P (λT). According to this relationship, the relationship curve can be obtained as shown in the figure below: (1) As the temperature increases, the stronger the radiant energy of the object. This is the basis of the theory of infrared radiation and the design basis of a single-band infrared thermometer. (2) As the temperature rises, the radiation peak shifts to the short-wave direction (to the left) and satisfies the Wien shift theorem. The wavelength at the peak is inversely proportional to the absolute temperature T, and the blue curve is the line connecting the peaks. This formula tells us why the high temperature thermometer works mostly in the short wave and the low temperature thermometer works mostly in the long wave. (3) The rate of change of radiant energy with temperature is larger at the short wave than at the long wave, that is, the thermometer working at the short wave has a relatively high signal-to-noise ratio (high sensitivity) and strong anti-interference. This is particularly important at wavelengths, especially for small targets at low temperatures.Figure3. Planck's Law of Blackbody RadiationIV The Working Principle of Infrared ThermometerThe infrared thermometer consists of the optical system, photodetector, signal amplifier, signal processing and display output. The radiation of the measured object and the feedback source is adjusted according to the modulator and input to the infrared detector. The difference between the two signals is amplified by the inverse amplifier and the temperature of the feedback source is controlled so that the spectral radiance of the feedback source is the same as that of the object. The display indicates the brightness temperature of the object being measured.How does an Infrared Thermometer work?V Differences in Accuracy of Different Types of Infrared Thermometers5.1 Three Categories of Infrared ThermometersAccording to different uses and accuracy, infrared thermometers can be roughly divided into medical-grade infrared thermometers, consumer-grade infrared thermometers, and industrial-grade infrared thermometers. Strictly divided, medical-grade infrared thermometers have the highest accuracy requirements. The accuracy needs to be between 0.1 and 0.2 degrees. High-precision infrared ear thermometers can meet the medical-grade temperature standards. However, to avoid cross-infection, hospitals use ear thermometers. One-time sheath is needed for warm guns; consumer grades are next, and accuracy around 0.5 can meet our daily temperature measurement needs. The accuracy is about 0.3 degrees, which belongs to the consumer-grade infrared thermometer; the industrial grade has the lowest, generally the maximum allowable error is more than ± 1 ° C, and the distance is far.5.2 Differences Between Mainstream Infrared ThermometersIn fact, whether it is a medical or industrial infrared thermometer, they use the same principle of receiving infrared waves from the human body, but the object distance ratio has been adjusted differently, and the surface temperature is measured. The normal forehead temperature is about 2-3 ° C lower than the temperature of the armpit, and the forehead is directly affected by the environment. It is for preliminary investigation and reference and cannot be used as a basis for medical diagnosis. In addition, the temperature of the ear and neck will be more stable than the temperature of the forehead and barely affected by the environment. This is one of the reasons why the ear thermometer is more accurate than the forehead.5.3 Infrared Temperature Gun The medical thermometer has been revised by software or the relevant range has been limited by the software before leaving the factory. The emissivity of a normal human body is 0.98 (the thermometer defaults to 0.95), so the measured result is about 34-35 ° C. All infrared products (infrared cameras) can correct the difference by changing the emissivity to 0.8 to avoid inaccurate body temperature when used by non-professionals; and industrial-grade thermometers provide more realistic feedback on temperature measurement. It shows the actual temperature detected.Figure4. Infrared Temperature GunVI Infrared Thermometer Accuracy And Factors Affecting Accuracy6.1 Precision of Infrared ThermometerThe accuracy of contact measurement is about 0.1 degrees. Compared with contact temperature measurement, the accuracy of non-contact temperature measurement is lower. The infrared thermometer with higher accuracy is about 0.2 degrees, and the worse temperature error is 1 degree. Even above 1 degree. In general, the accuracy of infrared thermometers is ± 2 ° C. Today, temperature measurement products such as handheld infrared thermometers on the market are easily affected by measurement distance and ambient temperature, and the measurement error is often around 1 degree.6.2 Factors Affecting The Accuracy of The Infrared Thermometer Measurement6.2.1 EmissivityAll objects reflect, transmit, and emit energy, and only the emitted energy can indicate the object's temperature. When the infrared thermometer measures the surface temperature, the instrument can receive all three kinds of energy. Therefore, all infrared thermometers must be adjusted to read only the emitted energy. Measurement errors are usually caused by infrared energy reflected from other light sources.  Some infrared thermometers can change the emissivity, and emissivity values for many materials can be found in published emissivity tables. Other instruments have a fixed pre-set emissivity of 0.95. The emissivity value is the surface temperature of most organic materials, paints or oxidized surfaces, which is compensated by applying a tape or flat black paint to the measured surface. When the tape or lacquer reaches the same temperature as the base material, measure the temperature of the surface of the tape or lacquer, which is its true temperature.Figure5. Emissivity6.2.2 Ratio of Distance To Light SpotThe optical system of the infrared thermometer collects energy from a circular measurement spot and focuses it on the detector. The optical resolution is defined as the ratio of the distance from the infrared thermometer to the object to the size of the measured spot (D: S). The larger the ratio, the better the resolution of the infrared thermometer and the smaller the spot size to be measured. 6.2.3 Field of ViewMake sure the target is larger than the spot size of the infrared thermometer. The smaller the target, the closer it should be. When accuracy is particularly important, make sure the target is at least 2 times the spot size.Figure6. Field of ViewVII Factors to Consider When Choosing An Infrared Thermometer(1) Temperature rangeThe temperature measurement range is actually the range of the infrared thermometer, and the range of different thermometers will be different. The temperature measurement range is generally -50 ~ 360 ° C, -30 ~ 380 ° C, -18 ~ 280 ° C, -32 ~ 450 ℃, -32 ~ 650 ℃, -32 ~ 1050 ℃, etc., and the range for measuring body temperature is generally 35 ~ 42.5 ℃. You need to choose the appropriate range according to the temperature range of the measured object. (2) Measurement accuracyMeasurement accuracy is the only indicator to ensure the accuracy of the measurement, and it is also a key indicator to determine the performance of the infrared thermometer. Accuracy is usually expressed as ± X ℃ or ± X%. The smaller the value, the higher the accuracy. (3) Display resolutionThe display resolution is the last digit of the temperature display, usually 0.1 ° C or 0.1 ° F. (4) Optical resolutionThe optical resolution is the ratio of the distance D from the thermometer to the target to the diameter S of the measurement spot, that is, the ratio of the distance to the spot diameter D; S, D: S, the greater the accurate temperature measurement distance. In order to obtain accurate temperature readings, the distance between the thermometer and the test target must be within a suitable range. If the pyrometer must be measured away from the target due to environmental conditions, and a small target is to be measured, a pyrometer with high optical resolution should be selected. (5) EmissivityEmissivity is the ratio of the energy radiated by an object at a specific temperature to the energy radiated by an ideal radiator at the same temperature. Different objects have different emissivities. Some infrared thermometers have a fixed emissivity of 0.95, while others are adjustable. The emissivity of the infrared thermometer can be adjusted according to the material of the measured object to ensure the accuracy of the measurement results. (6) Response timeThe response time is the time it takes for the infrared thermometer to reach 95% of its final reading. It represents the speed at which the infrared thermometer responds to changes in the measured temperature. The response time of the new infrared thermometer can even reach 1ms. If the target moves fast or measures a fast-heated target, a fast-responding infrared thermometer should be selected; otherwise, a sufficient signal response cannot be achieved, which will reduce the measurement accuracy.Figure7. Infrared ThermometerVIII How To Make Infrared Thermometers More Accurate(1) Accurately determine the emissivity of the measured object;(2) Avoid the influence of high-temperature objects in the surrounding environment;(3) For transparent materials, the ambient temperature should be lower than the temperature of the measured object;(4) The thermometer should be vertically aligned with the surface of the measured object. Under no circumstances should the angle exceed 30 ° C.(5) Can be applied to the temperature measurement of bright or polished metal surfaces, and cannot be measured through the glass;(6) Correctly follow-off coefficient, the target diameter is full of field of view;(7) If the infrared thermometer is suddenly in a situation where the ambient temperature difference is 20 ° C or higher, the measurement data will be inaccurate, and then take the measured temperature value after the temperature is balanced. IX One Question Related to Infrared Thermometers9.1 QuestionWhat is infrared radiation?A. It's the transfer of energy by electromagnetic wavesB. The radiation given off by radioactive particlesC. Infrared radiation is a type of gasD. It is the reaction that occurs by freezing water9.2 AnswerA X FAQ1. How do you accurately use an infrared thermometer?Keep the Infrared Thermometer Close to the TargetThe Distance-to-spot ratio is the surface area being able to be detected compared to the distance taken from the target. As a rule of thumb, the closer you are to the target, the smaller the measurable surface area is, thus the more accurate the measurement. 2. How does the infrared temperature sensor work?These sensors work by focusing the infrared energy emitted by an object onto one or more photodetectors. These photodetectors convert that energy into an electrical signal, which is proportional to the infrared energy emitted by the object. 3. How accurate are thermal thermometers?Research has shown that, when used correctly, infrared or no-contact thermometers are just as accurate as oral or rectal thermometers. No-contact thermometers are popular among pediatricians, as kids often squirm around when trying to get a temperature read, but it also holds true in mass temperature screenings. 4. What is normal forehead temperature with an infrared thermometer?Normal forehead skin temperature can vary several degrees depending on your environment (indoors or out), exercise, perspiration, direct heat or air conditioning, etc. It would be normal to read an actual forehead skin surface temperature between 91F and 94F if using a general-purpose infrared thermometer. 5. Are infrared thermometers dangerous?As long as the Non-Contact Infrared Thermometers are used properly, they do not represent a risk of possible eye damage, as these Thermometers do not use lasers to measure body heat, the authorized thermometers measure infrared light; therefore they are not dangerous. 6. How far away should you hold an infrared thermometer?Usually, 6 inches is considered the ideal distance for using an infrared thermometer and correctly monitoring the temperature. 7. What is the benefit of using an infrared thermometer?IR thermometers are handy for use in measuring drafts and insulation breakdown. They can pick up hot spots in electrical systems and bearings and help monitor cooling systems. They are even used to measure food storage temperatures and can do this with no cross-contamination. 8. Are digital or infrared thermometers more accurate?Ranging from 0 to 600 Fahrenheit, the best IR Thermometer has a correct accuracy of about ±3.5 Fahrenheit. A digital thermometer could be used in three different ways. The accuracy of each might differ from one another. 9. What are the benefits of a non-contact infrared thermometer?• The non-contact approach may reduce the risk of spreading disease between people being evaluated.• Easy to use.• Easy to clean and disinfect.• Measures temperature and displays a reading rapidly.• Provides the ability to retake a temperature quickly. 10. How do I know if my digital thermometer is accurate?Add a little clean water until the glass is full and stir. Wait for about three minutes before inserting the sensor on the thermometer into the ice-filled water. Wait for about thirty seconds and check that the thermometer reads 32°F. If it does, then it is accurate, but if not, it requires calibration. 

Ⅰ IntroductionAs for operational amplifier applications, in electronic circuit, it is usually combined with a feedback network to form a certain functional module, with a special coupling circuit and feedback. Its output signal can be input signal addition, subtraction or differentiation, integration, etc, which early used in analog computers to do mathematical operations. Now they widely used in the electronics industry, regarded as precision AC and DC amplifiers, active filters, oscillators and voltage comparators.This Video is Introducing Operational Amplifier Applications in the CircuitCatalogⅠ Introduction1.1 Integrated Op AmpⅡ Op-amp ParametersⅢ Application MattersⅣ Classic Amplifier CircuitsⅤ One Question Related Op Amp and Going Further5.1 Question5.2 Answer1.1 Integrated Op Amp1.1.1 Evaluation AnalysisIntegrated operational amplifiers are one of the most widely used devices in analog integrated circuits. In various systems, because of different application requirements, the performance requirements of operational amplifiers are also different.Where there are no special requirements, try to use a universal integrated operational amplifier as much as possible, which can reduce costs and easily replace. When using multiple op amps in a system, use as many op amp integrated circuits as possible. For example, LM324 and LF347 always integrate four op amps together in a circuit.The evaluation of integrated op amps depends on their overall performance. Generally, the merit coefficient K is used to measure the excellent degree of integrated operational amplifiers, which is defined as: where SR is the slew rate and the unit is V / ms. The larger the value, the better the AC characteristics of the operational amplifier; The input bias current of the amplifier is lib, the unit is nA; VOS is the input offset voltage in mV. The smaller the Iib and VOS values, the better the DC characteristics of the op amp. Therefore, for circuits that amplify AC signals such as audio and video, op amps with large SR are better; for circuits that handle weak DC signals, op amps with high accuracy are more suitable (both offset current, offset voltage and temperature drift are relatively small).When selecting an integrated op amp, some factors should be considered in addition to the figure of merit coefficient K. For example, the signal source is a voltage source or a current source; the nature of the load, and whether the output voltage and current of the integrated op amp meet the requirements; operating voltage range, power consumption, and volume of the integrated op amp.Figure 1. Using Operational Amplifier as a Comparator1.1.2 Integrated Op Amp Basics Power supplyThe integrated op amp has two power terminals + VCC and -VEE, with different power supply methods. For different power supply modes, the requirements for input signals are different.1) Dual power supplyOp amps are mostly powered in this way. The positive power (+ E) and negative power (-E) relative to the common terminal (ground) are connected to the + VCC and -VEE pins of the op amp, respectively. In this way, the signal source can be directly connected to the input pin of the op amp, and the amplitude of the output voltage can make the positive and the negative symmetrical.2) Single power supplySingle-supply operation connects the -VEE pin of the op amp to ground. At this time, in order to ensure that the internal unit circuit of the operational amplifier has a suitable static operating point, a DC potential must be added to the input end of the op amp. Zero settingDue to the influence of the input offset voltage and input offset current of the integrated op amp, when the input signal is zero, the output is often not equal to zero. In order to improve the operation accuracy of the circuit, it is required to compensate the error caused by the offset voltage and the offset current. This is the zero setting of the operational amplifier. Commonly used zeroing methods include internal zeroing and external zeroing. For integrated op amps without internal zeroing terminals, external zeroing methods should be used. Self oscillationThe operational amplifier is a high-amplitude multi-stage amplifier. Under the condition of deep negative feedback, it is easy to cause self-excited oscillation. To make the amplifier work stably, a certain frequency compensation network must be added to eliminate the self oscillation. In addition, to prevent low-frequency oscillation or high-frequency oscillation caused by the internal resistance of the power supply, an electrolytic capacitor (10mF) and a high-frequency filter capacitor (0.01 mF ~ 0.1mF) should be connected. Device protectionThere are three aspects to the protection of the integrated op amp safety: power protection, input protection and output protection.1) Power protectionCommon faults of power supply are reverse polarity and voltage jump. For a power supply with poor performance, voltage overshoot often occurs at the moment when the power is turned on and off. Protection measures such as the use of FET current source and voltage regulator clamping protection. The voltage regulator’s voltage value is greater than the normal operating voltage of the integrated op amp and less than the maximum allowable operating voltage of the integrated op amp, and the current of the FET tube should be greater than the normal operating current of integrated op amp.2) Input protectionIf the input differential/common mode voltage of the integrated op amp is too high beyond the limit parameter range of the integrated op amp, it will be damaged.3) Output protectionWhen the integrated op amp is overloaded or the output is shorted, the op amp will be damaged if there is no protection circuit. However, some integrated op amps have internal current limit protection or short circuit protection, and no additional output protection is required to use these devices.Figure 2. An Inverting Op Amp CircuitⅡ Op-amp ParametersTo use the op amp better in the circuit, you must have a certain understanding of its internal parameters. Here are the technical parameters closely related to the op amp: Unity-gain bandwidth Definition: Under the condition that the closed-loop gain of the op amp is 1 time, a constant amplitude sinusoidal small signal is input to the input end of the op amp, and the closed-loop voltage gain measured from the output end of the op amp is reduced by 3dB (or equivalent to 0.707 times of the input signal of the op amp), that is to say, the frequency at which the output signal is reduced by -3dB is unity-gain bandwidth. It is a very important indicator. For a sinusoidal small signal amplification, the unity-gain bandwidth is equal to the product of the input signal frequency and the maximum gain at that frequency. In other words, when you know the frequency and gain of the signal to be processed, the unity-gain bandwidth (gain bandwidth = amplification * signal frequency) can be calculated to select the appropriate op amp. The higher the bandwidth, the higher the frequency of the signal that can be processed, and the better the high frequency characteristics, otherwise the signal will be easily distorted.    For small signals, the unity-gain bandwidth is also called the gain-bandwidth product, which can roughly show the ability of the op amp to process the frequency of the signal. For example, the gain bandwidth of a certain operational amplifier is 1MHz, if the actual closed-loop gain is 100, then the maximum frequency for theoretical processing of small signals is 1MHz / 100 = 10KHz.For the bandwidth of a large signal, that is, the power bandwidth, the influence of the slew rate SR is the major factor, and the unit is V/uS. In this case, the power bandwidth calculated by FPBW = SR / 2πVp-p, that is, the gain bandwidth and power bandwidth must be satisfied at the same time when designing the circuit.For DC signals, bandwidth issues are generally not considered, and accuracy and interference are mainly considered.When the amplification factor of an amplifier is n times, it does not mean that all input signals are amplified n times. When the signal frequency increases, the amplification capability decreases. Open bandwidthThe open-loop bandwidth is defined as: inputting a constant-amplitude sinusoidal small signal to the input of the op amp, the frequency measured at which the open-loop voltage gain decrease 3dB from the output of the op amp to the dc gain of the op amp. This is used for very small signal processing. Slew rate SRWith the op amp connected in a closed loop, a large signal (including a step signal) is input to the input of the op amp, and the output rise rate of the op amp is measured from the output of the op amp called SR. Because the input stage of the op amp is switched during the conversion, the feedback loop of the op amp does not work, that is, the conversion rate is independent of the closed-loop gain. The slew rate is a very important index for large signal processing. For general op amps, the slew rate SR <= 10V / μs, and the slew rate of high speed op amps is SR> 10V / μs. The highest conversion rate SR of current high-speed op amps reaches 6000V / μs. The larger the SR, the better the response of the op amp to the input signal changing at high speed. The larger the signal amplitude, the higher the frequency, and the greater the SR. This is used for op amp selection in large signal processing. Full-power bandwidthAt the rated load, under the condition that the closed-loop gain of the op amp is 1 time, a constant-amplitude sinusoidal large signal is input to the input end of the op amp, so that the output frequency of the op amp reaches the maximum (allowing certain distortion) signal. This frequency is limited by the slew rate SR of the op amp. Approximately, full power bandwidth is calculated by formula SR / 2πVop (Vop is the peak output amplitude of the op amp). It is a very important indicator for op amp selection in large signal processing. Setting timeAt the rated load, under the condition that the closed-loop gain of the op amp is 1 time, the time required to input a step large signal to the input of the op amp to increase the output from 0 to a given value. Because it is a step large signal input, a certain jitter will occur after the output signal reaches a given value. This jitter time is called the stabilization time. At this moment, stabilization time + rise time = settling time. For different output accuracy, there is a big difference in the stabilization time. The higher the accuracy, the longer the stabilization time. Equivalent input noise voltageIt refers to any AC random interference voltage generated at the output of an op amp with good shielding and no signal input. When this noise voltage is converted to the input of the op amp, it is called the input noise voltage of the op amp (sometimes expressed by noise current). For broadband noise, the effective value of the input noise voltage of ordinary op amps is about 10 ~ 20μV. This value often corresponds to a certain frequency band. Output impedanceIt refers to the ratio of the change in voltage to the corresponding change in current when the signal voltage is applied to the output of the op amp working in the linear region. At low frequencies it only refers to the output resistance of the op amp. Common mode input resistenceRefers to the ratio of the change in the input voltage of the common mode to the corresponding change in the input current when the two inputs of the op amp input the same signal. At low frequencies, it behaves as a common mode resistance. Generally, the common mode input impedance of the op amp is much higher than the differential mode input impedance, with a typical value above 108Ω. Common mode rejection ratioSame as the definition in the differential amplifier circuit, it is the ratio of the differential mode voltage gain to the common mode voltage gain, which is usually expressed in decibels. It is a parameter that measures the degree of symmetry of the input stage differential amplifier and the ability of the integrated op amp to suppress common mode interference signals. The larger the value, the better. Power supply rejection ratioThe power supply voltage rejection ratio is defined as the change ratio of the input offset voltage of the op amp with the power supply voltage in the linear region. The power supply voltage rejection ratio reflects the effect of power supply changes on the output of the op amp. At present, the power supply voltage suppression ratio is only about 80dB. Therefore, when used for DC signal or small signal processing for analog amplification, the power supply of the op amp needs to be carefully set. Of course, an op amp with a high common mode rejection ratio can compensate a part of the power supply voltage rejection ratio. In addition, when using dual power supplies, the power supply voltage rejection ratio of the positive and negative power supplies may be different. Differential mode input resistanceRefers to the ratio of the change in voltage at the two input terminals to the corresponding change in current at the input terminals when the op amp is operating in the linear region. The differential mode input impedance includes the input resistance and input capacitance, and refers only to the input resistance at low frequencies. General products specification only give input resistance. The input resistance of the op amp using the bipolar transistor as the input stage is not greater than 10MΩ; the input resistance of the op amp as the input stage of the field effect transistor is generally greater than 109Ω. Input offset voltageWhen the input voltage is zero, the output voltage is divided by the voltage gain, plus the negative sign, which is the offset voltage converted to the input. It is the compensation voltage applied at the input when the output voltage is zero. The input offset voltage actually reflects the circuit symmetry inside the op amp. The better the symmetry, the smaller the input offset voltage. The input offset voltage is a very important indicator of the op amp, especially when it is a precision op amp or used for DC amplification.The input offset voltage has a certain relationship with the manufacturing process. It is between ± 1 and 10 mV when op amps use the bipolar process (that is, the standard silicon process). If the field effect tube is used as the input stage, it will be greater. For precision op amps, it is generally below 1mV. The smaller the input offset voltage, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps. Input offset voltage driftWithin the specified operating temperature range, it is the ratio of the change in input offset voltage with temperature to the change in temperature. It is actually a supplement to the input offset voltage, which is convenient for calculating the drift of the amplifier circuit due to temperature changes within a given operating range. It is an important indicator for measuring the temperature effect to the op amp. Under normal circumstances, it is about (10 ~ 30) uV / C (degree Celsius), the high quality can be <0.5uV / C. Input offset currentIt is defined as the difference between the base current of the differential pair of the differential input stage when the output DC voltage of the op amp is zero. Used to characterize the degree of asymmetry of the differential input current. The better the symmetry, the smaller the input offset current. Input offset current is a very important indicator for op amps, especially for precision operational amplifier or DC amplifier. The input offset current is approximately one to one-tenth of the input bias current. It has an important impact on small signal precision amplification or DC amplification, especially when a large resistor is used outside the op amp. The effect of input offset current may exceed the effect of input offset voltage on accuracy. The smaller the input offset current, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps. Input offset current temperature driftWithin the specified operating temperature range, the ratio of the amount of change in input offset current with temperature to the amount of temperature change. It refers to the temperature coefficient of within the specified operating range, and is also an important indicator to measure the temperature effect on the op amp. It is usually about (1-50) nA / C, and the high quality is about several pA / C. This value is only given in the precision op amp parameters, and it needs attention when it is used for DC signal processing or small signal processing. Input bias current   It is defined as the average value of the bias currents of the two input terminals when the output DC voltage of the op amp is zero, in other words, it is the average current flowing into the input terminal when the operational amplifier is operating in the linear region. The input bias current has a greater impact on the places where input impedance is required, such as high-impedance signal amplification and integrator circuits. The input bias current has a certain relationship with the manufacturing process. If a field effect tube is used as the input stage, the input bias current generally lower than 1nA. It always used to measure the input current of the differential amplifier pair. Maximum differential mode input voltageIt is a voltage that the two input ends of the op amp can withstand. When it is exceeded, the reverse breakdown of the differential tube will occur. The NPN tube made by the plane process has a value of about 5V, and the Vidmax of the horizontal PNP tube can reach more than 30V. Maximum common mode input voltageIt an allowable range of common mode input voltage under normal operating conditions of the op amp. When the input differential pair saturates, the amplifier loses common mode rejection ability. In the case of interference, it is necessary to pay attention to this problem in the use of the circuit. Output peak to peak voltageWorking in the linear region, under the specified load, when the op amp is powered by the large power supply, it is the maximum voltage amplitude that the op amp can output. Except for low voltage op amps, the output peak-to-peak voltage of general op amps is greater than ± 10V, but less than the power supply voltage. This is due to the design of the output stage. The output stage of modern low-voltage op amps has been specially treated. The output peak-to-peak voltage is close to within 50mV of the power supply voltage, so it is called a full-scale output op amp, also known as a rail-to-raid op amp. It should be noted that the output peak-to-peak voltage of the op amp is related to the load, and the value is different for different loads; the positive and negative output voltage swings of the op amp are not necessarily the same. For practical applications, the closer the output peak-to-peak voltage is to the supply voltage, the easier the power supply design.Figure 3. Input Offset Voltage of an Op-ampⅢ Application Matters1) A single-supply op amp must be DC biased, otherwise it will not work properly. For the virtual ground design, in addition to the DC potential, it is necessary to pay attention to the voltage stabilization (it is best to use the reference voltage chip), and also to ensure low impedance AC decoupling, that is, low-frequency decoupling parallel to at least 10uF and high frequency decoupling under 0.1uF.2) The input of the non-inverting amplifier must be biased to ground as a DC path.3) Ordinary op amps cannot directly drive capacitive loads. If there is need, you must use capacitors for phase compensation or output series resistors and then connect the load.4) For the op amp input of the external interface, a TVS tube must be connected in parallel to the positive and negative input pins to prevent the op amp from reversing the polarity due to the too large input voltage signal, forming a parasitic false signal output.5) For amplifier circuits with a gain of more than 10 times, pay attention to controlling the bandwidth gain of the op amp to prevent the device from self oscillation.6) The output of the power amplifier needs to be protected by switching diodes to the power supply and ground, especially when inductive loads are connected.7) When using multiple op amps to process multiple signals, care must be taken to prevent the instantaneous changes in one of the signals from causing crosstalk to the other signal. Therefore, it is recommended not to use one op amp to process multiple signals.8) Most op amp chips are ESD sensitive devices, so pay more attention when using them.9) The pins of unused op amps (excess channels in multiple op amps) should not be left floating, and  grounded or connected to positive and negative power supplies. It is recommended to connect it as a follower (the output is connected to the reverse input) and the non-inverting input is connected to a potential between the power rails (the ground of the dual power system or any suitable point in the circuit). They can also used as buffer amplifiers and add them to a small impact location in the system.Figure 4. Op Amp 741Ⅳ Classic Amplifier CircuitsFigure 5. Inverting AmplifierFigure 5: The grounded non-inverting terminal of op amp is 0V. The inverting and non-inverting terminals are short-circuit, so the inverting end is also 0V. The input resistance of the inverting input terminal is very high, and it is virtual open. In other words, there is almost no current pass through. Therefore, the current flowing through each component in a series circuit is the same, that is, the current flowing through R1 and R2 are the same.Current flowing through R1: I1 = (Vi-V-)/R1Current flowing through R2: I2 = (V--Vout)/R2V- = V+ = 0, I1 = I2Solve the above algebraic equation to get Vout = (-R2/R1)*Vi, it is the input-output relationship of the inverting amplifier. Figure 6. Non-inverting AmplifierIn Figure 6, Vi and V- are virtual short, where Vi = V-. Because of the virtual open, there is no current flow through at the reverse input terminal, then R1=R2. If the current is I, which is obtained by Ohm's law: I = Vout/(R1+R2);Vi is equal to the partial voltage on R2, that is: Vi = I*R2.Virtual short: Vi = V-, R1=R2Ohm's law: I = Vout/(R1+R2), Vi = I*R2Where Vout=Vi*(R1+R2)/R2, represents the non-inverting amplifier. Figure 7. AdderFigure 7: Knowing from the Kirchhoff's law and virtual open theory, the sum of the current through R2 and R1 is equal to the R3, V- = V+ = 0 (short circuit), so (V1 – V-)/R1 + (V2 – V-)/R2 = (Vout – V-) /R3 can be transferred as V1/R1 + V2/R2= Vout/R3. If R1=R2=R3, then the formula becomes Vout=V1+V2, which is an adder. Figure 8. AdderIn Figure 8, because of the virtual open, no current flows through the non-inverting terminal, where V+ = V-, R1=R2, R4=R3, therefore, (V1 – V+)/R1 = (V+-V2)/R2, (Vout – V-)/R3 = V-/R4 can be simplified as V+ = (V1 + V2)/2 V- = Vout/2. So Vout = V1 + V2 is also an adder. Figure 9. SubtractorFigure 9 shows that the current through R1 is equal to the R2, and R4=R3, therefore, (V2– V+)/R1 = V+/R2, (V1 – V-)/R4 = (V--Vout)/R3. If R1=R2, then V+ = V2/2; if R3=R4, then V- = (Vout + V1)/2, because of V+ = V-, so Vout =V2-V1 is a subtractor. Figure 10. Integrator CircuitIn Figure 10, the input voltage at the inverting terminal is equal to the non-inverting terminal because of short circuit; the current through R1 is equal to the C1 because of virtual open. The current flowing through R1 and C1 are Ri=V1/R1, Ci=C*dUc/dt=-C*dVout/dt, respectively. So Vout=((-1/(R1*C1))∫V1dt, which is a integrator circuit. If V1 is a constant voltage U, then the above formula is transformed to Vout = -U*t/(R1*C1)t, then the Vout is a straight line that changes with time. Figure 11. Differential CircuitIn Figure 11, the current through capacitor C1 and resistor R2 is equal because of virtual open; V+ = V- because of short circuit, where Vout = -i * R2 = -(R2*C1)dV1/dt, which is a differential circuit. If V1 is a DC voltage, the output Vout corresponds to a pulse in the opposite direction to V1. Figure 12. Differential Amplifier CircuitFigure 12:Vx = V1……a, Vy = V2……bthen R1, R2, R3 can be regarded as a series, R1=R2=R3, the current I=(Vx-Vy)/R2……cwhere Vo1-Vo2=I*(R1+R2+R3) = (Vx-Vy)(R1+R2+R3)/R2 ……dIf R6=R7, then Vw = Vo2/2 ......e, similarly, if R4=R5, then Vout – Vu = Vu – Vo1, so Vu = (Vout+Vo1)/2 ……fdue to short circuit, Vu = Vw ……g, based on efg formulas, Vout = Vo2 – Vo1 ……hGet from dh, Vout = (Vy – Vx) (R1+R2+R3)/R2, where (R1+R2+R3)/R2 is a fixed value. This value determines the amplifier multiple of the difference (Vy-Vx), thus it is a differential amplifier circuit. Figure 13. Amplifier CircuitIt is a relatively common amplifier circuit. Many controllers accept 0~20mA or 4~20mA current from various measuring instruments. The circuit converts the current into voltage signal to become a digital signal by ADC. Figure 13 is such a typical circuit. As shown in Figure, 4~20mA current flows through the sampling 100Ω resistor R1, there will be a voltage difference of 0.4~2V on R1. Due to virtual open circuit, R3= R5 and R2=R4.Therefore: (V2-Vy)/R3 = Vy/R5 ……a  (V1-Vx)/R2= (Vx-Vout)/R4 ……bShort circuit: Vx = Vy ……cCurrent changes from 0~20mA, then V1 = V2 + (0.4~2) ……dPut cd formulas into b formula: (V2 +(0.4~2)-Vy)/R2 = (Vy-Vout)/R4 ……eIf R3=R2 , R4=R5, then e-a gets Vout =-(0.4~2)R4/R2 ……fIn Figure 13, R4/R2=22k/10k=2.2, then f formula Vout = -(0.88~4.4)V, that is to say, the current of 4~20mA is converted into a voltage range of -0.88~-4.4V. Current can be converted into voltage, and voltage can also be converted into current. Figure 14 is such a circuit. The negative feedback in the above figure does not directly feedback through the resistor, but the emitter junction of the transistor Q1 is connected in series. But it isn't a comparator. As long as it is an amplifying circuit, the law of short circuit and virtual open still conforms.Figure 14. Amplifier CircuitDue to virtual open, no current flows through the input of the op amp,Then (Vi – V1)/R2 = (V1 – V4)/R6 ……aSimilarly (V3 – V2)/R5 = V2/R4 ……bsince short circuit, V1 = V2 ……cIf R2=R6, R4=R5, then V3-V4=Vi can be obtained from abc.The above formula shows that the voltage across R7 is equal to the input voltage Vi, then the current through R7 is I=Vi/R7. If the load RL<100KΩ, the current through R1 and R7 are basically the same. Ⅴ One Question Related to Op Amp and Going Further5.1 QuestionWhat the Application of an Op Amp as a Phase Shifter?5.2 AnswerIn electronic circuit, op amp is used for direct coupling procedure and so DC voltage level at the emitter terminal increases from phase to phase. This rapidly increasing DC level is likely to shift the operating point of the upcoming stages. Thus to move down the increasing voltage swing, this phase shifter is applied.The phase shifter performs by adding a DC voltage level to the output of fall stage to pass the output to a ground level. Frequently Asked Questions about Operational Amplifier Applications1. Why is it called operational amplifier?It's called an “operational” amplifier because it performs a mathematical operation. The most obvious one is multiplication - it amplifies an input signal by a constant. ... But many different 'operations' can be performed by different circuit topologies. 2. What is inside an operational amplifier?Operations amplifiers — op-amps for short, are integrated circuits, constructed mostly out of transistors and resistors. These integrated circuits multiply an input signal to a larger output. You can use these components with voltage and current in both DC and AC circuits. 3. What are operational amplifiers used for?Op amps are used in a wide variety of applications in electronics. Some of the more common applications are: as a voltage follower, selective inversion circuit, a current-to-voltage converter, active rectifier, integrator, a whole wide variety of filters, and a voltage comparator. 4. What are linear applications of op amp?A linear amplifier like an op amp has many different applications. It has a high open loop gain, high input impedance and low output impedance. It has high common mode rejection ratio. Due to these favourable characteristics, it is used for different application. 5. How does an operational amplifier work?An operational amplifier, or op amp, generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance (no greater than 100 Ω). ... That is, the output gets fed back to the inverting input through some impedance. 6. What do you mean by differential amplifier?A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs and and one output in which the output is ideally proportional to the difference between the two voltages. 7. What are the non linear applications of op amp?Non-Linear Applications of Op AmpVoltage comparator.Two applications of comparator as window detector and zero crossing detector.Schmitt trigger circuit with the extension of regenerative comparator.Multivibrator circuits.Precision rectifier or super diode with the combination of op amp as voltage follower and a diode. 8. Why do we use differential amplifier?Differential amplifiers are used mainly to suppress noise. ... Noise is generated in the wires and cables, due to electromagnetic induction, etc., and it causes a difference in potential (i.e., noise) between the signal source ground and the circuit ground. 9. What does an operational amplifier do?An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. 10. What is an ideal operational amplifier?Operational amplifier: The ideal op amp is an amplifier with infinite input impedance, infinite open-loop gain, zero output impedance, infinite bandwidth, and zero noise. It has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions.

CatalogI IntroductionII Definition, Symbol and Labeling of Variable Resistor  2.1 Definition   2.1.1 What is Variable Resistance?   2.1.2 What is Variable Resistor?  2.2 Symbol  2.3 Labeling Method of Variable ResistorIII How The Variable Resistor WorksIV Features of Variable Resistor ShapeV Structure and Function of Variable Resistor  5.1 Basic Structure  5.2 Schematic Diagram of Two Variable Resistors  5.3 The Role of The Variable ResistorVI Types of Variable Resistors  6.1 Resistance box  6.2 Sliding Rheostat  6.3 Potentiometer  6.4 Specific Classification of Variable Resistors   6.4.1 Film Variable Resistor   6.4.2 Wire Wound Variable ResistorVII Typical Application Circuits of Variable Resistor  7.1 Variable Resistor Circuit in Transistor Bias Circuit  7.2 Stereo Balance Control Variable Resistor CircuitVIII Causes and Solutions of Variable Resistor Malfunctions  8.1 Causes of Variable Resistor Malfunctions8.2 Characteristics of Variable Resistor Malfunctions  8.3 Methods For Repairing Variable Resistor  8.4 Testing a Variable Resistor with a Multimeter   8.4.1 Method   8.4.2 PrecautionsIX Active Variable Resistors with Wide Range of Load ImpedanceX One Question Related to Variable Resistors  10.1 Question  10.2 AnswerXI FAQ I IntroductionA resistor is a current-limiting element. After the resistor is connected to the circuit, the resistance of the resistor is fixed. It generally has two pins, which can limit the current flowing through the branch connected to it. Those whose resistance cannot be changed are called fixed resistors, and those with variable resistance are called potentiometers or variable resistors.Setting Up A Variable Resistor, Rheostat, or Fixed ResistorII Definition, Symbol and Labeling of Variable Resistor2.1 Definition2.1.1 What is Variable Resistance?Variable resistance is a kind of resistance, which can play the role of resistance in electronic circuits. The difference from ordinary resistance is its resistance can be continuously changed within a certain range. In some cases where the resistance value is required to change but does not change frequently, a variable resistor can be used. 2.1.2 What is Variable Resistor？A variable resistor is an electronic component with adjustable resistance. It consists of a resistor and a rotating or sliding system. It is usually used in the circuit that needs to adjust the resistance frequently and plays the role of adjusting the voltage, adjusting the current, or controlling the signal. Its main parameters are basically the same as those of the fixed resistor. 2.2 SymbolThe symbol of the variable resistor is R and the unit is Ω. 2.3 Labeling Method of Variable Resistor(1) The variable resistor uses the direct standard method to indicate the nominal resistance value, that is, the nominal resistance value is directly marked on the variable resistor. In the case of high current applications, the variable resistor is also marked with the rated power parameter. In addition, the resistance value of small variable resistors is expressed in three digits, which is the same as that of resistors.(2) For variable resistors used in small-signal circuits, we generally only care about their nominal resistance and have no power requirements. III How The Variable Resistor WorksWhen a voltage is applied between two fixed electric shocks of the resistor body, the position of the contact on the resistor body is changed by rotating or sliding the system, and a position is formed between the movable contact and the fixed contact. Certainly related voltage. In other words, the resistor body of the variable resistor has two fixed ends. By manually adjusting the rotating shaft or sliding handle to change the position of the moving contact on the resistor body, the relationship between the moving contact and any fixed end is changed. The resistance value changes the magnitude of voltage and current. IV Features of Variable Resistor Shape(1) The volume of the variable resistor is larger than that of the general resistor, and at the same time, the variable resistor in the circuit is less, and it can be easily found in the circuit board.(2) There are three pins in the variable resistor, and they are different from each other. One is a moving pin and the other two are fixed. Generally, the two fixed pins can be used interchangeably, but the fixed and moving pins cannot be used interchangeably.(3) There is an adjustment port on the variable resistor. Use a flat-blade screwdriver to protrude into this adjustment port. Turn the screwdriver to change the position of the moving plate and adjust the resistance value.(4) The nominal resistance value can be seen on the variable resistor. This nominal resistance value refers to the resistance value between two fixed chip pins and is also a fixed chip pin and a moving chip pin. The maximum resistance value between.(5) The vertical variable resistor is mainly used in small-signal circuits. Its three pins are vertically downward and mounted vertically on the circuit board. The resistance adjustment port is in the horizontal direction.(6) Horizontal variable resistors are also used in small-signal circuits. Its three pins are at 90 ° to the resistance plane and are mounted vertically on the circuit board with the resistance adjustment port facing upward.(7) The variable resistance of the small plastic case is smaller and has a circular structure. Its three pins are down and the resistance adjustment port is up.(8) Variable resistors (wire-wound structure) for large power applications. The volume is large, and the moving blade can slide left and right to adjust the resistance. V Structure and Function of Variable Resistor5.1 Basic StructureThe variable resistor is chiefly composed of a moving piece, a carbon film body, and three pins. The three pins are two fixed pins (also called fixed pieces) and one moving piece pin. The moving piece of the variable resistor can be rotated left and right. When using a flat-blade screwdriver to reach into the adjustment port and rotate, the contacts on the moving piece can slide on the resistance piece. According to diverse uses, the resistance material of the variable resistor includes metal wire, metal sheet, carbon film, or conductive liquid. For currents of general magnitude, metal-type variable resistors are frequently used. When the current is slight, it is better to use a carbon film type. When the current is large, the electrolytic type is most suitable. 5.2 Schematic Diagram of Two Variable Resistors Figure3. Schematic Diagram of Two Variable Resistors5.3 The Role of The Variable Resistor(1) A variable resistor is an adjustable electronic component, which is composed of a resistor body and a sliding system. The variable resistor resistance is a resistor that can be adjusted for the current or change of the circuit In the case of circuit resistance, the light can be dimmed, and the motor can be controlled to start its speed. (2) The variable resistor mainly controls the current in the series circuit by changing its own resistance, thereby protecting some electrical components with requirements for the current. The variable resistor is generally used in circuits that do not require frequent adjustment, mainly To fix the same value for the resistor. VI Types of Variable Resistors6.1 Resistance BoxVariable resistors are divided into three types: resistance box, sliding rheostat, and potentiometer. The resistance box is a variable resistance device that uses a conversion device to change its resistance value. This conversion device usually adopts a decimal disc type (knob type) structure, and can also adopt a plug type and an end button type structure as required. The circuit of the resistance box can be divided into series lines and series-parallel lines. Compared with the sliding rheostat, the resistance box can continuously change the resistance in the connected circuit, while the sliding rheostat cannot display the resistance value of the connected circuit.Figure4. Resistance Box6.2 Sliding RheostatA sliding varistor is one of the commonly used devices in electricity. Its working principle is to change the resistance by changing the length of the resistance line in the circuit, thereby gradually changing the current in the circuit. The resistance wire of a sliding rheostat is generally a nickel-chromium alloy with a high melting point and a large resistance, and a metal rod is generally metal with low resistance. As a result, when the cross-sectional area of the resistor is constant, the longer the resistance wire, the greater the resistance; the shorter the resistance wire, the smaller the resistance.Figure5. Sliding Rheostat6.3 PotentiometerA potentiometer is a resistance element with three lead-out terminals whose resistance can be adjusted according to certain change law. A potentiometer usually consists of a resistor and a movable brush. When the brush moves along the resistor body, a resistance value or voltage having a certain relationship with the amount of displacement is obtained at the output end. The potentiometer can be used as a three-terminal element or a two-terminal element. The latter can be regarded as a variable resistor. Because its role in the circuit is to obtain an output voltage that has a certain relationship with the input voltage (external voltage), it is called a potentiometer.Figure6. Potentiometer6.4 Specific Classification of Variable ResistorsThe variable resistor can be divided into the film-type variable resistor and wire-wound variable resistor according to the material. 6.4.1 Film Variable ResistorMembrane variable resistors are usually composed of a resistor body (synthetic carbon film), a movable contact (a movable metal reed or a carbon contact), an adjustment part, and three pins (or solder pads). Two of the fixed pins are connected to both ends of the resistor body, and the other pin (center tap) is connected to the movable contact piece. You can change the resistance between the center tap and the two fixed pins by turning the adjustment part with a small flat-blade screwdriver and changing the contact position of the movable contact with the resistor. Membrane variable resistors are available in hermetic, semi-hermetic, and non-hermetic configurations. (1) Fully sealed film variable resistors are also called solid variable resistors. The resistor is made of carbon black, quartz powder, an organic binder and other materials, and then pressed into plastic or epoxy resin. The matrix of the material is polymerized by heating. The movable contacts use carbon contacts and the adjustment parts are made of plastic. The resistor body and the movable contact are sealed by a metal casing (there is an adjustment hole above the metal casing). Its advantage is that it has good dustproof performance and rarely has bad contact failure. (2) The manufacturing process of the resistor body of the semi-sealed film variable resistor and the resistor body of the fully sealed variable resistor is basically the same. The movable contact piece adopts a metal reed, and the outer plastic cover is sealed. When the plastic cover is rotated, the movable contact piece also rotates with it. This variable resistor is easy to adjust, but its dust resistance is not as good as a fully sealed film-type variable resistor. (3) Unsealed film variable resistors are also called chip tunable resistors. The resistor body is made of carbon black, graphite, quartz powder, an organic binder, etc. to form a suspension, which is coated on a glass fiberboard or glue. Made from wooden boards. The movable contact piece uses a metal reed, and the reed has an adjustment hole, and no separate adjustment component is provided. Its disadvantages are poor dust-proof performance, the contacts are susceptible to oxidation, and prone to failure due to poor contact with the synthetic carbon film. 6.4.2 Wire Wound Variable Resistor(1) High-power wire-wound varistor is also called sliding wire varistor, which is divided into axial ceramic tube-type wire-wound variable resistor and porcelain disc-type wire-wound variable resistor. It adopts an unsealed structure.(2) Low-power wire-wound variable resistors include round vertical wire-wound variable resistors, round horizontal wire-wound variable resistors, and square wire-wound variable resistors, all of which are fully sealed. Package structure.In addition, the variable resistor can be divided into a vertical variable resistor and a horizontal variable resistor according to the structure.Figure7. Wire Wound Variable ResistorVII Typical Application Circuits of Variable Resistor7.1 Variable Resistor Circuit in Transistor Bias CircuitThe figure below shows a variable-resistor voltage-dividing bias circuit. In the circuit, the transistor VT1 constitutes a high-frequency amplifier, and RP1, R1, and R2 constitute a voltage-dividing bias circuit. The output voltage of the voltage dividing circuit is determined by the resistance of three resistors, RP1, Rl, and R2. R1 and R2 are fixed resistors. The variable resistor RP1 is adjusted, and then the VT1 static operating current is adjusted. The amount of current determines whether VT1 can work in the best state. Figure8. Variable Resistance Voltage Divider Bias Circuit7.2 Stereo Balance Control Variable Resistor CircuitThe following figure shows the left and right channel gain balance adjustment circuits in the audio amplifier. RP1 in the circuit is a variable resistor in series with R1. Figure9. Left and Right Channel Gain Balance Adjustment Circuit in Audio AmplifierIn the audio circuit, for a two-channel amplifier, we need to strictly require that the left and right channel amplifiers have an equal gain (balanced), but the discreteness of the circuit components makes this impossible. In order to ensure that the gains of the left and right channel amplifiers are equal, left and right channel gain balance adjustment circuit needs to be provided, which is referred to as a stereo balance circuit. In the right channel circuit, the resistance of R2 is determined, so that the gain of the right channel amplifier is fixed. Taking the gain of the right channel amplifier as a reference, changing the resistance of RP1 so that the gain of the left channel amplifier is equal to the gain of the right channel amplifier can achieve the same gain of the left and right channel amplifiers. VIII Causes and Solutions of Variable Resistor Malfunctions8.1 Causes of Variable Resistor Malfunctions(1) The use time is long, causing oxidation.(2) The failure of the circuit caused the variable resistor to overcurrent and burned the carbon film. At this time, the burned trace of the variable resistor can also be seen from the appearance. 8.2 Characteristics of Variable Resistor Malfunctions (1) Damage to the carbon film of the variable resistorThe carbon film of the variable resistor is worn or burned. At this time, the contact between the moving piece and the carbon film is poor or cannot be contacted.(2) Poor contact between the moving piece of the variable resistor and the carbon film causes the contact resistance between the moving piece and the carbon film to increase.(3) The variable resistor pin is broken. 8.3 Methods For Repairing Variable Resistor (1) When the track of the contact of the moving blade on the carbon film is worn, the contact on the moving blade can be bent inward to change the original track of the contact of the moving blade.(2) The contacts of the moving blade are dirty. You can clean the contacts with pure alcohol.(3) There is a disconnection between one stator and the carbon film. At this time, if it is used as a variable resistor (not used as a potentiometer), this stator that is not disconnected can be used instead. Resistance value.(4) A pin is broken due to twisting. A lead can be welded with a hardwire as a pin.Figure10. Test a Variable Resistor8.4 Testing a Variable Resistor with a Multimeter8.4.1 MethodThe detection method of the variable resistor is basically the same as that of the resistor. The resistance between the primers is measured with an ohmic block. The measurement can be performed directly on the circuit board, or the variable resistor can be disconnected from the circuit. (1) Measure the nominal resistance of the variable resistor. The multimeter is placed in the proper range of the ohmic block. The two-meter bars are connected to the two fixed pin pins of the variable resistor. At this time, the measured resistance value should be equal to the nominal resistance value of the variable electrical accessory, otherwise, the variable resistance is explained. The device is damaged. (2) Measure the resistance between the moving resistor and the stator of the variable resistor. The multimeter is placed in the proper range of the ohmic block. One meter rod is connected to the fixed piece, and the other one is connected to the moving piece. In this measurement state, when the variable resistor moving piece is rotated, the needle is deflected and the resistance value increases from zero To the nominal value, or decrease from the nominal value to zero. 8.4.2 PrecautionsDue to the particularity of the variable resistor, the following issues should be noted during the detection process:(1) If the resistance between the moving piece and a fixed piece is 0Ω, at this time, you should see whether the moving piece has turned to the end of the fixed piece. To exclude the effects of external circuits). (2) If the resistance value between the moving piece and any certain piece is greater than the nominal resistance value, it means that the variable resistor has an open circuit fault. (3) In the measurement, if the measured resistance between a moving piece and a certain piece is less than the nominal resistance value, it does not mean that it is damaged, but you should look at the position of the moving piece, which is different from ordinary resistors. (4) When taking off the measurement, you can use the appropriate range of the multimeter's ohmic stop.-One rod is connected to the pin of the pad, and the other rod is connected to afoot. Then use a flat screwdriver to slowly rotate the pad in a clockwise or counterclockwise direction. At this time, the hands should continuously change from 0Ω to the nominal resistance. The same method is used to measure the change of wake value between another fixed film and a moving film. The measurement method and test result should be the same. In this way, the variable resistor is good, otherwise, the variable resistor is damaged.Figure11. Digital MultimeterIX Active Variable Resistors with Wide Range of Load ImpedancePower resistors, variable resistors, and other electronic loads are often used to test power supplies and voltage regulators, as shown in the following figure: Figure12. Active variable resistors with several orders of magnitude constant resistanceAlthough the function is the same as a mechanical potentiometer, it is based on an active device, which can provide a wide range of load resistance, high resistance adjustment resolution, and less heat than a mechanical potentiometer. Analyzing the circuit shown in the figure above, the voltage expressions of the non-inverting and inverting ends of the operational amplifier are: Figure13. FormulaThese two voltages are equal, so Figure14. FormulaThe whole circuit can be regarded as the resistance of the non-inverting terminal IN + and the inverting terminal IN-. The non-inverting and inverting equivalent resistances are constant and independent of the test voltage (VIN). RSENSE includes several series resistors that provide multiple orders of magnitude in impedance selection. For example, if 10Ω is required, the terminal is IN + and "B" near IN-1 (points A, C, and D are not connected). For high power loads, pay attention to the rated power of the sense resistor and nFET. The power supply of the operational amplifier can be a battery or any other DC power supply. Its maximum working current is only 20 μA. It is powered by a 9V battery. Under normal circumstances, the active load can be used for 1-2 years.X One Question Related to Variable Resistors10.1 QuestionVolume control regulator in a CD receiver, radio and amplifier also useA.transistorB.variable resistorC.thermistorD.fixed resistor10.2 AnswerB  XI FAQ1. What is a variable resistor do?A variable resistor gives the user more control over the resistance, as it allows for variance or for the resistor to be changed in order to meet the resistance requirements of the user. Changing the resistance as a user is actually very simple. 2. What are the two types of variable resistors?The different types of variable resistors include Potentiometer. Rheostat. Thermistor. 3. What is the difference between a variable resistor and a potentiometer?In the potentiometer, the resistance of the track remains the same as the wiper moves and only the potential on the wiper changes. In a variable resistor, the resistance of the track apparently changes as the wiper moves and short circuits more or less of the track resistance. 4. What is the advantage of a variable resistor?The advantage of variable resistors is that you have more control over the voltage. You can also adjust the amount of voltage flowing through a circuit. 5. What is the symbol of a variable resistor?A variable resistor also called an adjustable resistor, consists of two terminals, where one of the terminals is a sliding or moving contact often known as a wiper. The variable resistor IEC symbol is represented by a rectangular box and an arrow across (or above) it, like that shown in the figure below. 6. How do you identify a variable resistor?The variable resistor is represented by a zig-zag line and an arrow across (or above) it, like that shown in the figure below. 7. How many types of variable resistors are there?Variable resistors can be categorized into three types: Potentiometers. Rheostats. Digital potentiometers. 8. Is LDR a variable resistor?An LDR is a component that has a (variable) resistance that changes with the light intensity that falls upon it. This allows them to be used in light sensing circuits. 9. Do variable resistors have polarity?Resistors are blind to the polarity in a circuit. Thus, you don't have to worry about installing them backward. Current can pass equally through a resistor in either direction. 10. Why is a variable resistor needed in a circuit?Simply put, a variable resistor is able to have its electrical resistance adjusted. These devices are used when working with electrical circuitry because they help to control voltage and/or currents. They specifically work with voltage and currents that are a part of the circuit. 

Ⅰ Working Principle1.1 TerminologyA diode is a two-terminal electronic device characterized by unidirectional conductivity—it allows current to flow easily in one direction but severely restricts current from flowing in the opposite direction. Historically, diodes are divided into vacuum tube diodes (formerly called electron diodes) and semiconductor diodes (crystalline diodes). Due to the high heat loss, large size, and lower efficiency of vacuum tubes, semiconductor diodes are the standard in modern electronics.The fundamental principle of a modern diode relies on the PN junction. Adding leads and a protective package to this PN junction creates the discrete component we know as a diode.A semiconductor diode consists of a PN junction formed by joining a P-type semiconductor and an N-type semiconductor. A depletion region (space charge layer) forms at the interface, creating a self-built electric field. In the absence of applied voltage, the diffusion current (caused by the difference in carrier concentration) and the drift current (caused by the internal electric field) balance each other out, resulting in a state of electrical equilibrium.Forward Bias: When a forward voltage is applied, the external electric field opposes the self-built field. This lowers the barrier, causing the diffusion current of carriers to increase significantly, resulting in a forward current (conduction).Reverse Bias: When a reverse voltage is applied, the external field reinforces the self-built field. This widens the depletion region and prevents majority carriers from crossing. Only a tiny "reverse saturation current" flows (leakage), which remains roughly constant over a specific voltage range.Breakdown: When the reverse voltage exceeds a critical threshold, the electric field strength in the depletion layer becomes high enough to trigger a multiplication of carriers. This generates a large number of electron-hole pairs, causing a sharp increase in reverse current. This is known as the breakdown phenomenon. It is worth noting that reverse breakdown is categorized into two types: Zener breakdown (in highly doped junctions at lower voltages) and Avalanche breakdown (at higher voltages). Figure 1. P-type Semiconductor and N-type Semiconductor 1.2 PN JunctionA PN junction is the boundary interface between two types of semiconductor materials: P-type and N-type. The "P" (Positive) region contains an excess of holes, while the "N" (Negative) region contains an excess of free electrons. Due to the concentration gradient, free electrons from the N region diffuse into the P region, and holes from the P region diffuse into the N region. This movement creates the depletion region at the junction.Metal leads are connected to these regions to form terminals: the lead connected to the P-region is the Anode (positive pole), and the lead connected to the N-region is the Cathode (negative pole).1.2.1 Doping PrincipleP-type formation: Intrinsic semiconductors (pure silicon) are doped with trivalent impurities (Group III elements), such as Boron. A Boron atom has only three valence electrons. When it forms covalent bonds with surrounding silicon atoms (which have four electrons), a "hole" (a lack of an electron) is created in the lattice. This hole can accept an electron, effectively making the Boron atom a static negative ion. In P-type material, holes are the majority carriers.N-type formation: Similarly, when intrinsic silicon is doped with pentavalent impurities (Group V elements), such as Phosphorus, the impurity atoms form covalent bonds with silicon. Since Phosphorus has five valence electrons, one excess electron is left free to move. In N-type material, free electrons are the majority carriers. Figure 2. PN Junction StructureWhen these two regions meet, the diffusion of electrons and holes across the boundary disrupts the electrical neutrality near the junction, creating an electric field that eventually stops further diffusion, establishing equilibrium.1.2.2 Feature: Unidirectional ConductivityWhen forward voltage is applied (Anode positive, Cathode negative), the external field pushes holes and electrons toward the junction. This narrows the depletion region and neutralizes the internal electric field. Once the voltage exceeds the threshold voltage (typically ~0.7V for Silicon, ~0.3V for Germanium), the diode conducts current with very low resistance.1.2.3 Supplementary NoteForward Bias: Current flows easily; the diode acts like a closed switch (low impedance).Reverse Bias: Current is blocked; the diode acts like an open switch (high impedance). Ⅱ Diode ApplicationsDiodes are ubiquitous in electronics. From simple power conversion to complex signal processing, they protect circuits, regulate voltage, and enable logic functions. Understanding the diode is the first step to mastering electronics.Function of a Diode in Circuit Design2.1 Main FunctionsDiodes serve four primary roles in modern circuitry:(1) Switching Circuit (Current Steering)In digital logic and computing, diodes utilize their unidirectional conductivity to act as automatic switches. They ensure current flows only when specific conditions are met (like in AND/OR logic gates). Switching diodes (like the 1N4148) are optimized for speed, offering much faster response times than mechanical switches and preventing damage from reverse currents.(2) Limiter/Clipper Circuit (Signal Control)Limiter circuits (or clippers) use diodes to restrict the voltage amplitude of a signal. By placing diodes in parallel with the signal path, any voltage exceeding the diode's forward drop (plus any series reference voltage) is shunted to ground. This is essential for protecting sensitive inputs on microcontrollers or audio equipment from signal spikes.(3) Regulator Circuit (Voltage Stabilization)Zener diodes are the key component here. Unlike standard diodes, Zeners are designed to operate in the reverse breakdown region reliably. If the voltage across a Zener exceeds its "Zener Voltage" (Vz), it conducts heavily, clamping the voltage at that level. This makes them perfect for creating simple voltage references or low-power regulators.(4) Varactor Circuit (Tuning and Frequency Control)Varactor diodes (or Varicaps) act as voltage-controlled capacitors. When reverse-biased, the width of the depletion layer changes with voltage, which changes the junction capacitance. These are widely used in Voltage Controlled Oscillators (VCOs) for tuning radios, TVs, and mobile phones, as well as in frequency modulation (FM) circuits. 2.2 Typical Diode ApplicationsLight-emitting diode (LED)Figure 3. Light-emitting DiodeLEDs emit light when electrons recombine with holes at the PN junction, releasing energy in the form of photons. They have revolutionized lighting due to their safety, high efficiency, durability, and fast response time.Key Applications:1. Consumer Electronics: Backlights for LCD TVs, computer monitors, and smartphone screens.2. Automotive: Used in headlights, brake lights, and turn signals. Their fast switching speed improves safety (brake lights trigger faster than incandescent bulbs), and their longevity reduces maintenance.3. Industrial & Mining: Due to their robustness and efficiency, LEDs are replacing traditional lamps in harsh environments like underground mining.4. Urban Lighting: Replacing high-voltage, fragile neon tubes with LED strips for signage and architectural lighting reduces energy costs and fire risks.Zener diodeZener diodes maintain a constant voltage across their terminals when reverse-biased, even as current fluctuates. They are categorized by their breakdown voltage (e.g., 3.3V, 5.1V, 12V). They can be connected in series to achieve higher regulated voltages. Figure 4. Zener Diode CircuitRectifier diodeRectifier diodes allow current to flow only in one direction, converting Alternating Current (AC) into pulsating Direct Current (DC). This is the fundamental component of power supplies. Figure 5. Full Wave Rectifier CircuitLow Frequency (Mains): For standard 50Hz/60Hz rectification, the 1N400x or 1N540x series are standard. Key parameters are Maximum Rectified Current (Io) and Peak Inverse Voltage (PIV).High Frequency: In Switching Mode Power Supplies (SMPS), standard rectifiers are too slow. Fast Recovery Diodes (FRD) or Schottky diodes are required to handle high switching frequencies efficiently.Detector diodeDetector diodes (often Germanium or Schottky point-contact diodes) possess high detection efficiency and low junction capacitance. They are used to demodulate Amplitude Modulated (AM) signals in radios, extracting the audio signal from the carrier wave.  Figure 6. Detector Diode CircuitSchottky diodeA Schottky diode uses a metal-semiconductor junction rather than a P-N junction. This gives it two distinct advantages: 1. Low Forward Voltage Drop: Typically 0.15V to 0.45V (compared to 0.7V for Silicon), which reduces power loss and heat. 2. High Speed: Zero reverse recovery time makes them ideal for high-frequency switching power supplies, inverters, and motor drivers.Switching diodeDesigned specifically for rapid on/off operations. In the circuit below, VD1 acts as a switch to control the charging path of capacitor C2. Figure 7. Switching Diode CircuitFast recovery diode (FRD)FRDs are PN junction diodes doped to have a significantly reduced Reverse Recovery Time (trr). While a standard rectifier might take microseconds to stop conducting when voltage reverses, an FRD stops in nanoseconds. This is critical in modern power electronics like inverters and PWM controllers to prevent short-circuit currents. Update for 2025: In high-power applications, Silicon Carbide (SiC) diodes are increasingly replacing traditional silicon FRDs due to their ability to handle higher voltages and temperatures with almost zero switching loss.Transient voltage suppressor (TVS)Transient Voltage Suppressors (TVS) are specialized avalanche diodes designed to absorb high-energy spikes. They are the primary defense against ESD (Electrostatic Discharge) and voltage surges in sensitive electronics. Figure 8. Diode Circuit Symbols Ⅲ One Question Related to Diode Functions and Going Further3.1 QuestionWhy do we use diodes in a circuit?3.2 AnswerThe primary function is to serve as an electronic "check valve" or "one-way street" for electricity. This enables: 1. Rectification: Converting AC power (wall outlet) to DC power (batteries/electronics). 2. Protection: Blocking reverse polarity (if you put a battery in backward) or clamping high-voltage spikes (TVS). 3. Signal Manipulation: Demodulating radio signals or creating logic gates. 4. Reference: Providing a stable voltage reference (Zener). Ⅳ Diode Distributors RecommendationWhether you are sourcing standard rectifiers or advanced SiC power diodes, reliability is key. Here are some recommended sources for diode components:Mouser Electronics (Global Distributor)onsemi (Leading Manufacturer)KYNIX Semiconductor (Electronic Component Distributor)Digi-Key Electronics (Global Distributor) Frequently Asked Questions about Diode Function1. What is a diode used for?Its most common function is to allow electric current to pass in one direction (forward direction) while blocking it in the opposite direction (reverse direction). This is used for rectification, protection, and signal isolation. 2. What is the main function of a PN junction diode?It controls the flow of electrons. By manipulating the PN junction bias, it acts as a switch that is either ON (conducting) or OFF (insulating), depending on the direction of voltage applied. 3. What is the function of a rectifier diode?Rectifier diodes are specifically built to handle the conversion of AC (Alternating Current) to DC (Direct Current). They are robust enough to handle the high currents found in power supply units. 4. Do diodes output AC or DC?Diodes do not generate power. However, when an AC source is fed into a diode, the output is pulsating DC. The diode blocks the negative half of the AC cycle, leaving only the positive flow. 5. What is the function of a Zener diode?Zener diodes are used for voltage regulation. Unlike standard diodes, they are designed to conduct in reverse at a specific breakdown voltage (Vz). They are used to stabilize voltage rails and protect circuits from over-voltage surges. 6. What is the difference between a diode and a rectifier?"Diode" is the broad name for the component type (a two-terminal device). "Rectifier" is a function or a specific type of diode designed for power conversion. All rectifiers are diodes, but not all diodes are rectifiers (e.g., LEDs, Zener, and Varactors are diodes but are not used as rectifiers).