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IntroductionThe potentiometer is a three-terminal resistive element whose resistances can be adjusted according to a certain change rule. According to it, it is used in a large variety of electrical and electronic circuits, such as voltage dividers, variable resistor, and current controllers. The potentiometer is usually composed of a resistor body and a movable brush. When the brush moves along the resistor body, the resistance value or voltage will be changed at the output end. Due to its special structure and function, it is necessary to pay attention to its damage and take regular maintenance during operation.Potentiometers - Basic IntroductionCatalogIntroductionⅠ Potentiometer Using TipsⅡ How to Clean Potentiometer?Ⅲ How to Test Potentiometer?3.1 General Methods3.2 Variable Potentiometer TestⅤ Replacing Potentiometer with 4 StepsⅠ Potentiometer Using Tips1) The resistor body of the potentiometer is mostly made of polycarbonate synthetic resin. Avoid contact with the following items: ammonia, other amines, aqueous alkali solutions, aromatic hydrocarbons, ketones, lipid hydrocarbons, and strong chemicals (excessive acid-base value), etc. Because chemical reaction with those will affect their performance.2) The terminal of the potentiometer should avoid using water-soluble flux when soldering, which will cause metal oxidation and mold material. In addition, avoid using inferior flux, and poor soldering may cause difficulty in soldering, resulting in poor contact or open circuit.3) If the soldering temperature is too high or the soldering time is too long, it may cause damage to the potentiometer terminals. The pin terminal should be soldered at 235℃±5℃ within 3 seconds, and the soldering space should be more than 1.5mm away from the potentiometer body. Do not use solder to hit through the circuit board when soldering, and wire terminal soldering should be soldered at 350℃±10℃ within 3 seconds. Except that, the terminal should avoid heavy pressure, otherwise it is easy to cause poor contact.4) During soldering, the height of the rosin (flux) entering the printing machine board should be adjusted properly, and the flux should be prevented from entering the potentiometer, otherwise it will cause poor contact between the brush and the resistor, resulting in INT, noise and other undesirable phenomena.Potentiometer Structure5) The potentiometer is best used in the voltage adjustment, and the connection method should choose "①" pin grounding. The current adjustment structure should be avoided, because the contact resistance between the resistor and the contact piece will stop the passage of large currents.6) Avoid condensation or water droplets on the surface of the potentiometer, and avoid using it in a humid place to prevent insulation deterioration or short circuit.7) When installing the rotary potentiometer, the strength should not be too tight to avoid damage to the screw teeth or poor rotation. When install the sliding type potentiometer, avoid using too long screws, otherwise it may affects the movement of the sliding handle, and even directly damages the potentiometer body.8) In the process of putting the potentiometer on the knob, the pushing force used should not be too large (not exceeding the parameter index of the pushing and pulling force of the shaft in the specification note), otherwise it may cause damage to the potentiometer.9) The operating force (rotation or sliding) of the potentiometer will become faster as the temperature rises, and slower as the temperature drops. If the potentiometer is used in a low temperature environment, it needs a kind of special low temperature resistant grease.10) The shaft or sliding handle of the potentiometer should be as short as possible when designing it. The shorter the shaft or sliding handle, the better and stable the hand feel. On the contrary, the longer the shaking, the greater the shaking, and the feel is easy to change.11) The power of the carbon film of the potentiometer can withstand the ambient temperature of 70°C, and its function may be lost when the temperature is higher than it.12) The resistor body of the sealed potentiometer is mostly made of polycarbonate synthetic resin. Avoid mixing with ammonia, aromatic hydrocarbons, lipid hydrocarbons, ketones, and strong chemicals (excessive pH), other amines, alkaline aqueous solution, etc, because they will affect its performance.Potentiometer TypesⅡ How to Clean Potentiometer?The potentiometer is to wrap the carbon sheet with POM, PC, ABS and other plastic materials. After assembly, the carbon sheet will not be exposed to the outside, it is not easy to oxidize, and dust is not easy to enter, which protects the potentiometer body.Cleaning Steps of Potentiometer1) Use a screwdriver to carefully open the sealing cover fixing card of the sealing potentiometer, and remove the protective cover.2) Remove the fixed spring card of the rotating shaft and pull out the rotating shaft.3) If some sealed potentiometers cannot take out the shaft, you can directly wipe the carbon film and the metal contacts on the shaft with a cotton ball dipped in pure alcohol.4) Adjust the position and angle of the metal contacts, changing the contact position with the carbon film and increasing the pressure.5) Apply some lubricating oil or special grease on the carbon film to delay the service life.6) Reinstall and fix the metal cover to complete the entire cleaning process. Ⅲ How to Test Potentiometer?3.1 General Methods1) Before detecting the potentiometer by the method of appearance and manual adjustment, firstly observe its appearance. Rotate the knob to check whether the rotation is smooth, whether the switch is flexible, whether the "click" sound is crisp when the switch is turned on and off, and listen to the sound of friction between the internal contact points of the potentiometer and the resistor body, if there is a loud noises indicate that the quality is not good. Normally, the handle should be slightly damped when turning.2) Using the multimeter to measure the potentiometer, you should first select the appropriate ohm gear of the multimeter according to the nominal resistance of the measured potentiometer and then do the measurement. When measuring, touch the red and black test leads of the multimeter to the pins of the fixed pins on both sides, and the multimeter reading should be the nominal resistance of the potentiometer. If the multimeter reading is much different from the nominal resistance value, it indicates that the potentiometer has been damaged.When the nominal resistance of the potentiometer is normal, then measure its changing resistance and whether the movable contact is in good contact with the resistor (fixed contact). At this time, one test lead of a multimeter is connected to the moving contact pin (usually the middle pin), and the other test lead is connected to a certain contact pin (pins on both sides).After connecting the test leads, the multimeter should display zero or the nominal resistance value, and then rotate the multimeter's shaft from one extreme position to the other extreme position, and the resistance value should continuously change from zero (or nominal resistance) to the nominal resistance value (or zero). During the rotation or sliding of the shaft of the potentiometer, if the pointer of the multimeter moves steadily or the displayed indication changes uniformly, it means that the measured potentiometer is in good condition. If the resistance reading of the multimeter fluctuates when the shaft is rotated, it means the movable contact has a fault with poor contact.3.2 Variable Potentiometer Test1) Measure the total resistance at both ends to see if it matches the nominal value.2) Measuring the resistance between a fixed end and the sliding end: rotary the potentiometer to see if the resistance change is continuous. Then measuring the resistances between the other fixed end and the sliding end, if the measured intermediate resistance value changes discontinuously, it indicates that there is a poor contact in the sliding process.PotentiometersⅣ Replacing Potentiometer with 4 StepsThere are many types of potentiometers, and most models cannot be used interchangeably, otherwise the control effect will not be very good. When replacing it, the nominal resistance value should be the same as the damaged variable resistance value or the close to. At the same time, its packages must be considered, otherwise the installation will be difficult. Therefore, we must distinguish between linear potentiometers, exponential potentiometers and logarithmic potentiometers before use. In addition, please note that the precision resistor can only be replaced with a same one when it is damaged, and cannot be replaced with an ordinary variable resistor, otherwise its adjustment accuracy will also be affected.The potentiometer has multiple pins. In order to prevent the wrong pins from being connected during replacement, the following specific operation steps and methods can be used:Step 1: Remove the set screw of the original potentiometer, but do not take off the leads on the potentiometer.Step 2: Install the new potentiometer and fix it.Step 3: Solder a lead on the original potentiometer pin slice, solder it on the corresponding pin slice of the new potentiometer, and the welding method is the same as the old one.Step 4: In the same way, solder each pin wire. Pay attention, welding the next one and then the other one can avoid the wrong position of the leads being welded to each other. Frequently Asked Questions about Potentiometer Uses and Its Replacement1. What is the use of potentiometer?The measuring instrument called a potentiometer is essentially a voltage divider used for measuring electric potential (voltage); the component is an implementation of the same principle, hence its name. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. 2. What causes a potentiometer to fail?An electrical short or open will cause the indication to fail at one extreme or the other. If an increase or decrease in the potentiometer resistance occurs, erratic indicated valve position occurs. 3. What does a potentiometer measure?A potentiometer is an instrument which is used for measurement of potential difference across a known resistance or between two terminals of a circuit or network of known characteristics. A potentiometer is also used for comparing the emf of two cells. 4. How do you troubleshoot a potentiometer?Set your ohmmeter to a setting higher than the total resistance of the potentiometer. For example, if your potentiometer is rated at 1,000 ohms, set your ohmmeter to 10,000 ohms. Look at your potentiometer. There should be three tabs sticking out of it. 5. Does a potentiometer need to be grounded?This configuration also acts as a voltage divider and can be used in a number of ways to control a signal. Like any resistor, potentiometers per se do not need to be connected to the ground plane of the circuit, but in the majority of configurations/uses, they will be.

The insulated gate bipolar transistor (hereinafter referred to as IGBT) is a composite device of MOSFET and GTR. Thus it has the advantages of MOSFET and GTR, it is an ideal switch device to replace GTR, which is widely used at present with its ability to turn off, and it’s also widely used in all kinds of solid-state power supply.     Catalog   I. What is IGBT? II. The Driving Requirement of IGBT III. The Overcurrent Protection Analysis of IGBT IV. Simulation and Experiment FAQ   I. What is IGBT?   The insulated gate bipolar transistor (hereinafter referred to as IGBT) is a composite device of MOSFET and GTR. Thus it has the advantages of MOSFET, including fast operation speed, high switching frequency, high input impedance, simple drive circuit, and good thermal temperature; it also contains the advantages of GTR, like large current-carrying capacity and high blocking voltage. It is an ideal switch device to replace GTR, which is widely used at present with its ability to turn off and is also widely used in all kinds of solid-state power supply.   And it requires a reasonable drive circuit, but its improper control may cause damage, such as IGBT damage due to overcurrent, and affects the performance of the whole machine. In a word, the drive circuit is very important to IGBT. So this paper mainly discusses the driving and short-circuit protection of IGBT, based on the analysis of its working principle, then designs and simulates the overcurrent protection of the drive circuit.     Electronic Basics #28: IGBT and when to use them     II. The Driving Requirement of IGBT   Driving Requirement IGBT is a voltage-type control device. To make IGBT turn on and off safely and reliably, the driving circuit must meet the following conditions.  And the gate capacitance of IGBT is much larger than that of MOSFET. To increase the switching speed, it is necessary to have a suitable gate bias voltage and gate series resistance.   Gate Voltage In any case, the gate drive voltage in the open state can not exceed the limited value (generally 20V) given by the parameter table, and the optimal gate forward-bias voltage is 15 V ±1.5V. This value is sufficient to allow IGBT to reach saturation and then getting conduction, which can minimize the conduction loss. In the case of gate voltage is cutting off with the value of zero, to reduce the turn-off time and improve the withstand voltage and anti-interference ability of IGBT, a reverse voltage of -5 ~ -15 V can be added between the gate and the source electrode when the IGBT is in a blocking state.   Gate Series Resistance Core The selection of appropriate gate series resistance (RG) is very important for the drive of IGBT. The effect of RG on switching loss is shown in Fig.1. Fig. 1 The Effect of RG on Switching Loss It is the dynamic current of charging and discharging the input capacitance rather than the DC current that is required in a static state, and the input impedance of IGBT is up to 109 ~ 1011. In this case, the DC gain can reach 108 ~ 109, almost without any power consumption.   To decrease the steepness of the front and rear edges of the control pulse, prevent oscillation and reduce the voltage tip pulse with a large IGBT collector, it is necessary to add a gate series resistor RG. When the RG increases, the on-off time will prolong and the energy consumption of the IGBT will increase; in turn, the RG reduces, the di/dt will increase and may damage IGBT.   Thus, according to the current capacity and voltage rating, and switching frequency of IGBT, it is necessary to select a suitable RG, usually from dozens of ohms to hundreds of ohms. To get a more specific value of RG, it is suggested to refer to the device manual. Fig.2 Main Circuit of Inverter Power Supply   Requirements for Driving Power The switching process of IGBT consumes a certain amount of power from the driving power supply. The difference between the gate forward bias voltage and the reverse bias voltage is the △VGE; working frequency is f, the gate capacitance is CGE; and the minimum peak current of the power supply is:     Overcurrent Protection for IGBT The overcurrent protection of IGBT is limiting the short-circuit current and its I-V track to the short circuit safe working area when the device overflows, and the IGBT is turned off before the device is damaged to avoid the damage of the switch tube. When the upper and lower arms conducting, the power supply voltage is almost all added to the two ends of the switch, at this time, the larger the short circuit current is, the smaller the saturation voltage drop will be, during this time, the device would be damaged due to the large current.     III. The Overcurrent Protection Analysis of IGBT   Based on the above analysis, an IGBT drive circuit which contains isolated optocoupler and over-current protection has been put forward in this article, as shown in Fig.3. Fig.3 The Drive and Overcurrent Protection Circuit of IGBT  In Fig.3, the high-speed optocoupler 6N137 realizes the electrical isolation of the input and output signals, which is suitable for high-frequency applications. The main drive circuit adopts push-pull output mode, which effectively reduces the output impedance of the drive circuit, improves the driving ability, and makes it suitable for the drive of high power IGBT.   The over-current protection circuit uses the principle of desaturation of the collector. When an over-current occurs, the IGBT will be turn off. The V1, V3and V4 constitute the driving pulse amplifier circuit; V1 and R5 constitute an emitter follower. The emitter follower provides a fast current source, which reduces the turn-off time. Using the collector desaturation principle, D1, R6, R7, and V2 form a short-circuit signal detection circuit. D1 is a fast recovery diode, to prevent the high voltage on the collector from running into the driving circuit when IGBT is turned off.   In order to prevent the power device from being misled by static electricity, bidirectional voltage regulators D3 and D4 are connected in parallel between the gate sources.   Normal When the control circuit sends a high-level signal, the optocoupler 6N137 turns on, V1, V2 turns off, V3 turns on and V4 turns off. And the drive circuit provides IGBT a driving voltage of +15V to turn it on. When the control circuit sends a low level signal, the optocoupler 6N137 turns off, V2 and V3 conduct, and the drive circuit provides a voltage of -5v to IBGT, making IGBT shut down.   Overcurrent When a short-circuit fault exists, the voltage of 15V is almost all added to the IGBT. At this time, the voltage of V2 cuts off in the short circuit detection circuit, and the electric potential of point A depends on the partial voltage of D1, R6, R7, and VCES.  When the main circuit works normally and the IGBT is on, the A point is kept low, which is lower than the B point potential. All A1 output low level, this time V5 cuts off, and the C point is high level.   So when operating normally, the input to the optocoupler 6N137 is always consistent with the output. When overcurrent occurs, the IGBT collector is desaturated, A point potential rises, when it is higher than B potential ( the setting potential), that is, when the current exceeds the designed fixed value, the A1 overturns and outputs a high level, meanwhile, V5 is switched on, thereby making C in a low potential state. The input signal to the optocoupler 6N137 is always low level regardless of whether the control circuit is sent to a high level or a low level to turn off the power tube. Thus, over-current protection is achieved until the circuit is troubleshot and then restarted.   Fig. 4 Strong Driving Circuit of IGBT with Short-Circuit Protection   IV. Simulation and Experiment   Input to the drive circuit with a high level of 15V and a low level of -5V square wave signal. The output waveform of IGBT is shown in Fig.5  Fig.5 IGBT Output Signal According to the above principle and analysis, the actual output waveform of the circuit is shown in Fig.6  Fig.6 Actual Circuit Output Waveform Conclusion (1) Providing -5V and +15V driving voltage for IGBT to ensure IGBT's turn on and off. (2) Having over-current protection to prevent the IGBT from being damaged when the current is overcurrent. (3) Using in a wide range because the circuit can dynamically adjust the maximum current according to the load. (4) Adopting discrete components as the driving circuits to reduce the cost of the whole system.     FAQ   1. How does an insulated gate bipolar transistor work? The IGBT combines the simple gate-drive characteristics of power MOSFETs with the high-current and low-saturation-voltage capability of bipolar transistors. The IGBT combines an isolated-gate FET for the control input and a bipolar power transistor as a switch in a single device.   2. Which insulated gate bipolar transistor? IGBTs are widely used as switching devices in the inverter circuit (for DC-to-AC conversion) for driving small to large motors. IGBTs for inverter applications are used in home appliances such as air conditioners and refrigerators, industrial motors, and automotive main motor controllers to improve their efficiency.   3. How do I trigger IGBT?   An IGBT is simply switched “ON” and “OFF” by triggering and disabling its Gate terminal. A constant +Ve voltage i/p signal across the 'G' and the 'E' will retain the device in its “ON” state, while deduction of the i/p signal will cause it to turn “OFF” like BJT or MOSFET.   4. Why use an IGBT instead of a Mosfet? The main advantages of IGBT over a Power MOSFET and a BJT are: 1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced.   5. Why IGBT is used an inverter? The Insulated Gate Bipolar Transistor (IGBT) is used in VFD inverter modules as the preferred electronic power switch for the following reasons. ... The IGBT has a fast switching speed. This minimises switching losses and allows for high switching frequencies which is good for motor harmonic and noise reduction.   6. What is difference between IGBT and SCR? SCR is a silicon control rectifier and igbt is a insulated gate bipolar transistor. ... scr has anode ,cathode and gate and igbt has base ,emitter, gate ,and collector. In the both devices gate terminal is used for triggering. Scr has only one insultive layer but igbt has 2 insulated silicon layers.   7. What is IGBT principle? IGBT Principle of Operation：IGBT requires only a small voltage to maintain conduction in the device unlike in BJT. The IGBT is a unidirectional device, that is, it can only switch ON in the forward direction. This means current flows from the collector to the emitter unlike in MOSFETs, which are bi-directional.   8. What causes IGBT failure? The failure modes for the IGBT are in the form of degradation of certain key electrical parameters (e.g., leakage current, threshold voltage) or the loss of functionality (inability to turn-off). The failure causes can be due to environmental conditions or operating conditions.   9. Is IGBT unipolar or bipolar? The IGBT cannot conduct current in the reverse direction (from emitter to collector) even with a positive Vge applied to it, because it has a bipolar-type structure.   10. Which IGBT used in VFD? IGBT (insulated gate bipolar transistor) provides a high switching speed necessary for PWM VFD operation. IGBTs are capable of switching on and off several thousand times a second. A VFD IGBT can turn on in less than 400 nanoseconds and off in approximately 500 nanoseconds.   11. Can we use IGBT instead of Mosfet? Due to the higher usable current density of IGBTs, it can usually handle two to three times more current than a typical MOSFET it replaces. This means that a single IGBT device can replace multiple MOSFETs in parallel operation or any of the super-large single power MOSFETs that are available today.   12. How fast can an IGBT switch? The typical switching time of IGBT is about hundreds of nanoseconds and the value varies with load current, junction temperature, and other factors [17–20]. However, the change of IGBT switching time is very small [4,5] (range from several to tens of nanoseconds) when the health status of the IGBT module changes.   13. Is IGBT faster than Mosfet? When compared to the IGBT, a power MOSFET has the advantages of higher commutation speed and greater efficiency during operation at low voltages. ... The IGBT combines the simple gate-drive characteristics found in the MOSFET with the high-current and low-saturation-voltage capability of a bipolar transistor.   14. How many IGBT are in a VFD? Six IGBTs. In a typical six pulse drive there are six IGBTs pulsing voltage up to 15,000 times per second. Since their introduction in the 1980's, IGBTs have literally switched up the market and now play a large role in many modern day power electronics applications where speed and process control are needed.   15. What is the function of IGBT? The IGBT combines, in a single device, a control input with a MOS structure and a bipolar power transistor that acts as an output switch. IGBTs are suitable for high-voltage, high-current applications. They are designed to drive high-power applications with a low-power input.   16. Is IGBT a rectifier? IGBTs have a pretty good current handling capacity when compared to standard BJTs (Bipolar junction transistor) and MOSFETs (metal–oxide–silicon transistor). IGBTs are devices whose switching is fully controlled electronically. Most standard rectifiers in the market are typically 6-pulse rectifiers.   17. How many types of IGBT are there? two types. The IGBT is classified as two types based on the n+ buffer layer, the IGBTs that are having the n+ buffer layer is called the Punch through IGBT (PT-IGBT), the IGBTs that does not have an n+ buffer layer are called the Non-Punch Through- IGBT (NPT- IGBT).   18. How do you prevent IGBT failure? IGBT turn-off requires that the IGBT be driven to the cutoff region of operation so that it can successfully block the reverse high voltage across it once the high-side IGBT has turned on. In principle this can be achieved by reducing the IGBT gate-emitter voltage to 0 V.   19. What is the difference between unipolar and bipolar devices? As their name implies, Bipolar Transistors are “Bipolar” devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a “Unipolar” device that depends only on the conduction of electrons (N-channel) or holes (P-channel).   20. What is IGBT and Igct? GTO stands for Gate Turn-Off Thyristor, IGCT stands for Insulated Gate Commutated Thyristor and IGBT stands for Insulated Gate Bipolar Transistor. The comparison between the three devices are derived with respect to symbol, characteristic, advantages, disadvantages and applications.   You May Also Like The First Fully 2D FETs Lead A Faster Electronic Future The First Printed 2D Transistor Is Discovered by Researchers The First Chemical Circuit Developed Smarter transistors could be three times more efficient

Introduction How to Read an Electrical Diagram Lesson What is a circuit Diagram? Circuit diagram is the basic of engineering research and planning. A schematic layout diagram, which is drawn with the standard symbol of physical electricity, can show the working principle of each component and device relationship, Each electronic component has a symbol. After seeing a few circuit diagrams, you’ll quickly learn how to distinguish the different symbols, and provide planning plan for installing electrons or electrical products. Circuit diagram is one of the basic skills that must be learned by electronic engineers. So this paper gathers the classical circuit materials related to regulated voltage power supply, DCDC conversion power supply, switching power supply, charging circuit, constant current source to provide the most practical circuit diagram reference for engineers. Schematic Symbols Basic Devices   A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.   An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a coil around a core.     An electric battery is a device consisting of one or more electrochemical cells with external connections provided to power electrical devices such as flashlights, smartphones, and electric cars.[1] When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode.[2] The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal.       A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal.           Five Parts to Understand Circuit Diagrams *Regulated Power Supply 1. The voltage adjustable range is between 3.5V~25V, the output current is large, using VR- tube circuit to obtain the stable output voltage. Working principle: after rectifying and filtering, DC voltage is supplied by R1 to the base of the adjusting tube, so that the adjusting tube can be switched on. When the voltage passes through the RP, R2 of the V1 conduction, V2 switched on, and then V3 is switched on. At this time, the emitter and collector voltage of V1, V2 and V3 do not change (it acts exactly like a voltage stabilizer). A stable output voltage can be obtained by adjusting RP, and the ratio of R1, PR, R2 to R3 determines the output voltage of the circuit. T: 80W～100W     Input: AC220VOutput Duplex Winding: AC28VRP: 1W (resistance: 250K～330K)FU1: 1A                FU2: 3A~5A VD1 | VD2: 6A02C4: 470µF/35V(electrolytic capacitor)C1: 3300µF / 35VC2 | C3: 0.1µF (MONO CAP)R1: 180～220Ω / 0.1W～1W     Fig 1. VR-tube Circuit 2. Regulated Voltage Adjustable Power Supply Circuit Diagram Whether the computer detection or electronic product can not be separated from the regulated power supply(RPS). This paper introduces one kind of RPS: a DC voltage continuously adjustable from 3V to 15V, the maximum current can be up to 10A, and the circuit uses a high precision standard voltage source integrated circuit (TL431) with temperature compensation which makes the voltage stabilizer more accurate. If there is no special requirement, it can basically meet the normal maintenance. The circuit is shown in the figure below. Fig 2. Regulated Voltage Adjustable Power Supply Circuit Diagram Its working principle is divided into two parts. The first part is a fixed 5V/1.5A power supply circuit; the second part is a high precision and large current regulator circuit which can be adjusted continuously from 3V to 15V. The first circuit is very simple. The DC voltage rectified by silicon bridge QL1 is filtered by C1 from the secondary 8V AC voltage of transformer, then the 5V three-terminal stabilizer block LM7805 can produce a fixed 5V | 1A power supply at the output end without any adjustment. This power supply can be used as an internal power source when the computer board is overhauled. The second part is basically the same as the common series power supply. The circuit is simple, the cost is low, but the voltage stabilizer performance is very high. The resistor R4, the regulator TL431, potentiometer R3 constitutes a continuously adjustable constant voltage source, which provides the reference voltage for the BG2 base. The regulated voltage value of the regulator TL431 is continuously adjustable, which determines the maximum output voltage of the power supply. If you want to expand the range of adjustable voltage, you can change the resistance values of R4 and R3, of course, the secondary voltage of transformer should also be increased. The power of the transformer can be controlled flexibly according to the output current, and the secondary voltage is about 15 V. Bridge rectifier QL, using 15A-20A silicon bridge, compact structure, fixed screws in the middle, can be directly fixed on the shell aluminum plate, better for heat sink. What adjusts the tube is the high current NPN metal shell silicon tube, because it has the very big heat, if the chassis allows, buying the big radiator as far as possible to expand the heat dissipation area; if does not need the big current, a smaller power silicon tube can be used to makes it smaller. The filter uses three 50V/4700uF electrolytic capacitance C5 and C7 in parallel, respectively, to make the output of large current more stable. In addition, this capacitor should be bought with a relatively larger volume, and those smaller ones will also mark 50V/4700uF, but the voltage fluctuates frequently, Or easy to fail for a long time lay idle. Finally, the power transformer can buy a ready-made switching power supply of more than 200W instead of the transformer. In this way, the voltage stability can be further improved, but the manufacturing cost is not too high, and other electronic components have no special requirements. After installation is completed, it can work properly without too much adjustment.   *Switched Power Supply(specific examples) The working principle of integrated control IC-UC3842 for PWM switching power supply The following is the UC3842 internal block diagram and pin diagram. UC3842 uses a fixed frequency pulse width controllable modulation mode, a total of 8 pins, each foot function as follows: Pin① is the output of the error amplifier, and the external resistor-capacitor unit is used to improve the gain and frequency characteristics of the error amplifier; Pin② is the feedback voltage input, which is compared with the 2.5 V reference voltage at the same phase of the error amplifier to generate the error voltage, thus controlling the pulse width; Pin③ is the current detection input, when detecting voltage exceeds 1V, the pulse width is reduced so that the power supply is in the state of intermittent operation; Pin④ is the timing end, the operating frequency of the internal oscillator is determined by the external resistor-capacitor time constant, f=1.8 / (RT×CT); Pin⑤ is the common ground; Pin⑦ is a DC power supply terminal with the function of undervoltage and overvoltage locking, the chip power consumption is 15mW. Pin⑧ is the output terminal of 5V reference voltage, its load capacity is 50mA. Fig 3. IC-UC3842 Electrical Diagram   UC3842 Internal Schematic Diagram UC3842 is an integrated controller of PWM switching power supply with excellent performance, wide application and simple structure. Because it has only one output, it is mainly used for voice control. The UC3842 pin7 is a voltage input with a starting voltage range of 16V-34V. When the power supply is on, the VCC is less than 16V, and the output of the Schmidt comparator is 0. At the same time, no reference voltage is generated and the circuit does not work. When Vcc > 16V, the input voltage Schmidt comparator sends out a high voltage to the 5V fern voltage regulator, which generates a 5V reference voltage. On the one hand, this voltage used in internal circuit; on the other hand, it provides a reference voltage to the outside through pin8. Once the Schmidt comparator flips to a high level (when the chip starts working), Vcc can change in the 10V-34V range without affecting circuit; when the Vcc is below 10V, the Schmidt comparator flips to a low level and the circuit stops working. When the reference voltage stabilizer has a 5V reference voltage output, the reference voltage detection logic comparator outputs a high level signal to the output circuit. At the same time, the oscillator will generate the oscillation signal of the f=Rt/Ct according to the parameters of the pin④ external Rt and Ct, which is added directly to the input of the totem pole circuit, the other is added to the position end of RS flip-flop made by PWM pulse width modulator, and the output end of R connects the output of current-detection comparator. The R-terminal is the control end of the duty ratio. When the R voltage rises, the Q pulse is widened. At the same time, the pulse width of pin⑥ is widened (duty cycle increased); when the R voltage drops, The Q pulse narrows and the pin⑥ pulse width becomes narrow (duty cycle reduced). The sequence of UC3842 points is as shown in the diagram. Only when the E point is in high level, and meanwhile, a point and b point is all in high level, the d point sends out the high level, the c point sends the low level, otherwise the d point sends the low level, c point sends out the high level. Pin② generally connects the feedback signal. When the pin②voltage increases, the pin① voltage will decrease, and the R-terminal voltage will also decrease, so the pin⑥ pulse will narrow, on the contrary, the pin⑥ pulse will become wider. Pin③ is a current sensing terminal. Usually, a small sample resistor is inserted into the source or emitter of the power transistor to convert the current passing through the switch to a voltage, and the voltage is introduced into the pin. When the load short circuit or other reasons cause the current of the power transistor to increase and the voltage on the sampling resistance exceeds 1V, the pulse output pin⑥ is stopped, which can effectively protect the power transistor from damage. Fig 4. UC3842 Internal Schematic Diagram TOP224P 12V | 20W Switching DC Power Supply Circuit Based on Regulated Voltage Two integrated circuits are used in the circuit: TOP224P three-terminal monolithic switching power supply (IC1) and PC817A linear optical coupler (IC2). After UR and Cl rectifier filter, AC power supply produces DC high voltage Ui, to supply primary winding of high frequency transformer T. VDz1 and VD1 can clamp the peak voltage of leakage inductance to the safe value and can attenuate the ringing voltage. VDz1 adopts P6KE200 type transient voltage suppressor with reverse breakdown voltage 200V, and VDl uses UF4005 type UFRD in 1A/600V. The secondary winding voltage is filtered by V, C2, L1 and C3 rectifier, getting 12V output voltage Uo. Uo value is set by the sum of the forward voltage drop UF, R1 of LED and the value of regulated voltage Uz2. Other output voltage values can be obtained by changing the turn ratio of high frequency transformer and the regulated voltage value of VDz2. R2 and VDz2 also provide a false load for 12V output to improve the load adjustment rate at light load. The feedback winding voltage is filtered by VD3 and C4 rectifier to supply the bias voltage required by TOP224P. Since the control current is regulated by R2 and VDz2, the output duty cycle is changed to stabilize the voltage. The common mode choke L2 can reduce the common mode leakage current generated by the waveform of the high voltage switch connected to the D by the primary winding. C7 is a protective capacitor used to filter out interference caused by coupling capacitors of primary and secondary windings. C6 can reduce the differential mode leakage current caused by the fundamental and harmonic waves of the primary winding current. C5 can not only filter the peak current added to the control terminal, but also determine the self-starting frequency, compensating the control loop with R1 and R3. Fig 5. TOP224P 12V | 20W Switching DC Power Supply Circuit The Main Technical Specifications of This Power Supply are as Follows AC Voltage: u=85～265V Voltage Regulation: η=78％ Grid Frequency: fLl=47～440Hz Input Voltage (Io=1.67A): Uo=12V Working Temperature: TA=0～50℃ Maximum Output Current: IOM=1.67A Maximum Output Ripple Voltage: ±60mV Continuous Power Output: Po=20W /TA=25℃ or 15W /TA=50℃）   *DC-DC Power Supply 3V→+5V or +12V Circuit Portable electronic products powered by batteries generally use low power supply voltage, which can reduce the number of batteries and product size. In order to ensure the stability and accuracy of the circuit, it is necessary to use a regulated power supply. If the circuit uses 5V working voltage, but one component requires a higher working voltage, this often makes the designer feeling hard. In this paper, a circuit composed of two booster modules is introduced to solve this problem, and only two batteries are used to supply power. The circuit has fewer components, small size, light weight, stable output of 5V or 12V, and meets the requirements of portable electronic products. +5V power supply can output 60mA, and +12 V power supply maximum output current is 5 mA. Fig 6. 3V→+5V or +12V Circuit The circuit is shown above. It is composed of AH805 and FP106 booster module. AH805 is a kind of boost module with an input of 1.2V~3V and an output of 5V, which can output 100mA current at 3V. FP106 is a chip boost module with input of 4V~6V and output fixed voltage of 29 ±1V, the output current up to 40 mA.  AH805 and FP106 are both a level-controlled to shut down the power. The output voltage of two 1.5V alkaline batteries is 3V, inputting to the AH805, and its output voltage is 5V, inputting 5V to the FP106, and the output voltage is 28V~30V, and then the output voltage is 12 V after through the voltage stabilizer. It can be seen from the diagram that different output voltages can be obtained by changing the stabilizer voltage. Pin⑤ of FP106 is the closing end of controlling the power supply. When Pin⑤ is added a high level > 2.5V, the power supply is switched on; When adding the low level is less than 0.4V, the power supply is off. It can be controlled by circuit or manually. If it is not necessary, Pin⑤ is connected to Pin⑧. MC34063 3.6V→9V Circuit Working State: No-load: Output 3.65V| 18uA  Load: Output 9.88V | 50.2mA; Input 3.65V | 186.7mA, efficiency 72% Working Principle: When there is no load, the IC has no power on pin⑥ and stops working. The input current is only 18uA with input 3.65V. When there is a load (Q1 has Ieb current), the EC pole of 8550 is switched on and the IC is operating. Whether the IC works is determined by whether there is a load or not, it is quite a battery. Using IC has a high voltage conversion efficiency and output stably. If this circuit adds a point of improvement, for example, when increasing power, it can turn into a power supply from 4.2V to 5V without switch. You can use a battery box as a backup power source for your phone. Fig 7. MC34063 3.6V→9V Circuit   *Charging Circuit lm358 basic Battery Charger Circuit Diagram Fig 8. lm358 basic Battery Charger Circuit Diagram There are two different arguments about whether alkaline batteries can be recharged. Some can be filled; the other say it has a risk of explosion. In fact, alkaline batteries can be rechargeable, generally 30-50 times of its service life. In fact, due to the charging methods, there are two different consequences. First of all, there is no doubt that alkaline batteries can be rechargeable, and in the battery instructions, it is mentioned that alkaline batteries are not rechargeable and that charging can lead to explosions. That's true, but note that the word is "could". Actually, it can be viewed as a manufacturer's self-protection statement of exemption. The key to charging alkaline batteries is temperature. As long as you can charge the battery without high temperature, you can successfully do it. The right charging method requires several points: small current: 50mA  charge 1.7V  discharge 1.3V After some people tried charging practice, they said categorically that they could not recharge. The reason for the problems such as lack of charging, short electricity consumption, leakage, explosion, actually, most are charger problems. If the charging current of the charger is too large, far more than 50 ma, and some fast chargers is above 200ma, the direct result is that the temperature of the battery is very high. If the battery is hot, the batteries will leak, and the serious will explode. Some people use Ni-MH rechargeable battery charger to charge, low grade charger does not automatically stop charging function, after long time charging will lead to overcharge then causing battery leakage and explosion. A better charger has the function of automatic shutdown, but the stop charge voltage is generally set to 1.42 V of the Ni-MH rechargeable battery, while the voltage of the alkaline battery is about 1.7V when it fully charged. As a result, the voltage is too low which causing fake charge. And not to wait until the battery is completely out of power to charge, it will lead to poor lifetime of the battery. It is recommended that the voltage of alkaline battery is not less than 1.3V. Therefore, if you plan to charge the alkaline battery, you must have a qualified charger, charging current around 50mA, and charging cut-off voltage is about 1.7V.   Related Description Alkaline manganese rechargeable battery: based on alkaline zinc manganese battery, it is also called mercury-free alkaline manganese battery because of the use of mercury-free zinc powder and new additives. The battery can be recharged for dozens to hundreds of times without changing the discharge characteristics of the alkaline battery, which is more economical. Alkaline zinc-manganese battery was developed in 1882. It was developed in 1912 and put into production in 1949. It has been found that when KOH electrolyte solution replaces NH4Cl as electrolyte, both the electrolyte and the structure change greatly, its performance improved significantly. Features Open voltage is 1.5V Working temperature is between -20℃ to 60℃, it is suitable in alpine region. The capacity of high current continuous discharge is about 5 times that of acid zinc-manganese battery. 2.75W USB Charger This design adopts Power Integrations's LinkSwitch series product LNK613DG. This design is well suited for mobile phones or similar USB charger applications, including mobile phone battery chargers, USB chargers, or any application with constant voltage or constant current. In the circuit, the diode D1 to D4 rectifies the AC input, and the capacitors C1 and C2 filter the DC. The L1, C1 and C2 form a π type filter to attenuate the differential mode conduction EMI noise. These are connected by E-sheild technology of Power Integrations transformers. This design can easily meet the requirements of EN55022 B-type conduction EMI with sufficient margin, and no Y capacitor is required. Fire proof, fusible, winding resistor RF1 provides fault protection and limits surge current generated during startup. Fig 9. 2.75W USB Charger Circuit Fig 9 shows that U1 is powered by optional offset power, which reduces no-load power to less than 40 mW. The value of by-pass capacitance C4 determines the number of cable voltage drop compensation. The value of 1μF corresponds to the compensation of a 0.3Ω / 24 AWG USB output cable. (10μF capacitance compensates 0.49 Ω / 26 AWG USB output cable.). In the constant voltage stage, the output voltage is regulated by switch control. The output voltage is maintained by skipping the switching cycle. By adjusting the ratio of the prohibition period to maintain voltage regularly. This also optimizes the efficiency of the converter throughout the load range. Under the condition of light load (trickle charge), the current limit will be decreased to reduce the magnetic flux density of the transformer, thus reducing the audio noise and switching loss. With the increase of load current, the current limit will increase, and the skipping period will be reduced continuously. When no longer skipping any switching period (maximum power point), the controller in the LinkSwitch-II switches to constant current mode. When the load current needs to be further increased, the output voltage will decrease, and it reflects in the FB pin voltage. In response to the voltage drop of the FB pin, the switching frequency will decrease linearly to achieve constant current output. The RCD-R clamping circuit is composed of D5, R2, R3 and C3, which is used to limit the leakage voltage spike caused by leakage inductance. Resistance R3 has a relatively large value to avoid drain voltage waveform oscillations caused by leakage inductance, which prevents excessive oscillation during turn-off, thus reducing EMI conduction. Diode D7 rectifies secondary and C7 filters it. C6 and R7 together limit the transient voltage spike on D7 and reduce EMI conduction and radiation. The resistor R8 and Zener diode VR1 form an false output load which ensures that the output voltage is within an acceptable limit and that the battery does not discharge completely when the charger is off. Feedback resistors R5 and R6 set maximum operating frequency and output voltage at constant voltage stage.   *Constant-Current Source 1. Discussion on How to Design Three-wire Constant Current Source Driving Circuit The constant current source drive circuit is responsible for driving the temperature sensor Pt1000, to convert its sensing resistive signal with temperature into measurable voltage signal. In this system, the required constant current source should have good temperature stability, large output resistance, output current less than 0.5mA (upper limit of Pt1000 without self-heating effect), earthing at one end of load, and variable polarity of output current. Because the influence of temperature on the parameters of integrated operational amplifier is less significant than of the transistor or FET, the constant current source composed of integrated operational amplifier has the advantages of better stability and higher constant current performance. Especially in the case where one end of the load needs grounding, it has been widely used. So use the dual operational amplifier constant current source shown in figure 2. Amplifier UA1 is used as adder, UA2 as follower, UA1 and UA2 are gain bipolar operational amplifier OP07,  which having low noise, low misalignment and high open-loop. Fig 10. Three-wire Constant Current Source Driving Circuit Vb and Va are the up and down potential of the reference resistor Rref in figure 2: Va is the output of in-phase adder UA1. When taking the resistor R1= R2 , R3=R4, the output current of the Va=VREFx+Vb. It can be seen that the dual operational amplifier constant-current source has the following remarkable characteristics: Load earthing The output current is bipolar when the operational amplifier is supplied by a dual power source. The constant current can be achieved by changing the input reference VREF or adjusting the reference resistor Rref0. It is easy to obtain stable small current and compensation calibration. Because of the mismatch of the resistor, the voltage at both ends of the reference resistance Rref0 will be affected by the terminal voltage Vb of its driving load. At the same time, as a constant current source, Vb will definitely change with the load, which will affect the stability of the constant current source. Therefore, the four resistors R1, R2, R3, R4 are chosen according to the principle that the mismatch should be as small as possible, in addition, the mismatch direction of each pair of resistors should be consistent. In practice, a large number of precision resistors of the same batch can be screened, and 4 resistors with close resistance values can be selected. 2. High Voltage Constant Current Source Circuit Diagram(switch power model) The instrument needs a constant current source that can generate 1mA current on 0 to 3 megabytes ohmic resistance. A design composed with 12V storage battery and UC3845 has be made: the transformer uses a color TV high voltage packet, in which L1 enamelled wire is wound 24 turns on the core of the original high voltage package; L3 uses a coil of the original high voltage package and L2 with the high voltage part of the high voltage packet; L3 and LM393 constitute a voltage limiting circuit which limits the output voltage too high and adjusts the open-circuit output voltage by adjusting R10. Fig 11. High Voltage Constant Current Source Circuit Diagram(switch power model) You May Also Like Filtering Circuit Tutorial (Schematic Diagrams) Switch Mode Power Supply Circuit Design Tutorial Selection Guidance of Five Main Materials for Flexible Circuit Board Production Recommendation MC34063A SOP8 LM7805A UC3842AD   FAQ 1. What are the basic elements of electronics?When building electronic circuits, you will work with a number of basic electronic components, including resistors, capacitors, diodes, transistors, inductors and integrated circuits.   2. What is the schematic symbol represented in the electrical and electronic diagram?It is also called a schematic symbol. Each component has typical functionality according to its operational characteristics. An electronic circuit or schematic drawing uses a wired path between electronic components to complete the circuit. These components are represented by respective symbols for it.   3. What are the 5 components of electricity?The Basics of Electrical ComponentsResistors. The very first component that you should know about is the resistor.CapacitorsLight Emitting Diode (LED)TransistorsInductorsIntegrated Circuit (IC)   4. What are the types of electronics?Electronics has branches as follows:Digital electronicsAnalogue electronicsMicroelectronicsCircuit designIntegrated circuitsPower electronicsOptoelectronicsSemiconductor devices   5. What are the different schematic symbols?Schematic Symbols:Wires (Connected)Wires (Not Connected)DC Supply VoltageGroundNo Connection (nc)ResistorCapacitor, Polarized (Electrolytic)Light-Emitting Diode (LED)   6. What are the electrical diagrams?Image result for Electrical DiagramElectrical diagrams are drawings which are used to represent electrical circuits, these circuits are represented by using lines, symbols, and number combinations. Electrical diagrams show the wiring between components and the relative position of the components.   7. What are the three types of electrical diagrams?There are three ways to show electrical circuits. They are wiring, schematic, and pictorial diagrams. The two most commonly used are the wiring diagram and the schematic diagram.    8. What are the four types of electrical diagram?Image result for Electrical DiagramSome of these electrical drawings or diagrams have been described below.Block DiagramSchematics Circuit DiagramSingle Line Diagram or One-line DiagramWiring DiagramPictorial DiagramLadder Diagram or Line DiagramLogic DiagramRiser Diagram   9. What are the 2 main types of electricity?Current electricity is a constant flow of electrons. There are two kinds of current electricity: direct current (DC) and alternating current (AC).   10. What are the 2 types of electric circuit?Types of Electric CircuitsThere are two types of circuits found in homes and other common devices; namely series circuits and parallel circuits.   11. What is electrical block diagram?Block Diagram – A block diagram shows the major components of electrical or mechanical interrelations in block, or square or rectangular, form. The lines between the blocks represent the connections between the systems or components.   12. What are the 4 basic components of a circuit?Every electric circuit, regardless of where it is or how large or small it is, has four basic parts: an energy source (AC or DC), a conductor (wire), an electrical load (device), and at least one controller (switch). Visualize what happens when you switch on a room light.   13. What is type of wiring diagram?Schematic Diagrams often called a ladder diagram, is intended to be the simplest form of an electrical circuit. This diagram shows the circuit components on horizontal lines without regard to their physical location. It is used for troubleshooting because it is easy to understand the operation of the circuit.   14. What is the main purpose of electrical diagram?Electrical drawings, sometimes referred to as wiring diagrams, are a type of technical drawing that provide visual representation describing electrical systems or circuits. They are used to explain the design to electricians or other workers who will use them to help install or repair electrical systems.   15. Which software is used for electrical design?Top 8 Software For Electrical EngineersAutoCAD ElectricalPLC ProgrammingSCADA SoftwareAC/DC Drive SoftwareProteus And PspiceOrCADXilinxKeil

IntroductionCurrent divider equations and voltage divider formulas help you better understand resistor functions in electronic circuits. The current divider circuit is a parallel circuit in which the source current or power supply current divided into a multiple parallel paths. In a parallel circuit, the terminals of all components are connected together, sharing the same two end nodes. This results in the current to flow or pass through different paths and branches. However, the current through each component can have a different value. While a voltage divider circuit is a very common circuit that takes a higher voltage and converts it to a lower one by using a pair of resistors.The main feature of a parallel circuit is that, although the branch circuit currents are different, the voltages of all connection paths are the same. Therefore, there is no need to find the voltage of each resistor, so that the branch current can be easily found by Kirchhoff's current law (KCL) and Ohm's law.Figure 1. Voltage and Current Divider Current CircuitsCatalogIntroductionⅠ Resistive Voltage Divider CircuitⅡ Resistive Current Divider CircuitⅢ Duality (Electrical Circuits)Ⅳ Frequently Asked Questions about Resistor Voltage Divider and Current Divider Rules and FormulasIn this section, through the discussion of the commonly used resistor series voltage divider circuit and resistors in parallel divider circuit to find their rules. This article contains plenty of equations based on Kirchhoff's current law and Ohm's law for you to master voltage divider and current divider circuits.  A Discussion of the Useful Voltage Divider and Current Divider Circuits.Ⅰ Resistive Voltage Divider CircuitIn electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage that is a fraction of its input voltage. It is a simple circuit which turns a large voltage into a smaller one. The basic voltage divider circuit with two resistors in series as shown in the Figure 2. is analyzed, and some useful formulas are obtained:Figure 2. Basic Voltage Divider CircuitThe following equation is given by Kirchoffs Current Law (KCL):The following equation is given by Kirchoffs Voltage Law (KVL):Equation of voltage current relation of circuit elements:Substituting the Ohm's law of the resistance element into the KVL equation, the calculation formula for the current i is obtained:Then substitute it into the Ohm's law of the resistance element, the voltage division formula for calculating the resistance voltage is obtained:Generally speaking, when N resistors are connected in series, the voltage on the Kth resistor can be calculated according to the following voltage division formula:The resistor series voltage divider formula shows the relationship between the voltage of a certain resistor and the total voltage. The voltage division formula expresses that the voltage of a resistor is proportional to its resistance value, that is, when the resistance increases, the voltage also increases.According to the voltage reference direction obtained by the above voltage divider circuit formula, it can be seen that it has nothing to do with the selection of the current reference direction. When the reference direction of the voltage variable uk or us involved in the formula changes, a negative sign will appear in the formula.As shown in the Figure 3, find the voltage Uab when R=0Ω, 4Ω, 12Ω, ...∞.Figure 3. Voltage Reference DirectionThe voltage Uac and Ubc can be obtained by using the resistor series voltage divider formula:Substituting the resistance R into the above formula, after obtaining the voltage Ubc, then using KVL to obtain the voltage Uab, the calculation result is as follows:It can be seen from the calculation results that as the resistance R increases, the voltage Ubc gradually decreases, and the voltage Uab changes from negative to positive, indicating that its actual direction will varies with the change of the resistance R.The Figure 4. below shows the dual-supply DC voltage divider circuit. Try to find the range of potential change at point a when the sliding end of the potentiometer moves.Figure 4. Dual-supply DC Voltage Divider CircuitSolution: Replace the two potentials of +12V and -12V with two voltage sources to obtain the circuit shown in Figure 4. (b).When the sliding end of the potentiometer moves to the bottom end, the potential at point a is the same as that at point c:When the sliding end of the potentiometer moves to the top, the potential at point a is the same as that at point b:When the sliding end of the potentiometer gradually moves from bottom to top, the potential at point a will continuously change between -10V to 10V.Here discusses the change law of load current i and voltage u when an actual supply powers to a variable resistor load. As shown in the Figure 5, RL is a variable resistance load, and R0 represents the internal resistance of the power supply:Figure 5. Variable Resistor LoadLoad current i:Among them, k=RL/R0 represents the ratio of the load resistance to the internal resistance of the power supply, and isc=us/R0 represents the current when the load is short-circuited.Load voltage u:Among them, uoc=us represents the voltage when the load is open.Power absorbed by load resistor:When the coefficient k=RL/R0 takes different values, a series of relative values of current, voltage and power are calculated, as shown in the following table:K=RL/R000.20.40.60.81.02.03.04.05.0∞i/isc10.8330.7140.6250.5550.50.3330.250.20.1670u/uoc00.1670.2860.3750.4440.50.6670.750.80.8331p/pimax00.5560.8160.9380.98810.8890.750.640.5560According to the above data, the curve of voltage, current and power changing with load resistance can be drawn, as shown in the Figure 6:They show:1. When the load resistance gradually increases from zero, the load current gradually changes from the maximum value isc=us/R0 to zero. When the load resistance is equal to the internal resistance of the power supply, the current is equal to half of the maximum value.2. When the load resistance gradually increases from zero, the load voltage gradually increases from zero to the maximum value uoc=us. When the load resistance is equal to the internal resistance of the power supply, the voltage is equal to half of the maximum value.3. When the load resistance is equal to the internal resistance of the power supply, the current is equal to half of the maximum value, the voltage is equal to half of the maximum value, and the power absorbed by the load resistance reaches the maximum value, and pmax=0.25uocisc.The non-linear change law of the current when the load resistance changes can be seen from the resistance scale of an ordinary multimeter. The circuit model of a multimeter electric blocking is a series connection of a voltage source and a resistor. When we use a multimeter to measure unknown resistance, we should first short-circuit the multimeter and adjust the zero potentiometer pointer to 0Ω. At this time, the current is the largest and the meter pointer is fully deflected. When the short-circuit wire is removed, the pointer of the multimeter returns to ∞, and the measured current is zero at this time.When the multimeter is connected to the measured resistor, as the resistance value changes, the current of the meter head will change accordingly, the pointer will be deflected to the corresponding position, and the measured resistance value can be directly read according to the scale on the surface. There is a special case, when the measured resistance value is just equal to the internal resistance of the multimeter, the current is half of the full deflection current, and the pointer stays in the middle position. Conversely, the internal resistance can be known from the reading in the middle of the multimeter’s electrical barrier scale. For example, the reading of a 500-type multimeter when the pointer stays in the middle position is 10, the internal resistance when using a ×1k electrical barrier is 10kΩ, and the internal resistance is 1kΩ when using a ×100 electrical barrier. If necessary, use Voltage Divider Calculator to calculate the output voltage of a resistor divider circuit for a given set of resistor values and source voltage. Ⅱ Resistive Current Divider CircuitA current divider is defined as a linear circuit that produces an output current that is a fraction of its input current. The following formula describing a current divider is similar in form to that for the voltage divider. The Figure 7. shows a circuit in which a current source supplies power to two parallel resistors, and some useful formulas are drawn from its analysis. Figure 7. Resistive Current Divider CircuitThe following equation is given by Kirchoffs Voltage Law (KVL):The following equation is given by Kirchoffs Current Law (KCL):Equation of current voltage relation of circuit elements:Substituting the Ohm's law of the resistance element into the KCL equation, the calculation formula for the voltage u is obtained:Then substitute Ohm's law into the resistive current divider equation for calculating the resistor current:The resistive current divider formula of two parallel resistors expressed by resistance parameters is:Generally speaking, when n resistors are connected in parallel, the current on the Kth resistor can be calculated according to the following formula:The resistive current divider in parallel formula indicates the relationship between the current of a resistor and the total current. It shows that the resistance current is proportional to its conductance value. For example, the current will increases when the conductance increases.According to the current reference direction obtained by the above formula, it can be seen that it has nothing to do with the selection of the voltage reference direction. When the reference direction of the current is or ik changes, a negative sign will appear in the formula.Figure 8. Resistive Divider CircuitAccording to the characteristics of two resistors in parallel, the current in the 3Ω and 6Ω resistors is obtained:Then, the current in the 12Ω and 6Ω resistors is obtained:Calculate the current i5 in the short-circuit line according to the KCL equation of node a:i5 can also be calculated according to the KCL equation of node b:It should be noted that the current i5=1A in the short circuit is different from the total current.  If necessary, the Current Divider Calculator can be used to determine the current going through any branch in a parallel circuit. Enter a current source and resistance values to calculate the current through each resistor. The calculator will display the current through each resistor entered. Ⅲ Duality (Electrical Circuits)According to the above-mentioned analysis of the resistive voltage divider circuit and current divider circuit, there is a certain similarity between them.Figure 9. Duality Circuit ExamplesThe equations of the resistor divider circuit are listed as follows:It can be seen that the equations of these two circuits have a dual relationship. If the current i in the KCL equation of a certain circuit is replaced with the voltage u, the KVL equation of another circuit is obtained; the voltage u in the KVL equation of a certain circuit is replaced with the current i, and the KCL equation of another circuit is obtained. This similar relationship in circuit structure is called topological duality. Similarly, replace u in the VCR equation of a certain circuit with i, i with u, R with G, G with R, etc., you can get the VCR equation of another circuit. This similar relationship of the element VCR equation is called element duality. If two circuits are both topological duality and component duality, they are called dual circuits.The circuit equations of the dual circuit are dual, and the various formulas and results derived therefrom are also dual. For example, the dual formula derived for the dual circuit of Figure 9 (a) and (b) is as follows:This section is a simple analysis of dual circuits, dual formulas, dual theorems and dual analysis methods in order to better grasp the basic concepts of circuit theory and various analysis methods. Here are a few test questions that can be used to test how well you learn about voltage divider and current divider circuits:1) Find the voltages u1 and u2 in the circuit shown in the following figure:2) Find the current i1 and i2 in the circuit shown in the following figure:3) Find the current i2, is and voltage u in the circuit shown in the following figure: Ⅳ Frequently Asked Questions about Resistor Voltage Divider and Current Divider Rules and Formulas1. What is VDR and CDR?The Voltage Divider Rule formula (VDR) shows how the voltage distributes among different resistors in a series circuit. Similarly, the Current Divider Rule formula (CDR) shows how current distributes in a parallel circuit. 2. What is the current divider rule with examples?When two resistors are connected in a parallel circuit, the current in any branches will be a fraction of the total current (IT)). If both the resistors are of equal value, then the current will divide equally through both the branches. 3. Why does a voltage divider need two resistors?One resistor can be used to drop voltage (if the load draws current) but to divide voltage you need something to create a division ratio. To be a voltage divider the output voltage needs to be a constant proportion of the input voltage. ... Note that this need for two resistors only applies to DC. 4. Where are current divider used?By using a current divider, the current flowing through a component can be minimized and thus smaller component size can be used. For example, in a case where larger resistor wattage is required; adding multiple resistors in parallel decreases the heat dissipation, and smaller wattage resistors can do the same job. 5. What is voltage divider formula?A voltage divider is applying a voltage across a series of two resistors. We may draw in a few different ways, but they should always essentially be the same circuit. Thus formula is given as follows: V_{out} = \frac{R_b}{R_a+R_b} \times V_{in}

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

CatalogIntroductionⅠ What is an AC Capacitor? 1.1 AC Capacitor Circuit1.2 What does the AC Capacitor do？Ⅱ Why do AC Capacitors Fail?2.1 Signs of a bad AC Capacitor2.2 Reasons for AC Capacitor Problems2.3 Effects of a bad AC CapacitorⅢ How to test an AC CapacitorⅣ Difference Between AC & DC CapacitorsⅤ AC Capacitor Replacement CostⅥ How to Choose a AC Capacitor ReplacementⅦ How to Replace an AC CapacitorⅧ Frequently Asked Questions about AC Capacitor1. What Happens When an AC Capacitor Fails? 2. What to do When the Capacitor Breaks Down?3. How long does AC Capacitor last?4. Can I replace my AC capacitor myself ?5. How to maximize the life of AC capacitor ?6. Will My AC Unit Still Work with a Bad AC Capacitor?7. What is the difference between a start capacitor and a run capacitor?IntroductionThe cost of your AC capacitor will be determined by the cost of the unit plus the labor necessary for installation. When it's time to begin a new cycle of cold air, your ac capacitor stores energy to provide a boost to the unit. If the capacitor fails, your system may fail when it is most needed (which is always, of course). Don't worry, this is a straightforward and inexpensive fix. This essay will educate you on AC.How to Test Motor Start and Motor Run AC Capacitor of ac fan and compressorⅠ What is an AC Capacitor? An AC capacitor is a small electrical component that stores energy and provides a power surge. In this situation, the capacitor stores energy until your thermostat sends a signal indicating that your air conditioner must be turned on.At this point, the capacitor releases a burst of energy to supply a beginning current to your AC unit's compressor.This is necessary since the ordinary power supplied to your AC is insufficient to start the motor on its own. This rapid boost is required for the motor to start. Once the engine has started, the power from your house will suffice to keep it running.The AC capacitor itself resembles a battery, with two or three wires protruding from the end. Some colored bands around the body of the capacitor will also be utilized to identify how much power it is rated for.1.1 AC Capacitor CircuitThe capacitor in the purely capacitive circuit above is linked directly across the AC supply voltage. As the supply voltage rises and falls, the capacitor charges and discharges in proportion. We know that the charging current is proportional to the rate of change of the voltage across the plates, with the rate of change being largest when the supply voltage crosses over from its positive half cycle to its negative half cycle, or vice versa, at points 0o and 180o along with the sine wave.As a result, when the AC sine wave crosses over at its maximum positive peak ( +VMAX ) and its minimum negative peak ( -VMAX ), the voltage rate of change is the slowest. The sinusoidal voltage is constant at these two points in the cycle, hence its rate of change is 0, so DV/DT is zero, resulting in zero current change within the capacitor. When DV/DT = 0, the capacitor serves as an open circuit, therefore I = 0, as illustrated below.1.2 What does the AC Capacitor do？A capacitor in a central air conditioning system is intended to provide a power increase at the start of each system cycle. This is required to get the air conditioner's fan to run at maximum speed. When the fan motor reaches its maximum speed, the capacitor stops working until the system is restarted.Ⅱ Why do AC Capacitors Fail?Capacitors are a component of your air conditioner or heat pump system; they will eventually wear out and need to be replaced. Overheating is the most prevalent cause of air conditioner capacitor failure. On visual inspection, the ac capacitor will be enlarged and may even rupture due to the pressure caused by overheating. This is a dead giveaway that your capacitor is faulty.Here are a few reasons why an ac capacitor can overheat.Extended or abnormal run-time: a heatwave or an inadequately charged refrigerant level in your air conditioner.Compressor Age: Just like people, compressors take more energy to start up as they age. This can overwork a capacitor and signal the impending failure of a compressor.Lightning or Power Surge: Power grid spikes or fluctuations, which are frequently caused by lightning strikes, can wreak havoc on a capacitor.Capacitor Age: The quality of capacitors manufactured nowadays is simply not what it once was. A capacitor's average life expectancy is only 8-12 years.2.1 Signs of a bad AC CapacitorWhen an AC capacitor needs to be replaced, you'll notice a variety of symptoms, including:Your air conditioner is taking too long to start chilling.Your air conditioner shuts down on its own.Your air conditioner does not operate at all.Your air conditioner makes a noise but does not provide chilly air.Your air conditioner is making a buzzing or humming sound.You smell a burning odor or see smoke coming from your unit.Your utility bills are inexplicably high.An AC unit's capacitor might fail due to age and regular wear and tear, an overheated system, an unknown short circuit, lightning strikes or power surges, or excessively hot temperatures.2.2 Reasons for AC Capacitor ProblemsThere are numerous causes for an air conditioner's capacitor to fail. While only a professional heating and cooling specialist can establish the exact cause of capacitor breakdown in your specific air conditioning machine, the following are some of the most typical reasons that this part fails:Physical damage to the capacitor, such as when a piece of debris strikes the unit.Inadequate voltage or current flowing through the capacitor.The unit has overheated.Wear and tear caused by aging.2.3 Effects of a bad AC CapacitorThe rising warmth inside your home is the first clue that your capacitor is no longer functioning properly. Other consequences may not be as obvious, but they can be harmful to your cooling system.A faulty capacitor prevents the outside unit from performing its function, preventing the cooling process from taking place. Incorrect voltage might easily damage other sections of the machine.Second, in an attempt to compensate for the failing capacitor, other components will begin to overwork. An rise in energy use may result in an unexpected increase in your monthly energy bill.Ⅲ How to test an AC CapacitorAs previously stated, the capacitor inside your heating and cooling system can be quite deadly if mistreated. As a result, it's advised to contact a local HVAC repair professional to test or replace your capacitor.When the technician arrives, they will use a multimeter to calculate the capacitor's current, resistance, and voltage. In layman's words, they'll check to see if the capacitor is keeping the charge required to start and finish the cooling system. If the readings are faint or do not register at all, it is time to replace the AC capacitor.Testing a capacitor is not suggested, even if you have a multimeter. While dozens of YouTube videos may make the procedure appear simple, it's advisable to avoid the DIY route and hire a professional. Capacitor testing is only possible after the power has been turned off, the wiring has been disconnected, and the voltage remaining in the capacitor has been drained.It's a perilous task, and even after watching the most detailed how-to video, it's not safe to attempt. Use a professional.Ⅳ Difference Between AC & DC CapacitorsA capacitor is an electronic device made up of two plates of electrically conducting material separated by a non-conductive layer, known as an insulator. It is utilized in A/C (alternating current) and D/C (direct current) electrical applications and circuits to accomplish certain effects based on the capacitor's ability to store and discharge current.Capacitors in DC CircuitsElectrolytic capacitors on circuit boardA capacitor's two plates, which are electrically insulated from each other, store energy in the form of capacitance. When DC is applied to a circuit consisting merely of resistance and capacitance, the capacitor charges to the applied voltage level. Because DC only flows in one direction, there is no more current flow once the capacitor is fully charged. This property enables capacitors to "block" DC flow.Capacitors in AC CircuitsIn alternating current circuits, the alternating current alternately charges the capacitor in one direction and then the other. As the plates discharge during the direction shift, the capacitor output current alternates in phase with the alternating current voltage. This is how capacitors are said to "pass" alternating current.Ⅴ AC Capacitor Replacement CostAccording to Home Advisor, the cost of replacing an AC capacitor ranges between $120 and $250, with the majority of fixes falling within the $170 range.HVAC capacitor brand, model, and voltage are all factors that will influence the repair cost. The component itself typically costs between $9 to $45, while top-rated brand-name parts may be more expensive.Labor and installation will consume the majority of your budget. Professional capacitor replacement often costs between $60 and $200. (By comparison, the average EMERGENCY ROOM VISIT costs $774, reinforcing our recommendation to hire a professional.) A technician should be able to do the job in approximately an hour.Without an AC capacitor, your HVAC system would not function properly. This small but powerful component is responsible for keeping your home cool when summer temperatures climb. Schedule your seasonal HVAC maintenance with a skilled technician to guarantee that your capacitor and unit as a whole work optimally.Ⅵ How to Choose a AC Capacitor Replacement You must choose the correct replacement if you are replacing your AC capacitor yourself. When it comes to ac capacitor replacement, the size and shape aren't important, but you will want to know two things: the voltage rating and the microfarads (F).The voltage rating does not have to be the same as your present capacitor, but the microfarad must be the same. The voltage and microfarad are marked on your capacitor and may look like "35/5 F and 370V." When you go to your local home goods store, make a note of this, as well as the brand and model of your air conditioning system.Finally, because capacitors are universal parts, form, size, brand, and other basic criteria are unimportant — just make sure to acquire the correct voltage and microfarad and you'll be fine.Ⅶ How to Replace an AC CapacitorAn AC Capacitor replacement can be purchased at a hardware store. Then it's time to put everything together:Step 1Turn off the power to your air conditioner at the breaker panel.Step 2To access the capacitor, unscrew the side panel of the condenser unit.Step 3Locate the capacitor and turn off the power.Step 4Remove the old capacitor and take note of how the wires are connected.Step 5Carefully unplug the wires from the three capacitor connectors labeled HERM, FAN, and C. Note or photograph which colored wires link to which connector for future reference.Step 6 Install the replacement capacitor according to the instructions.Step 7Replace the side panel on the condenser unit.Ⅷ Frequently Asked Questions about AC Capacitor1. What Happens When an AC Capacitor Fails? When an air conditioner capacitor fails repeatedly, the compressor motor in your system is unable to start. Your system may appear to be running, but the motor will never start, and you will not receive the chilly airflow you expect. In reality, while the motor tries and fails to start, you may hear a ticking or clicking sound.2. What to do When the Capacitor Breaks Down?When the air conditioner's capacitor fails, an AC capacitor repair is required. An expert AC service technician can determine whether the capacitor can be fixed or if it must be replaced. Our air conditioning repair technicians have new capacitors in the service vehicles they drive on all service runs, so you won't have to wait for this service if your capacitor needs to be replaced.3. How long does AC Capacitor last?The lifespan of HVAC capacitors varies slightly depending on the manufacturer and model. An AC capacitor has a 10-year average lifespan. SCHEDULE ROUTINE SEASONAL MAINTENANCE ON YOUR HEATING AND COOLING SYSTEM TO ENSURE YOU GET THE MOST OUT OF YOUR UNIT.Annual maintenance on your HVAC system will allow a professional to detect any potential problems with the capacitor. Solving the problem before the part fails will save you the trouble of locating an emergency HVAC contractor and will keep you from experiencing unpleasant INDOOR TEMPERATURES in the heat of summer.4. Can I replace my AC capacitor myself ?You can't do it. An expert HVAC professional should be able to correctly remove your faulty capacitor and replace it with a new one, restoring your AC to normal operation.5. How to maximize the life of AC capacitor ?Avoid inconsistent voltage rating and exposing outdoor components to intense temperatures to extend the life of your ac capacitor. Regular checkups will also help to ensure the longevity of your equipment.6. Will My AC Unit Still Work with a Bad AC Capacitor?While your air conditioner will continue to operate, it will struggle to function properly. The system will eventually cease to function. Internal harm might be exacerbated by prolonged use.We recommend hiring a professional to do the repairs so that your air conditioner is not damaged.7. What is the difference between a start capacitor and a run capacitor?A start capacitor, in essence, assists in starting the motor by providing a voltage boost at startup. A run capacitor keeps a motor going by producing a phase shift in the stators, allowing the rotor to "grab" and turn the next stator. When a run capacitor fails, this phase change does not occur, causing the motor to work harder, overheating and destroying the bearings.