diagram Related Articles

Introduction Latching relay is a new type of relay and also an automatic switch. Like other electromagnetic relays, it turns on and off the circuit automatically. The difference is that the normally closed or normally open state of it is completely dependent on the action of permanent magnets, and the switching state of it is triggered by a pulse electric signal of a certain width. It has the characteristics of power saving, stable performance, small size, large carrying capacity, and superior performance than general relays. Latching Relay Basics in 2 Minutes Catalog Introduction Ⅰ Working Principle 1.1 Action Principle 1.2 Action Process Ⅱ Main Functions and Advantages 2.1 Average View 2.2 Function Lists 2.3 Application Area Lists 2.4 Latching Relay Advantages Ⅲ Tech Parameters Ⅳ Latching Relay Test 4.1 Measuring Contact Resistance 4.2 Measuring Coil Resistance 4.3 Set Voltage and Current 4.4 Reset Voltage and Current Ⅴ Relay Selection 5.1 The Necessary Conditions 5.2 Relevant Information Search 5.3 Installation Layout Consideration Ⅵ FAQ Ⅰ Working Principle 1.1 Action Principle The on and off state of the latching relay is usually held by the magnetic force generated by the permanent magnet. When the contacts of the relay need to be opened or closed, only the positive (reverse) DC pulse voltage is needed to excite the coil, and the relay completes the state transition between opening and closing in an instant. Usually when the contact is in the holding state, the coil does not need to continue to be energized, and the state of the relay can be maintained unchanged only by the permanent magnet force.   1.2 Action Process When the contacts of the relay need to be set, it is only necessary to excite the coil J2 with a positive DC pulse voltage. The magnetic poles generated by the coil J2 after excitation interact with the magnetic poles of the permanent magnet. As we all known, the same polarities repel each other, but the opposite polarities attract each other. The state transition from reset to set is completed in an instant. The following schematic diagrams demonstrates the specific state transition process. The process of the latching relay changing from the set state to the reset state, which are the same. Figure 1. Reset Latching Relay Figure 2. Constant-Current Pulse Monment Figure 3. Constant-Current Pulse Monment Figure 4. Latching Relay Reset   Ⅱ Main Functions and Advantages 2.1 Average View Latching relay is an automatic switching element with isolation function. It is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment. It is one of the most important control elements in electricity.Magnetic latching relays generally have an induction mechanism (input part) that can reflect certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.). It has the ability to turn on/off the controlled circuit. In addition, between the input part and output part of the relay, there is an intermediate mechanism (drive part) for coupling and isolating the input, functional processing and driving the output part. 2.2 Function Lists The latching relay has the following functions:1) ExpansionFor example, when the control signal of a multi-contact relay reaches a certain value, multiple circuits can be switched, disconnected, and connected at the same time according to different forms of contact groups.2) AmplificationFor example, magnetic latching relays can control a large-power circuit with a very small control quantity.3) IntegrationFor example, when a plurality of control signals are input to a multi-winding relay in a prescribed form, they will be compared and integrated to achieve a predetermined control effect.4) Automation, remote control and monitoringFor example, on the automatic device and other electrical appliances, magnetic latching relays can form a program control circuit to realize automatic operation. 2.3 Application Area Lists 1) Smart meters: IC card meters, prepaid meters, single-phase meters, three-phase meters.2) Reactive power compensation: synchronous switch, composite switch, smart capacitor.3) Intelligent control: smart home, solar street light control, automation equipment, etc. 2.4 Latching Relay Advantages 1) They only need pulse excitation, and can work with single and double coils.2) Small size, easy installation.3) Low power consumption and strong load capacity.4) Safe and reliable, long service life. Figure 5. General Relay Structure Ⅲ Tech Parameters 1) Rated VoltageIt refers to the voltage required by the coil when the relay is working normally. Depending on the model of the relay, it can be AC voltage or DC voltage.2) DC ResistanceIt refers to the DC resistance of the relay coil, which can be measured by a multimeter.3) Pull-in CurrentIt refers to the minimum current that the relay can produce the pull-in action. In normal use, the given current must be slightly larger than the pull-in current, so that the relay can work stably. As for the working voltage applied to the coil, generally do not exceed 1.5 times the rated working voltage, otherwise it will generate a larger current and burn the coil.4) Release CurrentIt refers to the maximum current that the relay generates to release the action. When the current in the pull-in state of the relay is reduced to a certain level, it will return to the unpowered release state. The current at this time is much smaller than the pull-in current.5) Switch Voltage and CurrentThis refers to the voltage and current that the relay allows to load. It determines the magnitude of the voltage and current that the relay can control, and you cannot be exceeded this value during use, otherwise it is easy to damage the contacts of the relay.6) Coil Resistance RThe resistance produced by winding a T circle with an enameled wire with a diameter of Φ: R=￡*(T/Φ).7) TemperatureThe higher the temperature, the greater the resistance, and the lower the resistance, the smaller the resistance. Generally speaking, the coil resistance refers to the coil resistance at 20°C. When the temperature is higher or lower than 20℃, there is a calculation formula: Rt=R20[1+(T℃-20℃)×0.004].8) Contact Resistance CRIt is the resistance between the contacts of the relay. And it is the sum of the shrinkage resistance Re and the surface film resistance Rf: Rk=Re+Rf.Note:🔺The factors that form shrinkage resistance Re:♦️The size of the contact pressure determines the size of the shrink resistance. The relationship between the two is inversely proportional, the greater the contact pressure, the smaller the shrinkage resistance.🔺The factors that form the surface film resistance Rf:♦️Dust in the air.♦️Harmful gases in the air: H2S, SO2, etc.♦️Organic vapor in the air: plastic, glue and rosin.♦️Oil stains on the contact surface during the production process.9) Pull-in VoltageThe minimum voltage required to close the relay contacts.10) Release voltageThe minimum voltage required to open the relay contacts.11) Insulation ResistanceThe resistance value that appears when measured with a specified DC voltage between conductive parts that are insulated from each other.12) Medium Withstand VoltageAlso known as dielectric degree, it refers to the maximum voltage that can withstand between two conductive parts without breakdown.13) Reversing RetentionThe minimum force applied on the armature assembly handle to open or close the contacts.14) Contact PressureThe interaction force generated between the moving and static contacts is equal to the contact pressure equal to the reaction force generated by the over-travel of the reed head. Figure 6. Latching Relay Product Ⅳ Latching Relay Test 4.1 Measuring Contact Resistance Use the resistance profile of the universal meter to measure the resistance of the normally closed contact and the moving point, which should be 0. The contact resistance can be measured in a more accurate way within 100 milliohms, while the resistances of the normally-open contact and the moving point should infinite. From this, it can be distinguished which is a normally-closed contact or a normally-open contact.   4.2 Measuring Coil Resistance The resistance value of the relay coil can be measured with the universal meter R×10Ω, so as to judge whether there is an open circuit phenomenon in the coil.   4.3 Set Voltage and Current Get an adjustable regulated power supply and an ammeter, input the set voltage to the relay, and insert an ammeter in the power supply loop for monitoring. Slowly increase the power supply voltage, and when you hear the sound of the relay picking up, write down the set voltage and set current. In order to be accurate, you can try several times. Pay attention to, the setting current should be the average value, and the setting voltage should be the maximum value.   4.4 Reset Voltage and Current Repeat the above operation. But there is a little difference that the reset current is the average value, and the reset voltage is the maximum value.   Ⅴ Relay Selection 5.1 The Necessary Conditions ① The power supply voltage of the control circuit, the maximum current that can be provided.② The voltage and current in the controlled circuit.③ How many sets and types of contacts are needed for the controlled circuit. When selecting a relay, the power supply voltage of the general control circuit can be used as the basis for selection. The control circuit should be able to provide enough working current to the relay, otherwise the relay will be unstable when it is closed.   5.2 Relevant Information Search After consulting the relevant information to determine the conditions of use, you can search for the relevant information to find out the model and specification number of the required relay. If you already have a relay on hand, you can check whether it can be used based on the data. Finally, consider whether the size is appropriate.   5.3 Installation Layout Consideration If it is used for general electrical appliances, in addition to considering the volume of the case, it is necessary to consider the installation layout of the circuit board. For small electrical appliances, such as toys and remote control devices, ultra-small relay products should be used.   Ⅵ FAQ 1. What is magnetic latching?The design of a Magnetic Latching Relay is such that when a short pulse of electrical energy is applied to the solenoid coil, sufficient magnetic force is generated to over-come the force of the relay' return mechanism. 2. How does a latching relay work?One latching type has two opposing coils with an over-center spring or permanent magnet hold the contacts in position after the coil is de-energized. A pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. 3. Where is latching relay used?This type of relay is most suitable in applications like ON/OFF devices from multiple places with push-button or momentary switch. For example, it is used in a lighting circuit or conveyer to control from different locations. 4. What is a magnetic latching relay used for?A magnetic latching relay is a device in which the solenoid principle is applied to open and close light-current electrical circuits. The same device applied in heavy-current circuits is called a contactor, or circuit breaker. 5. How does a latching relay reset?Resetting is very simple. The coil circuit needs to be opened and shortened to the coils ground potential. The capacitor will be discharged through the coil and drives a current pulse with opposite polarity through the coil.

Introduction Potentiometer is a common instrument that uses compensation principle and comparison method to accurately measure DC potential difference or power supply electromotive force. It has high accuracy, convenient use, and stable and reliable measurement results. But even so, when we do potentiometer experiments, we still have to deal with different error problems. The content of this article tells you how to avoid too many errors without getting too large deviations in the experimental results. Potentiometer Experiment (Compare EMF of Two Cells) Catalog Introduction Ⅰ Potentiometer Principle Analyses 1.1 Compensation Principle 1.2 Operational Principle Ⅱ UJ25 DC Potentiometer Overview Ⅲ UJ25 DC Potentiometer Application 3.1 Working Current Adjustment 3.2 Experimental Content 3.3 Laboratory Apparatus Ⅳ Discussion of Experimental Results Ⅴ FAQ Ⅰ Potentiometer Principle Analyses If you want to firmly acquire the use of the basic potentiometer, you must first understand its compensation principle and operational principle. 1.1 Compensation Principle The electromotive force (EMF) of the power supply is theoretically equal to the voltage of the two poles when there is no net current flowing inside the power supply. If you directly use a voltmeter to measure it, the result is actually the terminal voltage not the EMF. Because the power supply has internal resistance r0, if the voltmeter is directly connected in parallel to the two ends of the power supply, there must be a current I through the inside of it, and also there is inevitably a potential drop Ir0 inside. So the indicated value of the voltmeter is only the terminal voltage of the power supply (U=E-Ir0) size. Obviously, in order to be able to accurately measure the EMF of the power supply, the current I must be zero. At this time, the terminal voltage U of the power supply is equal to its electromotive force E. Figure 1. Closed Loop As shown in the figure on the right, connect the electromotive force as Es, Ex and galvanometer G to form a closed circuit. When Es<Ex, the current direction is as shown in the figure, and the pointer of the galvanometer is biased to one side. When Es>Ex, the direction of current is opposite to the direction shown in the figure, and the pointer of the galvanometer is biased to the other side. Only when Es=Ex, there is no current in the loop. At this time, i=0, and the pointer of the galvanometer is not deflected. We call these two electromotive forces in a compensation state. Conversely, if i=0, then Es=Ex, this method is called zero-show method. 1.2 Operational Principle As shown in the figure, the compensation principle shows that Ex can be determined by measuring Vab. The next step is how to accurately measure Vab. Here, the comparative measurement method is used. Connect Ex to the tap of Rab. When the tap is slid to position Rab, no current flows in G, then Ex=I*Rab, where current I is the main circuit current. Then connect a standard battery EN with known EMF in the circuit, when the tap slides to the position Rcd, G is 0 again, then EN=I*Rcd, where This method is to obtain the ratio relationship between the voltage to be measured and the EMF of the standard battery through the comparison of resistance. Because R is a precision resistance, Rab/Rcd can be read accurately, EN is a standard battery with high-accuracy EMF. Therefore, as long as the auxiliary power supply E is stable and the galvanometer G has sufficient sensitivity during the measurement process, Ex can have a very high measurement accuracy. The voltage measuring instrument made according to the above principle is called a potentiometer. Figure 2. Auxiliary Circuit It should be pointed out that the condition for the establishment of  is that the working current of the auxiliary circuit in the two compensations must be equal. In fact, in order to facilitate the reading, I=EN/Rcd should be standardized, so that the corresponding resistance value can be directly read out abV, which is Ex.Actually, there is no sliding rheostat in the instrument provided to us in the experiment, only 2 resistance boxes. This experiment requires us to use a rheostat box to replace the sliding rheostat. Therefore, we will use a resistor box R1 instead of the compensation method to measure the sliding rheostat RP, the other resistor box R2 acts as Rab. Since the resistance of them can be read directly, we can easily keep the current through the auxiliary circuit unchanged, that is, keeping R1+R2 constant.   Ⅱ UJ25 DC Potentiometer Overview UJ25 DC Potentiometer is a kind of high potential device, the upper limit of measurement is 1.911110V, the accuracy is 0.01 grade, and the working current I=0.1mA. Its principle is shown in the figure, the bottom of the right figure is its panel, and the functions of the upper 12 binding posts have been indicated on the panel. The Rab in the figure is two step resistance knobs, marked with the value of the standard battery EMF at different temperatures for correction when adjusting the working current. RP is used to adjust the working current I. Rcd is the six large knobs marked with voltage values, used to measure the unknown voltage value at the lower left corner of the function switch. When it is off, the potentiometer does not work; when it is at N, it can be connected to check and adjust the working current. When it is at X1 or X2, it can measure the unknown voltage of the first channel and obtain the second channel. The three buttons marked G0, G1, and short circuit are the control switches for rapid current detection. By being in the off state and pressing G0, the galvanometer is on in the circuit, but a large resistor R is connected in series to compensate for the principle. At the same time, protect the galvanometer; press G1 down, the galvanometer is directly connected to the circuit, so that the potentiometer is in a high-sensitivity working state. When the damping switch turns on, the galvanometer coil is short-circuited, and the coil does not swing due to the large electromagnetic damping. Figure 3. UJ25 DC Potentiometer Circuit   Ⅲ UJ25 DC Potentiometer Application 3.1 Working Current Adjustment Turn the function switch to N, turn the temperature compensation resistor Rab to the last two digits of the corrected standard battery EMF "1.018V", press the "G0" and "G1" respectively, and adjust RP to zero for the galvanometer.Measure the voltage to be measured.Switch the function switch to X1 or X2, press the "G0" and "G1" buttons respectively, and adjust Rcd to the galvanometer zero, finally the displayed value is the voltage to be measured. 3.2 Experimental Content 🔺Assemble Potentiometer(1) Design and connect the potentiometer circuit, the following is the standard battery temperature correction formula: (2) Standardize the working current, and measure the electromotive force of the dry battery.(3) Measure the sensitivity of potentiometer. 🔺UJ25 DC PotentiometerUse UJ25 box-type potentiometer to measure dry cell electromotive force. 3.3 Laboratory Apparatus ZX-21 resistance box (two), pointer galvanometer, standard battery, regulated power supply, dry battery to be tested, double pole double throw switch, UJ25 box type potentiometer.Data Processing and Error Quantitative Analysis.🔺Raw DataStandard battery electromotive force: E20=1.01186V, UJ25 measurement Ex=1.469285V, accuracy level 0.01Ambient temperature: T1=20.5℃, T2=21.5℃ EN R1=1018.6Ω R2=1983.8Ω EX R'1=1469.8Ω R'2=1532.6Ω Sensitivity Measurement/14div R''1=1484.1Ω R''2=1518.3Ω 🔺Potentiometer Measurement ResultsStandard Electricity Correction Value where ，get EN=1.01857VPosition battery EMF calculation 🔺Error and Uncertainty Analysis(1) Instrument Error get Similarly Knowing that R1, R2, R'1, R'2 are independent of each other, then the data in (1) can be obtained: (2) Sensitivity ErrorSensitivity  (3) Effects of the Temperature Change Assuming the temperature is constant, then Because of , therefore, this part of the error and its uncertainty can be ignored.(4) EN Stability Because of therefore, this part of the error and its uncertainty can be ignored.(5) Error Analysis and Synthesis of UncertaintyFrom the calculation of (3) and (4), it can be seen that the combination of uncertainty can omit the error of EN indication, and omit the error caused by the change of the auxiliary power supply and the standard battery EN during the two zero indications. Also the sensitivity error of the circuit during the two times of zero display, and because the readings of multiple measurements are almost unchanged. So only one measurement result is recorded and used, and we do not consider the impact of EN error on the measurement of Ex.Compared with the uncertainty of (2) obtained by (1), the uncertainty of (2) is about one-tenth of the uncertainty of (3), but considering that the uncertainty of (3) is of the order of 10^(-3), it can ignore the magnitude of 10^(-4). In the end , get the final result of the measurement.   Ⅳ Discussion of Experimental Results The use of UJ25 potentiometer can more accurately measure the electromotive force of the unknown power source, so as to further analyze the measurement results of the self-assembled potentiometer.Knowing that the measurement result of UJ25 potentiometer is EX=1.469258, and calculate the sensitivity error of the instrument: Because the readings of multiple measurements are consistent, it is ignored.That is, the actual measurement result of UJ25 potentiometer is .The measurement result is .That is, the relative error is .The operation of this experiment is relatively simple, but the data processing is slightly complicated, especially the calculation of uncertainty. Because of its many sources, it is impossible to analyze the errors one by one, so the smaller influencing factors are ignored to simplify the calculation. In this process, we understand that the principle of compensation to eliminate the internal resistance of the electric meter and the battery will be of great help to subsequent experiments.   Ⅴ FAQ 1. What is a potentiometer in a circuit?A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. ... Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. 2. What is the purpose of the potentiometer?A potentiometer is a type of position sensor. They are used to measure displacement in any direction. Linear potentiometers linearly measure displacement and rotary potentiometers measure rotational displacement. 3. How does a potentiometer affect a circuit?The potentiometer is a three-wire resistive device that acts as a voltage divider producing a continuously variable voltage output signal which is proportional to the physical position of the wiper along the track. 4. What happens when you turn potentiometer?It will behave like a normal resistor. When the circuit is connected to a center lead, and an outside lead, the potentiometer will behave like a variable resistor - turning the post of the potentiometer will increase (clockwise), or decrease (counter-clockwise) the resistance of the potentiometer. 5. How does a potentiometer change resistance?As you turn the knob of a potentiometer, the change in the resistance can be either linear or logarithmic. The way the resistance changes is called the taper. With a linear taper potentiometer, turning a knob a certain amount will change the resistance by a set amount, no matter the position of the knob. 6. How much voltage can a potentiometer handle?The easiest way to think about it is that there is a maximum current through the pot. If you have a 1W 100 ohm potentiometer, the max. current is 100mA (full voltage = 10V); if you are using only 27 ohms of the potentiometer then the max. 7. How does current flow in a potentiometer?Assume V to be the voltage produced by the cell in the primary circuit across the length of the potentiometer wire, and E to be that produced by the cell of the secondary circuit. 8. What is the formula for potentiometer?It is calculated as V/L, where V is the potential difference between two points and L is the distance between two points. Also K = (IρL/A)/L = Iρ/A. 9. How is potentiometer power calculated?Imax = √(P/R) where Imax is the maximum amount of current that can pass safely through any part of the pot, P is the specified power rating of the pot, and R is the specified resistance of the pot. For example, a 10,000-ohm, 1-watt potentiometer can safely pass √[1/(1 x 104)] amperes, or 10 milliamperes. 10. How do you calculate the output voltage of a potentiometer?Measure the total battery voltage, and then measure the voltage between the same two points on the potentiometer (wiper and negative side). Divide the potentiometer's measured output voltage by the measured total voltage. 11. What is the working principle of potentiometer?The principle of a potentiometer is that the potential dropped across a segment of a wire of uniform cross-section carrying a constant current is directly proportional to its length. The potentiometer is a simple device used to measure the electrical potentials (or compare the e.m.f of a cell). 12. What is potentiometer calculate the internal resistance of a cell?To calculate internal resistance, we use a potentiometer to first calculate the voltage across the battery, with no current through it. Then we attach a resistor in parallel to the battery and recalculate the voltage across it. ... Using the battery equation, we calculate the internal resistance. 13. What are the two uses of potentiometer?The applications (uses) of the potentiometer:Voltage divider: The potentiometer can be used as a voltage divider to change the output voltage of a voltage supply.Audio control: Sliding potentiometers are commonly used in modem low-power audio systems as audio control devices. 14. How do you calculate the emf of a cell using a potentiometer?Using a potentiometer, we can determine the emf of a cell by obtaining the balancing length l. Here, the fall of potential along the length l of the potentiometer wire is equal to the emf of the cell, as no current is being drawn from the cell. 15. How can potentiometer be used to calculate potential difference?A Potentiometer can be to measure e.m.f of a cell which cannot be measured by a voltmeter. When a voltmeter is connected in a circuit it draws current through the circuit and thus can measure the potential difference across the cell terminals. ... Thus it measures the e.m.f. of the cell. 16. What is the principle of potentiometer support with equation?The basic potentiometer working principle is based on the fact that the potential across any piece of the wire is directly proportional to the length of the wire, which has a uniform cross-sectional area and the constant current flowing through it. 17. What is potentiometer write its principle and construction?The potentiometer is a device used to compare the e.m.f of two cells. It works on the principle that when a constant current flows through a wire of uniform cross-sectional area, a potential difference between its two points, is directly proportional to the length of the wire between the two points.

Introduction Can a step-down transformer be used as a step-up transformer? This involves not only the principle of the transformer, but also the specific components and their functions in circuit. In terms of working principle, the transformer can step down and step up. Does this mean they can be converted? But it is worth noting that the voltage grade, impedance characteristics, impedance voltage characteristics and winding current, etc. all determine whether the step-down transformer can be used for step-up. So here we will explain it in detail. Step-up and Step-down Transformers Working & Applications Catalog Introduction Ⅰ Electrical Transformer Working Principle Ⅱ Differences between Step-down and Step-up Transformers Ⅲ Example Analysis Ⅳ Theoretical Analysis Ⅴ FAQ Ⅰ Electrical Transformer Working Principle Transformer is a common electrical equipment that can be used to transform a certain value of alternating voltage into another one with the same frequency. A step-up transformer is a device used to transform a low alternating voltage into another higher value with the same frequency. While the step-down transformer is a very important equipment in the power transmission and transformation system. That is, its normal operation is not only related to its own safety and reliable power supply for users, but also directly affects the stability of the power system.Transformers generally have two functions, one is the buck-boost function, and the other is the impedance matching function. Let me talk about the former. Usually we use a variety of voltages in applications. For example, the life lighting power is 110V, the industrial safety lighting is 36V, and the voltage of the welding machine needs to be adjusted. These are inseparable from the transformer. For example, according to the principle of mutual inductance, the transformer passes through the main and auxiliary coils to reduce the voltage to the voltage we need. Figure 1. EMF Formula The main parts of the transformer are the iron core and the windings on it. The two windings are only magnetically coupled but not electrically connected. Add an alternating voltage to the primary winding to generate alternating magnetic flux that links the primary and secondary windings, and induce the electromotive force (EMF) in the two windings respectively. As long as the number of turns of the primary and secondary windings is different, the purpose of voltage transformation can be achieved by transformer.   Ⅱ Differences between Step-down and Step-up Transformers 1) The step-down transformer converts the higher voltage at the input of the power supply into a lower voltage for our normal use to achieve the purpose of step-down.2) The step-up transformer can convert a low voltage into a higher voltage. (Additionally, the inverter transformer is also a kind of step-up transformer). In principle, the step-down transformer and the step-up transformer are the same, the specific difference is the inductance, copper consumption, and winding capacity of the high-voltage side and the low-voltage side. The same transformer, no matter it is used for step-up or step-down, the iron loss is the same. Under no-load conditions, the high-voltage side winding of the step-down transformer has many turns, large impedance, large inductance, small current and low copper loss, in addition, the high-voltage side winding has a larger capacity. At this time, it becomes a step-up transformer, the iron loss is the same, but the low-voltage side winding has a small number of turns and a small impedance. The inductance is small and the copper loss is small, and the primary side capacity is smaller than the secondary at this time.But there is a question. When the step-down transformer is converted to a step-up transformer, can the rated parameters of the low-voltage side coil withstand the loss under no-load conditions? If so, how much power is left for the high-voltage side.Whether to increase or decrease voltage depends on the ratio of the number of turns of the primary coil and the secondary coil. 1:1 is only for isolation. Therefore, the step-down transformer can be used as a step-up transformer, but it may not work in practice. Figure 2. Transformer Voltage Conversion Ⅲ Example Analysis As above mentioned, step-up transformer and step-down transformer cannot be used as a reverse conversion. Because the step-up transformer is equivalent to stepping up low-voltage power into high-voltage power. For the system, its low-voltage side is equivalent to absorbing electric energy, and the high-voltage side sending electric energy is equivalent to the power source. That is, the load of the system accepts the standard rated voltage, and the voltage output on the power supply side takes into account the voltage drop of the circuit and the transformer itself, about 10%. In order to ensure that the voltage delivered to the user is exactly the rated voltage, the voltage output on the high voltage side is 10% higher than the rated voltage.For example, if the rated voltage of the low-voltage side of a step-up transformer is 20kV and the high-voltage side is 110kV, the receiving voltage of the low-voltage side is 20kV, and the high-voltage side is 10% higher, about 121kV. If you consider the transformation ratio, suppose that the low-voltage side has 20 turns, and the high-voltage side cannot be 110 turns but 121 turns. If this step-up transformer is used as a step-down transformer, its high-voltage side can be regarded as a load from the system and can only receive a rated voltage of 110kV, and meanwhile the output voltage of the low-voltage side cannot reach 20kV, which can’t work normally. Similarly, the step-down transformer cannot be used as a step-up transformer. In the actual application process, the structure and protection part of the step-down transformer is different from that of the step-up. So this action will slowly reduce the stability of the transformer and may affect its service life.Of course, there is also a case where a step-down transformer can be used as a step-up one, as long as the voltage does not exceed the primary and secondary voltage. Figure 3. Transformer Phase Change Ⅳ Theoretical Analysis Nowadays, it is very common that the voltage instability fluctuates during our usual mains electricity use. Therefore, each family needs to install a power supply device for its own power line. Considering that some people often use low voltage, and some people's home voltage is always high, so there are step-up transformers and step-down transformers.We first look at the rectifier transformer. We found that the secondary wire on its surface is particularly thick, which is due to the larger current in the secondary circuit. It can be imagined from this that if the secondary circuit is used as the primary side, its impedance must be very small, and the power supply must provide a large current to obtain the required voltage on the secondary side of the transformer, resulting in low conversion efficiency. Ordinary transformers do have this possibility. For example, the electric energy generated by the user's self-provided low-voltage generator may pass the power transformer (step-down) back to the grid. So once the self-provided generator starts, you need to open the circuit breaker connected to the grid. Even with this possibility, it is not arbitrarily that the electric energy can be fed back to the grid through the transformer.Let's look at the expression of AC voltage: . Note that U on the right side of the equal sign is the effective value of the voltage, and this voltage must meet the specified rated value, f is the frequency (which must also meet the condition of the standard value), and Φ is the phase difference.We call these three parameters on the primary side of the transformer consistent with the grid requirements on the secondary side of the transformer, which is called synchronous operation. It is a necessary operation that must be performed for the power supply and the power grid to be combined. And the same period value must fully comply with the specific specification value given by the specification standard.Since the synchronization parameters of the power grid are fixed, the generator must adjust its own synchronization value. The adjustment process of the same period is not very easy. The synchronous period can only be satisfied in an instant. We can only achieve as close as possible, that is, quasi-synchronous. If it is found that the quasi-synchronization is completed, immediately close the circuit breaker, and the electric energy generated by the generator can be boosted by the transformer and sent to the grid. It can be seen that this is not easy, and it can only be achieved by supporting a synchronous measuring instrument or a relay.Pay attention to the wiring problem of the transformer, that is, the connection group of the transformer. Generally, the phase of the high-voltage side of the transformer is deviated from the low-voltage side. Standards and specifications are vividly expressed using a clock. For example, Y11 and Y0, respectively indicate the connection at 11 o'clock and 0 o'clock (11 o'clock means that the difference between the two is 30 degrees in electrical angle, and 0 o'clock has no deviation). Therefore, when doing synchronous operations, we must also consider what time the transformer wiring is. In U.S, many households have solar power generation devices as auxiliary power supplies to generate electricity for own use. When the electricity is enough, it can be fed back to the grid and get benefit. Obviously, there are synchronization devices and power transformers here. Figure 4. Phase Deviation   Ⅴ FAQ 1. What is a step up transformer used for?In the National Grid, a step-up transformer is used to increase the voltage and reduce the current. The voltage is increased from about 25,000V to 400,000V causing the current to decrease. Less current means less energy is lost through heating the wire. 2. What is difference between step up and step-down transformer?The main difference between the step-up and step-down transformer is that the step-up transformer increases the output voltage, while the step-down transformer reduces the output voltage. 3. How does a step up transformer work?Generally, a step-up transformer comes with more turns of wire in the secondary coil that increases the received voltage in the secondary coil. ... Hence, in simple words, a step up transformer increases the electricity voltage from lower to higher in the secondary coil according to the requirement or the application. 4. What is an example of a step up transformer?As an example, a 10:1 step-up transformer requires ten times the turns on the secondary winding: In this formula, we converted the voltage from 5V to 50V (step-up) in a transformer with ten turns on the primary winding, and 100 turns on the secondary winding. 5. What appliances use step up transformer?While this is done to make it suitable for general use, there are certain appliances like electrical motors, microwaves, X-ray machines etc. that require a high voltage to start. A step-up transformer is used to convert the existing power supply to the desired voltage. 6. What is the formula for step up transformer?Using this formula, P = E x I, and its direct derivatives, I = P / E and E = P / I, all transformer attributes can be calculated. For example, if the transformer's rating is 10 KVA and has a 240-volt output, it has a current capacity of 41.67 amperes (10,000 watts / 240 volts = 41.67 amps). 7. What is the main function of a step down transformer?Transformers are classified by their function, which is either step up or step down. Step-up transformers increase the voltage of the incoming current, while step-down transformers decrease the incoming current's voltage. 8. How does a step down transformer work?Primarily, a step-down transformer works on the basic principle of electromagnetic induction. According to Faraday's first law of electromagnetic induction, a conductor when placed in a varying electromagnetic field will see an induced current based on the rate at which the flux changes. 9. Why do we use a step down transformer?The higher the current, the more heat is lost. To reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage. ... These high voltages are too dangerous to use in the home, so step-down transformers are used locally to reduce the voltage to safe levels. 10. Where do we use step up and step down transformers?Step-up and step-down transformers use electromagnetic induction to convert voltage between two circuits. We use both types in the distribution of power from supply stations to the end user, as well as to ensure that the appropriate voltage goes into a circuit on many personal devices. 11. Why do we need to step down voltage?Increased voltage allows decreased current which dramatically reduces power loss. Once the power completes its journey, we decrease its voltage at a step-down transformer to make it safer and more useable in the neighborhood. 12. What is transformer explain step up and step down transformer?A transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer. 13. How does a transformer step down voltage?The concept of a step-down transformer is actually quite simple. The transfer has more turns of wire on the primary coil as compared to the turns on the secondary coil. This reduces the induced voltage running through the secondary coil, which ultimately reduces the output voltage. 14. Does step down transformer consume electricity?Thus, if you plug a 300W load into a step-down transformer (assuming the transformer is rated for more than 300W), expect it to draw a little more, perhaps 325W - 375W depending on quality of construction. 15. Does step down transformer increase current?A step-up transformer increases voltage and decreases current, whereas a step-down transformer decreases voltage and increases current.

Introduction The transistor is a current-control device. For example, control the collector-emitter current by changing the base current. In a general voltage amplification occasion, this amplification effect comes from the use of resistors to convert current into voltage. In the small-signal model, the source of the base current is the ratio of the input voltage to the base-emitter dynamic resistance rbe, which is usually kΩ. So the base current is very small, and may only be a few tenths of mA. Through the amplification of the transistor, the base current is generated between the collector and the emitter by β times. This article will introduce how transistor works in the common-emitter amplifier circuit. Transistor Amplifiers Circuit Introduction Catalog Introduction Ⅰ Common-emitter Amplifier Circuit Formula Ⅱ Common-emitter Amplifier Circuit Design 2.1 Design Steps 2.2 Circuit Analysis 2.3 Common-emitter Circuit Design 2.4 Circuit Performance Parameters Ⅲ Common-emitter Amplifier Circuit Expansion 3.1 Increase Magnification 3.2 Low-voltage and Low-loss Circuit 3.3 Differential Output Circuit 3.4 Filter and Tuning Amplifier Circuit Ⅳ Summary Ⅴ FAQ Ⅰ Common-emitter Amplifier Circuit Formula Here, take the common emitter amplifier circuit as an example: Figure 1. Transistor Common-emitter Amplifier Circuit △Vo=VCC-△ieRc=VCC-β△ibRc=VCC-△Vi·Rc/rbe△Vi/rbe=△ibThus, the collector generates a current of β times ib:△ie=β△ibFurthermore, the output voltage can be obtained by the relative positive power supply potential:△Vo=VCC-△ieRc=VCC-β△ibRc=VCC-△Vi·Rc/rbeThus, we can get an inverted amplified voltage signal by AC coupling and controlling the collector resistance Re. But generally the emitter will have a resistance to control the gain, so the above formula is not practical. When designing a circuit in non-extreme situations, we often hope that the circuit can work with most general-purpose transistors, avoiding the parameter that depends on component parameters such as rbe. At the same time, it is very cumbersome to consider the base current in the specific calculation. Therefore, in the general design process, the existence of the base current is ignored in an approximate calculation (In some circuits, although the base current is ignored, it is still necessary to give the base a certain current drive to make the circuit working normally). In addition, the calculation of gain is the external circuit resistance not the rbe.Among them, the base-emitter tube voltage drop VBE is also a very important parameter, which is generally equal to 0.6V (silicon tube). The parameters of the transistor circuit can all be obtained according to VBE=0.6V and Ohm's law.The cumbersome part of the transistor circuit lies in the setting of the static operating point. Usually, careless design will cause clipping and distortion of the output waveform. Therefore, the selected values of some experimental values can be used for reference. The overall design idea is: quantitatively determine the voltage and current to calculate the resistance.   Ⅱ Common-emitter Amplifier Circuit Design The common-emitter amplifier circuit is a typical inverting amplifier, which has a wide range of applications and stable effects. First show the overall design ideas, and then explain the purpose and principles of the design in steps. 2.1 Design Steps 1) Determine the supply voltage VCC, and determine the static emitter current IE according to the frequency curve/noise curve/others.2) Determine VE, where selects 1~2V to absorb temperature drift.3) According to VE and IE, calculate the emitter static resistance RE ( IE≈IC).4) Determine the magnification Av, and apply the relationship Av=RC/RE to calculate the static collector resistance RC. At this point, the static working point has been established.5) Check whether the static operating point meets the requirements: positive output swing limit=VCC-IE·RC, negative output swing limit=IE·RC-VE. It is necessary to ensure that the amplified output voltage does not exceed the swing limit (usually the swing limit is larger). If RC is too large, there will be a downside clipping, so is the small RC. In addition, determine whether the power exceeds the limit: PC=VCE·IC.6) Determine the base bias voltage as follows: According to VBE=0.6V, it is easy to get VB=VE+0.6 (divide the voltage from the power supply through the resistor). Since ib is considered to be small and negligible, the current IB0 flowing through the base voltage divider resistors (R1, R2 in the above figure) should be much larger than ib. ib is approximately calculated as IC/β, and IB0 is about an order of magnitude larger than ib, so R2=VB/IB0, R1=(VCC-VR2)/IB0.7) Finally, determine the AC coupling capacitor value and the power supply decoupling capacitor value.Let's first use a designed common-emitter amplifier circuit to intuitively understand the waveforms of the next parts: Figure 2. Transistor Common Emitter Amplifier Circuit Design As shown in the figure, the circuit uses 2SC2240 tube, 15V power supply, and the input and output are AC coupled. The output signals are as following:  Figure 3. 4-channel Signal Waves The pale blue waveform is the input signal, selecting the sine wave of 1kHz, 1Vpp.The green is the output signal, amplified by about 5 times, and it is inverted.The blue is the base signal, which can be seen because the DC level is raised due to the influence of the base bias resistance.The red is the emitter signal, which is only a fixed value away from the base signal.   2.2 Circuit Analysis First, perform a DC analysis, that is, determine the static operating point. In the initial design process, the design and verification of static operating points are also the first to proceed. The static potential of the base can be easily calculated according to the base bias resistance, and the static potential of the emitter can be determined according to the voltage drop of the base-emitter tube as a constant. Therefore, according to the magnitude of the emitter resistance, the magnitude of the collector-emitter current can be obtained, and then the collector static potential can be obtained from the power supply voltage.Why is the static operating point important? Take the NPN transistor as an example, which is equivalent to two back-to-back diodes. If requiring the diode work, you must give it a proper bias to make it reasonably conductive. In the circuit, the base-collector diode prevents internal feedback, and the base-emitter diode is the key to achieving amplification. In other words, it is enough to design an external circuit so that the current flows normally in the base-emitter diode. This idea will be mentioned in the analysis of the carrying capacity of the emitter follower.Find the AC voltage gain. When the input voltage changes △vi, it will cause the emitter current to produce an AC change △ie. Since the base emitter voltage drop is constant, it does not contribute to the AC change, so △ie=vi/RE. Therefore, the emitter AC output voltage can be determined as vo=△ieRC=vi·RC/RE, and the AC gain is Av=RC/RE. This conclusion can quickly analyze the magnification of the common-emitter circuit.The output power rails are VCC and VE respectively, which are determined by the current characteristics of the transistor during operation, and there is generally no rail-to-rail output. According to the output power rail and the AC amplification factor, the circuit can be used.When the input and output are not AC coupled, the input (especially for DC) will cause the output waveform to be distorted.   2.3 Common-emitter Circuit Design After understanding the circuit characteristics, you can design the common emitter circuit according to the design steps at the beginning of this section. The static operating point and magnification have been determined during the analysis, and the other parts are designed below.Supply voltage: According to the swing of the output voltage, we can determine the size of the voltage. Usually the power supply voltage is larger than the output peak-to-peak value.Transistor: Select the appropriate transistor according to the operating frequency, required power, noise level and β, etc.Emitter current: Determine the size of the emitter current according to the frequency characteristics by consulting the device manual.RC and RE: Determined by the emitter voltage and current, and the magnification, pay attention to review the upper and lower limits of the swing and the rated power.Base bias resistance: VB is determined according to VE, thereby determining the voltage divider resistance of the power supply. Note that the current flowing through the voltage divider resistor should be one to two orders of magnitude higher than the base current. The base current is calculated by dividing the collector-emitter current by β.Coupling capacitor: The AC coupling capacitor is generally 10uF. Note that the coupling capacitor of the output stage and the input impedance of the next stage will form a high-pass filter. The cutoff frequency of the filter should be handled carefully.   2.4 Circuit Performance Parameters Through the method of AC analysis, we can obtain some characteristic parameters of the designed circuit, such as input and output impedance, magnification and so on.Input impedance: According to AC analysis, the input impedance is the parallel value of the base bias resistance. In small signal analysis, the base emitter dynamic resistance rbe should also be connected in parallel.Output impedance: The method to determine the output impedance is to add a load to the circuit. When the peak-to-peak output value drops to half of the no-load, the load impedance is the output value. Generally, the output impedance of the common-emitter amplifier circuit is the collector resistance RC.Magnification: Due to the influence of the base current, the actual magnification is about 10% lower than the design value. So the design formula is more practical.   Ⅲ Common-emitter Amplifier Circuit Expansion By improving the general common-emitter amplifier circuit, various application circuits with other characteristics can be obtained. This section introduces the means to increase the magnification, the low-voltage power supply circuit, the differential output circuit, and the tuning amplifier circuit. 3.1 Increase Magnification According to the introduction of the design circuit, the voltage gain is mainly determined by the ratio of the collector resistance RC to the emitter resistance RE. So it is common to change the ratio of the resistance to change the gain. However, the problem arises: these two resistors are responsible for determining the working current at the same time. Because the DC operating point is changed arbitrarily, the circuit is likely to be distorted or even not work.From another perspective, voltage gain belongs to the category of "AC Analysis", and the static operating point belongs to "DC Analysis". So add some reactive components to the circuit to change the ratio under the AC perspective, the resistance value during DC analysis does not change.This can be achieved by connecting the emitter resistor in parallel, or making the resistor in parallel with the capacitor, that is, modifying the circuit in the first section: Figure 4. Common-emitter Amplifier Circuit Pay attention to the emitter in the above figure. In the AC analysis, the resistor R4 is short-circuited by the capacitor. At this time, it is equivalently considered that the emitter resistor is only R7 (330Ω). From the signal source and the oscilloscope, the signal has been amplified nearly 50 times at this time. It is much larger than the original design value (10k/2k=5), thus realizing the expansion of voltage gain. If the original emitter resistance is not split, but the entire capacitor is connected in parallel, the maximum gain βRC/rbe will be obtained at this time.How to choose the capacitance value? It should be noted that after the capacitors are connected in parallel, the entire circuit will have high-pass characteristics, and the cut-off frequency is f=1/2πRC. If this high-pass characteristic is not required, the C capacitance value can be selected to a larger value between 47uF~100uF.In addition, the capacitor C6 has the function of temperature compensation. 3.2 Low-voltage and Low-loss Circuit If the op amp circuit is powered by a dry battery (1.5V), it is not realistic, but the transistor circuit can be done. The key is to use the conduction voltage drop of the external diode to offset the base-emitter voltage and have small small. The circuit in the figure below can still amplify small signals as designed even under 1.5V power supply: Figure 5. Common-emitter Amplifier Circuit But the disadvantage is that the maximum voltage of the system is always below the supply voltage. Because of the small circuit loss, it is suitable for low power consumption. 3.3 Differential Output Circuit Fully differential op amps can provide dual-mode output, and many transmission lines also require differential transmission. Transistor circuits can also perform differential output. In addition to the principle of a common emitter amplifier circuit, the principle of an emitter follower is also used. The following figure shows the circuit connection of the differential output. Figure 6. Common-emitter Amplifier Circuit It can be seen that two differential signals with the same shape and opposite phase are output. The collector signal is in phase with the input signal, and the emitter output signal is in phase with the input signal. However, the output impedance of the two signals is different due to the different lead-out positions. The output impedance of the inverted output is higher (RC), and the output impedance of the non-inverted output is lower, which is suitable for driving the load. The inverted output is generally connected to the emitter follower before driving.In addition, the static potential of the base should be set between VCC and GND as much as possible to expand the undistorted output range.   3.4 Filter and Tuning Amplifier Circuit The introduction of reactive components in the circuit will cause the properties of the circuit to change with the frequency. We can use this property to design LPF, HPF, and tuning amplifier commonly used in high-frequency circuits. Actually, it uses the characteristic that the impedance of the reactance element changes with the frequency, and then changes the voltage gain at the current frequency. The impedance at the resonance frequency is often purely resistive and has an extreme value to achieve frequency selective amplification. The following show low-pass, high-pass and frequency selective amplifiers at specific frequencies:① LPF Figure 7. Common-emitter Amplifier Circuit As shown in the figure, a low-pass filter is constructed (the input of the bode tester is placed at the base instead of the output of the signal generator, because the input coupling capacitor will form a high-pass filter with the input resistor, which affects the observation effect), and its cut-off frequency is about 1.06kHz, calculated by f=1/2πRcC.From the sinusoidal steady-state analysis, the impedance of the RC parallel loop is R/√(1+(wRC)^2). As the frequency increases, the impedance decreases, so the voltage gain decreases, forming a low-pass characteristic.② HPF Figure 8. Common-emitter Amplifier Circuit As shown in the figure, a high-pass filter is constructed, and the calculation of its cut-off frequency is similar to that of LPF.At the gain peak point, the voltage gain reaches 50dB, which is close to the β value of the transistor. Then the gain is attenuated due to the deterioration of the transistor's frequency characteristics.③ 10.7MHz Figure 9. Common-emitter Amplifier Circuit By replacing RC with an LC network with a resonance frequency of 10.7MHz, a frequency selective amplifier can be obtained. As shown in the figure, the amplification factor is 35dB at 10.7M, while the amplification factor when detuning 1MHz is only 12.6dB. The disadvantage is that the pass-band is slightly wider, the rectangular coefficient is not good enough, and the equivalent quality factor of the loop is about 65.2, which is relatively large. In addition, the high-frequency decoupling capacitor has been changed to 1uF. Resonant Amplifier Circuit Example: Figure 10. Resonant Amplifier Circuit Example   Ⅳ Summary Transistor amplifier circuit is the basis of an operational amplifier circuit, and common-emitter configuration is the most commonly used form. Drawing lessons from the feature that the amplifier's magnification can be easily determined by the ratio of two resistors, and the gain of the common emitter amplifier can also be approximated by the ratio of the two resistors.   Ⅴ FAQ 1. What are transistor amplifiers used for?Amplifiers are derived from the transistors because they are capable of operating under three regions active, cut-off and saturation. For the purpose of amplification, the focus will be on the active region. The main purpose of these amplifiers is to enhance the strength of the applied input signal without alteration. 2. How does a transistor amplify current?Transistors are normally used as amplifiers. ... The small current travels from the voltage source into the base of the transistor. A current at the base turns on the transistor. The current is then amplified and travels from the emitter of the transistor to the collector. 3. What is a common emitter transistor amplifier?The common emitter amplifier is a three basic single-stage bipolar junction transistor and is used as a voltage amplifier. The input of this amplifier is taken from the base terminal, the output is collected from the collector terminal and the emitter terminal is common for both the terminals. 4. Why common emitter is used in amplifier?Common emitter (CE) configuration. ... Common emitter transistors are used most widely, because a common emitter transistor amplifier provides high current gain, high voltage gain and high power gain. This type of transistor gives for a small change in input there is small change in output. 5. What is the use of CE amplifier?In electronics, a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor (BJT) amplifier topologies, typically used as a voltage amplifier. It offers high current gain (typically 200), medium input resistance and a high output resistance. 6. How does transistor work as amplifier?A transistor acts as an amplifier by raising the strength of a weak signal. The DC bias voltage applied to the emitter base junction, makes it remain in forward biased condition. ... Thus a small input voltage results in a large output voltage, which shows that the transistor works as an amplifier. 7. What is common emitter amplifier circuit?The Common Emitter Amplifier circuit has a resistor in its Collector circuit. The current flowing through this resistor produces the voltage output of the amplifier. ... The Base of the transistor used in a common emitter amplifier is biased using two resistors as a potential divider network. 8. What are the main parts of a transistor amplifier circuit?A Single stage transistor amplifier has one transistor, bias circuit and other auxiliary components. The following circuit diagram shows how a single stage transistor amplifier looks like. When a weak input signal is given to the base of the transistor as shown in the figure, a small amount of base current flows. 9. What is the phase difference in common emitter amplifier?The phase difference between the input and output voltage of CE amplifier circuit is. The phase difference of 1800 between the signal voltage and output voltage in a common emitter amplifier is known as phase reversal. 10. When an NPN transistor is used as an amplifier?For a npn transistor to be used as an amplifier, forward bias has to be applied on the transistor. Thus, when an npn transistor is used as an amplifier, holes move from base to emitter. So, the correct answer is option D i.e. holes move from base to emitter. 11. When an NPN junction transistor is used as an amplifier in CE mode?A transistor is used in the common emitter mode as an amplifier then: (A) the base emitter junction is forward baised. (B) the base emitter junction is reverse baised. (C) the input signal is connected in series with the voltage applied to bias the base emitter junction. 12. How is an NPN transistor used as an amplifier show with its circuit diagram?The circuit of a common-emitter amplifier using an n-p-n transistor is shown below : In a common emitter amplifier circuit, the input signal voltage and output collector voltage are in opposite phase. i.e 180° out of phase. Thus the phase difference between the input signal and output voltage is 180°. 13. How does a common emitter amplifier work?Operation of Common Emitter AmplifierWhen a signal is applied across the emitter-base junction, the forward bias across this junction increases during the upper half cycle. This leads to an increase in the flow of electrons from the emitter to a collector through the base, hence increases the collector current. 14. What is β for a CE configuration?Base Current Amplification Factor (β)The base current amplification factor is defined as the ratio of the output and input current in a common emitter configuration. In common emitter amplification, the output current is the collector current IC, and the input current is the base current IB. 15. What is current gain CE configuration?The current gain of a transistor in CE configuration is defined as the ratio of output current or collector current (IC) to the input current or base current (IB). The current gain of a transistor in CE configuration is high. Therefore, the transistor in CE configuration is used for amplifying the current.

Introduction The operational amplifier has a non-inverting input terminal and an inverting input terminal in the electronic circuit. The polarity of the input terminal and the output terminal are the same is a non-inverting amplifier, and the polarity of the input terminal and the output terminal are opposite called inverting amplifier. The inverting amplifier circuit has the function of amplifying the input signal as inverting output. Inverting Op Amp and The Concept of Virtual Ground in Op Amp Catalog Introduction Ⅰ Inverting Amplifier Basics Overview 1.1 Working Principle 1.2 Inverting Amplifier Gain Calculator 1.3 Inverting Amplifier Features 1.4 Inverting Amplifier Functions Ⅱ Inverting Amplifier Applications Ⅲ Inverting Amplifier Explain with Diagrams: NE5532 Ⅳ Inverting Amplifier Circuit Design Steps Ⅴ FAQ Ⅰ Inverting Amplifier Basics Overview 1.1 Working Principle As shown in Figure 1, the inverting amplifier circuit has the function of amplifying the input signal as inverting output. "Inverting" means that the positive and negative signs are reversed. This amplifier uses negative feedback technology, which used to return a part of the output signal to the input. In Figure, the wiring method of connecting the output Vout to the inverting input terminal (-) via R2 is negative feedback. Figure 1. Inverting Amplifier Circuit Operational amplifiers have such characteristics. When the power supply voltage is not applied to the output terminal, the non-inverting input terminal (+) and the inverting input terminal (-) are considered to have the same voltage, that is to say, it can be regarded as a virtual short circuit. Therefore, when the positive input terminal (+) is 0V, the voltage at output is also 0V.The input impedance of the operational amplifier is extremely high, and there is basically no current in the inverting input terminal (-). Therefore, when the current flows to R2, the I1 and I2 are basically equal. Based on the above conditions, using Ohm's Law for R2, we get Vout=-I1xR2. I1 is negative because I2 flows from point A where the voltage is 0V. From another point of view, when the input voltage of the inverting input terminal (-) rises, the output will be inverted and amplified greatly in the negative direction. Since the output voltage in the negative direction is connected to the inverting input terminal via R2, the voltage rise of the inverting input terminal (-) will be blocked. Both the inverting input terminal and the non-inverting input terminal voltage become 0V, and the output voltage is stable.   1.2 Inverting Amplifier Gain Calculator Calculate the gain through the relationship between the input and output in this amplifier circuit. The gain of an inverting op amp is the ratio of the feedback resistance to the input resistance, that is, the ratio of Vout to Vin, and the formula is Vout/Vin= (-I1xR2) /(I1xR1)=-R2/R1. The resulting gain is negative, indicating that the waveform is inverting.The current flowing through R1: I1=(Vi-V-)/R1...aThe current flowing through R2: I2=(V--Vout)/R2……bV-=V+=0………………cI1=I2……………………dSolve the above algebraic equations to get Vout=(-R2/R1)*Vi.This is the input and output relationship of the inverting amplifier circuit.   1.3 Inverting Amplifier Features It can reduce the input impedance or keep a certain value.It can be used as a current input type.Virtual short-circuit point is generated at a certain potential.Its positive input port is free.If the signal source impedance is low, it is easier to obtain a required S/N.The magnification is -Rf/R.   1.4 Inverting Amplifier Functions The inverting amplifier is the basic gain stage in the CMOS circuit. It adopts a common source structure, and the load can be an active load or a current source.Advantages: The potential of the two input terminals is always approximately zero (the non-inverting terminal is grounded, and the inverting terminal is virtual ground). With only differential mode signals,it has strong anti-interference ability.Disadvantages: The input impedance is very small, equal to the resistance of the series resistance from the signal to the input.   Ⅱ Inverting Amplifier Applications Figure 2. Basic Inverting Amplifier Circuit 1) As a IntegratorThe original resistor R2 of the inverting amplifier is replaced by a capacitor C2. At this time, the relationship between the input signal Vi and the output signal Vo forms an integral relationship.2) As a DifferentiatorReplace the original resistor R1 of the inverting amplifier with an electric capacitor C. At this time, the relationship between the input signal Vi and the output signal Vo is differential.3) As a AdderIf the inverting amplifier is slightly changed, the relationship between the input signal and the output signal Vo at this time, if R1 = R2 = R3 =...= Rn = Rf, it can be simplified to Vo = -(V1+V2+V3+.. .+Vn), is additive.   Ⅲ Inverting Amplifier Explain with Diagrams: NE5532 The equivalent resistance seen between the input terminal and the ground of the inverting amplifier circuit is equal to the equivalent resistance between the input terminal and the virtual ground, so the input resistance of the circuit is Ri=R. It can be seen that although the input resistance of the ideal operational amplifier is infinite, the input resistance of the inverting proportional arithmetic circuit is not large because of the parallel negative feedback introduced by the circuit. Figure 3. NE5532 Audio Amplfier Circuit In order to increase the input resistance, R must be increased. For example, when the scale factor is -50, if Ri=10kΩ, R should be 10kΩ and Rf should be 500kΩ. If Ri=100kΩ, R should be 100kΩ and Rf should be 5MΩ. In fact, when the resistance in the circuit is too large, on the one hand, due to the process, the stability of the resistance is poor and the noise is large, on the other hand, when the resistance is of the same order of magnitude as the input resistance of the integrated op amp, the proportional coefficient -Rf/R of the circuit will change greatly, and its value will not only be determined by the feedback network. Therefore, it is necessary for practical applications to use a resistor with a smaller resistance value to get a larger scale factor and a larger input resistance.Look at the following two simulations: Figure 4. Current and Voltage Measuring From above, it doesn't matter without R0, take a look at this below. Figure 5. Current and Voltage Measuring Their output is different, if the expected result is -4V. The reading value -3.608V obviously does not meet the design requirements. We now know that the resistance value of Rs in Figure 5 is orders of magnitude greater than the input resistance of the integrated operational amplifier. Next, if have R0, look at the picture below. Figure 6. Current and Voltage Measuring It can be seen from Figure 6 that after adding R0, the output of the op amp is normal. Why is this?In a TTL circuit, the transistor has a bias current, which will produce a DC voltage drop on the feedback resistor of the e pole. Although it is small, the amplifier has a high amplification factor, which affects the output accuracy greatly. A resistor in the same value as the negative terminal is connected to the positive terminal to cancel the effect of the bias current.R0 is a compensation resistor, which minimizes the bias current error to ensure the symmetry of the differential amplifier circuit of the input stage. When its value is u=0 (that is, the input terminal is grounded), the inverting input terminal is always the equivalent resistance, that is, the parallel connection of the resistance of each branch, so R0=Rs/Rf, through Rf in the circuit, induce negative feedback. According to practical experience, it is best to add a compensation resistor to improve the stability of the circuit. Of course, it can be omitted under normal circumstances.   Ⅳ Inverting Amplifier Circuit Design Steps Inverting amplifiers are several commonly used amplifier types. How to use operational amplifiers design inverting amplifier circuit? The following sharing is the detailed steps.Step 1: Determine the magnification.As shown in the figure below, the amplification factor of the inverting amplifier is (-R2/R1). Figure 7. Determine the Magnification Step 2: Determine the supply voltage.Ensure that the output voltage after the input voltage Vin is multiplied by the amplification factor (-R2/R1) will not exceed the power supply voltage. If it is not the rail-to-rail operational amplifier used, it is better to have a margin of 1~2V. Figure 8. Determine the Supply Voltage Step 3: Determine the gain bandwidth product (GBW).If you are amplifying an AC signal, you need to consider the gain bandwidth product. The calculation formula is: bandwidth of input signal × design gain, select an operational amplifier whose GBW is greater than the required one. Step 4: Check the bandwidth with the slew rate (SR).If the amplifying is a large AC signal, there may be insufficient bandwidth, and it may not be accurate enough to calculate based on the gain-bandwidth product.SR = 2*pi*f*Vp -> f = SR/(2*pi*Vp), where Vp: peak output voltage.If the calculated value f is less than the input voltage frequency, the operational amplifier is not suitable and needs to be replaced. The actual bandwidth should be the smaller of the gain bandwidth product and the slew rate. Step 5: Determine the input offset voltage.Since the offset voltage is also a DC signal, if it is to amplify the DC signal, it should be noted that the offset voltage will also be amplified by the corresponding multiple. If the accuracy is high, try to choose an operational amplifier with a small offset voltage. Step 6: Determine the resistance value.In step 1, the ratio of R1 and R2 has been determined. R1 is generally 1k~10k. A small value is prone to cause gain errors, and a larger value will increase noise (resistor thermal noise). R2 takes the resistance value corresponding to the multiple of R1.It is better to choose the chip resistor, because the parasitic parameters are small.R3=R1/R2, if R1 and R2 are connected in parallel, which are not required.   Ⅴ FAQ 1. What is the inverting amplifier?An inverting op amp is an operational amplifier circuit with an output voltage that changes in the opposite direction as the input voltage. In other words, it is out of phase by 180o。   2. What is inverting amplifier and its application?The inverting amplifier is an important circuit configuration using op-amps and it uses a negative feedback connection. An inverting amplifier, like the name suggests, inverts the input signal as wells as amplifies it.   3. How does an inverting amplifier circuit work?In an inverting amplifier circuit, the operational amplifier inverting input receives feedback from the output of the amplifier. Assuming the op-amp is ideal and applying the concept of virtual short at the input terminals of op-amp, the voltage at the inverting terminal is equal to non-inverting terminal.   4. What are the applications of inverting amplifier?op-amp inverting amplifier. Op amp summing amplifier: Based around the inverting amplifier circuit with its virtual earth summing point, this circuit is ideal for summing audio inputs. It is widely used in audio mixer and many other applications where voltages need to be summed.   5. Why is it called inverting amplifier?It is called Inverting Amplifier because the op-amp changes the phase angle of the output signal exactly 180 degrees out of phase with respect to input signal. Same as like before, we use two external resistors to create feedback circuit and make a closed loop circuit across the amplifier.   6. What are the characteristics of inverting amplifier?1) No Current Flows into the Input Terminals.2) The Differential Input Voltage is Zero as V1 = V2 = 0 (Virtual Earth)   7. What is the formula of inverting amplifier?One final point to note about the Inverting Amplifier configuration for an operational amplifier, if the two resistors are of equal value, Rin = Rƒ then the gain of the amplifier will be -1 producing a complementary form of the input voltage at its output as Vout = -Vin.   8. What are advantages and disadvantages of inverting amplifier?Advantages and Disadvantages of Inverting AmplifierIt follows the negative feedback. The gain factor of these amplifiers is very high. The output generated will be out of phase with the applied input signal. The potential values at both the inverting and the non-inverting terminals maintained at zero.   9. What are the advantages of inverting amplifier?The op amp circuit for the inverting amplifier offers many advantages including relatively low input impedance, a low output impedance and the level of gain that is required (within the limits of the op amp and the gain required from the overall circuit.   10. What is the use of inverting amplifier?The inverting amplifier is an important circuit configuration using op-amps and it uses a negative feedback connection. An inverting amplifier, like the name suggests, inverts the input signal as wells as amplifies it.   11. What is mean by inverting amplifier?An inverting amplifier takes an input signal and turns it upside down at the op amp output. When the value of the input signal is positive, the output of the inverting amplifier is negative, and vice versa. ... The amount of amplification depends on the ratio between the feedback and input resistor values.   12. How an opamp is used as inverting amplifier?Theory: An inverting amplifier using opamp is a type of amplifier using opamp where the output waveform will be phase opposite to the input waveform. The input waveform will be amplifier by the factor Av (voltage gain of the amplifier) in magnitude and its phase will be inverted.   13. What is an inverting amplifier used for?op-amp inverting amplifier. Op amp summing amplifier: Based around the inverting amplifier circuit with its virtual earth summing point, this circuit is ideal for summing audio inputs. It is widely used in audio mixer and many other applications where voltages need to be summed.   14. How does an inverting amplifier work?An inverting amplifier takes an input signal and turns it upside down at the op amp output. When the value of the input signal is positive, the output of the inverting amplifier is negative, and vice versa.   15. What is the gain of an inverting amplifier?The gain of inverting amplifier is Av= – Rf/Ri.

2026 Executive SummaryThis authoritative guide explores the function, diagnostics, and wiring of Start Relays in modern HVAC and automotive systems. As of 2026, start relays remain the critical failure point in 15-20% of refrigeration breakdowns. We cover the three primary architectures (Current, PTC, and Potential), provide step-by-step troubleshooting for multimeter testing, and detail updated 12V wiring standards for automotive ignition systems.Introduction: The Role of Start Relays in 2026The Start Relay is a specialized electromechanical component designed to initiate the rotation of single-phase asynchronous motors. In the 2026 landscape of home appliances and automotive engineering, its primary function is to momentarily engage the auxiliary (start) winding or starter solenoid to overcome inertia. While variable-frequency drives (VFDs) are gaining popularity, the vast majority of residential refrigerators and air conditioners still rely on single-phase split-phase induction motors, necessitating precise relay activation. Once the motor reaches approximately 75% to 80% of its rated speed, the relay automatically disconnects the start circuit to prevent the auxiliary winding from overheating or burning out.Ⅰ What is a Start Relay and How Does It Work?A start relay is an automatic switch that utilizes electromagnetic force or thermal resistance to control the high-current startup phase of an electric motor.Technically, start relays fall under the category of momentary control switches. They utilize electromagnetic and electromechanical principles to bridge contacts within a control circuit. A relay system comprises two distinct loops:The Control System (Input Loop): Responds to physical quantities like electricity or heat.The Controlled System (Output Loop): Manages the high-load circuit.When the input parameter (e.g., inrush current) hits a specific threshold, the output state changes abruptly from zero to a set value, effectively managing circuit protection and power transmission without manual intervention.Figure 1. Standard Electrical Relay Symbols (IEC/NEMA Standards)Ⅱ Applications: HVAC vs. Automotive SystemsStart relays are predominantly used in single-phase refrigeration compressors to engage torque windings and in automobiles to switch high-amperage starter currents.1. HVAC & Refrigeration:The starting relay is the control element that automates the induction motor startup. When a refrigerator compressor cycles on, the motor winding is energized; once stable operation is achieved, the relay cuts power to the start winding. In 2026, the three industry-standard types found in appliances are:Current Relays: Common in older, smaller units.PTC (Positive Temperature Coefficient): The standard for modern residential fridges.Potential (Voltage) Relays: Used in high-torque commercial HVAC units.2. Automotive Systems:In vehicles, the start relay acts as a low-current switch controlling a high-current circuit. It preserves the ignition switch by handling the heavy load required to engage the starter solenoid. When activated, it drives the magneto rotor, inputs an ignition pulse, and ultimately allows the spark plugs to ignite the air-fuel mixture in the cylinders. Ⅲ Types of Start Relays: 2026 Industry Overview3.1 Current Starting Relays (Magnetic)Current relays operate by sensing the high inrush current drawn by the motor at a standstill.The coil is connected in series with the compressor's run winding. When the motor is stationary, the current is high, creating a strong magnetic field that closes the contacts to engage the start capacitor/winding. As speed increases, current drops, and gravity (or a spring) opens the contacts.(1) Heavy Hammer (Gravity) RelayThis legacy design relies on gravity to reset the armature. It consists of a coil, armature, moving contact, and static contact.Figure 2. Structure of a Heavy Hammer Start RelayMechanism: The contacts are Normally Open (NO). Upon power-up, the massive starting current (often 5-6x rated amps) magnetizes the coil, lifting the armature to close the start circuit. As the motor speeds up, current drops, and the armature falls, disconnecting the start winding. Note: These must be mounted perfectly vertical to function.(2) PTC Start Relay (Solid State)The most common relay in modern refrigerators. The PTC element is a barium titanate semiconductor. In its cold state (room temperature), resistance is low (approx. 4.7Ω to 33Ω), allowing current to pass.Mechanism: As high current flows during startup, the ceramic disc self-heats to its Curie point (100°C - 140°C). Resistance spikes effectively to infinity (open circuit), cutting off the start winding.Figure 3. PTC Start Relay Wiring SchematicAdvantages: No moving parts, high reliability, and low cost. Disadvantages: Requires a "cool down" period of 3-5 minutes between cycles to reset low resistance.(3) Mercury Start RelayA high-durability, non-arcing design often used in hazardous environments. It uses a plunger coil and a mercury reservoir.Figure 4. Mercury Relay Internal StructureWhen energized, the plunger displaces mercury, bridging the electrodes to complete the circuit. While highly reliable, environmental regulations in 2026 have limited their production due to mercury toxicity.Figure 5. Automotive Start Relay Assembly3.2 Potential (Voltage) RelaysPotential relays are voltage-sensing devices used in high-torque applications (central AC units, heat pumps).Figure 6. Potential Relay Internal ArchitectureThe coil operates on Back Electromotive Force (Back EMF) generated by the start winding. The contacts are Normally Closed (NC).Startup: Contacts are closed; full power goes to start capacitor/winding.Run: As motor speed hits ~80%, the Back EMF voltage across the start winding increases.Disengage: When voltage exceeds the "Pick-Up" rating (e.g., 300V), the coil energizes, opening the contacts and removing the start gear. Ⅳ Troubleshooting: Why Do Start Relays Fail?4.1 Symptoms of Relay FailureA failed relay usually results in a compressor that "hums" but won't start (clicking sound) or a car that won't turn over.Common Failure Modes:Contact Fusion: Contacts weld together due to electrical arcing, keeping the start winding engaged until the overload trips.Coil Burnout: The internal copper winding breaks or shorts due to overheating.Carbon Buildup: Increases resistance across contacts, causing voltage drops.Fatigue: Return springs lose elasticity over thousands of cycles.Relay wire connections should also be checked for corrosion or looseness, which mimics relay failure.4.2 Automotive Diagnostic Case StudyScenario: The driver turns the key, but the engine does not crank.🔺Case 1: Total Silence (No Crank)Potential Causes:Power Supply: Battery voltage < 12.4V or corroded terminals.Ignition Switch: Signal not reaching the relay control terminal (86).Relay Coil: Open circuit in the relay electromagnet.Diagnostic Steps:Check Power: Turn on headlights. Significant dimming suggests a weak battery.The "Bypass" Test: Use a screwdriver to momentarily bridge the large terminals on the starter solenoid. (Caution: Sparks will occur). If it cranks, the starter motor is good, pointing to a bad relay or ignition switch.Relay Swap: Swap the starter relay with a similar relay (e.g., Horn or Wiper) from the fuse box to test function.🔺Case 2: Slow Cranking (Dragging)Causes: High resistance in relay contacts or worn starter brushes.Fix: Measure voltage drop across the relay terminals while cranking. A drop >0.2V indicates bad contacts.🔺Case 3: Starter Spinning (Whirring) but Engine Not TurningAnalysis: The starter motor is running, but the bendix gear is not engaging the flywheel. This is typically a mechanical failure of the starter drive (Bendix), not the relay itself.Figure 7. Thermal Overload Relay Structure (Often paired with Start Relays)For a visual guide on testing, refer to the tutorial below:Video: How To Test and Replace A Starter RelayⅤ Step-by-Step: Wiring a 12V Starter RelayWiring a standard 4-pin 12V relay follows the DIN 72552 standard numbering system.The goal is to use a low-current signal (Pin 85/86) to switch a high-current path (Pin 30/87).Figure 8. 12V Start Relay Wiring DiagramStandard Pin Configuration:Pin 30 (High Power In): Connect directly to the Battery Positive (+). Fused.Pin 87 (High Power Out): Connect to the load (Starter Solenoid/Motor).Pin 86 (Control Power): Connect to the Ignition Switch (Start position).Pin 85 (Ground): Connect to the Chassis Ground (-).Installation Tips for 2026: Ensure wire gauge for Pins 30/87 is sufficient for the amperage (typically 10-12 AWG or larger for main starter leads). Control wires (85/86) can be thinner (16-18 AWG). If the relay has a diode (protection), ensure Pin 85 and 86 are not reversed to avoid shorting. Ⅵ FAQ: Top Questions About Start Relays1. What is the primary purpose of a starting relay?A starting relay manages high-current loads. It allows a low-current signal (like turning a key) to activate a high-current device (like a starter motor) without melting the ignition switch or wiring. 2. How do I know if my refrigerator relay is bad?The most common sign is a "click-buzz-click" cycle where the compressor tries to start but fails. Additionally, if you remove the relay and shake it, a rattling sound indicates the internal ceramic PTC disc has shattered. 3. Can I bypass a refrigerator start relay temporarily?Technically yes, for testing purposes only. You can momentarily bridge the Run and Start pins on the compressor to jump-start it. However, never leave it bypassed permanently, as the start winding will overheat and destroy the compressor within minutes. 4. What are the symptoms of a bad automotive starter relay?Symptoms include a silent start (no noise when turning key), a rapid clicking sound (insufficient voltage transfer), or the starter remaining engaged after the engine starts (welded contacts). 5. How long is the lifespan of a starter relay?Modern OEM relays are designed for approximately 50,000 to 100,000 cycles, typically lasting the life of the vehicle (100,000+ miles) or 10-15 years for household appliances. 6. Is a starter relay the same as a starter solenoid?They are often confused but distinct. The relay is a small remote switch (usually in the fuse box) that sends power to the solenoid. The solenoid is physically mounted on the starter motor; it pushes the drive gear into the flywheel and bridges the massive battery cables.{ "@context": "https://schema.org", "@graph": [ { "@type": "Article", "headline": "Start Relays Explained: Types, Diagnostics, and Wiring (2026 Guide)", "datePublished": "2021-10-18", "dateModified": "2026-01-09", "description": "A comprehensive guide to Start Relays for HVAC and Automotive applications. Learn about PTC, Current, and Potential relays, including wiring diagrams and troubleshooting steps.", "image": "https://www.kynix.com/editor_u/image/20211018/2021101815335454.jpg", "author": { "@type": "Organization", "name": "Kynix Electronics" } }, { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What is the primary purpose of a starting relay?", "acceptedAnswer": { "@type": "Answer", "text": "A starting relay manages high-current loads. It allows a low-current signal (like turning a key) to activate a high-current device (like a starter motor) without melting the ignition switch or wiring." } }, { "@type": "Question", "name": "How do I know if my refrigerator relay is bad?", "acceptedAnswer": { "@type": "Answer", "text": "The most common sign is a 'click-buzz-click' cycle where the compressor tries to start but fails. If you shake the relay and it rattles, the internal PTC disc is likely shattered." } }, { "@type": "Question", "name": "Is a starter relay the same as a starter solenoid?", "acceptedAnswer": { "@type": "Answer", "text": "No. The relay is a low-current switch in the fuse box that activates the solenoid. The solenoid is a high-current device mounted on the starter motor that engages the physical gears and main battery power." } } ] }, { "@type": "HowTo", "name": "How to Wire a 12V Starter Relay", "step": [ { "@type": "HowToStep", "name": "Connect High Power Input", "text": "Connect Pin 30 directly to the positive terminal of the battery (fused)." }, { "@type": "HowToStep", "name": "Connect Control Input", "text": "Connect Pin 86 to the ignition switch output." }, { "@type": "HowToStep", "name": "Connect Ground", "text": "Connect Pin 85 to the vehicle chassis ground." }, { "@type": "HowToStep", "name": "Connect Load", "text": "Connect Pin 87 to the starter solenoid or motor input." } ] } ]}