Introduction Operational amplifiers will oscillate in many practical applications. For example, there are many kinds of loads that will cause them to oscillate. A feedback network that is not properly designed can cause them to become unstable. Insufficient power supply bypass capacitors may also make them unstable. Even the input and output may oscillate into a single-port system. This article will tell some common causes that cause the op amp to oscillate and the corresponding countermeasures. Catalog Introduction Ⅰ Basic Op Amp Circuits Ⅱ Example: LTC6268 Amplifier Ⅲ Decompensated Amplifiers Ⅳ Feedback Network Ⅴ Load Problem Ⅵ Strange Impedance Ⅶ Power Ⅷ Conclusion Ⅸ FAQ Ⅰ Basic Op Amp Circuits Figure 1. shows a block diagram of a non-rail-to-rail amplifier. The input controls the gm box, which drives the gain node and is buffered at the output. The compensation capacitor Cc is the main frequency response component. The return pin of Cc should be grounded, if there is such a pin and the op amp is not grounded, the capacitor current will return to one or two power supplies. Figure 1. Block Diagram of a Non-Rail-to-Rail Amplifier Figure 2. is a block diagram of a rail-to-rail output amplifier. The output current of the input box gm is sent through a current coupler, which divides the current into two parts and supplies them to the output transistor. The frequency response is determined by two Cc/2s, which are actually connected in parallel. Figure 2. Block Diagram of a Rail-to-Rail Output Amplifier Figure 3. shows the frequency response of the ideal amplifier. Although the electrical principles of the two circuits are different, the behavior is similar. The single pole compensation formed by gm and Cc provides a unity gain bandwidth product frequency of GBF = gm/(2πCc). In the vicinity of GBF/Avol, the phase lag of these amplifiers changes from -180° to -270°, where Avol is the open-loop DC gain of the amplifier. When the frequency is much higher than this low frequency, the phase stays at –270°. This is the well-known "dominant pole compensation", where the Cc dominates the frequency response, hiding the various frequency limitations of the active circuit. Figure 3. Frequency Response of the Ideal Amplifier   Ⅱ Example: LTC6268 Amplifier Figure 4. shows the open-loop gain and phase response of the LTC6268 amplifier with frequency. The LTC6268 is a small and low-noise 500MHz amplifier with rail-to-rail output and only 3fA bias current. It can be used as a good example to illustrate the performance of real amplifiers. The -90° phase lag of the dominant pole compensation starts from about 0.1MHz, reaches -270° around 8MHz, and moves down by more than -270° when it exceeds 30MHz. In fact, all amplifiers have high frequency phase lag, except for the basic dominant compensation lag caused by the additional gain stage and output stage. Generally, the starting point of the additional phase lag is around GBF/10. Figure 4. Open-Loop Gain and Phase Response of the LTC6268 Amplifier with Frequency The stability of the feedback is a matter of loop gain and phase, or Avol multiplied by the feedback coefficient, which is the loop gain. If we connect the LTC6268 in a unity gain configuration, 100% of the output voltage is fed back. At very low frequencies, the output is the negative value of the "–" input, or the phase lags by -180°. Compensation adds a -90° hysteresis through the amplifier, introducing a –270° hysteresis from the "–" input to the output. When the loop phase lag increases to ±360° or its multiples, oscillation will occur, and the loop gain is at least 1V/V or 0dB. The phase margin is a measure of how much the phase lag differs from 360° when the gain is 1V/V or 0dB. Figure 4. shows that the phase margin is about 70° (10pF red curve) at 130MHz, and the phase margin as low as about 35° is feasible.A topic that is not often mentioned is gain margin, although it is an equally important parameter. When it is reduced to zero at some higher frequencies, the amplifier will oscillate if the gain is at least 1V/V or 0dB. As shown in Figure 4, when the phase drops to 0° (or a multiple of 360°, or –180° as shown in the figure), the gain is about –24dB around 1GHz. This is a very low gain and no oscillations will occur at this frequency. In fact, people want the gain margin to be at least 4dB.   Ⅲ Decompensated Amplifiers Although the LTC6268 is fairly stable at unity gain, there are still unstable op amps. By designing the amplifier compensation to be stable only at higher closed-loop gains, the design trade-off can provide a higher conversion rate, wider GBF, and lower input noise than the unity gain compensation scheme. Figure 5. shows the open loop gain and phase of the LTC6230-10. The amplifier is intended to be used with a feedback gain of 10 or greater, so the feedback network will attenuate the output by at least 10 times. Through this feedback network, you can find the frequency when the open-loop gain is 10V/V or 20dB, and find that the phase margin is 58° at 50MHz (±5V power supply). At unity gain, the phase margin is only about 0°, so the amplifier oscillates. Figure 5. LT6230-10 Gain and Phase Change with Frequency It is observed that when the closed-loop gain is higher than the minimum stable gain, all amplifiers will be more stable. Even a gain of 1.5 will make a unity gain stable amplifier much more stable.   Ⅳ Feedback Network The feedback network itself may also cause oscillations. In Figure 6, put a parasitic capacitor in parallel with the feedback divider resistor. It is inevitable that each terminal of each component on the circuit board has a capacitance of about 0.5pF to the ground, and there is also a wiring capacitance. Figure 6. Parasitic Capacitance In fact, the minimum capacitance of the node is 2pF, and there is about 2pF of wiring capacitance per inch of trace. The accumulated parasitic capacitance can easily reach 5pF. Using LTC6268, in order to reduce the power, we set the values of Rf and Rg to a very high 10kΩ. When Cpar = 4pF, the feedback network has a pole at 1/(2π*Rf||Rg*Cpar) or 8MHz. The phase lag of the feedback network is -atan(f/8MHz), we can estimate that the loop will have a phase lag of 360° around 35MHz. At this time, the phase lag of the amplifier is -261°, and the feedback network lags about -79°. At this phase and frequency, the amplifier still has a gain of 22dB, and the gain of the voltage divider is .At the 0° phase, the amplifier's 22dB multiplied by the feedback divider's –19dB produces a +3dB loop gain, and the circuit oscillates. In order to operate normally in the presence of parasitic capacitance, we must reduce the value of the feedback resistor so that the feedback pole can far exceed the unity gain frequency of the loop. That is, the ratio of the pole to the GBF should be at least 6 times.The input end of the op amp itself may also have a considerable capacitance, the same as Cpar. In particular, low noise and low Vos amplifiers have large input transistors and may have larger input capacitance than other types of amplifiers, and the input capacitance is loaded on the amplifier's feedback network. We need to consult the data sheet to understand how much capacitance will be connected in parallel with Cpar. Fortunately, the LT6268 has only 0.45pF capacitance, which is already very low for such a low noise amplifier. The macro model running on LTspice® provided free of charge by ADI can be used to simulate a circuit with parasitic capacitance. Figure 7. shows how to improve the capacitor tolerance of the voltage divider. Figure 7(a) shows a non-negative output amplifier configuration with Rin. Assuming that Vin is a low impedance source (<Rin), Rin will effectively attenuate the feedback signal without changing the closed-loop gain. And it will also reduce the impedance of the voltage divider and increase the feedback pole frequency, which is expected to far exceed GBF. In addition, Rin reduces the bandwidth around the loop and amplifies the input offset and noise.Figure 7(b) shows a negative output configuration. Rg still performs loop attenuation without changing the closed loop gain. In this case, the input impedance is not affected by Rg, but the noise, offset and bandwidth parameters will deteriorate.Figure 7(c) shows the preferred method of compensating Cpar in a non-inverting amplifier. If we set Cf* Rf = Cpar * Rg, then we have a "compensation attenuator", so that the feedback divider now has the same attenuation at all frequencies and solves the Cpar problem. The mismatch in the product will cause "bumps" in the passband of the amplifier and "shelf" in the response curve (At this time, the low-frequency response is flat, but becomes straight near f = 1/2 * Cpar * Rg.).Figure 7(d) shows the equivalent Cpar compensation for the negative output amplifier. The frequency response must be analyzed to find a correct Cf, and the bandwidth of the amplifier is part of the analysis.Here are some comments on current feedback amplifiers (CFA) in turn. If the amplifier in Figure 7(a) is a CFA, then "Rin" has little effect on changing the frequency response, because the negative input is very low impedance and actively copies the positive input. The noise index will degrade slightly, and the additional negative input bias current will actually appear in the form of Vos/Rin. Similarly, in terms of frequency response, the circuit in Figure (b) is not changed by "Rg". The inverting input is not just a virtual ground, it is a real ground with low impedance, and Cpar has been tolerated (only in negative output mode). The DC error is similar to the situation shown in (a), (c) and (d) may be the preferred solution for voltage input op amps, but CFA can't tolerate a direct feedback capacitor without oscillation at all.   Ⅴ Load Problem Just as the feedback capacitor can damage the phase margin, the load capacitor can do the same. Figure 8 shows the change in LTC6268 output impedance with frequency in the case of several gain settings. Note that the unity gain output impedance is lower than the output impedance at higher gains. Full feedback enables the open-loop gain to reduce the inherent output impedance of the amplifier. Therefore, in Figure 8, the output impedance at a gain of 10 is generally 10 times the output impedance at unity gain. Since the feedback attenuator reduces the loop gain, the gain around the loop is 1/10, otherwise it will reduce the closed-loop output impedance. The open-loop output impedance is about 30, which is obvious in the high-frequency flat region of the curve with a gain of 100. In this area, from around gain bandwidth frequency (about 100) to gain bandwidth frequency, there is not enough loop gain to reduce the open loop output impedance. Figure 8. Impedance and Frequency of LTC6268 Under Three Gain Conditions The capacitor load will cause the phase lag and amplitude attenuation of the open-loop output impedance. For example, a 50pF load and our LTC6268 output impedance form another pole at 106MHz, where the output has a –45° phase lag and –3dB attenuation. At this frequency, the amplifier has a phase of -295° and a gain of 10dB. Assuming unity gain feedback is used, we have not fully realized the oscillation because the phase is not brought to ±360° (at 106MHz). However, at 150MHz, the amplifier has 305° phase lag and 5dB gain. The phase of the output pole is –atan(150MHz/106MHz) = -55°, and the gain is .Multiplying the gain cyclically, we get a 360° phase and +0.2dB gain, which is another oscillator. 50pF seems to be the minimum load capacitance that will force the LTC6268 to oscillate.The most common way to prevent oscillations caused by the load capacitor is to simply connect a small resistor in series to the capacitor after the feedback connection. The resistance value of 10Ω to 50Ω will limit the phase lag that may be caused by the capacitive load and isolate the amplifier and low capacitive impedance when the speed is very high. Disadvantages include DC and low frequency errors that vary with load resistance characteristics, capacitive load frequency response is limited, and signal distortion caused if the load capacitance is not constant when the voltage changes.Increasing the closed-loop gain of the amplifier can often prevent the oscillation caused by the load capacitance. Operating the amplifier with a higher closed-loop gain means that at frequencies where the loop phase is ±360°, the feedback attenuator also attenuates the loop gain. For example, if we use the LTC6268, its closed-loop gain is +10, then we will see that the amplifier has a gain of 10V/V or 20dB at 40MHz and a phase lag of 285°. To ignite the oscillation, an output pole is required, causing an additional 75° hysteresis. By -75° =-atan(40MHz/Fpole) →Fpole =10.6MHz, we can find the output pole. This pole frequency comes from a load capacitance of 500pF and an output impedance of 30Ω. The output pole gain is .When the unloaded open-loop gain is 10, the loop gain at the oscillation frequency point is 0.26, so there is no oscillation this time, at least no oscillation caused by the simple output pole. In this way, we increased the tolerable load capacitance from 50pF to 500pF by increasing the closed-loop gain.In addition, unterminated transmission lines are also very bad loads because they will cause "runaway" impedance and phase changes that repeat with frequency (See the impedance of an unterminated 9-foot cable in Figure 9).If your amplifier can safely drive the cable under certain low-frequency resonance conditions, it is likely to oscillate at a higher frequency because its own phase margin is reduced. If the cable must be unterminated, a "back-match" resistor in series with the output can isolate the cable's extreme impedance changes. In addition, even if the transient reflection from the this end of the cable just recoils back to the amplifier, if the resistance of the backward matching resistor matches the characteristic impedance of the cable, the resistor can properly absorb this energy. If the backward resistor does not match the cable impedance, some energy will be reflected from the amplifier and terminals, and back to the unterminated end. When the energy reaches this end, it is quickly reflected back to the amplifier. As a result, there is a series of pulses bouncing back and forth, but attenuate each time. Figure 9. Impedance and Phase of the Unterminated Coaxial Cable Figure 9 shows a more complete output impedance model. The ROUT is the same as what we discussed in the LTC6268, and it is also 30Ω, in addition, add the Lout item. This is a combination of physical inductance and electronic equivalent inductance. The physical package, bonding wire, and external inductance add up to 5nH to 15nH. The smaller the package, the smaller the total value. Figure 10. Inductive Component of Amplifier Output Impedance In addition, any amplifier has an electrical inductance of 20nH to 70nH, especially bipolar devices. The finite Ft of the device turns the parasitic base resistance of the output transistor into an inductance. The harm is that Lout and CL may interact to form a series resonant circuit, then the same problem comes again. If there is no greater phase lag in the loop, the impedance of the series resonant circuit may drop to a level that Rout cannot drive. This may cause oscillations. For example, set Lout = 60nH and CL = 50pF. Resonant frequency is .Just within the passband of the LTC6268. In fact, this series resonant circuit is loaded to the output terminal during resonance, which changes the phase of the loop greatly near the resonant frequency. Unfortunately, Lout is not mentioned in the amplifier's data sheet, but its effect can sometimes be seen on the open-loop output impedance circuit. In short, for amplifiers with a bandwidth of less than 50MHz, this effect is not important.One solution is shown in Figure 10. Rsnub and Csnub form a so-called "shock absorber" whose purpose is to reduce the Q value of the resonant circuit so that the resonant circuit does not have a very low resonant impedance to the output of the amplifier. The value of Rsnub is usually estimated as the reactance of CL to reduce the Q value of the output resonance circuit to about 1. Adjust the size of Csnub to fully insert Rsnub into the output resonance frequency, that is, the reactance of Csnub <Cl. Csnub = 10 * CL is practical. Csnub unloads the amplifier at intermediate and low frequencies, especially at DC. If it is very large, Rsnub will put a heavy load on the amplifier at intermediate frequency, which will affect the low frequency, gain accuracy, closed-loop bandwidth and distortion. However, after a little fine-tuning, shock absorbers are often useful for controlling reactive loads, but shock absorbers must be adjusted through experiments. Figure 11: Using an Output Shock Absorber The negative input of the current feedback amplifier is actually a buffer output and will also have the series characteristics shown in Figure 8. Therefore, it may oscillate under the action of Cpar, just like the output terminal. You should try to reduce Cpar and any related inductance. Unfortunately, the damper on the negative input terminal modifies the relationship between closed-loop gain and frequency, so it is not very useful.   Ⅵ Strange Impedance Many amplifiers have an abnormal input impedance at high frequencies. This is most true for amplifiers with two input transistors in series, such as the Darlington configuration. Many amplifiers have PNP/NPN transistor pairs at the input, and their behavior changes with frequency similar to the Darlington configuration. The real part of the input impedance will become negative at some frequencies (generally much higher than GBF). Inductive source impedance will resonate with the input and circuit board capacitance, and negative real components may provoke oscillations. When driving with unterminated cables, this can also cause oscillations at many repetition frequencies. If it is inevitable to use a long inductive wire at the input, you can disconnect the wire with several series-connected resistors that can absorb energy, or install a medium-impedance shock absorber (about 300Ω) on the input lead of the amplifier.   Ⅶ Power The last source of oscillation to consider is power supply bypass. Figure 10 shows part of the output circuit. LVS+ and LVS– are the unavoidable packaging, IC bond wires, the physical length of the bypass capacitor (inductive like any conductor), and the series inductance of the circuit board traces. It also includes the external inductance that connects the local bypass component to the rest of the power bus (if not the power plane). Although 3nH to 10nH may seem small, at 200MHz, it is 3.8 to 12Ω. If the output transistor conducts a large high-frequency output current, there will be a voltage drop across the power inductor. Figure 12. Power Supply Bypass Capacitor Details The rest of the amplifier needs a noise-free power supply, because these parts cannot suppress power supply noise as the frequency changes. In Figure 13 we can see the power supply rejection ratio (PSRR) of the LTC6268 with frequency. In all operational amplifiers, because there is no ground pin, the compensation capacitor is connected to the power supply, which will couple power supply noise into the amplifier, and gm must cancel this noise. Due to the compensation, PSRR decreases with 1/f, in addition, the power supply rejection actually increases after 130MHz. Figure 13. LTC6268 Power Supply Rejection with Frequency Variation At 200MHz, due to the increase of PSRR, the output current may interfere with the power supply voltage inside the LVs inductor. Through the amplification of PSRR, the interference becomes a strong amplifier signal, driving the output current, generating internal power signals, etc., causing the amplifier to oscillate. This is why the power supplies of all amplifiers must be carefully bypassed with traces and components with very small inductance. In addition, the power supply bypass capacitor must be much larger than any load capacitor.If consider the frequency around 500MHz, then the range 3nH to 10nH becomes 9.4Ω to 31.4Ω. This is enough for the output transistor to generate self-oscillation by its inductance and IC component capacitance, especially when the output current is large (transistor gm and bandwidth increase). Because the bandwidth of transistors is very large, special attention needs to be paid, especially at high output currents.   Ⅷ Conclusion In short, the designer needs to consider the parasitic capacitance and inductance associated with each op amp terminal and the natural characteristics of the load. Usually the designed amplifier is very stable in the nominal environment, but each application needs to analyze it by itself.   Ⅸ FAQ 1. Does your op amp oscillate?Well, it shouldn't. We analog designers take great pains to make our amplifiers stable when we design them, but there are many situations that cause them to oscillate in the real world. ... Improperly designed feedback networks can cause instability. Insufficient supply bypassing can offend. 2. What is oscillator in op amp?An oscillator is an electronic circuit that produces a periodic signal. ... The feedback network takes a part of the output of amplifier as an input to it and produces a voltage signal. This voltage signal is applied as an input to the amplifier. 3. What causes an amplifier to oscillate?Causes of parasitic oscillationParasitic oscillation in an amplifier stage occurs when part of the output energy is coupled into the input, with the correct phase and amplitude to provide positive feedback at some frequency. ... Similarly, impedance in the power supply can couple input to output and cause oscillation. 4. How do you compensate an op amp?Another effective compensation technique is the miller compensation technique and it is an in-loop compensation technique where a simple capacitor is used with or without load isolation resistor (Nulling resistor). That means a capacitor is connected in the feedback loop to compensate the op-amp frequency response. 5. How can an op amp improve stability?To ensure stability, the value of RX should be such that the added zero (fZ) is at least a decade below the closed loop bandwidth of the op amp circuit. With the addition of RX,circuit performance will not suffer the increased output noise of the first method, but the output impedance as seen by the load will increase. 6. What are the requirements of oscillations in an amplifier?Oscillations around the 3dB bandwidth of the amplifier are usually due to input/output feedback. Higher frequency oscillations may only be visible on a spectrum analyzer. They may cause waveform distortion and be affected by touching the amplifier on power and signal cables. 7. How do you stop an oscillating op amp?If the op-amp still oscillates, try these things, in this order:1) Add a small resistor to the op-amp's output, either inside or outside the feedback loop. ...2) Do the same as in the previous step, except use a ferrite bead or chip ferrite instead of the resistor. ...3) Raise the amp's gain a bit. 8. How do you increase the gain margin of an op amp?You can increase the phase margin by making a dominant pole nearer to the zero frequency origin. This is accomplished by compensating the op amp through adding a shunting capacitor in the highest impedance node of the amplifier. This is a very well known technique which is used commonly to increase the phase margin. 9. Why the gain of op amp deteriorate with frequency?All opamps have a limit on upper frequency. In a LPF, at low frequencies, the output amplitude is equal to input. But as the frequency increases, the capacitive reactance decreases and the output amplitude starts to decrease. 10. What is used to avoid or minimize instability in amplifiers?It is often desirable to use capacitance to ground from an amplifier's active input terminals to reduce high-frequency interference, RFI and EMI. This filter capacitor has a similar effect on op amp dynamics as increased stray capacitance. 11. Why op amps oscillate an intuitive look at two frequent causes?With delay in the loop, the amplifier does not immediately detect its progress toward the final value. ... It overreacts by racing too quickly toward the proper output voltage. Note the faster initial ramp rate with delayed feedback. 12. How does an op-amp oscillator work?The Op-amp Multivibrator is an astable oscillator circuit that generates a rectangular output waveform using an RC timing network connected to the inverting input of the operational amplifier and a voltage divider network connected to the other non-inverting input.

ⅠIntroduction The most common system is single-phase, which is mostly used in homes, whereas three-phase is commonly used in industrial or commercial buildings where heavy loads of power are required. Catalog ⅠIntroduction Ⅱ Three-phase Power Related Video: Ⅲ Single-phase AC Power Basics 3.1 What is Single-phase AC power? 3.2 Advantages of Single-phase 3.3 Disadvantages of Single-phase   Ⅳ 3-phase Power Explained 4.1 What is 3-phase Power? 4.2 Advantages of Three-Phase System 4.3 Disadvantages of Three-Phase System Ⅴ Why We Need 3-phase Power？ Ⅵ What Are the Differences Between Single-Phase Power and Three-Phase Power? Ⅶ FAQ   Ⅱ Three-phase Power Related Video: Three-Phase Power Explained   Three-phase Video Description: This video will take a close look at three-phase power and explain how it works. Three-phase power can be defined as the common method of alternating current power generation, transmission, and distribution. It is a type of polyphase system, and is the most common method used by electric grids worldwide to transfer power.   Ⅲ Single-phase AC Power Basics Single-phase electric power is the distribution of alternating current electric power using a system in which all of the supply voltages vary in unison. When the loads are mostly lighting and heating, with only a few large electric motors, single-phase distribution is used.   3.1 What is Single-phase AC power? Before delving into that topic, it's a good idea to first understand single-phase alternating current (AC). Single-phase alternating current (AC) power is delivered via a three-wire system consisting of one "hot" wire, one neutral wire, and one ground wire. With alternating current power, the power current or voltage reverses on a regular basis, flowing one way on the hot wire that supplies power to the load and the other way on the neutral wire. During a 360-degree phase change, a full power cycle occurs, and the voltage reverses itself 50 or 60 times per second, depending on the system in use in different parts of the world. It is 60 times or 60 hertz in North America (Hz). It is critical to note that the two current-carrying legs are always 180 degrees apart. Consider the power as riding a wave, specifically a sine wave with a defined frequency and amplitude. During each cycle, the waves on each wire pass through zero amplitude twice (see Figure 1). There is no power delivered to the load during these times. Figure1:Single-phase   These brief interruptions have no effect on residential and commercial building applications such as office environments, but they have serious consequences for the motors that power large machinery, as well as computers and other IT equipment.   3.2 Advantages of Single-phase Single-phase connections are designed for household supplies and residential homes. This is due to the fact that most appliances, such as televisions, lights, fans, refrigerators, and so on, require only a small amount of electricity to function.A single-phase connection works in a straightforward manner. It consists of a compact and lightweight unit in which the flow of electricity through the wires is reduced as the voltage increases.Because of the power reduction, it ensures that the power from a single-phase connection operates at peak efficiency and effectively transmits power.A single-phase connection is best suited for units rated up to 5 horsepower.   3.3 Disadvantages of Single-phase     Ⅳ 3-phase Power Explained Three-phase electric power (abbreviated 3), is a type of alternating current that is commonly used in power generation, transmission, and distribution. It is a type of polyphase system that uses three wires (or four if a neutral return wire is used) and is the most common method used by electrical grids around the world to transfer power.   4.1 What is 3-phase Power? As the name implies, three separate currents are provided by three-phase power systems, each separated by one-third of the time it takes to complete a full cycle. However, unlike single-phase, where the two hot legs are always 180 degrees apart, the currents in 3-phase are separated by 120 degrees. Figure 2 shows that when one line is at its peak current, the other two are not. When phase 1 reaches its positive peak, phases 2 and 3 are both at -0.5. In contrast to single-phase current, there is no point at which no power is delivered to the load. In fact, one of the lines is at a peak positive or negative position at six different points in each phase. In practice, this means that the total amount of power supplied by all three currents remains constant; there are no cyclical peaks and valleys as with single-phase. Many computers and motors used in heavy machinery are built with this in mind. Instead of having to account for the variation inherent in single-phase AC power, they can draw a steady stream of constant power. They use less energy as a result. Consider the difference between a single-cylinder and a three-cylinder engine. Both use a four-stroke engine (intake, compression, power, exhaust). With a single-cylinder engine, you only get one "power" cycle for every four-cylinder stroke, resulting in rather uneven power delivery. A three-stroke engine, on the other hand, produces power in three alternating phases (again separated by 120 degrees), resulting in smoother, more consistent, and efficient power. Figure2:Three-phase 4.2 Advantages of Three Phase System There are numerous reasons why this power is preferable to single-phase power. The single phase power equation is   Figure3: single phase power equation Which is a function that changes over time. In contrast, the three-phase power equation is   Figure4: three-phase power equation Which is a constant function that is independent of time. As a result, the single-phase power is pulsing. This has no effect on low-rated motors, but it causes excessive vibration in higher-rated motors. As a result, three-phase power is preferable for high-tension power loads. A three-phase machine has a 1.5 times higher rating than a single-phase machine of the same size. Because single-phase induction motors have no starting torque, we must provide an auxiliary means of starting, whereas three-phase induction motors are self-starting and do not require any auxiliary means. In the case of a three-phase system, the power factor and efficiency are both higher. Which is a constant function that is independent of time. As a result, the single-phase power is pulsing. This has no effect on low-rated motors, but it causes excessive vibration in higher-rated motors. As a result, three-phase power is preferable for high-tension power loads. A three-phase machine has a 1.5 times higher rating than a single-phase machine of the same size. Because single-phase induction motors have no starting torque, we must provide an auxiliary means of starting, whereas three-phase induction motors are self-starting and do not require any auxiliary means. In the case of a three-phase system, the power factor and efficiency are both higher.   4.3 Disadvantages of 3-phase Power The most significant disadvantage of a three-phase connection is that it cannot handle the overload. As a result, it may cause damage to the equipment, increasing the likelihood of costly repairs. This is due to the high cost of individual components. Because the unit voltage is so high, a three-phase power connection necessitates a significant investment in insulation. Insulation varies with voltage, and wire size is determined by power distribution.   Ⅴ Why We Need 3-phase Power？ The ability to deliver ever-increasing amounts of power is especially important as data centers and server rooms become denser. More powerful computing systems are being crammed into the same spaces that once housed servers that used a fraction of the electrical power that today's computers and networks require. Not long ago, a single IT rack of ten servers would consume a total of five kilowatts (kW). Today, that same rack may house dozens of servers, each drawing 20 or 30 kW. At those levels, efficiency is important, as even a small percentage improvement in power consumption will result in significant dollar savings over time. Another issue is wiring. Take a look at a 15 kW rack. Using single-phase power at 120 volts AC (VAC), it takes 125 amps to power the rack, which would necessitate a wire almost one-quarter inch in diameter (AWG 4) — too thick to work with easily, let alone affordably. Because three-phase is more efficient, it can deliver the same amount of power (and more) while using less wiring. To support the same 15 kW rack with 3-phase power, three wires capable of supplying 42 amps (AWG 10) are required, each less than one-tenth of an inch in diameter.   Ⅵ What Are the Differences Between Single-Phase Power and Three-Phase Power? The following are the key distinctions between a single-phase and three-phase connection. Ⅶ FAQ 1. How is 3phase power generated? Electric power is generated as three phase alternating current (AC) by turning mechanical turbines from the forces of water, steam, or other means in order to turn generators, thereby, converting the mechanical energy into electric energy. In the US, generators turn at 60 revolutions per second or at 60 hertz (Hz). 2. Why does three phase not need a neutral? A neutral wire allows the three phase system to use a higher voltage while still supporting lower voltage single phase appliances. In high voltage distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases (phase-phase connection). 3. How many wires does 3 phase have? four wires Three-phase has four wires: three actives (called phases) and one neutral. The neutral wire is earthed at the switchboard. 4. How do you make 3 phase voltage? In a 3 phase system, there are three equal voltages or EMFs of the same frequency having a phase difference of 120 degrees. These voltages can be produced by a three-phase AC generator having three identical windings displaced apart from each other by 120 degrees electrical. 5. Does three-phase need a ground? Does the National Electrical Code (NEC) require a 480-volt (V), three-phase, 3-wire, delta-connected system to be grounded? No, it is optional. This article examines the NEC's electrical-system grounding provision. 6. What is the symbol for 3 phase? A three-phase system may be arranged in delta (∆) or star (Y) (also denoted as wye in some areas). 7.Is 240V single phase or 3 phase? 240V power is used in the US and parts of the world. In the US 120 / 240V 1 Phase 3 Wire is the standard for homes and 240V 3 Phase Open Delta is the standard for small buildings with large loads. In parts of the world 240V Single Phase 2 Wire is the standard for homes. 8. What is the value of 3 phase voltage? 3 phase system is expressed with line voltages. The line votage is 440 volt. Also the voltage between any one phase and neutral for a 3 phase system is 240 volts. 9. What is single-phase power used for? Single-Phase Power generates electricity to residential homes and domestic supplies, since most appliances require only a small amount of power to function, including fans, heaters, television, refrigerator, and lights. 10. Why does single phase have 2 wires? Two hot wires and one neutral wire provide the power. Each hot wire provides 120 volts of electricity. The neutral is tapped off from the transformer. A two-phase circuit probably exists because most water heaters, stoves and clothes dryers require 240 volts to operate. 11. Can we use 2 AC in single phase? You can, yes. The main MCB has a current rating of at least 25 ampere. If you use 1.5 ac, it has max load current of 7 to 8 amperes for a single ac, and the MCB size is to be selected. 12.Is 240 volt single-phase? Single Phase 120/240 It may also be called Split Phase 240. This configuration consists of 2 voltage legs that are 180 degrees apart. The voltage between the two legs (called phase to phase or line to line) is 240V and the phase to neutral voltage is 120V.  

Ⅰ IntroductionA motion sensor is a kind of security system. And the linchpin of your security system is a motion sensor (or motion detector) as it detects when someone is in your home who should not be there. A motion sensor detects movement in an area with one or more technologies.When a sensor detects motion, it sends a signal to the control panel of your security system, which is connected to your monitoring center. This notifies you and the monitoring center that there is a potential threat in your home.CatalogⅠ IntroductionⅡ Motion Sensor Related Video:Ⅲ What is a Motion Sensor?Ⅳ Types of Motion SensorsⅤ How do Active Ultrasonic Sensors and Passive Infrared (PIR) Work?5.1 Active Ultrasonic Sensors5.2 PIR SensorsⅥ How to Install a Motion Sensor?Ⅶ Other Uses for Motion SensorsⅧ FAQ Ⅱ Motion Sensor Related Video:How PIR Sensor Works and How To Use It with ArduinoMotion Sensor Video Description：In this Arduino Tutorial we will learn how a PIR Sensor works and how to use it with the Arduino Board for detecting motion. Ⅲ What is a Motion Sensor?A motion sensor (or motion detector) is a genre of electronic device that detects and calculates movement. We can often find motion sensors in the home and business security systems,  as well as in phones, paper towel dispensers, game consoles, and virtual reality systems. Unlike many other types of sensors, motion sensors can not be handled and isolated as they are in embedded systems comprised of three major components: a sensor unit, an embedded computer, and hardware (or the mechanical component). Because motion sensors can be customized to perform highly specific functions, these three parts vary in size and configuration. Motion sensors, for example, can be used to activate floodlights, sound audible alarms, activate switches, and even alert the police. Figure1: Motion SensorⅣ Types of Motion SensorsActive Ultrasonic SensorsActive sensors have a transmitter as well as a receiver. This sensor detects motion by measuring changes in the amount of sound or radiation that is reflected back into the receiver. Passive infrared (PIR)A passive infrared sensor detects body heat (infrared energy) by monitoring temperature changes. This is the most common type of motion sensor found in home security systems. Figure2:Passive infrared (PIR) Microwave (MW)This type of sensor emits microwave pulses and detects reflections from moving objects. 1 They have a larger coverage area than infrared sensors, but they are more expensive and susceptible to electrical interference. Figure3:Microwave (MW) Dual technology motion sensorsThis type of sensor emits microwave pulses and detects reflections from moving objects. 1 They have a larger coverage area than infrared sensors, but they are more expensive and susceptible to electrical interference. Figure4: Dual technology motion sensorsEach sensor type operates in a different part of the electromagnetic spectrum (ranging from passive to active). Dual technology motion sensors are less likely to cause false alarms than other types because both sensors must trip to sound an alarm. This is not to say that they never cause false alarms. Less common types of motion detectorsTomographic motion sensors are composed of several nodes. The nodes connect to form a mesh network. When the link between two nodes is broken, these sensors detect the presence of a person or object.Vibration motion sensors detect people and objects by detecting small vibrations caused by movements such as footsteps. Ⅴ How do Active Ultrasonic Sensors and Passive Infrared (PIR) Work?The two most common motion sensor technologies are active ultrasonic sensors and passive infrared sensors, both of which are well-known for their accuracy and dependability.5.1 Active Ultrasonic SensorsActive ultrasonic sensors produce ultrasonic sound waves that are higher in frequency than the human hearing range. These waves are bouncing off nearby objects and returning to the motion sensor. A transducer within the sensor serves as a signal waypoint, sending the pulse and receiving the echo. The sensor calculates the distance between itself and the target by measuring the time between signal transmission and reception. Most motion sensors allow you to adjust the sensitivity, which means it won't trigger if the distance between the sensor and the object is too great. If the received signal falls within the specified parameters, the motion sensor will activate, alerting you that someone or something is close to the sensor.Motion sensors installed at entry points such as windows and doors can be programmed to sound a burglar alarm. Door and window sensors are specifically designed to detect an intruder, so you should not experience false alarms or excessive notifications.Ultrasonic sensors are capable of detecting objects regardless of color, surface type, or material type (i.e., metallic vs. non-metallic). They can detect translucent objects as well, though this is typically reserved for industrial applications.Figure5:Active ultrasonic sensors 5.2 PIR SensorsPIR sensors are more complicated than active ultrasonic sensors, but the results are the same.Walls, floors, stairwells, windows, cars, dogs, trees, people—you name it—emit heat. Temperature can be detected using infrared waves. Infrared motion sensors detect the presence of a person or object by measuring the temperature change in a specific area. 5.3 Example of PIR SensorsTo demonstrate how this works, we'll use a motion detection camera, though any PIR motion sensor will do.A PIR camera contains two sensors. When no one is present, the PIR camera detects ambient IR emitted by background objects such as walls and doors. When a person (or animal, object, etc.) moves in front of the camera, the first sensor detects their heat signature, causing the camera to activate, triggering your alarm, and sending you an alert. If the object moves out of the camera's field of view, the second sensor will activate, noting the sudden drop in temperature.These temperature changes are used by a PIR motion sensor to detect the presence of a person or object. PIR sensors, like active ultrasonic sensors, can be configured to ignore small changes in IR, allowing you to walk around your home or business without setting off alarms all day and night. Ⅵ How to Install a Motion Sensor?Typical motion sensors have a range of up to 80 feet, which means that a single sensor will most likely not cover a long hallway or an open workspace. You can have your security system installed by a security company such as Bay Alarm. Our installers will examine the layout of your space to determine the best location for motion sensors. Our goal, as with security cameras, fire alarms, and burglar alarm installations, is to make your home or business as secure as possible, with devices and components strategically placed.After the sensors have been installed, a security agent will integrate them with your burglar alarm system. Using one of two apps: SureHome by Bay Alarm or Bay Alarm Access, you'll have quick access to your entire security system from your phone.If you decide to do your own security, make sure to follow the instructions that come with the sensor. Here are some pointers for installing motion detectors in your home or business: Step1:Take your motion detector out of the box.Your motion sensor kit should include instructions as well as mounting hardware. If your device has separate batteries, insert them into your motion sensor now. Step2:TDecide on a locationCorners are ideal because they allow you to position infrared sensors to cover the most ground. Most motion sensor designs have angled edges with screw holes to fit neatly into a room's corner.Mount your motion detector high on the wall to get the best coverage—but avoid putting it over a large piece of furniture, like a bookshelf or entertainment center, because it will limit the passive infrared energy range.Mount your motion sensor opposite the main entrance—this applies in every room or hallway where you place these sensors so they can detect intruders right away. Step3:Mount the sensorBecause passive infrared sensors are lightweight, you won't need drywall anchors or studs. A standard screwdriver will suffice, but an electric screwdriver or drill will expedite the process.Most motion detectors include a mounting bracket that detaches from the main body of the device, allowing you to screw it into the wall first, then clip the motion sensor back in. This also makes removing the motion detector from the wall during maintenance easier. Other infrared sensors may necessitate a complete disassembly before mounting. Step3: Connect your sensor to your systemConnect your motion sensor to your system according to the manufacturer's instructions. Most DIY systems will walk you through this process, frequently using the main keypad or a mobile app to configure and adjust your motion detectors.TIPS: Z-Wave-enabled smart motion sensors connect to your phone for easy access and notifications. Whether you're just getting started with your smart home build or you already have dozens of connected devices, Z-Wave-enabled motion sensors are a worthwhile addition. Step4: Adjust your motion detection settingsWhen you arm your system, most motion detectors have three main settings:In instant mode, any movement sets off an alarm.In entry delay mode, the sensor operates on a delay; even if it detects motion, you have approximately 30–60 seconds to disarm the system before an alarm is triggered.Interior follow-up mode operates on an entry delay, but only when the door contact triggers first—it sounds an instant alarm if it detects motion in the home without the door contact triggering. Step6: Maintain your motion detectorDust and debris can accumulate on the screen of your motion sensor over time, interfering with the infrared energy and making it less effective at motion detection. Use a dry or slightly damp microfiber cloth to clean it at least once every couple of months.If you decide to paint a wall near your motion sensor, make sure to first remove the device. If paint gets on a passive infrared motion sensor, it must be replaced. Additional tips for installing motion sensorsTake into account the size of your pets.Overhangs reduce range.Do not obstruct the infrared.Not all motion sensing light switches are created equal. Ⅶ Other Uses for Motion SensorsMotion sensors are useful for more than just home security. Many industrial fields use them on assembly lines to count the number of products and to shut down dangerous equipment if someone gets too close.Here are a few other uses for motion sensorsTo automate the opening and closing of doorsTo activate and deactivate automatic water faucets and toiletsWhen a person enters a room, lights are turned on.ATM display controlAt ticket vending machinesFor certain parking meter Ⅷ FAQ1. Which motion sensor is best?Best Motion SensorsPhilips. Hue Smart Motion Sensor. A solid choice if you are looking for a motion sensor for indoor use that's also intuitive. ...First Alert. Motion Sensing Light Socket. ...SadoTech. Wireless PIR. ...Chamberlain. Wireless Motion Sensor. ...1byone. Safety Driveway Patrol.2. Are motion sensors effective?Motion sensors are proven to be effective at leading to apprehensions. ... Motion sensors can be more cost-effective for rooms with many windows that would require several sensors to protect. A motion detector can alert you immediately if there is movement is detected.3. What can set off a motion detector?What can set off a motion detector? Moveable objects such as balloons, curtains, decorations, and pets can set off motion detectors. How to prevent this: Consider positioning motion sensors above waist level so pets can move around freely, and away from curtains and other items that may move or drift.4. Do motion detectors work in the dark?The short answer is yes. Motion sensors do work in complete darkness, as none of the motion sensors mentioned above are reliant on using images to detect motion. Instead of images, PIR motion sensors detect changes in the level of received infrared. Likewise, ultrasonic motion sensors also do not require images.5. How long do motion sensors last?On average, a motion detector light will stay on for up to 20 minutes. That amount of time is extended each time a sensor detects fresh movement, so it is possible for a motion detector light to stay on for much longer than 20 minutes at a time.6. Does motion sensor have camera?Most smart security cameras are motion sensor cameras. This means that they have a smart sensor built-in – and that's the key to your smart camera always being ready to record when something happens.7. What is the difference between PIR and motion sensor?As the name implies, motion sensors detect moving objects outside or even inside your home. They are often tied to lights, alarms, security cameras, and most recently, smart doorbells. ... PIR or Passive Infrared motion sensors are designed to reliably detect people, large pets & other large warm moving objects. 

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.

ⅠIntroductionA direct current (DC) motor is a type of rotary electrical motor that converts direct current electrical energy into mechanical energy. The most common types are based on magnetic field forces. Almost all types of DC motors have an internal mechanism, either electromechanical or electronic, that changes the direction of current in a portion of the motor on a regular basis.  CatalogⅠIntroductionⅡ Dc Motor Related VideoⅢ What is a DC Motor?Ⅳ How DC Motors Work？Ⅴ Types of DC Motors5.1 Shunt Wound DC Motor5.2 Series Wound DC Motor5.3 Compound Wound DC MotorⅥ Applications of DC MotorsⅦ Popular DC Motor BrandsⅧ What is the Difference Between an AC and DC Motor?8.1 AC Motor and It’s Mechanism8.2 Difference Between AC and DC MotorⅨ FAQ Ⅱ Dc Motor Related VideoDC Motor, How it works? Dc Motor Video Description：The working of a DC motor is well explained in this video with the help of animation. Construction details of DC Motor, Shunt & Series motor, concept of back EMF are also explained in this video. Ⅲ What is a DC Motor?A DC motor is an electric motor that runs on direct current (DC) (unlike an induction motor that operates via an alternating current). A direct current motor converts direct current electrical energy into mechanical energy.A direct current (DC) motor is a type of rotary electrical motor that converts direct current electrical energy into mechanical energy. The most common types are based on magnetic field forces. Almost all types of DC motors have an internal mechanism, either electromechanical or electronic, that changes the direction of current in a portion of the motor regularly. Figure1：What is a DC Motor?Ⅳ How DC Motors Work？Any rotary electrical machine that shifts direct current electrical energy into mechanical energy is referred to as a 'DC motor.' Small motors in toys and appliances to large mechanisms that power vehicles, pull elevators and hoists, and drive steel rolling mills are examples of DC motors. But how do direct current motors work?A stator and an armature are the two main components of a direct current motor. The stator is the motor's stationary component, while the armature rotates. In a direct current motor, the stator generates a rotating magnetic field that causes the armature to rotate.A simple DC motor generates an electromagnetic field aligned with the center of the coil by using a stationary set of magnets in the stator and a coil of wire with a current running through it. To concentrate the magnetic field, one or more windings of insulated wire are wrapped around the core of the motor.Insulated wire windings are connected to a commutator (a rotary electrical switch), which applies an electrical current to the windings. The commutator enables each armature coil to be energized in turn, resulting in a consistent rotating force (known as torque).When the coils are on and off in sequence, a rotating magnetic field is created that interacts with the varying fields of the stator's stationary magnets to produce torque, which causes it to rotate. These key operating principles of direct current motors enable them to convert electrical energy from direct current into mechanical energy via rotating movement, which can then be used for object propulsion. Figure2：working principleⅤ Types of DC MotorsDirect motors are classified based on how the field winding is connected to the armature.There are 3 main types of DC Motors: 5.1 Shunt Wound DC MotorFigure3：Shunt Wound DC Motor A DC shunt motor (also known as a shunt wound DC motor) is a type of self-excited DC motor in which the field windings are shunted to or paralleled with the motor's armature winding. The armature and field windings are exposed to the same supply voltage because they are connected in parallel. Though, as shown in the figure below, there are separate branches for the flow of armature current and field current.Figure4：DC shunt motor    5.2 Series Wound DC MotorFigure5：Series Wound DC Motor A series wound DC motor like a shunt wound DC motor or a compound wound DC motor, is a type of self-excited DC motor that gets its name from the fact that the field winding is connected internally in series to the armature winding. As a result, unlike a shunt motor, the field winding is exposed to the entire armature current.  Figure6：wound DC motor circuit 5.3 Compound Wound DC Motor A compound wound DC motor (also known as a DC compound motor) is a type of self-excited motor that is composed of both series and shunt field coils connected to the armature winding, as shown in the figure below.  Figure7：DC compound motor Both field coils provide the required amount of magnetic flux, which connects with the armature coil and produces the torque required to allow rotation at the desired speed. As we can see, a compound wound DC motor is created by combining a shunt wound DC motor and a series wound DC motor to achieve the best of both types. A shunt-wound DC motor, like a shunt-wound AC motor, has an extremely efficient speed regulation characteristic, whereas a DC series motor has a high starting torque.As a result, the compound wound DC motor strikes a balance between these two characteristics, offering a good combination of proper speed regulation and high starting torque.Though its starting torque is lower than that of a DC motor, and its speed regulation is not as good as that of a shunt DC motor. The overall characteristics of a DC shunt motor fall somewhere between these two extremes. Studying our electrical MCQs will help you learn more about motors.Types of Compound Wound DC Motor：Long Shunt Compound Wound DC MotorShort Shunt Compound Wound DC MotorCumulative Compounding of DC Motor  Ⅵ Applications of DC MotorsBecause of the various types of DC motors available, DC motors have a wide range of applications. The preceding section discussed some of the various applications and circumstances in which DC motors are used, as well as the advantages of the various types of motors.While each type has advantages, a DC motor can be used in a variety of ways. Small DC motors are used in tools, toys, and various household appliances at home. Conveyors and turntables are examples of DC motor applications in retail, while large DC motor applications in the industry include braking and reversing.Here are a few more specific uses for DC motors:DC motors for fansDC motors for pumpsDC motors for toysDC motors for electric carsDC motors for robotsDC motors for bikes Ⅶ Popular DC Motor BrandsPlease search the below online to view DC motors produced by some of our most popular brands.                                                                                  RS PRO                                                                               Crouzet                                                                                   Maxon  Ⅷ What is the Difference Between an AC and DC Motor?Electric motors are broadly classified into two types. They are the alternating current (AC) motor and the direct current (DC) motor. The AC motor is powered by alternating current, whereas the DC motor is powered by direct current.Figure8：Difference Between an AC and DC Motor 8.1 AC Motor and It’s MechanismA hoop of electromagnets is organized across the outside of an AC motor (making up the stator). Which can be configured to generate a rotating magnetic field. An axle made of solid metal, a wire loop, a coil, a squirrel cage made of metal bars, and interconnections are all found inside the stator. Other freely rotating metal parts that can conduct electricity are also present.The rotor, which is suspended within the magnetic field, acts as an electrical conductor. The magnetic field is constantly changing as a result of its rotation. The magnetic field generates (or induces) an electric current inside the rotor, according to Faraday's law of electromagnetism. If the conductor is a ring or a wire, the current flows in a loop around it. Instead, eddy currents swirl around a solid piece of metal if the conductor is simply a solid piece of metal.In any case, the induced current generates its magnetic field and, according to another electromagnetism law (Lenz's law), attempts to stop whatever is causing the rotating magnetic field by rotating as well. AC motors provide a relatively efficient way of generating mechanical energy from a simple electrical input signal.  Figure9：AC motor and DC notor 8.2 Difference Between AC and DC MotorAC MotorDC MotorAC motors do not require current conversion.Current is converted from alternative (AC) to direct (DC) output in DC motors.AC motors are available in two-phase, single-phase, and three-phase configurations.DC motors are all single phase.Armatures in alternating current motors do not rotate in tandem with the continuous rotation of magnetic fields.The armature rotates while the magnetic field rotates in DC motors.Repairing is not expensive.Repairs are quite expensive.Have a longer life expectancy.Have a shorter life expectancy.To begin operation, AC motors require effective starting equipment such as a capacitor.DC motors do not require any external assistance to begin operation.There are three input terminals.You should have two input terminals.When the load changes, AC motors are slow to respond.DC motors respond quickly to changes in load.AC motors are suitable for applications requiring high speed and variable torque.DC motors are appropriate for applications requiring high torque and variable speed.The speed of an alternating current motor is simply controlled by varying the frequency of the current.The speed of a direct current motor is controlled by varying the current of the armature winding.Implemented for large-scale industrial use.Intended for small-scale domestic use.The distinction between AC and DC motors is significant not only from a technical standpoint. It is also required for practical demonstrations. Whether you're an engineer or a business enthusiast, you can't choose the right one for your needs unless you understand the fundamental technical differences. Ⅸ FAQ1. How can you tell if a motor is AC or DC?Look for the stator core construction and rotor. If there is no commutator, then it is a AC motor. If there is a commutator and brushes, it may be either a DC motor or an AC commutator motor (Universal motor).2. Which motor is powerful AC or DC?AC motors are generally considered to be more powerful than DC motors because they can generate higher torque by using a more powerful current. However, DC motors are typically more efficient and make better use of their input energy.3. Why starter is used in DC motor?Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor's armature winding and restricts the current to an acceptable level.4. What is the voltage of a DC motor?Typical DC motors may operate on as few as 1.5 Volts or up to 100 Volts or more. Roboticists often use motors that operate on 6, 12, or 24 volts because most robots are battery powered, and batteries are typically available with these values. Operating Current.5. Is a brushless motor AC or DC?There are two types of commonly used DC motors: Brushed motors, and brushless motors (or BLDC motors). As their names imply, DC brushed motors have brushes, which are used to commutate the motor to cause it to spin. Brushless motors replace the mechanical commutation function with electronic control.6.Does Tesla use DC or AC motors?Tesla, for example, uses alternating current (AC) induction motors in the Model S but uses permanent-magnet direct current (DC) motors in its Model 3. There are upsides to both types of motor, but generally, induction motors are somewhat less efficient than permanent-magnet motors at full load.7. Are Tesla motors brushless?Today, all the hybrids are powered by DC brushless drives, with no exceptions. The only notable uses of induction drives have been the General Motors EV-1; the AC Propulsion vehicles, including the tzero; and the Tesla Roadster. Both DC brushless and induction drives use motors having similar stators.