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IntroductionDo you know buffer amplifier or isolation amplifier? The operational amplifier is an extremely efficient and versatile device. As we all known, the op amp is a component that amplifies the weak signal, which can be made into different forms according to the circuit requirements, and the voltage follower is one of them. Most voltage follower circuit will use an Op-amp. A follower is specifically an op amp wired to have a gain of +1. IE, the output is the same polarity and voltage as the input. That is, the output signal is exactly the same as the input signal. Here op amp voltage follower is used to isolate the signal and enhance load capacity. Op-amp as Voltage FollowerIntroductionⅠ Voltage Follower OP AmplifierⅡ Voltage Follower Characteristics2.1 Op Amp Impedance Matching2.2 Buffer Amplifier & Isolation AmplifierⅢ Op Amp Follower Circuit Analysis3.1 Op Amp Voltage and Load3.2 Op Amp Voltage Follower Stability3.3 Op Amp Phase Difference Problem3.4 Adding Feedback ResistanceⅣ Op Amp Voltage Follower ApplicationⅠ Voltage Follower OP AmplifierThe op amp follower sacrifices the voltage amplification factor in exchange for the performance of increasing the input impedance and reducing the output impedance. Because the gain of the op amp is extremely high, the input impedance of the op amp follower tends to be infinite, and the output impedance tends to zero. Within the rated output current range, the feedback voltage is equal to the output voltage, the output voltage is in phase with the input voltage, and the output voltage is slightly smaller than the input voltage. It should be noted that voltage follower is a special case of negative feedback amplifier (voltage series).Op amp voltage follower is actually a simple circuit structure which play a role in impedance matching. When a weaker signal is used to drive a relatively high current, voltage follower is often added in the middle, so that it can make weak signal stronger. It improves the load capacity to a considerable extent, while ensuring that the waveform and amplitude of the signal remain unchanged.For example, a single-chip microcomputer outputs a PWM signal to control LED lights. One LED does not require much current, so there is generally no big problem, however, when multiple LEDs need to light, current may definitely not large enough. If the current output is not enough, which may affect the signal output by the single-chip microcomputer, in this way, the voltage follower comes in handy.Ⅱ Voltage Follower Characteristics2.1 Op Amp Impedance MatchingWhen the op amp gain is approximately 1, that is, the magnification is approximately 1. The "follow" in the follower means that the voltage remains unchanged before and after, and the output waveform is almost not lost. It can be composed of transistors or operational amplifiers (best). Because the op amp input impedance is large and the output impedance is small, voltage follower can reduce the impact on the signal and improve the load capacity.2.2 Buffer Amplifier & Isolation AmplifierHere is a question, how to understand the buffering effect? Is the voltage of the former having a small impact on the back circuit? No, it is equivalent to a constant voltage source. Within the design requirement, no matter how the circuit connected to the subsequent stage changes, the output voltage is constant and does not change. In this way, the magnification or other performance of the previous stage can be kept unchanged. Otherwise, if the previous-stage input impedance is large, and the latter stage is small, the signal will definitely be distorted. For example, if a sinusoidal voltage waveform with a peak value of 10V, the sinusoidal peak value loaded to the latter stage may only be 8V. After adding a voltage follower, the waveform loaded on the input of the voltage follower will basically not change, and the input-output stage voltage ratio is very close to unity. So there will be no distortion.Since the output impedance of the voltage amplifier is generally relatively high, usually in the range of several kiloohms to tens of kiloohms. If the input impedance of the subsequent stage is relatively small, part of the signal will be lost in the output resistance of the previous stage. At this time, a voltage follower is needed to buffer from it. Another advantage of applying a voltage follower is that the op amp input impedance is increased, so that the capacity of the input capacitance can be greatly reduced, which provides a prerequisite guarantee for the application of high-quality capacitors.Another question, what about isolation? Because the op amp input impedance of the voltage follower is very large, it can be approximated as an open circuit. Of course, this open circuit is for the previous circuit. In this case, the previous circuit will not affect the subsequent circuit. However, "open circuit" means what, is it really open? No, the previous voltage is transmitted, but the corresponding current is not transmitted. This is the isolation effect.For example, if the MCU outputs a PWM waveform, you want to use it to control the brightness of a small light bulb. However, the output capacity of the IO port of the general MCU is limited. You can directly use the PWM output from the IO port to drive one light bulb. More than one doesn't work. In this case, you can add a voltage follower, so that the voltage is still the original voltage, but the driving ability has improved. Of course, the output capacity is not increased out of thin air, but comes from the input power of the op amp. In electronics, the diode has current amplification capability, and its source of amplification capability also comes from the power supply.In Hi-Fi circuits, the controversy about negative feedback has been around for a long time. In fact, if there is no negative feedback, most amplifying circuits will not work well. However, due to the introduction of a large loop negative feedback circuit, the back EMF of the speaker will pass through the feedback circuit and be superimposed with the input signal. The sound quality is blurred and the clarity is reduced. Therefore, some of the final stages of the power amplifier adopt a circuit without large loop negative feedback, trying to eliminate the disadvantages by disconnecting the negative feedback loop. However, since the operating current of the final stage of the amplifier varies greatly, its distortion is difficult to control. Here, the function of the voltage follower is just for the application. Putting the circuit between the front stage and the power amplifier can cut off the interference effect of the back electromotive force of the speaker on the front stage, so that the clarity of the sound quality is greatly improved. Ⅲ Op Amp Follower Circuit Analysis3.1 Op Amp Voltage and LoadFigure 1. Op Amp Voltage Follower SchematicThe output and the inverting input terminal are connected in series with a 10k resistor to ensure excellent characteristics. An ac signal is input at the non-inverting input terminal. Of course, dc and ac are all okay, so you will get a very high voltage at the output terminal. AC voltage that is similar and has excellent load capacity, with buffering and isolation effects.3.2 Op Amp Voltage Follower StabilityThe problem of using a voltage follower to keep the operational amplifier stable, that is, how to reduce the oscillation in the amplifier circuit using negative feedback to maintain stability, there is still no final conclusion. The ideal operating state of the op amp is that the output voltage and the input voltage are in phase, that is, when the applied voltage at the negative input causes the output to increase, the op amp can reduce the increased voltage accordingly. However, there is always a difference in phase between the input and output in reality. When the phase difference between the output and the output is 180°, the negative input and the positive input are exactly the same, but the output that should have been reduced is enhanced. It becomes a state of positive and negative collapse. If it falls into this state in a specific frequency band and still maintains the original amplitude, then the output frequency and oscillation state will continue.Figure 2. Feedback Loop3.3 Op Amp Phase Difference ProblemThe main reason for the phase difference between the input and the output:1) Due to the inherent characteristics of op amps.2) Due to the characteristics of the other feedback loop in circuit.Figure 3. Gain-frequency, Phase-frequency CurveFig 3(a), Fig 3(b)and Fig 3(c) respectively represent the voltage gain-frequency characteristic and phase-frequency characteristic of the operational amplifier. As shown in the figure, the voltage gain and phase vary with frequency. The difference between the op amp gain and the gain after feedback (0dB when using a voltage follower) is the gain (feedback gain) of the feedback loop. If the feedback gain is less than 1 time (0dB), then, the phase changes by 180° and returns to the positive feedback state, the negative gain will gradually attenuate in the circuit and theoretically will not cause oscillation.On the contrary, when the phase changes by 180°, if the loop gain corresponding to the frequency is 1 time, the original amplitude will be maintained. If the loop gain corresponding to the frequency is greater than 1, the amplitude will gradually diverge. In most cases, in the process of amplitude divergence, the amplitude is limited due to the influence of nonlinear elements such as the maximum output voltage, and the oscillation state will be maintained.Therefore, the difference between the phase corresponding to the frequency when the loop gain is 0dB, 180° is an important factor for judging the stability of the negative feedback loop, and this parameter is called the phase margin. Unless otherwise specified, when a single amplifier is used as a voltage follower, sufficient phase margin must be maintained (Fig 3b.).3.4 Adding Feedback ResistanceWhen the operational amplifier is used as a follower, when the internal resistance of the signal source is large, adding a feedback resistor with the same resistance as the internal resistance of the signal source can reduce the output offset voltage and improve the follow accuracy. The follower with feedback resistance has a certain current limiting protection effect on the circuit when the circuit is "blocked", which is its advantage.The voltage follower is originally a non-inverting operational amplifier. One of the common features of it is that a common-mode voltage is added to the non-inverting terminal and the inverting terminal.Once this common-mode voltage exceeds the allowable common-mode input voltage range, for example, if the inverting terminal signal is too large, it will cause the input stage transistor to saturate. The inverting terminal signal will be directly added to the second stage of the op amp, making the inverting input becomes non-inverting input, that is, negative feedback becomes positive feedback, and the output signal passes through the feedback loop to further saturate the input stage transistor. As a result of this, the amplifier is of course no longer in normal working condition. Even if the input signal is canceled, it will not immediately return to the normal state. This phenomenon is called blocking.When it occurs, if the feedback loop resistance is not large enough, the current in the feedback loop may burn the input stage transistors and even harm the second stage. In order to avoid blocking, in addition to choosing an op amp with a large common-mode input voltage range, a clamp circuit is often added to the input of the amplifier to ensure that the common-mode voltage at the input does not exceed the allowable range.Of course, in a small-signal inverting operational amplifier, especially in circuits with capacitive elements such as integrating operational amplifiers, blocking may also occur. The processing method is the same as that of the non-inverting amplifier. Ⅳ Op Amp Voltage Follower ApplicationIn many typical circuit designs, there will be an op amp follower before the AD converter. Whether this follower is necessary or not depends on the requirements of the circuit based on the understanding of the function of the follower. First analyze the role of the voltage follower here:The function of the voltage follower here is impedance transformation.Impact 1: The input impedance becomes very high, so that the impact on the input signal can be small.Impact 2: The output impedance becomes very low, and the impact of AD input impedance on the input signal can be very small.It can be seen that the follower is very meaningful. Secondly, analyze your own circuit and the signal under test to make a decision whether to use a follower. Here are some rules to confirm:1) If the output impedance of the signal is very small, then the Impact 1 can be ignored.2) If the input impedance of AD converter is very large, then two impacts can be ignored.3) If both impacts can be ignored, no voltage follower is necessary.4) If there is an impact, a voltage follower is needed. Frequently Asked Questions about Op Amp Voltage Follower1. Which amplifier is called as voltage follower Why?This means that the op amp does not provide any amplification to the signal. The reason it is called a voltage follower is because the output voltage directly follows the input voltage, meaning the output voltage is the same as the input voltage. 2. What is the use of voltage follower?A voltage follower can be used as a buffer because it draws very little current due to the high input impedance of the amplifier, thus eliminating loading effects while still maintaining the same voltage at the output. 3. What do you mean by voltage follower circuit?A voltage follower is also known as a unity gain amplifier, a voltage buffer, or an isolation amplifier. In a voltage follower circuit, the output voltage is equal to the input voltage; thus, it has a gain of one (unity) and does not amplify the incoming signal. 4. What is an op amp buffer?An op-amp voltage buffer mirrors a voltage from a high-impedance input to a low-impedance output. 8 min read. A voltage buffer, also known as a voltage follower, or a unity gain amplifier, is an amplifier with a gain of 1. It's one of the simplest possible op-amp circuits with closed-loop feedback. 5. What is an op amp buffer circuit used for?A buffer is a unity gain amplifier packaged in an integrated circuit. Its function is to provide sufficient drive capability to pass signals or data bits along to a succeeding stage. Voltage buffers increase available current for low impedance inputs while retaining the voltage level.

IntroductionThe transistor is one of the basic semiconductor components, which has the function of current amplification in electronic circuit. It is made of two PN junctions very close to each other on a semiconductor substrate. Two PN junctions divide the entire semiconductor into three parts: The middle part is the base area, and the two sides are the emitter and the collector. What is NPN Transistor? For BeginnerCatalogIntroductionⅠ NPN Transistor Arrangement and SymbolⅡ How Do NPN Transistors Work?Ⅲ NPN Transistor Uses: A Controllable ValveⅠ NPN Transistor Arrangement and SymbolBefore explaining the principle, let's first understand the basic structure and symbols of the NPN transistor. To identify the NPN transistor pins, it will be Collector (c), Base (b) and Emitter (e).Figure 1. NPN Transistor Structure and SymbolNPN transistor is composed of two N-type semiconductors and one P-type semiconductor. Generally, an NPN transistor has a piece of P-type silicon (the base) sandwiched between two pieces of N-type (the collector and emitter). The arrangement is shown in the Figure 1. Ⅱ How Do NPN Transistors Work?Here is the main description to illustrate the basic principle and function of NPN transistors.1) Current AmplificationThe following analysis is only for NPN silicon transistors. As shown in the figure above, we call the current flowing from the base B to the emitter E the base current Ib; the current flowing from the collector C to the emitter E is called the collector current Ic. The directions of these two currents are both flowing out of the emitter, so an arrow is used on the emitter E to indicate the current direction.The amplification function of the transistor is: the collector current is controlled by the base current (assuming that the power supply can provide a large enough current to the collector), and a small change in the base current will cause a large change in the collector current: the change in the collector current is β times the change in the base current, that is, the current change is amplified by β times, so we call β the magnification of the transistor (β is generally much larger than 1). If we add a changing small signal between the base and the emitter, it will cause a change in the base current Ib. After the change in Ib is amplified, it leads to a big change in Ic. If the collector current Ic flows through a resistor R, it can be calculated according to the Ohm's Law formula U=R*I, and the voltage on this resistor will change greatly. According to the voltage on this resistor, so we can get the amplified voltage signal. In short, the change satisfies a certain proportional relationship.2) Bias CircuitWhen the transistor is used in the actual amplifier circuit, it is also necessary to add a suitable bias circuit. There are several reasons for this. First of all, due to the non-linearity of the transistor's BE junction (equivalent to a diode), the base current must be generated after the input voltage reaches a certain level (for silicon tubes, 0.7V is often used). When the voltage between the base and the emitter is less than 0.7V, the base current can be considered as zero. However, in practice, the signal to be amplified is often much smaller than 0.7V. If no bias is applied, such a small signal is not enough to cause a change in the base current (because when it is less than 0.7V, the base current is all 0).Add a suitable current to the base of the transistor (called the bias current, and the resistor in the figure used to provide this current, is called the base bias resistor). When a small signal follows this bias current are superimposed together, a small signal will cause a change in the base current, and the change in the base current will be amplified and output on the collector. Another reason is meeting the requirement of the output signal range. If there is no bias, then only those increased signals will be amplified, but the decreased signals will be invalid (because the collector current is 0 when there is no bias, and it cannot be reduced). With bias, let the collector have a certain current in advance. When the input base current becomes smaller, the collector current can be reduced; when the input base current increases, the collector current increases. Both the reduced signal and the increased signal can be amplified.3) NPN Transistor SwitchLet's talk about the saturation mode of the transistor. As shown in the figure above, because of the limitation of resistance Rc (Rc is a fixed value, then the maximum current is U/Rc, where U is the power supply voltage), the collector current cannot increase indefinitely. When the base current increases and the collector current cannot continue to increase, the transistor enters a saturated state. The general criterion for judging whether the transistor is saturated is: Ib*β>Ic.In a saturation state, the voltage between the collector and the emitter of the transistor will be very small, which can be understood as a switch. In this way, when the base current is 0, the collector current is 0 (this is called the triode cut-off), which is equivalent to the switch off; when the base current is large, it is equivalent to the switch on. In cut-off and saturation state, a transistor is equal to a switch.4) Operational StateIf we replace the resistor Rc with a bulb in the above figure, then when the base current is 0, the collector current is 0, so the bulb is off. If the base current is relatively large (greater than the current flowing through the bulb divided by the magnification β), the transistor will saturate, and the bulb will light up. Since the control current only needs to be a little larger than β of the bulb current, a small current can be used to control the on and off of a large current. If the base current increases slowly, the brightness of the bulb will also increase (which is a saturation process).The figure below is a basic transistor switch circuit. The base should connect a base resistor (R2), and the collector connects with a load resistor (R1).Operational ModeNPNCut-offUne<UonUc>UbActiveUbe>UonUc>UbSaturationUbe>UonUc<UbNPN transistor uses the B-E current (IB) to control the C-E current (IC). The E pole has the lowest potential, and usually the C pole has the highest potential during normal amplification, that is, VC>VB>VE.NPN base extremely high voltage, the collector and emitter are short-circuit and low-voltage, and the collector and emitter are open-circuit.NPN is suitable for two situations:If the input is a high level and the output needs a low level, NPN is better.If the input is a low level and the output needs a high level, NPN is better.2N2222 NPN Transistor PinoutⅢ NPN Transistor Uses: A Controllable ValveNPN is a component that uses b (base) current Ib to drive the current Ic flowing through CE, and its working principle is much like a controllable valve.Figure 2. A Controllable ValveThe blue water flow in the thin pipe on the left impacts the lever to open the valve of the large water pipe, allowing the larger red water flow to pass through the valve. The larger the blue water flow, the greater the red water flow in the big pipe. If the magnification is 100, then when the blue water flow is 1 kg/hour, then 100 kg/hour of water is allowed to flow through the large pipe. The principle of the transistor is the same. When Ib (base current) is 1mA, a current of 100mA is allowed to pass through Ice.Figure 3. NPN Transistor DiagramLet's analyze this circuit. If its magnification is 100, and ignore the base voltage. The base current is 10V÷10K=1mA, so the collector current should be 100mA. According to Ohm's law, the voltage on Rc is 0.1A×50Ω=5V. Then the remaining 5V is on the C and E poles of the transistor. Now if we let Rb be 1K, then the base current is 10V÷1K=10mA, according to the magnification of 100, is Ic 1000mA? If it is really 1A, then the voltage on Rc is 1A×50Ω=50V. The power supply voltage has been exceeded, and the transistors have become generators? This is not the case. See below:Figure 4. NPN Transistor Compared to A ValveContinue the metaphor. When the control current is 10mA, the valve on the main water pipe is opened to allow 1A current to flow, but can 1A be realized? No, because there is a resistor on it, it is equivalent to a fixed valve. It is stringed on top of the main water pipe. When the opening of the lower controllable valve is greater than the opening of the upper fixed resistor, the water flow will not increase any more, but will be equal to the water flow passing through the fixed valve opening above. Therefore, it is useless to open the lower transistor to a large opening. Therefore, we can calculate the maximum current of the fixed resistor 10V÷50Ω=0.2A, which is 200mA. That is to say, in the circuit, the base current increases and the collector current also increases. When the base current Ib increases to 2mA, the collector current increases to 200mA. When the base current increases again, the collector current will no longer increase, and it will not move at 200mA. At this time, the upper resistor also acts as a current limiter.  Let us understand the status of the IO in the microcontroller.Figure 5. AT89S51/52 The circuits with 24 IO ports of P1-P3 in the single-chip microcomputer are as shown in the figure above. Usually the purpose of using electronic circuits is to allow devices to obtain a certain current to make them work. For example, to make light-emitting diodes bright, a current of more than 1mA is generally required. However, the single-chip microcomputer is a smart chip. It can make logical analysis and judgments by detecting the voltage value of each IO port, and outputs high or low voltage as the result signal. Therefore, it can be seen that the IO ports of the single-chip microcomputer focus on voltage, not the current flowing through R and the transistor. Here what is the relationship between the voltage and current of the IO port in the single-chip microcomputer?  Continue the water pipe example.Suppose we let the valve of R open larger and let the control valve below be fully closed. At this time, as shown in Figure 6, it can be seen that the pressure at point P is the same as the water tank. When we fully open the following control valve, as shown in Figure 7, the water will flow through the pipeline with a large flow, and the pressure at point P is 0 at this time. This principle is very similar to electronic circuits. The logic quantity measured at the output point P is 1 (power supply voltage) or 0 (0 potential) by transistor turning off or on. However, there is a problem with this process, that is, when the output of point P is required to be 0, the transistor will be turned on very large, and the current flowing through it will be very large. There are 32 IO ports on the single-chip microcomputer, which consumes a lot of power. Look at Figure 8. If we close the upper valve R very small and close the lower control valve fully, then the pressure at point P will still the same as the water tank, which is the same as in Figure 6 above. When we open the control valve greatly, as shown in Figure 9, although the pressure at point P is also 0, the flow of water passing through at this time is greatly reduced. In this way, we can either output 1 or 0. So very little water is consumed. The circuit in the single-chip microcomputer does exactly this. The resistance R on it is about 50K, and the maximum current is 5V÷50K=0.1mA. In other words, when P outputs 1, no current is consumed, and when P outputs 0, the current consumed is 0.1mA. Because of its large pull-up resistance R, for beginners, it is necessary to have certain methods to directly drive LEDs or other loads. Here to share the various situations when the IO port is connected to the load.Figure 10. AT89S51/52 & 74HC373Let's take a look at the situation of connecting TTL devices first. When P1.0 is connected to an input pin of 74HC373, and the input impedance of TTL is very high, about a few hundred K to M ohm level. We assume 500K resistor to P1.0 to ground. In this way, when the transistor is turned on, the P1.0 point is at a low level, and a current of 0.1mA flows through Rc and then through the transistor to the ground, and no current flows through Ri. When the transistor is cut off, the current flows through Rc and then flows to the ground through Ri. Due to the resistor voltage divider effect, there are partial voltages on Rc and Ri, and the voltage at point P1.0 is the divided voltage of Rc and Ri. Total current is 5V÷(50K＋500K)=0.009mA, then the voltage at point P1.0 is 0.009mA×500K=4.5V. TTL stipulates that output 2.4~5V is high level. So this connection is correct. Now let's take a look at the situation of using S51 to drive the LED.AT89S51 Correct ConnectionLet’s take a look at the situation in Figure 11. Obviously, only P1.0 is a high potential to light the luminous tube, so the transistor must be cut off. In this case, the current flows through Rc to the luminous tube and then to the ground. To make the luminous tube turn on, there must be a threshold voltage exceeding 2.1V at both ends of the luminous tube. Therefore, the current flowing through the luminous tube is (5V-2.1V)÷50K=0.058mA, which is too weak to conduct.Look at Figure 12. It can be seen from the figure that P1.0 must be at a low potential if the luminous tube turned on. The transistor of the P1.0 port must be turned on. At this time, the current flows all the way through Rc to the transistor and then to the ground. The other way consumes 2.1V on the luminous tube. Then current flows through with almost no resistance, but the maximum current of the triode of the IO port cannot exceed 15mA. If it exceeds, the triode will be burned out, so this connection method is incorrect. So how can these two connections be able to drive the light-emitting tube? See below: AT89S51 Incorrect ConnectionLooking at Figure 13, a resistor Ri is connected between P1.0 and Vcc. When the transistor is turned on, two currents will flow through its c, e pole, one is the 0.1mA current on the internal R, and the other is the current on Ri. In order to prevent the transistor from over-current and burn out, we must make sure the resistance value, Ri=5V÷15mA=0.333K, which is about 330 ohms. At this time, the current flowing through the transistor is about 15mA, and the light-emitting tube is not bright at this time. When the transistor is turned off, both currents will flow through the luminous tube. The current flowing through the internal resistance of S51 is (5V-2.1V)÷50K=0.06mA, which is so small that we can ignore it. The current flowing through Ri is (5V-2.1V)÷330Ω=0.0087A, which is 8.7mA. However, the current consumed when the luminous tube is off is greater than the current consumed when the luminous tube is on. If many IO ports are used to light up many LEDs, such a circuit is not economical.Look at Figure 14, after connecting a resistor in series with the luminous tube between Vcc and P1.0. When the transistor is turned on, the two currents will flow through the c, e after confluence. The current on the internal resistance is still 0.1mA. The current on the ce should be less 15mA. If exceeds 15mA, the resistance is determined as (5V-2.1V) ÷ 15mA = 0.193K, which is about 200 ohms. In this way, the current flowing through the luminous tube is about 15mA, and the luminous tube is on. When the transistor is cut off, it blocks the paths of these two currents, so no current is consumed. Low level P1.0 directly drives the light-emitting tube. It can be seen that this circuit consumes 15mA of current when the light-emitting tube is on, and does not consume current when it is off, so this circuit is effective. S51 direct drive digital tube generally also uses this principle. Frequently Asked Questions about NPN Transistor1. What is meant by NPN transistor?An NPN transistor is the most commonly used bipolar junction transistor, and is constructed by sandwiching a P-type semiconductor between two N-type semiconductors. An NPN transistor has three terminals– a collector, emitter and base. The NPN transistor behaves like two PN junctions diodes connected back to back. 2. How do NPN transistors work?The NPN transistor is designed to pass electrons from the emitter to the collector (so conventional current flows from collector to emitter). The emitter "emits" electrons into the base, which controls the number of electrons the emitter emits. ... The transistor is kind of like an electron valve. 3. What is a NPN transistor used for?NPN transistors are mainly used in switching applications. Used in amplifying circuit applications. Used in the Darlington pair circuits to amplify weak signals. NPN transistors are used in the applications where there is a need to sink a current. 4. Which is better PNP or NPN transistor?A NPN transistor has electrons as majority charge carriers whereas the PNP transistor has holes as majority charge carrier. ... mobility of electrons is more than hole,so as a result npn transistor are faster than pnp that's why they are preferred. 5. What does NPN mean?NPN stands for Negative, Positive, Negative. Also known as sinking.

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

IntroductionA stable power supply is necessary for normal operation of the electrical system. Except for the use of solar cells or chemical batteries in certain special occasions, the direct current of most circuits is converted from the alternating current of the grid. The bridge rectifier is commonly used to convert AC into DC, which is the most commonly used circuit that uses the unidirectional conductivity of diodes for rectification. There are many types of bridge rectifiers: flat, round, square, bench-shaped (plug in and SMD), etc., having GPP and O/J structures. The maximum rectified current ranges from 0.5A to 100A, and the maximum reverse peak voltage ranges from 50V to 1600V.What is Bridge Rectifier?CatalogIntroductionⅠ Bridge Rectifier Diode CircuitⅡ Bridge Rectifier Circuit FeaturesⅢ Single Phase Rectification vs Three Phase Rectification3.1 Single Phase Bridge Rectifier Circuit3.2 Three Phase Bridge Rectifier CircuitⅣ Role of Bridge RectificationⅤ Bridge Rectifier Wiring DiagramⅥ Difference between Bridge Rectifier and Full-wave Rectifier CircuitⅠ Bridge Rectifier Diode CircuitThe bridge rectifier uses four semiconductor diodes to be connected in pairs. When the positive half of the input sine wave is turned on, the two tubes are turned on, and the positive output is obtained; on the contrary, when the negative half of the sine wave is input, the other two tubes are turned on. Since the two tubes are reversely connected, the output is still the positive part of the sine wave. In addition, the utilization efficiency of the input sine wave by the bridge rectifier is twice as high as that of the half-wave rectifier.The rectifier bridge stack is generally used in a full-wave rectifier circuit, and it is divided into a full bridge and a half bridge. The full bridge is composed of 4 rectifier diodes connected in the form of a bridge full-wave rectifier circuit and packaged as a whole. The half bridge is to seal the half of the two diode bridge rectifiers together. Two half bridges can form a bridge rectifier circuit, and a half bridge can also form a full wave rectifier circuit with a center tap of the transformer. When choosing a rectifier bridge, the rectifier circuit and operating voltage must be considered carefully.The forward current of the full bridge has various specifications such as 0.5A, 1A, 1.5A, 2A, 2.5A, 3A, 5A, 10A, 20A, 35A, 50A, etc. The withstand voltage (the highest reverse voltage) is 25V, 50V, 100V, 200V, 300V, 400V, 500V, 600V, 800V, 1000V, etc.In this chapter, the rectifier diode is regarded as an ideal component, that is, its forward conduction resistance is considered to be zero, and its reverse resistance is infinite, because of the convenience of analyzing the rectifier circuit. However, in practical applications, it should be considered that the diode has internal resistance, and the output amplitude of the waveform obtained after rectification will be reduced by 0.6~1V. When the input voltage of the rectifier circuit is large, this part of the voltage drop can be ignored. On the contrary, if the input voltage is small, for example, if the input is 3V, the output is only 2V, and the influence of the diode forward voltage drop needs to be considered.Current Direction of the Bridge Rectifier CircuitFigure 1.In the positive half cycle of u2, D1 and D3 are turned on, D2 and D4 are turned off, and the current returns from the upper end of the TR secondary to the lower end via D1→RL→D3, and a half-wave rectified voltage is obtained on the load RL.In the negative half cycle of u2, D1 and D3 are off, D2 and D4 are on, and the current returns from the lower end of Tr secondary to the upper end of Tr secondary via D2→RL→D4, and the other half-wave rectified voltage is obtained on the load RL. Ⅱ Bridge Rectifier Circuit Features(1) The rectification device used is twice that of full-wave rectification.(2) Rectified voltage pulse changing direction is the same as full-wave rectification.(3) The reverse voltage that each device bears is the peak value of the power supply voltage.(4) The utilization rate of the transformer is higher than that of the full-wave rectifier circuit. Ⅲ Single Phase Rectification vs Three Phase Rectification3.1 Single Phase Bridge Rectifier CircuitFigure 2.The single phase bridge rectifier circuit is composed of four diodes connected in the form of a bridge. Its disadvantage is that it only uses half a cycle of the power supply, and at the same time the rectification voltage has a large pulsation.The above Figure 2 (a) shows the direction of current in the single-phase bridge rectifier circuit. The solid arrow indicates the situation when the AC power supply is in the positive half cycle, and the dotted arrow indicates the situation when the AC power supply is in the negative half cycle.It can be seen that the four diodes are divided into two parts: positive half cycle and negative half cycle. However, the current direction on the load does not change. This is full-wave rectification. In addition, the single-phase bridge rectifier circuit can be implemented with an integrated device "bridge stack" in practice.In Figure 3. shows the waveform diagram of the single phase bridge rectifier circuit. According to the diagram, the average voltage is: Uo ≈ 0.9U2 (where U2 is the effective value of the output voltage of the transformer secondary side).Figure 3. Wave Form (single phase)3.2 Three Phase Bridge Rectifier CircuitFigure 4.The three phase bridge rectifier circuit is developed from a uncontrolled half-wave rectifier circuit, which is essentially a series connection of a set of common cathode and a set of common anode with three semiconductor diodes.In addition, the three phase bridge circuit must have two thyristors turned on at the same time, one in the common cathode area and the other in the common anode area to form a loop.Circuit Analysis LawThe diode with the highest anode potential in the common cathode group is turned on.The diode with the lowest cathode potential in the common anode group is turned on.Circuit Analysis ExamplesFigure 5. t1 ~ t2In the common cathode group, the potential at point U is the highest, and V1 is on.In the common anode group, the potential at point V is the lowest, and V4 is on.The voltage across the load is the line voltage Uuv. Figure 6. t2~t3In the common cathode group, the potential at point U is the highest, and V1 is on.In the common anode group, the potential at point W is the lowest, and V6 is turned on.The voltage across the load is the line voltage Uuw. Figure 7. t3~t4In the common cathode group, the potential at point V is the highest, and V3 is on.In the common anode group, the potential at point W is the lowest, and V6 is turned on.The voltage across the load is the line voltage Uvw.......SummeryIn a full-wave cycle, it can be divided into 6 intervals, each of which is powered by a pair of phase wires to the load.In a full-wave cycle, each diode is turned on for one-third of the time (the conduction angle is 120°).During the 6 periods in a cycle, the voltage of the load can be seen as a periodic change. Ⅳ Role of Bridge Rectification1. Convert the alternating current generated by the alternator into direct current to power the electrical equipment and charge the battery.2. Limit the battery current to flow back to the generator to protect the generator from being burnt out by the reverse current.Figure 8. Bridge Rectifier AC to DC Flow ChartⅤ Bridge Rectifier Wiring DiagramThe bridge rectifier circuit overcomes the shortcomings that the full-wave rectifier circuit requires the transformer secondary to have a center tap and the diode to withstand large reverse voltage, but two diodes are used. With the rapid development of semiconductor devices and low cost today, this shortcoming is not obvious, so bridge rectifier circuits are widely used in practice.It needs to be pointed out that the diode as a rectifier component should be selected according to different rectification methods and load values. If choose improperly, you may not be able to work safely, or even burn the pipe, causing waste.Figure 9. Schematic Diagram of Bridge Rectifier CircuitThe bridge rectifier circuit can also be considered as a kind of full-wave rectifier circuit. The transformer is connected to four diodes according to the method shown in Figure 9. D1～D4 are four identical rectifier diodes connected in the form of a bridge, so they are called bridge rectifier circuits. Using the guiding function of the diode, the secondary output can be directed to the load even in the negative half cycle. It can be seen from the figure that D1 and D2 lead the current through RL from top to bottom during the positive half cycle, and D3 and D4 lead the current through RL from top to bottom during the negative half cycle. In this structure, if the same DC voltage is output, the secondary winding of the transformer needs only half of the winding compared with the full-wave rectification. However, if the same amount of current is to be output, the diameter of the winding should be increased accordingly.Because the output voltage of the rectifier circuit contains larger pulsating components. In order to reduce the pulsation component as much as possible, on the other hand, it is necessary to keep the DC component as much as possible to make the output voltage close to the ideal DC. This measure is filtering. Filtering is usually achieved by using the energy storage effect of capacitors or inductors.Figure 10. Bridge Rectifier Circuit with CapacitorIn this experimental circuit, capacitor filtering is used, that is, a filter capacitor C is connected in parallel with the load resistance RL. The circuit is shown in Figure 11, and the filtered waveform is as shown in the figure below.Figure 11. Full-wave Rectification Filter WaveformThe DC component of the full-wave rectified output voltage (compared to the half-wave) is increased, and the pulsation is reduced, but the transformer needs a center tap, which is troublesome to manufacture, and the rectifier diode needs to withstand high reverse voltage, so it is generally suitable for the low output voltage.Figure 12. Half-wave Rectification Filter WaveformHalf-wave rectification is the most commonly used circuit that uses the unidirectional conductivity of a diode for rectification. Ⅵ Difference between Bridge Rectifier and Full-wave Rectifier Circuit1) Don't need a center tap on the secondary side of the bridge rectifier circuit transformer, but use 2 more rectifier diodes.2) The full-wave rectifier circuit uses less than 2 rectifier diodes, but the secondary side of the transformer should be center-tapped.3) The reverse withstand voltage of the rectifier diode used in the full-wave rectifier circuit is twice that of the bridge rectifier.4) Rectification and full-wave rectification have different requirements for the number of secondary transformers. The former requires only 1 set of coils, while the latter requires 2 sets.5) Rectification and full-wave rectification have different requirements for the secondary current of the transformer, the former is twice the latter. Frequently Asked Questions about Bridge Rectifier Circuit1. What does a bridge rectifier do?A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding. ... Diodes are also used in bridge topologies along with capacitors as voltage multipliers. 2. How does a bridge rectifier convert AC to DC?Bridge rectifiers convert AC to DC using its system of diodes made of a semiconductor material in either a half wave method that rectifiers one direction of the AC signal or a full wave method that rectifies both directions of the input AC. 3. What happens when a bridge rectifier fails?Without capacitor smoothing, when 1 diode fails open in a bridge rectifier, both voltage and current reduce. With capacitor smoothing, when 1 diode fails open in a bridge rectifier, the voltage remains fairly constant but the current increases. 4. Why do we use 4 diodes in bridge rectifier?The bridge rectifier consisting of four diodes enables full wave rectification without the need for a centre tapped transformer. The bridge rectifier is an electronic component that is widely used to provide full wave rectification and it is possibly the most widely used circuit for this application. 5. Why is a bridge rectifier more preferable than a full wave rectifier?Bridge rectifier is driven by a single winding which carries current both cycles in load. ... Full wave is better than bridge in one more aspect i.e. the output DC voltage is slightly higher than bridge. This is because it has only 1 diode drop from AC to DC.

For so many years, tube amplifier has always been a “controversial” component in the electronic field, people are attracted by its premium sound quality but discouraged by its price.   Today we are going to talk about tube amplifiers, to understand what this device is, why its price is so much higher than other amplifiers, what are its advantages and disadvantages compared with other amplifiers, and so on. Catalog I. What is a Tube Amplifier? II. Pros and Cons of Tube Amplifier? III. How Does the Tube Amplifier Work? IV. Tube Amplifier VS Solid State Amplifier? V. Tube Amplifier VS Transistor Amplifier? VI. Things Needing Attention While Using a Tube Amplifier VII. Why is Tube Amplifier So Expensive? Is It Worth It? VIII. How to Extend the Life of   the Tube Amplifier?    FAQ I. What is a Tube Amplifier? The tube amplifier is one of the earliest electrical signal amplifiers.   The cathode electron emission part, the control grid, the acceleration grid, and the anode (panel) lead enclosed in a glass container (generally a glass tube) are welded to the tube base.   The electric field is used to inject an electronic modulation signal into the control grid in the vacuum, and the signal data of different parameters after signal amplification or feedback oscillation is obtained at the anode.   Tube amplifiers were used in electronic products such as televisions and radio amplifiers in the early days. In recent years, they have been gradually replaced by amplifiers and integrated circuits made of semiconductor materials. However, in some high-fidelity audio equipment, tube amplifiers with low noise and high stability coefficient are still used. II. Pros and Cons of Tube Amplifier? Pros: 1. The tube amplifier has a large input dynamic range and a fast conversion rate.   2. Electronic tube amplifiers mostly use discrete components, manual wiring, and welding, which are low in efficiency and high in cost. This is especially obvious in developed countries.   3. The open loop index of the tube amplifier is better than that of the transistor amplifier. It does not need deep negative feedback and can work stably without adding phase compensation capacitors, so its dynamic index is better.   4. The sound quality of the tube amplifier is generally soft and pleasant. More specifically, the low-frequency sound of the tube amplifier is soft and clear, and the high-frequency sound is slender and clean. The performance of human voice is its strong point.   5. The treble of the tube amplifier is smoother, has enough air, and has a sound coloring that quite a few people like. The soft and slightly fuzzy sound is very beautiful.   6. The tube amplifier mainly causes even-numbered second harmonics. This harmonic component is very pleasing, just like adding rich overtones and beautifying the sound.   Cons: 1. The service life of the tube amplifier is relatively low, and some technical indicators will drop significantly after one to two thousand hours of use.   2. The tube amplifier consumes high power and often works in Class A state, which reduces the efficiency. However, there are basically no harmful sound quality factors such as transient intermodulation distortion, switching distortion and crossover distortion.   3. The tube amplifier is not at all superior to the transistor amplifier in terms of weight, efficiency, and lifespan.   4. In use, the tube amplifier should have good ventilation and heat dissipation. Overheating of the temperature will inevitably shorten the life of the tube amplifier, so it is necessary to keep the temperature of the tube amplifier as low as possible.   5. Vibration is not good for tube amplifiers, so it is important to take anti-vibration measures to avoid vibration as much as possible. III. How Does the Tube Amplifier Work? This is a basic overview of some of the components of a tube guitar amp and how they work, without getting too technical. IV. Tube Amplifier VS Solid State Amplifier? A solid-state amplifier converts an electrical signal into an audio wave using transistor circuitry. Instrumental amplifiers have two amplification stages: the preamp stage at the beginning of the circuit and the power amp stage at the end.    The physical difference between a solid-state amp and a tube amp is that a solid-state machine employs electronic transistors for amplification, whereas a tube amp employs vacuum tubes (also known as valves). Transistors differ from tubes in that they do not deform pleasantly when pushed to their limits.   The key difference between tube amplifier and solid state amplifier is: solid-state amplifiers are ideal for guitarists that require a lot of power (a.k.a a loud, clean, undistorted signal). However, without any natural distortion, an electric guitar can sound brittle. As a result, solid-state amplifiers are more popular among bassists and keyboard players than guitarists. Compared with tube amp, solid-state amp has several advantages: 1.    They are less expensive. Almost all solid-state amplifiers are less expensive than tube amplifiers. They have fewer parts and the ones they do have are reasonably inexpensive.  2.    They are less bulky. Weight can be an issue if you're a gigging musician who needs to transport an amp around town. Tube amplifiers are almost always heavier than solid-state amplifiers. This is due to the circuitry necessary to operate the glass tubes, not the glass tubes themselves (which are hollow). 3.    They require less maintenance. Tube amplifiers need routine maintenance. Most gigging guitarists replace their power tubes once a year and their preamp tubes every two years. Solid-state amplifiers, on the other hand, do not require part switching. They can function for decades with all of their original components. V. Tube Amplifier VS Transistor Amplifier? A transistor amplifier, as the name implies, is used to amplify power, voltage, or current signals. It has a common emitter amplifier, a common collector amplifier, and a common base amplifier. This is the most basic. There are also differential, push-pull, and so on. The audio is actually a power (transistor) amplifier. The difference between transistor amplifier and tube amplifier: 1. Working characteristics and circuit structures are different Transistor amplifiers work under low voltage and high currents. The working voltage of transistor power amplifiers is within tens of volts, and the current reaches several amperes or tens of amperes. In the circuit design, direct-coupled (OCL, BTL, etc.) non-output transformer circuits are mostly used. The output power can be very large, up to several hundred watts, and the various electrical properties are very high. The tube amplifier works under high voltage and low current conditions. The screen voltage of the final power amplifier tube can reach 400-500V or even thousands of volts, and the current flowing through the electron tube is only tens of milliamps to hundreds of milliamps. The input range is too large and the conversion rate is fast. Most of the tube amplifiers use discrete components, manual wiring, and welding, which are low in efficiency and high in cost. Transistor amplifiers mostly use a combination of transistors and integrated circuits, and printed circuit boards are widely used, with high efficiency, stable soldering quality, and high electrical performance indicators. 2. Power reserve and anti-overload ability are different The dynamic range of the high-fidelity amplifier should be 120dB, so as to meet the needs of the sound from the slightest to the peak of the climax, the amplifier output is not clipped, so the amplifier must have sufficient power reserve. If the dynamic range of the audio voltage is 3:1, since the power is proportional to the square of the voltage, the power dynamic range is 9:1. That is to say, a power amplifier with a power of 90W can only be turned on to 10W to achieve high-fidelity playback. Therefore, the transistor amplifier needs a large power reserve to avoid overload distortion. Once the ground is loaded, its distortion will almost rise in a vertical line, which can damage the transistor in severe cases. The anti-overload capability of the tube amplifier is far stronger than that of the transistor amplifier. In case of overload, the peak of the music signal only becomes slippery than the normal waveform, and the sound is not deformed much. For transistor amplifiers, clipping will occur at this time, and the sound quality will deteriorate significantly. 3. Efficiency, life, and cost are different Tube amplifiers are not superior to transistor amplifiers in terms of weight, efficiency, and lifespan. The service life of the electron tube is relatively low, and some technical indicators will drop significantly after one to two thousand hours of use. The lifetime of transistors and integrated circuits is much longer. In addition, the tube amplifier consumes high power and often works in the Class A state, which reduces the efficiency. However, there are no harmful sound quality factors such as transient intermodulation distortion, switching distortion, and crossover distortion. In terms of cost, for the same grade of amplifiers, tube amplifiers are generally significantly higher than transistor amplifiers. The main reasons are the high cost of electronic tubes and output transformers, and the production process of electronic tube power amplifiers is not easy to automate, and the production efficiency is low. 4. Different sound quality The sound quality of the tube amplifier is significantly better than that of the transistor amplifier. Transistor power amplifiers have a sense of overwhelming when listening to high and medium and high frequencies, and less low frequencies. Transistor power amplifiers sound hard, especially low-frequency sounds are not soft enough, and high-frequency sounds are sharp and dry. Sometimes it sounds like there is crossover distortion in the high-frequency range. These phenomena become more obvious when the frequency increases and the volume is louder. However, the transistor amplifier has large dynamics and high speed, which is especially suitable for music with greater dynamics. As for the sound effects of guns and lightning, it is certainly better than a tube amplifier. Generally speaking, the sound quality of the tube amplifier is soft and pleasant. Specifically, the low-frequency sound of the tube amplifier is soft and clear, and the high-frequency sound is slender and clean. The performance of the human voice is its strong point, and therefore it is more valuable. All in all, the choice of amplifier varies from person to person. If you like orchestral music, especially chamber music and vocals, then tube amplifiers should be your first choice. If you like jazz, rock, and modern music, then transistor amplifiers are the choice. VI. Things Needing Attention While Using a Tube Amplifier? 1.    The tube amplifier must be used under the limit parameters. Although it can still work normally under the limit parameters, the life of the tube amplifier will be shortened quickly. Therefore, the tube should be used under the rated parameters. 2.    The location of the components in the device should be conducive to the heat dissipation of the tube amplifier. To control the temperature of the tube case of the tube amplifier, the allowable temperature of the glass case of various tube amplifiers is different. For example, the allowable limit temperature of the power output tube during operation does not exceed 90°C in principle. 3.    Except for the high-reliability tube amplifier with a special structure that can work at higher accelerations, other receiver amplifier tubes can only withstand small shocks for a short time. Therefore, pay attention to the shock absorption of the tube when using it. 4.    When using small tubes (thumb-finger type) and other tubes without tube bases (but with tube needles), use tube sockets specified by the Ministry of Electronics Industry. Prevent cracking or damage to the glass shell. When plugging and unplugging the tube, its direction should be perpendicular to the plane of the tube base. When inserting an electronic tube, prevent damage to the normal position of the contact reed in the socket socket of the tube socket, and avoid using the empty foot of the tube socket as a connecting pad. 5.    When using an indirectly heated tube amplifier, the potential difference between the cathode and the filament must not exceed the specified limit. For this reason, a dedicated filament transformer is often used for power supply. In order to eliminate the effect of leakage current instability, under the condition of not hindering the operation of the circuit, a shunt resistance of about several ohms can be connected between the cathode and the filament. VII. Why is Tube Amplifier So Expensive? Is It Worth It? In short, tube amplifiers are costly because they use pre and power tubes as their primary amplification source. Each tube costs approximately $50 and can have up to four of them in a single unit. Second, these amplifiers have more expensive components, larger casings, and more complicated circuitry than solid-state amplifiers.   Whether tube amplifiers are "worth it” or not, well, that’s more of a subjective question.   If your goal is to build a pristine audio chain that cleanly reproduces the input signal you give it, a tube amplifier is definitely not worth it. By spending extra money to put a tube in your signal chain, you are intentionally distorting the sound.   Note that modern high end A/D/A conversion equipment (which aims for perfect signal reproduction) never uses tubes. The marketing pitch on tube equipment is that it does change the sound that you give it. Don't buy a tube amplifier unless that is what you want.   Now, if your goal is not to amplify signal accurately, but rather to make a sound that you personally find pleasing, a tube may yield some benefits.   You can listen to some tube amps at different levels to decide what you personally prefer. Does this make a tube amp worth it? Bear in mind that there are many ways of creating harmonic distortion (in the analog domain, or emulated with digital techniques), and many are cheaper than tubes, which are expensive to produce.   The high cost of tubes is not a function of the fact that it was difficult to engineer their particular audio qualities. The way tube amplifiers color audio is a historical function of the fact that engineers were not able to compensate for the changes they introduce.   Many people have now decided that this is a valuable property - but the production of tubes is becoming relatively more expensive as demand for them diminishes and they require specialty, limited-run manufacturing (compared to transistors, demand for which is growing).   In all, thinking from your practical needs before jump into any conclusion, whether tube amplifier is worth it or not, there’s no absolute answer to this question. VIII. How to Extend the Life of the Tube Amplifier?    The problem of short life of the tube amplifier is often criticized, but this is often not a problem of the tube amplifier itself, but a defect in the circuit design and a problem in use. It should be noted that a good quality tube amplifier must have a correctly designed circuit, sufficient heat dissipation, and thoughtful shock absorption.   In use, the tube amplifier must have good ventilation and heat dissipation. Overheating of the temperature will inevitably shorten the life of the tube, so the tube amplifier should be kept as low as possible.   Vibration is not good for tube amplifiers, so it is important to take anti-vibration measures to avoid vibration as much as possible. If these two can be achieved, the service life of the tube amplifier can be at least doubled. For this reason, there should be a proper space around the tube amplifier equipment, especially above it, in order to have good convection ventilation, if possible, a fan can be used to help dissipate heat.   When the cathode of the tube amplifier has not reached the required temperature, the high-voltage power supply is immediately applied, and its cathode will be damaged, which will also shorten the life of the tube amplifier.   Therefore, if the tube amplifier equipment has a preheating device, it must be used. For example, first turn on the filament low-voltage power supply to preheat, and then turn on the high-voltage power supply. If there is no preheating device, don't rush to connect the input signal, you can turn the volume down to the minimum, wait for 20-30 minutes to warm up the machine before using it.   If the indirectly heated rectifier tube is used to supply the high voltage of the whole machine, it just provides a simple and effective high voltage delay. In addition, do not switch the power supply frequently during normal use.   Of course, if the tube amplifier circuit is designed correctly and the wrong use is avoided, the tube amplifier will not "die young". It should be normal for the tube amplifier to use thousands of listening hours.   The most common mistakes in circuit design are: 1. The potential difference between the filament and the cathode of the tube amplifier is too high 2. The screen or screen grid voltage of the tube amplifier is applied to the maximum value 3. The filament voltage of the tube amplifier is too low or too high 4. Improper installation position of the tube amplifier causes the electrode to overheat and the high-voltage power supply does not have a delay device, etc.   Therefore, these problems should be avoided when designing the circuit to effectively extend the service life of the tube amplifier. FAQ 1. Why is a tube amp better? Tubes, like analog recordings, have a more full-bodied sound than transistor gear. There's a "roundness" to tube sound that solid-state gear never equals. Tubes are less forgiving about mismatches, so to get the best out of a tube amp it must be used with just the right speaker. 2. What is tube amplifier used for? Tube amplifiers, or tube amps as they're commonly called, are tiny electronic or electromagnetic components that are used to boost electric current in devices to improve their performance. It's what makes your hearing aid pick up sounds through a microphone from all around you. 3. Are tube amps worth it? In many cases, tube amps do not require the amount of maintenance that they have a reputation for. As long as you properly take care of your gear, owning a tube amp is simple and very well worth it for the tone. 4. How long should a tube amp warm up? 20 to 30 minutes. As a rule of thumb, your tube amp needs to be warmed up for 20 to 30 minutes at least before you can start playing your guitar. 5. Why are tube amps louder? When tubes are driven outside their linear region, for the first 12db or so of overdrive the harmonics that they produce trick the human ear into thinking that the sounds are getting louder, when in fact the sound is getting progressively more distorted. 6. How does a tube amplifier work? The power transformer and rectifier work together as an electron pump which pulls electrons out of the amp circuit creating a positive voltage (electron scarcity = positive voltage). The amplifier's electronics need DC to amplify. The amp is powered by DC but the guitar signal moving through the amp is AC. 7. What's the difference between a tube amp and a regular amp? The physical difference between a solid-state amp and a tube amp is that a solid-state machine derives amplification from electronic transistors, while a tube amp uses vacuum tubes (also known as valves). ... Solid-state amps are great for players who want maximum headroom (a.k.a a loud, clean, undistorted signal). 8. Which is better tube amp or solid state? Tube amps are generally more expensive in initial cost and to operate (because you need to replace the tubes occasionally), and solid-state amps are generally less delicate and more reliable. Many players, however, feel that tube amps yield a warmer, more musical tone and more musical-sounding distortion. 9. How often should a tube amp be serviced? 15 years. If its a well made amp, recap every 10 or 15 years, retube as needed. Fenders might go many years without needed a power tube replaced. 10. How many watts do I need in a tube amp? 100 watts. You'll need a solid state amp that has around 100 watts, or a valve amp that has around 50 watts. This will usually give you enough volume that you can be heard over the drummer, without having to push your amp's volume too hard so that the distortion becomes overbearing.

IntroductionUSB is very common, because it is indispensable for data transmission and charging. In modern life, we can see one or more USB ports on desktop computers, laptops, TVs, game devices, cars, media players, phones, and other electric devices, etc. USB devices are very important for our life. Look at your computer or smart phones, we probably know what it used for, however, fewer people know the full name of USB and what the real meanings of USB protocols and USB types.USB Ports, Cables, Types, & ConnectorsCatalogIntroductionⅠ Figure USB Ports and Standards OutⅡ USB Port Colors MeaningⅢ USB-C vs Type CⅣ USB 2.0 vs USB 3.0Ⅴ According to Labels Behind USB PortsHere are some easy steps to identify USB ports with different standards.Ⅰ Figure USB Ports and Standards OutUSB (universal serial bus) aims for input and output interfaces standard. It is widely used in information transformation products such as personal computers and mobile devices. The USB interface has hot-swappable, plug-and-play functions, and can be connected to a variety of external devices, such as a mouse and keyboard, etc. Our mobile phone charging uses the USB connector. These USB devices give us great convenience. USB chargers, USB connectors, USB hub, USB ports and USB cables, are all USB the same? What is USB 2.0 and USB 3.0? Low speed, full speed, and high speed mean what? What are Type-A, Type-B, and Type-C? Here you will get a full answer.Versions of USBThe USB 1.0/2.0/3.0 we often say refers to the technical specifications. The biggest difference among them is speed, that is, they indicate the speed of USB transfer files. The maximum transmission bandwidth of USB 3.0 is up to 5.0Gbps (640MB/s). Now many high-speed U disks or hard drives of portable electric devices use USB 3.0 or USB 3.1. USB also includes the old USB 1.1 standard and  USB 2.0 standard. The traditional maximum transfer rate of USB 1.1 is 12Mbps. Generally, manufacturers call its products that comply with the USB 1.1 standard as "full-speed USB." When the high-speed USB 2.0 was first introduced, the highest transmission rate was only 240Mbps. Later, the USB Promoter Group increased the rate to 480Mbps in October 1999, which is 40 times faster than the traditional USB 1.1. USB 2.0 is backward compatible with USB 1.1. Of course, USB 1.1 devices are "upward compatible" with USB 2.0, but they cannot reach the transmission speed of USB 2.0 and automatically stay at low speed. The maximum length of the USB 2.0 cable is 5 meters, but if five USB adapters are used, the maximum length can be up to 30 meters.Although you'll still be able to connect old-school devices with USB Type-A or USB Type-B connectors, but now you have more choices, that is USB4. USB4 is a USB system specified in the USB4 specification which was released in version 1.0 on 29 August 2019 by USB Implementers Forum. It leverages the Thunderbolt 3 protocol to deliver speeds up to twice as fast as the USB version it replaces. The USB4 architecture defines a method to dynamically share a single high-speed link with multiple end device types to best serve the transfer of data by type and application. USB-A, USB-B, and USB-C Port Types-Which is faster?Type-A/B/C determines the appearance of the USB ports. For example, the mouse, keyboard, USB flash drive and other interfaces we use are generally Type-A, which is also the most widely used interface. Type-B is more common in printers, monitors and other devices. In the past, Micro USB and Mini USB commonly used in mobile phones were portable versions of USB 2.0. The appearance of Type-C is very recognizable, slimmer. Its biggest feature is flippability, that is, USB-C connector has no up or down orientation, so you never have to flip it over to plug it in.1) Type-A: Standard USB PortType-A is the most common types of USB ports on computers. It has a notable feature: direction requirements. The connector (male port) must be inserted into the interface (female port) from a certain direction, in addition, because the appearance of the two sides of the USB male port is very close, this insertion process often makes mistakes.2) Type-B: Commonly used in printer equipmentType-B is the most common and popular data interface type on printers and displays, and some displays will also use it.3) Type Micro-B: USB standard for mobile devicesCurrently, most Android phones use the Micro USB interface (USB Micro-B), which is still widely used in various mobile portable devices.4) Type-C: It will become mainstreamAlthough Type-C has just appeared, it is foreseeable that as the USB Type-C technology matures, various notebooks, tablets and even smart phones in the future will begin to use the USB Type-C interface. Ⅱ USB Port Colors MeaningColorUSB ConnectorUSB Speed StandardNoteWhiteUSB-A or USB-B  Micro USB-AUSB 1.0 or USB 1.1*BlackUSB-A or USB-B Micro USB-BUSB 2.0 Hi-Speed*BlueUSB-A or USB-BUSB 3.0 Super Speed*RedSleep-and-Charge USB-AUSB 3.1 Gen 2 USB 3.2Usually denotes an "always on" portYellowSleep-and-Charge USB-AUSB 2.0 or USB 3.0Higher power or "always on" portⅢ USB-C vsType CThe Type-C is the same as the USB C, because the USB C is also called USB Type-C. However, there are slight differences between them. Let’s look at the following facts.Features of USB-C Connector:1. Ultra-thinThe old USB port size is 14mm * 6.5mm, while the USB-C is only 8.4mm * 2.6mm.2. No OrientationLike the Lightning, there will be no problem regardless of whether it is plugged in or reversed. It claims to be able to up to 10,000 times of repeated plugging and unplugging.3. Fast Transfer RateThe maximum transfer rate of the USB-C port is 10Gb per second, which is much faster than USB 3.0.4. Two-way TransmissionUnlike the old USB port, the power can only be transmitted in one direction. The USB-C port is bidirectional, so it can have two transmission power ways. Therefore, users can not only use laptops to charge mobile devices, but also use other devices or mobile power sources to charge laptops.5. Strong Power Supply CapabilityThe standard specification cable equipped with Type-C connector can pass 3A current, and it also has a super USB power supply capacity, which can up to 100W of power.6. Backward CompatibilityUSB-C can be compatible with the old USB protocol, but users need an additional adapter.USB-C refers to the Type C port that uses the USB 3.1 standard, but it should be noted that USB-C is not equal to Type C. Because there are many Type C devices that can only reach USB 2.0 or USB 3.0 transfer rate.With the improvement of technology, Type-C also supports the USB3.1 standard. Because the voltage and current increase, the coding consumption is reduced, from 20% of USB 3.0 to 3%. In other words, users can quickly transfer data and video through Type-C, or charge faster. Also users can charge other devices with their mobile phones. As for the display, when using Type-C for data transmission, there is no need to use another power cord to power the display, which solves the problem of messy desktop cables. Even the relatively high-end HDMI and DP ports cannot do it.The USB-C connector can be expanded into three: power supply/ USB transmission/ VGA or HDMI, which is the next-generation mainstream USB interface. The type-c cable is also of great help to the arrival of the 5G. Because the port of it becomes smaller, the flattening of electronic products is promoted. And in the transmission of audio and video, the tc data line has faster speed. At present, well-known technology manufacturers such as Sony and Apple have widely used type-c cables on their electrical devices because they can support multiple formats and reduce the limitations of USB. In short, the arrival of the 5G actually wants everyone to experience faster bandwidth, so the corresponding supporting facilities should also keep up. The type-c cable is undoubtedly one of them. Ⅳ USB 2.0 vs USB 3.0Although USB has developed to the USB3.1 protocol, we often see two types of USB 2.0 and USB 3.0 on devices. How do we distinguish these two interface types in daily use? Some people will say that USB 3.0 port is blue and USB2.0 port is black, which is easy to distinguish. In fact, it is not. Even though most USB3.0 ports use blue, there are many special cases. Here are some examples. The color of the USB ports on some models does not have any special treatment, and it looks no different from USB 2.0 type, and it is all black. However, it is often marked with "SS" in front of the logo. "SS" is the abbreviation of "SuperSpeed USB", which means connector or port that uses the USB 3.0 standard. The black USB type is also suitable for USB 3.0. The USB ports in Apple's new MacBook notebooks are all USB 3.0 standard, but in order to keep in harmony with the color of the computer cover, a white connector design is adopted. The USB ports on the Razer gaming notebooks are also USB 3.0, but in order to match the bright green keyboard backlight on the body and the Razer logo, the color of the USB port adopts "green". It improves the recognition of the machine and the brand, because no third-party manufacturer has adopted a green USB interface design. In addition, distinguish the metal pins of the USB ports. Generally, USB 2.0 uses a row of 4 pins, while USB 3.0 has a two-row pin design, with 5 pins in the front row and 4 pins in the back row. In addition, there is also a hybrid port of eSATA and USB 2.0, which can plug in both USB devices and eSATA interface devices. However, they are common in business models of previous years. Ⅴ According to Labels Behind USB Ports"+" sign - It represents the USB interface with high current output capability. The ordinary USB interface provides a maximum current of 500mA, but it may not be able to drive when encountering "high energy consumption" devices such as mobile hard disks and USB optical drives. Therefore, when it appeared, the output current on this interface can reach 1000mA (1A), which greatly enhances the drive capability."SS" - It is actually a symbol of USB 3.0. If the USB port has “SS” (or “SuperSpeed”) on its label, it’s a USB 3.0 port. If it’s“SS 10”, it’s a USB 3.1 port."Lightning Logo" -It generally appears on notebooks, and the USB port with it has a power-off charging function. That is, it can use its own battery or an external power supply to charge the mobile device when it is turned off. The lightning mark with an arrow indicates the Thunderbolt 3: two-way charging and two-way data transmission. Thunderbolt 3 supports for up to 40Gbps of throughput, alongside reduced power consumption and the ability to move as much as 100 watts of power over the interface. And it also means that a single cable is all you need to push power and transfer a large amount of information (up to and including video data for two 60Hz 4K displays) to and from even a complex device like a computer, something many laptop manufacturers have been quick to take advantage of.USB is an important interface on the computer. Almost 90% of the external devices are connected by it for mobile hard drives, such as U disks, printers, etc. Understanding the above information can analyze and solve the most common problems of unrecognized external devices of USB. At the same time, it is also very useful for us to choose USB products. Ⅵ Frequently Asked Questions about USB Types and USB Versions1. What are the different types of USB ports?Types of USB Ports and ConnectorsUSB-AUSB-BUSB-B MiniUSB-B MicroUSB-CLightning 2. How can I tell the difference between USB 2.0 and 3.0 ports?You can generally tell the difference between USB 1.0, 2.0, and 3.0 by color alone. While the size and shape may be identical, the key is to look at the color of the plastic inside the device. The USB 1.0 features a white plastic color, while USB 2.0 is black, and the USB 3.0 is blue. 3. What is the difference between USB Type A and C?The USB-A has a much larger physical connector than the Type C, Type C is around the same size as a micro-USB connector. ... The beauty of Type C is that it can be inserted any way up as the connector pins are the same on either side. 4. Are USB 2.0 and 3.0 ports the same?The A connectors still work properly so any 2.0 device with a 2.0 cable can be used with 3.0 ports or hubs. To sum up: USB 3.0 devices require 3.0 cables. ... USB 2.0 cables can be used with 3.0 ports but the transfer rate will fall back to 2.0. 5. Why is my USB 3.0 port not working?Update to the Latest BIOS, or Check USB 3.0 is Enabled in BIOS. In many cases, your motherboard will be responsible for software issues related to your USB 3.0 ports or any other ports on the motherboard. For this reason, updating to the latest BIOS may fix things.