What is the principle of the voltage follower following characteristic circuit? In order to further improve your understanding of the voltage follower, this article will introduce the following characteristics of the voltage follower and the circuit principle of the voltage follower. If you are interested in the content of this article, you may wish to continue reading the following main text.

First, the characteristics of the voltage follower

The voltage follower has the characteristics of high input resistance and low output resistance. If you understand it at an extreme point, when the input impedance is high, it is equivalent to an open circuit to the front-end circuit. When the output impedance is very low, it is equivalent to a constant voltage source for the latter-stage circuit, that is, the output voltage is not affected by the impedance of the latter-stage circuit. . A circuit that is equivalent to an open circuit to the front-end circuit, and the output voltage is not affected by the impedance of the latter-stage, of course, has an isolation effect, even if the front-end circuit and the latter-stage circuit do not affect each other. The isolation function is to isolate the influence of the load on the input terminal. The role of the voltage follower

In the circuit, the voltage follower is generally used as a buffer stage and an isolation stage. Since the output impedance of the voltage amplifier is generally relatively high, usually in the range of several thousand ohms to tens of thousands of ohms, if the input impedance of the subsequent stage is relatively small, a considerable 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 it. Play a linking role. Another advantage of applying a voltage follower is that the input impedance is improved, so that the capacity of the input capacitor can be greatly reduced, which provides a prerequisite for the application of high-quality capacitors.

Another function of the voltage follower is isolation. In the HI-FI circuit, the controversy about negative feedback has been around for a long time. In fact, if there is no negative feedback function, I believe that most amplifier circuits cannot work well of. However, due to the introduction of a large loop negative feedback circuit, the back electromotive force 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 power amplifiers use a circuit without large-loop negative feedback in the final stage, trying to eliminate the drawbacks caused by the large-loop negative feedback by disconnecting the negative feedback loop. However, since the working current of the final stage of the amplifier varies greatly, its distortion degree is difficult to guarantee.

Here, the role of the voltage follower just reaches the application, placing 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.

Second, the following characteristics of the voltage follower

1. We take the CD voltage follower as an example to illustrate the following characteristics

2. The reason why CD has a voltage following effect is that its output is in the input loop, and the output impedance is relatively small, so it can be connected to a resistor, but the connected resistance is not unlimited, there is a minimum limit, because if the resistance If it is too small, there will be no follow feature. The resistance in the picture is too small, causing the tube below to enter the linear region

3. When the resistance is 1K, the output voltage is 264mv

4. When the resistance is 10K , the output voltage is 637mv

5. When the resistance is 50K , the output voltage is 750mv

6. When the resistance is 100K, the output voltage is 769mv

7. As can be seen from the above, when the load resistance is larger, the output voltage is higher, indicating that the following characteristics are better. Why do you say this? Because when the load is higher, the less current flowing through the load, the current is mainly determined by the current of the constant current source load tube, and the current of the constant current source load tube is constant, indicating that the output follows the input change.

Third, the circuit characteristics of the voltage follower

The input of the common collector circuit is high impedance and the output is low impedance, so that it can play the role of impedance matching in the circuit, and can make the amplifier circuit of the later stage work better. To give a typical example of application: the signal output of an electric guitar is high impedance. When connecting to a recording device or speaker, adding this voltage follower before the tone processing circuit will make the impedance match and the tone more perfect. This circuit is used in the input section design of many electric guitar effects.

The output voltage of the voltage isolator is similar to the input voltage amplitude, and it is in a high-resistance state for the front-stage circuit and a low-resistance state for the latter-stage circuit, thus "isolating" the front-end circuit.

The voltage follower is often used as an intermediate stage to "isolate" the influence between the front and rear stages, which is called a buffer stage at this time. The basic principle is to use its characteristics of high input impedance and low output impedance.

The voltage follower has the characteristics of high input impedance and low output impedance, which can be understood at an extreme point. When the input impedance is high, it is equivalent to an open circuit to the front-stage circuit; when the output impedance is very low, it is equivalent to a post-stage circuit. Constant voltage source, that is, the output voltage is not affected by the impedance of the subsequent circuit. A circuit that is equivalent to an open circuit to the front-end circuit, and the output voltage is not affected by the impedance of the latter-stage, of course, has an isolation effect, even if the front-end circuit and the latter-stage circuit do not affect each other.

Fourth, the principle of the voltage follower circuit diagram

The voltage follower is a common collector circuit, the signal is input from the base and the emitter is output, so it is also called the emitter output device. The base voltage is in phase with the collector voltage, that is, the input voltage is in phase with the output voltage. The main features of this circuit are: high input resistance, low output resistance, and the voltage gain is approximately 1, so it is called a voltage follower.

So what does the voltage follower do? In a nutshell, the voltage follower plays the role of buffering, isolating, and improving the load capacity. The input of the common collector circuit is high impedance and the output is low impedance, so that it can play the role of impedance matching in the circuit, and can make the amplifier circuit of the later stage work better. To give a typical example of application: the signal output of an electric guitar is high impedance. When connecting to a recording device or speaker, adding this voltage follower before the tone processing circuit will make the impedance match and the tone more perfect. This circuit is used in the input section design of many electric guitar effects. The output voltage of the voltage isolator is similar to the input voltage amplitude, and it is in a high-resistance state for the front-stage circuit and a low-resistance state for the latter-stage circuit, thus "isolating" the front-end circuit. The voltage follower is often used as an intermediate stage to "isolate" the influence between the front and rear stages, which is called a buffer stage at this time. The basic principle is to use its characteristics of high input impedance and low output impedance.

The voltage follower has the characteristics of high input impedance and low output impedance, which can be understood at an extreme point. When the input impedance is high, it is equivalent to an open circuit to the front-stage circuit; when the output impedance is very low, it is equivalent to a post-stage circuit. Constant voltage source, that is, the output voltage is not affected by the impedance of the subsequent circuit. A circuit that is equivalent to an open circuit to the front-end circuit, and the output voltage is not affected by the impedance of the latter-stage, of course, has an isolation effect, even if the front-end circuit and the latter-stage circuit do not affect each other. The emitter follower, also called the emitter follower, is a typical negative feedback amplifier. In terms of how the transistors are connected, it is actually a common collector amplifier. The emitter limit follower is essentially a voltage series negative feedback amplifier. The feedback voltage uf is the output voltage Usc namely: Therefore, the input voltage usr=ube+usc. Usually Usc>Ube, ignoring Ube, then usr≈usc. Obviously, this means that the voltage magnification of the emitter limit follower is approximately equal to 1.

Look at the phase relationship between the output voltage and the input voltage. When Usr increases, both ib and ie increase, and the emitter voltage ue(usc) also increases. Conversely, when Usr decreases, Usc also decreases. This means that the output voltage is in phase with the input voltage, precisely because not only is the output voltage equal in magnitude to the input voltage, but also in phase. The output voltage changes closely with the input voltage, and we call this circuit with the following characteristics "the emitter limit follower". As mentioned above, the voltage amplification factor of the emitter limit follower is close to 1, and there is no voltage amplification capability. But the emitter follower can get a large output current (ie=(1+β)ib) with a small input current. Therefore, it has the functions of current amplification and power amplification.