Voltage Follower Tips (1), Voltage Follower Features + Features Voltage Follower Circuit

Voltage followers are used in major electronic devices, but most people do not understand voltage followers. In order to improve everyone's understanding of the voltage follower, this article will reveal the true face of the voltage follower, and introduce the characteristics of the voltage follower and its circuit, let's understand together.

1. What is a voltage follower?

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 and the collector voltage are in the same phase, that is, the input voltage and the output voltage are in the same phase, that is, the voltage amplification factor of the voltage follower is always less than and close to 1. When RF=0, R1=∞, that is, uo=ui, Auf=1, the output voltage follows the input voltage to make the same change, which is called a voltage follower.

Second, the calculation and analysis of the voltage follower

A voltage follower is a circuit with a gain equal to one whose output voltage follows the input voltage

In the non-inverting DC amplifier, when R1=∞, the voltage follower shown in Figure (a) can be obtained; when R1=∞, and Rf=R2=0, the voltage follower shown in Figure (b) can be obtained device. According to the calculation formula of the non-inverting DC amplifier Auf, it can be obtained: Auf≈1

Third, 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.

Fourth, 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.

The above is the relevant content of the "voltage follower" brought by the editor. Through this article, I hope you have a certain understanding of the voltage follower.