How to judge voltage and current feedback
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How to judge voltage and current feedback

Posted Date: 2024-01-22

In electronic circuits, measures (or processes) that apply part or all of the output quantity (output voltage or output current) to the input loop through a certain circuit form to affect the input voltage or input current of the input amplification circuit) - —called feedback.

There are two key points to note when understanding the concept of “feedback”:

(1) A path must be established between the output terminal and the input terminal;

(2) After the output quantity acts back to the input terminal, it must have a certain impact on the input quantity.

A certain circuit form that connects the output terminal to the input terminal and has an output that affects the input signal is often called a feedback path.

What are the feedback types of amplifier circuits?

The feedback types of amplifier circuits usually include the following:

1. Voltage Negative Feedback: This is the most common and commonly used type of feedback. In voltage negative feedback, part of the output signal is fed back to the input and subtracted from the input signal to reduce the difference between the output signal and the input signal. This feedback method improves the gain, frequency response and nonlinear distortion of the amplifier circuit, thereby improving the stability and performance of the system.

2. Current Negative Feedback: In current negative feedback, part of the output current is fed back to the input terminal, subtracting from the input current. This feedback method can reduce the nonlinear distortion of the amplifier circuit and improve the stability and linearity of the voltage gain. Current negative feedback is often used in amplifier circuits that require high precision and low distortion.

3. Positive Feedback: Positive feedback will make the output signal and the input signal in phase or enhance the phase relationship. This feedback method will cause the gain of the amplifier circuit to become unstable and even cause oscillation. Therefore, the use of positive feedback is generally avoided in amplifier circuit design, and negative feedback is used to stabilize the system.

Although negative feedback is widely used in most amplifier circuits, different amplifier circuits may require different types of feedback to meet specific needs.

How to judge voltage and current feedback

Judgment of voltage and current feedback

(1) Definition method

Direct judgment based on voltage and current feedback definitions. That is, when the size of the feedback signal is proportional to the output voltage, it is voltage feedback; when it is proportional to the output current, it is current feedback.

(2) Output short circuit method

'Short circuit' the output voltage, or set the load R=0. If the feedback signal no longer exists at this time, that is, X=0, it is voltage feedback; if the feedback signal still exists, it is current feedback.

The feedback principle of the amplifier circuit is to re-introduce a part of the output signal to the input end and combine it with the input signal to change the working state and performance of the amplifier circuit. The specific principles are as follows:

Feedback network: A feedback network is introduced into the amplifier circuit to feed part of the output signal back to the input. This feedback network can be composed of resistors, capacitors, operational amplifiers and other components. Through the feedback network, the introduced feedback signal is mixed with the input signal.

Error signal: Subtract the mixed feedback signal from the input signal to obtain the difference signal, which is the error signal. The error signal represents the difference between the output signal and the desired signal.

Adjust the input signal: adjust the input signal according to the error signal. By correspondingly adjusting the amplitude, phase and other characteristics of the input signal, the output signal is made closer to the desired signal.

Adjust the working state: The introduction of feedback signals will affect the working state of the amplifier circuit, such as operating point, bias current, etc. By adjusting these working states, the gain, linearity and other characteristics of the amplifier circuit can be changed.

Stability: Feedback systems can help stabilize the operation of amplifier circuits. When external factors cause the operating point of the amplifier circuit to change, the feedback signal can adjust the output of the amplifier circuit accordingly to maintain system stability.

Generally speaking, through the feedback principle, the amplifier circuit can adjust itself according to the error signal and change its working state to make the output signal closer to the desired signal. Negative feedback can also reduce gain, improve linearity, extend frequency response, and adjust input and output impedance. Therefore, the feedback principle is an important method for designing and optimizing amplifier circuits.

Review Editor: Huang Fei


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