Composition, advantages and disadvantages of overvoltage protection self-locking control circuit

Knowledge about overvoltage protection circuits, an example of an overvoltage protection self-locking control circuit, introduces the circuit composition of the overvoltage protection circuit, the working principle of the circuit, the advantages and disadvantages of the circuit, and friends in need can refer to it.

Overvoltage protection self-locking control circuit

1. Overview (circuit category and main function description)

In a power supply system, when the feedback loop fails, the output voltage is out of control and the voltage rises beyond the specified range. At this time, the excessively high output voltage may cause damage to subsequent electrical equipment. In order to solve this problem, an overvoltage protection circuit is usually added to the power supply.

Here are three ways of overvoltage protection:

1) Clamping type: When the feedback fails, the output voltage is clamped at a fixed value through the overvoltage clamping circuit.

2) Intermittent protection type: When the feedback fails, the output voltage is restarted back and forth through the protection circuit, and the highest point of the output voltage is the overvoltage protection point.

3) Self-locking type: When the output voltage reaches the overvoltage protection point, the circuit is activated, the PWM is turned off so that the module has no output. After troubleshooting, restart the power supply, and the output can be powered normally.

2. Circuit composition (schematic diagram)

The following circuit is a self-locking control circuit:

3. Working principle analysis (main functions, performance indicators and implementation principles)

The figure above shows an isolated self-locking control circuit. When the overvoltage protection signal CONTROL terminal gives a high level, the transistor in U1 is turned on, and VCC is the power supply terminal of the entire circuit. Vcc gives Q2 a base current through R5, Q1 is turned on and enters the saturation state, the SHUT terminal is pulled to a low level by Q2, and the PWM power supply is turned off without output. Q2 also controls the conduction of Q1. When Q2 is turned on, the base current of Q1 goes to the ground through R2, Q1 is turned on, and another base current is provided to Q2 through R3 to maintain the conduction of Q2. Q1 and R1, R2, and R3 constitute the positive feedback circuit of Q2.

4. Advantages and disadvantages of the circuit

Advantages: It can effectively perform self-locking protection, and the entire circuit is equivalent to a thyristor.

Disadvantages: The entire circuit requires a fixed Vcc. When there is no power supply at the PWM power supply end, the VCC voltage in the above figure must also be guaranteed to exist.

5. Precautions for use

1) This circuit requires continuous power supply to be self-locking.

2) This circuit should not be used in unattended power supply systems.