Typical four circuits of varistors

Inter-line application circuit

The characteristic of this circuit is that the varistor R is connected in parallel between the power line incoming line or between the signal line and the ground line. When the voltage across R1 reaches the breakdown voltage, the resistance of R1 is rapidly reduced to achieve overvoltage protection. purpose.

As a varistor, a typical application is to protect the electronic product when the power line and the signal line transmitted over a long distance encounter lightning strikes and the line has a surge pulse. Generally, the connection of the varistor between the lines can be effective for the induced pulse between the lines, and the connection of the varistor between the line and the ground is effective for the induced pulse between the transmission line and the ground.

2. Inductive load application circuit

In the circuit, it is assumed that R1 is a varistor. When the clerk switch S1 is disconnected, a large back electromotive force is generated at both ends of the inductive load. At this time, R1 is used to limit this back electromotive force for protection purposes.

The varistor can usually be connected directly in parallel to the inductive load, but depending on the type of current and the amount of energy, a RC series snubber circuit can be considered.

3. Switch circuit contact application circuit

In the circuit, it is assumed that R1 is a varistor which is connected between the two contacts of the power switch S1 for absorbing the arc when the switch is opened and preventing the switch contacts from being burned by the arc.

4. Protect the semiconductor device circuit

A varistor is used to protect the semiconductor device circuit. In the circuit, it is assumed that R1 is a varistor which is connected between the collector and the emitter of the transistor VT1 to prevent the voltage between the collector and the emitter of the VT1 from being too high to damage the transistor. The protection circuit can also be used in semiconductor device circuits such as thyristors, high-power transistors, etc., which is an effective protection circuit for semiconductor devices, generally in parallel with the protection device to limit the withstand voltage lower than the protected device.