Typical examples of varistor applications in the circuit

With the extensive development of science and technology, it has also led to the application of capacitors. Varistors are used in voltage protection, lightning protection, suppression of inrush currents, absorption of spikes, clipping, high voltage arcing, noise reduction, and protection of semiconductor components. What are the applications of varistors in the circuit? The editor will introduce you in detail.

1. Circuit input overvoltage protection:

Atmospheric over-voltage caused by lightning, most of the inductive overvoltage, lightning overvoltage generated on the transmission line discharge, this overvoltage voltage is very high, up to 100 ~ 10000V, causing great harm. Therefore, it is necessary to take measures against electrical equipment to prevent atmospheric over-voltage. Varistors can be used. Generally used in parallel with the equipment. If the electrical equipment requires a low residual pressure, multiple levels of protection can be used.

2. Prevent operation overvoltage protection circuit:

Operation overvoltage is a kind of overvoltage generated when the circuit working condition changes abruptly and the electromagnetic energy is rapidly transformed and quickly released. To prevent such overvoltage, varistor can be used to protect various power supply devices and motors.

3. Overvoltage protection of semiconductor devices:

In order to prevent the semiconductor device from being burned when overvoltage is generated due to some reasons during operation, commonly used varistors are used to protect the overvoltage between the emitter and the collector of the transistor, or the varistor is connected to the transformer once. Damage to the transistor. Under normal conditions, the varistor is in a high-impedance state with only a desired leakage current. When subjected to an overvoltage, the varistor quickly changes to a low-resistance state. Overvoltage energy is absorbed by the varistor in the form of a discharge current. After the surge voltage disappears, when the circuit or component is subjected to normal voltage, the varistor returns to high impedance. For diodes and thyristors, the varistors are generally connected in parallel with these semiconductor elements or parallel to the power supply, and should meet two requirements: First, the direction of the repeated action voltage should be greater than the varistor residual voltage, and second, non-repetitive actions. The reverse voltage is also greater than the residual voltage of the varistor.

4. Contactor, relay protector:

When the circuit containing the inductive load such as a contactor and a relay is cut off, the overvoltage can exceed several times the power supply voltage. Overvoltage causes arcing and spark discharge between contacts, burns the contacts, and shortens the life of the equipment. Because the varistor shunts at a high potential, the contacts are protected. When the varistors are connected in parallel with the coils, the overvoltage between the contacts is equal to the sum of the supply voltage and the residual voltage of the varistors. The energy absorbed by the varistors is the stored energy of the coils. When the varistors are connected in series with the contacts, the contacts The overvoltage is equal to the residual pressure of the varistor. The energy absorbed by the varistor is 1.2 times the stored energy of the coil.