Why choose a varistor for protection circuits? 1

A varistor is a passive component whose resistance changes significantly with voltage, classified as a nonlinear semiconductor device. Its characteristic is that it exhibits high resistance under normal operating voltage, having minimal impact on circuit performance, while rapidly reducing resistance during overvoltage events to absorb substantial electrical energy, thereby protecting downstream circuits from damage caused by high-voltage surges.diode

The working principle of a varistor can be likened to a voltage-controlled resistive valve. Under normal operating voltage, this "valve" remains essentially closed, making it difficult for current to pass, thus exhibiting a high-resistance state. Once the voltage exceeds the preset threshold (known as the breakdown voltage), the "valve" rapidly opens, allowing current to flow smoothly. At this point, the varistor's resistance drops sharply, enabling it to conduct large currents in a short time, thereby dissipating the energy of the overvoltage and preventing damage to the circuit.diode

The reasons for selecting a voltage-dependent resistor (VDR) for protection circuits are as follows:diode