Understanding Varistors: Protection Against Voltage Surges and Transient Spikes

Varistors, also known as voltage-dependent resistors (VDRs) or metal-oxide varistors (MOVs), are electronic components that protect devices from voltage surges and transient voltage spikes. They consist of a ceramic material with a high resistance coefficient doped with metal oxides, such as zinc oxide or titanium dioxide. The doping process alters the electrical properties of the ceramic material, allowing it to act as a voltage-dependent resistor. The ceramic material is sandwiched between two metal electrodes of zinc or copper connected to the external circuit.

Varistor Series (Source littelfuse.com)

The working principle of a varistor is based on the nonlinear relationship between the voltage and current in a material with a high coefficient of resistance. When the voltage across the varistor exceeds its breakdown voltage, which is determined by the composition and doping of the ceramic material, the resistance of the varistor drops dramatically, allowing current to flow through it. This behavior provides a low-resistance path for surge current, protecting the device from damage.

Varistors are commonly used in electronic circuits to protect sensitive components from voltage surges and transient voltage spikes. They are essential components in power supplies, AC line protection, and surge protectors for electronic equipment. Additionally, varistors can regulate voltage in certain applications by selecting a varistor with a specific breakdown voltage. This allows designers to develop circuits that regulate the voltage across the varistor and prevent it from exceeding a certain level.

In conclusion, varistors are critical components in modern electronics that protect devices from voltage surges and spikes. Their design and working principle are based on the nonlinear relationship between voltage and current in a high-resistance material, making them essential in power supplies and surge protection devices. With their ability to regulate voltage in certain applications, varistors play an important role in electronic circuit design.