How is varistor connected in circuit?
Varistors are connected in circuits across a mains supply either phase-to-neutral, phase-to-phase for AC operation, or positive-to-negative for DC operation and have a voltage rating to suit their application.
What is the use of varistor in power supply?
Varistors, also called metal-oxide varistors (MOVs), are used to protect sensitive circuits from a variety of overvoltage conditions. Essentially, these voltage-dependent, nonlinear devices have electrical characteristics similar to back-to- back Zener diodes.
What causes MOV to fail?
When subjected to stresses above its ratings, an MOV can fail as a short circuit. If applied conditions significantly exceed the energy rating of the device, and current is not limited, the MOV may be completely destroyed. For this reason, the use of current-limiting fuses is suggested.
What is the function of a a varistor?
A varistor is a voltage-limited protection device. Utilizing the non-linear characteristics of the varistor, when an overvoltage occurs between the two poles of the varistor, the varistor can clamp the voltage to a relatively fixed voltage value, thereby achieving protection of the subsequent circuit.
What is the clamping voltage of a varistor?
This is due to its high resistance acting as an open circuit and remains constant until the voltage across the varistor (either polarity) reaches a particular “rated voltage”. This rated or clamping voltage is the voltage across the varistor measured with the specified DC current of 1mA.
How does the resistance of a varistor change with voltage?
This Varistor has two semiconductor elements, and provides over voltage protection in a circuit, similar to a Zener diode. So how does the change in applied voltage change its resistance? Well, the answer lies in its composition. Since it is made of semiconductor material, its resistance dips as the voltage across it increases.
What is a non-conductive varistor?
A varistor remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its “clamping voltage”, thus varistors are typically used for suppressing line voltage surges. Varistors can fail for either of two reasons.