What is a varistor and its function in transient overvoltage protection?
1 Answer
A varistor, short for "variable resistor," is an electronic component designed to protect sensitive electronic devices and circuits from transient overvoltage events. Transient overvoltages, often referred to as voltage spikes or surges, are brief and sharp increases in voltage that can occur in electrical systems due to various reasons such as lightning strikes, switching operations, or other electrical disturbances.
The primary function of a varistor in transient overvoltage protection is to act as a voltage-dependent resistor. In normal operating conditions, the varistor has a relatively high resistance, allowing only a small current to flow through it. However, when the voltage across the varistor exceeds a certain threshold, typically referred to as its "clamping voltage," the varistor's resistance drops dramatically, allowing a large amount of current to flow through it.
This sudden decrease in resistance effectively diverts the excess current away from the sensitive components or circuitry that need protection. By shunting the excess voltage to ground or another lower-voltage path, the varistor prevents the voltage from reaching levels that could damage the connected equipment. Once the transient event passes and the voltage returns to a safe level, the varistor's resistance increases again, allowing the normal operation of the protected circuit to resume.
Varistors are commonly used in surge protectors, power strips, and electronic devices to provide a level of defense against transient overvoltages. They are particularly effective in safeguarding devices that are sensitive to voltage fluctuations, such as computers, televisions, and telecommunications equipment.
It's important to note that while varistors can provide effective transient overvoltage protection, they have limitations. Varistors have a finite lifespan and can degrade over time with repeated exposure to transient events. Additionally, extremely high-energy transient events, such as a direct lightning strike, might exceed the capabilities of standard varistors. In these cases, additional protective measures, like grounding and lightning rods, may be necessary.
The primary function of a varistor in transient overvoltage protection is to act as a voltage-dependent resistor. In normal operating conditions, the varistor has a relatively high resistance, allowing only a small current to flow through it. However, when the voltage across the varistor exceeds a certain threshold, typically referred to as its "clamping voltage," the varistor's resistance drops dramatically, allowing a large amount of current to flow through it.
This sudden decrease in resistance effectively diverts the excess current away from the sensitive components or circuitry that need protection. By shunting the excess voltage to ground or another lower-voltage path, the varistor prevents the voltage from reaching levels that could damage the connected equipment. Once the transient event passes and the voltage returns to a safe level, the varistor's resistance increases again, allowing the normal operation of the protected circuit to resume.
Varistors are commonly used in surge protectors, power strips, and electronic devices to provide a level of defense against transient overvoltages. They are particularly effective in safeguarding devices that are sensitive to voltage fluctuations, such as computers, televisions, and telecommunications equipment.
It's important to note that while varistors can provide effective transient overvoltage protection, they have limitations. Varistors have a finite lifespan and can degrade over time with repeated exposure to transient events. Additionally, extremely high-energy transient events, such as a direct lightning strike, might exceed the capabilities of standard varistors. In these cases, additional protective measures, like grounding and lightning rods, may be necessary.