Define a varistor and its role in transient voltage suppression.
1 Answer
A varistor, short for "variable resistor," is an electronic component designed to exhibit a non-linear electrical resistance in response to changes in voltage. It is commonly used to protect electronic devices and circuits from transient voltage spikes or surges, which can occur due to lightning strikes, switching events, electromagnetic interference, or other sources.
The key role of a varistor lies in transient voltage suppression, where it acts as a voltage-clamping device. Here's how it works:
Normal Operation: Under normal operating conditions, a varistor has a relatively high resistance and conducts only a small current. This allows the circuit to function without any significant impact from minor fluctuations in voltage.
Transient Voltage: When a transient voltage surge occurs, such as a lightning strike or sudden power disturbance, the voltage across the varistor increases rapidly. Due to its non-linear voltage-current characteristics, the varistor's resistance drops sharply as the voltage surpasses a specific threshold known as its "clamping voltage."
Voltage Clamping: Once the voltage exceeds the clamping voltage, the varistor starts to conduct heavily, creating a low-resistance path for the excess current to flow. This effectively diverts the transient surge away from the sensitive components downstream, preventing the voltage from reaching dangerous levels and thus protecting the connected circuitry.
Absorption and Dissipation: The varistor absorbs and dissipates the excess energy in the form of heat. This heat is generated due to the high current flowing through the varistor during the transient event. Most varistors are designed to handle short-duration, high-energy transients without becoming damaged themselves.
Recovery: After the transient event subsides and the voltage returns to normal levels, the varistor's resistance returns to its higher state, allowing the circuit to resume its normal operation.
It's important to note that varistors have limitations. They can handle transient events up to a certain energy level, beyond which they might fail or degrade. Additionally, varistors are not suitable for protecting against prolonged overvoltage conditions or sustained power surges, for which more sophisticated protection mechanisms may be required.
In summary, a varistor plays a crucial role in transient voltage suppression by providing a controlled path for excess current during voltage surges, protecting sensitive electronic components from potential damage.
The key role of a varistor lies in transient voltage suppression, where it acts as a voltage-clamping device. Here's how it works:
Normal Operation: Under normal operating conditions, a varistor has a relatively high resistance and conducts only a small current. This allows the circuit to function without any significant impact from minor fluctuations in voltage.
Transient Voltage: When a transient voltage surge occurs, such as a lightning strike or sudden power disturbance, the voltage across the varistor increases rapidly. Due to its non-linear voltage-current characteristics, the varistor's resistance drops sharply as the voltage surpasses a specific threshold known as its "clamping voltage."
Voltage Clamping: Once the voltage exceeds the clamping voltage, the varistor starts to conduct heavily, creating a low-resistance path for the excess current to flow. This effectively diverts the transient surge away from the sensitive components downstream, preventing the voltage from reaching dangerous levels and thus protecting the connected circuitry.
Absorption and Dissipation: The varistor absorbs and dissipates the excess energy in the form of heat. This heat is generated due to the high current flowing through the varistor during the transient event. Most varistors are designed to handle short-duration, high-energy transients without becoming damaged themselves.
Recovery: After the transient event subsides and the voltage returns to normal levels, the varistor's resistance returns to its higher state, allowing the circuit to resume its normal operation.
It's important to note that varistors have limitations. They can handle transient events up to a certain energy level, beyond which they might fail or degrade. Additionally, varistors are not suitable for protecting against prolonged overvoltage conditions or sustained power surges, for which more sophisticated protection mechanisms may be required.
In summary, a varistor plays a crucial role in transient voltage suppression by providing a controlled path for excess current during voltage surges, protecting sensitive electronic components from potential damage.