How does voltage affect the behavior of a varistor (voltage-dependent resistor)?
1 Answer
A varistor, also known as a voltage-dependent resistor (VDR), is an electronic component designed to have a highly nonlinear resistance-voltage characteristic. This means that its resistance changes dramatically in response to variations in applied voltage. Varistors are commonly used to protect electronic circuits and devices from overvoltage conditions by absorbing excessive voltage and limiting the voltage across the protected component.
Here's how voltage affects the behavior of a varistor:
Normal Operation:
At low voltages, varistors exhibit a high resistance and behave similarly to a regular resistor. This resistance is typically much higher than the rated voltage of the varistor. In this range, the varistor has negligible impact on the circuit's behavior.
Breakdown Voltage:
When the voltage across the varistor exceeds a certain threshold called the "breakdown voltage" or "clamping voltage," the varistor's resistance drops dramatically. This is the critical point where the varistor starts to conduct significantly. The breakdown voltage is determined by the material composition and construction of the varistor. Once this voltage is reached, the varistor effectively becomes a low-resistance path for current flow.
Clamping Effect:
As the voltage continues to rise beyond the breakdown voltage, the varistor's resistance remains low, which causes it to act like a short circuit. In this state, the varistor "clamps" the voltage across it to a relatively constant value, preventing further voltage increases. This clamping effect is crucial for protecting sensitive electronic components from voltage surges.
Energy Absorption:
The energy associated with the excessive voltage is absorbed by the varistor in the form of heat. This energy absorption prevents the voltage from reaching downstream components, thus safeguarding them from potential damage due to overvoltage events.
Recovery:
After the overvoltage event subsides and the voltage across the varistor decreases below its breakdown voltage, the varistor's resistance returns to its high state. This allows the circuit to return to normal operation.
It's important to note that varistors have limitations. They are designed to handle short-duration transient voltage spikes, such as those caused by lightning strikes or power surges, rather than sustained overvoltage conditions. If subjected to prolonged overvoltage conditions, a varistor can degrade or fail, potentially compromising its protective function.
In summary, the behavior of a varistor is strongly influenced by the applied voltage. Its resistance changes dramatically at its breakdown voltage, allowing it to protect circuits and devices by clamping excessive voltages and dissipating energy as heat.
Here's how voltage affects the behavior of a varistor:
Normal Operation:
At low voltages, varistors exhibit a high resistance and behave similarly to a regular resistor. This resistance is typically much higher than the rated voltage of the varistor. In this range, the varistor has negligible impact on the circuit's behavior.
Breakdown Voltage:
When the voltage across the varistor exceeds a certain threshold called the "breakdown voltage" or "clamping voltage," the varistor's resistance drops dramatically. This is the critical point where the varistor starts to conduct significantly. The breakdown voltage is determined by the material composition and construction of the varistor. Once this voltage is reached, the varistor effectively becomes a low-resistance path for current flow.
Clamping Effect:
As the voltage continues to rise beyond the breakdown voltage, the varistor's resistance remains low, which causes it to act like a short circuit. In this state, the varistor "clamps" the voltage across it to a relatively constant value, preventing further voltage increases. This clamping effect is crucial for protecting sensitive electronic components from voltage surges.
Energy Absorption:
The energy associated with the excessive voltage is absorbed by the varistor in the form of heat. This energy absorption prevents the voltage from reaching downstream components, thus safeguarding them from potential damage due to overvoltage events.
Recovery:
After the overvoltage event subsides and the voltage across the varistor decreases below its breakdown voltage, the varistor's resistance returns to its high state. This allows the circuit to return to normal operation.
It's important to note that varistors have limitations. They are designed to handle short-duration transient voltage spikes, such as those caused by lightning strikes or power surges, rather than sustained overvoltage conditions. If subjected to prolonged overvoltage conditions, a varistor can degrade or fail, potentially compromising its protective function.
In summary, the behavior of a varistor is strongly influenced by the applied voltage. Its resistance changes dramatically at its breakdown voltage, allowing it to protect circuits and devices by clamping excessive voltages and dissipating energy as heat.