How do varistors protect electronic circuits from voltage spikes?
1 Answer
Varistors, also known as voltage-dependent resistors or VDRs, are electronic components designed to protect electronic circuits from voltage spikes and transient overvoltages. They are commonly used as transient voltage suppressors (TVS) to safeguard sensitive components from damage due to sudden increases in voltage. Varistors work based on a property called "voltage-dependent resistance."
Here's how varistors protect electronic circuits from voltage spikes:
Voltage-Dependent Resistance: Varistors are made of semiconductor materials, typically zinc oxide. They exhibit a non-linear, voltage-dependent resistance characteristic. Under normal operating conditions, they have a relatively high resistance, so only a small amount of current passes through them.
Response to Voltage Spikes: When a voltage spike occurs, for example, due to lightning strikes, electromagnetic interference, or sudden power surges, the voltage across the varistor increases.
Breakdown and Conductance: Once the voltage across the varistor reaches a certain threshold (known as the "clamping voltage" or "breakdown voltage"), the semiconductor material inside the varistor undergoes a transition. This transition causes a significant decrease in the resistance of the varistor, turning it into a low-impedance path for current.
Diverting Excess Current: With the varistor now offering a low resistance path, it diverts the excess current away from the sensitive components or devices in the circuit. This, in turn, prevents the voltage spike from reaching and damaging the protected components.
Absorption and Dissipation: Varistors can absorb and dissipate the energy associated with the voltage spike. They behave like a voltage-activated switch, effectively "clamping" the voltage to a safe level.
Recovery: After the transient event passes and the voltage returns to normal levels, the varistor's resistance goes back to its high value, allowing normal operation of the electronic circuit to resume.
It's important to note that varistors have limitations, and their protective capabilities are not unlimited. They have a maximum energy-handling capability, which is usually specified by the manufacturer. If the energy of the voltage spike exceeds this limit, the varistor might fail to protect the circuit effectively. For high-energy transients or repeated overvoltage events, additional protective measures like fuses, circuit breakers, or gas discharge tubes might be necessary to ensure complete protection of the electronic circuit.
Here's how varistors protect electronic circuits from voltage spikes:
Voltage-Dependent Resistance: Varistors are made of semiconductor materials, typically zinc oxide. They exhibit a non-linear, voltage-dependent resistance characteristic. Under normal operating conditions, they have a relatively high resistance, so only a small amount of current passes through them.
Response to Voltage Spikes: When a voltage spike occurs, for example, due to lightning strikes, electromagnetic interference, or sudden power surges, the voltage across the varistor increases.
Breakdown and Conductance: Once the voltage across the varistor reaches a certain threshold (known as the "clamping voltage" or "breakdown voltage"), the semiconductor material inside the varistor undergoes a transition. This transition causes a significant decrease in the resistance of the varistor, turning it into a low-impedance path for current.
Diverting Excess Current: With the varistor now offering a low resistance path, it diverts the excess current away from the sensitive components or devices in the circuit. This, in turn, prevents the voltage spike from reaching and damaging the protected components.
Absorption and Dissipation: Varistors can absorb and dissipate the energy associated with the voltage spike. They behave like a voltage-activated switch, effectively "clamping" the voltage to a safe level.
Recovery: After the transient event passes and the voltage returns to normal levels, the varistor's resistance goes back to its high value, allowing normal operation of the electronic circuit to resume.
It's important to note that varistors have limitations, and their protective capabilities are not unlimited. They have a maximum energy-handling capability, which is usually specified by the manufacturer. If the energy of the voltage spike exceeds this limit, the varistor might fail to protect the circuit effectively. For high-energy transients or repeated overvoltage events, additional protective measures like fuses, circuit breakers, or gas discharge tubes might be necessary to ensure complete protection of the electronic circuit.