The clamping voltage of a varistor (Vc) is defined as the voltage at which the varistor begins to conduct significantly and "clamp" or limit the voltage across its terminals. Varistors are voltage-dependent resistors that protect electronic circuits from voltage spikes or transients by diverting excess voltage away from sensitive components.

During an overvoltage event, the varistor responds almost instantaneously by providing a low-resistance path between its terminals. This action diverts the excessive current away from the sensitive components in the circuit, thus preventing damage. Once the transient voltage subsides and returns to normal levels, the varistor returns to its high-resistance state, ready to protect the course from the next overvoltage event. The clamping voltage (Vc) of a varistor is a critical parameter that determines its effectiveness in suppressing transient overvoltages.

Clamping Voltage in a Varistor

Benefits of Clamping Voltage

• Circuit Protection: The primary purpose of using a varistor is to protect sensitive electronic components from voltage surges or spikes. When an overvoltage event occurs, the varistor responds by clamping and providing a low-impedance path for the excess current. The clamping voltage sets the maximum voltage allowed across the varistor during this transient event, ensuring that the voltage-sensitive components are not subjected to damaging levels of voltage.
• Voltage Limitation: The clamping voltage acts as a threshold level beyond which the varistor's resistance drops significantly, allowing it to conduct excessive current. By setting the clamping voltage appropriately, the varistor ensures that the voltage across the protected circuit does not exceed a safe limit, safeguarding sensitive devices and preventing damage.
• Let-Through Voltage: Although varistors are effective in limiting voltage spikes, they do exhibit a small amount of "let-through voltage" or "clamping overshoot" during activation. The clamping voltage should be carefully selected to minimize this overshoot and keep it well below the maximum ratings of the protected components.
• Application Suitability: Different electronic circuits may require different levels of protection depending on the sensitivity of the components and the expected overvoltage events. Varistors with specific clamping voltage ratings can be selected to suit the application's requirements, providing optimal protection without unnecessary overdesign or inadequate safeguarding.
• Safety and Compliance: Varistors with appropriate clamping voltage ratings ensure that electronic systems comply with safety guidelines and industry standards, reducing the risk of accidents, malfunctions, or failures.

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