What is the primary use of a varistor in electrical circuits?

A varistor, also known as a voltage-dependent resistor, is primarily used in electrical circuits to protect against voltage surges. It functions by changing its resistance based on the voltage applied across it. When the voltage exceeds a certain threshold, the resistance of the varistor decreases significantly, allowing it to shunt excess current away from sensitive components in the circuit. This rapid response helps prevent damage that could be caused by voltage spikes, such as those from lightning strikes or switching surges.

In contrast, the other options describe functions that do not align with the specific purpose of a varistor. Amplifying signals is typically the role of components like transistors or operational amplifiers, while storing energy is usually a function of capacitors or inductors. Regulating current flow is the responsibility of devices like resistors or current regulators. Thus, the primary use of a varistor remains its protective capability against voltage transient events, making it an essential component in safeguarding electrical systems.