Transient over-voltage

A transient over-voltage or spike is an electrical impulse of short duration but high energy that is induced onto an electrical or electronic circuit from external sources; these may be repetitive or random. Repetitive examples include switch-on or -off of electrical motors or other heavy machinery, but random events like lightning strikes or electrostatic discharge (ESD) can also induce spikes onto vulnerable circuits.

The risk of transient over-voltage events, and ways to mitigate them, have become of increasing concern as electronic systems become ever-more essential to our working and personal lives. Data centres house ranks of potentially vulnerable servers, but equally susceptible devices exist in our cars, homes and pockets.

As these devices have proliferated, they have also become ever-smaller. This miniaturization has resulted in increased sensitivity to electrical stresses. Microprocessors for example, have structures and conductive paths which are unable to handle high currents from ESD transients. Such components operate at very low voltages, so voltage disturbances must be controlled to prevent device interruption and latent or catastrophic failures.

Accordingly, circuits are designed with transient protection devices that limit voltage or current amplitude, or transient times. Diodes, particularly Zener types, provide good overvoltage protection because they start conducting, and provide an alternative path for transient energy, if their input voltage exceeds a safe threshold. Current limiting can be provided by fuses, circuit breakers and thermal trip devices.

Capacitors, ferrite beads and resistors can be used to slow transient risetimes.