Transient voltage suppression diode
A transient voltage suppression diode
is a device used to protect sensitive electronics
from voltage spikes induced on connected wires. The device can be represented by two mutually opposing zener diodes in series with one another connected in parallel with the circuit to be protected. While this representation is schematically accurate physically the devices are now manufactured as a single component. The device operates by shunting excess current when the induced voltage exceeds the zener breakdown potential.
Another method for transient suppression is the varistor.