Varistors
Varistors are manufactured from a non-homogeneous material, giving a rectifying action at the contact points of two particles.Many series and parallel connections determine the voltage rating and the current capability of the varistor.
Varistors provide reliable and economical protection against high voltage transients and surges which may be produced. They have the advantage over transient suppressor diodes in as much as they can absorb much higher transient energies and can suppress positive and negative transients.