Metal Oxide Varistor： ： Application Note Equipment Protection against Line Transient Damage The varistors have many advantages which make it ideal for use as a suppressor on AC or DC power line. AC/DC Equipment to be protected Equipment to be protected AC/DC Fig.4 Absorption of line-line and line-ground surge in single-phase system Fig.3 Absorption of line-line surge in single-phase system System. AC220V Equipment to be protected Equipment to be protected AC220V Fig.6 Absorption of line-line and line-ground surge in three-phase system Fig.5 Absorption of line-line surge in three-phase system Protection of Components Switching Inductive Load The transistor in Fig.7 is to operate a solenoid, inductive load. The energy stored in inductor is dissipated in the reverse bias conduction of the transistor and might cause transistor breakdown. A varistor can be connected, collector-to-base, to dissipate the stored energy in the forward bias state without damaging the transistor. V+ Fig.7 Solenoid circuit with varistor protection. THINKING ELECTRONIC INDUSTRIAL Co., LTD. 1 www.thinking.com.tw 2008.07 Metal Oxide Varistor： ： Application Note Transient Protection of Solid State Circuit Modern electronic equipments and appliances contain solid state circuits that are susceptible to malfunction or damage caused by transient voltage spikes. Fig.8 Semiconductor protection Extend the Life of Relay Contacts When the current in inductive load is interrupted by mechanical contacts, the voltage across the contacts builds up and cause arcing which is destructive to the contacts. Varistors can be applied to prevent initiation of the arc. M THINKING ELECTRONIC INDUSTRIAL Co., LTD. 2 Fig.9 Contact protection www.thinking.com.tw 2008.07