Metal Oxide Varistor： Application Note 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 MOV Equipment to be protected MOV AC/DC MOV MOV Fig.4 Absorption of line-line surge in single-phase system MOV MOV Fig.5 Absorption of line-line and line-ground surge in single-phase system MOV Equipment to be protected AC220V Equipment to be protected Equipment to be protected AC220V MOV MOV MOV MOV Fig.7 Absorption of line-line and line-ground surge in three-phase system Fig.6 Absorption of line-line surge in three-phase system Protection of Components Switching Inductive Load The transistor in Fig.8 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 to dissipate the stored energy in the forward bias state without damaging the transistor. V+ MOV THINKING ELECTRONIC INDUSTRIAL Co., LTD. All specifications are subject to change without notice. 4 Fig.8 Solenoid circuit with varistor protection www.thinking.com.tw 2014.05 Metal Oxide Varistor： Application Note Transient Protection of Solid State Circuit Modern electronic equipments and appliances contain solid state circuits, and the circuits are susceptible to be malfunctioned or damaged by transient voltage spikes. Fig.9 Semiconductor protection MOV 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 causes arcing which is destructive to the contacts. Varistors can be applied to prevent initiation of the arc. M MOV Fig.10 Contact protection LED Driver Surge Protection & LED ESD Protection I out Vin Full Bridge Recitifier Switch AC Varistor For Surge Protection Boost I out LED Driver IC R ext I out PWM I out LED 1 SMD Varistor For ESD Protection LED 2 LED 3 Fig.11 LED protection THINKING ELECTRONIC INDUSTRIAL Co., LTD. All specifications are subject to change without notice. 5 www.thinking.com.tw 2014.05 Metal Oxide Varistor： Application Note Thermally Protected Varistor Application Circuit Current Fuse L Power Input Thermal fuse element Thermally Thermally Varistor protected varistor TVT Series TVT Series Monitor Lead Circuit to be protected R MOV Fig.12 Thermally protected varistor for power protection LED N IC Protection against Electro-Static Discharge (SMD Varistor Application) +VCC Signal line IC Power supply SMD Varistor SMD Varistor Fig.13 IC protection Noise Suppression (SMD Varistor Application) SIG.1 SIG.2 SIG.3 SIG.4 SMD Varistor Equipment to be protected Fig.14 Protection of signal equipment COM THINKING ELECTRONIC INDUSTRIAL Co., LTD. All specifications are subject to change without notice. 6 www.thinking.com.tw 2014.05 Metal Oxide Varistor： Application Note USB Protection (SMD Varistor Application) PPTC Resettable fuse VBUS D+ USB Port DGND SMD Varistor Fig. 15 USB protection Low capacitance ESD Suppressor THINKING ELECTRONIC INDUSTRIAL Co., LTD. All specifications are subject to change without notice. 7 www.thinking.com.tw 2014.05