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.
MOV
Equipment AC/DC Equipment AC/DC MOV To be To be protected protected
MOV M OV
Fig.5 Fig.4 Absorption of line-line Absorption of line-line GDT and line-ground surge in single-phase system surge in single-phase system System.
MOV MOV
Equipment AC Equipment AC To be 220V To be 220V protected MOV protected MOV MOV
MOV
MOV
Fig.6 Fig.7 Absorption of line-line and Absorption of line-line GDT surge in three-phase system line-ground 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 Fig.8 Solenoid circuit with varistor protection
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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 MOV 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 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
Vin I out Full Bridge Recitifier Boost I out Switch LED Driver IC R ext I out
Varistor PWM I out AC For Surge Protection
LED 1 SMD Varistor LED 2 For ESD LED 3 Protection Fig.11 LED protection
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Thermally Protected Varistor Application Circuit
Current Fuse L
Monitor Lead Thermal fuse element Circuit to be Power Thermally Thermally protected Input protectedVaristor R TVTvaristor Series MOV TVT Series LED Fig.12 Thermally protected varistor for power N protection
IC Protection against Electro-Static Discharge (SMD Varistor Application)
+VCC Signal line Power supply IC
SMD Varistor SMD Varistor Fig.13 IC protection
Noise Suppression (SMD Varistor Application)
SIG.1 SIG.2
SIG.3 Equipment Fig.14 to be Protection of signal SIG.4 protected equipment SMD Varistor COM
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USB Protection (SMD Varistor Application)
PPTC Resettable fuse
VBUS D+ USB Port D-
GND Fig. 15 USB SMD protection Varistor
Low capacitance ESD Suppressor
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