Metal Oxide Varistor

Metal oxide varistor ( MOV ) is a voltage dependent resistor with symmetrical voltage-current characteristics that is design to protect all kinds of electronic devices or elements from switching and induced lighting surges. Its non linear exponenet characteristics with broad using range and mass production is gradually being used by varuous level of electric engineering.

1. Fast response time.
2. Excellent voltage ratio.
3. Low standby power and no follow on current.
4. High performance in surge current handling capability.
5. Low leakage current.
6. Wide voltage & energy ratio.

1. Varistor voltage : The varistor voltage is the voltage across the varistor measured at a specific current Ic(0.1 mA or 1.0 mA) of specified duration.
2. Maximum allowable voltage : The Maximum allowable voltage corresponds to the rest state of the varistor. The rest state voltage offers a low leakage current in order to limit the power consumption of the protected device and not to disturb the circuit to be protected.
3. Maximum clamping Voltage : Maximum clamping voltage is the maxumum voltage Vp between two terminals with the specified standard impulse current lp (8x20 Micro sec). The voltage value is an indication on the protective function of the varistor.
4. Withstanding surge current : Withstanding surge current is the maximum peak current for the varistor with the specified standard impulse current ( 8x20 Micro sec.) applied one time or two times and corresponding to a permissible variation of 10% in the varistor voltage change.
5. Energy : Maximum energy from one or a burst of pulses. It is the value within the varistor change of +10% when one impulse of 10x1000 Micro se. is applied. E = K x Vm imx T,E: Energy, K: Constant = 1.4 Vm : Max. clamping voltage at lm. T: Duration of surge current (1000 Micro sec.) Im : Max. allowable single surge current of 10x1000 Micro sec.
6. Rated power : The maximum power that can be applied within the specified ambient temprature. Capacitance : The capacitance of varistor is the reference value measured between the varistor terminals at specified frequency.

1. Direct lighting surges.
2. From magnetic induction.
3. Surge voltage by switching operation.
4. Surge voltage by grounding fault.
5. Induced lighting surges.
6. From electrostatic induction.

1. Identify the operating AC/DC voltage.
2. Select varistor operating voltage (AC/DC) about 10-20% higher than input voltage to allow line fluctuations.
3. MOV diameter be selected based on expected maximum surge energy.
4. Ensure the clamping voltages sufficient to protect your system.