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In the power circuit on the primary side of the circuit, to solve transient inrush current is typically metal oxide varistor (MOV). These devices will clamp the input surge current at a voltage level, the level of the power components can not be affected and work. The main selection criteria including MOV voltage, energy performance, and peak pulse current handling performance.
MOV MOV operating voltage is the breakdown can not work properly (become conductive) and voltage level. The voltage is usually the first to determine the parameters, and simple. To specify the operating voltage, line voltage equipment will have to increase by 20% to allow for growth in the power system voltage. The aim is to ensure MOV transient events in the system to respond, not react to the temporary status. Figure 1.
Integrated device helps reduce component count
Under normal operating conditions, applied to the MOV on the AC line voltage will not exceed the device maximum AC RMS voltage (VAC RMS) rating, and assume that as long as the transient energy does not exceed the maximum rating of the MOV, short time transient events can be clamped in a suitable voltage level. However, sustained abnormal over-voltage / limited current conditions (such as neutral loss) may lead to MOV into thermal runaway state.
Usually placed in series with a thermal cut MOV (TCO) device to protect the MOV from overheating damage. A typical line voltage transient protection scheme can also be integrated an overcurrent protection devices (such as fuses), to protect the system from the over-current exceeds a predetermined level of damage caused by overload.
Over-current conditions and thermal runaway
Tyco Electronics AC 2Pro. Device is a polymer positive temperature coefficient (PPTC) element and an MOV components into a thermal protection device in order to overcurrent or overvoltage condition provides the reset function. This integrated approach can help device manufacturers meet IEC61000-4-5 and IEC60950 industry requirements.
Unprotected standard components are usually limited to MOV 275VAC RMS, in order for the universal input voltage range. Loss in the neutral conditions, they may overheat and negative results, even if the circuit has been used upstream fuse or power resistors.
AC 2Pro device of PPTC devices help prevent thermal runaway, rheostat to maintain the surface temperature to 150 ° C and prevent the device from overvoltage transients to the insecurity caused by the temperature.
Work
Although applied to a MOV on the AC line voltage is generally not exceed the device's maximum continuous operating voltage rating, but may occur beyond these limits over-voltage transients. 2Pro PPTC device will integrate technology with MOV, MOV when a long period of sustained overvoltage condition, it can enhance the over-current and thermal protection.
In the case of overvoltage transients, shown in Figure 2 of the neutral loss events, 2Pro devices in the PPTC element will heat, escape and enter a high impedance state, MOV device to help reduce the risk of failure.
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