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Temperature protection circuit working in the AC grid

2016-09-22 06:50  
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Temperature protection circuit working in the AC grid
It is very dangerous that many devices are working with the over-allowable temperature, so we must set the protection circuit. The thermistor showes the low resistive in lower temperature. With the increasing of temperature, it's resistance increases in proportion. The final resistance can be up to several megohms. If we add the thermistor between the two-way SCR's cathode and anode to let the two-way SCR connects to the 220 AC power supply through the load, so in the normal temperature, the two-way SCR will be trig whenever the voltage is over-zero, at this time, the SCR is equivalent to the entire conduction, and the load gets the power. Otherwise, if the outside temperature exceeds the rated temperature, the thermistor will be high resistive, the so that the thyristor is not conduction any more to cut off the load circuit.