Thermal switches provide circuit disconnect

Posted on Jan 6, 2013

A microcontroller implements the proper protective action when one of the temperature monitors detects an overtemperature condition. It is sometimes easier and more cost-effective to simply disconnect the offending circuit from the power supply without involving a microcontroller. A simple thermal-protection circuit (Figure 1) includes two temperature switches, IC1 and IC2, with active-high outputs. Temperature thresholds for these switches depend on resistors R1 and R2, and the switch outputs connect to the inputs of a dual-input OR gate, IC3.

You must take precautions to ensure that the SCR does not trigger on a false gate pulse. Power-supply transients can cause a false high signal at the output of the OR gate and cause the SCR to turn on. Once triggered, the SCR cannot turn off, and the fuse

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