Temperature sensitive regulator for electric heater - uses thermistor in bridge circuit to sense temp. and uses error to drive LED-photoresistor combination to alter timing of oscillator

摘要

The appts. temp. sensitive regulation of the operation of an electrically powered heater. A thermistor in a bridge circuit is used to sense the ambient temperature, and the bridge error amplified by an operational amplifier whose output drives a light emitting diode. The light emitting diode is placed near a photoresistor which is connected in parallel to a potentiometer which acts as the timing resistor in a relaxation oscillator using an integrated circuit connected in astable oscillator mode, operating at a low frequency. The output of the astable oscillator controls the gate of a triac which switches the AC mains through the electric heating load.