Temperature control circuit

Abstract

A temperature control circuit is disclosed for controlling the firing angle of a thyristor such as a silicon controlled rectifier connected in series with a heater across an alternating power source. The control circuit comprises a field effect transistor having its source and drain electrodes connected for firing of the rectifier when the field effect transistor is rendered conductive, and a bias phase control connected to the gate of the field effect transistor for generating a fixed A.C. voltage component which is phase shifted by about 90.degree. with respect to the voltage of the power source together with a temperature dependent D.C. voltage component to control the firing angle of the silicon controlled rectifier in accordance with the heat generated by the heater, the sum of the A.C. and D.C. voltage components being fed to the gate of the field effect transistor. The temperature dependent D.C. voltage is generated by a circuit comprising a parallel arrangement including an adjustable resistor connected in series with a first diode and a temperature sensitive resistor connected in series with an oppositely poled second diode, each of such diodes being poled so as to produce a more negative D.C. voltage component with increasing temperature and vice-versa.

Dependencies are inferred from the claim text.