Circuit for controlling power dissipated by an electrical resistance

Abstract From the Canadian patent

A circuit for controlling the power dissipated by an electrical resistance coupled to a supply voltage which varies, includes a feedback circuit, coupled to the electrical resistance, for producing a feedback current corresponding to the current flowing through the heater. A correction circuit produces a correction current corresponding to variations in the supply voltage. An integrator receives the correction current and the feedback current and amplifies the error indicated by the correction current and the feedback current. A pulse width modulator receives the amplified error and controls the ON time of a switching device to control the flow of current through the electrical resistance. …