Abstract: An electrical resistance heater controller is provided with a plurality of circuit branches connected in parallel with each other and in series with a heating element and an external AC power source. Each circuit branch includes the series connection of a capacitor and a solid state switch. The switches are controlled by a gating device to switch during the zero crossing of the AC source voltage waveform. Power delivered to the heating element is controlled by varying the amount of series capacitance in the circuit.

Abstract: A controller system using high frequency switching by providing a bilateral switch gated on and off at a frequency about ten times the source frequency and the duty cycle determined by pulse width modulation of the high frequency waveform in accordance with window heater temperature.

Abstract: In a control interface circuit for selectively applying a signal to initiate a function in a control device, such as solid state power controller, there is an optical coupler whose primary side is connected in series with a plurality of impedance elements. The transistor switch elements are associated with the various impedances to selectively modify the amount of impedance in the active circuit between the control input terminals. The transistor switch elements are optically controlled by optical coupler devices receptive of inputs from the control device and are maintained with a means for supplying operating voltage that limits the voltage to a value that can be charged in less than the sampling pulse time.

Abstract: A control circuit for turning on an optical isolation unit only when an input signal is at least of a given magnitude or threshold level. The circuit exhibits a resistive input below the threshold level and a constant current characteristic above the threshold. An arrangement of transistors is provided to bypass the opto-isolator below the threshold and to drive the opto-isolator with substantially constant current above the threshold.