Abstract: A switched mode power supply circuit is provided that converts an input DC or AC voltage to a constant DC output voltage. The circuit uses a combination of a switch and an inductor at the output stage. When the switch is open, a current through the inductor decreases linearly until it reaches zero. Then the switch is closed, and the inductor current increases linearly until it reaches an upper limit, at which time the switch is opened, and the inductor current starts decreasing again. The upper limit of the inductor current is computed by a support circuit, and thus it does not need to be provided by sensing the input voltage independently. The computation uses the durations ratio D of a recent fall time duration of the inductor current divided by a recent rise time duration of the inductor current. The maximum inductor current is computed by multiplying a constant current value by D.times.(1+D). The result is a circuit with resistive only input impedance.

Abstract: An illumination control system uses two photocells, one directed toward an illuminated lamp and the other directed from the ceiling downwardly into the illuminated zone. A feedback signal is derived from the two photocell signals and a reference intercept signal. The feedback signal and a reference set point signal are input into an error amplifier. The error amplifier generates a control signal for setting the illumination in controlled lamps. The photocell signals are variously scaled to provide balancing between them and matching with the intercept signal. Scaling factors and intercept signal level arc set in a calibration procedure that establishes feedback circuit response consistent with a design set point transfer function.