Abstract: A constant power circuit for causing a constant power level to be dissipated by a load when an overpower condition is detected. The overpower condition is detected by measuring the voltage across and current drawn by the load in accordance with a programmed load value and determining whether the sum of the measured current and voltage exceeds the power limit for the load. In a preferred embodiment, the sum of the voltage and current is compared to a linear piecewise approximation of a constant power curve in the current-voltage plane, the curve representing the power limit for the load for the range of current and voltage magnitudes in which the load circuit may safely operate. When an overpower condition is detected, the power is dissipated by the load at a constant power level defined by the constant power limit by oscillating the power level within a hysteresis band about the constant power limit.

Abstract: Measurement of load current when a digitally controlled power supply is in a constant voltage mode and of voltage when it is in a constant current mode is achieved by dropping the current represented by the digital current selection signal in one case and the voltage represented by the digital voltage selection signal in the other case until the power supply would change its mode of operation as indicated by comparators. Actual change of mode is prevented by delaying or interrupting the application of the digital selection signals to their respective regulation circuits.

Abstract: A field effect transistor that shunts a gain control resistor of an operational amplifier is slowly rendered conductive by charging a capacitor through a gate to source resistor and rapidly rendered non-conductive by a transistor connected in parallel with said capacitor so as to prevent undesired transients in the output of the amplifier when the gain is changed from one discrete level to another.

Abstract: One junction field effect transistor is connected in shunt with an operational amplifier so as to render its gain zero when no voltage is applied to its gate and another junction field effect transistor is connected so as to shunt the output of the amplifier to ground when no voltage is applied to its gate.