Abstract: A power converter apparatus adapted for use in a defibrillating cardiac pacemaker, to selectively provide a prescribed high voltage useful in treating a cardiac fibrillation. A pulse generator-cyclically applies a relatively low battery voltage V.sub.s to a step-up transformer, to controllably charge a high-voltage capacitor. The time durations of the cyclic applications of the battery voltage V.sub.s are controlled by digital feedback of several parameters, including peak transformer current, average transformer current., battery voltage V.sub.s, and the voltage on the high-voltage capacitor. If any of the measured parameters is determined to be outside a predetermined limit, the pulsing of the transformer is incrementally modified. A smooth, efficient charging of the high-voltage capacitor thereby is provided.

Abstract: A switch, especially for use in a hand-operated storage-battery electric tool with a DC motor is proposed, in which control electronics are provided for changing the speed of the DC motor. In order to produce the switch as compactly as possible and without additional connecting lines to the power transistor and in order furthermore to influence positively the heat budget inside the switch, a contact system (5) and a freewheeling diode (8) are pivoted to a common bearing plate (11) which is connected in current-carrying and heat-conducting fashion via a connecting bolt (12) to a power transistor (7) on the housing. In this arrangement, the power transistor is cooled by a heat sink provided on the switch housing.