Power supply with current regulating circuit

Abstract

A power supply which includes terminals for connection to an electric power source, a storage capacitance, an electrical charging circuit and an operative arrangement for connecting storage capacitance in series with the charging circuit across the terminals. The power supply has a charging circuit which includes a first resistor, a second resistor, a third resistor and a rectifier, constituted by at least one diode, in series. A first transistor, which has a collector-emitter path and a base-emitter path, is operatively connected so that the base-emitter path is connected in parallel with the first resistor. A fourth resistor is provided, the fourth resistor being connected in series with the collector-emitter path of the transistor and the third resistor. In one embodiment, a plurality of additional transistors, connected in Darlington configuration, includes a second transistor and a final transistor, each of the additional transistors having its collector connected to a circuit point between the third resistor and an electrode of the diode. The first transistor and the last transistor have their emitters connected via a current-limiting PTC fifth resistor which may act as a fuse. The first transistor and the second transistor have their respective collector and base conductively connected. The connection of the third resistor provides internal feedback. The fifth resistor, when in series with the first resistor in the base-emitter circuit, provides external feedback. A field-effect transistor, preferably a MOSFET, can replace the Darlington configuration.