Patent ID: 6816002
Filing Date: 2004-11-09
Classification: G05F

Abstract:
A circuit arrangement for controlling a current through a load comprising:a first and a second input terminal for connection of a supply voltage; a first and a second output terminal for connection of a load wherein the first output terminal is connected to the first input terminal; a first bipolar transistor, having a collector connected to the second output terminal, an emitter connected to the second input terminal and a base forming a base-emitter path; a first resistor, having a first terminal connected with the first input terminal and a second terminal connected with the base of the first bipolar transistor; a control circuit having a first terminal connected to the base of the first bipolar transistor and a second terminal connected to the emitter of the first bipolar transistor for evaluating the base-emitter voltage of the first bipolar transistor; the control circuit forming a bypass to the base-emitter path of the first bipolar transistor and branching the current through the first resistor such that the base current of the first bipolar transistor is virtually independent of the supply voltage across the input terminals, wherein the control circuit comprises a second and a third bipolar transistor each having an emitter, a collector and a base, the emitter of the second bipolar transistor being connected with the emitter of the first bipolar transistor the base of the second bipolar transistor being connected with a first terminal of a second resistor, whose second terminal is connected with the base of the first bipolar transistor, the collector of the second bipolar transistor being connected with a first terminal of a third resistor, whose second terminal is connected with the base of the second bipolar transistor, the collector of the second bipolar transistor being connected with the base of the third bipolar transistor, the emitter of the third bipolar transistor being connected with the base of the first bipolar transistor, and the collector of the third bipolar transistor being connected with the emitter of the first bipolar transistor, such that the second bipolar transistor is the same circuit type as the first bipolar transistor.