Patent ID: 8050544

Claim:
An electronic control device for regulating the voltage across a high-side load, especially for regulating a fan in a motor vehicle, with a control voltage (V 1 ) which is referenced to system ground and which is mirrored to positive high-side supply voltage, wherein the control voltage (V 1 ) is supplied to the base of a first transistor (Q 1 ) operated in common-emitter connection, which transistor (Q 1 ) has, in the emitter circuit, a first resistor (R 1 ) and, in the collector circuit, a second resistor (R 2 ) and, in series with the latter, the base-emitter diode of a second transistor (Q 2 ); the second transistor (Q 2 ) is of the same conductivity type as the first transistor (Q 1 ); the first and second transistors (Q 1 , Q 2 ) are parameter-matched, thermally coupled transistors of the same conduction type; the base-emitter diode of the second transistor (Q 2 ) compensates for effects of the base-emitter diode of the first transistor (Q 1 ), whereby the voltage drop across the series connection composed of the base-emitter path of the second transistor (Q 2 ) and the second resistor (R 2 ) is an exact image of the voltage drop across the series connection composed of the base-emitter path of the first transistor (Q 1 ) and the first resistor (R 1 ); the voltage drop across the series connection composed of the base-emitter section of the second transistor (Q 2 ) and the second resistor (R 2 ) serves as a command variable for the regulation.