Robert Boschgmbh

David V Belzen

Immanuel Krauter

Thomas Aberle

To protect electrical equipment against excessive applied input signals which, for example, may be analog signals, excessive with respect to positive or negative excess voltage in relation to an upper reference level (U.sub.Ref) and/or a lower reference level (GND), collector current control of the transistor (12) at the input (3) of the protective circuit by three transistors (11, 13, 14) holds the voltage level at the input (3) at the reference voltage level when a driving or signal supply circuit provides an excess voltage. The input transistors, and the further transistors, are connected in the form of a current mirror. The circuit can be constructed in dual form (11-14; 21-24) to provide for protection against negative over-voltage as well. Due to the symmetrical circuit structure, excellent temperature compensation is obtained. The circuit can easily be constructed in the form of an integrated circuit.

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Hemmingen, Germany

David V Belzen