Importance

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Abstract

A conventional circuit for blocking a semiconductor switching device (7) on overcurrent, the semiconductor switching device (7) having at least one continuously driven semiconductor switch (9), comprises a diver circuit (11), which has a driver stage (12) for each semiconductor switch (9), a control pulse generator (10) for producing control pulses (P.sub.1 to P.sub.6), which are fed in operation to a control input of the semiconductor switching device (7) via the driver circuit (11), and a monitoring device (34), which measures the current (I) flowing through the semiconductor switching device (7) and, when an overcurrent occurs, generates a fault signal (E), which initiates blocking of the semiconductor switching device (7). When the semiconductor switching device is being blocked, a high overvoltage can occur therein, possibly leading to destruction of the semiconductor switching device. In order to reduce, with little outlay, the overvoltage in the semiconductor switching device during blocking thereof, provision is made such that the operating voltage (U) of the driver circuit (11) is arranged to be switched over briefly by the fault signal to a lower, interim value corresponding to a lower current (I) through the semiconductor switching device (7) and then, within the maximum permissible duration for loading the semiconductor switching device (7) with an overcurrent, to be switched off completely.

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First Claim