| 摘要 |
The main switching transistor 11 is serially connected between a load 12, 12' and a source of supply 13, R. An auxiliary transistor 15, the base of which is controlled through a voltage sensing device, for example a Zener diode 18 has its main switching path connected to the base of the main switching transistor 11 to control the main switching transistor 11 to become conductive in case of overvoltage, sensed by breakdown of the Zener diode 18. If the load is inductive, an additional inductive turn-off current bypass transistor 22, 22' can be provided (FIG. 2, 3), rendered conductive when overvoltage of an inductive kick is sensed, to bypass turn-off current around the main semiconductor switching transistor, or, in an alternative connection, to control the main switching transistor to again become conductive and itself bypass the inductive turn-off current, so that current flow due to overvoltages, or inductive turn-off current will be conducted by semiconductors operated under conditions of controlled conduction.
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