| 摘要 |
PURPOSE:To attain sure driving without being affected by the variation of the characteristic of a power transistor (TR) and the temperature change by providing a turn-off detecting circuit of a TR, and controlling a reverse voltage applied to the power TR. CONSTITUTION:The TR turn-off detecting circuit 8 supervises a vase voltage VB of the power TR4 and is operated to be a positive voltage when the voltage VB is within the set level Ev of a comparator 8 and to be a negative voltage when the voltage VB exceeds the set level. When a base signal is turned off, an otput of a comparator 6 attains a positive voltage, the TR4 is driven, a TR5 is turned on and a reverse voltage is applied to the base of the TR4. When the TR4 is turned off, the voltage VB is a negative voltage, the output of the comparator 8 is a negative voltage, the TR4 is turned off and the reverse voltage by the TR5 is turned off. Thus, the storage time and the falling time of a carrier are decreased, thereby ensuring the operation of the TR4. |
