| 摘要 |
PURPOSE:To reduce the power loss of a control transistor (TR) when a load is short-circuited, by providing a diode and a resistance in series to the base of a control TR connected in series to a DC line. CONSTITUTION:To the base of a control TR1 connected in series to a DC line, a diode D and a resistance R8 are connected, and the other terminal of the resistance R8 is connected to the base of a current limit type protecting TR3 via a resistance R9; and one terminal of a current detecting resistance R4 is connected to the emitter of the TR3, whose collector is also connected betweem resistance R1 and R8. In normal operation, the base current of the TR1 is brought under the control of a TR4 to obtain a constant output voltage. If a current more than rated one flows to a load RL, the across voltage of the resistance R4 rises to turn on the TR3 and the base current of the TR1 is shunted to the TR3, decreasing a load current. In this case, the across voltage of the circuit of the resistance R8, diode D, and the base and emitter of the TR1 rises and the current flowing to the base of the TR decreases, thereby reducing the power loss of the TR1. |
