| 摘要 |
PURPOSE:To prevent the destruction of switching transistor and diode due to excessive current, by providing a current limit circuit with a switching transistor. CONSTITUTION:A resistance R5 is connected between the emitter of a transistor Q3 and the smoothing circuit, and two diodes D2, D3 are connected at the cross point between the base of the transistor Q3, resistor R5 and smoothing circuit. The collector current of a transistor Q2 is the base current of the transistor Q3, and when the base current of the transistor Q3 is increased, the collector current Ic of the transistor Q3 is increased. The collector current Ic is limited at the value, which is equal to the sum of the voltage caused with the collector current Ic and the emitter resistance R5 and the base to emitter voltage VBE of the transistor Q3, enabling to decrease the excessive current of the transistor Q3 and the excessive current of the diode D1. |
