| 摘要 |
PURPOSE:To prevent the flow of a backward current to a transistor (TR), by cutting off the base voltage of the TR when the power supply voltage of a voltage stabilizing circuit which supplies the power supply voltage to a load via the TR is lower than the output voltage of the TR. CONSTITUTION:A capacitor C12 which forms a circuit together with resistances R11 and R12 and diodes D11 and D12 absorbs the voltage at a point C where the reference voltage is produced while the ripple contained in the power supply voltage VCC, and load voltage VL12 receives no effect. When the ripple increases to satisfy VCC<VL, a differential circuit consisting of TRs 18 and 19 works. Then the collector current of the TR18 starts to flow and is turned back by a current mirror consisting of TRs Q20-Q22 and a diode D14 to be supplied to the base of a TRQ23. Then the TRQ23 and the TRQ17 are turned on and off respectively, and the base current and therefore the current of a TRQ11 are also turned off. The electric charge of a capacitor 11 does not flow to the power supply side but compensates the drop of V4. As a result, a countermeasure is possible to a large ripple by increasing the capacitance of the capacitor 11. |
