| 摘要 |
PURPOSE:To operate a constant-voltage to a low voltage area, and to reduce a cost by splitting a resistance for supplying a current to a constant-voltage diode from a high voltage side power source, and connecting the diode to said resistance. CONSTITUTION:In a constant-voltage circuit of a series dropper type, a control transistor (hereinafter, TR) Q21 is controlled by an error amplifying TRQ22. These TRs Q22, Q23 form an error amplifying circuit, and a split potential of an output terminal 22 is compared with a reference voltage VDZ of a constant-voltage diode DZ21. As a result, a main power source is obtained from a low voltage input terminal 21 and a reference voltage is obtained from a high pressure side input terminal 23, but in this case, a Zener current is supplied to said constant-voltage diode DZ21 through resistances R26, R27, and also connected to the low voltage side input terminal 21 through a diode D21 from a connecting point of both the resistances. In this way, when an input voltage VIN becomes equal to the reference voltage VDZ, a current flows to the diode D21, and an output voltage Vout drops equally to VIN. |
