| 摘要 |
<P>PROBLEM TO BE SOLVED: To reduce the cost of components by simplifying a circuit structure needed for performing constant voltage control of a power source for driving an interphone load circuit, and save the power by reducing the power consumption. <P>SOLUTION: Of a main transistor Tr1, an error amplifier transistor Tr2, a diode D1 and a Zener diode ZD1 which constitute a low saturated constant voltage control part 12, the error amplifier transistor to which a base bias current is applied when Low level is applied to a control transistor Tr3 compares a reference voltage V1 of a reference voltage source generated by the Zener diode and applied to a base and an output voltage V2 between collector-earth of the main transistor negatively returned to an emitter through the diode, or the output voltage to the interphone load circuit 10, and changes the base bias current of the main transistor based on the comparison result, whereby the output voltage is made constant. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
