Power supply having a predetermined value of input impedance

Claim 1

A circuit for power supply, comprising: a comparator circuit means for comparing an input signal voltage, in which alternating current signals are superposed on a direct current voltage, with a reference voltage and producing a non-inverted signal when said input signal has a fluctuation less than said reference voltage and an inverted signal when said input signal has a fluctuation more than said reference voltage; a first constant-output-cuurent circuit means for generating a constant-output-current in response to a non-inverted output current from said comparator circuit means; a first output-voltage-stabilizing circuit means for generating a stabilized output voltage in response to an output from said first constant-output-current circuit means; a second output-voltage-stabilizing circuit means for receiving said input signal voltage and generating said reference voltage; and a second constant-output-current circuit means including a first current mirror circuit means driven in response to an inverted output current from said comparator circuit means and a second current mirror circuit means driven by an output from said first current mirror circuit means and having NPN type transistors for flowing a superfluous current to a low potential line, said NPN type transistors each being connected at the collector thereof to a high potential line and at the emitter thereof to said low potential line.