Amplifier circuit and power supply provided therewith

Abstract

An amplifier circuit includes first and second resistors that are serially connected to each other between bases of first and second transistors that flow the same current as that in a differential transistor pair made up of two transistors. A capacitor is provided between a junction of the first and second resistors and the collector of the first transistor on the output side. The amplifier circuit has a gain whose frequency characteristic is determined by a low-pass filter realized by the second resistor and capacitor connected to the second transistor. The frequency characteristic lowers a gain of the frequency that causes output oscillation, thereby preventing output oscillation. The two resistors divide a resistance between the bases of the sub transistors, so as to reduce a resistance of the second resistor. As a result, the effect of phase compensation becomes weaker and the load response characteristic of the power supply improves. This enables the DC regulated power supply, even if it is of an intermediate current type which produces an output current of about 500 mA, to prevent output oscillation without reducing the load response characteristic, even when a chip-stacked ceramic capacitor is used as the output capacitor.