Patent ID: 7948223
Filing Date: 2011-05-24
Classification: G05F

Abstract:
1. A constant voltage circuit that converts an input voltage input to an input terminal into a predetermined constant voltage and outputs the predetermined constant voltage from an output terminal, the constant voltage circuit comprising: an output voltage control transistor that receives an input control signal from the input terminal and outputs a current according to the input control signal to the output terminal; a reference voltage generating circuit unit that generates and outputs a predetermined reference voltage; an output voltage detection circuit unit that detects an output voltage from the output terminal, and generates and outputs a proportional voltage that is proportional to the detected output voltage; and a first error amplifier that conducts the operation control of the output voltage to adjust the proportional voltage to correspond to the reference voltage; and a second error amplifier with a higher response speed for responding to a change in the output voltage compared to the response speed of the first error amplifier, the second error amplifier being configured to increase the output current of the output voltage control transistor for a predetermined amount of time in response to a sudden decrease in the output voltage, wherein the second error amplifier includes: a control transistor that conducts operation control of the output voltage control transistor according to an input control signal; a differential amplifying circuit that includes a first input terminal and a second input terminal, and is configured to input a predetermined bias voltage via the first input terminal and conduct operation control of the control transistor to adjust a voltage of the second input terminal to correspond to the predetermined bias voltage; a condenser that is connected between the second input terminal of the differential amplifying circuit and the output voltage; and a fixed resistor that is connected between the first input terminal and the second input terminal of the differential amplifying circuit.