Patent ID: 7538537
Filing Date: 2009-05-26
Classification: G05F

Abstract:
1. A constant-voltage circuit which converts an input voltage input to an input terminal into a predetermined constant voltage and outputs the predetermined constant voltage from an output terminal, comprising: an output voltage control transistor which outputs a current corresponding to an input control signal to the output terminal; and a control circuit section which detects a voltage of the output terminal and controls operations of the output voltage control transistor so that the detected voltage becomes a predetermined voltage; wherein the control circuit section amplifies a change of the voltage output from the output terminal, and makes the output voltage control transistor increase the output current for a predetermined period when the voltage of a signal obtained by amplification of the change is suddenly decreased at a speed more than a predetermined speed, the control circuit section includes an output voltage detecting circuit section which detects the voltage output from the output terminal and generates a voltage proportional to the detected voltage and outputs the generated proportional voltage; a first control circuit section which controls the operations of the output voltage control transistor so that the proportional voltage becomes the reference voltage; an amplifier circuit section which amplifies the change of the voltage output from the output terminal and outputs the amplified change through an output of the amplifier circuit section; and a second control circuit section including a coupling capacitor coupling the output of the amplifier circuit section to an input of the second control circuit section, wherein said second control circuit section makes the output voltage control transistor increase the output current for the predetermined period when the voltage of the signal output from the amplifier circuit section is suddenly decreased at a speed more than a predetermined speed, and whose response speed is greater than that of the first control circuit section for the change of the voltage output from the output terminal.