Patent ID: 7579817

Claim:
A constant-voltage circuit, comprising: a common output terminal; a switching regulator operable to convert an input voltage to a rated voltage to be output at the common output terminal, the switching regulator including: a reference voltage generator, and a soft-start circuit connected to the reference voltage generator and operable to raise an output voltage of the reference voltage generator at a constant speed until the output voltage of the switching regulator has reached the rated voltage, wherein the soft-start circuitry and switching regulator are configured to start operating on receipt of a selection signal; and a series regulator connected to the soft-start circuit and operable to regulate a current so that an output current of the series regulator does not exceed a predetermined value and to convert the input voltage to the rated voltage to output to the common output terminal, the series regulator being configured to start operating simultaneously with the switching regulator on receipt of the selection signal and stop outputting a current to the output terminal on receipt of an operation completion signal from the soft-start circuit, and wherein the selection signal is input from outside the constant-voltage circuit for exclusively causing one of the switching regulator and the series regulator to operate.