Patent ID: 6225709
Filing Date: 2001-05-01
Classification: H04N

Abstract:
A power supply circuit for an electric device having a main power supply switch and a stand-by switch, comprising:a main power supply switch for turning ON/OFF the electric power which is inputted from a commercial power source;a stand-by switch which is provided in the subsequent stage of said main power supply switch for turning ON/OFF the power supply to a main power supply circuit;a stand-by power supply circuit which is provided in the subsequent stage of said main power supply switch and is able to output a first power supply voltage necessary for a stand-by circuit in an electric device according to the voltage from said commercial power source, and wherein said first power supply voltage falls with a predetermined time constant with turning off of the voltage supply from said commercial power source;controlling means which is included in said stand-by circuit, operated by said first power supply voltage, provided with a signal detection terminal and a control terminal to control said stand-by switch, and is able to control turning ON/OFF of said stand-by switch according to the control signals from said control terminal; anda second switch which is connected between an output terminal of said stand-by power supply circuit and said signal detection terminal of said controlling means, turned ON/OFF in the manner interlocking with turning ON/OFF of said main power supply switch, and supplies voltage, which varies with turning ON/OFF of said main power supply switch, to the signal detection terminal of said controlling means,wherein said controlling means is able to store the turning off of said main power supply switch in a storing means by comparing the voltage of said first power supply voltage which varies with said time constant with the voltage of said signal detection terminal which varies with the interlocked operation of said second switch when said main power supply switch is turned off, and controls an electric device so as to be put in the operation status by turning on said stand-by switch according to the stored content in said storing means when said main power supply switch is turned on again.