Patent ID: 8035367

Claim:
An electronic device comprising: a system circuit operating based on an adaptor voltage which is input to a power source terminal; and a detection circuit detecting the adaptor voltage and an adaptor current corresponding to the adaptor voltage by a resistor coupled between the power source terminal and the system circuit, wherein the detection circuit comprises: an error amplifier outputting an error signal corresponding to a difference between the adaptor voltage and a reference signal; a current control circuit coupled to a control terminal through which an identifying voltage is input and outputting, based on the error signal, a control current corresponding to the adaptor voltage; a monitoring circuit coupled to the control terminal, comparing a reference voltage with a voltage corresponding to a potential of the control terminal based on the identifying voltage, and producing, based on a result of the comparison, a detection signal indicating whether or not an external power source connected to the power source terminal is suitable; a switch control circuit turning on/off, based on the detection signal a switch coupled between the power source terminal and the resistor; and a setting circuit setting the potential of the control terminal.