Audio signal output device in which optical signals are not output when a plug is not connected to an S/PDIF output terminal

1. An information processor including a digital signal output terminal, said information processor comprising:

optical signal generation means;

drive means for controlling said optical signal generation means based on received digital signals;

detection means for detecting whether or not a plug is connected to said digital signal output terminal; and

power supply cutoff means for cutting off the power supply to said drive means when said detection means has detected that a plug is not connected to said digital signal output terminal,

wherein said power supply cutoff means comprises:

a PNP transistor including a base that receives a connection detection signal that indicates whether or not a plug is connected to said digital signal output terminal and an emitter that is connected to a high-level voltage;

a pull-up resistor for pulling up said connection detection signal to a high-level voltage; and

an n-channel MOS transistor including a gate connected to the collector of said PNP transistor, a drain connected to a power supply voltage, and a source connected to the power supply input terminal of said drive means.

2. An information processor according to claim 1 , wherein said detection means comprises a detection pin that is connected to said connection detection signal and that, by being connected to a low-level voltage and by contacting a fitting metal part that is provided for fitting with said plug, sets said connection detection signal to a low level when a plug is inserted in the jack of said digital signal output terminal.

3. An information processor according to claim 1 , wherein said digital signal output terminal comprises an S/PDIF output terminal.

4. An information processor according to claim 2 , wherein said digital signal output terminal comprises an S/PDLF output terminal.

5. An audio signal output device including a digital signal output terminal, said audio signal output device comprising:

an optical signal generation means;

a drive means for controlling said optical signal generation means based on a received digital signal;

a detection means for detecting whether or not a plug is connected to said digital signal output terminal; and

a power supply cutoff means for cutting off the power supply to said drive means when said detection means has detected that a plug is not connected to said digital signal output terminal,

wherein said power supply cutoff means comprises:

a PNP transistor including a base that receives a connection detection signal that indicates whether or not a plug is connected to said digital signal output terminal, and an emitter that is connected to a high level voltage;

a pull-up resistor for pulling up said connection detection signal to a high-level voltage; and

an n-channel MOS transistor including a gate connected to the collector of said PNP transistor, a drain connected to the power supply voltage; and a source connected to the power supply input terminal of said drive means.

6. An audio signal output device according to claim 5 , wherein said detection means comprises a detection pin that is connected to said connection detection signal and that, by being connected to a low-level voltage and by contacting a fitting metal part that is provided for fitting with said plug, sets said connection detection signal to low level when a plug is inserted in the jack of said digital signal output terminal.

7. An audio signal output device according to claim 5 , wherein said digital signal output terminal comprises an S/PDIF output terminal.

8. An audio signal output device according to claim 6 , wherein said digital signal output terminal comprises an S/PDIF output terminal.