Patent ID: 6928176

Claim:
A switching circuit built in IC for earphone and loudspeaker of portable information device, comprising a ear phone jack, a diode, two input bias resistors, and an operational amplifier; one terminal of each of said two input bias resistors is connected respectively with a positive terminal and a negative terminal of said operational amplifier, the other terminal of each of said two input bias resistors is connected with the ground; an output of said operational amplifier is used for driving a loudspeaker; excepting said ear phone jack and said loudspeaker, said diode, said two input bias resistors and said operational amplifier are designed integrally to form an IC; when a earphone plug is not inserted into said earphone jack, an audio output is passed through a switch in said earphone jack to be fed to said positive terminal of said operational amplifier, said audio output is also passed through said diode to be fed to said negative terminal of said operational amplifier; when said earphone plug is inserted into said earphone jack to open said switch, said audio output is fed to an earphone, and said audio output is not fed to said positive terminal of said operational amplifier, but is passed through said diode to be fed to said negative terminal of said operational amplifier.