| 摘要 |
<p>PURPOSE:To obtain a circuit that has excellent reliability and can be improved in electric characteristics and IC-implemented by selectively activating the 1st amplifier for the 1st sound radiator and the 2nd amplifier for the 2nd sound radiator by detecting the connection state of the 2nd sound radiator. CONSTITUTION:The 1st amplifier 6 for the 1st sound radiator, e.g. a loudspeaker, and the 2nd amplifier 7 for the 2nd sound radiator, e.g. an earphone, are provided and when the contact of earphone jack 3 is opened with the earphone plug inserted, switch circuit 8 detects the above-mentioned state electrically to turn on amplifier 6 while putting amplifier 7 into operation. When the contact of earphone jack 3 is closed with the earphone plug uninserted, on the other hand, switch circuit 8 detects the output DC potential of amplifier 7 to put amplifier 6 into operation while turning off amplifier 7.</p> |
