| 摘要 |
PURPOSE:To prolong the service life of a battery by turning on/off an output current corresponding to a difference voltage between a battery voltage and a reference voltage based on an intermittent signal and amplifying the output current controlled at its on/off to drive a speaker. CONSTITUTION:A reference voltage Vref from a generating part 101 is applied to the base of one transistor(TR) out of a pair of differential TRs 124 in a conversion part 102 and a voltage Vif is impressed to the base of the other TR. When an intermittent signal to be an external input is applied from a decoding part in a receiver to the base of a switching TR 131 in a switching part 104, the TR 131 executes switching operation in response to its ringing command. Consequently, an output current sent from a current mirror 127 of a conversion part 102 to an amplifying part 103 is controlled so as to be turned on/off and a speaker 111 is driven so as to generate ringing sound. At the time of generating the ringing sound, the power supply voltage VCC is driven so as to be always secure the minimum operation voltage Vmin and above, so that the battery 113 can be used up to the Vmin and the service life of the battery 113 can be prolonged. |
