| 摘要 |
An in-line amplifier is readily connectable to a standard telephone so as to allow for user adjustment of the volume presented to the receiver portion 15 of the handset 14. The in-line amplifier draws electrical power from a replaceable battery 18 so as to be easily attached to the telephone base unit 12. The in-line amplifier includes a voltage level detector 20, which operates to determine when the battery voltage level has fallen below the minimum operating voltage of the in-line amplifier. Ordinarily, the audio signal is passed from the telephone base unit 12 through a controllable amplifier 16 to the receiver portion 15 of the handset 14. However, when the voltage level detector 20 determines that the battery voltage level has fallen below the minimum operating voltage level, a signal is delivered to a low voltage bypass 17, providing a direct electrical path around the controllable amplifier 16 so as to couple the audio signal directly from the base unit 12 to the receiver 15. Within the controllable amplifier 16 a modified class B output stage is employed to provide the current driving capabilities necessary for proper operation of the receiver 15.
|
