Power supply circuit for a subscriber's telephone set

摘要

A power supply circuit for providing a local power supply replenished from the exchange for a telephone instrument. An electrical energy storage device is connected in parallel with an impedance by a device providing a unidirectional transfer of electrical energy from a direct current path through the impedance. A by-pass circuit is connected in parallel with the impedance. The impedance is a zener diode, the storage device is a capacitor, the unidirectional transfer device is a diode, and the by-pass circuit is a transistor responsive to the state of charge of the capacitor. A trickle charge circuit is connected to transfer energy to the capacitor irrespective of the by-pass circuit and a speech-frequency by-pass circuit is in parallel with the zener diode. A switch responsive to on-hook/off-hook conditions is used to confine energy storage to off-hook periods.