TELEPHONE LINE SOURCED POWER SUPPLY

摘要

In a device attached to a telephone line, power is provided by taking power from the telephone line when the device is off-hook. When the device remains onhook, power is maintained to the circuitry in the unit by a charge stored in a capacitor. The capacitor charge is reduced to a level no longer able to sustain operation of the system, the device is briefly taken off-hook, allowing the capacitor to recharge. This is performed either by discrete circuitry or by a microcontroller, and further includes provisions preventing the device from remaining off-hook for an unduly long period of time.