POWER SUPPLY SYSTEM OF TELEPHONE TERMINAL

摘要

PURPOSE:To attain the application of a battery of small capacity by providing a voltage detector to check whether or not the voltage of a station power supply is reduced less than a prescribed level and stopping the power supply to the circuits excluding a microcomputer from a built-in power supply with the output signal of said voltage detector. CONSTITUTION:The current is supplied to a microcomputer 12 and a peripheral circuit 13 from a station via a subscriber line, a diode bridge, the emitter and the collector of a transistor TR10 and a resistance 9. A voltage detector 20 detects the voltage applied to an input terminal VDD of the computer 12. Then a signal is sent to the computer 12 when the voltage applied to the terminal VDD is reduced less than a prescribed level. The computer 12 receives said signal and controls the base voltage of the TR10 via a resistance 11 to turn of the TR10. Instead a built-in battery 7 supplies the prescribed voltage via a diode 8 and also controls the base voltage of a TR21 to turn off the TR21. Thus the power supply is stopped to a peripheral circuit 13.