| 摘要 |
<p>PURPOSE:To evade a problem of runaway of a microcomputer due to discharge of a backup power supply when a hook switch is hooked off in the case of using a telephone set by outputting a reset signal to the microcomputer when a backup voltage of the backup power supply is decreased to reset the microcomputer. CONSTITUTION:When a hook switch Hs is hooked off, a minimum holding voltage outputted from a diode bridge circuit 1, a constant voltage generating circuit 2 and a minimum holding voltage generating circuit 3 is given to the emitter of a transistor(TR) Q1 and compared with a charging voltage of an electrolytic capacitor C representing the holding voltage of the holding voltage and when the holding voltage is at a lower level than the minimum holding voltage. the TR Q1 is turned on, a TR Q2 is turned on and a DC voltage is applied to a reset terminal RS of a microcomputer 6 as a reset signal. Thus, the microcomputer 6 disabling to hold the memory data is reset.</p> |
