| 摘要 |
PURPOSE:To prevent a device which performs control operation on a reset signal from malfunctioning by not sending a wrong reset signal out when a set voltage at which the reset releasing signal is sent out is exceeded. CONSTITUTION:At the time of hot-line insertion or extraction of the key telephone system, the voltage 5V of a source voltage VDD drops monentarily with a rush current due to the charging of an electric field capacitor mounted on a circuit board. In this case, the base voltage of a transistor(TR) Q1 passing through a resistor R2 does not drop because of the connection of a capacitor C. Consequently, the collector voltage of the TR Q1 never varies and the voltage at the reset terminal R of a CPU 11 from an inverter 18 has no variation; when the set voltage at which the reset releasing signal is sent out is exceeded, no wrong reset setting signal is outputted and the CPU 11 never malfunctions. |
