Abstract: A switchable order wire circuit installed in addition to a trunk connecting a master station which includes an exchanger and a dependent station in a telephone system. The order wire circuit includes a first telephone terminal located in the master station, a second telephone terminal located in the dependent station, and a pair of telephone lines connecting the first and second telephone terminals. The order wire circuit also includes a hooking detection system installed in the master station, for detecting a hooking operation of the second telephone terminal. In addition, a circuit for switching the telephone lines from the first telephone terminal to a public line when the hooking operation is specifically detected is included.

Abstract: If a rectifier having Walk-in characteristics is directly connected to a dc-dc converter, an output current of the rectifier violently fluctuates because of the Walk-in characteristics of the rectifier. The Walk-in characteristics have been improved by connecting an apparatus in parallel with the rectifier. The apparatus includes a storage battery and a switch. During the Walk-in period, the switch is closed and the storage battery supplements the capacity of the rectifier. After that, the switch is opened and the storage battery is charged by a current flowing through a diode and a resistor.