| 摘要 |
PURPOSE:To hold the working of a relay of call loudspeaking system for a prescribed period of time and to prevent instantaneous break of a call, by delaying the recovery of the relay in case the feed is cut off from a power supply part while the relay is working. CONSTITUTION:A call current is supplied to a talking circuit NET from telephone circuits L1 and L2 via a hook switch HS. At the same time, a working current is supplied from a power supply part PW to an amplifier connected to a transformer TR for repeating of sound, a control part CNT, and a relay P for both closure of channel DC and switching of loudspeaking speech reception, the transistors TRQ1, Q2, etc. of the related circuit. A capacitor C and a reverse current preventing diode D2 are connected between the part PW and the relay P. In a call loudspeaking system of such constitution, a current is flowed in a route of the relay P, a TRQ2 and a diode D3 with the discharge of the capacitor C when the supply of current is cut off to the part PW in a busy mode. This prevents instantaneous break of a call. |
