| 摘要 |
PURPOSE:To stabilize a call signal, by transmitting an earth signal after the transmission of a transmission signal is completed and the turn-off time of a semiconductor switch is elapsed when the call signal is transmitted in a subscriber's circuit of a telephone exchange. CONSTITUTION:In case that the call signal and the earth signal are transmitted alternately to a subscriber's line 2 through current self-holding semiconductor switches 11 and 12, conduction or non-conduction of p-n-p-n transistors TRs 11a, 11b, 12a, and 12b constituting semiconductor switches is detected by a detecting circuit 15 and is inputted as one control information to a controlling circuit 14. A control signal is transmitted to the first gate driving circuit 13a and the second gate driving circuit 13b through delay circuits 21 and 38, which give a delay longer than the turn-off time of semiconductor switches, to prevent the simultaneous operation of two semiconductor switches, and thus, switches are not broken down, and malfunctions are prevented. |
