| 摘要 |
1396768 Ring-trip circuits PLESSEY CO Ltd 26 June 1973 [16 Sept 1972] 43040/72 Heading H4K In a ring-trip circuit which is connectible at X1, X2 to a two-wire line and which rings a magneto bell in series with a capacitor across the line, e.g. in a subscribers sub-station by applying a ringing current waveform to one wire and negative ring-return battery to the other wire, in the absence of a D.C. loopcondition at the line a sustained positive potential is generated at C2 from the ringing current waveform and this potential maintains a first transistor T1 OFF, whereas a second transistor T2 is switched ON and OFF by successive negative and positive half-cycles respectively of the ringing current waveform. Continuous ringing tone is applied to the circuit at CR to be replaced, after 300 ms., by intermittent ringing tone at IR. If the line is looped during a "silent" period, i.e. when earth is applied at X1, ring-return battery extended over the loop turns T1 and T2 ON immediately. After a delay, caused by C3 and R10, T3 is turned ON. With T2, T3 both ON, the gate comprising D5 and D6 is operated and T4 is switched OFF. Transistor T5 is accordingly driven to saturation and earth is introduced via T5 to whichever of relays CT, INT is currently operative, thereby releasing the relay and disconnecting the corresponding ringing current source. If the line is looped during a "ringing" period T1 and T2 are turned ON after a delay produced by R4, R6 and C1, and the above sequence occurs. |
