The phone dialing circuit

Published:2011/6/2 23:56:00 Author:Seven | Keyword: dialing circuit | From:SeekIC

In Figure 11.3 is a key dialing circuit which is made of DF320. When the phone is picked up, the circuit is on. The NPN VT2 is conducting due to the input basic polarity of R2, and VT1 is also conducting, so the power supply charges C2 to 0.7V by R3 and VD1. When the LEV reaches the minimum working voltage of VDD, DF320 is linked to the power supply, and the circuit is reset by C1 and R8. The telephone net is linked to the circuit by VT1, and DF320 net, as an impedance, connects with the phone in the parallel way.



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