Cordless telephone ringing circuit diagram

The oscillation circuit in the SN739 mobile phone includes two audio oscillators and an output push stage. The low-frequency oscillator of the previous stage modulates the frequency of the high-frequency oscillator of the latter stage to produce a pleasant vibrato ringtone. Normally, pin 14 of MC3361 is at low level, and the circuit stops vibrating; when the mobile phone is waiting, if it receives the CALL signal from the desktop computer, pin 14 jumps to high level to cause ringing . The TL780 machine uses the same ringing circuit as an ordinary touch-tone telephone . Because this circuit contains a ring current detection function and requires high voltage to start, a high-voltage winding is added to the power transformer.