Phone doorbell circuit

Circuit working principle: The telephone circuit includes four parts: sending, receiving, issuing, and ringing
. The ringing circuit is shown in Figure 5-18. CS8204 is a dedicated ringing integrated circuit
. When a call comes in from the outside line, the telephone switch inputs a 90 V, 25 HZ
ring current signal from the outside line . It is limited by G and Rs, and VD. A VD. Bridge rectifier, VD, voltage stabilization and
C. After filtering, a stable DC voltage is applied between pins 1 and 5 of CS8204.
CS8204 enters the working state, the ringing signal is output from pin 8, and the
phone ringing sound is emitted through the speaker. Since there is usually a 48 V direct voltage on the outside line of the telephone, C, has
the function of blocking DC and AC. When C, the circuit bell does not ring. When c5 is short-circuited , the phone bell rings for a long time.
Therefore, two wires are drawn from both ends of c and connected to the doorbell. On button AN, as long as the doorbell button AN is pressed
, c5 will be short-circuited , and the 48 V DC voltage
will be added . There will be an operating voltage between pins 1 and 5 of CS8204, and the phone will ring. It
rang.