why zener diode is used in this DTMF circuit..?

[nithin kamath]

I have attached the DTMF decoder circuit using MT8870 IC. I that circuit, at the input section two zener diodes are used face to face..
I want to know why it is used...???

i am using a mobile phone instead of telephone.... its working fine... but can i remove those zener diodes...???



Thanks in advance,

 

[mister_rf]

The two zener diodes in the circuit '5V6' = 5.6V (You may use also 6V2 type= 6.2V) and were included to protect the IC from telephone line transients. If you are using a mobile phone you may remove those diodes.

 

[tpetar]

Thise zeners is one of parts which keep voltage on low level as safety. When telephone ring occur voltage may go up to 80-90V.