Detailed working principle of the telephone

The two lines of the ordinary telephone line, although added to the DC feed, there is a positive and negative, but when connected to the ordinary telephone, unnecessary to distinguish between the two lines can be connected casually. The polarity conversion circuit (4 diodes) inside the telephone ensures that the telephone gets the correct polarity voltage and works properly.

Ordinary telephone line function: Simply put, it is to feed the electricity, transmission signaling signals and language signals. Signaling signals include: ringing signals, dial tone, DTMF, and so on.

Feeder: supply the telephone work of electrical energy. China's telephone line feed voltage 48 V. Ordinary telephones rely on the switchboard feed to work.

The telephone is 48 volts before the call

Ringing signal: 60-80V20Hz AC signal rated voltage 48v (DC), but generally up to a little more than 50 (non-stop power, battery voltage without load, will be slightly higher).

Ringing voltage 7.5v () or so, but off the phone call voltage will drop to 10 a few V (DC) (this is not precisely known), the current is very small. During a call,the voltage is a bit less I don't remember if it's 4.2 or 2.0 volts