Circuit Operation (Handset) - Panasonic KX-TD7895 Service Manual

8. CIRCUIT OPERATION (HANDSET)

8.1. MAIN BOARD
8.1.1. POWER SUPPLY CIRCUIT
The power supply circuit consists of 4 regulators. IC314 supplies the power to the CPU(IC307).
IC301, IC305 and IC308 are controlled by the CPU(IC307). Each output voltage is 3.0V.
8.1.2. RINGER CIRCUIT
When the Ring signal is received with the power switch of the handset ON, the ringer is
activated. When the ring signal is received, IC307(45) and IC307(46) are, set High or Low.
(Depends on Ringer Vol setting) After Q302 and Q305 are set High or Low, Q304 and Q300 are
switched on by the ringer frequency in IC307(45) (Q300 is a High Current Driver) and the buzzer
is then ON.
8.1.3. RECEIVED VOICE SIGNAL