Panasonic KX-TCD420GS, Service Manual, Page: 65 / 129

- All data signals (forming/analyzing ACK or CMD signal)
- All interfaces (ex: Key, Detector Circuit, Charge, DC/DC Converter,
EEPROM, LCD)
- RF Module: IC3
- PLL Oscillator
- Detector
- Compress/Expander
- Amplifier for transmission and reception
22.2. Power Supply Circuit/Reset Circuit
Circuit Operation:
When power on the Handset, the voltage is as follows;
BATTERY(2.2 V ~ 2.6V: TP3) TP14(4V) IC3(6, 27), D3 IC1(37) IC1(39, 63) (2.65V)
The Reset signal generates R19, C23 and 2.65V.
22.3. Charge Circuit
Circuit Operation:
- When charging the handset on the Base Unit, the charge current is as
follows;
DC+(5.5V ~ 6V) D4 R43, R44 (Base)
(Handset) L4 Q2 F1 ... Battery ... BATTERY-
R21 GND L5 CHARGE-(Handset) CHARGE-(Base) GND
DC-(GND)
- When charging the handset on the Charger Unit, the charge current is
as follows;
DC+(5.5V ~ 6V) D1 R1, R2 (Charger Unit) CHARGE
+(Handset) F1 ... Battery ... BATTERY- R21 GND
CHARGE-(Handset) CHARGE-(Charger Unit) GND DC-(GND)
In this way, the BBIC on Handset detects the fact that the battery is charged.
The charge current is controlled by switching Q2 of Handset.
Refer to Fig.101 in
Power Supply Circuit ().
22.4. Battery Low/Power Down Detector
Circuit Operation:
"Battery Low" and "Power Down" are detected by BBIC which check the voltage from battery.
The detected voltage is as follows;
- Battery Low
Battery voltage: V(Batt) < 2.3V
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