Charge Circuit - Panasonic KX-TG4771B Service Manual

4.7.3.

Charge Circuit

Circuit Operation:
When charging the Portable on the Base Unit, the charge current is as follows;
DC+(6.5 V) → F301 → R371 → R372 →CHARGE+(Base) → CHARGE+(Portable) → Q3 → F1 → BATTERY+... Battery...
BATTERY- → R45 → GND → CHARGE-(Portable)→ CHARGE-(Base) → GND → DC-(GND)
In this way, the BBIC on Portable detects the fact that the battery is charged.
The charge current is controlled by switching Q9 of Portable.
Refer to Fig.101 in Power Supply Circuit/Reset Circuit (P.12).
CHG +
CHG -
GND
4.7.4. 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)
The BBIC detects this level and "
• Power Down
Battery voltage: V(Batt)
The BBIC detects this level and power down.
4.7.5. Speakerphone
The hands-free loudspeaker at SP+ and SP- is used to generate the ring alarm.
R8
R4 Q4
47K
R6
10K
Q9
GND
R7
100K
2.35 V ± 100 mV
" starts flashing.
2.1 V ± 50 mV
Q2
C27
R2
Q3
BATT +
BATTERY
2CELL
BATT +
GND
19
KX-TG4771B/KX-TG4772B/KX-TG4773B/KX-TGA470B
CHG CTRL (32)
BBIC
IC1
CHG DET (34)