Charge Circuit; Battery Low/Power Down Detector; Speakerphone - Panasonic KX-TG4221N Service Manual

KX-TG4221N/KX-TG4222N/KX-TG4223N/KX-TG313SK/KX-TG4224N/KX-TG4225N/KX-TGA421N
4.7.3.

Charge Circuit

Circuit Operation:
When charging the handset on the Base Unit, the charge current is as follows;
DC+(5.5 V)  F301  R371  R372 D362  CHARGE+(Base)  CHARGE+(Handset)  Q4  D7 F1  BATTERY+...
Battery...
BATTERY-  R45  GND  CHARGE-(Handset) CHARGE-(Base)  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 Q9 of Handset.
Refer to Fig.101 in Power Supply Circuit/Reset Circuit (P.13).
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.
Q4
R4
R6
NC
NC
R3
1K
C121
NC
GND GND
R7
1.2K
2.25 V ± 50 mV
" starts flashing.
2.0 V ± 50 mV
D7
BATT +
R31
100
BATTERY
2CELL
Q9 BATT +
R8
100
GND
CHARGE_CTRL (33)
22
BBIC
IC5
CHARGE (34)