Panasonic KX-TD7685 Service Manual page 7

4.2.3. Charge Circuit (Include Charger)
When charging the handset on the charger, Q1 of charger is turned on and battery charging starts, the charge current is as fol-
lows;
DC+(6.5V) → L1 → Q1 → R3 → JT1(Charger) → JT101(Handset) → L101 → Q101→ D102→ L104 → BATTERY+ ... Battery ...
BATTERY- → GND → R115 → L102→ JT102(Handset) → JT2(Charger) → R4 → R2 and R5 → GND
In this way, the BBIC on Handset detects the fact that the battery is charged.
The charge current is controlled by switching Q101 of Handset.
When charging is completed, the BBIC (IC201) of the handset sets the base of Q103 to "High", then Q102 is turned OFF. As a
result, the charging stops.
4.2.4. Battery Low/Power Down Detector
"Battery Low" and "Power Down" are detected by BBIC (IC201) 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.
4.2.5. TX Audio Path
Microphone
An audio signal from microphone is input to pin 76 (MIC+) of IC201 via headset jack (CN404).
In IC201, the audio signal is converted from the analog signal to ADPCM, then to burst data, and sent from pin 19 (TXDA) to RF
Module (IC601). The stabilized supply voltage is fed to the microphone. From pin 77 (VREF+) of IC201.
To reduce consumption current, this voltage is supplied only while calling or receiving.
Headset
When a headset is inserted, a signal from microphone is cut off and an audio signal from a headset is input to pin 76 (MIC+).
Headset detection
When a headset is inserted, pin 23 (ADC2) of IC201 goes from High (around 1V) to Low and BBIC (IC201) detects the insertion
of the headset.
3.5V ± 50mV
" starts flashing.
3.3V ± 50mV
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KX-TD7685