Sharp MD-MT20H(BL) Service Manual page 41

Battery voltage measurement
When the battery is being used or while it is being charged, the output of pin 17 should be H (battery voltage measurement output).
The output should be held L in the power-off mode and in the other modes. However, when it is necessary to measure the battery
voltage, pull pin 17 (battery voltage measurement output) H temporarily, to make the measurement.
Power supply change
When one of the power supplies is selected, the port settings are as follows:
Port name
Pin 3 Charge ON output
Pin 85 Charging current control output Output port L
Pin 89 Battery OFF output
The port settings in the power-off mode are as follows:
Port name
Pin 3 Charge ON output
Pin 85 Charging current control output Output port L
Pin 89 Battery OFF output
Charging test mode
For details about the test mode, see the separate page.
Charging circuit description
The charging current value is determined by measuring the voltage across R250/R251.
The charging current is controlled by IC805, Q252, IC803, the rechargeable battery, and R250/R251.
The reference voltage for IC401 is output from pin 85 (DA port) and is input on pin 5 on IC805.
Since the charging current is controlled by the NFB loop, the circuit is designed so that pin 5 on IC805 will have the same potential
as the voltage across R250/R251. Since R250/R251 is 0.5 ohms, the desired charging current can be obtained by varying the
potential of pin 5 on IC805.
Battery voltage measurement
The battery voltage can be measured using either of the following two modes.
1) Pin 51 on IC401 Output L
The output should always be L except during the following charging voltage measurement mode.
2) Pin 51 on IC401 Output H
The output should be H while in the charging voltage measurement mode.
Since the charging voltage is measured at intervals of five minutes while in the charging mode, the output should only be H about
500 msec every 5 minutes.
3
R257
100K
Reference voltage
input section
When operating from the AC adaptor When operating from the battery
L
H (1)
When operating from the AC adaptor When operating from the battery
L
H (1)
D812
S
SB10015C
D
Q253
IC803
RN1113 FDT439N
G
CHARGING
2
CIRCUIT
1
TP808
R259
Q252
82K
2SC4738 GR
R261
270K
R262
24K
C258
8 7 6 5
0.0047
IC805
NJM022V
L
Output port H
L (3)
L
Output port L
L (3)
VCC3
Q254
RN1113
3
2
1
R254
2.2K
D S
1 6
D D
2 5
G S
3 4
IC806
NDC631N
– 41 –
MD-MT20H/16E
H
3-mode output
L
SW801
Ni-MH
BATTERY
DETECTION
R804
1.0A
VCC4
TP803
TP804
BATTERY
TERMINAL
Resistor to
detect the
charging
current
When charging
NFB loop