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KSC-4 (RAPID CHARGER)
7) Charging Status Detect Circuit
This
circuit
detects
the completion
of charging
and
outputs a signal to stop charging. When no battery pack is
inserted
or charging
is completed,
a High
(''H'')
Reset
signal is applied
to D15.
When a battery is inserted the
Reset signal applied
to D15
is cleared.
When
the
Reset
signal is cleared, pin 4 of IC2 holds the reset state due to
the
charge
in C8 for the duration
of the
R46-C8
time
constant,
then
goes
"'L" to clear
the reset
state. Pins 8
and
9 of
IC2
receive
divided
portions
of the
battery
voltage.
These
inputs are tracked
as the charging
is per-
formed
in the long-term
memory
capacitor "MD''. As the
Ni-Cd battery charges, the battery voltage reaches a peak,
then declines. (See Figure 6.)
The "MD"
stores the peak voltage, which is compared
with
the divided voltages at pins 8 and 9, When
the dif-
ference AV
is the same, a ''L" signal is output from pin
11 to indicate
that charging
is complete.
The
signal
in-
dicating completion
of charging
is applied to the charging
status memory circuit.
from Fig5
EO
—e—
11V
(C2
R47
R50
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R48
D14
to Fig. 2
"CHARGING
CONTROL"
COMPLETE
: "L"
R51
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Fig. 7 Charging Status Detect Circuit Block Diagram
98
8) Timer Circuit
Battery
defects
may
result
in
charging
continuing
indefinitely
without
completion,
so this timer outputs a
signal that stops charging
approximately
1.7 hours after
charging begins. When charging begins and the Reset signal
is cleared at pin 3, 1C3 : AN6780
begins counting. At the
first count of 16384 pin 6 goes from "'H" to "L".
The output
from
pin 6 is connected
to the Stop input
(pin 2), so the output of IC3 is held in the "'L'' state until
1C3 receives another
Reset signal
(for example, when the
battery is removed).
AN6780
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2.
3
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Fig.8 Timer Circuit
7
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OUTPUT
1
(6)
;
LI ;
L
i)
+
T1——__»i
————— Ti
= 1638470
Fig.
9
TIMER TIME T1(s}= 11 R1KQ)-CT (uF)
g.
TIMER TIME 74 (s)= 11x56 (K9)-10 (uF) =6160 (s)
9) Voltage Comparator Circuit
This circuit monitors the output (EO) of the sensor level
switching
circuit
and
indirectly
detects
abnormal
condi-
tions
in the
battery
pack
connected
to
the
charging
terminal. When
the EO voltage falls to 5.2V or lower, the
charging control line goes ''L"' to halt charging.
Eo
from Fig. 5
R26
6
1€4(2/2)
-—*
+
CHARGING
CONTROL
"L" . CHARGING
STOP
R27
R29
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11V
q
Fig. 10 Voltage Comparator Circuit Block Diagram
vo
5.2V
"= Eo
Fig. 11
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