Icom IC-H6 Service Manual page 51

CIRCUIT DESCRIPTION
This charger provides proper charging current for various
battery packs which is selected by charging current selector
on the bottom of the battery pack.
Also a constant charging current is provided by controlling
conducting phase angle of the SCR in the circuit. It keeps
the current constant even if various battery packs which
have different output voltage, has been used.
1. CONDUCTING ANGLE CONTROL CIRCUIT
A gate pulse is used to control the thyristor (SCR) in the
circuit. This gate pulse is a part of a full-wave rectified
wave and its phase angle is controlled by a saw tooth pulse
which is synchronized to the full-wave rectified wave.
The pulse falltime of the saw tooth pulse is controlled by
an actual charging current, and it decides the phase angle of
the gate pulse of between 40 degrees and 160 degrees.
The saw tooth pulse generate circuit consists of 02, 05 and
C9.
A full-wave rectified voltage is applied to the base of 02
through R4 and turns 02 on at near its base line (D portion
in the figure), and charges C9 to +9V which from regulator
01. When the rectified voltage exceeds +9V (out of D
portion), 02 is turned off and the charged voltage of C9 is
discharged through 05, and a saw tooth wave is generated
across
C9.
This saw tooth pulse is fed to Pin 12 of IC2.
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When the pulse voltage decreases less than gate's threshold
voltage, Pin 11 of IC2 puts out H level voltage. This turns
04 and 03 on, and a portion of full-wave rectified voltage
is fed to the gate of D6 SCA through 03, and 06 is turned·
on.
When the SCA has been turned on, it holds this condition
until the power source voltage becomes zero or its cathode
is biased by reverse voltage. Thus, when the full-wave
rectified voltage becomes less than +9V (D portion in the
figure), the SCA will be turned off.
Rated charging current is decided by R37 - R42. R37 -
R42 are selected by S3 - S5 which are turned on or off by
a battery pack's charging current selector, and are in series
with the charging battery.
A voltage across R37, R38 or R39 - R42 is integrated by
R14 and C16, then fed to the base of 06. 05 and 06
compose a differential amplifier. A reference voltage which
is divided from +9V by R11 and R12, is applied to the base
of 05, thus the collector current of 05 is varied by the base
voltage of 06, and controls discharging time of C9.
For example, when the charging current increases more
than the specified charging current, 06 collector current
increases, 05 collector current decreases, C9 discharging
time becomes longer, the phase angle of D6 gate pulse
delays (the pulse width becomes narrower), and the charg-
ing current decreases.
When the charging current decreases less than the specified
charging current, the circuit functions the opposite way and
keeps the charging current constant.
2. LOGIC CIRCUIT
The logic circuit is controlled by the charging current select
switches S3 - S5, and the charging detector 010.
When charging 1C-CM2 or IC-CM5, S5 is turned on by the
charging current selector on the battery pack.
The charging current (600mA) flows through R39 - R42,
and a voltage across these resistors is applied to the base of
010 and turns it on. Thus, a gate input Pin 1 and 2 of IC2
becomes L level, its output Pin 3 H level. This puts out H
level at Pin 4 of IC1, output of a flip-flop consisting of a
gate of ICl and a gate of IC2. Also Pin 10 of IC1 puts out
H level and Pin 10 of IC2 L level.
This grounds the emitter of 04 through R10 and Pin 10 of
IC2, and 03 is turned on during Pin 11 of IC2 is H level and
charges the battery pack.