Mitsubishi Electric C-6479 Series Manual page 33

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3.8 PCB-POWER UNIT
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POWER REGURATOR CIRCUIT.
AC power from Line Filter is rectified by D901, and ~~en
chopped by Q903. This chopped wave voltage is trans-
formed by T902 which secondary widing supplies power to
D907 to generate dc power on connector J903. IC901 is
a all in one PWM Power control IC. See Fig. 3-7. It
includes an error amplifier, an oscillator, and a
comparator, etc.
Pin #1 and pin #2 are the input
terminals of an error amplifier. Outp~t voltage con-
ducted on pin *.1 is always compared with the voltage on
pin #2 which is one-twice of pin #16 (reference voltage) .
When the output voltage is higher, the output of error
amplifier is lower. So the output pulse width of a
comparator which compares the output voltage of error
amplifier with
a
sawtooth wave of Pin #7 is wider. Two
outputs of three inputs NOR gates are high in case of
three inputs are low. The outputs of driver transistors
Ql and Q2 are respectively. Finally ~~e pulse width of
Q904's base is narrower which makes the output voltage
to lower.
Q90l is a triac to shorten R903 which decreases inrush
current.
Q902 and T90l consist of a blocking oscillator to pro-
vide a power for control IC.
3-17
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