Iiyama Vision Master Pro 451, Руководство по обслуживанию

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4. CIRCUIT DESCRIPTION
4-1. POWER SUPPLY circuit
Power supply circuit consists of MAIN POWER circuit on PWB-MAIN and SUB POWER circuit on PWB-VIDEO.
These circuits are an asynchronous switching power supply circuit of secondary output feedback with using IC901
and IC951 built-in output FET and control IC.
Power supply start procedure is as follows;
Q
Power switch is turned ON.
R
SUB POWER circuit (5V and 8.5V output) is turned on.
S
K901 (RELAY) is turned on.
T
POWER FACTOR circuit (400V output) is turned on.
U
MAIN POWER circuit (80V, 28V, 15V and -12V output) is turned on.
V
Monitor is activated.
(1) POWER FACTOR circuit
The voltage waveform from current is controlled to be in proportion with input voltage at pressor chopper circuit.
This circuit is prevented from being harmonic by compared with following waveforms.
Q
The full-wave rectified voltage waveform from D950 via PWB-STAND and smoothed voltage waveform from
C959.
R
The voltage waveform from Q950 of source terminal.
Q
and
R
waveforms are compared at IC952. Q950 is turned off when
R
exceeds
Q
, and turned on when
R
is
0V. This repetition is to change input current to substantially sinusoidal waveform and it corrects harmonic
distortion.
The output voltage is set to 400V for world wide compliance.
The switching frequency is not constant as Q950 is turned on or off by monitoring input voltage and load current.
The switching frequency is approx. 50-250kHz.
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D950
AC-IN
90-132/
198-264V
T951
IC952
Q950
C959
400V