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#6 Feedback circuit
PC123 is a photo-coupler and TL431 is a shunt regulation. They are used to detect the
output voltage change and be the primary and secondary isolation. When output
voltage changes, the feedback voltage will be compared and duty cycle will be decided
to control the correct output voltage. (See Fig.7)
R709
2K
IC602
PC123FY 1
12
43
IC702
LM431A
A K
R
R710
10K
C711
0.1U K
R713R712
3.32K F
R711
22K F
Fig. 7
A-3.) Control board introduction:
The main parts of the control board are a push button, and a LED.
(a) Push button:
It’s a simple switch function, pressing it for “ON” to do the auto adjustment
function, releasing it for “OFF” to do nothing.
(b) LED:
It indicates the DPMS status of this LCD monitor; blue light means DPMS on
(Normal operating condition). Amber light means DPMS off (Power off condition).
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