MEA 1786FD2
CRT Monitor Service Guide
Circuit Operation Theory
16
When power is initially applied to the circuit, capacitor C626 charges through R624, R623, ZD601.
When the voltage across C607 reaches a level of 16V, IC601 is turn-on the +5Vdc will be
set up at pin8 then R613, C615 generate a fixed frequency sawtooth wave to pin4, at this time
MOSFET will be drived by pin6 with square wave the pulse width of square wave is decided by
pin2 , pin3 is current feedback control, It will to sense MOSFET current. The D613, D612, R614,
C617 are soft start components to avoid the duty too large when power starts up.
3.6 Feedback circuit
This power supply adopt feedback circuit of +45V and +13V. It used IC702 for voltage regulation
and IC602 for primary-secondary isolation, The output voltage differential signal will be detected
and sensed to the pin2 of UC3842 for comparison then the duty cycle of MOSFET will be decided
to control the output voltage.
+45V
3
4
2
1
R
K
A
+
IC602
C611
C610
R737
Q767
IC702
Q765
Q766
C766
VR701
C725
C730
R768
R736
R735
R734
R767
R617
R738
R616
R726
R766
D766
R775
TLP721F
250V
3300P
250V
3300P
1/4W
20K
(OPEN)
TL431
(OPEN)
(OPEN)
(OPEN)
500
(D)
50V
0.47U
(OPEN)
(OPEN)
(SHORT)
1.2K
1/4W
39K
(OPEN)
1K
(OPEN)
1/2W
82
10K
470
(OPEN)
(OPEN)
(OPEN)
REF
REF
+14VA
+6.5VA
+6.5VA
SGND
Содержание 1786FD2
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