Samsung SF-530 Service Manual page 123

3-4-2-8. MHV (Electrification Output Enable)
Electrification Output Enable is the electrification output control signal 'PWM-LOW ACTIVE'.
When MHV-PWM LOW signal is received, Q401 turns on and the steady voltage will be accepted to the non-inverting ter-
minal of OP-AMP 324. As the voltage higher than the inverting reference voltage of OP-AMP, which is set to R405 and
R406, OP-AMP output turns high.
This output sends IB to the TRANS auxiliary wire through current-restricting resistance Q402 via R408 and C403 and Q402
turns on. When the current is accepted to Q402, Ic increases to the current proportional to time through the T401 primary
coil, and when it reaches the Hfe limit of Q402, it will not retain the "on" state, but will turn to "off". As Q402 turns 'off', TRANS
N1 will have counter-electromotive force, discharge energy to the secondary unit, sends current to the load and outputs
MHV voltage through the high voltage output enable, which is comprised of Regulation– circuit.
U2 7407
MHV-PWM
R411 2.2K
Samsung Electronics
18V
R405 220K
Q401 A708
R403 130K
R404
27K
R402
82K
C408
R412 2K
104
R406
2.2K
24VS
Q402
D526
24VS
R408 R409
+
47K 390
_ KA324
C403
333
CIRCUIT DESCRIPTION
T401
MHV OUTPUT
C404
3K/471
C406
D402
3K/471
4KV
R416
15M
R417
15M
Repair Manual
3-33