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During the On-time of Q901, energy is stored in T900. At this time the polarity of the output windings
is such that all output rectifiers are reverse biased and no energy is transferred. Primary current is
sensed by R907 and compared to a DC level that is determined by voltage feedback. When this level
is reached, Q901 is turned off and the polarity of all T900 windings reverses , forward biasing the
output rectifiers. All the energy stored is now transferred to the output capacitors. Many cycles of this
store/release action are needed to charge the outputs to their respective voltages.
The feedback voltage across R931, D909 is smoothed by C911 and through cross the divider which
assembled by R914,R916,R917 and VR901 to the error amplifier (U901 pin2) and compared to an
internal 2.5V reference.
6.4
SNUBBER CKT
Energy stored in the leakage inductance of T900 cause a voltage spike which be added to the normal
reset voltage across T900 when Q901 turn off. The clamp consisting of D905, R904 and C907 limits
this voltage excursion from exceeding the Vds rating of Q901. In addition, a turn off snubber made up
of D906, R905 and C908 keeps power dissipation in Q901 low by delaying the voltage rise until drain
current has decreased from its peak value. This snubber also damps out any ringing which may occur
due to parasitic.
6.5
SYNCHRONIZED CKT
The oscillator frequency is defined by R912 , C912. The equation is approximately : Fosc=1.8/
(R912*C912). The external signal "FBP"
that comes from horizontal circuit can synchronize the working frequency of power circuit by through
cross R919,R918 and D911.
POWER SAVING CKT
The monitor has ON, Suspend/Standby and OFF states. The monitor enters the Suspend/Standby
mode if either V-sync or H-sync signals are removed. When the machine in the Suspend/Standby
State, PS1 should be low to turn off +13Vs. In this state, input power should be less than 15W and
D960 LED illuminate yellow. The monitor enters OFF mode if both H-sync and V-sync are removed.
When in the OFF State, PS1 and PS2 should be low simultaneously to turn off +13Vs and +7.5Vs
outputs. In this state, input power should be less than 5W and D960 LED illuminate amber.
When the monitor wakes up from the OFF mode to the ON mode , the +13Vs will provide power to
heat the heater of CRT for a time via Q940 and L944, that can make sure the recovery time less than
5 sec.
Deflection:
27
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