July 2009 LCD DV 42LH40
21
POWER SUPPLY SECTION
POWER SUPPLY SECTION
This switch mode power supply has the ballast section built in.
The power supply develops Stand By 5V, 12V and 24V for the Main
board.
This power supply draws a little less that 1 watt during stand
by mode. The fuse F501 reads 157V (from hot ground) during
this time. When the controller chip (on the back) receives the
PWR-ON command via P201 Pin 19, the primary section
increases its current supplying ability. The Primary fuse F501
now reads 380V.
12V is routed out P201 pins 5 and 6 and
24V is routed out P201 pins 1 and 2.
Internally, the power supply also sends B+ (390V) voltage to
the Ballast section but it is not turned on at this time.
When the power supply receives the INV-ON command via
P201 pin 20, it is routed to the driver for the ballast (on the
back of the board). The driver now starts to deliver drive
information to the output FETs (on the far left hand heat sink)
which in turn switch the primary sides of the two ballast
transformers T703 and T704. They output 1.2Kv (48Khz)
pulses to the backlights via P401 and P402.
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