how to work the LCD power supply

Many technical difficulties in tracing seek damages LCD power-supply. This is because they "do not understand the inner workings of power-supply as a whole". So through this paper we invite engineers to understand the functions and workings of each part of the power-supply

Power-supply large LCD screen generally as shown in the example block diagram below. Consists of three main parts, namely:

PFC (Power Factor Correction) - NCP1606, FET, tranfo PFC, Diode, large Elko 450V
The main power supply - NCP1392, 2 pieces & tranfo FET switching
Power supply stand-by - NCP1351, switching FET & tranfo
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Before studying the working parts of the power-supply, then there are some points that need to be understood in advance:

Powwer suply lcd

PFC:

Consists of PFC control ic, FET, tranfo PFC, diode, and a great elko 450V.
Here from the diode bridge is not directly connected to the large elko, but go first to tranfo PFC.
PFC works transform into a dc voltage 300v 390v dc voltage at large Elko.
At the time of st-by PFC has not worked. Then the voltage at large elko only 300v.
The new PFC work after "power-on" so that the voltage at large Elko changed rose to 390v.
Supply Vcc for the PFC control ic given of tranfo st-by pass "transistor bias" on-off controlled via the photo-coupler "start st-by" by section Mikrokontrol contained in the mother-board.


St-by power supply:

In the example image consists of ic SMPS PWM control, FET and tranfo switching.
Sometimes for st-by used a single ic like kind STR
Serves to provide a voltage st-by (5v) for part Mikrokontrol mother-board


Power supply-main :

Consists of ic type of resonant converter, 2 pieces of FET, and tranfo switching.
At the time of st-by-the main power supply is not working.
Controlled on-off by part Mikrokontrol contained in the mother-board.
If PFC malfunction (big elko voltage fails rose to 390v), then the main power-supply also does not want to work (although the power is "on")
Serves to provide supply to the inverter section and other parts on the mother-board like Panel, Audio amplifier etc. (eg voltage 12v and 24v)
Just like part PFC - suply Vcc for PFC control ic given of tranfo st-by pass "transistor bias" on-off controlled through the photo-coupler "start st-by".


From the example picture above - then found 3 pieces of photo-coupler which each function:

Photo-coupler.1 - for the feedback path of power-supply st-by
Photo-coupler.2 - for the feedback path of power-supply main
Photo-coupler.3 - for on-off control lines PFC & Power-supply main.
There is a possibility found no photo-coupler to-4. It usually serves to track the AC circuit-det (will be explained in the next article)


Our experience of the two kinds of power supply as described above, the power supply SMPS type PWM type used for the st-by course that can be modified using Gacun.

If installed gacun voltage typically would be greater than 5v although VR has a minimum
So that the voltage may drop to 5v, then attach the blue wire on the photo-coupler. Photocoupler for st-by, in the circuit generally hot chassis are connected directly to ground.
Sometimes the output voltage rocking up and down. So to eliminate this interference can be mounted load R 200 ohm / 2w at 5v voltage lines to ground

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