Understanding LCD Monitor Power Supply Board

The switch mode power supply used to power up LCD Monitor can be either the external or internal type. The function of the power supply is to convert the main supply AC 230 volts into DC output voltages to supply to the necessary boards in LCD Monitor.

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LCD Power Supply Board

230 Volts AC supply enters the power supply and to the bridge rectifier ac pins (normally is the 2^nd and the 3^rd leg). The AC supply is then converted into DC output voltage (about 300 VDC-in USA about 155 VDC) where the big filter capacitor filtered off the ripple so that the power supply will have a nice constant of DC voltage. This high voltage DC supply is then given to a switching power FET Transistor. This switching FET transistor circuit is switched on and off at a very high speed by a control circuit (power IC) which generates very high frequency square wave pulses.

The power FET and power IC (UC3842BThe switching FET transistor circuit switches the given high voltage DC, on and off at the same high frequency and gives square wave pulses as the output. These square wave pulses are then given to the primary winding of Switch Mode Power Transformer. These pulses induce a voltage at the primary winding of the transformer which will generate voltage at the secondary winding. This voltage at the secondary winding is then rectified and filtered to produce the required output.

The build in power supply have output of usually 12 volts and 5 volts where the 12 volts enters the inverter IC and also audio power amp IC.The 5 volts will go through one or two voltage regulators to get the 3.3 and 2.5 volts to power the Scalar IC, MCU, EEprom and even the LCD driver/controller board.

The power FET transistor already integrated into the power IC

Please take note that many latest designs of LCD Monitor power supply designs have the switching power FET transistor already integrated into the power IC thus you will not find the power FET in the power supply board.