A 300-W, Universal Input, Isolated PFC Power Supply for LCD TV

This guide documents a low-profile power supply that is suitable for powering LCD TVs or other flat screen


applications. The power supply accepts a universal AC line-input voltage (85 VRMS to 265 VRMS), and produces

an output voltage of 24-VDC for loads up to 12 A (288 W).

The requirements for a flat-panel display include a physical profile and the ability to operate from the ac-line input

at close to unity power factor. Therefore a flat-panel display application demands that an internal power supply be

thin so as to fit behind the screen inside the TV case, and comply with the power quality requirements defined in

the IEC standard, 61000-3-2. In addition, the combination of a tight physical package and the desire to meet

Energy Star® guidelines requires that the design also demonstrates very high efficiency. Described herein is a

practical design that uses standard components. It achieves the requirements using a traditional two-stage power

converter topology along with state-of-the-art power circuit control methods. The first stage is an interleaved,

transition-mode, power factor correcting (PFC) boost pre-regulator. This is followed by an isolated LLC seriesresonant

DC-DC main converter.

The design takes advantage of three integrated circuit (IC) power controllers. The PFC pre-regulator stage is

controlled by the UCC28061, a dual-phase, interleaved, transition-mode PFC controller. The resonant LLC

converter uses the UCC25600; a low-cost 8-pin controller. The third IC is the UCC2813D-4. This is used to

control a small 5-W flyback converter that provides a bias supply voltage. The bias supply is optional. It is

provided for convenience so that the circuit can be demonstrated without the need for a bench supply.
 
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