HV9931 Unity Power Factor LED Lamp Driver

Focus:

This 18-page application note presents a design based on the HV9931 controller IC that implements a power-factor-corrected ac-dc power supply for driving high-power LEDs. The two-stage design is a novel topology consisting of an input buck-boost stage followed by an output buck stage with both stages sharing a single power MOSFET. Since both stages can step down voltage, the power supply as a whole can operate with a high stepdown ratio. That eliminates the need for the stepdown transformer required by other designs employing a boost input stage. This design also avoids the need for a large electrolytic smoothing capacitor as required by flyback converters to attenuate ac ripple. Operation of this design is described in detail: design equations are derived including those required for calculating values/ratings of inductors, capacitors, rectifiers and MOSFET; protection and dimming requirements are discussed. A design example is presented for a universal input, 25-V 750-mA dc output LED power supply.

What you’ll learn:

• How to design a nonisolated offline power supply with near-unity power factor for driving high-power LEDs
• How to design a nonisolated offline LED power supply that needs no transformer or large electrolytic capacitors

Notes:

Supertex Design Note AN-H52. Also see the related design notes DN-HO5 "56W Off-line, 120VAC with PFC, 160V, 350mA Load, Dimmer Switch Compatible LED Driver" and DN-HO6 "14W Off-line LED Driver, 120VAC, PFC, 14V, 1.0A Load".

View the Source

Author & Publication:

no author listed, Supertex, Vendor website, Feb 27 2009

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