Single-Stage Flyback LED Driver Meets Class C Limits on Harmonic Currents

Focus:

This article presents a single-stage LED driver with a variable PFC boost inductor for the universal input voltage (90 to 270 Vrms). The proposed circuit overcomes the limitations of the conventional single-stage PFC flybacks. For example, it avoids the need for post regulators, which are required by PFC flyback circuits without an energy-storage capacitor on the primary side. And when compared with PFC flybacks with the energy-storage cap, the proposed design does a better job of reducing line-current harmonics, enabling the LED driver to meet the Class C limits imposed by IEC 61000-3-2 and JIS C 61000-3-2 while still keeping bulk-capacitor voltage levels within a practical range. In this article, the authors review the prior art, explain how their new design overcomes previous limitations, and then verify its operation by presenting experimental results for a 24-V, 91-W prototype circuit.

What you’ll learn:

• How to build a universal ac input, single-stage LED driver that meets class C limits on harmonic currents without requiring post regulators
• How to understand tradeoffs of various single- and dual-stage LED drivers with active PFC

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Author & Publication:

Yuequan Hu, Laszlo Huber, and Milan M. Jovanovic, Delta Products, Delta Power Electronics Laboratory, Research Triangle Park, NC, How2Power Today, Apr 29 2011

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