Partial BCM Mode Of Operation Improves Efficiency For Primary-Side Regulated Flyback LED Driver

by Roy Mi, Fairchild Semiconductor, Chicago, Ill.; John Jing, Fairchild Semiconductor, Los Angeles, Calif.; and Jason Guo Sr., Fairchild Semiconductor, San Jose, Calif., How2Power Today, Feb 15 2015

Focus:
This 17-page article explains the operating principles of the primary-side regulated (PSR) flyback topology in the LED lighting application with high power factor (PF) and high operating efficiency. The basics of the PSR flyback LED driver are presented and its merits are addressed. A design procedure is proposed and described in detail for engineers to achieve the optimum design balance between the ac-dc LED driver’s efficiency, PF, THD and flyback transformer design. The unique approach to PSR flyback design described here allows the driver to operate partially in boundary conduction mode (BCM) at low input voltage. This enables the driver to achieve high efficiency, while maintaining high power factor and low THD. A quick design example based on the FL7733A controller is also given at the end of the article for verification.

What you’ll learn:

• How to design a primary-side regulated flyback LED driver that achieves high efficiency, high PF and low THD
• How to operate a a primary-side regulated flyback converter in a partial boundary conduction mode to achieve high efficiency

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