Active Clamp Flyback Converters — How They Work And Tips For Design Success

by Michael O’Loughlin, Texas Instruments, Manchester, N.H., How2Power Today, Mar 15 2019

Focus:
In low-power applications (150 W or less), the active-clamp flyback (ACF) converter is becoming a popular choice over the quasi-resonant flyback (QRF) converter. When designed correctly, an ACF topology will have a nearly lossless leakage energy clamp and achieve zero voltage switching (ZVS) on the primary MOSFET over a wide input voltage and output load range. This article reviews the benefits and operation of an ACF and gives design guidance on applying it using the UCC28780 controller in a 45-W reference design. Design guidance includes tips on transformer design, selection of input and output capacitors, setting up the controller to achieve ZVS, designing for frequency variations, and the need for design iterations. Data on the efficiency of the example ACF reference design over line and load is presented, and the improvement versus a QRF is noted.

What you’ll learn:

• How to design an active clamp flyback converter using the UCC28780 controller.
• How to understand the operation an active clamp flyback converter

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