Nikkei Electronics Asia -- April 2009
Solutions -- Web Articles
Synchronous MOSFET Controller Improves Efficiency of Flyback Converter

Apr 2, 2009 15:00 Nikkei Electronics Asia

Several regulatory bodies around the world address efficiency issues in external power supplies (EPS) and aim to reduce energy consumption in the compliant adaptors. One example of these is the Energy Star V2.0 standard, which targets both the issues of active mode efficiency as well as no load power consumption. 

This article addresses the challenges of complying with the voluntary standard in a flyback converter typically employed as an EPS below 100W output power. 

In particular, it discusses the efficiency improvement with the aid of the ZXGD3101 synchronous MOSFET controller, and its practical limit against normal rectification method. An experimental verification is also employed to demonstrate efficiency improvement in a universal input 60W (19V 3.2A) flyback adapter.

Much of a flyback adapter's inefficiency is caused by the Schottky or ultra-fast recovery diode used on the secondary side.

When a normal and ultra-fast diode rectifier is substituted with a low resistance synchronous MOSFET, it is possible to achieve the standards set out by Energy Star V2.0.

Using the ZXGD3101 to control and drive the synchronous MOSFET provides efficient conduction path with optimized delay in sensing the sharp drop of current during the turn-off phase, ensuring no reverse conduction. The gate driving scheme combined with properly designed magnetic and power stages minimizes circuit losses while maintaining the power supply in active mode, and ensures the no-load conditions are satisfied.

by Adrian Wong & Yong Ang, Diodes Inc

Full article:
http://techon.nikkeibp.co.jp/NEA/solutions/0904002.pdf

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