How to get higher efficiency at lower loads: A new LLC platform makes it possible

March 30, 2015 //By Erwin Seinen
How to get higher efficiency at lower loads: A new LLC platform makes it possible
Erwin Seinen, NXP International Product Marketing Manager considers how to achieve higher efficiency at lower loads.

For designers of power supplies, it can be challenging to sort through the various requirements for reducing power consumption. Meeting these requirements isn’t really optional – since most products can’t leave the factory without being certified compliant with one or more of them – but sifting through the details can be both confusing and frustrating. Issued by different governing authorities, in different regions, these various initiatives and directives cover different types of end equipment, and may have different requirements for different power levels.
There are, to name a few, publications from the California Energy Commission (CEC) and EnergyStar program (including 80+), the U.S. Department of Energy’s (DOE’s) External Power Supply (EPS) guidelines, the One-Watt Initiative, issued by the International Energy Agency (IEA), Australia’s House Energy Rating program, the European Code of Conduct (CoC) for power supplies (Tier 2), and the Eco-Design Directive for Energy-Using Products (EuP) requirements (Lot 6).
The guidelines don’t always agree, but, having boiled it all down, there is an emphasis on reducing “phantom” or standby power consumption, which involves minimizing waste at light and no-load conditions. Every milliwatt counts, and it can be difficult, especially in high-power systems, like PCs, gaming consoles, and high-definition displays, to reach the most recent target of consuming no more than 0.5 W during standby. Add to this the fact that most electronic systems compete in highly cost-sensitive markets, and you have a two-fold challenge: maximize light-load efficiency, without increasing the bill of materials (BoM).
Meeting the low-load challenge

A new power platform, developed by NXP Semiconductors, aims to help designers meet this two-fold challenge. Providing better performance at low loads while minimizing component count, the new platform builds on what is, for many designers of high-power power supplies, a familiar format: the LLC resonant topology.
The new NXP LLC platform uses synchronous rectifier (SR) control with patented gate drive, without minimum on-time and without reverse current,

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