El Segundo, CA—What would you give for "just" another two percent improvement in efficiency? But think about it another way: if efficiencies are already in the 92%+ range, with your loss is around 8%, then two points gained is a 25% decrease in losses.
If this seemingly modest gain in efficiency is important to you, then check out the latest in the DirectFET family from International Rectifier. Their IRF6811 and IRF6894 DirectFETplus MOSFETs reduce on-state resistance (Rds(on)) and gate charge (Qg), but also cut gate resistance (Rg). As noted by Omar Hassen, executive director, Low Voltage DirectFET Products, Enterprise Power Business Unit, Rg is a second-order source of loss, but its importance that grows as the most obvious sources--Rds(on) and Qg—are pushed to very small values, see Figure:
Using these new MOSFETs in a representative design, IR shows the efficiency reaching 94.5%, see Figure:
The IRF6811 control MOSFET is available in a small can package while the IRF6894 synchronous MOSFET is offered in a medium can, footprint compatible with previous devices. This packaging, with the silicon die bonded directly to the package, eliminates wire leads and straps, thus significantly reducing dc losses as well as parasitic inductance and capacitance—all virtues for effective high-frequency switching with low losses. The can package also gives current and heat a lower-resistance path compared to the path through the PC board, for better flow of both factors.
The IRF6894 also features a monolithically integrated Schottky diode which reduces losses associated with body-diode conduction and reverse recovery..
Pricing and availability: The IRF6811STRPBF and IRF6894MTRPBF begin at $0.75 and $1.75 each respectively in 10,000-unit quantities, and are available now.
For more information: Datasheets and application notes for the devices are at http://www.irf.com.