EL SEGUNDO, CA, January 24, 2000 -- International Rectifier (IR^®), the power conversion experts, now offers two new families of HEXFET^® power MOSFETs optimized to provide the best possible efficiency for the primary and secondary sections of isolated DC-DC converters with outputs of 3.3 volts. Using these devices in their existing designs, DC-DC converter manufacturers can eliminate more than 25 percent of the losses in their 3.3V-output 200W product lines with minimal design changes. This can translate into a full-load efficiency gain of more than 4 percent for some typical 3.3-volt converters. Considerable gains can also be achieved using the devices in lower power converters.

Carl Blake, Technical Marketing Manager for DC-DC Components at IR indicated that component selection went far beyond normal MOSFET data sheet specifications like BV_DSS, R_DS(on), Qg, or Qgd that are often applied in isolation from the application. In fact, a matrix of more than 200 possible component definitions was eventually tested for each application covering every major power semiconductor technology including trench, planar, stripe and cellular processes.

On the primary side of a DC-DC converter, most applications currently use a forward converter topology with either active or passive reset of the transformer. A new planar technology was chosen for the primary MOSFETs of the forward converter because it provides the best efficiency trade off between switching and conduction losses (See chart below). Using these primary-side MOSFETs alone can yield as much as 3 percent improvement in total end converter efficiency versus competitive solutions.

Primary FETs

Part No.	BVDSS	Vgs	RDS(on) max	Qg typ	Qgd typ	Package	Application
IRFS31N20D	200V	30V	82mOhms	65nC	30nC	D2Pak	Primary MOSFET,Forward converter,Passive Resetup to 120W
IRFS41N15D	150V	30V	45mOhms	67nC	32nC	D2Pak	Primary MOSFET,Forward converter,Active Resetup to 150W
IRFR13N20D	200V	30V	235mOhms	25nC	12nC	D-Pak	Primary MOSFET,Forward converter,Passive Resetup to 50W
IRFR18N15D	150V	30V	125mOhms	25nC	13nC	D-Pak	Primary MOSFET,Forward converter,Active Resetup to 50W

What may initially seem to be an inferior device, the IRFR18N15D, would in fact work better for lighter load current due to its superior switching characteristics. The lower cost of this D-Pak device, due to the use of less silicon, makes it an ideal choice in lower power converters.

On the secondary side of a forward converter, the choices of MOSFETs depend on the overall switching topology with different optimization techniques controlling the cost/efficiency trade off. It is possible to increase end efficiency of the whole converter close to one percent just by using optimized secondary devices (See chart below). Typically a designer will use either single or paralleled 30V SO-8 devices to obtain the output current. The choice of multiple packages is very useful, spreading the heat more evenly throughout the system to reduce thermal density. However, for higher power designs the new Super-D²Pak™ IRFBL3703, replacing up to 4 SO-8s, is an excellent device for higher current space-critical designs.

Secondary FETs

Part No.	BVDSS	Vgs	RDS(on) max	Qg typ	Qgd typ	Package	Application
IRF7463	30V	12V	8mOhms	36nC	12nC	SO-8	Secondary MOSFET, ICControlled Synchronous Rectification, Iout = 10A +
IRF7455	30V	12V	7.5mOhms	45nC	13nC	SO-8	Secondary MOSFET,Synchronous Rectification,Iout = 10A +
IRF7456	20V	12V	6mOhms	45nC	13nC	SO-8	Secondary MOSFET,Synchronous Rectification,Iout = 10A +
IRFBL3703	30V	16V	2.5mOhms	159nC	33nC	Super-D2Pak™	Secondary MOSFET,Synchronous Rectification,Iout = 50A +

"These new MOSFETs are just part of IR's overall commitment to provide benchmark performance and solutions for the DC-DC market," said Alex Lidow, CEO at IR. "The MOSFETs fit perfectly with a new synchronous rectification IC just being introduced, as well as MOSFETs optimized for synchronous buck applications that we introduced earlier. Our goal is to provide the best possible component set for DC-DC converters to maintain efficiency at acceptable levels as logic voltages continue to drop."

Samples and data sheets for all devices are available immediately on IR's special DC-DC conversion web site at http://dc2dc.irf.com, with volume shipments commencing in March, 2000.