MOSFETs keep cool to boost conversion efficiency

A new chipset enables a bus convertor solution capable of delivering 336W with 97% efficiency in a footprint 29% smaller than a "quarter-brick" convertor.

A new DirectFET chipset maximises DC bus convertor efficiency when used with IR's recently announced IR2086S full-bridge bus convertor IC.

The chipset enables a bus convertor solution capable of delivering 336W with 97% efficiency in a footprint 29% smaller than a "quarter-brick" convertor.

The IRF6646 and IRF6635 are optimised for 48V regulated and 36 to 60V input bridge topologies in isolated DC/DC bus convertors, synchronous buck nonisolated DC/DC topologies, 18 to 36V input forward and push-pull convertors for mobile communication, and secondary-side synchronous rectification in regulated output isolated DC/DC applications.

A typical industry standard, 300W quarter-brick contains as many as ten MOSFETs (four in the primary-side and six in the secondary-side), a pulsewidth-modulated (PWM) IC and two half-bridge driver ICs.

IR's new chipset solution consists of six MOSFETs (four in the primary and two in the secondary side) and a single IC, yielding a 46% reduction in power semiconductor part count.

In addition, isolated bus convertor DC/DC applications made with this chip set achieve 29% reduced board space and operate with as much as 1.5% better efficiency.

The new IRF6646 80V MOSFET has a maximum on-state resistance of 9.5mohm, which sets an industry best in this form factor by approximately 37%, and is tailored for primary-side bridge topologies, while the IRF6635 30V MOSFET has a maximum on-state resistance of 1.8mohm and is optimised for secondary-side synchronous rectification.

The IRF6635 also achieves the lowest on-state resistance in this form factor by up to 22%.

This MOSFET pair combines with the recently introduced IR2086S full-bridge DC bus convertor IC and the existing IRF6608 30V DirectFET MOSFET, used as a secondary-side gate clamp.

"IR's new IRF6646 and IRF6635 achieve higher efficiency and operate at about 40C lower case temperature when compared with SO-8 devices".

"Device temperatures have a direct impact on overall failures-in-time (FIT) rates and mean time between failures (MTBF), since temperature is a first-order parameter in these calculations".

"In general, failure rate is reduced by 50% for each 10 degrees temperature reduction", said Carl Blake, Director of Technical Marketing, Computing and Communications group.

Back to top