Roman Black wrote: >Which explains: >1. why very high current (low Rds) MOSFETS have such >low voltage limits. Uh, it has nothing to do with it. It has to do with the gate oxide thickness. You can make MOSFETs with 100V and more insulated gates but it will likely not go together with low turn-on control voltage. In fact such things exist and there are a couple of switching mode supplies that use this to good effect. But they are not consumer equipment. 27A is not 'very high current'. The part I used was rated 55A, 50V, in TO220. >2. Why we see such high failure rate of high current >MOSFETs in inverters and the like compared to similar >high current low-sat bipolar transistors. One of the >reasons I will always choose NPN over a FET, and the >NPN is normally cheaper for the similar spec, if >you discount drive current. I'd prefer to sacrifice >drive current for reliability and ruggedness anyday. The state of the art in switching FETs off the shelf seems to be at about 1500V and 7A or so, in a modified TO220 (insulated). It is about as easy to do these in as a bipolar. The part choice for current consumer OEM lies with cost and supply, not technology. The turnover of this equipment is so fast, that nobody in a sane mind cares what will happen in 5 years. They apply statistical fault modelling, do some HALT, and dump the thing into production if it passes what they set as criteria. I can't see very much use in an ultra reliable over-engineered SMPSU in an all plastic VCR that will self destruct by munching its own gears and bushings to dust within about 3 years of semicontinuous domestic operation. Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body