On Friday 29 August 2014 08:10:01 Erik Christiansen did opine And Gene did reply: > On 13.08.14 20:03, Gene Heskett wrote: > > Now, if I could just find a 3x higher voltage version of the IRFP250N > > hexfet with about the same gate driving capacitance load. The 200v I > > managed to punch thru a couple days back. Thats a 35 amp device, and > > there is a 78 amp 650 volter available but I wasn't able to compare > > gate input capacitance. But I'd bet that 78 amp puppy is 10x the 30 > > amp version. > > > > Sadly, my 8+feet of semi manuals is now pushing 15 to 20 years out of > > date. > > Gene, what's the part number of the 650 volter?
Its from Vishay Siliconix, the SiHW73N60E TO-247AD packaging. Rds(on) at a 10v gate is .039 ohms Qg max (nC) is 362 > I've recycled a > wheelbarrowload of dead-tree semiconductor data manuals, and now only > use a suitably organised directory tree of PDFs, all snarfed after a > quick google for e.g. "IRFP250 datasheet". (All suitably backed up too, > naturally, to defeat the Murphy-Heisenburg surprise: Data which exists > only in one place exists only in your imagination - if not now, just > wait.) > > Many of 'em I've never printed out, since a quick glance on-screen is > enough for checking pin-out or a parameter. > > <2c> > Incidentally, I've moved from comparing gate capacitance to using Qg, > the "total gate charge" figure, since that's what's needed for > turn-onآ¹, and dividing it by the desired turn-on time directly gives > the required gate drive current. On almost any MOSFET datasheet, > looking at the graph for "Typical Gate Charge Vs. Gate-to-Source > Voltage" shows the ramp-plateau-ramp switch-on characteristic which > makes a mockery of a single gate capacitance number, I figure. That > graph often also tells you how much harder to drive it if you up the > Vds significantly. (OK, not much, but it's good to know.) > </2c> > > Erik > > آ¹ For comparable Vgs(on), which has to be the case if we're > substituting without changing the gate driver. Correct. Generally speaking the better the supply rail bypassing is AT that gate driver chip, the better off we are, but to do it right needs both tantalum and mylar caps in give the bean counter ulcers sizes. I blew the hexfet in that teeny little controller they use for that 200 watt motor on the micro-mill, and started opening up and reading numbers on the switch chips use by the jillions in computer PSU's but I didn't have to look far, the first one I opened up had a pair that were obviously rated well in excess of the one that blew. So I wrapped its leads in some stripped kynar wire and transplanted it. It worked. And no hot drivers could be found with my IR thermometer. And 3 years later with at least 300 hours of run time on it, its still working. It may at some point, get to try running the 400 watt motor I took out of the lathe. That whole outsized box on top of its spindle will have to go because I'll make a sliding motor mount to allow belt shifting with a target speed of about 2k in low range and as high as I can get pulleys to do in high range for engraving usage. There will also be room for an encoder when I do. Old voltage gone low PSU's are something I keep quite a few of around, the components in them are generally speaking top of the line stuff. And are (the most important thing to someone on SS) free. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that matters. http://tv.slashdot.org/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
