On Tue, 21 May 2013, Gene Heskett wrote: > Date: Tue, 21 May 2013 22:04:34 -0400 > From: Gene Heskett <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: [email protected] > Subject: Re: [Emc-users] Superglue, or Loc-tite for that motors flywheel? > > On Tuesday 21 May 2013 21:53:39 Jon Elson did opine: > >> Gene Heskett wrote: >>> Humm, is there an IC that will function as the switch driver, and >>> whose output could be controlled with a PWM mode? Something that >>> would start at 15% duty and taper to 100% when the applied voltage >>> had dropped to say 20 volts. Then the Q is how fast can these be >>> switched, I get the impression I'm still looking at hexfets I can >>> steal out of dead computer PSU's. These things speed (lack thereof) >>> will cause their own SOA self destruction I expect. >> >> I use the IR2113 and similar chips to drive FETs. You'd need some op >> amps and/or comparators to generate the PWM. Lack of speed? The >> IRFB31N20D was so fast it caused problems with the dV/dT (and dI/dT) >> affecting the rest of the >> circuitry. Easily 100 ns turn-on/turn-off times, even with resistors in >> the gate circuit. > > Those are problems you should like Jon, they are telling you that your > ground & power planes need to be wider, and need more bypassing. Both of > those translate to reduced switching losses & cooler devices. Often you > will need both a .05 ceramic on very short leads or better yet, surface > mount, AND a 10uf in order to get enough bypassing. > > Of course I'm far enough away its not worth getting in the car to come and > beat some manners into me. :) I think. > > FWIW, resistors in the gate to slow the rise & fall times will raise the > switching losses, in some cases enough to destroy the device long before > your finger says its even getting warm. > > But you knew all that. > >> Jon
In practical Hbridges, gate resistors for assymetrical gate drive (fast off slow on) are often needed to prevent dVdT turn-on of the high side by the low side switches or vice versa. If your choice is a little bit of switching loss vs shoot-through, its easy to choose... > Cheers, Gene > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! > My views > <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> > Questionable day. > > Ask somebody something. > A pen in the hand of this president is far more > dangerous than 200 million guns in the hands of > law-abiding citizens. > > ------------------------------------------------------------------------------ > Try New Relic Now & We'll Send You this Cool Shirt > New Relic is the only SaaS-based application performance monitoring service > that delivers powerful full stack analytics. Optimize and monitor your > browser, app, & servers with just a few lines of code. Try New Relic > and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Try New Relic Now & We'll Send You this Cool Shirt New Relic is the only SaaS-based application performance monitoring service that delivers powerful full stack analytics. Optimize and monitor your browser, app, & servers with just a few lines of code. Try New Relic and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
