I worked with power MOSFETs in the past and found that the reverse recovery characteristics (soft versus abrupt) correlated with emissions, but we could not derive a quantitative acceptance criteria. Vendors could easily specify and sort by reverse recovery time, but that was a different parameter, and was inadequately related to emisions levels.
Technically the best solution was to test and approve FETs by batch number, based on the measured emissions of a sample product. "Cook, Jack" wrote: > > The practice of die shrinking & speedups causes problems in the digital IC > arena also. The old but once heavily used 8051 processor is an example. > Original designs were with the NMOS (HMOS?) version but later began being > replaced by faster CMOS versions. We could see some of that clearly in > certain product audits. > > Jack Cook, > Xerox EMC Engineering > > -----Original Message----- > From: Dan Kwok [mailto:[email protected]] > Sent: Thursday, October 25, 2001 1:16 PM > To: Jim Eichner; 'EMC-PSTC - forum' > Subject: Re: Shrunk-die power MOSFET's and compliance > > Jim, > > You have my sympathies. Some manufacturers don't seem to realize that their > so called product "improvements" may actually cause undue grief and > hardships > on their customers. "Specifications subject to change without notice" is a > common catch clause associated with far many products on the market these > days. > > In one company where I worked many years ago, we had an incoming inspection > department that routinely carried out random samplings and measured critical > parameters for crystals and semiconductors. With this approach, most > out-of-spec devices simply did not make it to the store bins. > > On the brighter side, speeding up a FET is hard to do. Slowing it down in a > circuit is much easier for EMC purposes. > > --------------------------------------------------------------------- > Dan Kwok, P.Eng. > Principal Engineer > Electromagnetic Compatibility > Intetron Consulting, Inc. > Ph (604) 432-9874 > E-mail [email protected] > Internet http://www.intetron.com > > ----- Original Message ----- > From: "Jim Eichner" <[email protected]> > To: <[email protected]>; "Jim Eichner" <[email protected]>; > "'EMC-PSTC - forum'" <[email protected]> > Sent: Wednesday, October 24, 2001 11:54 AM > Subject: RE: Shrunk-die power MOSFET's and compliance > > > > > Well for example, I have just finished specifying what compliance > re-testing > > I am going to need to do on 4 different products whose power conversion > > stages use IRF630's, IRF740's, IRF840's, and RFP50N06's, but the list goes > > on and on. If you are using power FET's in power electronics, chances are > > they have changed or will soon. The main manufacturers that come to mind > > are IR, Fairchild/Harris, Philips, and STM-Thomson. Not all have forced > > changes to the shrunk-die version - some have agreed to keep the old style > > available - and all have at least added a suffix to their markings on the > > devices so you can tell if it's the new revision die or old. In one case, > > however, we received modified parts with no markings differentiating them > > from the old rev parts, for almost a year with no communication from the > mfr > > telling us about the change. We found out through other channels and then > > contacted them. They seem to be behaving as if fundamental changes to the > > performance and specifications of the part are none of our business. > > > > I am re-doing radiated and conducted emissions, some thermal testing, and > a > > bunch of functional testing and looking at waveforms on 4 different > products > > affected by this change. Those are only the products I am responsible > for - > > as a company we're doing functional testing and possibly compliance > > re-testing on many more products. > > > > This is not a simple component substitution exercise, if your products are > > or use power electronics! I would advise everyone potentially affected to > > have your procurement department look into this. > > > > Regards, > > Jim Eichner, P.Eng. > > Manager, Engineering Services > > Xantrex Technology Inc. > > Mobile Power > > web: www.xantrex.com <http://www.xantrex.com> > > Any opinions expressed are those of my invisible friend, who really > > exists. Honest. > > > > > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the old > messages are imported into the new server. > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the old > messages are imported into the new server. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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