TO220--thin leads--high current--How?
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From: John Larkin on 2 May 2010 15:46 On Sun, 02 May 2010 14:33:49 -0400, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Sun, 2 May 2010 12:58:24 -0500, the renowned "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>I once accidentially burned out a capacitor lead at 50A. It was 0.6mm >>diameter, active section about 2-3mm long. >> >>I was testing a high current power supply, which was operating happily at >>50A, with unusually low output voltage. Ten seconds later, *phut*, poof. >>;-) My fault for clipping a large alligator clip to a fairly small >>capacitor. >> >>The only thing you need to know about MOSFETs is use them at half rated >>current. As an added bonus, the Rds(on) is relatively small, so you need >>even less heatsinking. >> >>Tim > >So, in the case of a D2Pak rated at 429A (asterisk) continuous or >1640A pulsed (160A package limit) would you run it at 820A, 214.5A or >80A? > > 429?!!! The most ludicrous IR claim I've seen for a D2PAK was 340. A new record! John
From: Tim Williams on 2 May 2010 16:43 "Nico Coesel" <nico(a)puntnl.niks> wrote in message news:4bddc8f5.725822671(a)news.planet.nl... > The counterside is that the gate capacitance is much larger so the > turn on/turn off time is larger which results in extra heat losses. I > like to choose the smallest MOSFET that fits the worst case scenario. Ah yes, I got burned by transformer-coupled-gate-drive switching loss on that recently. More incentive to use Jeorg's favorite chip, I guess. ;) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 2 May 2010 16:46 "Spehro Pefhany" <speffSNIP(a)interlogDOTyou.knowwhat> wrote in message news:t4hrt5dacufuntdfcsnb0sogplcvoouab2(a)4ax.com... > So, in the case of a D2Pak rated at 429A (asterisk) continuous or > 1640A pulsed (160A package limit) would you run it at 820A, 214.5A or > 80A? Ahh... allow me to amend that, then... Half rated current, or 50A, whichever is lower. Adjust 50A as needed for package size, of course (DPAK maybe 25A, D2PAK/TO-220 50A, TO-3P/TO-247 100A). Are MOSFET and IGBT modules still rated sanely? They've got a lot of plastic in them, doesn't seem like nucleated boiling would help much. 'Course, they're a much simplified product line, too. Find the volts and amps you need, double it, then find something in the product line. Check that it's fast enough and it's got whatever doowhackeys you need (layout, diodes, etc.), order. But they're still insanely priced. I guess your choice is, madness in ratings, or madness in pricing, when it comes to high power electronics. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: mook johnson on 2 May 2010 16:50 "Michael Karas" <mkaras(a)carouselDASHdesign.com> wrote in message news:MPG.264733834ab7a603989684(a)news.eternal-september.org... > In article <a93rt5p9mdaf97ejj31kvs4d6v38utud50(a)4ax.com>, > jjlarkin(a)highNOTlandTHIStechnologyPART.com says... >> >> >> Continuous 80 amps into a TO220 is insane. >> >> John > > Real world experience here. I once did a design of a motor driver with > T0220 parts mounted vertical from a heat sink right down into a plated > through hole. The FETs were capable of handling the "design to" current > specification I was given. However when the motor was exposed to stall > conditions the leads of the T0200 would completely vaporize. The PSU was > rated at 80A that was current limited so the fusing was happening at > somewhat over 80A (what ever design margin was used in the PSU for its > limit threshold). > > -- > - mkaras Doesn't mean 80 amps was the peek. A locked rotor would discharge the capacitance on the motor rail and could be as high as [Rail V / (motor DCR + Ron*2+ Cap ESR)] until the caps discharged. With a high voltage with some decent capacitive bypassing you can get some serious amps before the 80 amp current limit kicked in.
From: Tim Williams on 2 May 2010 16:54
"mook johnson" <mook(a)mook.net> wrote in message news:2AlDn.135639$mn6.7092(a)newsfe07.iad... > Doesn't mean 80 amps was the peek. A locked rotor would discharge the > capacitance on the motor rail and could be as high as [Rail V / (motor DCR > + Ron*2+ Cap ESR)] until the caps discharged. With a high voltage with > some decent capacitive bypassing you can get some serious amps before the > 80 amp current limit kicked in. Good thing I put a shunt at the motor. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |