TO220--thin leads--high current--How?
in [Design]
|
From: Tim Williams on 2 May 2010 13:58 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 -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "vkj" <tranquine(a)n_o_s_p_a_m.n_o_s_p_a_m.gmail.com> wrote in message news:LbSdnfKyx5evGEDWnZ2dnUVZ_jOdnZ2d(a)giganews.com... >I have a somewhat basic question. I am using a high current MOSFET > (IRF3205) rated at 80A cont. Acc to convential wisdom for a copper > conductor at about 4A/sqmm ct. dens. the conductor shd be about 20 sqmm, > while the TO220 lead is a small fraction of that. At 80A this thin lead > would probably fuse. > > How does one actually use this package? > > Thanks, > > vkj > > --------------------------------------- > Posted through http://www.Electronics-Related.com
From: oparr on 2 May 2010 14:04 > The only thing you need to know about MOSFETs is use them at half rated > current. Okay it's official....May 2 is now "Old wives' tale" day. On May 2, 1:58 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: >
From: Spehro Pefhany on 2 May 2010 14:33 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? Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Nico Coesel on 2 May 2010 15:07 "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. 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. Sending tens of amps through a small lead is insane. Mains terminal blocks carrying less than 20 amps can cause problems. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: John Larkin on 2 May 2010 15:44
On Sun, 2 May 2010 10:42:44 -0700 (PDT), "oparr(a)hotmail.com" <oparr(a)hotmail.com> wrote: >>Continuous 80 amps into a TO220 is insane. > >If you do a parametric search on MOSFETs with continuous drain of 80A >or more and with TO220 case it will return several manufacturers, not >just IR. Me thinks you're making a mountain out of a molehill in >singling out IR specs. > >>And the 200 watt dissipation spec is absurd. > >Ditto on Power Max 200W and over. > > >On May 2, 10:43�am, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> IR published one brochure where they claimed that a D2PAK was good for 340 amps. Having parts and boards blow up, and source leads vaporize, is not a "molehill." One has to read the IR datasheets very carefully, including the SOAR curves, to figure out how much current and power they can reasonably stand. If you read the headlines or the abs max specs on the datasheet, and design around that, things *will* fail. I bet a lot of beginners get "burned" that way. What's the point of them headlining 120 amps for the silicon and then putting a tiny footnote stating that it's "package limited" to 80, when it might be safe at 30? Be safe, don't buy IR. John |