TO220--thin leads--high current--How?

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

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vkj
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"vkj"

** Where did you get that nonsense figure ??

The fusing current of 1sq mm Cu wire is just under 100 amps.

** Not likely if soldered down to a PCB track.

.... Phil

Reply to
Phil Allison

I have delivered more than one rant on the deceptive nature of IR mosfet specs. Apparently they test them in boiling liquid, which keeps the leads from fusing. Seriously.

Their datasheet is a mess. Continuous Id is listed as 110(footnote),

80, and 75 amps. And the 200 watt dissipation spec is absurd. I never buy IR parts because they are such fools and/or liars.

Continuous 80 amps into a TO220 is insane.

John

Reply to
John Larkin

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).

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- mkaras
Reply to
Michael Karas

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.

Ditto on Power Max 200W and over.

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Reply to
oparr

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

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Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
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Reply to
Tim Williams

Okay it's official....May 2 is now "Old wives' tale" day.

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Reply to
oparr

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

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

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.

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Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
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Reply to
Nico Coesel

If the lead were very short and massively heat-sunk, it would be a little better. But if the thin part of the source or drain leads is used, and it solders to a pcb trace or pour, things are bad. The source lead is the worst, because it connects to a wirebond inside the package, and can't dump much heat in that direction.

It generally makes sense to parallel a few cheaper mosfets to get high current. 15 or maybe 20 amps each.

John

Reply to
John Larkin

That's what I did in the refurbish of the shuttle PSU's after I discovered "redundant" in the original designs meant "domino" :-( ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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

Reply to
John Larkin

429?!!! The most ludicrous IR claim I've seen for a D2PAK was 340.

A new record!

John

Reply to
John Larkin

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
Reply to
Tim Williams

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
Reply to
Tim Williams

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.

Reply to
mook johnson

Good thing I put a shunt at the motor.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

Look at al the BLDC speed controllers for RC electric motors- they have a huge array of small fets for good reason.... dumping huge continuous currents- 100A + @ 24 -42 V or even more. Mind you, when they do go, it's

100% meltdown of everything in sight. :)
Reply to
TTman

John, we have a piece of gear at work that uses IR fets at their maximum because of space constraint of where it slips into a rack. These are high current components that would normally vaporize the leads of its case. How ever, the leads are not soldered in place, instead, they are clamped into a much heavier load capacity connection and the body of the case up against the clamp. There are no visible leads. It has an extended heat sink on the back that does get a little warm.. I can't recall the IR part number but it's well over

150 AMP with very low (Ron) and does operate at near max 75% of the time when the machine is running. We've only had one incident of losing a Fet and that we think was caused my mother nature.. I may also add that losing that FET was a nice event. The blow out physically destroyed a near by cap.
Reply to
Jamie

The spec states that 429A is;

"Calculated continuous current based on maximum allowable junction temperature. Package limitation current is 160A."

The >

Reply to
oparr

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