Re: Maximum current for TO-220 package 75-95A, and how to connect heavy leads


"Terry Given" <my_name@xxxxxxxx> wrote in message
news:1149227114.43899@xxxxxxxxxx
Tony Williams wrote:
In article <127nnipbsb9vm6c@xxxxxxxxxxxxxxxxxx>,
Paul E. Schoen <pstech@xxxxxxxxx> wrote:

I am researching high current power MOSFETs for my DC-DC
converter and motor control applications. There are some with ON
resistance as low as 0.0024 ohms (IRF2903Z) which is rated 260
amps (silicon limited) but package limited in TO-220AB to 75 A.
An IRFBA90N20D has 0.023 ohms and is limited to 95 amps by its
"Super-220" package, which does not have a mounting tab, and has
three leads about 1.0 x 1.2 mm. The TO-220AB has leads about 0.6
x 0.9 mm. Wire of that size would probably be rated no more than
about 10 amps, but I suppose the ratings assume the leads are
very closely attached to a heavy PCB trace or other thermally
conductive connector.


Why not use MOSFETs in the ISOTOP package. OK it costs
more, but you don't have the expense of a pcb layout and
the fiddling around to make decent-sized connections.
ISOTOP is also easy to heatsink, with a lovely low
overall thermal resistance.


Or SEMITOP

Cheers
Terry

I would like to find the least expensive overall solution to making an
efficient high power converter. The TO-220 and its variants seem to be most
economical and widely available from multiple sources. I can minimize the
heat sinking requirements (and boost efficiency) by using a very low
resistance MOSFET. Of course, at higher voltages you have higher resistance
or higher cost. There are lots of 65 V MOSFETs that would be OK for up to
24 VDC supply, then 100 V for a 36 VDC supply. For a 48 VDC supply, I would
need at least 150 VDC, and they are relatively rare. There are more again
at 200 VDC, which would be OK for up to 72 VDC. Above that, the on
resistance and cost go up. I'll supply a breakdown of what I have found so
far:

IRFBA90N20D 200V 98A 650W 0.023R Super220 $7.20
IRFB260N 200V 49A 300W 0.04R TO247 $3.90
IRFPS3815 150V 105A 441W 0.015R Super247 $5.99
IRF52N15D 150V 60A 320W 0.032R TO220AB $2.10
IRF3415L 150V 47A 200W 0.042R TO220AB $1.87
STP40NF12 120V 40A 150W 0.032R TO220 $1.50
75645P 100V 75A 310W 0.014R TO220 $2.42
FB180SA10 100V 180A 480W 0.0065R SOT227 $29.95
IRFB3077 75V 210A 370W 0.0033R TO220AB $6.13
IRF3808 75V 140A 330W 0.007R TO220AB $2.58
STP60NF06 60V 60A 110W 0.016R TO220AB $1.06
IRF1405 55V 169A 330W 0.0053R TO220AB $1.53
IRFZ44N 55V 41A 83W 0.024R TO220AB $0.93
IRL2203N 30V 100A 130W 0.007R TO220AB $1.73
IRF2903Z 30V 75A 290W 0.0024R TO220AB $3.81
IRL3803 30V 140A 200W 0.006R TO-262 $3.38

I included the one ISOTOP device to show how much more expensive they are.
However, I might be able to use just one device rather than four in
parallel, and simpler assembly may make it worthwhile for any production.

I have some TO-3 versions of the 60N06 that I used for my prototype.
Unfortunately I destroyed them because the overcurrent shutdown was not
connected. I have two more, but I really need to use the TO220 or other
inexpensive package for higher power testing.

I have 50 pieces of the 75645P coming in (won on eBay for $32+$6), and they
should be good for supply voltages up to 36 VDC. I should be able to drive
them to about 40 amps at 50% duty cycle for power dissipation of about 11
watts each (probably closer to 20W at actual operating temperature). This
is a power input of 1440W, or about 2 HP. I should be able to use four in
parallel to get 5.6 kW with 160 amps input. Approximate efficiency would be
1-40W/1440W =97.2%.

For 48 VDC 40A input, the IRF52N15D would provide 1920 Watts, but power
dissipation would more than double. It would probably be OK on 60 VDC, for
2400 Watts, but the 150V would be marginal for 72 VDC. The efficiency would
be 1-80W/2400W = 96.7%.

The IRFBA90N20D would work up to 72 VDC and up to 50 amps, for 3600 Watts.
Power loss would be about 120 Watts, for efficiency of 96.7%. Three in
parallel would give me 10 kW, which is about what I was looking for.

Of course, I would not expect efficiency that high, because of copper
losses and transformer losses. However, I think 92-95% is realistic.

I may use a compression type lug on the leads, with solder, and then bolt
the lugs to bus bars. This will make it easier to replace any devices that
fail (and I'm sure they will, until I determine optimal snubbers and
overcurrent protection).

Thanks for your comments. Now to get back to work on this beast.

Paul


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