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

[Paul E. Schoen]

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.

I would need something like #10 or #8 AWG to come even close to 75-95 amps.
What is the best way to make such a connection? I would prefer not to
resort to extra heavy PCB material. I would rather obtain or make some sort
of copper connector. Probably something like 1/32" x 1/2" copper strip
folded or rolled over the leads and then soldered would provide enough
capacity, and then punch several holes in the copper for connecting several
#10 wires with crimp lugs.

If anyone has had experience in high current applications with this
package, I would appreciate any insight into the best way to make such a
connection. Thanks.

Paul

 

[Winfield Hill]

Paul E. Schoen 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.

Aren't you the fellow that we've been suggesting use higher battery
voltages? Does your selection of a 200V part indicate agreement?
Then can we assume more sensible lower currents?

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. I would need
something like #10 or #8 AWG to come even close to 75-95 amps.

Wire is allowed to self-heat; there's no sense requiring low copper
wire temps if you're allowing high junction temps. Conventional
wire ratings meant for conduit use, etc, are not aways appropriate.

What is the best way to make such a connection? I would prefer not to
resort to extra heavy PCB material. I would rather obtain or make some
sort of copper connector. Probably something like 1/32" x 1/2" copper
strip folded or rolled over the leads and then soldered would provide
enough capacity, and then punch several holes in the copper for
connecting several #10 wires with crimp lugs.

If anyone has had experience in high current applications with this
package, I would appreciate any insight into the best way to make
such a connection. Thanks.

I have multiple relevant experiences. One example, an 1800A switch,
was made from similar-cased MOSFETs. I wired all the FET drains and
sources together with a thick bus wire to promote current equality.
Each FET was restricted to 38A nominal. Each group of six FETs (225A)
was connected with nine #14 wires (25A each), soldered along the bus
wire. The #14 wires were of equal length, and each set of nine was
terminated in a compression lug and bolted to a wide thick copper bar
carrying 900A. This setup runs reasonably cool with simple fans for
the MOSFET heatsink assembly. The instrument (p/n RIS-254) has been
in steady use for 9.5 years, in the famous light-stopping experiments.

 

[Paul E. Schoen]

Paul E. Schoen wrote...

Aren't you the fellow that we've been suggesting use higher battery
voltages? Does your selection of a 200V part indicate agreement?
Then can we assume more sensible lower currents?

Yes. I figure that the maximum power for a 12 VDC source would be about 2.5
kVA (200 amps), and then I would use 24 VDC, 48 VDC, and a maximum of 72
VDC for 15 kVA. That is about 20 HP, and should be fine for vehicular
applications. Certainly it is easier to series connect batteries, and lower
currents involve less copper loss. I would like to keep the voltage below
100 VDC, although even 48 VDC can be dangerous. There are many protective
devices and components for 48 VDC (for telecom), so I might use that to
make a 6 kVA DC/DC module for 360 VDC for a 240 VAC VF drive, and then use
two in series for 720 VDC for 480 VAC VF drives.

Wire is allowed to self-heat; there's no sense requiring low copper
wire temps if you're allowing high junction temps. Conventional
wire ratings meant for conduit use, etc, are not aways appropriate.


I have multiple relevant experiences. One example, an 1800A switch,
was made from similar-cased MOSFETs. I wired all the FET drains and
sources together with a thick bus wire to promote current equality.
Each FET was restricted to 38A nominal. Each group of six FETs (225A)
was connected with nine #14 wires (25A each), soldered along the bus
wire. The #14 wires were of equal length, and each set of nine was
terminated in a compression lug and bolted to a wide thick copper bar
carrying 900A. This setup runs reasonably cool with simple fans for
the MOSFET heatsink assembly. The instrument (p/n RIS-254) has been
in steady use for 9.5 years, in the famous light-stopping experiments.

Did you solder the #14 wire directly to the source and drain pins? I think
I might use a crimp type butt connector without insulation, and use it to
solder more easily to the pins. I will probably use #12 or #10 wire and a
maximum of 50-60 amps per device. Since all the drains will be tied
together to the positive supply, I was thinking about bolting them all to a
copper bus bar attached to the heat sinks. Of course, this would not work
for the Super-220 package, but that is for the low voltage device. I assume
the drain tabs can carry the rated current.

I am not familiar with the light-stopping experiments. Is there a website
with more information?

Thanks for your help.

Paul

 

[John Larkin]

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.

IR does this, and it's insane. The large print says X amps, and the
fine print says X/3 or something. Who cares what the silicon is rated
for?

Personally, I wouldn't run a TO-220 at more than 25 amps or
thereabouts. TO-247's are better, but more cheap fets is prudent, as
compared to trying to get huge currents through bleeding-edge parts.

I would need something like #10 or #8 AWG to come even close to 75-95 amps.
What is the best way to make such a connection?

Again, more small fets allows you to keep all the connections on a pc
board and save a lot of hassle.

John

 

[bob]

IR does this, and it's insane. The large print says X amps, and the
fine print says X/3 or something. Who cares what the silicon is rated
for?

Personally, I wouldn't run a TO-220 at more than 25 amps or
thereabouts. TO-247's are better, but more cheap fets is prudent, as
compared to trying to get huge currents through bleeding-edge parts.



Again, more small fets allows you to keep all the connections on a pc
board and save a lot of hassle.

John

Many years ago, I watched Phantom test the breaking point of a
TO-220 FET leg. It was at about 150 Amps DC that it went fizz like
a fuse.

bob

 

[Tony Williams]

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.

 

[Winfield Hill]

Paul E. Schoen wrote...

Winfield Hill wrote in message news:[email protected]...

Those values are textbook-theory for 25C junctions. Reality requires
using corrections from the datasheet figure 10, plus wiring-resistance
losses, e.g., at least a factor of two worse, 5 milli-ohms or more,
and much less than 75A under continuous operation.

Again, apply the corrections, datasheet figure 4, use 3x worse, etc.

Yes. I figure that the maximum power for a 12 VDC source would be about
2.5 kVA (200 amps), and then I would use 24 VDC, 48 VDC, and a maximum
of 72 VDC for 15 kVA. That is about 20 HP, and should be fine for
vehicular applications. Certainly it is easier to series connect
batteries, and lower currents involve less copper loss.

Indeed, so why not double or triple those voltages?

I would like to keep the voltage below 100 VDC, although even 48 VDC
can be dangerous.

Just be careful. Most of the world uses 230 vac at home.

Did you solder the #14 wire directly to the source and drain pins?

No, "I wired all the FET drains and sources together with thick bus
wires" and "Each group of six FETs (225A) was connected with nine
#14 wires (25A each), soldered along the bus wire."

.. wiring scheme for 225A high-current paralleled MOSFET switch
..
.. bus wires
.. ______ || ||
.. | |===|| ########### The nine drain wires are shown,
.. | O |======|| same for the sources, not shown.
.. |______|=o || || The gates have individual small
.. ______ || ########### resistors to the gate-drive bus.
.. | |===|| ||
.. | O |======||
.. |______|=o || ###########
.. ______ || ||
.. | |===|| ########### nine #14 AWG wired together for 225A
.. | O |======|| (each wire 9" long = 0.21-milliohms,
.. |______|=o || || Pd = 1 watt in each wire, at 20°C)
.. ______ || ###########
.. | |===|| ||
.. | O |======||
.. |______|=o || ###########
.. ______ || ||
.. | |===|| ###########
.. | O |======||
.. |______|=o || ||
.. ______ || ###########
.. | |===|| ||
.. | O |======||
.. |______|=o || ###########
.. || ||

Perhaps I can post a photo to a.b.s.e., if you like.

I am not familiar with the light-stopping experiments. Is there a
website with more information?

http://www.rowland.org http://www.deas.harvard.edu/haulab/

 

[The Phantom]

Many years ago, I watched Phantom test the breaking point of a
TO-220 FET leg. It was at about 150 Amps DC that it went fizz like
a fuse.

bob

Yes, I remember that test well. I was skeptical of some of the FET's IR was
bringing around with current ratings over 100 amps. The test I did was to clamp
a huge copper clamp to the tab on the TO-220 case, and another clamp out at the
very tip end of the middle (drain) lead. I then turned up the current until the
lead turned red hot and melted, and Bob remembers correctly, it was at 150 amps.

The leads of a TO-220 neck down, and if you make a connection closer to the
body where the leads are wider, you will be able to carry 100 continuous amps
safely, if your connection at that point is heavy enough to be a good heat sink.

 

[przemek klosowski]

On Thu, 01 Jun 2006 02:36:36 -0700, Winfield Hill wrote:

nine #14 AWG wired together for 225A
(each wire 9" long = 0.21-milliohms,
Pd = 1 watt in each wire, at 20°C)

Hmm, (225A/9)^2 * .21 milliohm is .1 W. Your resistance is wrong:
http://www.epanorama.net/documents/wiring/wire_resistance.html
shows .00297 ohm/ft for #14 wire, so your piece would have 2.2
milliohms, and we are back at 1.4 W.

 

[Terry Given]

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

 

[Terry Given]

Yes, I remember that test well. I was skeptical of some of the FET's IR was
bringing around with current ratings over 100 amps. The test I did was to clamp
a huge copper clamp to the tab on the TO-220 case, and another clamp out at the
very tip end of the middle (drain) lead. I then turned up the current until the
lead turned red hot and melted, and Bob remembers correctly, it was at 150 amps.

Bwahahahahaha!

The leads of a TO-220 neck down, and if you make a connection closer to the
body where the leads are wider, you will be able to carry 100 continuous amps
safely, if your connection at that point is heavy enough to be a good heat sink.

Of course it will be less than fun to make said conenction.


Lies, Damned Lies, and things IR say in their datasheets. I've seen them
give power figures so high that run thru the devices own Rtheta they
give dT > 200C. They like to spec things with a junction at 25C...

The first thing I do when comparing Rdson is to scale it to Tj = 125C

Cheers
Terry

 

[Winfield Hill]

przemek klosowski wrote...

On Thu, 01 Jun 2006 02:36:36 -0700, Winfield Hill wrote:

nine #14 AWG wired together for 225A
(each wire 9" long = 0.21-milliohms,
Pd = 1 watt in each wire, at 20°C)

Hmm, (225A/9)^2 * .21 milliohm is .1 W. Your resistance
is wrong:

No, the nine wires are each 1.9 milliohms (according to my
wire table), and together are equivalent to 0.21 milliohms.
The dissipation is about 1.2 watts per wire; it runs cool.

 

[Paul E. Schoen]

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

 

[John Larkin]

Yes, I remember that test well. I was skeptical of some of the FET's IR was
bringing around with current ratings over 100 amps. The test I did was to clamp
a huge copper clamp to the tab on the TO-220 case, and another clamp out at the
very tip end of the middle (drain) lead. I then turned up the current until the
lead turned red hot and melted, and Bob remembers correctly, it was at 150 amps.

The leads of a TO-220 neck down, and if you make a connection closer to the
body where the leads are wider, you will be able to carry 100 continuous amps
safely, if your connection at that point is heavy enough to be a good heat sink.

OK, but the drain doesn't have wirebonds. The source does.

John

 

[Spehro Pefhany]

OK, but the drain doesn't have wirebonds. The source does.

John

Maybe that's why Id/Idm is specified on the data sheets rather than
Is/Ism. ;-)


Best regards,
Spehro Pefhany

 

[Jim Thompson]

OK, but the drain doesn't have wirebonds. The source does.

John

I don't know about these specific parts, but many high-power devices
use a spring-clip connection instead of wirebonds.

...Jim Thompson

 

[legg]

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.

I would need something like #10 or #8 AWG to come even close to 75-95 amps.
What is the best way to make such a connection? I would prefer not to
resort to extra heavy PCB material. I would rather obtain or make some sort
of copper connector. Probably something like 1/32" x 1/2" copper strip
folded or rolled over the leads and then soldered would provide enough
capacity, and then punch several holes in the copper for connecting several
#10 wires with crimp lugs.

If anyone has had experience in high current applications with this
package, I would appreciate any insight into the best way to make such a
connection. Thanks.

The weak link is not the wire, but the wire-bond connection to silicon
metallization.

If you check higher current mosfets, you may find unconventional
internal connections that don't involve single wire bonds. It can be
multiple wire-bonds or a pre-formed source lead that makes contact
directly at multiple points.

Getting DC or low-frequency AC current through the connection is not
the usual headache with these parts, but maintaining control for
higher-frequency repetitive transitions. Your 400Hz application is
close enough to DC that this may not be an issue.

Your concern should be with interconnection in the unit and thermal
control. This is made easier if your topology allows direct bonding of
the drain to heatsinks that can be used as conductors. Source contact
should be with a suitable conductor that also makes early connection
to a suitable bussbar.

Use of copper foil as gasketing or bussbars is effective, but is
difficult to employ in a manufacturing process, without careful
tooling.

RL

 

[The Phantom]

OK, but the drain doesn't have wirebonds. The source does.

John

My purpose in making the test described was to find out what current the
external leads were capable of handling, since they are (nearly) the same on all
devices that conform to the TO-220 spec; I didn't want the current to pass
through any internal bond wires for my test. The internal conductors can be
whatever the manufacturer chooses to make them, and lately some low-voltage
FET's internals have gotten better than the external leads. The external leads
are the limiting factor on those FET's, and, of course, the connection to the
leads has to be very good to get maximum capability. On a higher voltage FET
the external leads probably won't be the limiting factor.