PCB Design - Power MOSFETs

Discussion in 'The Projects Forum' started by nztech, Mar 2, 2009.

  1. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Hi all,

    Re PCB design I have these MOSFETs to drive a motor: STB180N55F3
    http://datasheet.digchip.com/456/456-40884-STP180N55F3.pdf

    I am going to make a double sided PCB and was wary about Track widths re power disipation.
    Based on the motor running full there is a possiblity to run at 50Amps.
    This is a fair amount over a PCB.

    Has anyone ever designed a board using this dsort of current.
    Supply Voltage is 12Vdc.

    The datasheet gives a foot print guide but I really feel the trach or surface area is to be around 50mm.
    Correct me if I'm mistaken.

    The MOSFET is suited to high current with heatsinking.

    As mentioned any feedback based on PCB copper layout would be greatly appreciated.

    Regards
    Blair
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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  3. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    that appears to be just over a width of a 100mm.
    how the hell am I gonna do that on a PCB that has a dimension of 60mm x 50mm......?
     
  4. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    One other option I suppose is to solder copper wire on the areas carrying high current.
    What is your thoughts on this? I can make the tracks somewhere around 5-10mm depending on spacing etc.

    Cheers
    Blair
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Here are some pictures of two units I built. One has tracks made of 0.025 copper sheet. I terminated with 1/4-20 brass screws. It carries a lot of current. The other is a slightly less capacity board using 4 oz copper. Some things to remember: 1) Both are on heat sinks; and 2) Mine have short bursts of continuous power (100% PWM duty cycle), maybe 30 to 60 seconds each burst with lots of time in between. Duty cycle will make a big difference as will cooling. I entered the following into the calculator sheet: 35A, 25°C rise, 2" long track, 4 oz copper, and 12 V and got a width of 6 mm with a power dissipation of 1.25W.

    I have seen people use heavy wire soldered to the traces. It works too.

    John
     
  6. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Thanks for that, I'll see if it is possible to impliment a similar solution through my design.
    Thanks for the info.

    Cheers
    Blair
     
  7. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    have you ever used a D2PAK?
     
  8. jpanhalt

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    Jan 18, 2008
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    Yes, I have used the D2Pak ,and the same principles apply. Whatever you do, be sure to look at the datasheet with regard to the package current limitations. It is quite common to find mosfets with high current ratings, like 190A, based on the Ids ON resistance, but the package may be limited to considerably less current.

    John
     
  9. John Luciani

    Active Member

    Apr 3, 2007
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    Copper wires will work.

    Similar to copper wire are busbars which are vertical rectangular copper strips.
    A number of companies make these PCB mount busbars for carrying high currents.
    The strips have tabs that you solder into holes along the PCB.

    (* jcl *)
     
  10. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Thanks, sound like a good option.
    Do you know the like of people who provide these busbars?

    Cheers
     
  11. Skeebopstop

    Active Member

    Jan 9, 2009
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    You can also just put a massive amount of solder all along the track to triple its current capacity. Make mountains of solder on it!

    The other thing, is your MOSFETs Rds low enough to allow 12V to push 50A through it? Even if it is <250mOhm, you'll be having 625 Watts of heat coming out of it and need one monster of a heatsink. Maybe consider some FETs in parallel and heatsink appropriately.
     
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