Mosfet thermal maximums

Discussion in 'General Electronics Chat' started by coinmaster, Nov 3, 2016.

  1. coinmaster

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  2. ronv

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    It assumes the heat sink is puurr - fect.
    What is 50 S?
     
  3. coinmaster

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    Seimens.
    So I cannot do better then 1.4 K/W with that mosfet?
     
  4. ronv

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    Hmm, confused the S out of me. :D
    You may find FETs around .5C/W
     
  5. ronv

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    Oh, I remember now. Your the tube guy. :D
     
  6. mcgyvr

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    yep... junction to case you are stuck with..
    junction to air you can change with a heatsink..
     
  7. coinmaster

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    Bah, it's gunna be hard to find a mosfet with reasonable capacitances and linearity that I can run at high GM then. Even .5 C/W to case is too low considering that I need to dissipate hundreds of watts. Worst case scenario I can use something like an H100i to cool it down. Why does the datasheet even display all those amps if it can't use them?
     
  8. kubeek

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    It can run "all those amps", or 80A continuous to be exact, but the transistor needs to be fully on.
    There is no way you will find a transistor that can have 60V Vds and 80A Id at the same time, it can either block 60V or run 80A through it but not both. Total power dissipation is 107W if you can keep the case at 25°C, so you should be able to easily dissipate around 30-50W into a large heatsink.
     
  9. coinmaster

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    Voltage rating isn't important to me in particular. I'm mostly concerned with low Crss and high gm. Low Crss most likely meaning high voltage and high gm most likely meaning high current meaning high dissipation.
    A conundrum.
     
    Last edited: Nov 4, 2016
  10. ronv

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  11. coinmaster

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    That was obviously my way of saying I don't feel like explaining my entire project. I knew people were going to ask for full schematic.
    I found a compromise in https://www.fairchildsemi.com/datasheets/FD/FDBL0630N150.pdf
    Linear, very low Crss, 0.3 C/W to case.
    But in order to keep the Crss low I need to compromise on heat. I'm thinking 300 watt for 40pf Crss making 300*.3=90C on the mosfet.
    What are the disadvantages of running a mosfet that high temperature other then skewed linearity, which shouldn't be a problem here I don't think because its linear up to 50A as it is and that's the lowest turn on voltage.
     
  12. ronv

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    upload_2016-11-5_9-25-32.png
     
  13. coinmaster

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    In theory, can a peltier or phase change cooling system lower the Thermal resistance, junction - case value since they can bring the temperature below ambient?
     
  14. crutschow

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    Yes.
     
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