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How can a MOSFET in TO220 handle this much current?

Discussion in 'General Electronics Discussion' started by sumeryamaner, Aug 16, 2020.

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  1. sumeryamaner

    sumeryamaner

    50
    13
    May 29, 2017
    Forgive me for this dumb question please but I cannot understand it.
    Let's say we have a MOSFET IRF1404. The specs say that it has a VDSS of 40 V, an RDS(on) of 0.004 ohm and a continuous drain current of 202 A!
    This MOSFET resides in a TO220 case.
    How can it be possible that 202 A current flows through it's contacts?
    (Btw. 202 A * 0.004 ohm = 0.808 V and this results in 163 Watts power dissipation. The specs say that it's max. power dissipation is 333 W. On the paper everything seems OK).
    What am I missing? How should I interpret the datasheet figures?
    Thank you very much.
     
  2. bertus

    bertus Moderator

    1,478
    584
    Nov 8, 2019
    Hello,

    Did you read this on page 2:

    IRF1404_notes.png

    Note 6 : Package limitation current is 75A.

    Bertus
     
    sumeryamaner likes this.
  3. sumeryamaner

    sumeryamaner

    50
    13
    May 29, 2017
    Great point. Thank you. But now I have two more questions:
    1- Package limitation is 75 A and there is no other package option for this MOSFET. So why the 202 A continuous drain current? How should I interpret this?
    2- Is 75 A OK for the source lead of the MOSFET?

    Thank you very much.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,999
    2,502
    Nov 17, 2011
    Just marketing speech. As stated this is a calculated value up to which the junction would presumably not be destroyed. Better to market the transistor as 202 A type than as 75 A type. Always read the small print.
    Obviously yes as the leads are part of the package.
     
  5. bertus

    bertus Moderator

    1,478
    584
    Nov 8, 2019
    Hello,

    Here I found an other reason for the limited current of the TO 220 mosfets.
    The bondingwires between the chip and the legs are very thin and will burn when to much current is going through them.
    On the digikey page on cooling you will find an image of the internals of a TO 220 (figure 1):
    https://www.digikey.nl/nl/articles/heat-sinks-a-step-by-step-guide

    Also the NXP selection guide has a nice comparisson on the different mosfet housings and their capabilities:
    www.nxp.com/docs/en/product-selector-guide/75017590.pdf

    Bertus
     
    Harald Kapp likes this.
  6. Wollowstone

    Wollowstone

    16
    3
    Mar 26, 2018
    The Vdss of 40V is the minimum garanteed voltage that can passthrough the IRF1404.
    The 121A is for a short pulse, as stated in the annotation (4) of the section Electrical Characteristics.
    Use the SOA (figure 8) to have an information which COMBINES voltage passing through AND current passing through ... but NOT JUST the maximum current or just the maximum voltage which can pass through the transistor. Figure 8 is for 25C without heat radiator, you may have to normalize accordingly figure 4 if temperature greatly differ than 25C.

    I used the datasheet at http://www.irf.com/product-info/datasheets/data/irf1404.pdf


    As example, for a single pulse of 10 ms of 10V, you should not use more than 32A. For a continuous current, figure 11 seems to indicate that we can generate not more than 20% heat, so I would reduce to 25A in that case... or do the computation at long.
     
    Last edited: Aug 20, 2020
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