+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Newbie level 3
    Points: 35, Level: 1

    Join Date
    Oct 2019
    Posts
    4
    Helped
    0 / 0
    Points
    35
    Level
    1

    Why are SMD components so much smaller than their THT versions?

    I've been doing my prototyping a high current circuit with 25ish amps using tht components. I recently ordered some smd versions of the same components to see the size they would be for a circuit board. I am stunned at how much smaller the smd version of a 200A mosfet is. I was able to solder some leads into it just because I couldnt believe it would handle the current the same way as the much larger THT component. To my surprise, after maybe an hour or so of keeping the large LED on, it didnt gain any more heat than the through hole mosfet.

    I'm just struggling to understand how something a mere fraction of the size can handle it?

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 24,286, Level: 37
    barry's Avatar
    Join Date
    Mar 2005
    Location
    California, USA
    Posts
    4,657
    Helped
    1032 / 1032
    Points
    24,286
    Level
    37

    Re: Why are SMD components so much smaller than their THT versions?

    The die is the EXACT SAME SIZE for through-hole or SMT devices. The TH parts are bigger in order to acommodate the larger lead frame. You'll notice that SMT leads are much smaller than TH leads...



    •   AltAdvertisement

        
       

  3. #3
    Advanced Member level 3
    Points: 5,888, Level: 18

    Join Date
    Feb 2014
    Posts
    838
    Helped
    278 / 278
    Points
    5,888
    Level
    18

    Re: Why are SMD components so much smaller than their THT versions?

    Well don't be fooled by mosfet ratings.

    When it comes to heat dissipation size matters. Even with the same "200A" die you'll be able to push more power from a bigger package.

    You need to carefully follow the junction-to-board or junction-to-ambient thermal impedance numbers to calculate actual current handling. You can only get about 1-2 watts from an SMT part in typical ambient conditions. To get more you need large areas of copper, heatsinks, airflow etc.

    Run the numbers and you'll find even 20A is hard to get from your "200A" fet.



    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 5
    Points: 14,971, Level: 29
    schmitt trigger's Avatar
    Join Date
    Apr 2013
    Posts
    2,488
    Helped
    805 / 805
    Points
    14,971
    Level
    29

    Re: Why are SMD components so much smaller than their THT versions?

    What ASDF44 said.

    If you attach the datasheets for the Mosfet you employed, we can help you with the thermal calculations.

    Even if you don’t require the help, for the benefit of other future readers, it would be sensational if you did so.
    My batteries are recharged by "Helpful Post" ratings.
    If you feel that I've helped you, please indicate it as a Helpful Post



--[[ ]]--