To220 mosfet KF5n50 vs SM mosfet KFn50 heat dissapation ?

Discussion in 'Power Electronics' started by frank55, Mar 25, 2017.

  1. frank55

    Thread Starter Member

    Dec 6, 2013
    288
    10
    Hi guys; i made this repair on my LCD TV power-supply-backlight-inverter circuit
    and shopjimmy sent me on a repair kit Q706 Q707 (KF5n50 mosfets)
    TO220 casing instead of SM mosfets,
    now i made the adaptation on the bottom of the board,but i'm a little worried about heat dissipation since the TO220 casing has no heat sink ,
    see pic; will this be alright or i have to get the SM mosfets instead? thanks in advance.
    http://www.electronica-usa.com/graphics/KF5N50.pdf
    https://postimg.cc/image/b8p9f5q8t/

    https://postimg.cc/image/bwo4wq46h/

    https://postimg.org/image/kkk31ub6z/
     
    Last edited: Mar 25, 2017
  2. #12

    Expert

    Nov 30, 2010
    18,078
    9,620
    It seems to me that the TO-220 packages have surface area similar to the circuit board copper and more 3D bulk. That should work. If in doubt, glue a quarter to each of them, or buy a real TO-220 heat sink for each. There's no such thing as too much heat sink, unless you can't get it to fit in the case.
     
  3. wayneh

    Expert

    Sep 9, 2010
    14,863
    5,346
    So the question is if the TO220 without a heat sink is as thermally protected as the surface mount part attached to the board.

    Hunch: Yes, they're OK. They're bigger and have some airflow. But that's just a hunch. If heat was a big problem I don't think those SM MOSFETs would fare so well either.

    I think my approach would be to turn it on and lay a finger on them. If they don't they don't get crazy hot, they're fine.
     
  4. frank55

    Thread Starter Member

    Dec 6, 2013
    288
    10
    Hi guys;today i decided to reopen my Vizio E321VL since the mosfets heating issue kept bugging me,and when something is bugging me i keep thinking on it and never stop till a fix it otherwise i don't sleep well,he.he,he.. i did check the temperature with my Fluke for about 5 minute with tv running to the existing mosfets without the heat sink,and it went up to 60C*,
    So story short i had 2 extra KF5N50 TO220 mosfets and a few Heat Sinks in my scrap,
    i made 3 holes in the board in each one,and the end result was this see attachment pics.
     
  5. #12

    Expert

    Nov 30, 2010
    18,078
    9,620
    Looks like a winner.
     
  6. frank55

    Thread Starter Member

    Dec 6, 2013
    288
    10

    Thanks bro; i do what i can with what i know and with what i'm can afford to pay for parts,though i'm very cheap, it costed me 20dollares plus 5 bucks for shipment for the kit but i only used the 2 TO220 mosfets,
    still have a whole lot of components for future repairs.
     
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