Looking for the perfect TO-220 heatsink

Discussion in 'The Projects Forum' started by jwilli, Jul 31, 2009.

  1. jwilli

    Thread Starter Active Member

    Apr 21, 2009
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    0
    I've got a TO-220 voltage regulator in my circuit that can get really hot depending on circumstances. I'm trying to find a really good heatsink to use with it, but I don't have that much room to work with as far as width or space on the frontside of the regulator. I also have no more than 2" of height to work with.

    Here is a picture of how it lays out on the board:

    [​IMG]

    As you can see, there is room on the flat (metal) side of the regulator because it doesn't matter if it sticks out over the edge of the board, but there's not much room anywhere else.

    I've been looking at this heatsink:

    http://mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMttgyDkZ5Wiuh6vt2S17U8%2f9D4W%2fbh0X7s%3d

    It's specs look pretty impressive:

    [​IMG]

    The only other thing I can think of is take one of these popular styles (or something similar) and turn it backwards so the majority of the heatsink sticks out on the metal side of the voltage regulator:

    [​IMG]

    Does anyone have any ideas or suggestions of some model that might work well?
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You forgot to say how many Watts the regulator must dissipate for us to calculate the chip temperature with this small heatsink.

    The thermal resistance of a 7805 regulator is 3 degrees C /W, the small heatsink is 20 degrees C/W, the connection between the two might be 1 degree C/W. So if the regulator dissipates 4W then its chip will be 96 degrees above the ambient temperature.
    If the ambient temperature is 30 degrees C then the chip will be at 126 degrees C which is slightly higher than the recommended max temperature. This is in freely moving air, not in a box.
     
  3. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    When at all possible, I try to keep the input voltage to regulators as close to the minimum required for good regulation. Doing so goes a long way in not wasting a sh_t load of power in the regulator.
     
  4. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
    0
    I'm using it on a 7815 and the heatsink I found is the Wakefield 667 series (2" height model). Here is the datasheet:

    http://www.wakefield.com/PDF/board_level_heat_sink.pdf

    The incoming watts of the regulator will vary, but this seems to be pretty good. The largest space I can accomodate on my board is 1.375" x 0.5" x 2" height and this fits the bill.

    I haven't found a stronger heatsink within those size limitations.
     
  5. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Can you mount the regulator to the metal case instead of the pc?
     
  6. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
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    The PCB is housed in a painted steel box (like an electrical disconnect panel or circuit breaker panel). I suppose I could screw it right onto the box, but is that really a good solution?

    Also, how would you *nicely* run a wire from the PCB to the regulator's legs?

    I've seen this done before but it looked sort of sloppy and this is for a product that is resold (a few dozen per month).
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The case is a much better heatsink overall, it is a matter of surface area. I've been known to use a sink a lot like yours, AND add a block of metal (some machining required via dremal) taking the heat to the nearest metal case wall.

    This arrangement also has the advantage of letting you touch that spot, and judging if something is going wrong.
     
  8. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
    0
    I was thinking of purchasing some 1.5" wide aluminum strips from the hardware store thin enough to be slightly flexible and cut them to any length I desire and screw them right into the regulator- sort of making my own heatsink. I could have as much surface area as I wanted!

    I just wasn't sure about how well the heat would transfer.
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Don't forget to use thermal compound. It really does work!
     
  10. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
    0
    I always use thermal compound. :)

    I think I'm going to install a traditional TO-220 heatsink and use a digital thermometer to measure the MOSFET temperature, then use a piece of aluminum from the hardware store and do the same... I'm wondering which works best. :cool:
     
  11. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
    0
    * what about connecting 2 LM7815's in parallel so a single regulator doesn't get so hot? I've always tried to avoid doing this but I've been thinking about it lately...
     
  12. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    Have you considered a switch mode regulator? They run very cool compared to linear regulators.
     
  13. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Not a good idea because they will be fighting with each other.
     
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