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High side switch

Discussion in 'General Electronics Chat' started by andy257, Feb 17, 2010.

  1. ronv

    ronv Well-Known Member Most Helpful Member

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    You might need a bigger diode and a small heatsink. The one you have looks like a 3 amp one? At 6 amps max load it will disapate almost 4 watts. So a TO 220 with a 10C/watt heatsink would be called for.
    Don't forget to make sure the cap is charged before you hook up the battery for the first time.
    Might want a little heatsink on the LM317 as well. It won't be out of spec, but will be 100C or so without it.
    Here is a good diode that will only require a small heatsink.
     
    Last edited: May 27, 2012
  2. mmmalmberg

    mmmalmberg New Member

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    OK Switching to a TO220 Schottky, already have heatsinks ordered for the mosfets, will order some small ones for both the diode and the LM317. I'll pre-charge the cap, that's going to be something to be careful about the whole time I'm working on them since I'll be taking apart & putting together a few times fixing this and that...

    Thanks Ron.
     
  3. ronv

    ronv Well-Known Member Most Helpful Member

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    Last edited: May 27, 2012
  4. dave

    Dave New Member

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  5. mmmalmberg

    mmmalmberg New Member

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    How substantial a heatsink should I have for the mosfets? The ones set up on my order right now are only 24.4 C/W.
     
  6. mmmalmberg

    mmmalmberg New Member

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    That's about like the heatsinks I'd lined up for the mosfets. I was going to flip all the heatsinks around so they point in toward the board, don't know if that's OK or not... The ones I was going to order don't have the solderable tab but I'm just remembering last time I used them the regulators they were on kept getting bent around so maybe a good idea for mechanical stability...
     
  7. ronv

    ronv Well-Known Member Most Helpful Member

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    What FETs are you using?
     
  8. mmmalmberg

    mmmalmberg New Member

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  9. mmmalmberg

    mmmalmberg New Member

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  10. ronv

    ronv Well-Known Member Most Helpful Member

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  11. mmmalmberg

    mmmalmberg New Member

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    Oops too late just fired off the order with the Vishay's. True about the battery and the cold. 'Nuther good reason for the cap. With this setup, even if the battery dies completely everything will still work. Down the road if I wanted I could replace with some more contemporary sort of long-lived battery and appropriate charging circuitry but if they last long enough I'll stick with the SLA's.
     
  12. ronv

    ronv Well-Known Member Most Helpful Member

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    That one will be a problem. It has Rds on (on resistance) of .14 ohms. At 6 amps thats 5watts (I^2R). With a 25degree C/watt heat sink thats around 150C in the shade. The other one has on resistance of .016 ohms so only .6 watts.
     
    Last edited: May 27, 2012
  13. mmmalmberg

    mmmalmberg New Member

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    Cool I will see if I can find those... Thanks for watching my back:)
     
  14. mmmalmberg

    mmmalmberg New Member

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    Both low voltage cutoffs working and dialed in. Haven't yet tested the current limiter for battery charging but it's there... View attachment 65246
     
  15. ronv

    ronv Well-Known Member Most Helpful Member

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    Cool, Can you post a picture of the "big birds"? I am impressed with them.
     
  16. mmmalmberg

    mmmalmberg New Member

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  17. ronv

    ronv Well-Known Member Most Helpful Member

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    Thanks,

    Hope the show goes well!
     
  18. mmmalmberg

    mmmalmberg New Member

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    Thanks Ron, me too:), your help has been deeply appreciated.
     
  19. mmmalmberg

    mmmalmberg New Member

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  20. mmmalmberg

    mmmalmberg New Member

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    They're up and running, I had to pull out one of the LVC's that seems to not be working, possibly the last of all the damage done when I connected the output of one of them backwards and blew up a bunch of stuff when the sun came up that morning... Show opens tomorrow, should be ok for the moment, going to try to get some parts overnighted, will be $4. worth of parts plus probably $25 shipping:)
     
  21. ronv

    ronv Well-Known Member Most Helpful Member

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    Really cool. ;)

    By the way, I see MikeML is back.
     
    Last edited: Sep 19, 2012

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