Help with high current PS?

Discussion in 'The Projects Forum' started by TSOMB, Aug 31, 2014.

  1. TSOMB

    Thread Starter New Member

    Jul 31, 2014
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    Hi folks, im looking to make a 50A 4vdc supply in which I can control the current via trimmer. I plan on using a hand wound transformer and the only thing im stuck on is the current regulation. I typically have used the NPN BD437 but that is only good to 4A. I went in my parts drawer and found some steel case transistors but they are all too high of a working voltage.

    So my question is this, which transistor would best suit my application, as well I need the ability to parallel the outputs. Im still new to electronics so please be gentle lol.

    Thanks!

    *edit I just came across 4 IRF130 rated 14A each, will these work?
     
    Last edited: Aug 31, 2014
  2. ISB123

    Well-Known Member

    May 21, 2014
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    No you would need 50+ A component.
     
  3. TSOMB

    Thread Starter New Member

    Jul 31, 2014
    21
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    So you cannot parallel the emitters? If not, any suggestion on a suitable transistor model?
     
  4. ISB123

    Well-Known Member

    May 21, 2014
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    You can.
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    Why do you need the current at that low voltage?

    Bertus
     
  6. TSOMB

    Thread Starter New Member

    Jul 31, 2014
    21
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    LASER power supply.
     
  7. b1u3sf4n09

    Member

    May 23, 2014
    115
    14
    You can use something like AO4576. You would want at least 4 in parallel, so I don't know how realistic that is for your available space. Also, if you go this route, make sure to use low resistance, high wattage resistors on the outputs to ensure equal current loading on each transistor.

    You may be able to get away with using something like PSMN3R0-30YL,115. That is a lot of current for 1 transistor to pass, so I would say tread with caution if this is the path you choose to take. Dedicated heat sink for the power transistor would be a given.
     
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  8. Theagentxero

    New Member

    Aug 26, 2014
    9
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    How about an IRFP064?
    those are rated for 110A @ 10v
    Ive used those in the past. They're lots of fun.
     
  9. TSOMB

    Thread Starter New Member

    Jul 31, 2014
    21
    2
    Thanks for the suggestions, though I have one other question... The load will be running between 2 ~ 4vdc when at full current, do the transistors posted above have any issue with minimum voltage out? Also what kind of voltage drop would be expected (if any) I looked at the datasheets but couldnt find that info which im sure is there. I plan on winding the transformer so that there is not too much surplus voltage to keep the heat as low as possible.
     
  10. Theagentxero

    New Member

    Aug 26, 2014
    9
    3

    As for your question on operating range:

    The IRFP064 would not work optimally at voltages below about 2 volts, but would still be able to provide about 100 amps or so at 2 volts.
    See Figure 8 of the datasheet here: http://www.irf.com/product-info/datasheets/data/irfp064n.pdf

    You SHOULD be able to get away with those voltages, here's the deal though. Alot of these high amperage single IC units are going to be FETs of one type or another:
    Most of them will want a considerable gate voltage to turn them on. The IRFP064 for example needs a minimum of 2 volts before it bothers to transconduct, but no more than 4 volts. (See Vgs(th) on above datasheet.)

    And Voltage Drop for a MOSFET is explained really well by a post sourced from HERE:
     
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  11. wayneh

    Expert

    Sep 9, 2010
    12,137
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    I believe a 200W laser is well outside the allowed range of items for discussion here.
     
  12. TSOMB

    Thread Starter New Member

    Jul 31, 2014
    21
    2
    Thanks for the info. So do you think it would be wise to use lower output components with paralleled outputs? Or do the smaller output components
    also have the same issue? The thing is that as the current is lowered, the vf also drops. So as example, when running at say 10amp which is approx
    threshold, the vf may be as low as 1v or just over. I am aiming to have full control right down to the threshold. Which would be the better route?



    I did not mention anything about power output, and lets not forget that DPSS systems are very inefficient. Also 50A is not going to net you "200W"
    with any laser medium I have encountered. Though if you know of one, please do share :)
     
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