High current regulated power supply

Discussion in 'The Projects Forum' started by jester1, Apr 20, 2011.

  1. jester1

    Thread Starter Member

    Feb 10, 2011
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    Im trying to make a high current power supply to test car stereo equipment. It's based on http://hmin.tripod.com/als/andysm/drawings/supplies/10A-PS10.GIF
    and http://www.reuk.co.uk/OtherImages/high-current-voltage-regulator.gif
    Also attached is an lt spice model of the circuit. Will this work okay or will the resistor values need to be different. Will this circuit handle near the 70 amps the bridge rectifier can. p.s. after the two 8200uf caps the output voltage is approximately 20.6v. thanks for any help.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, your simulation is incomplete, and I don't have warm fuzzy feelings about the schematics you posted.

    Member Rifaa built a high-power adjustable supply several months ago; not sure where that project is at the moment.

    There are a few more on here who have built high-power linear supplies.

    Have a look at Elliott Sound Products' site:
    http://sound.westhost.com/projects-4.htm
    That's the power supply project section.

    Here's one in particular to look at that is expandable:
    http://sound.westhost.com/project77.htm
     
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  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    I bought a 13.8v 12amp complete switchmode power supply new for about $50, it is voltage regulated at 13.8v and has short circuit current protection.

    They sell them for HAM radio use etc, to run large 12v equipment from the mains.
     
  4. jester1

    Thread Starter Member

    Feb 10, 2011
    14
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    This would be perfect http://sound.westhost.com/project77.htm thanks for the source, lost my link to those guys a while back.
    For a 70A output I'd need 18 2n3055 transistors at 10a each.How many 25A transistors would it take to output 70A; and if I upgraded the transistors amperage then wouldn't the wattage rating on the emitter resistors need to go up. Also would it be possible to use mosfets instead as there rated much higher ( for instance two of these http://pdf1.alldatasheet.com/datasheet-pdf/view/68119/IRF/IRF1404.html I have on hand).
     
    Last edited: Apr 21, 2011
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Well, you seem to have missed Rod Elliot's bullet points at the bottom of that page, two of which I'll paste here:
    • Use one 2N3055 for each 5A of peak output current (4A continuous) - Each transistor will dissipate about 40W
    • Assuming a current gain of 20 for the 2N3055s (fairly typical), one 5A TO-3 regulator will drive up to 100A (use 25 transistors)

    So, if you want 70A continuous output, you will require 70A/4A = 17.5 of the 2N3055 transistors; round that up to 18. I see you did calculate it properly, but you mis-typed the 4A as 10A.

    The big problem is the power dissipation in the pass transistors. If you try to use transistors that can pass more current, you will have to use much larger heat sinks for each one. As it is, 40 Watts per transistor will require a pretty hefty heat sink for each one, and you will probably have to use fan(s) to move enough air over them to keep them from overheating.

    I suggest using 120v fans, as if you use 12v fans, it will increase the requirements on the transformer/bridge/regulators. Also, you will need 3.5A current output from the regulator to drive the bases of the 18 transistors, assuming each 2N3055 transistor has a gain of 20 with 4A collector current.

    As current output from each 2N3055 increases, the gain drops dramatically. When Ic=4A, gain is ~20. When Ic=10A, gain is ~5.

    I am not going to be able to be much more help with this project, as my time here is very limited, and I may be offline for a period of time in the near future.
     
  6. jester1

    Thread Starter Member

    Feb 10, 2011
    14
    0
    This may be a shot in the dark, but would these work (http://pdf1.alldatasheet.com/datasheet-pdf/view/239957/STMICROELECTRONICS/2STC4468.html) I have ten of them lying around from a broken amp. If they would work would they be a direct swap for the 2n3055's. (will the rest of the circuit work with them) Presuming my math is correct a 2STC4468 will do 3A at 70 and 5A at 50 in hfe; so it would be fair to say it would do 7A at 30 which is way better than the 2n3055's rating.
     
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