Connect with us

Diodes in parallel to increase maximum current ?

Discussion in 'Electronic Design' started by hihihi, Feb 20, 2006.

Scroll to continue with content
  1. hihihi

    hihihi Guest

    Hi..

    Is it possible to place 4 diodes in parallel to increase the maximum
    current ?

    In this case it would be 4 times 1N5408 diodes.
     
  2. linnix

    linnix Guest

    Yes for making fireworks. They will pop one by one.
     
  3. hihihi

    hihihi Guest

    Thats what i feared.. :)

    Thanks for the very quick reply..
     
  4. Genome

    Genome Guest

    YES..... all you have to do is make sure they share the current or, if you
    don't care if they dont, then don't. Life is cool that way. Diodes have a
    negative temperature coeifficient thing so if you do some sums you might
    work out how much resistance you need to add to your circuit to make them
    agree with the answer without wandering about too much or some other stuff.

    It's all rather complicated but if you sign up here,
    http://www.ijsklontje.nl then you won't find out how.

    DNA
     
  5. DaveM

    DaveM Guest


    Well, you could put them in parallel, but it wouldn't serve your purpose.
    The reason is that each diode will likely have a different Vf. The diode
    with the lowest Vf will conduct first, possibly not allowing the others to
    turn on. The diode with the lowest Vf will hog current, possibly to the
    point of destruction, probably shorting, thus creating havoc with whatever
    lies downline. If it fails open, then the diode with the next lowest Vf
    conducts and repeats the cycle. A losing situation either way.
    Solution is to get the correct diode.

    Cheers!!!
    --
    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in
    the address)

    Never take a laxative and a sleeping pill at the same time!!
     
  6. Macgyver

    Macgyver Guest

    If your laid back approach were any more laid back you would be
    horizontal!

    And how is looking at porn going to solve this problem?
     
  7. John Fields

    John Fields Guest

     
  8. Genome

    Genome Guest

    Thank you for admitting that I have an immensly huge cock. Obviously I
    haven't but I appreciate the compliment (From A Texan) anyway.

    DNA
     
  9. Genome

    Genome Guest

    Chemists learn things without an incentive to find out more.

    DNA
     
  10. Rich Grise

    Rich Grise Guest

    And, as any woman will tell you, that's why a small one is better "in
    the long run", so to speak. ;-P

    Cheers!
    Rich
    --
    Elect Me President in 2008! I will:
    A. Fire the IRS, and abolish the income tax
    B. Legalize drugs
    C. Stand down all military actions by the US that don't involve actual
    military aggression against US territory
    D. Declare World Peace I.
     
  11. Rich Grise

    Rich Grise Guest

    Only problem with huge cocks is the same problem with huge tits and
    asses - when the body makes that much investment in genitalia, there
    isn't enough tissue left over to make an effective brain. ;-P

    Good Luck!
    Rich
    --
    Elect Me President in 2008! I will:
    A. Fire the IRS, and abolish the income tax
    B. Legalize drugs
    C. Stand down all military actions by the US that don't involve actual
    military aggression against US territory
    D. Declare World Peace I.
     
  12. On Mon, 20 Feb 2006 23:38:38 GMT, in sci.electronics.design Rich Grise
    see
    http://www.theregister.co.uk/2006/01/26/bat_revelation/


    martin
     
  13. Jim Thompson

    Jim Thompson Guest

    On Mon, 20 Feb 2006 23:38:38 GMT, Rich Grise

    [snip]
    [snip]

    That's just a restatement of Thompson's (40+ year old) Theorem... "The
    sum of mammary tissue plus brain tissue is a constant" ;-)

    ...Jim Thompson
     
  14. Jamie

    Jamie Guest

    hmm, not really, i assume your referring to things
    like supply line mains etc.
    if you get perfectly matched diodes you could do it
    how ever, the chance of getting 4 diodes to match the
    current curve is slim with in reason.
     
  15. Fred Bartoli

    Fred Bartoli Guest

    What shall we deduce, after all the time you've spent convincing us that you
    have a really huge brain?
     
  16. Phil Allison

    Phil Allison Guest

    "hihihi"


    ** Yes - it will likely work out just fine.

    The ***fuckwit doomsayers** here have simply never tried it.



    ** To get reasonable current sharing, the diodes should all be from the same
    batch and mounted in thermal contact.

    This means installing them snugly side by side, with short leads into large
    heat-sinking pads on a PCB.

    Or else - twisting the four leads together at each end.

    Long as the diodes are similar and the temps the same, close sharing is
    assured.

    However, four 3 amp diodes will not give you a 12 amp average current
    rectifier.

    Derating will be needed - to maybe 7 or 8 amps.





    ......... Phil
     
  17. If there is something else in each diode's circuit to ensure that they
    share the current approximately equally, then it is sometimes possible.

    You can use a resistor if the power loss isn't going to be a problem, or
    you might be able to make use of some existing loss, such as the winding
    resistance of a transformer.

    If you were using a mains transformer with four identical parallel
    secondary windings, keeping the windings separate with one diode on each
    winding would probably work - but you would have to test it thoroughly
    and de-rate the diodes sufficiently to allow for any imbalance.
    Similarly, if you are using a choke-input smoothing arrangement, a
    quadrifilar choke could be designed to do the job.

    I have used something like this in reverse, to distribute output
    transistor current in a large audio amplifier with a multi-primary
    output transformer.


    In all probability, none of these solutions will be possible for your
    particular problem - so the answer will be "no".
     
  18. Phil Allison

    Phil Allison Guest

    "Adrian Tuddenham"

    " In all probability, none of these solutions will be possible for your
    particular problem - so the answer will be "no". "



    ** **** off - you bloody idiot.




    .......... Phil
     
  19. Well, Yes, No, and maybe.

    You can't put them directly in parallel, as the one with the lowest
    voltage drop will hog the current, causing it to heat up.
    Unfortunately diodes have a several millivolt negative TC, so when it
    warms up it will hog more current, leading to more heat, more
    current,.... I think you see where this is going.

    You can definitely get this to work IF you add enough series resistance
    to EACH diode individually to compensate for the negative TC.

    "Enough" resistance is beyond my ability to compute, but a wild guess
    would be enough resistance to equal the diode voltage drop.

    Now this isnt too bad if we're talking about a high voltage power
    supply where another 0.7 volts won't matter. It is bad for a under 10
    volt PS where anotehr 0.6 volts is a big deal.
     
  20. John Fields

    John Fields Guest

    ---
    "Likely" isn't the same as an unequivocal "yes", which is what I
    think the OP was looking for.

    In any case, you've given him bad advice.

    Connecting diodes in parallel is, at best, very poor practice, and
    what you should have advocated was that he simply buy diodes
    specified to carry the current that he needs.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-