Building a 32v power supply...any ideas?

Discussion in 'General Electronics Chat' started by bigclick_dean, Feb 4, 2010.

  1. bigclick_dean

    Thread Starter Member

    Jan 24, 2010
    38
    0
    Hey again!

    I have finally received my eldoLED POWERdrive unit to control some of my cree LEDs but I am running the strings in lengths of 8 (~28v + POWERdrive overhead).

    I have been testing them in strings of 4 with a 24v regulated supply and all is going well.

    I now need to connect up strings of 8 and will need to increase my power supply.

    Can someone help me build a circuit to output the required 32v DC? I have a 24v 3A AC transformer or a 24v 300VA torrodial transformer I can use and I have a LM338K and LM317T if needed, I also have a couple of diode bridges to rectify the AC voltage but I am having a bit of trouble putting it all together.

    Any help would be much appreciated.

    Cheers,
    Dean
     
  2. bigclick_dean

    Thread Starter Member

    Jan 24, 2010
    38
    0
    any ideas? I have been having a bit of a play with MultiSIM but I cannot get it to work in practice.

    Cheers,
    Dean
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Sorry bigclick_dean, it's been pretty busy here and a lot of people want help with their projects.

    Post the specs on your eldoPOWER LEDdrive; I don't know what it's supposed to do.

    Post the specs on your Cree LEDs.
     
  4. bigclick_dean

    Thread Starter Member

    Jan 24, 2010
    38
    0
    Hi SgtWookie,

    That's cool, just didn't want it to disappear down the pages :)

    The POWERdrive can take any voltage input up to 32v and it regulates the current going out on 4 channels .

    The cree LEDs are the royal blue and the cool white in the XPE series, they have a Vf of 3.4 and 3.5.

    I have worked out that if I can supply 32v at around 3.5A I should be right.

    Cheers,
    Dean
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Then why don't you run two strings of four LEDs, and use two of the outputs of the POWERdrive?
     
  6. bigclick_dean

    Thread Starter Member

    Jan 24, 2010
    38
    0
    I need to run a total of 32 LEDs so I will need 4 x 8 LED strings, the POWERdrive can only deliver up to 1400ma from each group so the whites would be fine as they are 700ma each but the blues are 1000ma and would require more than the available output.

    Also the difference between the two strings would eventually mean one string would take more current than the other and gradually die :-( Unless I stuck a lm317 or something on each individual string to maintain the constant current.

    Cheers,
    Dean
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Rather than try to build your own supply, I suggest you look at these:
    http://www.mpja.com/products.asp?dept=465&main=1
    In particular, this one:
    http://www.mpja.com/prodinfo.asp?number=16033+PS
    28V @ 5.5A, and it has a +/-10% output voltage adjustment range.
    So, you should be able to "tweak" the output voltage up to around 31v.

    A switching power supply will be much more efficient, thus lower cost over the long run than a linear supply. Were you to use your existing 3A or 12.5A transformers, you would barely reach your desired 32v output under no load with large filter capacitors. You would need very large filter caps to reduce voltage ripple enough to make your transformer useable. Your resulting supply would be bulky and have very high startup current.

    I have bought from MPJA numerous times in the past; they have always shipped very quickly, and I have never been disappointed with anything I've ordered from them.
     
  8. bigclick_dean

    Thread Starter Member

    Jan 24, 2010
    38
    0
    I am in australia so we have alot of trouble finding switchmode power supplies. For a 24v 6A switchmode supply you are looking at well over $100.

    I cannot find any > 24v supplies in australia (bar a couple of 48v ones).

    The blue LEDs are CREE XPE Royal Blue, run at 1000ma and 3.5vf, they are VERY VERY bright...lol

    I have put together a supply and will be testing it tonight, so far I have 30V DC out and hopefully it will hold up, I will try and post the schematic soon.

    Cheers,
    Dean
     
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