Can I put several LM2577 in parallel for greater power?

Discussion in 'The Projects Forum' started by BringMeAnother, Oct 21, 2012.

  1. BringMeAnother

    Thread Starter New Member

    Oct 21, 2012
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    Hi, first time posting in this forum. I was wondering with this product I found

    http://www.ebay.ca/itm/170792120040...X:IT&_trksid=p3984.m1439.l2649#ht_3694wt_1397

    If I need more power than the maximum allowed, can I set up two or more of those in parallel and set them with the same output voltage?

    My specific case is that I need 19V output with 5V input. My output power must be 22W, so my input amperage must be a bit less than 5A which is higher than the 3A max.

    My question is, if I do put say two of those LM2577 set up with the same output voltage, would the current distribute itself equally in them and would I get the power I need?
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  3. BringMeAnother

    Thread Starter New Member

    Oct 21, 2012
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  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    That is not correct for calculating input current and power for a switcher. The input peak current is not a simple DC power conversion equation. The peak switch current will be a lot higher than the average value.

    Read the data sheet for details (page 15).

    http://www.ti.com/lit/ds/symlink/lm1577.pdf

    The peak allowable is 3A, but with ripple current and duty cycle, the average input current is probably closer to 2A which means about 10W total input power. Subtract a bit for efficiency, and it leaves about 8W - 9W ballpark for load power from each board running 5V input.

    I don't think you could get 22W total out of two of these at 5v input.
     
    Last edited: Oct 21, 2012
  5. BringMeAnother

    Thread Starter New Member

    Oct 21, 2012
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    Thanks. Well, I can always go with brute force. If two doesn't work, I'll put three or four.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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