Help with using a boost converter

Discussion in 'The Projects Forum' started by Vanush, Mar 25, 2012.

  1. Vanush

    Thread Starter Active Member

    Apr 19, 2008
    46
    0
    Hi,
    I'm trying to use a FAN5331 boost converter (www.fairchildsemi.com/ds/FA/FAN5331.pdf) but cannot get it working no matter what I try. I've followed the recommended schematic, layout as much as possible.

    Here's my schematic (note that the VIN and enable pins are swapped on this schematic):

    [​IMG]

    Here's my layout:

    [​IMG]

    Here's what I get on the switching node (SW to GND)

    [​IMG]

    Note that 1.6 MHz is the switching frequency of this device, and that Vpp/2 in this picture is approximately what my output should be.

    Here's what I get on the output node (VOUT to GND)

    [​IMG]

    PCB

    [​IMG]

    As my output should be Vout = 1.23*(1 + (150/39)), I should expect 6v on that output. But I don't get htat :(!! If anyone has an idea of what I should loook into, that would be good.
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,653
    632
    From the scope shot, it looks like your output is shorted. Could it have something to do with the grounded lead of D201? (I would check one with an ohmmeter to make sure).
     
  3. Vanush

    Thread Starter Active Member

    Apr 19, 2008
    46
    0
    Actually after I posted this thread, I tested the polarity of the diode (BAT54) and found that it was the opposite polarity than I expected: the manufacturer that given me a variation (BAT54A) with the anode and cathode pins swapped. It's quite ridiculous, since I ordered the correct one. I have been messing around with this for many months, many PCB's, many components! Utterly ridiculous! :rolleyes:
     
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