DC DC Boost Help

Discussion in 'The Projects Forum' started by Vanush, Sep 9, 2011.

  1. Vanush

    Thread Starter Active Member

    Apr 19, 2008
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    0
    Hello, I'm trying to implement a DC DC boost circuit using the FAN5331 (See: http://www.fairchildsemi.com/ds/FA/FAN5331.pdf and test circuit on Pg 3.)

    See attachment for what I set up on the breadboard for the test circuit. Note that I had to use BAT46 instead of BAT54 as there is no through hole version of BAT54.

    WHen I tested this circuit, I was getting an incorrect output (0.3 V instead of 15+ V). So to test, I put my multimeter nodes across the wires of the 10mH inductor. As soon as I did that, the IC blew up and started smoking. Any idea why this happened?

    The input is 5V DC
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Switching regulators don't "like" to be breadboarded, as there are far too many parasitic inductance and capacitance involved. This IC switches at around 1.6MHz depending on temperature. You need at least 10x that for bandwidth; and breadboards just won't work well. You need to make a PCB for it, and the traces need to be as short and as wide as possible.

    I'll bet a whole dollar that you had the meter set to measure current in amperes. This would cause the FAN5331's built-in switch to be connected directly to +V in, so infinite current tried to flow through the switch to ground. Since the switch in the FAN itself was the only thing limiting current, it got vaporized, and blew the lid right off the IC.

    The example circuit in the datasheet says 10uH, not 10mH. 10mH=10,000uH; quite a difference.

    You may have also blown the fuse in your meter.
     
  3. Vanush

    Thread Starter Active Member

    Apr 19, 2008
    46
    0
    Thanks for the informative reply.
    Nuts. I guess I will have to dive straight into PCB design.
    Do you think that it won't work at all on a breadboard?
    Also, my mistake it was 10uH. Also, I was trying to measure the voltage across the capacitor not current.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    At 1.6MHz it is better to go for a PCB.

    You was trying to measure the voltage but it seems the ammeter was set to amperes and not volts.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you try to use it in a breadboard again, you will get similarly poor or no results.

    You really need to build it on a custom PCB with very short and wide traces.
     
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