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This is something one cannot simulate ;)

Discussion in 'Electronic Design' started by Grant, Feb 24, 2011.

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  1. Grant

    Grant Guest

    Oops. The smell, the smoke...

    See http://grrr.id.au/image/magic-smoke-escaped-from-NCP3063.jpg

    That smell that seems to stick to the inside of one's mouth, the smoke rising
    after a muted pop, this was not just too much current through a resistor.

    No, this was a boost converter, and the switching transistor between pins 1
    and 2 forgot to turn off! See the photo, more of a pop ... phut ... smoke.

    Or something. By that stage it was 'okay, lets start over, something's very
    wrong here...' I'd socketed the 3063, but couldn't be bothered discovering
    why it smoked, too many alterations on the matrix board.

    So I build a new one and it works first time :)

    Funny thing is, the one that smoked is only one of three or four I built
    without a polyswitch and 16V, 1500W TVS diode! Murphy wins another round.
    So the next one has the protection components...

    Power is a little 12V 5AH SLA battery with 10 mOhm shunt, could'a been worse,
    there's a couple of 12V 100AH batteries on the floor, but they're fused 35A.

    Grant.
     
  2. Grant

    Grant Guest

    I was close to the 40V max output, around 36 or 37V. Yet today I saw 64V
    on output of another after I'd miswired the voltage feedback, no smoke!
    I turned it off smartly though. Wired the feedback properly and it still
    worked.

    After a while I'll give up on minimal components and just wire in
    something that'll work properly, get passed this part and move on. Can
    always revisit later to lower parts count.
    What I was doing at the time was connecting the minus end of a 36V zener to the
    feedback terminal, felt like I glitched it. The joys of hardware prototyping,
    trying to minimise external components. Though the feedback pin is next to Vcc,
    and rated up to Vcc -- probably something lodged under the PCB, it was getting
    messy, time for a new proto. anyway.
    I'm not trying to run anywhere near max power of the chip, high voltage yes.

    The chip gets a little warm, so does the inductor, when the LEDs are bunched
    up close, they get very warm at 20mA, so I may run them at 16 to 18mA. This
    is a lots of little LEDs driver, not using those monster LEDs (yet).

    Grant.
     
  3. Grant

    Grant Guest

    No, if the 36V zener was shorted from an earlier probe mishap, then I took comp
    input to 3 times Vcc, oops!?

    Grant.
     
  4. Was debugging a board once and my first thought was "I dont remember an
    LED being there". The copper track must have been molten
     
  5. Warren

    Warren Guest

    Grant expounded in
    Heh heh- reminds me of some left over/unmarked ICs I had around
    in the '80s. For kicks I soldered the AC power cord across both
    sides of the chip, and plugged it in.

    A nice *pop* and a little smoke for the fireworks display.

    Warren
     
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