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EA 40V/3A power supply kit problem

Discussion in 'Hobby Electronics' started by [email protected], Mar 30, 2006.

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  1. Guest

    Bought this kit a while ago when it was on special @ $100.

    Finally completed assembly and it works except for one annoying problem
    that I discovered during stress testing.

    When the output is short circuit, the current limiter works as it
    should but only to about 2A. Above that and the blinkety-blink of the
    ceiling fluro plays havoc with the positive rail regulator section. I
    wouldn't have discovered this problem had the fluro tube not started
    dying (blinkety-blinkety-blinkety-blink)

    When the current limit is set above about 2.2A and the fluro starts
    blinking, the positive regulator stops current limiting and fully
    saturates, dumping over 5A into the short before I flick the load
    switch off. When the fluro is turned off the limiter behaves normal.

    The negative regulator behaves normally all the way to 3A and is
    unaffected by the blinking.

    Anyone have any idea what is going on?!
  2. I built one of these when i was an apprentice. They have some nasty
    problems with oscillation, and if IIRC, the fix requires a cap across
    one of the pots and and across a couple of tracks. You might get lucky
    and find that google will turn up the fix.

    What is the kit number?
  3. Guest

    I have googled and only found a reference to a 0.47uF cap fitted to the
    voltage pot's wiper & gnd. I didn't have one handy so I tried a 0.1uF
    and it did not solve the +ve regulator saturation problem during fluro
    blinking. If anything I think it made the circuit worse because I can
    hear a (much louder) screeching noise from the supply during current

    I found no reference to the cap across tracks, so would be interested
    to know which nodes the cap is placed across.

    The DSE catalogue number for this kit is K3206.
  4. I think you may have done something wrong whilst constructing it. The
    design is a bit unstable, but your problems sounds nothing like what i
    remember. Time to recheck you construction me thinks.
  5. Guest

    That's what I initially thought so checked for solder bridges, blobs,
    dry joints, incorrect component placement, etc. Even replaced a number
    of components including the IC and the output transistors in the
    positive regulator stage. I don't think the PCB pads can't take much
    more rework before lifting!

    I tested the supply within the vincinity of other lights (incandescent
    & fluro), and the fridge. The circuit seems very susceptible to mains
    switching events.

    Like I said in my original post though, the circuit works perfectly
    with current limits of less than 2A, which is what I'll mainly use
    anyway. If I want to use higher currents I might have to keep it away
    from "highish-switch-on-current" appliances.

    What might help me would be voltage measurements around the circuit
    with the current limit set at 3A. The voltages given in the assembly
    manual have the output set to 1A and voltage checks at this current
    level were correct.

    One question though, what is it about the fluro and fridge switching
    that could be influencing the circuit? Is it the surge current in the
    mains line, or the RF/EMF pulse, or what?
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