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Voltage Regulation

Discussion in 'Electronic Basics' started by Henk Visser, Aug 21, 2003.

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  1. Henk Visser

    Henk Visser Guest

    I am using a LM3488 voltage regulator from National Semiconductor.
    The goal is to produce 12 VDC from an input of ~9V-18V. When I attach
    my multimeter it shows a value of about 12.5 volts. Not bad! But
    when I hook up my oscilloscope I see huge voltage spikes!

    My circuit is almost exactly that found in the datasheet at the link
    below. Page 20 is where you can find the ciruit.The only differences
    are some of the resistances to configure the output voltage.

    http://www.national.com/ds/LM/LM3488.pdf

    Any ideas why I am getting these huge spikes and how I can correct
    them would be greatly appreciated!

    -Henk Visser
     
  2. Brian

    Brian Guest

    Two things are very important in switching regulators, grounding paths
    and the type of filter capacitor. The filter capacitors need to have low
    ESR and ESL values.

    This is information taken from a different switching regulator, but it
    applies to your regulator too.

    Taken from application note AN920/D:
    High frequency circuit layout techniques are imperative with switching
    regulators. To minimize EMI, all high current loops should be kept as
    short as possible using heavy copper runs. The low current signal and high
    current switch and output grounds should return on separate paths back to
    the input filter capacitor. The R1, R2 output voltage divider should be
    located as close to the IC as possible, to eliminate any noise pick-up
    into the feedback loop.
    Hope this helps,
    Brian
     
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