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Choosing a filter cap for power supply

Discussion in 'Electronic Basics' started by CSB, Apr 27, 2004.

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  1. CSB

    CSB Guest

    Hi,
    I'm beginning in electronics and have been trying projects that almost
    all required different voltages, so I thought I'd build a PowerSupply unit
    from scratch, instead of using batteries. So here's what the rectifier
    part might look like:

    _____________
    +9VAC | bridge | |
    | rect. | |
    -9VAC ----------- | |
    | |+
    0VAC | --- C1 --- C2
    (CT) | |+ | ? µF
    _|_ _|_ _|_
    - - -

    (assuming that running a few v-regs in parallel works?)

    What kind of caps should I use for c1 and c2? Or is there a formula to
    find the values? And is there anything else I should add in that part
    (reverse-biased diodes to ground for each side, &c.)?


    Any information/source of info is very welcome.
    Thanks,
    CSB
     
  2. My rule of thumb for low voltage supplies is 4700 uf per amp out.
    According to the graph on page 2 of this tutorial:
    http://www.eetasia.com/ARTICLES/2000APR/2000APR15_AMD_PD_AN.PDF
    a 1 amp load on a 5000 uf cap gives a .8 volt peak to peak ripple
    voltage.
     
  3. Dave

    Dave Guest

    Go to your local Public Library (assuming you are in the US) and ask for the
    Reader's Guide to Periodical Liturature. Look up "Power supplies" in the
    '75 edition (or maybe '77, can't remember for sure. You may have to look
    for it.) There was an article in Popular Electronics on designing and
    building your own power supplies that covered nearly all bases. It tells
    you how to calculate the value needed for the filter cap. I have the
    article around here somewhere (looked it up a few months ago) and will give
    you a better date if I can.

    Dave
     
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