Shop OBEX P1 Docs P2 Docs Learn Events
Power supply filtering question — Parallax Forums

Power supply filtering question

ZetsuZetsu Posts: 186
edited 2012-12-12 15:26 in General Discussion
I have been reading about building power supplies lately and I came across this paragraph,
"It should be obvious that the smaller the XC of the filter capacitor in respect to the load resistance, the better the filtering action. By using the largest possible capacitor, we achieve the best filtering. The load
resistance is also an important consideration. If load resistance is made small, the load current increases,
and the average value of output voltage (Eavg) decreases"

So, this suggests just taking the largest cap I have available and use it to filter with ?? That doesn't sound correct to me for some reason.

Comments

  • davejamesdavejames Posts: 4,047
    edited 2012-12-12 13:45
    ...there's a bit more involved.

    Go here:
    http://www.onsemi.com/PowerSolutions/supportDoc.do?type=manuals

    and download the "Linear and Switching Regulator Handbook". It describes how the amount of filtering is defined for a given ripple voltage.
  • ZetsuZetsu Posts: 186
    edited 2012-12-12 14:11
    Thanks, because I mean I have seen capacitors that are almost as big as me ;x but I doubt I would want that on a PSU thats only giving off 15volts at 1amp ;x

    ^ That was a joke btw ;x
  • idbruceidbruce Posts: 6,197
    edited 2012-12-12 14:17
    What kind of power supply are you talking about? A linear unregulated power supply?
  • ZetsuZetsu Posts: 186
    edited 2012-12-12 14:28
    this is discussing full wave and 1/2 wave power supply's
    linear. ( have not got to the part about regulators yet...)
  • idbruceidbruce Posts: 6,197
    edited 2012-12-12 14:39
    First off, let me state that I am no expert, but if you are building an unregulated linear power supply for running motors, it is not uncommon to see the filtering capacitor in a range from 10,000 uF - 22,000 uF, with a full wave bridge.

    Here is a decent example:

    http://pminmo.com/simple-power-supply

    You may also want to read this:

    http://www.kpsec.freeuk.com/powersup.htm
  • RDL2004RDL2004 Posts: 2,554
    edited 2012-12-12 15:26
    I started building a lab bench type power supply several years ago and had 4 x 4700 uF caps as the filter. I remember how the lights would dim when I flipped the power switch on. It was only going to be a 5 amp supply and probably only one or two of those caps would have been enough. I never finished it because I decided it was going to be way more than I needed and built a smaller one instead.
Sign In or Register to comment.