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Basic Electronics Question — Parallax Forums

Basic Electronics Question

ajwardajward Posts: 1,130
edited 2014-02-08 20:40 in General Discussion
Hey All...

I've started building a power supply using a center tapped 12.6 volt, 3A transformer and a 400 volt, 4A bridge rectifier. My dilemma is I can't, for the life of me, remember how to design the filter circuit. I "think" I can remember using just capacitors or capacitors and chokes or capacitors, chokes and resistors, but it was just so darned long ago.

Any advice/links/suggestions?

Thanks a bunch!

Amanda

Comments

  • Mark_TMark_T Posts: 1,981
    edited 2014-02-08 13:29
    You can just use a capacitor on the output - however that tends to have a high current spike at
    switch-on and won't give an efficient conduction angle from the rectifiers.

    So adding a resistor between the output of rectifier and the capacitor will help limit maximum
    current and extend the conduction angle (at the expense of wasting a little voltage).

    A choke can make sense but can cause issues - if you are driving a switching load a choke thats
    too large will cause voltage spikes (although the second capacitor can be made larger to compensate).

    If you are going to power a DC-DC converter then regulation can be quite sloppy into its input
    as it'll just handle it. If you power a linear regulator you'll have to do the calculations to ensure
    you don't get drop-outs at full load.
  • skylightskylight Posts: 1,915
    edited 2014-02-08 13:37
    Hi Amanda,
    Found this schematic on the web, obviously ignoring voltages on output but shows filtering with caps

    Schematic
  • davejamesdavejames Posts: 4,047
    edited 2014-02-08 14:11
    ajward wrote: »
    Any advice/links/suggestions?

    Section 8 - all you would ever want to know...

    http://www.onsemi.com/pub_link/Collateral/HB206-D.PDF
  • xanatosxanatos Posts: 1,120
    edited 2014-02-08 16:14
    davejames wrote: »
    Section 8 - all you would ever want to know...

    http://www.onsemi.com/pub_link/Collateral/HB206-D.PDF

    I've been designing power supplies three-quarters of my life and that was STILL a fantastic link - Thanks!
  • davejamesdavejames Posts: 4,047
    edited 2014-02-08 19:48
    xanatos wrote: »
    ...STILL a fantastic link...

    Thanks Dave.

    It was originally the "National Semi Voltage Regulator Handbook" from the late '70s. On Semi pick it up when they acquired the linear regulator business from National.

    As you said, still my go-to book on the subject.
  • ercoerco Posts: 20,256
    edited 2014-02-08 20:40
    A filter. Really? Huh! Who knew?

    Maybe that explains all the erratic results and magic smoke I have coaxed out of my transformer-powered projects for lo these many years.

    Now what's this fuss about a rectifier?
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