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Capacitor size for BS2 voltage regulator — Parallax Forums

Capacitor size for BS2 voltage regulator

gc3076gc3076 Posts: 44
edited 2006-03-07 23:20 in BASIC Stamp
I am in the process of transfering a project onto a printed circuit board and am going to purchase a 5 Vdc voltage regulator.
I have read that it is a good idea to place a capacitor across the output of the regulator.
Any suggestions what size capacitor should be used ???

Comments

  • NewzedNewzed Posts: 2,503
    edited 2006-03-07 16:16
    Use 100uf across the input and .1uf across the output.

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    Sid Weaver
    Do you have a Stamp Tester yet?
    http://hometown.aol.com/newzed/index.html

    ·
  • Steve JoblinSteve Joblin Posts: 784
    edited 2006-03-07 17:41
    Proper set up for a voltage regulator is to have a cap on both the input and the output. If you are going to be using National Semiconductor's LM2940 (which is a Low Dropout 5 volt regulator), the datasheet calls for a .47uf across the input and at least a 22uf across the output.

    Newzed - strange that you are recommending almost the opposite... why?
  • ForrestForrest Posts: 1,341
    edited 2006-03-07 17:42
    Use 2 capacitors on the output side of the regulator. If you're using a 7805 regulator, then use a 10 uF next to the regulator and a .1uF near the load. www.tkk.fi/Misc/Electronics/circuits/psu_5v.html
  • Steve JoblinSteve Joblin Posts: 784
    edited 2006-03-07 17:57
    I assume this is why it is called the "art" of electronics... I just noticed that the BOE does not even have the set up that the datasheet suggests... have I been "over engineering" by following the datasheet?
  • NewzedNewzed Posts: 2,503
    edited 2006-03-07 17:59
    Steve, I have used those caps for a long time and have never had a problem.· No brownouts, no nothing.· Maybe I've got it backwards, but when I look at the output voltage on my scope it is nice and clean.

    Sid
  • radiodiverradiodiver Posts: 3
    edited 2006-03-07 23:09
    One needs to be concerned about the capacitor charging currents on both the input and output to the regulator.
    Will the input supply handle this charging current?
    The system reliability will suffer with a poor choice.
  • NewzedNewzed Posts: 2,503
    edited 2006-03-07 23:20
    Assuming 1 ohm resistance, which is probably much higher than in real life, ·a 100uf cap will charge in about 100us.· Even if the charging current is 10 times the rated current of the power supply, I doubt that the extremely short duration of the charging current could·harm a power supply.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Sid Weaver
    Do you have a Stamp Tester yet?
    http://hometown.aol.com/newzed/index.html

    ·
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