Power supply from scratch question

Discussion in 'Power Electronics' started by aidayley, Jul 27, 2016.

  1. aidayley

    Thread Starter New Member

    Jul 26, 2016
    29
    4
    I am building a power supply from scratch. I know how to do everything except, I do not know what size of a capacitor I need? what I want is for the dc to be able run chips

    Thank you
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    The capacitor size depends upon the load current and the allowed ripple voltage.
    Post a schematic of what you have so we can determine what you need.
     
  3. SLK001

    Well-Known Member

    Nov 29, 2011
    812
    225
    The "chips" are fairly forgiving on their acceptable ripple values. Something in the neighborhood of 10,000μF would be a good starting point. Cruts is correct though, in his statement above. YOU decide what is an acceptable ripple voltage.
     
  4. aidayley

    Thread Starter New Member

    Jul 26, 2016
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  5. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    Hello,

    Please upload the schematic to the forum using the "upload a file" button.
    The site asks me to login.

    Bertus
     
  6. aidayley

    Thread Starter New Member

    Jul 26, 2016
    29
    4
  7. SLK001

    Well-Known Member

    Nov 29, 2011
    812
    225
    100mV is a TON of ripple. Almost any capacitor will get you less than that.

    And what is SO HARD about uploading a file?
     
  8. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    Not for the output of a bridge rectifier as the op's schematic shows.
    The typical ripple at that point is more like a volt or two under full load.
     
  9. SLK001

    Well-Known Member

    Nov 29, 2011
    812
    225
    A link to a schematic is the equivalent to no schematic in my book. The OP is asking for advice - it is up to HIM to make sure all the information is presented in the question so that people he wants help from can have that information at their fingertips.
     
  10. crutschow

    Expert

    Mar 14, 2008
    12,993
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    If you don't want to click on a link that's fine, but then I don't see the point of offering design advice when you don't know what the op is referring to. :rolleyes:
     
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  11. SLK001

    Well-Known Member

    Nov 29, 2011
    812
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    Yeah, but where's the fun in that?
     
    aidayley likes this.
  12. aidayley

    Thread Starter New Member

    Jul 26, 2016
    29
    4
    Thanks for all the input,
    the goals of my power supple are,
    1 Learn
    2 Keep it as simple as possible (This is why the schematic is very basic)
    3 Make it to last
    4 Make it inexpensive.
    The reason I posted on this forum is to try to get a way to calculate how much ripple I will get for whatever amperage I draw.
    Also it would be great is someone could tell me how much ripple is aloud for chips

    Thanks
    AIDayley
     
  13. hp1729

    Well-Known Member

    Nov 23, 2015
    1,946
    219
    Voltage regulation is good. What chips did you want to power? Voltage depends on the type of chips.
    What parts do you have to work with for building a voltage regulator? Really basic? NPN and a Zener diode. LM78xx are actually cheaper, better and easier. Variable? LM317 or LM338 if you expect to use 3 Amps. You probably won't need 3 Amps unless you have specific design in mind.
    Size of capacitor? Figure 1,000 microfarads per Amp of current as a general rule.
     
    aidayley likes this.
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