eagle pcb design questions

Discussion in 'The Projects Forum' started by doors666, Sep 25, 2014.

  1. doors666

    Thread Starter New Member

    Mar 21, 2014
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    i am trying to design my first pcb, its for a power supply. For the filter caps, I want to provide both a small cap option and big cap option, e.g. C2 supporting both 5mm caps and 10mm caps. How can i do this without redrawing the part.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    i would enlarge the copper land and add a drill hole. no need to specify a part for just one additional hole.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    yeah or just add the hole and pull a trace from the main pad over to the new hole..
     
  4. kubeek

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    Sep 20, 2005
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    or you can put multiple different caps in the schematic.
     
  5. ISB123

    Well-Known Member

    May 21, 2014
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    Slide switch to switch connection between 10 mm and 5 mm cap?If that's what you meant?
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I meant put both parts into the schematic, place them one over the other on the pcb, and then popualate the one that you want when you assemble the board.
     
  7. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Kubeek said what I was thinking. Put two different capacitors connected in parallel, the smaller cap "inside" the footprint of the larger cap. A lot depends on the distance between pins. You may be able to do it like this:

    caps.png

    or, if your board house complains that there's overlap, you can turn one of them 90 degrees like this:

    caps_90.png

    EDIT: The first one really didn't work in this example, because the drill of the outer cap is cut off a bit. Like I said, it depends on the pin pitch.

    EDIT #2: Or you can do as I have seen professionals do and offset them a bit:

    caps_offset.png
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Also if you want to do it properly don't forget to make a note in the schematic that these two parts are alternate components.
     
  9. doors666

    Thread Starter New Member

    Mar 21, 2014
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    thanks guys, i like the idea of two parts in schematic, will give it a try.
     
    Last edited: Sep 26, 2014
  10. doors666

    Thread Starter New Member

    Mar 21, 2014
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    the pcb design and the schematic are attached below, could you guys please take a look at it and let me know if anything can be improved. board is approximately 3in x 2in.

    Also, is the bridge rectifier wired correctly in the schematic.I have only made the four bridge rectifier diodes with the high current traces, any other diode that might need to handle high current?

    schm.jpg

    brd.jpg
     
    Last edited: Sep 26, 2014
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    The schematic is quite hard to read, normally you would draw it like this, so that the highest voltage is on the top and lowest on the bottom. I also makes the design nice and symmetrical and the electrolytic caps oriented the same way.
    http://cdn.head-fi.org/a/ab/900x900px-LL-abc0779d_317_337Schematic.png

    Second thing is that large capacitors on the output are not necessary and might even ruin the stability of the regulator, so better put them at the input side instead. Also check the datasheet for the recommendations on the blocking caps near the regulators.
     
  12. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Hi doors666,

    When taking snapshots of schematics/PCB designs drawn in Eagle, it's best to use the "Export" option. Go to "File" --> "Export", browse for where you want to save the image, and set the DPI to 250 or higher, to ensure it is high quality (the higher the DPI, the further it can be zoomed before pixelating). You can do this on both the schematic and PCB designs.

    I recommend doing that, then re-uploading the files.

    Matt
     
  13. doors666

    Thread Starter New Member

    Mar 21, 2014
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    yeah, i realized that about the schematic after i saw some others on the net, but the damage was already done, it will be really hard to redo it now without disturbing the board.

    whats generally considered a good value for the output caps for this, I plan to use this as a general purpose bench supply for testing, as well as to power small audio gear.

    . not sure if I understand your comment about the blocking caps.
     
  14. DerStrom8

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    Feb 20, 2011
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    As for your circuit, where is the AC input? AC does not have a + or -, so do not label AC inputs with "plus" or "minus".
     
  15. doors666

    Thread Starter New Member

    Mar 21, 2014
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    Here are the new exported pics..

    brd2.png


    schm2.png
     
  16. DerStrom8

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    Feb 20, 2011
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    Again, where is your AC input? If "Vplus" and "Vminus" are supposed to represent your AC source, the circuit will not work. Think you should read up a bit more on how AC works. There are not separate lines for + and -, you have a + and - current on the same wire, with respect to neutral.
     
  17. DerStrom8

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    Feb 20, 2011
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    Try something like this instead:

    [​IMG]

    Connect your regulators to the +25 and -25 volt outputs.
     
  18. doors666

    Thread Starter New Member

    Mar 21, 2014
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    I have redone the schematic. Electrically the board was not changed, changed the text on the board. V+ and V- were there as I was initially planning to use an off board rectifier, and later added the diodes here and forgot to change the text on the board to ac power.

    question: this should work with dc supply also? Some of the diodes in the BR will never be conducting, but the circuit should work right?


    schm3.png

    brd3.png
     
    Last edited: Sep 27, 2014
  19. MrChips

    Moderator

    Oct 2, 2009
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    Matt, your switch S1 and fuse F1 must be interchanged.
    The first component that AC mains LIVE is connected to is the fuse.

    A 5A fuse is overkill for an 80VA transformer. I would specify 1A for starters.
     
  20. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    That's not my circuit, I just pulled it off google :p

    I just used it for illustration of how AC is converted to +/- DC.
     
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