Anyone decent at designing PCB's?

Discussion in 'General Electronics Chat' started by Mohrenberg, Sep 17, 2011.

  1. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    I've been playing with PCB designing software for hours and am not any closer to understanding it.
    I've got a very simple circuit that I have already built and tested that I would like to have circuit boards made for.

    It only has 3 components on it.
    It uses a voltage regulator, a single resistor and a single capacitor. It's a simple current regulator for laser diodes as a power supply. the resistor controls the current output, and the capacitor is to prevent voltage spikes.

    the entire thing needs to be around 10mm x 15mm

    If anyone is interested in helping me with this, i'd be willing to pay for your time.
     
    Last edited: Sep 17, 2011
  2. SgtWookie

    Expert

    Jul 17, 2007
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    10mm x 15mm? Good luck. You're going to need a good-size heat sink on the regulator, and 10mm x 15mm won't allow for that.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    There are times printed circuit boards are not the answer, and others they are the only way.

    You may want to start from the beginning assumptions.

    What is the input voltage you want to regulate the current from?

    What is the current you need, and what is the voltage drop of the LASER diodes?

    This will tell you how many watts you need to get rid of, which brings us to Wookie's comment. The heat has to go somewhere.

    Linear regulators, which is what you have designed, get hot. It is built into the design. SMPS regulators are much cooler, as well as much more efficient. This too is built into the design. They are also noisier, which may be a killer in your design.

    However, it is possible to mix the two. Use a SMPS (switching mode power supply) regulator to get the output power supply close to where to need it, then use a linear regulator to make it a clean power supply.

    One of the problems is we don't have enough information to offer a informed opinion. It may be your linear design won't get hot, but the odds are against it.

    I design PCBs with PCB express, then clean them up after using the free software to design it. I have an article on how I make PCBs I've made...

    How I make PCBs

    You will get all the help from this site you need, but you gonna have to give us information first. Welcome aboard to AAC!
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    So, you say there are only three components. I assume then that the battery and the LED are not located on the PCB.

    Are you going to use connectors for the leads to the battery and the LED or just soldered leads? What size wire?
    What is the wattage of the resistor? Do you have a datasheet for it?
    Which package are you using for the regulator IC? (My footprint for a TO-220 is about 10mm x 5mm even without a heatsink.)
    Is the capacitor radial or axial leads? Do you have a datasheet for it?
    What mounting arrangement are you going to use for the PCB, i.e., does it need mounting holes, and if so, how many and what size?

    With these questions answered, the layout would be simple, but the final size of the board is dependent on the size of the components.
     
  5. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    For the voltage input and as well for the output i want thru holes on each side of the pcb.

    The normal input voltage of these drivers will be ~8.5v
    IIRC the voltage drop of the diode is 4.2v at around 1.5A
    but these driver's get heat sinked anyways

    My testing was done with a 3 watt wirewound resistor. I would like to find an SMD or, even a row of 2 or 3 in parallel that could handle this application

    It doesn't need any mounting holes, as we usually just arctic silver them directly to aluminum blocks for heat sinking, or have them clamped down on aluminum somehow.

    This is the regulator: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00001883.pdf

    here is the cap: http://www.tdk.com/pdf/general_B11.pdf

    the 10x15 isn't set in stone. I just need the components squished together, size is very important as these have to fit inside the head of flashlights with room to spare.
     
  6. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    if it helps...

    i'm looking for a rectangle boards, which would have the regulator on one side.

    and on the opposite side of the board would have the resistor(s)

    and then the cap can be anywhere on the board....
     
  7. tracecom

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    Last edited: Sep 17, 2011
  8. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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  9. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Well, the best I can do with the information you've given would look something like this:

    [​IMG]

    In real life it would look something like this (you can't see it, but the capacitor is on the bottom of the board, and replace the red LED with a laser diode):

    [​IMG]

    The entire thing is roughly 12mm wide and 47mm long. It's a bit bigger than what you said you wanted, but it's still quite small.
    To get a better rendering, we really need more information. What regulator package were you planning on using? what type of laser diode? What do you plan to use the laser for? There are lots of things that need to be specified before anyone can actually give you a good design.

    P.S. Sorry about the huge second picture.

    EDIT: I guess there were a couple more posts as I was putting this together, so there's a bit more info now. sorry about that :D
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In the schematic you show a 47 μF capacitor.
    In the link you show a 0.47 μF capacitor, a factor 100 lower.

    Wich value is used?

    Bertus
     
  11. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    sorry, it's 47uf

    about a year ago the strongest laser diode was driven at around 400mA, which was really pushing it. People were putting caps in the driver design to stop voltage spikes from hitting the diode, as the voltage spike raised the current going into the diode.
    Of course now the diodes we're using are regularly driven at over 1.8A, so i'm not even sure voltage spikes are even a concern now.

    My original prototype just had the voltage regulator and single .75ohm resistor and it works perfectly fine.

    Here are a bunch some pictures of other drivers that are used for the same application.
     
    Last edited: Oct 5, 2011
  12. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The recommended footprint for the D2PAK/A package is 12.2mm x 16.9mm. I now have the PCB down to slightly less than 20mm x 25mm, but the resistors are the problem. How much smaller than 20mm x 25mm does it have to be?

    And post a link to the exact resistors you plan to use so I can know the actual measurements.
     
    Last edited: Sep 17, 2011
  13. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    I made a post earlier but apparently it's in the mod queue for approval...

    I'm thinking of just using someone else's design. He's offered to sell me the PCB's at $60 for a panel of 24 boards.
    Is $2.50 per PCB a decent deal?
    From the prices i saw to have my own manufactured it didn't look like it was going to be much cheaper than he's offering, and his drivers are proven and popular among the hobbyists.

    he's going to sell me the boards to the 1.8A version shown here
    https://sites.google.com/site/jibdrivers/
     
  14. tracecom

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  15. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    the $2.50 is also to give himself some profit. He no longer has the time to assemble,sell,package, and ship the drivers so i'
    ll pretty much take over. This allows him to continue making a little money off his driver, without having to devote any time to it.
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    If you really want to make it small and efficient, you'll need to go to a switching driver design. Linear is nice, but you're wasting about half of your input power by heating up your regulator.
     
  17. tracecom

    AAC Fanatic!

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    Well, I learned something today. ;)
     
  18. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    Alright so i'm back with some more specific info. I'm looking to have someone design this PCB for around $50. i'd prefer an Eagle .brd file.

    So i've got the simple schematic i posted in the attachments.
    the resistors are 2512 sized resistors
    i'd like it designed as a 2 layer (i think?) PCB. the regulator will be on the top, while the resistors will be on the bottom, so the board is going to have drilled holes that connect the two in certain places.
    I'd like input holes, and output holes on each side of the board.

    Also, I plan to have the PCB's made through this guy's group buy, if that helps with the design. I know he lists a lot of requirements i don't understand...
    http://dorkbotpdx.org/wiki/pcb_order

    Parts list:
    regulator: https://www.mouser.com/Search/Produ...Rvirtualkey51120000virtualkey511-LD1085CDT-TR

    1ohm resistor: https://www.mouser.com/Search/Produ...rtualkey66200000virtualkey66-LR2512LF-01-1R00

    2.21ohm resistor: https://www.mouser.com/Search/Produ...rtualkey66000000virtualkey660-RK73H3ATTE2R21F

    and the smaller, the better. If your interested in doing this let me know.
     
    Last edited: Oct 4, 2011
  19. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I don't do Eagle; I use DipTrace, which produces Gerber files that are the industry standard for PCB fabrication. If you want that, let's discuss it via PM. LMK.
     
  20. Mohrenberg

    Thread Starter New Member

    Sep 17, 2011
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    According to the info on that group buy page, a "set of gerber files" will work fine too. I'll send you a PM when i get home from medic school this evening.
     
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