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Thread: hardware-level technical scanner questions (for Arduino laser beam steering project)

  1. #21
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    Go to Digikey.com... Type DC to DC Converter in the search bar.. Make sure you get front to back isolation, and about six amps peak current capacity. Hang a filter cap off the unit, as galvos draw huge surge loads. Make sure you can meet the converter's minimum load requirements.

    Steve
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  2. #22

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    Okay. I get 0 results, what am I doing wrong?

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  3. #23

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    There simply aren't that many parts that take a single DC supply and create a bipolar supply, let alone at higher voltage or at enough current for a galvo driver.

    If you need 12V -> +/-15V, you'll have better luck finding a pair of isolated 12V->15V supplies and putting the outputs in series. If 12V->+/-12V will do, then you just need a single 12V->12V isolated converter, and its output goes in series with your main 12V supply. However, isolated DC-DC converters at more than a couple watts are not super common and tend to be fairly expensive.

    A non-isolated step down converter module can be used as an inverting boost converter for higher powers, except that the undervoltage lockout will typically prevent the convert from starting when the magnitude of the negative output is meant to be the same or higher than that of the positive input (so, a 5V output converter could be used to create -5V from +12V, but a 12V converter can't be used to create -12V from +12V, unless you modify it to decrease its UVLO threshold).

    If you have the ability, building your own non-isolated inverting converter from a standard buck controller IC will give you the most flexibility to meet moderate power needs at lowest cost. This is what our scanner driver does, and we do this on a couple of other boards as well.

  4. #24
    mixedgas's Avatar
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    At +/- 15V you'll have to consider that you are loosing headroom needed for a useful slew rate. The op-amps on a typical clone amp need a minimum of +/- 8.8 volts to run. Nearly all clones are based on Cambridge's 6850 or 67xxxx family of amplifiers , all of which have 7815 and 7915 voltage regulators on board. If you go look at a lm7815 or lm7915 data sheet, you'll see they need a minimum of 17.1 volts of input to function for the +15... and a bit more for the -15.
    ~
    As the cheapest scan amps use the 7815's voltage as the reference for the position detector, instead of a nice stable 10V reference chip like the better galvo amps, you'll need to fix that issue as well. Otherwise your images will shift around...
    ~
    Time to look for two 12V to 24V converters, that can take the spikes in the automotive environment...
    ~
    Steve
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  5. #25

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    Thanks all.
    For this project I could switch from a 12V plastic cover power supply to a 19V supply as those are common as well as are used for notebooks, then do the 19V to 12V for the rest of the components and 19V to 15V for the scanners.
    The requirement is a common plastic case PSU, doesn't matter if it will be 12V or 19V. 24V are far less common and affordable.

    Quote Originally Posted by Mattronium View Post
    An inverting buck converter is what I've used for a similar situation. I used the LM2596S-ADJ.
    In inverting topology it gives 1A max I think, but that ran a cheap scanner set fine.

    Just my 2 cents.
    I don't know how on earth I missed these posts from page 2.
    Thanks, I'll look into these.

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