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Thread: Using an LM317 as a galvo amplifer

  1. #1
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    Default Using an LM317 as a galvo amplifer

    Using a linear regulator with the 'adjust' leg as the input. Single ended though..not bi-polar.. Anybody done anything like this? It seems to have a fairly good slew rate, but I'd hate to see it fail (because that's not what it's designed for) in the middle of a show... any input? anybody?

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    just use a audio amplifier chip like everybody else does...
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    Got a good quality P/N?

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    LM3886 is a widely used chip
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  5. #5
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    Default

    go to electronic goldmine
    www.goldmine-elec.com
    look for a L149 by SGS-Thompson
    1.49$ each with heatsink , nice power opamp with 5 pins, remember to ground the enable on the L149.

    use the A102 schematic by general scanning, replace the power transistors with the L149 , that will give you damping

    go to www.gs-scanners.com
    click on galvo motors, a selector window will pop up
    click on product manuals archive
    then
    click on A102

    or use LM3886

    Steve

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    Wink

    Love, peace, and grease,

    allthat... aka: aaron@pangolin

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    LM317 as a galvo amp?! Never thought of doing that! I wouldn't waste your time steve-o, simply put, it wont work. If you're looking to build an amp for a set of G-124's, then you might want to look at building the amp with a TIP122 and a TIP127, a darlington push-pull emitter follower amp. They are insanely easy to build, just have to remember to bias each transistor with 2 diodes instead of 1 since they are darlington. I can draw you a schematic for it if you like, it wont give you very fast scanning, but it works fine for beams and abstracts. If you really want to push the G-124, then you would need an Accelerator124 Amp designed by Bill Benner. They are rather hard to find these days though.

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    Cool

    What's wrong with the amp in that E-bay acution that Aaron linked to above? $50 seems pretty cheap for a pair of scanner amps...

    Adam

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    Thanks you-all!
    My biggest problem is space conservation, also it seems like it only takes less than 2 volts (about 1.6 or +3.2 pk-pk) at 360 ma to achieve full swing of the G-124s. I'm thinking that its kind of overkill to run a 20 or 40 volt w/5 amp power supply and amps just to provide a very small current and voltage. I was thinking of single polarity for simplicity reasons (I know the G-124s are designed for bi-polar use). I'll probably go with the bi-polar and audio amps as suggested for full swing output. My plan is 2 amp chips with small transformer+PS- 9V/ 1A. I should be able to squeeze that in my 3 1/2 X 4" space I've got left in the projector.
    DZ- Yeah it works; I've hooked up an LM317 to a 4 ohm load, sig-gen input to the 'adjust' leg (w/ pot to gnd) and got a nice power square wave or sine (whatever I put into it) out and ran it for quite a while w/ no problems. Too bad its single polarity.. I could run the (-) leg of the galvo to below zero volts negative and run up the + for full movement but I'm afraid that might be excess current and inefficient.
    Steve- Thanks for the L149 suggestion- I'll go check it out...
    Aaron- Thanks but that looks a little big (Ive got space issues)

  10. #10
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    Cool

    Steve-o;

    If you're sold on using the LM317, what about a push-pull design centered around the LM317 for positive movement and an LM337 for negative movement?

    Eh - the more I think about it though, the more I agree with Dave... An audio amp would be easier...

    Adam

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