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Coil driver circuit?

  1. Jan 10, 2016 #1
    I have a signal generator that is used to generate 12kHz square waves. I want to use my signal generator to drive a transformer primary coil. My coil has 12 ohms resistance, 50mH, and will have 12V applied to it @ 1A.

    Can I buy a circuit to drive the coil from the signal generator pulse or do I have to make one?
    What is the correct terminology for such a circuit?
     
    Last edited: Jan 10, 2016
  2. jcsd
  3. Jan 11, 2016 #2

    meBigGuy

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    Do this:
    levitatorcoildriver.gif
    You can get fancy to drive it with faster edges, or use a power fet instead of a 2n3055, or do a search on coil driver and look at the images for one you like
     
  4. Jan 11, 2016 #3

    jim hardy

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    12 V square wave ? Does it go from 0V to +12V or from -6 to +6 ?
    What's the part number of your transformer ? Does it have a small air gap in the core ?
     
  5. Jan 11, 2016 #4
    Sorry, it's 0V to +12V, transformer is one a friend made for me, it has a small gap in the core but it's not a flyback. It's a step up transformer with a 1:5 turns ratio.
     
  6. Jan 11, 2016 #5
    Will my 5V signal from my signal generator be able to drive the 2N3055?
    Dumb question I know, it's just been a while since I played around with electronics and I've forgotten a lot.
     
  7. Jan 11, 2016 #6

    meBigGuy

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    Probably. Do you have a model number?
    Looking at the specs for an MJE3055 in a TO-220 package, it is rated for 0.6W without a heatsink. That's borderline for 1 amp. I'd use the to-220 and add a small heatsink.
    Like this http://www.mouser.com/ProductDetail/Aavid-Thermalloy/6237BG/?qs=sGAEpiMZZMttgyDkZ5WiuqcEpFN0QqoQfmtMCSJ6UoA%3d [Broken]

    For 1A, you probably want at least 100ma base current which would be at around 4volts with a 300 ohm resistor. Can your function generator drive 100ma? If it has a 50 ohm output, then no problem.

    If there is not enough drive you can go to a 2 stage circuit, or a darlington, or a mosfet. Regardless, a TO-220 package with a clip-on heatsink will be the most robust solution.

    Don't forget the diode --- the transistor will blow without it.
     
    Last edited by a moderator: May 7, 2017
  8. Jan 11, 2016 #7
    Cool, thanks for the suggestions, I'll use them. The function generator is 50 ohms! Any idea how fast the rise and fall time will be?
    Would adding a buffer like a 4050 reduce the rise and fall time?
     
    Last edited by a moderator: May 7, 2017
  9. Jan 11, 2016 #8

    meBigGuy

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    Again, it depends on your generators output. Since you are switching an inductor, the turn-on/off time may not have much effect overall. You can speed up the transistor switching with a very small cap across the 300 ohm, but again, it won't change much. If the 4050 is faster than your generator, then that will help.

    If speed is really an issue, then there may be better solutions than the 3055, like a power mosfet and a hefty mosfet driver (mosfets have huge gate capacitance)
    There is probably some power mosfet you can connect directly to the generator and drive it without a heatsink or a series resistor.

    I found some mosfets in this thread. Maybe that's a better way to go.
    https://www.physicsforums.com/threads/electromagnet-and-mosfets.831892/#post-5224970
     
  10. Jan 12, 2016 #9

    jim hardy

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    What's connected to the secondary of this transformer ?
     
  11. Jan 12, 2016 #10

    Svein

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  12. Jan 14, 2016 #11
    Connected to the secondary of the transformer is capacitor and resistive load of about 300 ohms
     
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