current control for a magnetic coil

Discussion in 'General Electronics Chat' started by llg74, Mar 16, 2011.

  1. llg74

    Thread Starter New Member

    Nov 25, 2010
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    Dear all,
    this is the first time I post a thread. I hope I do it the proper way.
    So here is my pb : I want to drive current into a coil so as to generate a magnetic field. This current should be quite strong (up to 5A) and I would like to drive it with various waveforms (square pulses or sinusoidal, up to 1kHz) provided by some external device (output board on a computer). It seems to me that I need a power transconductance circuit. But that's pretty much all I know because I'm not so good in electronics.
    Could anyone give me a schematic on how to buid this, or a link to a webpage that describes how to build it and explains the ins and outs?
    thanks in advance,
     
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Curious as to what it's for?
     
  3. John P

    AAC Fanatic!

    Oct 14, 2008
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    Depending on the inductance of the coil, you might have quite a challenge there. The issue would be the energy stored in the magnetic field, if you require very rapid changes. In fact I'd look at that first--the maximum voltage you'd need to apply would be equal to the inductance multiplied by the rate of change of current (Henries * amps/sec). Are you proposing a reasonable system? And then, what is the power required over some period of operation? Where does the energy end up going (now cooling becomes an issue)? Engineering is fun.
     
  4. llg74

    Thread Starter New Member

    Nov 25, 2010
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    THanks for your feedback. Here is a bit more detail on what I want to do :
    In fact I have 2 projects. The first one is the priority :

    1-one coil will have approximately L=6mH and R=3ohms (so the charact. time is 2ms) with a metallic core at the tip of which a high gradient of B field will be generated (I plan to move superparamagnetic microspheres so as to mechanically stimulated biological cells with it).
    For this I need a power amplifier that will act as a current source (up to 5A). I want to command this current source with a voltage. Thus, if I understand well, what I need is a power transconductance circuit (that uses whatever feedback to output a current that is proportional to the command voltage, whatever the load of the coil).

    2-one will be a bigger coil with L=80mH R=4ohms (char. time = 40ms). I want to use temporal variations on B field to move whiskers of mice (on which magnetic paint has been put). I have seen someone who just crudely fed the the coil with the 50Hz, 220V mains, with the possibility to change the voltage with a Variac. I thought that It would be better if I could choose myself the type of current waveform that I impose. This is why I guess having a voltage to current source would be best.
     
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