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How do I make a current source?

  1. Sep 14, 2010 #1
    I have an AC generator hooked up to a non-constant torque. The rate of change of flux through the wire loops will vary, thus the voltage will vary. However, I want to draw a constant current from this generator.

    How do I make a circuit that can limit a current regardless of voltage? Say I want a constant 250mA, given that my voltage is enough to sustain this power.

    Thanks for the help!
  2. jcsd
  3. Sep 14, 2010 #2


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    Staff: Mentor

    Is the output of the generator already rectified to some DC voltage range?

    Are you familiar with opamp circuits? You can use an opamp circuit driving a power transistor (PNP for high-side current source) to do what you want.
  4. Sep 14, 2010 #3
    An incandescence light bulb has sorta a constant current load. Would that work for you?

    More details about what you are trying to do would be helpful.
  5. Sep 14, 2010 #4
    Generator puts out varying (depending on torque supplied to generator) 0-24V (AC) and I want to use the energy to either charge a battery or capacitor or to run another motor at constant speed (constant current).

    On the other hand, a circuit that would yield a constant voltage is good too, say I want to convert my varying AC source into a 5V DC voltage source.

    I'm familiar with operational amplifiers, capacitors and inductors. I don't think I'll have a problem figuring out and tweaking circuits, I just need a starting point. I don't know how to use transistors. berkeman, can you post a diagram or source/link to the circuit you described?
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