How do I make a current source?

[Curl]

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!

 

[berkeman]

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!

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.

 

[Carl Pugh]

An incandescence light bulb has sort of a constant current load. Would that work for you?

More details about what you are trying to do would be helpful.

 

[Curl]

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?