How do I make a current source?

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Discussion Overview

The discussion revolves around creating a current source from an AC generator that produces varying voltage due to non-constant torque. Participants explore methods to achieve a constant current output, specifically targeting a current of 250mA, while also considering the possibility of converting the AC output to a stable DC voltage.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant inquires about creating a circuit that can limit current regardless of voltage variations from the generator.
  • Another participant questions whether the generator's output is rectified to a DC voltage range and suggests using an op-amp circuit driving a power transistor to achieve the desired constant current.
  • A suggestion is made that an incandescent light bulb may serve as a constant current load, although more details about the application are requested.
  • A participant describes the generator's output as varying between 0-24V AC and expresses interest in using this energy to charge a battery or capacitor, or to run another motor at a constant speed.
  • The same participant also expresses a desire for a circuit that could convert the varying AC source into a stable 5V DC voltage source and mentions familiarity with operational amplifiers, capacitors, and inductors, while indicating a lack of knowledge about using transistors.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the best approach to create a constant current source, and multiple competing views and suggestions remain in the discussion.

Contextual Notes

There are limitations regarding the assumptions about the generator's output and the specific requirements for the current source. The discussion also reflects varying levels of familiarity with circuit components among participants.

Who May Find This Useful

Individuals interested in circuit design, particularly those working with AC generators, current sources, and operational amplifier applications may find this discussion relevant.

Curl
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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!
 
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Curl said:
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.
 
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.
 
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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