precision current source

[hemnath]

Hey hi.. I have been following this forum from long time and this is my first post.

I would like to design a variable precision current source of 0 to 25mA. Should I use howland current pump method or bipolar current source method?

Out of curiosity, I would like to know how the high end multimeters will work? how they achieve that precision?

I am aware of certain things like selection of components with very low temp drift, low offset, low bias current, high precision voltage source.

Any reference circuit would be much appreciated?

Thanks in advance.

[hemnath]

Does this circuit provides 0 to 25mA? Should I consider any other things?

[Benta]

Not trying to be pedantic, but that's a current sink.

[hemnath]

Please check this circuit

[danadak]

Some questions -

1) Absolute accuracy desired ?
2) Resolution ?
3) Transient response settling time to N bits ?
4) Compliance range needed ?
5) Control method, processor with LCD or just pot or ?

Regards, Dana.

[David Hess]

I would like to design a variable precision current source of 0 to 25mA. Should I use howland current pump method or bipolar current source method?

Out of curiosity, I would like to know how the high end multimeters will work? how they achieve that precision?

Howland current pumps are more useful when you need a bipolar current source.  Their resistor ratio matching requirements are not conducive to high precision.

Multimeters usually drive a current mirror at the positive supply voltage with a ground referred current sink which is essentially two of this circuit in series except that there is a way to make an operational amplifier current mirror without an external FET:

http://www.linear.com/solutions/1563

[mmagin]

One of the easiest ways to achieve a reasonably precision current source in this range with widely available components would be a LT3092 and some fairly low-TC thin film resistors.