cheap precise current sources?

[coppercone2]

I don't normally use this word, but if you need a cheap current source, what are good parts?

Normally I would use a precise Vref and a op-amp to make a HCP... but how about pure current sources 100uA-1mA... are there any good IC's or weird solutions I missed? Something like a REF200. For biasing transducers etc.

I also looked at current output DACs before I think, but the best one was still pretty crappy compared to a discrete solution (meant for fan control or something).

Are there any amazing one chip solutions for this? I do like the REF200, it makes sense when you need 2 rtd or something since its pretty stable. But can you go cheaper?

[In Vacuo Veritas]

How about a NUMBER for what you consider cheap? Are we supposed to guess your budget?

AD5749ACPZ

[coppercone2]

hard to say i wanna see some parts to see if anything catches my attention with price/performance ratio

just brain storming

[SiliconWizard]

I like the REF200. I reckon it probably doesn't qualify as cheap though?

[IanJ]

Brainstormin here also........

I played with a test version of my PDVS2 and gave it an extra banana socket and a 0-2mA output (as well as the 0-10Vdc mode). If I remember correctly it's load range was something like 0 to 5kohm. It is based around the INA326 amp for the final current output drive which works pretty good.
I never put it into production as it put the BOM up more than I wanted it to........maybe I'l re-visit it eventually.

Ian.

[The Soulman]

lm317 and one resistor?  aprox. 30ct in small quantity's.
Performance may vary but I have had good luck with mine, used in various projects/applications.
About max 0,02% deviation over a couple years time, with cheap components. 

[Mechatrommer]

2 transistors and a resistor?

[coppercone2]

the ref200 is 25ppm/c

[SiliconWizard]

Another IC to consider is the TL431 which is much cheaper than the REF200. You can build constant current sources/sinks around those with just a couple resistors and a transistor. Overall cost < $1.
I doubt you'll quite get the performance of a REF200 but it's cheap.

[David Hess]

The LM334 produces an adjustable precision current which is proportional to absolute temperature but can be temperature compensated with an external diode.

The best way to build a precision floating current source is with an operational amplifier and precision reference.  Check out the LM10 datasheet for an example; the same configuration is used for operational amplifier 4 to 20 milliamp transmitters.