EEVblog #579 - Precision Low Current Source

Part 3 in the Precision Current Source series.
Dave breadboards a classic precision low current source circuit using the 10V REF102 voltage reference to generate accurate 1mA and 1uA currents.
Also some talk about the errors in a typical precision circuit like this.

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[meowcula]

No problems with video here.
Another great video Dave! What I like is not only that you discussed it's design and built it up for us, but you went to the trouble to explore the little traps as well as examining the error and noise. Education at its finest!

[EEVblog]

BTW, this should be one of my best quality videos ever, no extra compression using Handbrake. The file size was maybe 3 times bigger than my usual uploads.

[Graham_Wideman]

Hey wait a sec... 19:24 the non precision resistor is 9.91 Mohm, so the resulting current should be 10V/9.91 = 1.009uA, not 0.991uA that Dave says. Which we finally see measured at 23:20.

[jbuddyman]

I told my science teacher to check you out, because you are so awesome. Keep up the good work, and happy engineering!

[iSolarSunrise]

When I first clicked on the video, I complained "WTH another precision current source video? This is boring..."
But after 5 minutes, I am completely absorbed in the video. Awesome videos as always!

[ian-c.]

I get the impression that you can do all of this kind of stuff in your head and don't actually need to breadboard or measure anything, you just do it for demonstration purposes, thanks for taking the time and trouble !

[tubical]

Here YT let me select 1080p, thanx dave !

Great vid by the way learned a lot on the constant current thing. This is not on my focus, so i really do not care much about constant current sources. But you have done a very good job on telling us how they work.

[mortenlund]

You are awsome. These videos must end up as classic mandatory educational material - thanks thanks

[metaforest]

thanks again for showing how to read through test-config induced noise!

[linksmith]

I know this is old, but Dave you just solved an issue I’ve been having for weeks building a precision programmable constant current source for testing LED Luminosity. Used a rail to rail op-amp configured as a voltage follower and never have been able to get the damn thing to drop its current below 500 micro amps.

[uNQuDZ]

Yeah, took a while for the video to finish processing, we're a bunch of geeks who just can't wait to see the latest EEVblog :) Just youtube processing taking its time to finish, as this is another fairly long vid.

[mirceanicolaepop]

Yep, add a diode in series, then you've got quite a current source and a temperature sensor (with some specific noise distribution) in series with the load. Would it not have been better to use bipolar supplies or lower the ground of the load?

[dhpbear]

22:20 - That app note suggests there's a -Vs available. Couldn't you just tie pin 4 of tie op amp to -Vs rather than adding several diodes?

[EPaulIII]

I know this is an old one, but thanks, it is exactly what I need right now. If I can only find a source for the REF102 at 0.025%. Everybody seems to be out of stock.
Paul A.

[uski]

My guess : Either Dave needs a way to check the accuracy of the µCurrent, or we'll soon see a µCurrent Platinium edition with 1A, 1mA, 100µA and 1µA current sources built in... :)

[jjoster]

I really enjoyed this one Dave. Thank you.

[ericvieira]

Hi Dave
Are you planning a "micro Ohm" after the microcurrent? The precise low current sources could be used to measure resistors with low values using the voltage range of the multimeter just as you did with the microcurrent. It would also fill a nice gap since multimeters are not very good for measuring resistances well below 1 Ohm.

[Scorpio]

Enjoying your well done videos and projects, thank you for the excellent
quality, theory, testing, and techniques. There are a handful of
providers doing this and you are one of those in the "Top Ten" in the
world from my view. As a revisit, these would be great for the "legacy old school analog VOM/AVO meters list the Simpson 260/270 or the Triplett 310 series handheld VOM. One using 50ua/250mv and the other using a 60ua. Great Videos, theory review, etc. Oh by the way, love the eevblog multimeter ( Xmas Gift from my son. )

[HowToGuys]

I always wanted to learn something new in this way!

[nixie]

Yes, we enjoyed them!
Awesome work as always!