EEVacademy #8 - Howland Current Pump

David Ledger explains the Howland Current Pump building block circuit.

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[dough]

Thanks, the family is very proud of this circuit...

[deusimperator]

I used one of these in a design at work recently. I needed a very tightly regulated low current output that was tolerant of wide variations in load, both resistive and inductive. This circuit worked great.

[jdmc]

Thank you sooo much for this video. I have an exam next week and couldn’t see the woods from the trees- THANK YOU

[alecapristrudel]

This is probably the best explanation of this circuit I've seen so far!
Can you do more analog stuff like this? Maybe OTAs or impedance converters?

[DrFrank-xjbc]

Nice video with good, lucid explanations.
4 very versatile aspects have to be added:
1. the current source differential output resistance will become infinite, only if these four 100k have pairwise the same ratio.
So add a trim pot between 2 of the 100k, wiper into the OpAmps input, to trim the circuit for a precision constant current source, i.e no change of current at varying load resistor .
2. the circuit operates symmetrically to GND. Trivial, but explicitly to be mentioned, therefore it's a GND related current source. It also can act as AC constant current source, if a constant AC voltage is applied at the input.
3. The circuit acts as a precise voltage to current transformer, so it's also possible to create a DC + AC current by providing an additional summing input for separate VDC and VAC inputs.
4. There's a more precise circuit, called modified Howland current source, implementing a 2nd OpAmp, so the common mode voltages at the 1st OpAmp are zero, and the input voltages are related to GND also, that's more convenient for AC / DC voltage sources. Additionally, the small error from the current through the 100k vanishes, AND you can realize the current shunt resistor as a decade switching ladder, so to switch the output current decade wise.

[groveh]

Nice! Thanks for introducing me to the Howland current pump!

[siddacious]

Great video for someone like me who is still learning the fundimentals. More like this!

[VoidHalo]

I love CircuitMod. Playing around with it is a HUGE reason why I got into electronics.Of course there are other things that played a fundamental role in me getting into electronics. EEVBlog being another big one. Only just found this series and I love it. I was a bit weary with watching a video not hosted by Dave, but you did a great job. Cheers.

[pocoapoco]

I found I was able to further simplify the circuit by replacing the resistor between the voltage source and the non-inverting input and the resistor immediately following the op amp output and replacing them both with wires. An then moving the constant current output from the op amp output to the non-inverting input. changing the value of the resisrtor between the ouput and non-inverting input then determines the current.

[deanolium]

Good video, and quite a clever system. Showing how it's derived is really useful, and a good way to learn.

[Mustakari]

Excellent! I like this style. Clearly explained and the tempo is just right.

[NorbertHarrer]

Good job. Explained very well. Looking forward to more stuff from you, David.

[NetworkXIII]

Good video David, enjoyed it a lot. Op-amps are amazing devices.

[lezbriddon]

great vid, i have seen something like this in cheap ebike brushless motor controllers to get a stable 12v for the gate drives, because (apparently) normal voltage regulators dont respond quick enough to input voltage drops, which leads to the 12v dropping, not fully turning on the mosfets, and then them exploding due to internal heating....

[final]

I like this format, I would love to see more of these videos where circuit building blocks are explained

[JamesPotts]

a) I did learn something, and b) that end picture alone is worth a thumbs-up.

[toniturnwald]

Thank you, for uploading, from your films I can learn pretty good the electronic stuff. Cheers and bye bye Toni

[irawarnaca]

Thanks David, great building block. It would be helpful to see how to leverage this in a circuit. Show us an example please. Thanks again, I really do appreciate your videos, I would like to see more of them.

[Edson_Staack]

I laughed with the photo in the end! Unbelievable! :)

[fabiStgt]

Great explanation and also very nice software setup you're using to visualize the circuit!