Electronics > Projects, Designs, and Technical Stuff

Howland Current Pump

<< < (4/4)

David Hess:

--- Quote from: JoelK on December 10, 2019, 09:52:39 pm ---
--- Quote from: David Hess on December 10, 2019, 08:57:50 pm ---Below is an example from National Semicondcutor application note 32.  The DC precision could be considerably improved by adding a matched JFET current sink with matched series bipolar base-emitter junction.  Alternatively a DC servo loop could be used and I think without adding to the input capacitance.
--- End quote ---

But dont I get a simulare problem like trying to bootstrap the supply rails of the opamp? The input swing of the discret buffer won't be high neither.
--- End quote ---

Not all operational amplifier SPICE models support simulating bootstrapping the supply pins.

In the example shown, the bootstrapping is AC so can extend beyond the supply rails.


--- Quote ---
--- Quote from: David Hess on December 10, 2019, 08:57:50 pm ---What about adding a series output inductor to raise the output impedance at higher frequencies?
--- End quote ---

I will simulate this. Thank you!
--- End quote ---

It is a common way to improve AC impedance in current sources and sinks.  Just to be clear, the inductor goes between the current pump and the load.  Over a narrow frequency range, a parallel LC parallel resonant circuit provides higher impedance.  At lower impedance and higher frequencies, a resistor might be used because it has a higher resonant frequency.

T3sl4co1l:
Note that, for a source that has a Norton equivalent (current || resistance || capacitance), a series inductance increases the impedance but only around the resonant frequency; at best, at higher frequencies, the impedance is dominated by the damping of that inductance (which for critical damping, equals sqrt(L/C), and the impedance simply shelves at or near its peak).

In other words, you can shelve the impedance, but you can't keep it going up (inductive) forever.

Since this is a masters thesis -- perhaps it would be more beneficial to present the process one should follow to synthesize a desired source, or design and analyze a fixture?  These methods of improvement only scale so far, and depend critically on the components used.  There are limits, both among commercial supply, and sheer physics, on those components (especially GBW and stability where op-amps are involved), which simply cannot be as general as the more involved methods.

Tim

coppercone2:
there is a paper on this device for electromedical purposes if you care to find it (made in the 2000's )

it is called a circlotron (in this case op-amp based). the paper covers high Z at AC

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod