Other Parts Discussed in Thread: TINA-TI, , OPA551, OPA593, OPA454
Hi forum. First of all, thank you for your global active support. I have found in the past so many useful information, I would never got far enough without.
In the attempt to design a very accurate, high current source, for an automatic test system I came across an IEEE article from 2009 discussing an Howland Current Pump (HCP) with very high current output feature (source: Design of a High Precision Current Source). Following the indication of the article describing an “Enhanced-Improved HCP” basically a Howland Current Pump in the Improved version (the output resistor is split in two with a "shunt" resistor) adding 2 voltage followers, with a load resistor of about 200 ohms you actually can get a current of -71mA / +71mA. (Source/Sink).
Here an extract of the article:
The TINA-TI simulation that I attach actually demonstrates this:
Unfortunately, however, the main feature of the HCP of having a constant output current in this case is not respected and I don't understand why. A small fluctuation of the load impedance of a few tens of ohms (50 ohms) is enough to cause a sudden drop in the current of -5mA. (65mA is the output current), invalidating the first main feature of an HCP:
Now my question: is there a way to reduce the maximum current maybe to around 50mA on a mainly resistive load varying from 500 to max 1kohm ( understand that this leads maybe to a compliance voltage of around 100V) having a bipolar current generator constant on the whole resistive range or do I need to switch to other topologies?
I obviously need in the automatic test system a stable and predictable ILoad current without being so related to the varying Load impedance.
During the long period test infact the Load can vary to a 1kohm maximum.
Thank You all for your help.
Best Regards
