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Why is this circuit's transient response settling twice

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nikola22:
currently working on an improved Howland Current Source Architecture that I have built using this schematic. (R1=R2=R3=R4=10k & R5 = 10). configured with a gain of 1 and a transfer function of Io = Vin/R5 However, in the lab I am noticing an odd behavior with my transient response. It is actually settling twice! Instead of using a BJT as a current buffer I am using the TCA0372 as a voltage buffer. (https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF).

Would someone please be able to explain why I am seeing this transient response? Where this circuit is apparently settling twice? The yellow trace is VL and the Orange Trace is Iout. The input is a 0 to -300mV step input voltage. Appreciate any help!

The supply voltages are +/-12V. The load is either a resistive box of 85 ohms, or 85 ohms and 150mH.


Jay_Diddy_B:
Hi,

What is the load?

Those waveforms are consistent with an inductive load.

Try a resistive load.

Jay_Diddy_B

nikola22:
This photo was taken with an inductive load, but I believe I noticed the same behavior with my resistive load testing.

T3sl4co1l:
What supply voltages?

What does the intermediate node (op-amp output / buffer input) look like?

Tim

nikola22:
The supply voltages are +/-12V. The load is either a resistive box of 85 ohms, or 85 ohms and 150mH.

Here are waveforms from the non-inverting input terminal and the output of the buffer and the intermediate node.


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