You can sense the current on the high side using a differential amp. Values of R7/8/9/10 must be well matched. The 4 mA offset resistor can be a trim-pot for better adjustment.
The total loop resistance can't be more than roughly 1.1k (including the sense resistor R1) using a 24 V supply.
Hi E-design,
Just from curiosity but how much is the phase margin of the feedback system?
Thanks!
A couple of questions:
- The 5V reference means something like this one ?
- Does R1 control the current upper limit? I am trying to understand the circuit in general.
As a side one - what is the simulation software you are using - it looks interesting
I implemented this circuit in Tina and I got -25° for phase margin. I added the 220pF capacitor what you mentioned and it increased to -17°. Still oscillating.
Tina can use only gear and euler integration method, these supress oscillation under transient simulation. I am not sure I did the simulation well, I probably have got different model for LM358, but I am still suspicious that the 3 stage feedback system (2 OPAmp inverter + 1 PNP source follower) can be unstable even in typical condition without layout parasitics.
" And I have to disagree, if something doesn't work in simulation well we shouldn't believe it works after building. Reality usually worse than what we expect.
"LM358/MC" is the name what I have.
@E-design :
One more thing - as I am reading about ground connected load, it is almost always that the supply voltage has to be precise and stable. This is not the case here, because of the zener, right?
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