Help with designing a dummy load

LM385 datasheet: https://www.ti.com/lit/ds/symlink/lm158-n.pdf
My setup: https://obrazki.elektroda.pl/2925856800_1477180471.png

Hi again.

I need a bit of help.

"In the Linear Mode the Input Common-Mode Voltage Range Includes Ground and the Output voltage Can Also Swing to Ground, even though Operated from Only a Single Power Supply Voltage."

Does this means that I could get away with my circuit? I mean, does that mean that I will get 0V at op amp output for V+=0V, and that I'll get a constant increase in op amp output voltage/transistor current when I turn the potentiometer knob? Or does op amp has some other fancy property just waiting to ruin someone's day. :razz:

Quick circuit description: It's a dummy load. POT sets the voltage on V+ from 0-2V, V- = V+, so the op amp does it's thingy on the output to make the inputs equal, so it makes the inputs equal by letting the current through the transistors.
Note: It's still in progress, 7805 will actually be 7812, and few of the values are missing.

Also, if my idea is faulty in any other way, I'd like to know

Does this means that I could get away with my circuit? I mean, does that mean that I will get 0V at op amp output for V+=0V, and that I'll get a constant increase in op amp output voltage/transistor current when I turn the potentiometer knob? Or does op amp has some other fancy property just waiting to ruin someone's day.

Click to expand...

Yes it should work as drawn.

One problem you "may" encounter is instability at high frequencies, or maybe not.
Try it first and see.
If it does become unstable, you could make IC1A into an integrator, instead of running it at full open loop gain.
That involves placing a resistor in series with pin 2, and a capacitor between pin 2 and pin 1. But give it a go as it is first,

Thank you Tony, that's nice to hear, I'll start building the prototype tomorrow then

PS: forgot to add the BD139 base resistor for protecting the op amp when there's nothing attached to the 2n3055 collector.

I built one like yours a few years ago.

I would advise that:
You employ 10X, 1 ohm resistors for a full scale of 200 mV.
Add 10X gain on the first opamp, then the second opamp use it as an integrator.

Also....use power mosfet instead of the 2N3055s.