Electronics > Beginners

Constant current load Help needed again

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LukeB:
Hello again,

I have another really newbie question, sorry, I have this constant current load that I am building as a learning experience and as a tool. I think most of the circuit is all good but I want to know what you think about C2. Is that the best way to smooth out the load?? As you can tell I am still learning but I would like some criticism on my project here so that I can learn. Hopefully this doesn't waste anyone's time but I am here to learn.

Thanks for the help in advance.

BTW, VCC is probably going to be 12v or 9v and the load will probably be for a lead acid car battery. The max current really only needs to be 1A but up to 4 would be nice. Probably depends on mosfet temp.

Prithul0218:
I am new here. I am not an expert, just a young hobbyist. So judge my words before applying in your project.

It seems to me like what you're doing is smoothing the feedback signal. But that's not what you want to do. You want a fast changing feedback but your capacitor is actually slowing it down. Maybe a tiny capacitor would be ok, like, a few pFs but not necessary.

However, in order to make the load current smooth, what you should do is make the output of the op amp stable. Check the attached photo. It is from the part 1 of Scullcom Hobby Electronics DC load project which I highly recommend you take a look at, here's the full YouTube playlist with 10 videos: https://www.youtube.com/playlist?list=PLUMG8JNssPPzbr4LydbTcBrhoPlemu5Dt

You would probably want to use that type of RC filter configuration.

Correct my mistakes and help me grow.
Thanks.

Dave:

--- Quote from: Prithul0218 on September 28, 2018, 02:58:00 pm ---Correct my mistakes and help me grow.

--- End quote ---
No mistakes, your advice is solid.

Prithul0218:
Thank you Dave.  :)

LukeB:
So why do you need to tie it back to the inverting input?

With my method wouldn't smoothing the feedback out a bit cause the output to be smooth anyway?

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