Electronics > Projects, Designs, and Technical Stuff
0.13x vs 1.0x gain op amp regulated power supply - fail
HendriXML:
Made the current graph (purple, right axis).
It shows that initially a small change in current, means a large drop in the output voltage. This because the initial Vsg results in a high Rsd resistance (about 2k). In this regard resistance means voltage rise/amp (-> output drops). A tiny 1 mA would thus mean a 2V rise! But Vsg is regulated and climbs, but it's clearly not enough:
This can be caused by at least 2 effects:
* The gain (sensing Vout drop -> rising Vsg) is to low
* There's a delay (between sensing en responding)
Anybody any ideas?
Will (also) try to unravel the problem myself.
HendriXML:
I think I found a way to unravel the mystery of what gain is needed when an "amperage jump" is made.
Will do that in the other thread.
https://www.eevblog.com/forum/testgear/this-graph-brings-tears-to-my-eye/msg2203539/#msg2203539
HendriXML:
--- Quote from: xavier60 on February 14, 2019, 02:51:31 pm ---Also, the op-amps won't have to be powered at the full input voltage.
The balanced amplifier would need to have near perfect CMRR to prevent input voltage variations affecting regulation voltage.
--- End quote ---
When I was done experimenting, I thought why not see wether this circuit can operate on an adapter. The adapter is about 9V and I added 2 smoothing capacitors of 2200uF.
The result was that the output became very “noisy” with loads, I don’t think there’s even a repetition going on.
So as an experiment and a way to check out idea’s it did a good job. But as a proper supply I would call it a fail.
As a battery voltage dropper its probably ok, I will have to check that. But I think its going to be recycled :-+
Could you give an advise on an op amp which can regulate well on about 5-7 V, without being to sensitive to variations? Would be nice if it is THT and can be bought on AliExpress. But I wonder if it’s not the time get stuff elsewhere.
Kleinstein:
The circuit has a more general problem than just finding a suitable OP. I think it would be a good idea to take a step back and look at other, more normal voltage regulator circuits or read some more about the theoretical background.
Electronic systems with feedback can be quite complicated to understand - the theoretical background is only from the first half of the 20th century - so much of it is less than 100 years old. I don't know your mathematical background - so it's hard to give a suitable way learn about it.
It would probably help to start with something like stability in OP circuits. The simplest rule of thumb I know is aiming for a system that is slow at only one point and fast everywhere else. This leads to the simple case of dominant pole compensation.
For simple test on the bread board, I would keep it relatively slow, so OPs with a GBW of something like 0.3 - 2 MHz. Though not ideal the LM358 is a good start for a voltage-regulator on the bread board.
HendriXML:
--- Quote from: Kleinstein on February 17, 2019, 08:54:35 pm ---The circuit has a more general problem than just finding a suitable OP. I think it would be a good idea to take a step back and look at other, more normal voltage regulator circuits or read some more about the theoretical background.
Electronic systems with feedback can be quite complicated to understand - the theoretical background is only from the first half of the 20th century - so much of it is less than 100 years old. I don't know your mathematical background - so it's hard to give a suitable way learn about it.
It would probably help to start with something like stability in OP circuits. The simplest rule of thumb I know is aiming for a system that is slow at only one point and fast everywhere else. This leads to the simple case of dominant pole compensation.
For simple test on the bread board, I would keep it relatively slow, so OPs with a GBW of something like 0.3 - 2 MHz. Though not ideal the LM358 is a good start for a voltage-regulator on the bread board.
--- End quote ---
Thanks for the response, the LM358 seems a good one to experiment with.
As for my background, I’ve got me brain damaged, so I’m somewhat limited in my abilities to learn/comprehend stuff and the math stuff I did know has become a bit vague. So I’m just fine by doing experiments and to see how an idea turns out. As in this case: as a supply it may have failed. But checking my understanding about voltage rise/drop sensing and needed gain as an experiment was for me a success. If I now read something about this stuff I can link it to this practical experience (with blog!).
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