Electronics > Projects, Designs, and Technical Stuff
0.13x vs 1.0x gain op amp regulated power supply - fail
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HendriXML:

--- Quote from: xavier60 on February 14, 2019, 01:59:46 am ---An op-amp configured as a non-inverting amplifier with a feedback capacitor from the op-amp's output to inverting input will give the same result plus even more gain at DC. This will reduce the regulators steady state output voltage error to less than a millivolt if the layout is done right.

BTW, your output stage is current sourcing into a capacitor. For the feedback loop to be stable in this situation, the error amplifier(op-amp) needs to have some proportional gain. An op-amp configured as mentioned above has a gain that can only drop to one at higher frequency. This is well suited.

--- End quote ---

I think I understand most of what you say, but just to be sure I made a schematic. Will also use that to think things through and see the benefits. Losing the positive feedback is probably one of them. The change has some "double inversion" (low band -> highband, positive fb -> negative fb) to it, so it will probably change some characteristics too.
HendriXML:
Looking at the schematics I think you mean loosing the diff-amp stuff too, like so.
HendriXML:

--- Quote from: HendriXML on February 13, 2019, 09:04:50 pm ---To my understanding such a low gain in the first stage can only work if there’s some offset or voltage lift towards the Mosfet gate. Any idea how this normally is implemented/controlled?

--- End quote ---
I think the proposed schematics answers that question. Saves a lot of resistors  :-+.
xavier60:
A balanced input amplifier would be useful possibly for sensing voltage at the output terminals. I haven't given it much thought though and I have never been able to justify the need in the power supplies that I have built.
HendriXML:
One difference in the proposed schematic is that the capacitor is now sourced via R5. So a sudden increase in the supply voltage, might pull on the gate wouldn’t it? A phenomenon which has to be regulated, and might have effects on the output.
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