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Feedback on power supply 0-30V 0-4A

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d4n13l:
Hi,

I updated the schematic for a 0-15V 0-0.9A PSU. I added a second potentiometer so that I can tune the low currents, and I connected in the meter in parallel with C1. The only thing I notice is that there is about 10 mV with the lower for voltage instead of a perfect zero. I don't know if it's a limitation of the op amp but close enough.

It's easy enough to scale to 30V and 4A output as I originally planned but the voltage is outside specifications for the LM358 and I don't have a appropiate replacement.

Maybe it'll be helpful to someone.

David Hess:
Some bench power supplies add a deliberate offset to the error amplifier so the output goes negative by a couple of millivolts and zero can be reached under all conditions.

Jwillis:
Just a thought but I was wondering why theirs no feed back loop from pin 7 to pin 6 .In the first schematic your putting a -33V reference directly to the inverting pin.And on the second schematic theirs a -15 volt going to the inverting pin .All the current controls I've seen and built have a feed back from the out put to the inverting input.Wouldn't that stabilize your control more? I'm learning so if someone could explain it would be appreciated.

Also some digital volt and amp meters must have a separate power supply to operate and some don't .Some 4 wire meters don't use a common ground.Found that out the hard way.But it's difficult to find proper wiring diagrams for some particular meters.

d4n13l:
As I understand it, the negative feedback loop provides a path for the output of the op amp to regulate the inverting pin. In the schematic U1G2 can do the same by controlling U2.

I think you're right about the meter, I tried the 5V regulator as xavier60 suggested and it messes with the regulation, guess I'll have yet another small transformer.

---

David,

for the offset you mean something like the trimmer (R11) I had in the first schematic?

xavier60:

--- Quote from: d4n13l on July 31, 2019, 07:33:27 am ---As I understand it, the negative feedback loop provides a path for the output of the op amp to regulate the inverting pin. In the schematic U1G2 can do the same by controlling U2.

I think you're right about the meter, I tried the 5V regulator as xavier60 suggested and it messes with the regulation, guess I'll have yet another small transformer.

---

David,

for the offset you mean something like the trimmer (R11) I had in the first schematic?

--- End quote ---
I'm surprised about that. I couldn't find wiring instructions specific to your panel meter. Is there an instruction sheet that came with it?

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