Author Topic: Feedback on power supply 0-30V 0-4A  (Read 3622 times)

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Offline d4n13lTopic starter

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Re: Feedback on power supply 0-30V 0-4A
« Reply #25 on: July 30, 2019, 02:48:29 am »
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.
« Last Edit: July 30, 2019, 06:33:11 pm by d4n13l »
 

Offline David Hess

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Re: Feedback on power supply 0-30V 0-4A
« Reply #26 on: July 31, 2019, 02:30:17 am »
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.

 

Offline Jwillis

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Re: Feedback on power supply 0-30V 0-4A
« Reply #27 on: July 31, 2019, 03:17:33 am »
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.
 

Offline d4n13lTopic starter

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Re: Feedback on power supply 0-30V 0-4A
« Reply #28 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?
 

Offline xavier60

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Re: Feedback on power supply 0-30V 0-4A
« Reply #29 on: July 31, 2019, 07:48:04 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?
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?
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline xavier60

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Re: Feedback on power supply 0-30V 0-4A
« Reply #30 on: July 31, 2019, 07:58:12 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?
Do you have a diagram showing how the 5V regulator and meter were wired?
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline GigaJoe

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Re: Feedback on power supply 0-30V 0-4A
« Reply #31 on: July 31, 2019, 06:13:24 pm »
will charge pump 7660 work here, instead a second transformer and all around ?
 

Offline ggchab

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Re: Feedback on power supply 0-30V 0-4A
« Reply #32 on: July 31, 2019, 06:21:25 pm »
It's even possible to obtain the negative supply from the main transformer and use a voltage regulator (like a 79L05) if consumption is not too high.
 

Offline d4n13lTopic starter

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Re: Feedback on power supply 0-30V 0-4A
« Reply #33 on: August 01, 2019, 12:26:38 am »
Thanks on the tips... I'll try them out, so... I tested everything on the protoboard and worked great.. then tried it once soldered to a stripboard, the results were not that good.. I guess it's expected from my first project u.u

maybe someone can give me some tips, like do you tested the circuit each time you solder a component? also something I hadn't considered, how much current do these boards can handle?I don't know if it should have an external cable to handle the current or simething like that..
 

Offline GigaJoe

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Re: Feedback on power supply 0-30V 0-4A
« Reply #34 on: August 01, 2019, 01:48:19 pm »
not good, means, not a stable output when apply a load ? Need a symptoms
 

Offline d4n13lTopic starter

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Re: Feedback on power supply 0-30V 0-4A
« Reply #35 on: August 02, 2019, 04:38:03 am »
yep, I'm sure I screwed up somewhere in the wiring, I got an output range of about 3V on the upper end. I'm also a bit concern about the amount of current the stripboard can handle, apparently it may be somewhat higher that the ~1A I need but I'd like some confirmation.
 

Offline Jwillis

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Re: Feedback on power supply 0-30V 0-4A
« Reply #36 on: August 02, 2019, 05:38:01 am »
yep, I'm sure I screwed up somewhere in the wiring, I got an output range of about 3V on the upper end. I'm also a bit concern about the amount of current the stripboard can handle, apparently it may be somewhat higher that the ~1A I need but I'd like some confirmation.

I don't think you should have any problem with just 1 amp .But you can always double up the wire where most of the current travels. That would be the main ground plain and main positive plain.from rectifier to output.
I usual just check continuity between connections.This finds bad solder joints and solder shorts.If you tin the entire solder strip that also helps.A little extra flux won't hurt either.Just make sure that you clean the board well after soldering is complete.Sometimes just a tiny piece of dirt or carbon can cause problems..Another tip is to make a hard copy of the schematic so you can check off each connection as you weld it.
 

Offline ggchab

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Re: Feedback on power supply 0-30V 0-4A
« Reply #37 on: August 02, 2019, 06:24:49 am »
The biggest capacitor seems to be on the right side and not next to the bridge rectifier. Is it normal ?
May be you swapped some components ? It's easy to make mistakes  :(
 

Offline d4n13lTopic starter

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Re: Feedback on power supply 0-30V 0-4A
« Reply #38 on: August 05, 2019, 11:37:51 pm »
Hi ggchab,

What happened there is that I have a bridge rectifier that doesn't fit the holes in the stripboard as you can see in the picture.

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Anyway.. I finilly had time to try again and works great, the only problem is with the volt/amp meter that apparently I can't connect anywhere without messing up the current regulation in the circuit, I guess I'll just power it from a different source.

Thanks for the help

 


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