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pos neg power supply Answered

I see many pos neg power supply's with an op-amp on the neg side. What is the purpose and function that is has there?
There is two links with examples. First has an LM301 and the second has an OP27EP.




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steveastrouk
steveastrouk

Best Answer 9 years ago

You'll notice that there ISN'T an adjustment for the negative supply regulator. This is a TRACKING regulator, the op-amp is there to mirror the control voltage that the regulator needs to see on the ADJ pin, because the output of the op-amp, when the supply is mirrored should be exactly 0 V

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WWC
WWC

Answer 9 years ago

So is it safe to say when the op-amp is there then only one voltage adjustment is needed to operate both the neg and pos at the same time. One adjustment operates two outputs?

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WWC
WWC

Answer 9 years ago

WOW!

This is very good!
In the first picture there is a voltmeter hooked between gnd and +v. Example if this power supply has +10v to -10v and the meter is hooked to the gnd and +10v, it is going to show +10v? but we would have to double that because of the -v ?

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steveastrouk
steveastrouk

Answer 9 years ago

No, referenced to |GROUND its still 10V. Across the two terminals + and -, its 20V

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WWC
WWC

Answer 9 years ago

Yes but in regards to installing a dedicated analog volt meter on this power supply. Would we hook to gnd to +10v?

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WWC
WWC

Answer 9 years ago

How could we monitor the 0v to -10v side. We could hook up a gauge there also?

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steveastrouk
steveastrouk

Answer 9 years ago

Well, yeah, but if its working, its tracking. You could perhaps use the error signal from the opamp to drive an LED to say "out of range"

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iceng
iceng

Answer 9 years ago

The authors first pic uses a single meter for the positive reading and an LED
for both the negative and positive supply sides when the power supply is
turned on.

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WWC
WWC

Answer 9 years ago

I guess for me there is some amount of appeal to seeing the sweep of an analog gauge on something i have built. Note the links to 2 of my Instructables and you get the idea. https://www.instructables.com/id/Variable-Power-Supply/.
https://www.instructables.com/id/Zener-Diode-Checker/

I see duel sided supply's on here with no gauge at all maybe they use a DMM every time, eek how elegant is that.

I suspect that when i build one i will try to fit a gauge on both sides.

Thank You very much steveastrouk for staying with me on this clear to the end. You are very knowledgeable and helpful.

Thats not to say iceng wasn't helpful but in fact was very help full. I had seen those LEDs on pic 1 b4 but didnt make the complete connection of there usefulness until you pointed it out.

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steveastrouk
steveastrouk

Answer 9 years ago

You're welcome. Don't forget to award the "Best answer" now.

Steve

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iceng
iceng

Answer 9 years ago

You learn faster then LED people :-)

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WWC
WWC

Answer 9 years ago

Thank you very much friend.