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negative adjustable voltage

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yafch

New Member
hi all,
attached herewith is a circuit diagram of a power supply using lm723. its positive psu. my is can it be modified to provide a negative voltage. if yes how?. or any one can provide a working diagram of adjustable negative psu. i must use lm723,any 3-pin regulators are not allowed to me.
 

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Nigel Goodwin

Super Moderator
Most Helpful Member
Build the same circuit, and use the +ve output as ground, and the original ground output as negative. That's all you need to do, as long as it's an individual isolated supply.
 

yafch

New Member
nigel sir,can you explain a little more what you said i dont fully uderstand what you said. and actually i need dual power supply not the individual psu. thanks a lot for quick reply
 

Roff

Well-Known Member
nigel sir,can you explain a little more what you said i dont fully uderstand what you said. and actually i need dual power supply not the individual psu. thanks a lot for quick reply
You can still build another one and use it as a negative supply, as Nigel stated. You can use a single transformer if you get one with two individual secondary windings.
 

crutschow

Well-Known Member
Most Helpful Member
As Ron stated, as long as you have isolated transformer output windings, the regulator doesn't care which output is grounded.

Many years ago I made a dual bench supply in that way (which I still use) with a transformer that has dual isolated output windings. I can then ground the outputs as I choose, either to get a plus and minus supply, or connect them in parallel to get double the output current at a single voltage (the outputs have adjustable current limits to help balance the load when they are paralleled).
 

Boncuk

New Member
Hi,

that's what Nigel and Ron were talking about.

You can adjust any part of the two power supplies to any desired voltage.

E.g. supplying an OpAmp with +12V and -5V you adjust one supply to +12V and the other one to +5V. The junction between ground of the +12V supply and the positive output of the +5V supply will be circuit ground. The positive output will then be +12V and the ground output of the +5V supply will be -5V.

For clarity refer to the sketch.

Boncuk
 

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yafch

New Member
now i understand everything. many thanks to all of you. special thanks to boncuk for the sketch. sketches provide much better chance to understand. agian thanks to every body.
 
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