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-   -   why do we need negative voltage regulator ICs? (http://www.diyaudio.com/forums/solid-state/19212-why-do-we-need-negative-voltage-regulator-ics.html)

EJ 20th August 2003 01:39 PM

why do we need negative voltage regulator ICs?
 
Why do we need negative voltage regulator ICs? Is there any significant difference between positive and negative regulators? Has anyone tried a "reversed" 7812 as your negative voltage source, which is to use the output pin of 7812 as ground and the ground pin as your negative voltage source?

Dr G Scott 20th August 2003 03:10 PM

Negative regulator
 
As long as your have seperate windings or
separate transformers for the unregulated supplies, you can use positive regulators. The positive output for one regulator is connected to the ground of the regulator for the positive supply. The negative supply is now the ground of positive regulator being used as a "negative" regulator.

The performance of the LM317 and LT1086
are better than the coresponding negtive regulators. For seperate secondaries it will only cost you another diode bridge. This is often done and it works very well.

analog_sa 20th August 2003 03:52 PM

Quote:

Has anyone tried a "reversed" 7812 as your negative voltage source, which is to use the output pin of 7812 as ground and the ground pin as your negative voltage source?
Haven't tried. As it obviously won't work as a regulator. But it may be fun. Listen to the doctor's advice. He knows what he's talking about.

EJ 20th August 2003 05:17 PM

Quote:

Originally posted by analog_sa


Haven't tried. As it obviously won't work as a regulator. But it may be fun. Listen to the doctor's advice. He knows what he's talking about.

....well, I still don't see why it obviously won't work.
could you please explain in more detail?
thanks!

bocka 20th August 2003 05:24 PM

It works
 
Lay a mesh around the regulator, IC and bridge/trafo. It will work because current always flow out of the regulator. On the other side I would not use a 78xx regulator there are much better parts/circuits available.

paulb 20th August 2003 05:42 PM

Quote:

Originally posted by analog_sa


Haven't tried. As it obviously won't work as a regulator. But it may be fun. Listen to the doctor's advice. He knows what he's talking about.

It won't work if you need both positive and negative supplies, and they are coming from the same transformer secondary winding with the centre tap used for ground. In other words, if ground needs to be common between input and output. Otherwise it will work.

PMA 20th August 2003 06:42 PM

You can use positive regulator for positive voltage and the negative voltage can be derived by voltage power amplifier with gain of -1. Of course the later must be supplied from voltage higher than output stabilized one.

tbla 20th August 2003 07:25 PM

http://www.geocities.com/react_71/au.../gainclone.htm

sam9 20th August 2003 08:25 PM

I reversed polarity on the NTE equivalant of the LM317 once. It started a fire.

bocka 20th August 2003 10:21 PM

paulb:

completely correct, a dual secondary winding is needed, I implied this was the question (and I alyway do so).


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