why do we need negative voltage regulator ICs?

EJ · 20th August 2003, 01:39 PM

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

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

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).

20th August 2003, 01:39 PM	#1
EJ diyAudio Member Join Date: Jun 2002 Location: PA	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?

20th August 2003, 03:10 PM	#2
Dr G Scott diyAudio Member Join Date: Apr 2003 Location: California	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.

20th August 2003, 05:24 PM	#5
bocka diyAudio Member Join Date: Jul 2003 Location: Hannover	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.

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20th August 2003, 06:42 PM	#7
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	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.

20th August 2003, 07:25 PM	#8
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	http://www.geocities.com/react_71/au.../gainclone.htm

20th August 2003, 08:25 PM	#9
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	I reversed polarity on the NTE equivalant of the LM317 once. It started a fire.

20th August 2003, 10:21 PM	#10
bocka diyAudio Member Join Date: Jul 2003 Location: Hannover	paulb: completely correct, a dual secondary winding is needed, I implied this was the question (and I alyway do so).

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