LT1963A as a negative regulator - how?

[Glassman]

I have two LT1963As lying around that I want to use for the aditional power supply for my soundcard.. generating +/- 11V out of dirty +/- 12VDC from PCI

the question is how can I configure it as a negative regulator? in the datasheet there is stated +/- 20V input and output, but the application note/voltage setting formula seems to work just for positive voltages..

another question: do you know how to design appropriate LC filter instead of simple RC one?

thanks for your help!

 

[PeterR]

Those are just the maximum ratings - i.e. it will survive -20V at the input, but it works only as a positive regulator.

Quote:

(...)The input of the device will withstand reverse voltages of 20V. Current flow into the device will be limited to less than 1mA (typically less than 100µA) and no negative voltage will appear at the output. (...) The output of the LT1963 can be pulled below ground without damaging the device. If the input is left open circuit or grounded, the output can be pulled below ground by 20V. (...)

 

[tangent]

You can use two separate transformers and make two floating power supplies, tied together arranged so that one is "negative" relative to the other. You might even be able to do this with a single transformer that has two completely separate secondaries. It's the same principle as taking two 9V batteries and making a +/-9V supply, even though both batteries are thought of as positive supplies.

EDIT: You'll need two bridges for this to work, you realize. You're making two complete power supplies that just happen to be joined together in series.

 

[JohnFerrier]

See page 8 (PDF page 10) at the following link, to use a positive regulator as a negative regulator.

http://www.semicon.panasonic.co.jp/cat/pdf/A00036AE.pdf
This is a long document (184 pages) with other interesting circuits (pages 1-17).

The situation is as tangent describes (two transformer secondaries, two bridge rectifiers,...). The PDF shows a diagram with how to connect the regulators...

*EDIT*
Here is a 3 page PDF version. See last page (marked page 8).
http://www.semicon.panasonic.co.jp/c...A00036AE04.pdf


JF

 

[Glassman]

thanks guys, it seems I will need to look for negative counterpart of LT1963A, becouse I'm working with +/- 12VDC, so no transformers & bridges.. I just need to provide some regulation to polluted supply onboard..