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Old 16th January 2005, 06:37 AM   #11
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Quote:
However, this doesn't answer the question, "why would somebody buy a complimentary pair of regualators?"

But it does. In many situations you have to use a centre-tapped transformer. And you save a bridge rectifier.

It seems though that in practice the complementary regulators are not quite identical - the positive often perform better than the negative. In such situations using a positive regulator for both rails is better.
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Old 28th January 2005, 06:47 AM   #12
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Wink using positive reg. for negative supply

Hi fellas,

I bought a pair of LT1086 positive adjustable regs. on the advice of some net page claiming it wraps rings around the old 317. The data sheet from LT actually shows how a full range supply can be built by using just positive regs. Here is one design which I adapted from the data sheet. I plan to use it for chip pre amp and head phone amp, and a spare for tone control (shock horror!), hence three outputs. The rails are +/- 18v from a 2x18v transformer. The only thing I might add is AC filter before the bridge.

Hope this helps.

KK
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Old 28th January 2005, 09:13 AM   #13
moamps is offline moamps  Croatia
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Default Re: using positive reg. for negative supply

Quote:
Originally posted by kkchunghk
.... Here is one design which I adapted from the data sheet.....
...
Hi,
your design has serious error.
Regards,
Milan
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Old 28th January 2005, 09:27 AM   #14
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Question Re: Re: using positive reg. for negative supply

Quote:
Originally posted by moamps

Hi,
your design has serious error.
Regards,
Milan
Such as?
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Old 28th January 2005, 09:33 AM   #15
UrSv is offline UrSv  Sweden
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Shorting the lower regulator which is connected in a way that would not work?
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Those who say it can't be done should not stop those who are doing it.
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Old 28th January 2005, 09:44 AM   #16
moamps is offline moamps  Croatia
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Quote:
Originally posted by UrSv
Shorting the lower regulator which is connected in a way that would not work?
Yes.
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Old 28th January 2005, 11:58 AM   #17
AndrewT is online now AndrewT  Scotland
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Hi,
you need separate secondary windings, rectifiers and capacitors.
Keep both the + & - regulation completely separate and only after the regs connect the positive of reg1 to the negative of reg2 and call this connection common.
regards Andrew T.
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Old 28th January 2005, 12:46 PM   #18
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Unhappy psu

Hi Milan,

Thank you. I spotted the mistake after I post the schem. It should look like this. It shows that you have to be lightning quick in this forum.

KK
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Old 28th January 2005, 01:28 PM   #19
moamps is offline moamps  Croatia
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Hi,
sorry, but this design doesn't work too.
Read Andrew's post, please.
Regards,
Milan
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Old 28th January 2005, 05:08 PM   #20
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Question another go

Hi Andrew T and Milan,

Thank you for pointing the right direction. I think you two gentlemen are refering something like this. The preoccupation of skimping a rectifier, and saving PCB space led me the wrong way.
Any comments on this one?

kk
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