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Old 12th February 2012, 02:14 PM   #1
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Question Increasing efficiency of regulator circuit.

Hi everyone.

I'm afraid I'm a bit of a newb when it comes to voltage regulators, but I am trying!! Please bear with me, it's all appreciated


I currently have a PSU unit here that's used for a small equalization circuit.
Here is its current state:

9vAC (well.. 11v) input, into linear PSU, rectified at 13vDC and then into a small regulator design with one zener per rail between 8v-9v (and small electrolytics). Output is consistant with the 0.6v voltage drop, with the +ve rail always being pulled lower by around 0.3v.

SO +ve rail is generally around 7.7v, -ve around 8v.


However, I require the circuit to improve on its lousy efficiency! I planned to run a ±12vDC line in after the rectification but am worried about the Vdrop over the regulators (4v) still causing the power dissipation.

Ideally I would like to run a buck converter from ±12V line down to a regulated ±8v. Is this possible? Otherwise a buck down to ±9v into an LDO reg perhaps? I can't seem to be able to find any DC-DC converters that can do this.

Oh, and finally, the ±12v line is provided by (another) 18-75v buck converter off a battery supply.


Many thanks if you've managed to get this far! Hopefully I've made sense - I've spent too long on this bloody circuit for it to become any clearer to me

THANKS
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Old 12th February 2012, 02:19 PM   #2
dtproff is offline dtproff  United States
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Standard linear regulator is the easiest.

For a switcher try one of the "simple switchers" from National Semi. Here is to the swicher design tool. WEBENCH® Power Designer Tool | National Semiconductor ? Power Supply Design Tool

Tony
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Old 12th February 2012, 02:24 PM   #3
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Second that! Switchers such as LM2576-ADJ are real easy to use!!
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Old 12th February 2012, 02:33 PM   #4
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Wow, replies in 5 minutes

Thanks for the link, I'll check it out now!
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Old 12th February 2012, 05:05 PM   #5
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WEBENCH designer is brilliant!!

So far it seems the optimum design is a LM5576 based design. Input range 30-45v output of 16v. Efficiency of 95%!! Seems to be up on the simple switchers by 6%? The next SS is a LM2592HV-ADJ with a lovely easy schematic

I assume it's okay to split the 0-16v rail into two discrete ±8v rails by means of a potential divider? Or would I need two seperate supplies? One feeding the +ve and one the -ve rail, with the relevant outputs linked for the 0v?

Thanks again
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Old 12th February 2012, 06:07 PM   #6
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And the LM5576 is available as an evaluation board

Does anyone know about splitting the single rail with a potential divider? I'm getting the feeling it's either an extremely stupid thing to do or a standard way of doing things?

Thanks!
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Old 12th February 2012, 06:15 PM   #7
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Quote:
Originally Posted by zerokelvin99 View Post
And the LM5576 is available as an evaluation board

Does anyone know about splitting the single rail with a potential divider? I'm getting the feeling it's either an extremely stupid thing to do or a standard way of doing things?

Thanks!
If you only need low power you can use a chip like the TLE2426. Higher power "splitters" can be made from power op amps like the L165. Both datasheets provide examples.
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