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Old 20th March 2011, 06:19 PM   #1
FOXYE is online now FOXYE  Israel
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Default Low Noise 5V Reg

What do you think about the following circuit:

http://img859.imageshack.us/i/5vreg.jpg/

Last edited by FOXYE; 20th March 2011 at 06:22 PM.
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Old 20th March 2011, 06:56 PM   #2
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Well, it looks a lot like the feedforward 'clean-up' shunt regulator design of Wenzel Associates. Except that it has an second (incorrect) phase inversion due to having cascaded two grounded-emitter stages.
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Old 21st March 2011, 11:21 AM   #3
AndrewT is online now AndrewT  Scotland
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Why are R1 and R2 both in there?
Is something missing?
Why has you used a remote server to store the pic?
We will lose it when image shack decides to break the link.

Attach a compressed, appropriate resolution pic to your post.
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Old 21st March 2011, 09:38 PM   #4
ywara is offline ywara  United States
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I can't say I'm certain what you're trying to achieve here. You'll get a maximum 2dB rejection across the audio spectrum with full 1A load, and effectively zero rejection at reasonable loads.
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Old 22nd March 2011, 01:32 AM   #5
ywara is offline ywara  United States
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I found the original source of this topology (well, ONE original source) here: Finesse Voltage Regulator Noise! (Fig. 2)

Basically, the OP's circuit needs a PNP as the high-current shunt transistor.

The suggested PNP darlington pair wasn't too much fun to bias with only 0-5V to play with, so I gave the 2n4403 a shot. With proper biasing you can get around 18dB rejection at 120Hz. It also seems incredibly sensitive to the surrounding components, especially R1/R2. It doesn't seem terribly sensitive to differing loads.

It's a pretty useful topology, but with temperature drift and component tolerances potentially wreaking havoc on its ability to reject high frequencies, it might just be a waste of power.
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