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Low Noise 5V Reg
Low Noise 5V Reg
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Old 20th March 2011, 07:19 PM   #1
FOXYE is offline FOXYE
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Default Low Noise 5V Reg

What do you think about the following circuit:


Last edited by FOXYE; 20th March 2011 at 07:22 PM.
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Old 20th March 2011, 07:56 PM   #2
Ken Newton is offline Ken Newton  United States
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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, 12:21 PM   #3
AndrewT is offline 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.
regards Andrew T.
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Old 21st March 2011, 10:38 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, 02:32 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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