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What limits noise in voltage regulators?

Bandgaps are noisy. Recall the LM723, which had a buried zener and was recognized as one of the lowest noise regulators available.

I spent considerable time looking for a zener model that included noise without success. However, a zener has to be quieter than a bandgap.

Here is a circuit that uses a 1N751 in a variable output voltage regulator.

It has decent frequency response, -28dB at 1mHz, with a slight peak at 6 Hz,

-80dB at 120 Hz, -165dB from 100 KHz to 3 MHz, then falls from there. It probably would be much quieter than the Motorola TL431, and uses standard junk box quality parts.

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The best designs are no accident - sw
Reply to
Steve Wilson
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I made a very significant improvement by moving the source for the main capacitance multipler from Vin to the emitter of the first stage.

The attenuation is now -26dB at 1mHz, -40dB at 10 Hz, -110dB at 120 Hz, and >-160dB from 10KHz to 3Mhz. The effect of sneak paths is reduced by having two transistors in series, and the effect of zener noise is reduced by bypassing with a 100 uF capacitor.

The capacitors are a new product by KEMET: Aluminum Organic Polymer,

100uF 25V, ESR=14mOhms ESL=2.5nh Dia = 6.3mm Height = 5.7mm Part # A768EB107M1ELAE036 $0.47 Qty 1 at Mouser and Digi-Key. Both have stock.

Polymer is the way to go.

The LTspice files are at

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The best designs are no accident - sw
Reply to
Steve Wilson

All your zip files have viruses.

Reply to
Simon S Aysdie

It's not that they did away with it, but they don't properly account for newsgroups not being Google groups. So it is disabled because of inaction by the group administrator as there isn't one. Something about not having permission to view email addresses. Hell, I've not been able to get view email addresses to work for years!

Reply to
Rick C

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Reply to
Rick C

very cool!

Reply to
Simon S Aysdie

Yeah, I like the line, "If you won't take care of us, won't you please, please let us be?"

Reply to
Rick C

I download each zip and check it before posting.

The files are all LTspice ASC and PLT files.

Pretty hard to get a virus in a text file.

Reply to
Steve Wilson

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