To good to be true?

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Re: Re: To good to be true?

Steve Eddy said:


Geez, you have to have a user ID and password just to read a message there?

se
Seems to be so. Here is the message:
From: James Bongiorno <sstinc@e...>
Date: Tue Apr 20, 2004 5:30 pm
Subject: Re: [SAE_Talk] ATI Amps

Thanks for the compliment. Actually, that IC regulator in the Thaedra was quite
unique. I have since (after about 30 years) come up with something even better
which is in my Trinaural Processor and will be extensively used in my new
Ambrosia. I call it my "positive" feedback regulator. It's a real gem and very
simple. It is dead quiet and is as stable as a rock and only uses TWO
transistors. Enough for now.
James Bongiorno
:cool:
 
Well you can make a pretty reasonable fixed output LDO regulator with only two transistors, but you do seem some zeners!

The general arrangement shown below works.
 

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Zener Z1 sets a 10V reference at the base of T2.

Initially the output of the regulator is at 0v. The emitter of T2 is low so T2 is on, and current flows through T2 to pull the gate of the P-ch FET T1 down, so that current flows to the output. As the output rises, then at approx Vout = 36v then the emitter of T2 will approach the base voltage, slowly turning T2 off. This in turn starts to turn off T1 in a negative feedback loop, keeping the output regulated.

Vout = V(Z1) + V(Z2) - Vbe(T2). Or near enough.

The Cg-s of the FET is enough to keep it stable, but you normally need another zener (10v or so) across G-S of the FET to prevent Vg-s from getting too high.
 
Hi, Steven,

I like this very much.
The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
I also think analog is kind of "Art" while digitals are "Exact science"
 
djk said:
"Yes, but it really needs a zener to provide a reference voltage in series with the emitter lead of the lower transistor."

Why?

NAD use this type of regulator without a zener.


Sure it'll work as a bodge job, but the temperature stability of the output is atrocious if you only use the Vbe of the sense transistor as the voltage reference. (just Spice it and look at the temperature plots)
 
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