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Peter,

If you decide to try this Way-Improved Cascoded Shunt Regulator, I will suggest the following, same circuit as before but with resistor-value changes.

BTW, by taking the voltage to the 600K/Zeners from the Source of M3, an additional help is occurring. As UnRegHV goes up and the current drawn by Q1 increases through M3, Vgs3 gets larger so that node drops in voltage somewhat. Thus the Zener current drops somewhat and this helps hold the overall reference voltage (= 3*Vz + 3Vbe) more constant as Vbe1 increases with current.

Voila!? (wallah!)

OK, found it. Interesting.......

Mindsim tells me that doing that will reduce the feedback regulation of the voltage by essentially reducing the forward gain of the "opamp." By the "opamp," I mean the BJT whose collector current drives the load resistor which you are calling the "dropper resistor." That voltage gain = gm*Rload is the forward gain, and the feedback gain = (R1)/(R1+ R2 + R3 + R5). By taking the feedback point at less than the full forward gain, the loop gain is reduced, hence regulation is reduced.

It may well be that while you are introducing more loop gain error you are also compensating some other circuit error.....

That's my mindsim guess...

In the meantime check out my last posted circuit..... ("Even I was amazed" was a recurring joke-line in my old circuit design group in the 1980s. We were Designers once, and Young.....)

rogerw

On 4/1/2022 10:34 AM, peter via groups.io wrote:

Roger
Please see the attachment in message #299
After my boo-boo, which caused the voltage to sag, it was feedback. So I changed the amount of feedback until the voltage would not rise or fall much.

I will check spec of the zeners I have access to.
I try to find something that is close to -2.2mV/C at low current.
P


P

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rogerw
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-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.