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Attached is a simulated performance curve for the Darlington BJT Cascoded HV Regulator. As you can see, when UnRegHV goes from 1000V to 1200V, the RegHV output goes from 904V to 918V. I think that is about comparable to Zener strings I have used to regulate the same.

In fact if you think about it, this circuit derives its reference in the same way but with a zener at low voltage whose current will also increase proportionately as UnRegHV is increased.... hence the regulated voltage goes up even with perfect circuit feedback regulation because the zener voltage goes up.

Still, this is very good performance, very adequate to the task, and affords easy oppty for adjustment.

Also, if there is any reliability issues with HV Zeners in a string, this circuit may alleviate that. But a circuit failure here might have the same effect as a circuit failure in the zener string.

I ramped the simulated circuit from UnRegHV = 0V to 1200V and did not see any HV on the BJTs that might cause breakdown during power-on transient, which if it occurs can shorten the life of the BJT. So that seems safe......

rogerw

of course you can use any zener to cobble it up for functionality, and adjust the bottom resistor for correct output. 6.3V zener is just for the tempco.

rogerw

On 4/1/2022 12:34 AM, peter via groups.io wrote:

Roger:

Thank you again. Of course i will give this latest circuit a try.?
Hopefully, nothing exciting will happen this weekend, so I can tinker away.
I don't have any 6.3V zeners handy at home. I will swing by the parts cabinet at work tomorrow and get couple so I can cobble this circuit up.
P

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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.