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All,

Here is the current state of my self-styled "Way-Improved" version in simulation. That simulation result below is never varying more than about < +/-3V over temp and UnRegHV from 1000V to 1200V (~5V variation). So what might look like one regulation curve is actually 3 curves.

Also, I only have generic NMOS devices for the cascodes, not actual devices modeled there. That shouldn't actually make much difference in that cascode function.... but you never know till you breadboard.

Michael's VN0550N3-G are probably about perfect for the cascodes (Thanks again!).

I could point out again, for clarity, that n-ch cascodes could be either enhancement or depletion MosFets, OR, n-ch JFet, or even npn BJT's (but would need to each be a Darlington pair to avoid base current error). Just as long as it is HV any old n-ch or npn will do!

Cascoding in this manner accomplishes two things:

1) raises effective device output impedance via localized device feedback in the cascode itself, which helps the forward gain of Q1 in driving R1, and,

2) most important here is that it drops voltage down so that Q1 can be low voltage, while its current is passed up in voltage to R1.

Also, using a single Rohm 10V Zener did the temp compensation just about as well as the three 6.2V ones shown, but since the difference in absolute voltage is about half, R5 must be adjusted in half to bring the regulated output back to snuff. No big problem there, and that may be the most economical way to go...... I just like the larger reference voltage because it makes certain other potential errors look smaller.... :-)

rogerw

????

Michael,

?That VN0550N3-G looks to be perfectly suited, thanks! Looks like they only have 28 in stock presently, better make your purchase!

I may order a few too but I will wait till you and Peter (perhaps) get yours.

Yes, depletion mode will work fine in this circuit as csacodes. Only difference is the sign of Vgs, being negative. I have already simulated that, and in fact have looked for a similar n-ch JFET which is also naturally depletion mode.

rogerw

On 4/2/2022 11:10 AM, Michael J Emerson wrote:

Roger / Peter

I have been following this thread with much interest. Thank you

I looked for low current MOSFETs and found this one that is through hole and affordable : VN0550N3-G? $1.75 each

Before I purchase I would like your input

also -

the MOSFET post below is a depletion mode - will that work? Following along I thought the circuit required enhancement mode.

Thank you for your help

michael j

On 4/2/2022 10:06 AM, Roger Whatley wrote:

Peter,

Here is a HV n-ch MosFet? that looks very promising:

If it can be had in a thru-hole package......

rogerw

On 4/2/2022 8:27 AM, Roger Whatley via groups.io wrote:

Peter,

1) Well, I don't have an enviro chamber either..... in fact I don't even have a breadboard!? :-)

2) I thought the 2sk3563's had finally worked ok in earlier versions?

3) Best I found:

They are available at Mouser or Digikey, $2.58 at Digikey. Since it is 1000V only one cascode is needed, but two might still be worthwhile to avoid constant operation near the breakdown voltage (reliability).

4) I could not find any HV MosFet not in a power package like at least a TO-220. This circuit is extremely low power in the MosFets, never exceeding about 1/8 W in the cascodes.

"I don't like it but I guess things happen that way." - J. Cash

rogerw

On 4/1/2022 11:02 PM, peter via groups.io wrote:

Roger:
?I don't have an environmental chamber at home, I only have a hair dryer!.
I didnt temperature test. I did cobble the circuit using three 5.1V zeners( I did pick up the 6.2V Rohm zeners but didn't use them yet)
I think the over size MOSFETs (2SK3563) are causing issues because the regulation is not stiff, it still rises about 100V over 900V as the Vcc raised past 900V and up to 1150V.? Again, if I tie the top end of the resistor divider to Vcc instead of the drain of the upper mosfet, regulation improves, and I see only about a 25V increase.?

I got to look for some smaller 100mA size 1000V mosfets. Unfortunately I haven't found anything that uses every remotely close in the e-recycling bins! Most items have mosfets in the 200~ 500V range at several to tens of amps.

P

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rogerw
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The PanDemic is over, but the DemPanic goes on.
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-- 
rogerw
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ΜΟΛΩΝ ΛΑΒΕ

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

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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