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sounds great!

often a pot will develop a noisy wiper contact over time. If you decide to bypass the adjustable lower resistor, say with a ceramic cap, you need to also bypass the two 66M too, or probably better to just bypass the regulated HV out, as is normally done. The reason is that during startup the bypass cap on the lower resistor makes it look instantaneously like much less than 1M to 3.2M, and the instantaneous multiplied output is large. A good value bypass on the output should take care of that output transient though.

rogerw

Roger et al:

from the Vcc rail down: 1M, 66M, 66M, 1M? and 2.2M trimmer pot
Same Mosfets 2SK3563, 2sc3311? and 5.1V zener. Circuit works well and has a nice adjustable range.

P

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Good! And I was beginning to think it pretty good too!

I mentioned a slight possible improvement by compensating the base currents of Q1 and Q2. In the enclosure, the BJT Qx replaces the diode shunt on Q2 and function remains otherwise the same, but the Q1& Q2 base currents are supplied by Qx and taken from the most convenient 15V point....... Therefore the base current no longer give any error in the multiplying resistors. However, I think this will drop the nominal output voltage slightly and improve unit to unit variation slightly, but will not improve regulation much.

BTW, the Mosfets (vs the BJTs) simply provided more error voltage to be multiplied up, which should have resulted in a higher output voltage before than after the BJTs. So then tweaking up the two 28Meg resistors (or whatever combination you used) will give you an appropriate 900+ volts free of as much circuit error than before.

Qx may not improve overall performance noticeably, and you may already be exceeding expectations, since (890-882)/886 ~ +/-1% regulation over that span, not bad.

rogerw

Roger

Not many data points. Both circuits use the same mosfets, BJT are 2sc3311. Zeners are both 5.1V from the lot.
Dropper resistor is 1M, load is a 1G ohm DVM. input Vcc varied from 950~ 1100V
All mosfet varied from 842~ 884V
bjt/mosfet hybrid varied from 882~ 890V
You were right!

Still think this circuit will be a great addition for people who have geiger counters with a fixed HV and they want to lower the HV when using a different gm tube or a scintillator probe.


P

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Roger:

I noticed a weird behavior with the BJT-Mosfet version. I can set the voltage to 900V, and as I raise in the input significantly past 900V, the regulated voltage drops.
I wondered if the BJT's had enough bias or if the Vgs was high enough to be stable. I reduced the two 66M ohm resistors to 44 Mohms each. Same behavior.
Then I reduced the 44M to 22M and still the same.? I wonder why ? I? checked the voltage across the 1M resistor between the bjt and the lower fet. 18V~ 24V
Hmmh I didn't check the voltage across the 5.1V zener ? May be it doesn't get enough current? to be stable?

?

Will need to check tonight, again

p

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Geo:

?its the circuit that Roger posted.

Cliff, is Doug still active?

Geo

Dear Lenox, et al.;

All this, plus more, should be found in the Doug Moore Archives
in the files section.

~Cliff


***

Dear Lenox, et al.;

See further below for a replacement attached PDF (without all of
the gibberish) titled:

Re [GeigerCounterEnthusiasts] PRI 111B - Inverter [1 Attachment].pdf

Thanks.

~Cliff

***

Dear Lenox, et al.;

This is what I found in my archives. Thanks.

~Cliff

***

Roger et al:

from the Vcc rail down: 1M, 66M, 66M, 1M? and 2.2M trimmer pot
Same Mosfets 2SK3563, 2sc3311? and 5.1V zener. Circuit works well and has a nice adjustable range.

P

Roger

Not many data points. Both circuits use the same mosfets, BJT are 2sc3311. Zeners are both 5.1V from the lot.
Dropper resistor is 1M, load is a 1G ohm DVM. input Vcc varied from 950~ 1100V
All mosfet varied from 842~ 884V
bjt/mosfet hybrid varied from 882~ 890V
You were right!

Still think this circuit will be a great addition for people who have geiger counters with a fixed HV and they want to lower the HV when using a different gm tube or a scintillator probe.


P

Roger:
?My explanation was poor. I had to change the dropper resistor from 1M to 4.7M, due to the weaker regulation of the BJT+ Mosfet vs the all Mosfet version.
I will cobble it up in a few minutes and report back.

P

Your mind-sim works on Micro-Cap
had to increase the dropper resistor from 1M to 4.7M to get a flatter regulation zone.
so the impedance is higher in this circuit than with all MOSFETS ?
P

Roger:

?The 330V "zener"? were likely a ESD protection device. They work as advertised but I? never liked them as they fail. Either open or go to a low impedance.?
I can't remember their temperature coef, but they weren't designed for an accurate knee.
I was using them from various manufacturers for I/O port protection.?
I think someone else a few years ago had suggested them.?
If they fail going low impedance the poor HV supply or dropper resistor. IF they fail open then the pmt or gm tube gets stressed.

P

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Or, perhaps just vary the 1M resistor...... as it gets larger the multiplication ratio to the output becomes lower.

rogerw

Adjustable, yes. I would look at varying the voltage which is currently presented in the circuit by the zener...... Make this a variable voltage. Put a bypass cap on it too to suppress any potentiometer noise, which would be multiplied up at the output.

Yes, the HV Zeners do require sorting to match the voltage at a given current. I used a breadboarded cd V-700 style circuit to sort some 330V nominal Zeners into sets of 3 to give 900 to 930V. I thought it worked ok in a 700..... but if you tried t put that on a HV supply that can source much more current it would go closer to 330V nom x3 = 990Vnom..... not good.

rogerw

On 3/28/2022 12:31 PM, peter via groups.io wrote:

Roger:
?Yes.
But its my fault for not explicitly stating that my interest in the zener multiplier circuit( Codatron) is that I was thinking about using it in devices other than the CDV-700's.
1) I had poor luck in using surplus high voltage zeners. I bought a few bags of ~ 90V zeners but knee wasn't consistent. It was a bother to get the string to regulate at 900V.?
It also wasn't easily adjustable.
2) I had poor luck in using a resistive divider to make a properly regulated supply. I often got ripple due to the time constant of the feedback network, and also its susceptibility to noise as it was high impedance.
?I would add capacitance to cure the noise, but then I would get low frequency ripple.?

I was thinking that a shunt regulator while not efficient may not have ripple issues (2).
Or more likely? is it that I want something to tinker with.
I can also think of cases were I don't want to permanently change the voltage of my CDV-700 or some other device? and I could use an external shunt regulator.
I believe that this shunt regulator can be made easily adjustable so I could adjust the hv easily for temporary uses ?

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.