开云体育

1) So, in a Lionel the primary "flyback" voltage should be about 15.5V peak. Then after a diode drop and limited by the loading of the one-shot pulse detector on the -15V line. This -15V is regulated in the primary when the 900+ shunt regulator pulls energy in the secondary (and which energy is sucked from the primary....), ergo regulation on both ends of the transformer.

And in the similar ENi it is Zener regulated in the primary to 15.5V, ergo regulated in the secondary too, without a secondary shunt regulator.

2) I think I asked the earlier question without much clarity in my own mind..... Let me re-phrase:

In a Lionel with the secondary shunt regulation in place, what is the secondary winding peak voltage? 1350V?

In an ENi with the primary shunt regulation in place, what is the (unloaded, as is) secondary winding peak voltage? also 1350V, perhaps?

If 1350V is the right number, that suggests to me a windings ratio of 1350/15.5 = 87.? Off the top of my head, I think I was using ratio=77 2+ years ago..... which would be 1200V peak secondary.

I might go do some sims later with that.

rogerw

Yes I have measured totally unregulated rectified , and no that's not it. 1350 is where I pre regulate the made-from-CDV-700-transformer bias supplies for use in and with shop made testing equipment. Without that, it is much higher, too much in fact, probably the main cause of internal arcing/failure of them in the CDV-700's. Nothing on that PCB can withstand 2kV+

This is why when doing a HV rectifier upgrade, replace Corotron (if present, ENi has none) or add the Zener stack FIRST, check it for working, THEN replace the diode.

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 3:12:31 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Geo,

1) have you ever measured an unregulated HV output , after rectification but without Shunt Regulator loading, of a Vic/Lionel/ENi with a 1G meter?

?Is that the 1300V figure you used earlier?

2) The Vic 6/6A manual on page 4 says this will be about 1100V, but that is likely not open-circuit but rather loaded in-circuit.

rogerw

On 4/7/2022 2:55 PM, Geo Dowell wrote:

That tracks with bench measurements gentlemen, I'm seeing full rated V at 1000 M Ohms load and 1 kV DC, but not at 10,000 M Ohms.

Now on to the next measurement which requires an electrostatic Voltmeter.

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 2:33:36 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Ah! Excellent! Down to 1uA with 10uA being comfortably on the curve, and that is a 1/2Watt Zener which is the most common kind I see.

I notice the Zener (or Avalanche) voltage increases linearly up to about 1mA, then increases at a higher rate, no doubt due to extrinsic series resistance in the bulk material of the chip. I wonder why they spec operation in the tables at 5mA?

rogerw

On 4/7/2022 2:25 PM, peter via groups.io wrote:

Roger et al:
?figure 1 in the attached Rohm spec sheet show? current vs voltage for their various zeners.

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

Virus-free.

-- 
rogerw
On the Catclaw
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.

peter <epkoncept@...> added folder /Components/Zeners

开云体育

Geo,

1) have you ever measured an unregulated HV output , after rectification but without Shunt Regulator loading, of a Vic/Lionel/ENi with a 1G meter?

?Is that the 1300V figure you used earlier?

2) The Vic 6/6A manual on page 4 says this will be about 1100V, but that is likely not open-circuit but rather loaded in-circuit.

rogerw

That tracks with bench measurements gentlemen, I'm seeing full rated V at 1000 M Ohms load and 1 kV DC, but not at 10,000 M Ohms.

Now on to the next measurement which requires an electrostatic Voltmeter.

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 2:33:36 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Ah! Excellent! Down to 1uA with 10uA being comfortably on the curve, and that is a 1/2Watt Zener which is the most common kind I see.

I notice the Zener (or Avalanche) voltage increases linearly up to about 1mA, then increases at a higher rate, no doubt due to extrinsic series resistance in the bulk material of the chip. I wonder why they spec operation in the tables at 5mA?

rogerw

On 4/7/2022 2:25 PM, peter via groups.io wrote:

Roger et al:
?figure 1 in the attached Rohm spec sheet show? current vs voltage for their various zeners.

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

Virus-free.

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

开云体育

Ah! Excellent! Down to 1uA with 10uA being comfortably on the curve, and that is a 1/2Watt Zener which is the most common kind I see.

I notice the Zener (or Avalanche) voltage increases linearly up to about 1mA, then increases at a higher rate, no doubt due to extrinsic series resistance in the bulk material of the chip. I wonder why they spec operation in the tables at 5mA?

rogerw

Roger et al:
?figure 1 in the attached Rohm spec sheet show? current vs voltage for their various zeners.

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

开云体育

The winding ratio is the square root of the ratio of the inductances, so the secondary (measured with the two primary's open circuit) is probably in the several Henry region.......

I did come up with numbers I used in simulations, but with the Zener String Shunt Regulator at the output it was no so critical what UnRegHV was open-circuited........

I have never seen specs anywhere either.

Parenthetically, I do recall seeing inductance specs on the Vic transformer used in the GM pulse detect One Shot (which use to be called a Blocking Oscillator). Or was it just coil resistances I saw???? Don't recall....

rogerw

"

Have you ever seen a spec on the windings ratio(s) of the HV transformer for Vic/Lionel/Eni? (OR the inductances, from which the ratios can be calculated?) I tried (over 2yr ago) to measure the inductances.... worked fine on the primary's but my instrument was not stable on the secondary....)

rogerw"

No but they go from 3V to 900V in one step, and those secondary wires are very thin indeed. Never bothered to measure the inductances but?could if it was needed. Had to measure the resistance of the secondary for an overseas friend yesterday, 3730 Ohms from memory. Maybe I can get him to mike the diameter, he did take it apart to try to find the break. Or maybe some member here has a dead one to check wire gauge? That info would be good to have because it's sure to come up again. Those CDV-700 transformers are getting really scarce, as they age out.

Geo

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 2:01:48 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

1) Yes, I think so, but 10uA makes me much more comfortable. At 1uA I would expect it is low in the knee. At 10uA I would suspect it is high in the knee. That is all I know about that: suspicions based on simulations.

2) No spec I have ever seen. You would prefer the smallest (1/8 or 1/4Watt) Zener wattage? in order to be the smallest junction area so that current density is as high as possible.

3) yes, and that is why I was excited by that 2uA OpAmp. Essentially to duplicate the internal LM431 configuration but with very low current demand. But every attempt I have made to use it in simulation has oscillated. Too much phase lag thru the feedback? loop. I tried to frequency compensate to no avail. I also tried a similar higher gain-bandwith and 20uA version. No dice. If I kept going up in current consumption I assume I would find a sufficient phase margin for the loop, but that idea is on indefinite hold.

I like the Good Enough circuit just fine. What Peter showed this morning......

I also think I would like to pursue that same regulation idea, but in the LV primary, as you have suggested.

Have you ever seen a spec on the windings ratio(s) of the HV transformer for Vic/Lionel/Eni? (OR the inductances, from which the ratios can be calculated?) I tried (over 2yr ago) to measure the inductances.... worked fine on the primary's but my instrument was not stable on the secondary....)

rogerw

On 4/7/2022 1:29 PM, Geo Dowell wrote:

Let's? skip that for now.?

Will a single series Zener, say 100V, operate if the supply is limited to 1 uA by the load resistance?

Is there a spec for that?

We were talking about the LM431 the other day and you both correctly pointed out it needs 1 mA to operate, but what does a Zener need to operate, current wise, assuming there is more than adequate V present to break it over?

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 12:02:38 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Geo,

With UnRegHV = 1300V and dropping resistor = 1.8Meg,

No load, 910.00V

Rload = 1G, 909.99V

Rload = 100Meg, 909.86V,

Rload = 10Meg, 909.01V.

If one were to measure on the other side of the 3.3Meg resistor going up the cable to the GM tube, a very different result would ensue. 1G would be very handy! But, if ne knows the numbers, one can calculate from the loaded measurement what the infinite input impedance
scope would have seen

rogerw

On 4/7/2022 11:41 AM, Roger Whatley via groups.io wrote:

good question. I will hazard a MindSim answer, then will do the simulation.

As long? as the loading of the Zener String regulated node does not approach to close to the current flowing into the Zener, it will not drop the voltage too much.

(900+V/1G) << (1300V- 900+V)/1.8Meg? , or,

0.9uA << 222uA

So, the Zener String sees a very negligible change in current with a 1G loading at the anode of the string, since 222uA-0.9uA ~ 221uA is hardly any change. Even if you loaded it down to only 10uA in the Zener string you would not see a lot of change, as it depends on the regulation curve.

(By gosh! you just told me how I can measure the regulation curve over voltage with a fixed HV supply! Wallah!)

So, continuing Stream of Thought..... the more interesting case is not UnRegHV = 1300V but what if only 1000v? Then,

0.9uA << (1000V-900V)/1.8Meg? ,or,

0.9uA << 55.5uA

Still lots of room to load it and leave 10uA or more for the Zener String.

I actually think (I think, I am not sure) that the typical HV Generator is going to be current limited by the time it gets to maybe 20uA at some UnRegHV voltage well below the OpenCircuit voltage....... in that case:

0.9uA << 20uA (or whatever the current-limited number is. When I designed the Lionel and Vic HV Generators for lower power consumption, I shot for a 10uA output current.)

rogerw

On 4/7/2022 11:05 AM, Geo Dowell wrote:

I don't know, never saw that listed either.

Meantime do this simple sim for me.

+1300V DC to cathode of a Zener ( can be via? 1.8M Ohm res. or direct in this case only). Any Zener. On the other side of the Zener, a 1000 M Ohm load to ground(-).

What V does the infinite impedance scope probe show at the junction of anode and 1G load?

I am not good with simulators, but physically do this on the workbench every day.

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 10:46:43 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Geo,

Ok, I got a bit curious...... If a Zener String of 900+V can change +/-40V over -25degC to +75degC, what did the original Corotrons do?

IE, a Victoreen GV3A Corotron?

It turns out that this Vic catalog does not give a spec on the basic GV3A used, but does give temp info on the "High Temperature" version:

? page 15

So, you can see an original 900V High Temp Corotron only varied 16V from -65degC to 150degC...... pretty impressive I think.

We are replacing these things with Zener Strings with relatively high positive tempco......

I think the ultimate economic answer is to regulate in the primary circuit, just as you suggested, and as ENi did, and depend on the fixed transformer secondary ratio to get the regulated HV, and to temperature compensate the primary along with an adjustable trim capability.

rogerw

On 4/7/2022 9:58 AM, Roger Whatley via groups.io wrote:

1) yes, could be multiple junctions.

2) You have an exray machine?

3) We used to "de-pot" plastic packaged IC chips with acid to expose the die in the package, to examine under a microscope, photograph, etc. trace circuits that way....... might be hard to do with an axial lead diode.... I don't know.

rogerw

On 4/7/2022 9:49 AM, Geo Dowell wrote:

I've always assumed the multiple junction idea, because in practice the higher voltage rectifier diodes get longer and longer. Ones for a 100kV stack are a good 6 inches long each. Don't know, just guessing. Will have to X-Ray one, but when it's out of the X-Ray machine how to do that?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 9:43:53 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Well, the answer to your first question is: I am not sure, but I think it is probably just very lightly doped silicon pn junction. The light doping (and perhaps playing around with the doping profile - Its just fizzicks, ya' know!) gives higher reverse breakdown voltage. And the lighter doping also gives a higher bulk resistivity such that the extrinsic series resistance is higher than a LV diode, so higher forward drop at least is due to higher series resistance.

This is a "no-cost" contract. It is going to take an infinity of diodes!

rogerw

On 4/7/2022 9:32 AM, Geo Dowell wrote:

Question Roger, are HV (like 8kV) low current diodes a stack of normal PN junctions inside? or are they a single special PN junction? What I do measure is higher and higher Fwd V drop as the V (sub) max rating increases.

By the way, if you only need that many PN junctions to achieve thermal cancelling, try switching to Schottkey diodes. That will double or tripple the parts count. This is a "cost-plus-contract", right?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 9:06:12 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Geo,

Sure, enclosed, but I have already modified the Zener String with a temperature compensation scheme that will be somewhat familiar to the discerning eye. I am NOT suggesting this circuit for a build, merely playing around with ideas!

So, if I measure the voltage of the top of that Zener String alone, it is a nominal 788V at 25degC, and 821V at 75degC, and 754V at-25degC. That is a +67V change over 100degC or about +0.67V/degC tempco. (parenthetically, the original full Zener String was about +/-40V.)? If I compensate that with the negative tempco of a Vbe which is about -2.2mv/degC,

I need 0.67V/2.2mV = 304 Vbes...... whew! That's a lot of diodes!

Instead the BJT circuit is multiplying the sum of Q1&Q3 Vbe by 129 = 258Vbe's. All I can say about the difference from calculated is that the actual tempco of the bjt's is in the model somewhere and differs from my Mindsim approximation. And btw, the pnp BJT Q2 is a local feedback trick that is "fortifying" Q1...... without Q2 you get weak knee, with Q2 you get a sharp knee. Q2 and R3 can be removed and the circuit still functions but regulation suffers.

Anyway, the second enclosure shows the regulation performance over temperature. When I expand the scale I can see the regulated voltage at 906V nominal 25degC, 908V at 75degC, and 905V at -25degC.

So, for one thing, this whole exercise begs a question: Who lets their GM Counter get THAT hot or cold? I think that is a philosophical question.... If a GM Counter fell in the forest, in the winter up north, and there was not a woman there to turn it on, does it really matter? Does it even exist???

rogerw

On 4/7/2022 3:36 AM, Geo Dowell wrote:

Roger, show schematic of sim?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Wednesday, April 6, 2022 9:28:41 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Well I just simulated something I had not yet thought to do...... I simulated a Zener string.

Yeah, it worked...... ha!

Largest Zener I could find in the model library was 36V so I strung enough of those to make about 890V nominal with a 3.3Meg dropper resistor. Its regulation is very flat only rose about 3V from 1000V to 1200V input. That as good as my Penultimate Way-Good Cascode Shunt Regulator can do, and far less complex.

But guess what? over temperature it sucks big wind! +/-40V from -25 to 25 to 75degC! The Penultimate only varies about +/-3V over that temp range (overkill).

But the Good Enough Cascode Shunt Regulator, with its temperature compensation scheme, only varies less tha +/-5V. Regulation varies less than 10V from the knee to 950 to 1200V

On 4/6/2022 10:53 AM, Roger Whatley via groups.io wrote:

Peter,

Minor change, I noticed after I posted the note below that I had not specified the second BJT in the Darlington. The enclosed schematic is corrected and now the simulation predicts about dead-nuts on for the tempco of the output. Other than that, same comments as below. I think this is the best "good enough" cascoded shunt regulator.

rogerw

On 4/6/2022 10:40 AM, Roger Whatley via groups.io wrote:

Peter,Enclosed is a schematic of my suggestion below. That is an 8.2V Rohm Zener chosen for tempco to cancel the negative tempco of two Vbe's. It is slightly too positive in the result but quite "good enough." You willr just get much flatter regulation with the Darlington pair and that can be had in a single package.

Of course, depending on the Vcemax spec of your cascode MOSFET, you might have only one cascode instead of two..... That will not make a noticeable difference except to breakdown.

rogerw

On 4/6/2022 8:32 AM, Roger Whatley via groups.io wrote:

Peter,

I realize that circuit described below might be "good enough," but realize that making that one BJT a Darlington pair is a significant improvement to the regulation. You can even get the Darlington in one transistor package, of course, cheap.

As UnRegHV increases, the current in the BJT necessarily increases in order to regulate the loop. For every extra 0.1uA of extra base current required, the voltage drop in the feedback resistors (66M + 66M + 1M) goes up 0.1uA*(66M+66M+1M) = 13.3V and thus regulation suffers. The BJT current easliy goes from less than 10uA to over 200uA, thus the base current might go up by a worst-case of as much as 1uA, giving a 133V change in the output. So that is the motivation for the Darlington.

(In case anyone wonders, why not an FET instead of a BJT, that WAS the original circuit and it suffers worse circuit errors.....)

The next big error is that as the BJT current increases with UnRegHV increases, so does Vbe and Vz increase. Those are the motivations for subsequent circuit complications and resulting in the Penultimate Way-Improved version..... it is overkill, I know, to the requirement, but by simulating those improvements I gain insights as to just what the remaining errors were. And it was fun!

My take is that your present circuit, but with a Darlington Pair, will be "good enough" and if it were a purpose-built Darlington in one three-lead package, no more expensive or even board-space than a single BJT.

Of course, a single Zener voltage may be chosen to match the negative tempco of two Vbe's. Again, no extra expense or board space. (Off the top of my head, I am thinking about 8V Zener for +4mV/degC?)

rogerw

On 4/4/2022 10:33 PM, peter via groups.io wrote:

Roger:
?back to the circuit you posted in message #300
Simple cascode, with only 1 npn tr + 2 mosfets.
Since I found the 2SK3265, I removed the 2nd mosfet so its very basic circuit.
66Meg, two 1 Meg, 100k+ 2.2M trimmer , 5.1V zener, 2SK3265, 2SC3311
Set trimmer for 900V, Vary input from 950~ 1150, output only varied 5V or less.
Heated the circuit with a hair dryer, got it up from 25C to about 60C, voltage rose may be 5 or 6 volts. Good enough for me!
Time to make it small enough to stuff inside my CDV-700 !
It on the LHS of the attached jpg, circuit in message #300 is on the RHS
P

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

Virus-free.

-- 
rogerw
On the Catclaw
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.

-- 
rogerw
On the Catclaw
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.

-- 
rogerw
On the Catclaw
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.

-- 
rogerw
On the Catclaw
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.

-- 
rogerw
On the Catclaw
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.

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

开云体育

1) Yes, I think so, but 10uA makes me much more comfortable. At 1uA I would expect it is low in the knee. At 10uA I would suspect it is high in the knee. That is all I know about that: suspicions based on simulations.

2) No spec I have ever seen. You would prefer the smallest (1/8 or 1/4Watt) Zener wattage? in order to be the smallest junction area so that current density is as high as possible.

3) yes, and that is why I was excited by that 2uA OpAmp. Essentially to duplicate the internal LM431 configuration but with very low current demand. But every attempt I have made to use it in simulation has oscillated. Too much phase lag thru the feedback? loop. I tried to frequency compensate to no avail. I also tried a similar higher gain-bandwith and 20uA version. No dice. If I kept going up in current consumption I assume I would find a sufficient phase margin for the loop, but that idea is on indefinite hold.

I like the Good Enough circuit just fine. What Peter showed this morning......

I also think I would like to pursue that same regulation idea, but in the LV primary, as you have suggested.

Have you ever seen a spec on the windings ratio(s) of the HV transformer for Vic/Lionel/Eni? (OR the inductances, from which the ratios can be calculated?) I tried (over 2yr ago) to measure the inductances.... worked fine on the primary's but my instrument was not stable on the secondary....)

rogerw

Let's? skip that for now.?

Will a single series Zener, say 100V, operate if the supply is limited to 1 uA by the load resistance?

Is there a spec for that?

We were talking about the LM431 the other day and you both correctly pointed out it needs 1 mA to operate, but what does a Zener need to operate, current wise, assuming there is more than adequate V present to break it over?

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 12:02:38 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Geo,

With UnRegHV = 1300V and dropping resistor = 1.8Meg,

No load, 910.00V

Rload = 1G, 909.99V

Rload = 100Meg, 909.86V,

Rload = 10Meg, 909.01V.

If one were to measure on the other side of the 3.3Meg resistor going up the cable to the GM tube, a very different result would ensue. 1G would be very handy! But, if ne knows the numbers, one can calculate from the loaded measurement what the infinite input impedance
scope would have seen

rogerw

On 4/7/2022 11:41 AM, Roger Whatley via groups.io wrote:

good question. I will hazard a MindSim answer, then will do the simulation.

As long? as the loading of the Zener String regulated node does not approach to close to the current flowing into the Zener, it will not drop the voltage too much.

(900+V/1G) << (1300V- 900+V)/1.8Meg? , or,

0.9uA << 222uA

So, the Zener String sees a very negligible change in current with a 1G loading at the anode of the string, since 222uA-0.9uA ~ 221uA is hardly any change. Even if you loaded it down to only 10uA in the Zener string you would not see a lot of change, as it depends on the regulation curve.

(By gosh! you just told me how I can measure the regulation curve over voltage with a fixed HV supply! Wallah!)

So, continuing Stream of Thought..... the more interesting case is not UnRegHV = 1300V but what if only 1000v? Then,

0.9uA << (1000V-900V)/1.8Meg? ,or,

0.9uA << 55.5uA

Still lots of room to load it and leave 10uA or more for the Zener String.

I actually think (I think, I am not sure) that the typical HV Generator is going to be current limited by the time it gets to maybe 20uA at some UnRegHV voltage well below the OpenCircuit voltage....... in that case:

0.9uA << 20uA (or whatever the current-limited number is. When I designed the Lionel and Vic HV Generators for lower power consumption, I shot for a 10uA output current.)

rogerw

On 4/7/2022 11:05 AM, Geo Dowell wrote:

I don't know, never saw that listed either.

Meantime do this simple sim for me.

+1300V DC to cathode of a Zener ( can be via? 1.8M Ohm res. or direct in this case only). Any Zener. On the other side of the Zener, a 1000 M Ohm load to ground(-).

What V does the infinite impedance scope probe show at the junction of anode and 1G load?

I am not good with simulators, but physically do this on the workbench every day.

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 10:46:43 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Geo,

Ok, I got a bit curious...... If a Zener String of 900+V can change +/-40V over -25degC to +75degC, what did the original Corotrons do?

IE, a Victoreen GV3A Corotron?

It turns out that this Vic catalog does not give a spec on the basic GV3A used, but does give temp info on the "High Temperature" version:

? page 15

So, you can see an original 900V High Temp Corotron only varied 16V from -65degC to 150degC...... pretty impressive I think.

We are replacing these things with Zener Strings with relatively high positive tempco......

I think the ultimate economic answer is to regulate in the primary circuit, just as you suggested, and as ENi did, and depend on the fixed transformer secondary ratio to get the regulated HV, and to temperature compensate the primary along with an adjustable trim capability.

rogerw

On 4/7/2022 9:58 AM, Roger Whatley via groups.io wrote:

1) yes, could be multiple junctions.

2) You have an exray machine?

3) We used to "de-pot" plastic packaged IC chips with acid to expose the die in the package, to examine under a microscope, photograph, etc. trace circuits that way....... might be hard to do with an axial lead diode.... I don't know.

rogerw

On 4/7/2022 9:49 AM, Geo Dowell wrote:

I've always assumed the multiple junction idea, because in practice the higher voltage rectifier diodes get longer and longer. Ones for a 100kV stack are a good 6 inches long each. Don't know, just guessing. Will have to X-Ray one, but when it's out of the X-Ray machine how to do that?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 9:43:53 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Well, the answer to your first question is: I am not sure, but I think it is probably just very lightly doped silicon pn junction. The light doping (and perhaps playing around with the doping profile - Its just fizzicks, ya' know!) gives higher reverse breakdown voltage. And the lighter doping also gives a higher bulk resistivity such that the extrinsic series resistance is higher than a LV diode, so higher forward drop at least is due to higher series resistance.

This is a "no-cost" contract. It is going to take an infinity of diodes!

rogerw

On 4/7/2022 9:32 AM, Geo Dowell wrote:

Question Roger, are HV (like 8kV) low current diodes a stack of normal PN junctions inside? or are they a single special PN junction? What I do measure is higher and higher Fwd V drop as the V (sub) max rating increases.

By the way, if you only need that many PN junctions to achieve thermal cancelling, try switching to Schottkey diodes. That will double or tripple the parts count. This is a "cost-plus-contract", right?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 9:06:12 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Geo,

Sure, enclosed, but I have already modified the Zener String with a temperature compensation scheme that will be somewhat familiar to the discerning eye. I am NOT suggesting this circuit for a build, merely playing around with ideas!

So, if I measure the voltage of the top of that Zener String alone, it is a nominal 788V at 25degC, and 821V at 75degC, and 754V at-25degC. That is a +67V change over 100degC or about +0.67V/degC tempco. (parenthetically, the original full Zener String was about +/-40V.)? If I compensate that with the negative tempco of a Vbe which is about -2.2mv/degC,

I need 0.67V/2.2mV = 304 Vbes...... whew! That's a lot of diodes!

Instead the BJT circuit is multiplying the sum of Q1&Q3 Vbe by 129 = 258Vbe's. All I can say about the difference from calculated is that the actual tempco of the bjt's is in the model somewhere and differs from my Mindsim approximation. And btw, the pnp BJT Q2 is a local feedback trick that is "fortifying" Q1...... without Q2 you get weak knee, with Q2 you get a sharp knee. Q2 and R3 can be removed and the circuit still functions but regulation suffers.

Anyway, the second enclosure shows the regulation performance over temperature. When I expand the scale I can see the regulated voltage at 906V nominal 25degC, 908V at 75degC, and 905V at -25degC.

So, for one thing, this whole exercise begs a question: Who lets their GM Counter get THAT hot or cold? I think that is a philosophical question.... If a GM Counter fell in the forest, in the winter up north, and there was not a woman there to turn it on, does it really matter? Does it even exist???

rogerw

On 4/7/2022 3:36 AM, Geo Dowell wrote:

Roger, show schematic of sim?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Wednesday, April 6, 2022 9:28:41 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Well I just simulated something I had not yet thought to do...... I simulated a Zener string.

Yeah, it worked...... ha!

Largest Zener I could find in the model library was 36V so I strung enough of those to make about 890V nominal with a 3.3Meg dropper resistor. Its regulation is very flat only rose about 3V from 1000V to 1200V input. That as good as my Penultimate Way-Good Cascode Shunt Regulator can do, and far less complex.

But guess what? over temperature it sucks big wind! +/-40V from -25 to 25 to 75degC! The Penultimate only varies about +/-3V over that temp range (overkill).

But the Good Enough Cascode Shunt Regulator, with its temperature compensation scheme, only varies less tha +/-5V. Regulation varies less than 10V from the knee to 950 to 1200V

On 4/6/2022 10:53 AM, Roger Whatley via groups.io wrote:

Peter,

Minor change, I noticed after I posted the note below that I had not specified the second BJT in the Darlington. The enclosed schematic is corrected and now the simulation predicts about dead-nuts on for the tempco of the output. Other than that, same comments as below. I think this is the best "good enough" cascoded shunt regulator.

rogerw

On 4/6/2022 10:40 AM, Roger Whatley via groups.io wrote:

Peter,Enclosed is a schematic of my suggestion below. That is an 8.2V Rohm Zener chosen for tempco to cancel the negative tempco of two Vbe's. It is slightly too positive in the result but quite "good enough." You willr just get much flatter regulation with the Darlington pair and that can be had in a single package.

Of course, depending on the Vcemax spec of your cascode MOSFET, you might have only one cascode instead of two..... That will not make a noticeable difference except to breakdown.

rogerw

On 4/6/2022 8:32 AM, Roger Whatley via groups.io wrote:

Peter,

I realize that circuit described below might be "good enough," but realize that making that one BJT a Darlington pair is a significant improvement to the regulation. You can even get the Darlington in one transistor package, of course, cheap.

As UnRegHV increases, the current in the BJT necessarily increases in order to regulate the loop. For every extra 0.1uA of extra base current required, the voltage drop in the feedback resistors (66M + 66M + 1M) goes up 0.1uA*(66M+66M+1M) = 13.3V and thus regulation suffers. The BJT current easliy goes from less than 10uA to over 200uA, thus the base current might go up by a worst-case of as much as 1uA, giving a 133V change in the output. So that is the motivation for the Darlington.

(In case anyone wonders, why not an FET instead of a BJT, that WAS the original circuit and it suffers worse circuit errors.....)

The next big error is that as the BJT current increases with UnRegHV increases, so does Vbe and Vz increase. Those are the motivations for subsequent circuit complications and resulting in the Penultimate Way-Improved version..... it is overkill, I know, to the requirement, but by simulating those improvements I gain insights as to just what the remaining errors were. And it was fun!

My take is that your present circuit, but with a Darlington Pair, will be "good enough" and if it were a purpose-built Darlington in one three-lead package, no more expensive or even board-space than a single BJT.

Of course, a single Zener voltage may be chosen to match the negative tempco of two Vbe's. Again, no extra expense or board space. (Off the top of my head, I am thinking about 8V Zener for +4mV/degC?)

rogerw

On 4/4/2022 10:33 PM, peter via groups.io wrote:

Roger:
?back to the circuit you posted in message #300
Simple cascode, with only 1 npn tr + 2 mosfets.
Since I found the 2SK3265, I removed the 2nd mosfet so its very basic circuit.
66Meg, two 1 Meg, 100k+ 2.2M trimmer , 5.1V zener, 2SK3265, 2SC3311
Set trimmer for 900V, Vary input from 950~ 1150, output only varied 5V or less.
Heated the circuit with a hair dryer, got it up from 25C to about 60C, voltage rose may be 5 or 6 volts. Good enough for me!
Time to make it small enough to stuff inside my CDV-700 !
It on the LHS of the attached jpg, circuit in message #300 is on the RHS
P

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

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On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

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ΜΟΛΩΝ ΛΑΒΕ

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

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The PanDemic is over, but the DemPanic goes on.
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Clay,

Regarding the "stupidly overwhelmed' comment, "I resemble that remark!"

Thank you for your kind appreciation. Peter's latest circuit, posted today, looks very good to me, a balance of cost/complexity and performance. And it can be configured either as a Shunt oe Series Pass Regulator with or without the extra transistor (which can be a HV BJT or HV MosFet).

I was very impressed to find this morning how well a Vic Corotron might regulate, especially over Temperature. And I guess that was a point in the very beginning of this thread!

Our simple Zener Strings are not so hot performance after all!

rogerw

? A bit off my original topic here.? I have a large area diode detector in the collection, nothing to hook it to.? They are commercially available.? I haven't gotten around to doing anything with it unfortunately.? I can't get? to it at the moment.? I'll may post a picture later.? I didn't post my cleaned up Eltronics PR-13 pics because my phone camera has lost the menu to change resolution for some odd reason. I probably disabled too many "sharing features".

? I worked as an X-ray repair tech at my last job.? Medical and Veterinary X-ray at first, then the Medical side split off.? Mostly field portable stuff.? We had a really cool X-ray dosimeter tool that could be configured for different measurement units.? I may have some info on it still in my archives.? It would record the kVp, mAs, and dose from an exposure.? We used it to check the output of the X-ray generators.? The image detectors were basically the reverse of an LCD monitor.? I have some that are delaminating and have image quality issues due to the light not coupling well in the delaminated areas.? it is all at the edges so they are actually still usable.? The took in light in rows and columns.? There was a scintillating sheet married to the detector to capture the light from the exposure.? Getting a good image is somewhat software intensive.? Fun stuff, I loved the technology.? They were just getting into ultrasound when I quit.? I always wore a recording dosimeter and used protective gear.? The dose from a digital image is small, but I sometimes took hundreds of test shots in a day!? Seldom had any recorded dose at the end of the month.

? X-ray generators will tickle a Survey meter, even the portable ones I worked with.? I couldn't get a long enough pulse to for a reading to settle out, but you can get a definite upscale reading.? If I live long enough I will someday hook up a scope and see what I can capture.with a survey meter in a beam path.? The Ion chamber is quick to respond, the metering circuits not so much.? Could be fun.? If I knew another local enthusiast I would have had some motivation to do more with the hobby.? The world is becoming a very lonely place.

? I am glad I shared the info on the Corotron replacement with this topic.? I had been sitting on that planning to do what you guys are doing, but I would have struggled without simulating the circuits.? great work.? I wanted to get it out there in case I get hit by a truck or something.? You guys are doing interesting work, I was always just planning to do a Corotron replacement with low cost and parts count to keep it cheap and simple to build.? You have branched out a bit from that!? There is a Corotron catalog on the logwell site.

? I have been bogged down by my excesses.? I have a large collection of parts from HP and Ericsson surplus and have hit the point where I have so many parts? I can't find what I need and it is easier to buy them.? Stupidly overwhelmed at this point.? I literally have thousands of FETs, some just one, some on reels of 3000!? I have a list of most of what I have, but had not looked up specs on all of them.? Been doing the research and linking FET data sheets to my spreadsheet of parts.? But since I suck at making decisions I now have too many choices to pick from, none are what I thought was going to make the circuit simple.? And I just realized that if I move the parts data all the links will be broken.? Bummer when it comes time to share the list.

Time for a lunch break.

Clay

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I guess if I had finished reading your note, you already said that!

Sorry!

rogerw

looks very good. Q2 may easily need to be HV though.

rogerw

On 4/7/2022 11:45 AM, peter via groups.io wrote:

Roger and Geo:
?tried a simple series regulator
R6 is a dummy load of 100M( manually swept it down to 10k and seems to work)
Q2 is a cheapo 2n3904 and so are Q1 and Q3?
choice of Q2 depends on how much voltage needs to be dropped.?
If only 30V needs to be removed, ok.?
If 200V needs to be removed, need to pick a higher voltage tr for Q2
P

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The PanDemic is over, but the DemPanic goes on.
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Virus-free.

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The PanDemic is over, but the DemPanic goes on.
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looks very good. Q2 may easily need to be HV though.

rogerw

Roger and Geo:
?tried a simple series regulator
R6 is a dummy load of 100M( manually swept it down to 10k and seems to work)
Q2 is a cheapo 2n3904 and so are Q1 and Q3?
choice of Q2 depends on how much voltage needs to be dropped.?
If only 30V needs to be removed, ok.?
If 200V needs to be removed, need to pick a higher voltage tr for Q2
P

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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