开云体育

Now that I think about it some more, I think all the tube shunt regulators (or replaced with diode string) have a "dropping resistor" from the UnRegHV and then followed by another high value, say 1Meg to 3Meg, resistor to the GM tube. This is because the shunt-regulated node is also a low impedance (well kinda low....). However, the input resistance to the one-shot is not very high,either, depending on design...... I recall in the vicinity of 10K (just looked at a Lionel schematic, its about 22K//18K ~ 9K input resistance to the one shot).

So the dynamic resistance of those HV zeners in a 900+V string probably easily exceed 9K (this can be calculated from a regulation curve)....... but still there is no reason not to put the extra resistor to the GM tube, and Lionel put 3.3Meg there

rogerw

there would need to be a series resistor, say 1Meg, after the series pass regulator low impedance output (well only kinda low) and going to a GM tube. That kinda points out that this is not practical for a GM tube and a shunt regulator is fine. In fact the only advantage I can see of the Shunt Regulator we have been discussing over a diode string is that it is easily adjustable. It could even have switchable values, each with a trim adjust.

However there might be some advantage of a Series Pass with the photomultiplier detector bias ring which requires HV dc current?

rogerw

On 4/3/2022 7:47 AM, Geo Dowell wrote:

Q: what happens when the GM tube fires, essentially going to ground?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Sunday, April 3, 2022 7:40:32 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Peter,

The reason I ask is that this Shunt Regulator can be turned quite easily into a Series Pass Regulator such that the "dropping resistor" can become, say 10Meg and the bias currents to the regulator remain small while the load gets only whatever current it demands.

Interested?

rogerw

On 4/3/2022 12:40 AM, peter via groups.io wrote:

Roger:
?PMT resistor divider resistance is all over the place. The lowest I encountered was a commercially made socket for Hamamatsu R647 pmt, and its total resistance was about 3.3 M ohms.The pmt base is tiny and the resistors are inside the potted pmt socket, so no chance in modifying it.?

Many surplus 1 x 1x 3" NaI probes made by Bicron/Alpha Spectra are around 13M ohms. My home made resistor dividers are around 50M ohms~ 240M ohms.?
Many pmts are 8 or 10 stages so 9 or 11 resistors, often all the same value. I often choose 4.7M, 10M or 22M ohm resistors for each resistor.

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.

开云体育

there would need to be a series resistor, say 1Meg, after the series pass regulator low impedance output (well only kinda low) and going to a GM tube. That kinda points out that this is not practical for a GM tube and a shunt regulator is fine. In fact the only advantage I can see of the Shunt Regulator we have been discussing over a diode string is that it is easily adjustable. It could even have switchable values, each with a trim adjust.

However there might be some advantage of a Series Pass with the photomultiplier detector bias ring which requires HV dc current?

rogerw

Q: what happens when the GM tube fires, essentially going to ground?

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Sunday, April 3, 2022 7:40:32 AM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

Peter,

The reason I ask is that this Shunt Regulator can be turned quite easily into a Series Pass Regulator such that the "dropping resistor" can become, say 10Meg and the bias currents to the regulator remain small while the load gets only whatever current it demands.

Interested?

rogerw

On 4/3/2022 12:40 AM, peter via groups.io wrote:

Roger:
?PMT resistor divider resistance is all over the place. The lowest I encountered was a commercially made socket for Hamamatsu R647 pmt, and its total resistance was about 3.3 M ohms.The pmt base is tiny and the resistors are inside the potted pmt socket, so no chance in modifying it.?

Many surplus 1 x 1x 3" NaI probes made by Bicron/Alpha Spectra are around 13M ohms. My home made resistor dividers are around 50M ohms~ 240M ohms.?
Many pmts are 8 or 10 stages so 9 or 11 resistors, often all the same value. I often choose 4.7M, 10M or 22M ohm resistors for each resistor.

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.

开云体育

Peter,

The reason I ask is that this Shunt Regulator can be turned quite easily into a Series Pass Regulator such that the "dropping resistor" can become, say 10Meg and the bias currents to the regulator remain small while the load gets only whatever current it demands.

Interested?

rogerw

Roger:
?PMT resistor divider resistance is all over the place. The lowest I encountered was a commercially made socket for Hamamatsu R647 pmt, and its total resistance was about 3.3 M ohms.The pmt base is tiny and the resistors are inside the potted pmt socket, so no chance in modifying it.?

Many surplus 1 x 1x 3" NaI probes made by Bicron/Alpha Spectra are around 13M ohms. My home made resistor dividers are around 50M ohms~ 240M ohms.?
Many pmts are 8 or 10 stages so 9 or 11 resistors, often all the same value. I often choose 4.7M, 10M or 22M ohm resistors for each resistor.

P

-- 
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

In LTSpice, it is not a model for any actual Jfet, it is just an ideal Jfet model with no breakdown. I simulated the characteristic curve, such as Id vs Vds for Vgs= 5V just like a curve tracer would do, just to make sure breakdown was not modeled. it was flat to 1000V, no breakdown. Other than that it is just a small signal Jfet.......

Michael found two Mosfets at Digikey that will work: VN0550N3-G? or? LND150N3-G. the first is enhancement and the second is depletion (like the Jfet is). Either will work for the cascodes, I bought some of the second ones to try when I find time.

rogerw

Roger:
?Out of curiosity what generic JFET did you use ??
I am not familiar with high voltage JFETs. I've only used JFETs rated for 100V or less.

Michael:
?Happy to pass to prototyping torch to you!
I got to be patient until find some better mosfets.

Please keep us up to date as to your results.

P

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

Roger:
?PMT resistor divider resistance is all over the place. The lowest I encountered was a commercially made socket for Hamamatsu R647 pmt, and its total resistance was about 3.3 M ohms.The pmt base is tiny and the resistors are inside the potted pmt socket, so no chance in modifying it.?

Many surplus 1 x 1x 3" NaI probes made by Bicron/Alpha Spectra are around 13M ohms. My home made resistor dividers are around 50M ohms~ 240M ohms.?
Many pmts are 8 or 10 stages so 9 or 11 resistors, often all the same value. I often choose 4.7M, 10M or 22M ohm resistors for each resistor.

P

Roger:
?Out of curiosity what generic JFET did you use ??
I am not familiar with high voltage JFETs. I've only used JFETs rated for 100V or less.

Michael:
?Happy to pass to prototyping torch to you!
I got to be patient until find some better mosfets.

Please keep us up to date as to your results.

P

开云体育

Michael,

Great, I look forward to hearing results from your effort!

I also bought some of the depletion mode devices, to breadboard with when I can get around to it.

Peter,

You mentioned that your Photomultiplier(?) application has a bias string of resistors which I assume is a load to the RegHV= 900+V output.? I have casually seen these somewhere before but am not very familiar with it. What is the total resistance of that load?

I suppose the HV Generator for that is capable of many tens of uA? How many?

rogerw

Roger / Peter

I have ordered a few of each type of MOSFET

I have some 5.1v and 15v zeners to try in place of the 6.2v

Will try your 'improved' circuit and report back

mje

On 4/2/2022 1:17 PM, Roger Whatley wrote:

Michael,

My goodness, you are good at finding these things! I think that device will also work fine.

Again, I have already simulated a generic JFet for the cascodes, which is naturally a depletion mode.

rogerw

On 4/2/2022 12:04 PM, Michael J Emerson wrote:

Roger -

thank you for the confirmation

If depletion mode will work the there is the LND150N3-G

lots in stock at $0.57 each

mje

On 4/2/2022 12:22 PM, Roger Whatley wrote:

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

-- 
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.

开云体育

Roger / Peter

I have ordered a few of each type of MOSFET

I have some 5.1v and 15v zeners to try in place of the 6.2v

Will try your 'improved' circuit and report back

mje

开云体育

Michael,

My goodness, you are good at finding these things! I think that device will also work fine.

Again, I have already simulated a generic JFet for the cascodes, which is naturally a depletion mode.

rogerw

Roger -

thank you for the confirmation

If depletion mode will work the there is the LND150N3-G

lots in stock at $0.57 each

mje

On 4/2/2022 12:22 PM, Roger Whatley wrote:

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

-- 
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.

开云体育

Roger -

thank you for the confirmation

If depletion mode will work the there is the LND150N3-G

lots in stock at $0.57 each

mje

开云体育

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

-- 
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.

开云体育

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

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

-- 
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.

开云体育

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

开云体育

Notice that Bss126 is a depletion mode, not enhancement mode, but does not matter hardly at all in this circuit. It only means Vgs will be negative, not positive.

In fact, that realization has spurred me to wonder if there is a low-power HV n-ch JFet lurking out there...... that works too.

In fact, HV BJT's in Darlington form are probably ok too for the cascodes.

rogerw

Roger?

Good morning.
The Infineon BSS126 is a nice? 600V part. Thanks.
It bugs me that? these parts are not cheap, all the stores really mark up the prices or tack on some expensive shipping.
My patience battles my frugalness. I get the occasional business trips to Tokyo. My favorite place for cheap parts is Akizuki Denshi
Many mosfets around this class are under 100 yen. I got to find small cheap one and stock up! For example:?


The 2SK3563 works but I often had to tweak the values from your suggestions to get it to work.?
I also find that the regulation is not as tight as the simulations. For example with the 2SK3563, and using your latest circuit, it works, but the regulation is not stiff, it still creeps up above the set voltage as the input voltage is +50V or more above the setting.?
I got to look through my junk pile. I may have some other MOSFET, but still in the ~ Amp Id range.
P


?

-- 
rogerw
On the Catclaw
ΜΟΛΩΝ ΛΑΒΕ

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

Roger?

Good morning.
The Infineon BSS126 is a nice? 600V part. Thanks.
It bugs me that? these parts are not cheap, all the stores really mark up the prices or tack on some expensive shipping.
My patience battles my frugalness. I get the occasional business trips to Tokyo. My favorite place for cheap parts is Akizuki Denshi
Many mosfets around this class are under 100 yen. I got to find small cheap one and stock up! For example:?


The 2SK3563 works but I often had to tweak the values from your suggestions to get it to work.?
I also find that the regulation is not as tight as the simulations. For example with the 2SK3563, and using your latest circuit, it works, but the regulation is not stiff, it still creeps up above the set voltage as the input voltage is +50V or more above the setting.?
I got to look through my junk pile. I may have some other MOSFET, but still in the ~ Amp Id range.
P


?

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Peter,

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

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

rogerw

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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Geo,

I have now simulated the latest version I am playing with over temp from -25degC to 75degC.

It did NOT temp compensate well (the 3Vbe + 3Vz scheme) with the 6.2V OnSemi Zeners, but when I switched to Rohm 6.2V Zeners it was nearly flawless in temperature compensation over that range. I don't know what was going on with the OnSemi Zener , perhaps a modeling problem...... and I AM referring to simulation and not actual breadboard.

In fact I think it is working quite well at this point. (In simulation :-)?

Over voltage, 1000V to 1200V it went from 911V to 915V.

Over temp, -25 to +75, it went from 915V to 918V (at UnRegHV = 1200V)

A problem with the heat gun approach is that all components are not heated the same temp..... and temp. comp. can go awry even if it was really fine...... but, I know, I have also used the heat gun approach too. Its the best a poor fellow like me could do!

rogerw

"

The Rohm 6.2V should be fine.

I never simulated the temp performance, that was MindSim."

I was going to ask you both when the design is firmed up, to hit it with a heat gun and watch/record the results real-time.

Obviously,?the patent app was all about hi-temp operation,?but?we recognize the end-use here would be a stabilized adjustable HV for Geiger Counter and other experiments.

Geo

Geo

---

From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Friday, April 1, 2022 3:38:53 PM
Subject: Re: [CDV700CLUB] Question and an interesting site for those that modify CDV700s and more.

The Rohm 6.2V should be fine.

I never simulated the temp performance, that was MindSim. Generally, in what we usually call Zener Diodes, the are actually two breakdown mechanisms: Zener breakdown and avalanche breakdown. Zener breakdown dominates below about 5.1V and avalanche dominates above that voltage. Avalanche mechanism has a positive tempco and Zener has a negative tempco.

It is very common design practice to pair a 6.1V or 6.2V Zener with a silicon diode or base-emitter junction to achieve close to zero tempco.

If the Zener is above 5.1 volts some will call it an "avalanche diode" instead of Zener Diode..... Truth is, all Zener Diodes have both mechanisms going on to varying degrees, hence a nonlinear change of tempco vs voltage spec.

rogerw

On 4/1/2022 3:09 PM, peter via groups.io wrote:

[Edited Message Follows]

Roger:
?The closest mosfet in my Micro-Cap library was a 2SK311 to the 2SK3563 that I was proto-typing with.?
Since these mosfets are much higher current parts, than those you may have used in your sim,? they don't work as well in the simulation I ran using a 2SK311,?
I had to tweak R6 to 6.8M to get the circuit to work and as you simulated, temp stability is great.?
Now I have a few more things to cobble together tonight.
I looked up the part I will be using its a Rohm MTZJ-6.2? zener.
will try to make time this evening to melt some solder
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.