Developing HV DC Pulses...

[Anthony William Sloman]

On Thursday, May 11, 2023 at 1:24:33 AM UTC+10, John Larkin wrote:

On Wed, 10 May 2023 06:02:07 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Wednesday, May 10, 2023 at 12:55:20?AM UTC-5, Flyguy wrote:

I have worked on HV pulsers for field asymmetric ion mobility spectroscopy (FAIMS) that used resonant coils to produce the first few harmonics of a DC waveform. While this work was not published, here is another approach (which I tried, but didn\'t work):
https://citeseerx.ist.psu.edu/document?https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=398cb8bdd459203c8358449135f8e33473c15b59

Thanks for that, I\'m don\'t really understand what it is doing, and I think the high side low side driver gets complicated. Although later down the line
it might be worth having someone more knowledgeable look into that, It\'s in the file. Thanks.

I was shown this much simpler approach and want some feedback on it.
https://commons.wikimedia.org/wiki/File:Cascode-voltage-ladder.png
Possibly using these 1400V transistors,
https://www.mouser.com/ProductDetail/STMicroelectronics/STN0214?qs=pmcUWs1B1IKOCzUPe9wAgg%3D%3D
My concern, would improper layout add an inductance that could over voltage the devices at shut off?
The resistive voltage divider, How much voltage can you put across a resistor?
Will a 1W withstand a higher voltage the a 1/2 W? (Standard resistors)
I understand there are HV resistors.
Thanks, Mikek


You can easily get a single 1000 volt mosfet. A passive (resistive)
pullup would be all you need to drive a small capacitive load at low
duty cycle. So, given a HV dc supply and a pulse generator, 555 or
something, you need two parts.

He does seem to want to get up to 9 or 10kV. A 1kV MOSFET isn\'t all that interesting in that context.

Since his shortest pulse is 10msec, it\'s not offering him anything that he actually needs. Do try to answer the actual question rather than the one you\'d have preferred him to have asked.

> If an exotic HV resistor is a hassle, series a few 1-cent axials.

But mount them on teflon insulated stand-offs.

> Adding active pullup is easy too. 1 or 2 more parts.

But not at 9kV.

--
Bill Sloman, Sydney

 

[Lamont Cranston]

On Wednesday, May 10, 2023 at 10:24:33 AM UTC-5, John Larkin wrote:

You can easily get a single 1000 volt mosfet. A passive (resistive)
pullup would be all you need to drive a small capacitive load at low
duty cycle. So, given a HV dc supply and a pulse generator, 555 or
something, you need two parts.

If an exotic HV resistor is a hassle, series a few 1-cent axials.

Adding active pullup is easy too. 1 or 2 more parts.

I want to build it for 7kv just in case, may not need it but would like it available.

 

[Lamont Cranston]

On Wednesday, May 10, 2023 at 10:53:51 AM UTC-5, Anthony William Sloman wrote:

Since his shortest pulse is 10msec, it\'s not offering him anything that he actually needs.
If an exotic HV resistor is a hassle, series a few 1-cent axials.
But mount them on teflon insulated stand-offs.
Adding active pullup is easy too. 1 or 2 more parts.
But not at 9kV.

--
Bill Sloman, Sydney

I even have teflon standoffs!
Any comments on the Cascode Voltage Ladder?
https://commons.wikimedia.org/wiki/File:Cascode-voltage-ladder.png
With 7KV, all the Voltages on the resistor divider will be 7 times higher,
for the bottom one, would I adjust the value to get the 15V.
Mikek

 

[Lamont Cranston]

I got some feedback on the capacitance and resistance of the vessel with an emulsion in it.
With just air, 2 to 3 pf, with RP over 200MΩ, the limit of my DE-5000..
Plain water with acid was 120pf, with RP over 200MΩ.
With an emulsion 18pf with RP over 200MΩ.
Mikek

 

[John Larkin]

On Wed, 10 May 2023 09:20:46 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Wednesday, May 10, 2023 at 10:53:51?AM UTC-5, Anthony William Sloman wrote:

Since his shortest pulse is 10msec, it\'s not offering him anything that he actually needs.
If an exotic HV resistor is a hassle, series a few 1-cent axials.
But mount them on teflon insulated stand-offs.
Adding active pullup is easy too. 1 or 2 more parts.
But not at 9kV.

--
Bill Sloman, Sydney

I even have teflon standoffs!

Air is cheaper.

Any comments on the Cascode Voltage Ladder?
https://commons.wikimedia.org/wiki/File:Cascode-voltage-ladder.png
With 7KV, all the Voltages on the resistor divider will be 7 times higher,
for the bottom one, would I adjust the value to get the 15V.
Mikek

That would work with kilovolt mosfets too.

IXYS has an (expensive) 4500 volt mosfet. 1700 volts is more
affordable.

 

[John Larkin]

On Wed, 10 May 2023 09:08:39 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Wednesday, May 10, 2023 at 10:24:33?AM UTC-5, John Larkin wrote:


You can easily get a single 1000 volt mosfet. A passive (resistive)
pullup would be all you need to drive a small capacitive load at low
duty cycle. So, given a HV dc supply and a pulse generator, 555 or
something, you need two parts.

If an exotic HV resistor is a hassle, series a few 1-cent axials.

Adding active pullup is easy too. 1 or 2 more parts.

I want to build it for 7kv just in case, may not need it but would like it available.

There are high voltage reed relays too.

 

[Lamont Cranston]

On Wednesday, May 10, 2023 at 11:37:13 AM UTC-5, John Larkin wrote:

That would work with kilovolt mosfets too.

IXYS has an (expensive) 4500 volt mosfet. 1700 volts is more
affordable.

Is there something you don\'t like about the 1400V transistor? At $1.03 each..
https://www.mouser.com/datasheet/2/389/stn0214-1851406.pdf
I\'m thinking pulling say 5ma through the transformer secondary while the switch is closed,
and then opening the switch, to say a 5ua load, might cause an inductive spike.
Is that a concern?
I did find a 25,000V tube for $10.
https://tubes-store.com/product_info.php?products_id=807
Mikek

 

[Lamont Cranston]

On Wednesday, May 10, 2023 at 11:38:22 AM UTC-5, John Larkin wrote:

On Wed, 10 May 2023 09:08:39 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Wednesday, May 10, 2023 at 10:24:33?AM UTC-5, John Larkin wrote:


You can easily get a single 1000 volt mosfet. A passive (resistive)
pullup would be all you need to drive a small capacitive load at low
duty cycle. So, given a HV dc supply and a pulse generator, 555 or
something, you need two parts.

If an exotic HV resistor is a hassle, series a few 1-cent axials.

Adding active pullup is easy too. 1 or 2 more parts.

I want to build it for 7kv just in case, may not need it but would like it available.
There are high voltage reed relays too.

Would those work at 8hz?
Mikek

 

[John Larkin]

On Wed, 10 May 2023 09:49:38 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Wednesday, May 10, 2023 at 11:38:22?AM UTC-5, John Larkin wrote:
On Wed, 10 May 2023 09:08:39 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Wednesday, May 10, 2023 at 10:24:33?AM UTC-5, John Larkin wrote:


You can easily get a single 1000 volt mosfet. A passive (resistive)
pullup would be all you need to drive a small capacitive load at low
duty cycle. So, given a HV dc supply and a pulse generator, 555 or
something, you need two parts.

If an exotic HV resistor is a hassle, series a few 1-cent axials.

Adding active pullup is easy too. 1 or 2 more parts.

I want to build it for 7kv just in case, may not need it but would like it available.
There are high voltage reed relays too.

Would those work at 8hz?
Mikek

Easily. Reeds are fast. Even regular relays work in milliseconds.

Digikey has some HV relays.

 

[John Larkin]

On Wed, 10 May 2023 09:22:23 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

I got some feedback on the capacitance and resistance of the vessel with an emulsion in it.
With just air, 2 to 3 pf, with RP over 200M?, the limit of my DE-5000.
Plain water with acid was 120pf, with RP over 200M?.
With an emulsion 18pf with RP over 200M?.
Mikek

I\'d expect that the process is basically AC coupled, so the brief
pulses can be from quiescent HV and pulsed to ground. So a passive
pullup won\'t work very hard.

A glass capillary is going to be a lot of megohms. But even 200M is a
high impedance. Megohms of pullup would work.

 

[Lamont Cranston]

On Wednesday, May 10, 2023 at 12:55:22 PM UTC-5, John Larkin wrote:

On Wed, 10 May 2023 09:22:23 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:

I got some feedback on the capacitance and resistance of the vessel with an emulsion in it.
With just air, 2 to 3 pf, with RP over 200M?, the limit of my DE-5000.
Plain water with acid was 120pf, with RP over 200M?.
With an emulsion 18pf with RP over 200M?.
Mikek

I\'d expect that the process is basically AC coupled, so the brief
pulses can be from quiescent HV and pulsed to ground. So a passive
pullup won\'t work very hard.

A glass capillary is going to be a lot of megohms. But even 200M is a
high impedance. Megohms of pullup would work.

I\'m hoping to lead them into a different type vessel hopefully with less corona discharge,
I would hope somewhere in this process to get a somewhat accurate current measurement.
18pf at 60hz is 147MΩ, at 7000V is about 48ua through the vessel.
A dropping resistor of 10MΩ, drops about 500V before the load, a lot but easily adjusted at the variac.
7000V /10MΩ = 700ua
7000 x 700ua = 4.9 Watts, less if duty cycle is included.
Mikek
My son got his first shock today, says everything was off.
The 18pf could hold a charge, but, not long at all. ¯\\_(ツ)_/¯

 

[John Larkin]

On Wed, 10 May 2023 09:48:49 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Wednesday, May 10, 2023 at 11:37:13?AM UTC-5, John Larkin wrote:

That would work with kilovolt mosfets too.

IXYS has an (expensive) 4500 volt mosfet. 1700 volts is more
affordable.

Is there something you don\'t like about the 1400V transistor? At $1.03 each.
https://www.mouser.com/datasheet/2/389/stn0214-1851406.pdf

They look fine. Stack them if you need to, but bipolars need base
current, and mosfets don\'t.

I\'d look for some small, low-capacitance, protected-gate mosfets.

I\'m thinking pulling say 5ma through the transformer secondary while the switch is closed,
and then opening the switch, to say a 5ua load, might cause an inductive spike.
Is that a concern?
I did find a 25,000V tube for $10.
https://tubes-store.com/product_info.php?products_id=807
Mikek

Old color TVs sometimes had an HV shunt regulator tube, a tetrode?
Can\'t remember the part number. A tube would be cool, maybe cascoded
with a tiny mosfet.

 

[whit3rd]

On Wednesday, May 10, 2023 at 8:24:33 AM UTC-7, John Larkin wrote:

On Wed, 10 May 2023 06:02:07 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:

The resistive voltage divider, How much voltage can you put across a resistor?
Will a 1W withstand a higher voltage the a 1/2 W? (Standard resistors)
I understand there are HV resistors.

You can easily get a single 1000 volt mosfet. A passive (resistive)
pullup would be all you need to drive a small capacitive load at low
duty cycle. So, given a HV dc supply and a pulse generator, 555 or
something, you need two parts.

If an exotic HV resistor is a hassle, series a few 1-cent axials.

Two issues: a 1000 volt transistor might hold off 1 kV, but not be able to
turn ON with that voltage applied (like horizontal output transistors in
old CRT circuitry, the HV rating only applies with zero collector current).
And, a \"HV resistor\" is geometrically designed to not generate ions in air;
regular old air is NOT a good insulator at high fields, you can get corona
discharge by using thin wire, or pointy parts, or by a stray bit of lint...
Real HV resistors are fat things, and the fields around them are not
well controlled if you try to attach them to a PCB with either a ground
plane, or even just a fingerprint, to distort field symmetry (generate
ionizing hot spots). Those fat rings of metal around van de Graaff
generator parts are IMPORTANT. You can\'t print a wire on a PCB
with fat rings around it.

A 1-cent axial isn\'t fat enough to do real HV, unless you put it in a
vacuum, or pot the assembly.

 

[John Larkin]

On Wed, 10 May 2023 14:38:05 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Wednesday, May 10, 2023 at 8:24:33?AM UTC-7, John Larkin wrote:
On Wed, 10 May 2023 06:02:07 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:

The resistive voltage divider, How much voltage can you put across a resistor?
Will a 1W withstand a higher voltage the a 1/2 W? (Standard resistors)
I understand there are HV resistors.

You can easily get a single 1000 volt mosfet. A passive (resistive)
pullup would be all you need to drive a small capacitive load at low
duty cycle. So, given a HV dc supply and a pulse generator, 555 or
something, you need two parts.

If an exotic HV resistor is a hassle, series a few 1-cent axials.

Two issues: a 1000 volt transistor might hold off 1 kV, but not be able to
turn ON with that voltage applied (like horizontal output transistors in
old CRT circuitry, the HV rating only applies with zero collector current).

What use is a transistor if it can\'t turn on? Of course it can.

And, a \"HV resistor\" is geometrically designed to not generate ions in air;
regular old air is NOT a good insulator at high fields, you can get corona
discharge by using thin wire, or pointy parts, or by a stray bit of lint...
Real HV resistors are fat things, and the fields around them are not
well controlled if you try to attach them to a PCB with either a ground
plane, or even just a fingerprint, to distort field symmetry (generate
ionizing hot spots). Those fat rings of metal around van de Graaff
generator parts are IMPORTANT. You can\'t print a wire on a PCB
with fat rings around it.

A 1-cent axial isn\'t fat enough to do real HV, unless you put it in a
vacuum, or pot the assembly.

I suggested using several in series. That works fine.

7 KV is not very high voltage. People sell 20KV surface-mount
resistors.

 

[whit3rd]

On Wednesday, May 10, 2023 at 5:06:03 PM UTC-7, John Larkin wrote:

On Wed, 10 May 2023 14:38:05 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

... a 1000 volt transistor might hold off 1 kV, but not be able to
turn ON with that voltage applied (like horizontal output transistors in
old CRT circuitry, the HV rating only applies with zero collector current).

What use is a transistor if it can\'t turn on? Of course it can.

A CRT horizontal output has a 100V supply, switches ON, dropping it
to near zero V, then OFF, and flyback peaks the collector voltage at 1 kV.

It is NOT rated at 1 kV for its switching operation, only for reverse B-E bias
OFF conditions, during a flyback voltage excursion.

And, a \"HV resistor\" is geometrically designed to not generate ions in air;
regular old air is NOT a good insulator at high fields, you can get corona
discharge by using thin wire, or pointy parts, or by a stray bit of lint....
Real HV resistors are fat things, and the fields around them are not
well controlled if you try to attach them to a PCB with either a ground
plane, or even just a fingerprint, to distort field symmetry (generate
ionizing hot spots). Those fat rings of metal around van de Graaff
generator parts are IMPORTANT. You can\'t print a wire on a PCB
with fat rings around it.

A 1-cent axial isn\'t fat enough to do real HV, unless you put it in a
vacuum, or pot the assembly.

I suggested using several in series. That works fine.

It isn\'t end-to-end arcing that\'s the issue, but local E field causing corona
discharge (and chemical corrosion that can kill nearby components in a few months).
Diameter, not heating, is the critical bit. Spark plug wires are never less than 8mm or
so, and it isn\'t material properties of the insulator that sets that size, it\'s the air
at radius 4mm around a cylindrical conductor.

7 KV is not very high voltage. People sell 20KV surface-mount
resistors.

I suspect they\'re potted assemblies, then. I\'ve got some HV reed relays, THEY were potted.
The fat rings on a van de Graaff are for higher voltages, of course; megavolts, sometimes.

 

[Anthony William Sloman]

On Thursday, May 11, 2023 at 2:20:50 AM UTC+10, Lamont Cranston wrote:

On Wednesday, May 10, 2023 at 10:53:51 AM UTC-5, Anthony William Sloman wrote:

Since his shortest pulse is 10msec, it\'s not offering him anything that he actually needs.
If an exotic HV resistor is a hassle, series a few 1-cent axials.
But mount them on teflon insulated stand-offs.
Adding active pullup is easy too. 1 or 2 more parts.
But not at 9kV.

I even have teflon standoffs!
Any comments on the Cascode Voltage Ladder?
https://commons.wikimedia.org/wiki/File:Cascode-voltage-ladder.png

Run a Spice simulation of turn off and turn on. Each of the collector base capacitances has to charge up or discharge through the biassing string, and all the base currents have to come from it - MOSFETs might be a better choice, since the gates don\'t drawn any current when they are on or off. You might need a \"gate stopper\" in series with each gate to prevent oscillation.

> With 7KV, all the Voltages on the resistor divider will be 7 times higher, for the bottom one, would I adjust the value to get the 15V.

Whatever.

--
Bill Sloman, Sydney

 

[Anthony William Sloman]

On Thursday, May 11, 2023 at 2:37:13 AM UTC+10, John Larkin wrote:

On Wed, 10 May 2023 09:20:46 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Wednesday, May 10, 2023 at 10:53:51?AM UTC-5, Anthony William Sloman wrote:

Since his shortest pulse is 10msec, it\'s not offering him anything that he actually needs.
If an exotic HV resistor is a hassle, series a few 1-cent axials.
But mount them on teflon insulated stand-offs.
Adding active pullup is easy too. 1 or 2 more parts.
But not at 9kV.

I even have teflon standoffs!

Air is cheaper.

But doesn\'t provide much mechanical support.

Any comments on the Cascode Voltage Ladder?
https://commons.wikimedia.org/wiki/File:Cascode-voltage-ladder.png
With 7KV, all the Voltages on the resistor divider will be 7 times higher,
for the bottom one, would I adjust the value to get the 15V.

That would work with kilovolt mosfets too.

IXYS has an (expensive) 4500 volt mosfet. 1700 volts is more affordable.

The drain gate capacitance can be a problem, and it changes with applied voltage. Essentially you have to get fixed amount of charge into the drain-gate capacitance to turn the part on, and get it out again at turn-off. It\'s usually specified on the data sheet - with the usual production tolerance. The impedance of the divider chain is at a maximum in the middle and you run the risk of the MOSFETs turning on at different rates and getting excessive voltages over one or more of the MOSFETs during the process. Paralleling the divider chain with a string high voltage zeners - 270V is the highest I can find - could limit such turn-on and turn-off excursions.

--
Bill Sloman, Sydney

 

[John Larkin]

On Wed, 10 May 2023 23:26:36 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Wednesday, May 10, 2023 at 5:06:03?PM UTC-7, John Larkin wrote:
On Wed, 10 May 2023 14:38:05 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

... a 1000 volt transistor might hold off 1 kV, but not be able to
turn ON with that voltage applied (like horizontal output transistors in
old CRT circuitry, the HV rating only applies with zero collector current).

What use is a transistor if it can\'t turn on? Of course it can.

A CRT horizontal output has a 100V supply, switches ON, dropping it
to near zero V, then OFF, and flyback peaks the collector voltage at 1 kV.

It is NOT rated at 1 kV for its switching operation, only for reverse B-E bias
OFF conditions, during a flyback voltage excursion.

And, a \"HV resistor\" is geometrically designed to not generate ions in air;
regular old air is NOT a good insulator at high fields, you can get corona
discharge by using thin wire, or pointy parts, or by a stray bit of lint...
Real HV resistors are fat things, and the fields around them are not
well controlled if you try to attach them to a PCB with either a ground
plane, or even just a fingerprint, to distort field symmetry (generate
ionizing hot spots). Those fat rings of metal around van de Graaff
generator parts are IMPORTANT. You can\'t print a wire on a PCB
with fat rings around it.

A 1-cent axial isn\'t fat enough to do real HV, unless you put it in a
vacuum, or pot the assembly.

I suggested using several in series. That works fine.

It isn\'t end-to-end arcing that\'s the issue, but local E field causing corona
discharge (and chemical corrosion that can kill nearby components in a few months).
Diameter, not heating, is the critical bit. Spark plug wires are never less than 8mm or
so, and it isn\'t material properties of the insulator that sets that size, it\'s the air
at radius 4mm around a cylindrical conductor.

I was building 12 KV supplies when I was a kid, and I used strings of
series 1/4 watt carbon axial resistors, and they worked fine. A 1B3
makes a great series regulator.

Mid-air soldered junctions are great in other situations too. The old
Radio Amateur Handbooks warned against unsupported soldered junctions,
but Tek just did it and sold a lot of oscilloscopes.

7 KV is not very high voltage. People sell 20KV surface-mount
resistors.

I suspect they\'re potted assemblies, then.

How can you have usenet but no google?

I\'ve got some HV reed relays, THEY were potted.
The fat rings on a van de Graaff are for higher voltages, of course; megavolts, sometimes.

I am sure glad that you don\'t design electronics.

 

[Anthony William Sloman]

On Friday, May 12, 2023 at 12:45:22 AM UTC+10, John Larkin wrote:

On Wed, 10 May 2023 23:26:36 -0700 (PDT), whit3rd <whi...@gmail.com> wrote:
On Wednesday, May 10, 2023 at 5:06:03?PM UTC-7, John Larkin wrote:
On Wed, 10 May 2023 14:38:05 -0700 (PDT), whit3rd <whi...@gmail.com> wrote:

<snip>

I suspect they\'re potted assemblies, then.

How can you have usenet but no google?

I\'ve got some HV reed relays, THEY were potted.

The fat rings on a van de Graaff are for higher voltages, of course; megavolts, sometimes.

I am sure glad that you don\'t design electronics.

John Larkin trots out his standard insult. The irony is that John seems to evolve his electronics rather than designing anything.

Quite why an observation about van de Graaff generators suggests to him that Whit3rd doesn\'t design electronics isn\'t entirely clear.
Whit3rd does seems to be a physicist, and quite a few of them design electronics, not always all that well, but Whit3rd does post here which suggests enough interest in electronic design that he could do it well (as some physicists manage to do).

I was trained as a chemist and most of the chemists I worked with as graduate student were hopeless at electronics. Win Hill started off doing a Ph.D.. in chemical physics and he turned out pretty well.

--
Bill Sloman, Sydney

 

[Lamont Cranston]

In the famous words of Rodney King, \"Can\'t we just get along\"

Tell me how to control a tube. Can I drive it with a 555?
Do I need to run the 555 from plus 3V and minus 7V or some combination to get full off and full on?
Rather that a pull down resistor scenario, can I just put the tube in series with the load and switch it? 18pf, 200MΩ+ load.
That would be better for upscaling, eliminating a 100watt 10MΩ resistor.

Thanks, Mikek