48V to 2000V DC-DC smallest design

[mook Jonhon]

Its been a while but once again looking at a HV pulser type application.

It will charge up about 10nF to 2kV with about 1mA. Then keep it toped
off as that cap discharges into another capacitive much smaller
capacitive load. The 10nF will loose 100V or so then need to be
recharged witn 1mA before the next burst.

It need to be a custom approach due to environment constraints. Cost is
not a strong consideration but must be reasonable I can use custom
transformers etc.

The voltage does need to be variable from 1K to 2K.

no input to output ground isolation required. but sometime the load
shorts and the supply must go into current limit and not damage itself
when this happens.

looking for small topologies to do this.

1) boost inductor feeding a voltage multiplier (8-10 stage)
I have had 1A diodes blow when a previous VM design was shorted from
1.5kV. even with a 100K resistor in series with the output. never
investigated jsut sured up the source of the arcing and moved on with
fingers crossed.

2) flyback to do most of the boost with a doubler or tripler on the
output. This should keep the turns ratio reasonable.

3) straight pushpull making use of the primary voltage doubling action
to get soem volatge gain. PWM the center tap.

any other physically small power stage topologies to look into?

thanks

 

[Tim Williams]

How small is small?

I made this without any particular care of size,
https://www.seventransistorlabs.com/Images/HVPower2.jpg
https://www.seventransistorlabs.com/Images/HVPower.jpg
(What, a legible, hand drawn schematic? On SED? :^) )

Easy enough to fix up the DC supply side for efficiency (buck reg), fixed
output, and drop the sense amp that's not needed.

The chopper is kinda here-nor-there, but I do recommend a resonant type in
any case as the secondary capacitance is unavoidable, and the Baxandall
oscillator is fairly foolproof as oscillators go.

Also, that was 12V input, but 48 isn't any trouble with appropriate changes.

It seems there aren't many resonant controllers for smaller applications
(like DC-DC modules), so you may have to make a discrete or digital
controller if you want to go that route more formally.

Probably a CCFL transformer would do, no need for custom transformers
surprisingly enough.

If you need it small as balls*, you can stick CSP package GaN transistors to
the backside of a CCFL transformer, use a QFN or BGA controller (which
again, might end up sorta custom, an FPGA or something), a few ceramic caps,
probably a 4 or at most 6 layer board, and be done.

*Erm, huh... literally about right, I think. You'd take up the other ball
for the reservoir cap. And some insulation which might just wrap around the
whole thing like a scrotum. I'll, uh, stop now.

If that's too extreme, any combination of Si components and leaded or
no-lead parts will do, requiring only somewhat more board area.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"mook Jonhon" <mook@mook.net> wrote in message
news:4o17F.80540$OU6.70486@fx40.iad...

Its been a while but once again looking at a HV pulser type application.

It will charge up about 10nF to 2kV with about 1mA. Then keep it toped
off as that cap discharges into another capacitive much smaller
capacitive load. The 10nF will loose 100V or so then need to be
recharged witn 1mA before the next burst.

It need to be a custom approach due to environment constraints. Cost is
not a strong consideration but must be reasonable I can use custom
transformers etc.

The voltage does need to be variable from 1K to 2K.

no input to output ground isolation required. but sometime the load
shorts and the supply must go into current limit and not damage itself
when this happens.

looking for small topologies to do this.

1) boost inductor feeding a voltage multiplier (8-10 stage)
I have had 1A diodes blow when a previous VM design was shorted from
1.5kV. even with a 100K resistor in series with the output. never
investigated jsut sured up the source of the arcing and moved on with
fingers crossed.

2) flyback to do most of the boost with a doubler or tripler on the
output. This should keep the turns ratio reasonable.

3) straight pushpull making use of the primary voltage doubling action
to get soem volatge gain. PWM the center tap.

any other physically small power stage topologies to look into?

thanks

 

On Wed, 21 Aug 2019 01:46:40 GMT, "mook Jonhon" <mook@mook.net> wrote:

Its been a while but once again looking at a HV pulser type application.

It will charge up about 10nF to 2kV with about 1mA. Then keep it toped
off as that cap discharges into another capacitive much smaller
capacitive load. The 10nF will loose 100V or so then need to be
recharged witn 1mA before the next burst.

It need to be a custom approach due to environment constraints. Cost is
not a strong consideration but must be reasonable I can use custom
transformers etc.

The voltage does need to be variable from 1K to 2K.

no input to output ground isolation required. but sometime the load
shorts and the supply must go into current limit and not damage itself
when this happens.

looking for small topologies to do this.

1) boost inductor feeding a voltage multiplier (8-10 stage)
I have had 1A diodes blow when a previous VM design was shorted from
1.5kV. even with a 100K resistor in series with the output. never
investigated jsut sured up the source of the arcing and moved on with
fingers crossed.

2) flyback to do most of the boost with a doubler or tripler on the
output. This should keep the turns ratio reasonable.

3) straight pushpull making use of the primary voltage doubling action
to get soem volatge gain. PWM the center tap.

any other physically small power stage topologies to look into?

thanks

I did this out of standard parts we had in stock. A couple more diode
stages would get it to 2KV.

https://www.dropbox.com/s/e3n5af9sw1a1flh/28S840A_3.pdf?dl=0

With a different, maybe custom, transformer and higher voltage diodes
it could be smaller. I think Coilcraft has some HV type transformers.

I have the LT Spice model around here somewhere.

 

[Bill Sloman]

On Wednesday, August 21, 2019 at 11:46:45 AM UTC+10, mook Jonhon wrote:

Its been a while but once again looking at a HV pulser type application.

It will charge up about 10nF to 2kV with about 1mA. Then keep it toped
off as that cap discharges into another capacitive much smaller
capacitive load. The 10nF will loose 100V or so then need to be
recharged witn 1mA before the next burst.

It need to be a custom approach due to environment constraints. Cost is
not a strong consideration but must be reasonable I can use custom
transformers etc.

The voltage does need to be variable from 1K to 2K.

no input to output ground isolation required. but sometime the load
shorts and the supply must go into current limit and not damage itself
when this happens.

looking for small topologies to do this.

1) boost inductor feeding a voltage multiplier (8-10 stage)
I have had 1A diodes blow when a previous VM design was shorted from
1.5kV. even with a 100K resistor in series with the output. never
investigated jsut sured up the source of the arcing and moved on with
fingers crossed.

2) flyback to do most of the boost with a doubler or tripler on the
output. This should keep the turns ratio reasonable.

3) straight push-pull making use of the primary voltage doubling action
to get some voltage gain. PWM the center tap.

any other physically small power stage topologies to look into?

http://www.sophia-electronica.com/Baxandall_parallel-resonant_Class-D_oscillator1.htm

The circuit diagram at the bottom of the page shows a circuit which looks like option 3).

http://sophia-elektronica.com/PMT-transformer.html

talks about the transformer (and it's stray capacitance).

http://sophia-elektronica.com/website_pmt_psu1.htm

gives the .asc file (which you'd have to rename as a .asc file).

Starting from a +45V supply would make the transformer design a lot easier.

The MOSFETS at M1 and M2 would see a lot higher drain voltage when off - up to about 150V - and the scheme to mark-to-space the gate drives for M3 and M4 gets marginally trickier (not that I bothered working that out).

None of it would get hot, so keeping it small wouldn't be difficult.

IIRR my circuit ran at about 50kHz, limited by the stray capacitance in the secondary. The mark-to-space sequences had much the same frequency, which doesn't necessarily allow for particularly fine control of output voltage, if they are the same from one cycle to the next, but by alternating between two adjacent mark-to-space ratio's you can get finer control as long as the low pass filtering at the output averages out the alternation.

--
Bill Sloman, Sydney

 

[Mikko OH2HVJ]

"mook Jonhon" <mook@mook.net> writes:

Its been a while but once again looking at a HV pulser type application.

It will charge up about 10nF to 2kV with about 1mA. Then keep it toped
off as that cap discharges into another capacitive much smaller
capacitive load. The 10nF will loose 100V or so then need to be
recharged witn 1mA before the next burst.

Sounds a bit familiar - one our design discharged 47nF from 1000V to 4V
at 300Hz. We use a flyback step up from 12-16V to 4*250VDC, which are
then put in series. The transformer is a custom design. Starting from
48VDC should be easier, but I think 8*250V windings gets complicated, so
you'd have to take care of higher secondary voltages with this approach,
which increase the size.

There are also provisions for short circuit protection, low voltages,
flyback behaviour at low voltages etc.

--
mikko

 

[Jan Panteltje]

On a sunny day (Wed, 21 Aug 2019 01:46:40 GMT) it happened "mook Jonhon"
<mook@mook.net> wrote in <4o17F.80540$OU6.70486@fx40.iad>:

Its been a while but once again looking at a HV pulser type application.

It will charge up about 10nF to 2kV with about 1mA. Then keep it toped
off as that cap discharges into another capacitive much smaller
capacitive load. The 10nF will loose 100V or so then need to be
recharged witn 1mA before the next burst.

It need to be a custom approach due to environment constraints. Cost is
not a strong consideration but must be reasonable I can use custom
transformers etc.

The voltage does need to be variable from 1K to 2K.

no input to output ground isolation required. but sometime the load
shorts and the supply must go into current limit and not damage itself
when this happens.

looking for small topologies to do this.

1) boost inductor feeding a voltage multiplier (8-10 stage)
I have had 1A diodes blow when a previous VM design was shorted from
1.5kV. even with a 100K resistor in series with the output. never
investigated jsut sured up the source of the arcing and moved on with
fingers crossed.

2) flyback to do most of the boost with a doubler or tripler on the
output. This should keep the turns ratio reasonable.

3) straight pushpull making use of the primary voltage doubling action
to get soem volatge gain. PWM the center tap.

any other physically small power stage topologies to look into?

thanks

Not sure maybe I did not read it right what your power requirements are.

9 V to 500 V for GM tube
http://panteltje.com/panteltje/pic/gm_pic/

5 V to 1250 V for PMT
http://panteltje.com/panteltje/pic/sc_pic/

5 V to 1750 V for PMT
http://panteltje.com/pub/PMT_regulated_power_supply_diagram_img_3182.jpg

etc etc

Note the last one is a SINE oscillator, just a few turns on an E core
Stabilizing is via supply of the oscillator.
http://panteltje.com/pub/PMT_HV_supply_with_regulator_img_3175.jpg
it all depends, takes half an hour to wind a core like that.

Not always is flyback the way to go, harmonics...

 

[Winfield Hill]

mook Jonhon wrote...

2) flyback to do most of the boost with a
doubler or tripler on the output. This
should keep the turns ratio reasonable.

My flyback approach, previously detailed here
on s.e.d., is different. Three flyback stages,
each with its own MOSFET, all running from one
controller and gate driver. The DC input-V of
each stage is the previous stage's DC output.
Starting with say 12V, you need a 167x stepup.
Three 5.5x stages gets you to 2kV, and that's
a pretty mild step-up ratio. 66V, 363V, 2kV.
Stage currents and inductor values scale, since
they all run with the same time parameters.

Three feedback taps, each with a diode to the
controller's FB pin. The highest one controls,
to prevent any one stage from going excessively
over its voltage limit, but the last stage gets
the controlling vote. Very simple. Except for
HV winding technique of the 3rd inductor.


--
Thanks,
- Win

 

[mook Jonhon]

Tim Williams wrote:

How small is small?

I made this without any particular care of size,
https://www.seventransistorlabs.com/Images/HVPower2.jpg
https://www.seventransistorlabs.com/Images/HVPower.jpg
(What, a legible, hand drawn schematic? On SED? :^) )

Easy enough to fix up the DC supply side for efficiency (buck reg),
fixed output, and drop the sense amp that's not needed.

The chopper is kinda here-nor-there, but I do recommend a resonant
type in any case as the secondary capacitance is unavoidable, and the
Baxandall oscillator is fairly foolproof as oscillators go.

Also, that was 12V input, but 48 isn't any trouble with appropriate
changes.

It seems there aren't many resonant controllers for smaller
applications (like DC-DC modules), so you may have to make a discrete
or digital controller if you want to go that route more formally.

Probably a CCFL transformer would do, no need for custom transformers
surprisingly enough.

If you need it small as balls*, you can stick CSP package GaN
transistors to the backside of a CCFL transformer, use a QFN or BGA
controller (which again, might end up sorta custom, an FPGA or
something), a few ceramic caps, probably a 4 or at most 6 layer
board, and be done.

*Erm, huh... literally about right, I think. You'd take up the other
ball for the reservoir cap. And some insulation which might just
wrap around the whole thing like a scrotum. I'll, uh, stop now.

If that's too extreme, any combination of Si components and leaded or
no-lead parts will do, requiring only somewhat more board area.

Tim

Thanks Tim,

I see you used a royer (push pull) with a voltage doubler on the back
side.

by small I need something to fit in a 1" v 2" board with the tallest
components about 1/4" above or below the board. It could be 1/2" tall
as the board sits on 1/4" standoffs. think pot core bolted to teh
chassis on one end of the board. maybe some wiggle room to 2.5" in
length.


I will need ot run at highish frequencies (300+Khz) to get the
magnetics down but the continuous power levels will be low.


what you are suggesting is where I was going. Just making sure there
was not trick or "old magic" that I was not aware of to simply make
high votlage from low.

thanks

 

[piglet]

On 21/08/2019 9:34 am, Winfield Hill wrote:

mook Jonhon wrote...

2) flyback to do most of the boost with a
doubler or tripler on the output. This
should keep the turns ratio reasonable.

My flyback approach, previously detailed here
on s.e.d., is different. Three flyback stages,
each with its own MOSFET, all running from one
controller and gate driver. The DC input-V of
each stage is the previous stage's DC output.
Starting with say 12V, you need a 167x stepup.
Three 5.5x stages gets you to 2kV, and that's
a pretty mild step-up ratio. 66V, 363V, 2kV.
Stage currents and inductor values scale, since
they all run with the same time parameters.

Three feedback taps, each with a diode to the
controller's FB pin. The highest one controls,
to prevent any one stage from going excessively
over its voltage limit, but the last stage gets
the controlling vote. Very simple. Except for
HV winding technique of the 3rd inductor.

But surely that triple cascaded flyback topology you suggest would need
a MOSFET with 2000V Vds rating?

piglet

 

[Winfield Hill]

piglet wrote...

On 21/08/2019 9:34 am, Winfield Hill wrote:
mook Jonhon wrote...

2) flyback to do most of the boost with a
doubler or tripler on the output. This
should keep the turns ratio reasonable.

My flyback approach, previously detailed here
on s.e.d., is different. Three flyback stages,
each with its own MOSFET, all running from one
controller and gate driver. The DC input-V of
each stage is the previous stage's DC output.
Starting with say 12V, you need a 167x stepup.
Three 5.5x stages gets you to 2kV, and that's
a pretty mild step-up ratio. 66V, 363V, 2kV.
Stage currents and inductor values scale, since
they all run with the same time parameters.

Three feedback taps, each with a diode to the
controller's FB pin. The highest one controls,
to prevent any one stage from going excessively
over its voltage limit, but the last stage gets
the controlling vote. Very simple. Except for
HV winding technique of the 3rd inductor.

But surely that triple cascaded flyback topology you
suggest would need a MOSFET with 2000V Vds rating?

Details, details ... The HV MOSFET table in the
x-Chapters goes up to 4kV. But they're expensive.
The idea makes more sense up to 1.2 or 1.5kV.


--
Thanks,
- Win

 

[mook Jonhon]

mook Jonhon wrote:

Its been a while but once again looking at a HV pulser type
application.

It will charge up about 10nF to 2kV with about 1mA. Then keep it
toped off as that cap discharges into another capacitive much smaller
capacitive load. The 10nF will loose 100V or so then need to be
recharged witn 1mA before the next burst.

It need to be a custom approach due to environment constraints. Cost
is not a strong consideration but must be reasonable I can use custom
transformers etc.

The voltage does need to be variable from 1K to 2K.

no input to output ground isolation required. but sometime the load
shorts and the supply must go into current limit and not damage itself
when this happens.

looking for small topologies to do this.

1) boost inductor feeding a voltage multiplier (8-10 stage)
I have had 1A diodes blow when a previous VM design was shorted from
1.5kV. even with a 100K resistor in series with the output. never
investigated jsut sured up the source of the arcing and moved on with
fingers crossed.

2) flyback to do most of the boost with a doubler or tripler on the
output. This should keep the turns ratio reasonable.

3) straight pushpull making use of the primary voltage doubling action
to get soem volatge gain. PWM the center tap.

any other physically small power stage topologies to look into?

thanks

All great ideas and food for thought. great to see this group is
still a great resource. I tell my EE friends about it and that look
at me and ask "USEnet... whats that"

 

[Bill Sloman]

On Wednesday, August 21, 2019 at 9:39:01 PM UTC+10, mook Jonhon wrote:

Tim Williams wrote:

How small is small?

I made this without any particular care of size,
https://www.seventransistorlabs.com/Images/HVPower2.jpg
https://www.seventransistorlabs.com/Images/HVPower.jpg
(What, a legible, hand drawn schematic? On SED? :^) )

Easy enough to fix up the DC supply side for efficiency (buck reg),
fixed output, and drop the sense amp that's not needed.

The chopper is kinda here-nor-there, but I do recommend a resonant
type in any case as the secondary capacitance is unavoidable, and the
Baxandall oscillator is fairly foolproof as oscillators go.

Also, that was 12V input, but 48 isn't any trouble with appropriate
changes.

It seems there aren't many resonant controllers for smaller
applications (like DC-DC modules), so you may have to make a discrete
or digital controller if you want to go that route more formally.

Probably a CCFL transformer would do, no need for custom transformers
surprisingly enough.

If you need it small as balls*, you can stick CSP package GaN
transistors to the backside of a CCFL transformer, use a QFN or BGA
controller (which again, might end up sorta custom, an FPGA or
something), a few ceramic caps, probably a 4 or at most 6 layer
board, and be done.

*Erm, huh... literally about right, I think. You'd take up the other
ball for the reservoir cap. And some insulation which might just
wrap around the whole thing like a scrotum. I'll, uh, stop now.

If that's too extreme, any combination of Si components and leaded or
no-lead parts will do, requiring only somewhat more board area.

Tim


Thanks Tim,

I see you used a royer (push pull) with a voltage doubler on the back
side.

by small I need something to fit in a 1" v 2" board with the tallest
components about 1/4" above or below the board. It could be 1/2" tall
as the board sits on 1/4" standoffs. think pot core bolted to teh
chassis on one end of the board. maybe some wiggle room to 2.5" in
length.

I will need to run at highish frequencies (300+Khz) to get the
magnetics down but the continuous power levels will be low.

Step-up transformers with lots of turns have lots of stray capacitance. Doublers and triplers and Cockroft-Walton stacks let you get away with lower turns ratios, fewer turns and lower secondary inductance, but 300kHz might be a bit hopeful.

Getting something to fit on a 1" by 2" board (25mm by 50mm) and under half an inch (12mm) in height may be tricky too. Using printed windings in the transformer and inductor might help the height, but getting a much of a turns ratio might present problems.

Entertaining problem. Have fun.

With a Baxandall class-D oscillator - it may look like a Royer, but Peter Baxandall seems to have invented it to generate photomultiplier drive voltages and it's better than a Royer for that job - there's a pi/2 step up built in, so with a 45V rail you get 141V over the primary - 70.7V across the centre-tap at peak - so you'd only need a 15:1 turn ratio from primary to secondary to get to 2kV without a doubler.

> what you are suggesting is where I was going. Just making sure there
was not trick or "old magic" that I was not aware of to simply make
high votlage from low.

Baxandall's Class-D oscillator is old magic. It goes back to 1959. Jim Williams used it - much later - for his back-light driver (Linear Technology application notes AN45, AN49, AN51, AN55, AN61, AN65). It has been suggested that he got the circuit from the UK without the link to the Baxandall paper

http://sophia-elektronica.com/0344_001_Baxandal.pdf

which isn't all that easy to get hold of (which is why I put my copy on my website a few years ago).

--
Bill Sloman, Sydney

 

[Winfield Hill]

Bill Sloman wrote...

mook Jonhon wrote:
Tim Williams wrote:

I made this without any particular care of size,
https://www.seventransistorlabs.com/Images/HVPower2.jpg
https://www.seventransistorlabs.com/Images/HVPower.jpg

Push-pull osc. IMHO, way too high xfmr step-up ratio.

I see you used a royer (push pull) with a voltage
doubler on the back side.

Step-up transformers with lots of turns have lots of
stray capacitance. [ snip ]

With a Baxandall class-D oscillator - it may look like a
Royer, but Peter Baxandall seems to have invented it ...

A transformer with a push-pull primary driver is the best
way to get bipolarity output currents, needed for optimum
use of the Cockcroft-Walton diode step-up circuit. With
say six stages of that, you can keep your transformer
output voltages under 350V, greatly simplifying matters.

Get the push pull from a center-tapped transformer,
with several different possible driving schemes, or
better (more efficient, smaller xfmr), drive a single
primary with a half-bridge or full bridge. Available
in ICs, at low power levels, with no external MOSFETs.


--
Thanks,
- Win

 

On 21 Aug 2019 08:28:17 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Bill Sloman wrote...
mook Jonhon wrote:
Tim Williams wrote:

I made this without any particular care of size,
https://www.seventransistorlabs.com/Images/HVPower2.jpg
https://www.seventransistorlabs.com/Images/HVPower.jpg

Push-pull osc. IMHO, way too high xfmr step-up ratio.

I see you used a royer (push pull) with a voltage
doubler on the back side.

Step-up transformers with lots of turns have lots of
stray capacitance. [ snip ]

With a Baxandall class-D oscillator - it may look like a
Royer, but Peter Baxandall seems to have invented it ...

A transformer with a push-pull primary driver is the best
way to get bipolarity output currents, needed for optimum
use of the Cockcroft-Walton diode step-up circuit. With
say six stages of that, you can keep your transformer
output voltages under 350V, greatly simplifying matters.

Get the push pull from a center-tapped transformer,
with several different possible driving schemes, or
better (more efficient, smaller xfmr), drive a single
primary with a half-bridge or full bridge. Available
in ICs, at low power levels, with no external MOSFETs.

The flyback C-W circuit that I posted is simple and works fine. The
C-W stack just needs p-p voltage of most any sort.

https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1

That can deliver 8 watts at 1400 volts, so I had to heat sink the fet
and the transformer with copper pours. That DRQ127 is being abused at
that power.

The problem with board size is not the parts, it's keeping the HV
clearances. Conformal coating can help there.

 

[Tim Williams]

<jlarkin@highlandsniptechnology.com> wrote in message
news:hbpqlelas5jo4e929g3lemri8k9njthf8d@4ax.com...

The flyback C-W circuit that I posted is simple and works fine. The
C-W stack just needs p-p voltage of most any sort.

https://i.imgur.com/mbrcBLU.jpg
If it's got a CW hanging off it, it ain't flyback. It may be peaky, but it
ain't flyback.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

"mook Jonhon" <mook@mook.net> wrote in message
news:k3a7F.5747$452.4002@fx02.iad...

I see you used a royer (push pull) with a voltage doubler on the back
side.

NOT Royer -- the transformer is not saturating. Commutation is resonant,
albeit badly so, because the leakage of the transformer wasn't very high.
So it ran poorly under heavy load. But that's easily fixed with the right
style transformer. And under nominal load, it ran around 65kHz with nicely
rounded edges.

by small I need something to fit in a 1" v 2" board with the tallest
components about 1/4" above or below the board. It could be 1/2" tall
as the board sits on 1/4" standoffs. think pot core bolted to teh
chassis on one end of the board. maybe some wiggle room to 2.5" in
length.

Yeah, that sounds about like what I described.

what you are suggesting is where I was going. Just making sure there
was not trick or "old magic" that I was not aware of to simply make
high votlage from low.

I suppose the only "old magic" that applies is the Tesla coil, which is a
pulsed power application. If you have adequate leakage in the transformer,
you can drive it with a bridge for some number of cycles, and in that time
the output voltage (and input current!) will ramp up and up and up,
eventually flattening out as losses balance the input power (whether core
loss, arcover, or rectifiers turning it into DC). The available output peak
current is high, so the duty cycle is low.

But I don't think this saves you anything, and you can already get a cored
transformer of adequate rating, so you don't need to pound on an air-cored
transformer to get it going this way. You'd end up taking more space not
just for the coil but also the driver, because peak currents and energy
storage (the input ripple would be a bitch ).

The hysteretic approach to regulating output voltage may still be relevant.
Baxandall (and Royer) oscillators work over a surprisingly wide supply
voltage range, but they do eventually flounder at low voltages, and a
hysteretic control, starting and stopping the oscillator, may be more
efficient.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[John Larkin]

On 21 Aug 2019 10:55:02 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

jlarkin@highlandsniptechnology.com wrote...

Winfield Hill wrote:

A transformer with a push-pull primary driver is the best
way to get bipolarity output currents, needed for optimum
use of the Cockcroft-Walton diode step-up circuit. ...

The flyback C-W circuit that I posted is simple and works
fine. The C-W stack just needs p-p voltage of most any sort.

Yes, I know it works, and I puzzled over its asymmetry
at the time. A flyback is very strong in one direction,
but rather weak in the other. And your coupled inductor
was another confounding factor, with its high capacitance.

https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1

That can deliver 8 watts at 1400 volts, so I had to heat
sink the fet and the transformer with copper pours. That
DRQ127 is being abused at that power.

mook's power requirement is pretty low.

The mosfet source resistor sets the peak inductor current, hence the
max power output and inductor stress. That tiny LTC chip is great and
seems to always work. At low power, a smaller fet would be better...
less drain capacitance to charge up. As you note, boost ratio is
usually capacitance limited.

It might be Spiced, or breadboarded, to optimize for lower power. I
did both in my applications.

There may be an optimum way to connect the 4 wires of the dual
inductor autotransformer.

 

[Winfield Hill]

jlarkin@highlandsniptechnology.com wrote...

Winfield Hill wrote:

A transformer with a push-pull primary driver is the best
way to get bipolarity output currents, needed for optimum
use of the Cockcroft-Walton diode step-up circuit. ...

The flyback C-W circuit that I posted is simple and works
fine. The C-W stack just needs p-p voltage of most any sort.

Yes, I know it works, and I puzzled over its asymmetry
at the time. A flyback is very strong in one direction,
but rather weak in the other. And your coupled inductor
was another confounding factor, with its high capacitance.

https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1

That can deliver 8 watts at 1400 volts, so I had to heat
sink the fet and the transformer with copper pours. That
DRQ127 is being abused at that power.

mook's power requirement is pretty low.

The problem with board size is not the parts, it's keeping
the HV clearances. Conformal coating can help there.

--
Thanks,
- Win

 

[John Larkin]

On Wed, 21 Aug 2019 12:14:48 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

jlarkin@highlandsniptechnology.com> wrote in message
news:hbpqlelas5jo4e929g3lemri8k9njthf8d@4ax.com...
The flyback C-W circuit that I posted is simple and works fine. The
C-W stack just needs p-p voltage of most any sort.

https://i.imgur.com/mbrcBLU.jpg
If it's got a CW hanging off it, it ain't flyback. It may be peaky, but it
ain't flyback.

Tim

It doesn't care what you call it. It works great.

 

[Bill Sloman]

On Thursday, August 22, 2019 at 1:49:45 AM UTC+10, jla...@highlandsniptechnology.com wrote:

On 21 Aug 2019 08:28:17 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

Bill Sloman wrote...
mook Jonhon wrote:
Tim Williams wrote:

I made this without any particular care of size,
https://www.seventransistorlabs.com/Images/HVPower2.jpg
https://www.seventransistorlabs.com/Images/HVPower.jpg

Push-pull osc. IMHO, way too high xfmr step-up ratio.

I see you used a royer (push pull) with a voltage
doubler on the back side.

Step-up transformers with lots of turns have lots of
stray capacitance. [ snip ]

With a Baxandall class-D oscillator - it may look like a
Royer, but Peter Baxandall seems to have invented it ...

A transformer with a push-pull primary driver is the best
way to get bipolarity output currents, needed for optimum
use of the Cockcroft-Walton diode step-up circuit. With
say six stages of that, you can keep your transformer
output voltages under 350V, greatly simplifying matters.

Get the push pull from a center-tapped transformer,
with several different possible driving schemes, or
better (more efficient, smaller xfmr), drive a single
primary with a half-bridge or full bridge. Available
in ICs, at low power levels, with no external MOSFETs.

The flyback C-W circuit that I posted is simple and works fine. The
C-W stack just needs p-p voltage of most any sort.

https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1

That can deliver 8 watts at 1400 volts, so I had to heat sink the fet
and the transformer with copper pours. That DRQ127 is being abused at
that power.

The problem with board size is not the parts, it's keeping the HV
clearances. Conformal coating can help there.

The charm of the Baxandall class-D oscillator - as spelled out by Jim Williams, even if he didn't cal it that in Linear Technology's application notes AN45, AN49, AN51, AN55, AN61, AN65 - is that it can be 95% efficient, which can mean very little waste heat to be dissipated.

--
Bill Sloman, Sydney