48V to 2000V DC-DC smallest design

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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




  



Re: 48V to 2000V DC-DC smallest design

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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.


Re: 48V to 2000V DC-DC smallest design
On Wednesday, August 21, 2019 at 11:46:45 AM UTC+10, mook Jonhon wrote:
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http://www.sophia-electronica.com/Baxandall_parallel-resonant_Class-D_oscil
lator1.htm

The circuit diagram at the bottom of the page shows a circuit which looks l
ike 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 th
e low pass filtering at the output averages out the alternation.

--  
Bill Sloman, Sydney




Re: 48V to 2000V DC-DC smallest design

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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

Re: 48V to 2000V DC-DC smallest design
On a sunny day (Wed, 21 Aug 2019 01:46:40 GMT) it happened "mook Jonhon"

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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...





Re: 48V to 2000V DC-DC smallest design
mook Jonhon wrote...
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 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

Re: 48V to 2000V DC-DC smallest design
On 21/08/2019 9:34 am, Winfield Hill wrote:
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But surely that triple cascaded flyback topology you suggest would need  
a MOSFET with 2000V Vds rating?

piglet


Re: 48V to 2000V DC-DC smallest design
piglet wrote...
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 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

Re: 48V to 2000V DC-DC smallest design
On 8/21/19 8:19 AM, Winfield Hill wrote:
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Does this count as "custom":

two multi winding power transformers (220 instead of 120, say)

<https://www.dropbox.com/s/hv086gf97sgwuyz/Photo%20Mar%2019%2C%2011%2030%2008%20PM%20%28edited-Pixlr%29.jpg?dl=0

48 volt DC to 220 AC inverter:

<https://www.invertersupply.com/index.php?main_page=product_info&products_id31%043&gclid=CjwKCAjw1_PqBRBIEiwA71rmtUbYId5MEJqs7JBSBopoGTKSaxIOkUKkV6VA01VIocxgLAesoIymQRoCgboQAvD_BwE


Re: 48V to 2000V DC-DC smallest design
On 8/22/19 2:25 AM, bitrex wrote:
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(hell no I've never built this in case you're wondering.)

Re: 48V to 2000V DC-DC smallest design
bitrex wrote...
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 Why not both xfmr primaries to the 120, and their
 four secondaries on series?


--  
 Thanks,
    - Win

Re: 48V to 2000V DC-DC smallest design
mook Jonhon wrote:

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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"   :)


Re: 48V to 2000V DC-DC smallest design
Bill Sloman wrote...
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 Push-pull osc.  IMHO, way too high xfmr step-up ratio.

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 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

Re: 48V to 2000V DC-DC smallest design
wrote:

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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.



Re: 48V to 2000V DC-DC smallest design
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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
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Re: 48V to 2000V DC-DC smallest design
On Wed, 21 Aug 2019 12:14:48 -0500, "Tim Williams"

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


Re: 48V to 2000V DC-DC smallest design
snipped-for-privacy@highlandsniptechnology.com wrote...
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 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.

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 mook's power requirement is pretty low.

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--  
 Thanks,
    - Win

Re: 48V to 2000V DC-DC smallest design
wrote:

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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.


Re: 48V to 2000V DC-DC smallest design
On Thursday, August 22, 2019 at 1:49:45 AM UTC+10, jla...@highlandsniptechn
ology.com wrote:
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The charm of the Baxandall class-D oscillator - as spelled out by Jim Willi
ams, 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, whic
h can mean very little waste heat to be dissipated.

--  
Bill Sloman, Sydney

Re: 48V to 2000V DC-DC smallest design
snipped-for-privacy@highlandsniptechnology.com wrote in  

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Above 1000V it should be potted and no solder mask on the HV section.

  Potting boxes can be obtained or spec'd at just over the profile  
height of your multiplier section, which should be separated from the  
rest of that board.  That minimizes the section size needing a pot  
shell slipped over it.

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