48V to 2000V DC-DC smallest design

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

Reply to
mook Jonhon
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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.

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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.

Reply to
jlarkin

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lator1.htm

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

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

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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.

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Bill Sloman, Sydney
Reply to
Bill Sloman

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.

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mikko
Reply to
Mikko OH2HVJ

On a sunny day (Wed, 21 Aug 2019 01:46:40 GMT) it happened "mook Jonhon" wrote in :

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

9 V to 500 V for GM tube
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5 V to 1250 V for PMT

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5 V to 1750 V for PMT
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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.

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it all depends, takes half an hour to wind a core like that.

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

Reply to
Jan Panteltje

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. :-)

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 Thanks, 
    - Win
Reply to
Winfield Hill

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" :)

Reply to
mook Jonhon

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

piglet

Reply to
piglet

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.

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 Thanks, 
    - Win
Reply to
Winfield Hill

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

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.

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 Thanks, 
    - Win
Reply to
Winfield Hill

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.

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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.

Reply to
jlarkin

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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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Reply to
Tim Williams

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.

Yeah, that sounds about like what I described.

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 
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Reply to
Tim Williams

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

Reply to
John Larkin

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.

mook's power requirement is pretty low.

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 Thanks, 
    - Win
Reply to
Winfield Hill

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.

Reply to
John Larkin

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.

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Bill Sloman, Sydney
Reply to
Bill Sloman

Does this count as "custom":

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

48 volt DC to 220 AC inverter:
Reply to
bitrex

(hell no I've never built this in case you're wondering.)

Reply to
bitrex

arc lighter circuit:

This blocking flyback produces kilovolts in a singe step.

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there's also some with bank-wound secondaries on split square ring cores.

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  When I tried casting out nines I made a hash of it.
Reply to
Jasen Betts

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