24V to 500-1000V, 20W floating DC-DC converter

The transformer that I suggested should just work. Why wind transformers that are already stocked and available as samples?

The only interesting issue will be getting feedback from the isolated side. That might be done by inference on the low side (as I posted recently), or optocoupling, or a high-side regulator.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

I'm not entirely convinced OP knows what he needs either, charging up a

5uF cap bank to 1kV for a piezo driver? sure love to know what the application is.

Not particularly, as you say you're the man for the job. I'm just providing suitable encouragement. Can't wait to see it up and running on a sheet of copper clad and your measurements on it - it's going to be great!

I'll be taking you up on that offer. Hopefully I can get around to the design this weekend.

Fortunately I do know what I need. Your assumptions, insinuations and trolling throughout this thread is unwarranted. You are focused entirely too much on the bypass capacitors. The necessary information is that I have a load that needs 20W at 1000V.

OK, you're not MAN enough to approach a thousand volts. Even in simulation. You might get shocked and frightened and stuff. Post Traumatic Spice Disorder.

If I do the HV pulser for this customer, I will certainly post pics. I've posted lots of such things before.

(The best are proprietary)

With that sort of attitude, everybody will be lining up to give you free help, for sure.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Cool. Group designs are fun. We rarely do that here.

You'll need a model of the transformer, magnetizing and leakage inductance and maybe some capacitances. Those are easy to approximate.

I may not be the top engineer on the planet, but I am pretty good at spotting His Majesty and letting someone else handle him.

Look pal, if you want to learn about flyback converters, fine. If you know exactly what you need and want it designed and built to your precise spec consider hiring an engineer to do it. Or go to a Burger King if you just want to give orders.

Screening out arrogant asses who don't even understand the (hazardous!) circuits they're posting but want to play with even bigger toys is 100% good policy. If someone else wants to take you on for free I'm 100% happy for them to do that.

Lol

Well I hope you get compensated for your labor fairly. GL

This is the only company we have approved for high quality copper wire, specifically for SELV rated systems:

Awesome! I hope you'll share whatever pieces of the design here that you can. A few milliamps at 1kV can be used for lots of things. (I'm a flyback tadpole.. so just lurking. :^)

George H.

He's sure not going to hire you. You are afraid of electricity.

That's OK. Lots of people are afraid of electricity.

Less than half the things that we design and build turn out to be profitable. We bet too often on the success of our customers. And sometimes on their honesty.

A minority of the projects pay the bills. Almost all are fun and educational. So the trick to survival is to design a lot of stuff fast.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

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upply for a pulser. It needs to be a floating or negative converter.

. So far the only one I've come across that is isolated is Figure 50 of LT Application Note 29

It is specified for 1000V, 5W so not beefy enough. The transformer is also obsolete, but this comment mentions potenti al replacements.

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It's one approach. In evolution, it is called the low investment, high volu me, strategy.

If you design less stuff, and take long enough over it to do it well, you c an survive on a different basis. The people I worked were selling complicat ed solutions to difficult problem, and if you didn't do it well, the produc t didn't work and couldn't be sold.

--
Bill Sloman, Sydney

When my gut tells me a potential client isn't being straight up with me I push back on them, as above, and ask questions.

If and when they get pissy at my skepticism that tends to tells me all I need to know, which is that at minimum, I don't want them as my client.

From experience it also tends to mean they don't pay their bills on time.

You've watched "Shark Tank" and actually read Trump's book, right? There actually is a bit of decent advice in there.

On a sunny day (Thu, 23 Jul 2020 08:37:36 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in :

You could probably re-purpose an old CRT transistor color TV or monitor:

1.5 mA at 25kV is 37.5 W. Remove HV coil from EI transformer. Remove scan coils, those are about 440Vpp IIRC?? Use that winding, 1 x voltage doubling, 2 diodes. Designing and building from junk box is fun I once triggered a BU208 from an UJT to generate H scan and HV. Play around a bit.

On a sunny day (Thu, 23 Jul 2020 11:38:47 -0700) it happened John Larkin wrote in :

Yes

1 volt per turn For 24V DC in 24 turns primary Flyback voltage about 5 x 24 say 100V for simple-city. So secundary for 1000V is 10 x 24 = 240 turns. Look up wire diameter for currents. Look up EI core for 30 W or so. Use 16 kHz or a bit higher for switching frequency.

Transistor, flyback diode, MVB? pulse witdth feedback for stabilization for example.

Spice? I use lost of Chili :-)

I made this some time ago,

UC3843 based flyback, very much a stock circuit, with an RCD snubber added to the transistor I think. 12V input, but 24V is fine too, with a UC3842 and a couple component values changed.

Interesting part is the transformer, which has this windup,

3 layers of copper foil tape primary, with the secondary interleaved between layers 1-2 and 2-3. Each secondary is 15 turns 28AWG. They are wired in series, with the CT used as a ground point, and the rectifiers being complementary. Thus, effectively the output is (up to) +/-400V.

Core is EE33, slightly gapped. (Hmm, weird, I thought those cores were closer to 1uH/t^2 ungapped. Did that particular one just happen to overperform?..) Way overkill for this power level (under 50W) but I have a bunch of them on hand. :)

This module grounds the negative, so a positive output is obtained and a feedback divider can be used to regulate. (The divider is adjustable for a

100-800V range.)

For isolated application, the feedback divider has to be secondary side only and a TL431 used for error amp, into an opto, in the usual way. It should probably be powered by an aux winding, say 10V (about one turn?) so you don't have to draw several mA from the full HV to run it.

The balanced secondary design is essentially mandatory for an isolated converter. This cancels out most of the EMI; rather than 400V of delta V across the isolation barrier, there's only ~40V due to the primary's still unbalanced voltage. This could be improved further by adding shields, at some expense to leakage inductance.

I don't know where you would find such a transformer off-the-shelf. They're not hard to wind if you just need a few, or you could ask someone like Xfmrs to make them. The interleaving, and balanced design where possible, are critical to performance, and having sane EMI.

And by "sane" I mean, if the secondary is unbalanced, you'll literally be running a low amplitude EFT generator or some bullshit like that. Futile to filter. And you probably don't want too much filtering impedance so as to keep it reasonably well isolated at AC too..?

Tim

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

"Matt B"  wrote in message  
news:ce1d66d4-3a89-45f2-b03e-d45f5fd00d39o@googlegroups.com... 
I need to make a 24V to 500-1000V, 20W adjustable power supply for a pulser.  
It needs to be a floating or negative converter. 

My specs are: 
Input: 24-28V 
Output voltage: 500-1000V adjustable via control signal 
Output current: 10mA @ 500V (5W), 20mA @ 1000V (20W) 

I've been reading through threads on different HV designs. So far the only  
one I've come across that is isolated is Figure 50 of LT Application Note 29  
(https://www.analog.com/media/en/technical-documentation/application-notes/an29f.pdf).  
It is specified for 1000V, 5W so not beefy enough. The transformer is also  
obsolete, but this comment mentions potential replacements.  
https://groups.google.com/d/msg/sci.electronics.design/F120QpxWWkc/74ljdPZ_BQAJ 

There's also this design  
(https://www.edn.com/1-kv-power-supply-produces-a-continuous-arc/) that is  
1kV, 20W. I just don't know enough about making it adjustable and isolated. 

Thoughts on how to proceed?

And here is 50uF/900V, probably smaller:

Best regards, Piotr