12V - 1kV DC/DC Converter - Page 1
Forum section: electronics / general

author: nicknails
author_rank: Regular Contributor
timestamp: May 13, 2025, 02:57:21 pm
content: I'm not sure if this should go here, or in the projects forum.I'm looking to make a 12V in converter that can be adjustable from somewhere around 200V-1000V. The adjustability would come from an external 0-1V analog signal. The output power is only 0.75W (0.5mA @ 1kV) Max. I though of using a cockcroft-walton multiplier so the transformer doesn't need to go that high. However, I don't think that would work well with a flyback. Then I thought of doing a Royer or Baxandall, which is great for CW Multiplier, but more challenging for the transformer (my transformer theory is minimal).Funny thing is I used to work at a company that made this exact thing. Pretty sure it was a royer with a feedback signal to an op-amp for control. But I can't remember for the life of me how the op-amp actually adjusted the output.Are there any issues with just doing a flyback with a high turns ratio? I thought of doing a feedback network to a separate op-amp with the 0-1V signal as a reference, then feed the output of that into the feedback pin of whatever IC is used.

author: langwadt
author_rank: Super Contributor
timestamp: May 13, 2025, 03:13:29 pm
content: does it have to be small or efficient?

author: nicknails
author_rank: Regular Contributor
timestamp: May 13, 2025, 03:19:21 pm
content: Quote from: langwadt on May 13, 2025, 03:13:29 pmThe smaller the better, within reason. I don't really care about efficiency, as long as it doesn't get to an unreasonable temperature. I'd prefer not to have to have a heat sink.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: May 13, 2025, 06:20:16 pm
content: as a starting point you can modify a standard circuit - out since 40 yrs - for supplying Geiger tubes (~200 ... 500V plateau). Elektor (and many others) published it after '84 Cernobyl desaster. Based on a 555, a conventional tiny pcb transformer 220/6V operated in reverse direction and a 20 .. 100Mohm feedback line.

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 14, 2025, 09:26:47 pm
content: It is possible to do it in a single flyback converter. The challenges are:1. The large number of secondary turns makes the transformer's self-resonance frequency low, especially if the windings have multiple layers.2. You'll need a very high voltage flyback diode (probably 2kV or more).3. Need to be careful to prevent arcing within the transformer (both across the secondary and between primary and secondary).Another reasonable approach is to use a push-pull stage to boost the voltage up to >100V, then use a few stages of your favorite voltage multiplier circuit to get the rest of the way to 1kV. That makes the transformer a lot easier to manage.

author: uer166
author_rank: Super Contributor
timestamp: May 14, 2025, 09:32:44 pm
content: Quote from: mtwieg on May 14, 2025, 09:26:47 pmAgree that 1-stage Flyback with some care is the way to go. 2kV of diode is trivial these days, and tbh 1kV is low enough voltage where there are few acring concerns.

author: cdw
author_rank: Contributor
timestamp: May 15, 2025, 10:47:01 am
content: I've gone for a single-stage flyback too, in similar projects. Linear/Analog have an application note which shows a 1000V 1-10mA flyback using one of their ICs, that has a nice idea on the output stage: it's an off-the-shelf 1:10+10+10 transformer (still in production and available from stock) with separate diodes and capacitors on each of the three windings. That means you can use nicer 800V diodes, and 600V capacitors which are in more of a sweet spot for prices:https://www.analog.com/en/resources/technical-articles/1000-v-output-no-opto-isolated-flyback-converter.htmlI've used ES1K diodes with that transformer, for example.But for 200V-1000V, you'd probably want to do something else on the controller side if you use that transformer and output stage. You can easily make LT8304(-1) variable voltage by injecting current into the Rref pin to bias it, but the minimum current draw you need for stability goes up as you reduce the voltage, which makes it a pain for a wide voltage range. (Unless you/someone else has a cleverer idea than I can come up with to work around that.)