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Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Tue May 05, 2020 7:31 am
by John Futter
yes I was talking about reputable supplies not aliexpress or banggood both of the later sell knockoffs that generally take their specs from the original but the product is nowhere near the original
this also appies to components like gate driver ics mosfets, IGBTs, RF transistors, ZVS driver boards, just see what the tesla coiling people are saying ---STAY AWAY from the chinese junk you get exactly what you pay for --high priced rubbish

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Tue May 05, 2020 8:19 am
by Rex Allers
John,

Any chance you could find and share a link (Mouser or etc.) to the kind of supply you are talking about?

Or details of the manufacturer/model.

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Tue May 05, 2020 7:20 pm
by John Futter
Rex
I'll try
I'm in lockdown still but there are people at work who know what we bought i'll see

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Wed Jul 01, 2020 7:15 pm
by Cai Arcos
After the final exams and some unexpected health issues, I'm finally able to continue working. I just got the inverters for a power supply like that demonstrated by Nathan Marshall, but before that I'm (again) revising the HV supply.

More specifically, I've found a way to use the blocking oscillator effectively: by connecting an appropiate sized capacitor across the primary (the winding between Vcc and the collector) the charging and discharging happens in a resonant way, thus the output waveform is really similar to a sinewave and the noise (using the same filter as before: another thing I have to optimize) is way down: I cant distinguish it from background (which is around 100mV). This is promising, because it's a stellar performance (with a relatively stiff output too) for very few components and a very low cost.

I'm also using this cheap chinese flyback transformer (https://www.ebay.es/itm/15KV-High-Volta ... Sw-89ZRPh7) (I say flyback because despite not having any specifications, it has two small pieces of paper separating the yoke). The turns-ratio is also really high so I can operate at really low primary voltages.
The only thing I have to figure out is how to regulate the output without including excessive noise. In the internet I've seen a transistor stealing current from the base of the original oscillator, but without lineal control that seems noisy. Any ideas?

As soon as I have everything figured out, I will post en extensive explanation (LTSpice simulations, schematics, etc)

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Tue Jul 07, 2020 10:43 am
by Cai Arcos
After becoming tired of feedback compensation shanaenigans, poor regulation and spurious oscillations, i'm now looking to linear high voltage, maida style regulators.
I've even found the fascinating LR8, a one-package, 400V, cheap, linear regulator! Wow! Is there any problems or quirks (aside from power regulation) I should be aware of?

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Thu Aug 27, 2020 8:57 am
by Cai Arcos
This linear regulator are toys, with terrible regulation under load and tremendously easy to pop. I have finished the supply now, using a classic series regulator with a HV transistor from a CRT TV.
If anyone is interested in pursuing low noise power supplies, GET A DIFFERENTIAL PROBE! I can not tell you how many times I've being fooled by common mode noise and how many hours wasted tracking inexistent noise supplies. If you don't have it, you are handicapped (like me). Short ground clips (use the tiny ground springs) and always triggering the scope on the input waveform are a must. If the "noise" also does not trigger, or/and changes amplitude changing the lenght or shape of the ground clip, then you should most likely ignore it.
And do some serious indepth reading about noise before going down the rabbit hole.

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Thu Aug 27, 2020 10:26 pm
by Richard Hull
Sounds like you have a good grip on the effort related to noise. I bought a Tektronix differential probe system at a hamfest at a "silent key" sale of $10.00 (the sellers did not know what it was. It was listed at over a thousand dollars by Tek!!). It is a high voltage differential probe and can handle 1kv. Sweet! I have only needed it a couple of times since I bought it. You are right about triggering and grounding issues went poking about for noise. Did I mention, I hate noise!! I hate chasing it down.... Fortunately, noise is not an issue in most of my current work.

Richard Hull

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Fri Aug 28, 2020 4:46 pm
by Joe Gayo
Why not filter with a 2-stage RC filter, like what every preamp uses? Since the bias current is low the resistor values can be MOhms.

http://sim.okawa-denshi.jp/en/CRCRtool.php

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Sat Aug 29, 2020 7:59 am
by Cai Arcos
Joe:

If you use a fluorescent lamp inverter and this filter (just like Jim Williams used) the noise will be indistinguishable from background. However I wanted to add feedback as to make the supply regulated, and it always seemed to introduce noise. As of right now, and trying to learn as much as possible about feedback compensation and such, and are experimenting with a simple circuit that seems to work, more or less.
One of my main learning points have been that you can not say simply "add feedback to make it regulated" to a noiseless supply and expect it to stay that way without additional care.

Re: Help with HV adjustable power supplies for radiation detectors.

Posted: Sat Aug 29, 2020 3:23 pm
by Joe Gayo
Feedback will cause instability if the gain loop crosses 0dB at more than -20db/decade