Help with HV adjustable power supplies for radiation detectors.

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

Help with HV adjustable power supplies for radiation detectors.

Post by Cai Arcos »

Hi:

I'm in the process of building a variable (0-600V), relatively silent (400mV peak to peak noise maximum) and able to sustain it's output voltage under a 1Mega omh load power supply for work in development of radiation detectors. The schematic I post have achieved that, with a noise of around 360mV peak to peak. It is based on a design that appears at the 3rd edition of The Art of Electronics (also included), substituing the HV module with a CCFL inverter and a rectifier/filter. The idea to use a resistor in the output filter (as well as it's value) is from App Note 118 of LT "High Voltage, Low Noise, DC/DC converters" by Jim Williams. Along the prototyping part of the project I have developed some doubts that I hope this board can help me with:

1) If I understand correctly, the Cc and Rc in the original schematic serve to create a PI controller. When using them and adjusting the output voltage, the output comes to the needed voltage more slowly and also "rings" a little bit, which I believe proves their function. However, they also significantly increase the noise creating a sinusoidal wave (whose frequency is controlled by Rc and Cc) that with the values suggested reach around 1,5 V p-p (reducing the value of the capacitor reduces a little this value). This is the reason they are not in my schematic. Why this increase in noise? Do they serve other purposes?

2) What is the function of the 162 kilo ohm resistor present in the original schematic? Since the op amp practically draws no current, it seems useless.

3) This is the most puzzling. I originally used a 1.2k resistor and 6.1V zener to generate the 6V required at one leg of the pot that controls the feedback. This reasulted in a sinusoidal-ish noise output with around 1,6V p-p. The issue was completely resolved when this voltage was derived using only the divider. Furthermore, when the feedback pot is turned maximum (and thus the zener conducts to clamp the feedback voltage) the same effect (although slightly reduced) appears again. What is happening with the zener diode to create that noise at the output?

Thanks!
Attachments
AOE.jpeg
Schematic.jpeg
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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

Post by John Futter »

Why did you leave the high frequency gain reduction out??

Also a small cap across the 1 meg resistor would help inspeeding up the feedback loop

As it is the circuit is very short on stability ie it might oscillate rather than regulate
User avatar
Rich Feldman
Posts: 1470
Joined: Mon Dec 21, 2009 6:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

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

Post by Rich Feldman »

Are CCFL inverters OK with having one output terminal grounded?

If yes, then who needs bridge rectifier?

If no, then driving both AC terminals of a bridge rectifier won't make it OK to ground one of the DC terminals.

CCFL inverter does seem like compact and inexpensive way to avoid generating high frequency AC yourself.
Maybe the inverter outputs can be AC coupled into some kind of rectifier or multiplier circuit.

THere was some discussion on fusor.net about 10 years ago, about combining the power from many CCFL inverters using something like that.
All models are wrong; some models are useful. -- George Box
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

John:

I wrote this late at night and made an important mistake. The Rc and Cc components don't introduce oscillation. I thought so because I tested the whole circuit when using the zener diode (the source of noise). I have now included them back and the circuit works the same way (it didn't oscillate before at all, but better be safe than sorry). Sorry for the error.

I include two captures of the output (AC coupled). The one that is "silent" is using the circuit attached below with the high frequency roll of components included. The other is the same: except that the divider at one leg of the pot is replaced by a 2.2K and 6.1V zener. This is what is causing most of my headaches.

What value should the speed-up capacitor be?
Attachments
Voltage divider: no zener.
Voltage divider: no zener.
Zener used to derive a reference voltage.
Zener used to derive a reference voltage.
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

Rich:

I had found two posts regarding CCFL inverters:

viewtopic.php?f=13&t=12097&p=78757&hilit=CCFL#p78757
viewtopic.php?f=11&t=4775&p=31184&hilit=CCFL#p31184

In Doug Coulter's Forums there is also extensive discussion on noise and such: the problem is that no feedback is used in that case (which makes sense for what they're using it. As they say, you have problem if your He3 tube draws enough current to cause the output voltage to drop).

I think I've not expressed myself well (as per usual). The CCFL converter is a Royer Oscillator, whose output is a 120Khz sinusoidal voltage isolated from the input. I rectify/filter it, and then connect the ground of the bridge to the ground of the primary circuit because I don't need any isolation. I now see the schematic was not well made, and thus not clear.
Attachments
Rectifier.jpeg
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

John:

I problem I've noticed when using Rc and Cc: after leaving the circuit for around 2 or 3 minutes, the noise increases dramatically. I post the noise measurement with different values of Rc and Cc used and the result. It seems as this is the phenomena I was first describing. It seems as if the circuit is oscillating: which did not happened without them.
Attachments
Rc=1k Cc=10pF
Rc=1k Cc=10pF
Rc=10k Cc=10pF
Rc=10k Cc=10pF
Rc=10k Cc=10nF
Rc=10k Cc=10nF
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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

Post by John Futter »

Try a speed up cap across R1 47pf to 220pf but it should be ca 1kV type
User avatar
Rich Feldman
Posts: 1470
Joined: Mon Dec 21, 2009 6:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

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

Post by Rich Feldman »

When using scope to measure ripple on HV output, pay attention to the voltage rating of oscilloscope in AC mode.
It might be safer to use your own DC blocking capacitor, with well known voltage rating, and leave scope channel in DC mode.
All models are wrong; some models are useful. -- George Box
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

John:

In the end, I actually recreated one of the schematics posted in the attached posts and buffered the feedback. Probably due to the very limited slew rate of the LM324, no oscillations happened, an it fact the noise is now under control. Adding the speed capacitor actually reduces a little bit more the noise, and so I have added it. Now the problem is that the CCFL inverter I took from an emergency light does not have enough power, and now I'm looking for something like this:

https://www.pollin.at/p/ccfl-inverter-c ... -kv-121244

Rich:

I'm considering recreating what you have made in here:

viewtopic.php?f=13&t=12649&start=20

What roll-off frequency have you chosen?
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

Hi:

I've been using some time of the quarantine to work on the high voltage supplies. Unfortunately, due to somo environmental regulations I was unable to buy the inverters showed in a previous post, so I tried other ways.

I *must* recommend to everyone interested in this type of work the App Note 118 of Linear Technologies by Jim Williams "High Voltage, Low Noise, DC/DC Converters". What I did find was an old LCD monitor. I teared it up and discovered that the HV section was a center tapped transformed being push-pulled by two N-Channel MOSFETs. By operating the transformer at it's resonant frequency, and using the filter shown in the figure 13 of the App Note, I am able to get around 250mV of noise at 400 V. One can also add a small capacitor (100pF in my case) between gate and drain in order to slow down the transitions (in a manner similar to that shown in the App note but without the specialized IC), but the noise was worse than that obtained with the sinuisoidal voltage at resonance. In both cases, the supply is a lot more stiff that the CCFL inverter, not buckling under a 1M load and going down to around 350V with a 100K load (I can increase the power supply of the primary and sustain the 400V no problems). Salvaging these screens seems the way to go, and most come with two transformers (because of the number of cold cathode lamps in the display). In the future I probably will try to make it adjustable, but for my current quenching circuit experiments in GM tubes a fixed voltage should be good enough.

I also tried to use the always popular "Joule Thief" (in the version used by HV enthusiasts using a secondary). While undoubtedly a very ingenious and interesting circuit, it is most suited for applications needed a relatively low output impedance and low component count, since its discontinuous power delivery and high frequency content make it hard to obtain reliable low noise. One can, however, make a compromise on the output voltage and reduce the noise by reducing rise times by inserting a small capacitance between colector and base of the transistor.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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

Post by Richard Hull »

I have found these little high frequency transformers very handy for supplies up to 2kv. They can supply a decent amount of current of 1ma if driven hard. Most really large screen TV's that have twenty or more CCFL tubes used 4 or more of these on their driver boards. Such boards feed these with 24-48 volts DC. Yes, they are current hogs, but do supply decent current out of up to several mA needed to light the long tubes. Each transformer might supply 5 or more long tubes in banks. I have collected about 100 various types of these from scrapped flat screens. I originally hoped to use them as bias supplies for GM, PM and neutron detectors, but you have too many varieties in such a pile that each one or set of 4 would require to hand trim each group of supplies to spec. For one offs, they are great, however.

They can be made portable for battery power if under driven and only a few microamps are needed. I find the trend was to use 4-6 small transformers on the driver boards on big screens, but now they tend to use only two much larger, weighty transformers to reduce the component count. Battery, portable operation would tend to make these larger ones problematic, but mains operation could see these used for rather stiff high frequency, high voltage supplies.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Sarmad suseyn
Posts: 58
Joined: Sun May 03, 2020 1:37 pm
Real name: Sarmad
Location: Kuwait
Contact:

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

Post by Sarmad suseyn »

Hi .
Isn't easier to buy one?
Like this one it tried it works just fine
https://a.aliexpress.com/_dXvy7er
Good luck
Attachments
15885351676286295948080977026079.jpg
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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

Post by Richard Hull »

The board says 200 volts. Is that enough? Can you blast in more than the stated 5 volts to get more voltage. If so, what is the current drain from the low voltage supply. Will the pot on the board allow for more than 200 volt adjustment. Not many nuclear detectors will work at 200 volts. what is your detector? Ion chambers can work as low as 150 volts.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Sarmad suseyn
Posts: 58
Joined: Sun May 03, 2020 1:37 pm
Real name: Sarmad
Location: Kuwait
Contact:

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

Post by Sarmad suseyn »

Dear Richard Hull
No its not 200v !
On 5 volts maximum you will get 700v
But on 9 v you will get 1000v
There is a soldiering points fixed voltage 200v, 50v , 170v
The green terminal is the main out voltage
And you can adjust the voltage with the variable resistor
Have a good day
Attachments
Screenshot_20200504-023838_Samsung Internet.jpg
Screenshot_20200504-023225_AliExpress.jpg
Sarmad suseyn
Posts: 58
Joined: Sun May 03, 2020 1:37 pm
Real name: Sarmad
Location: Kuwait
Contact:

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

Post by Sarmad suseyn »

And the easiest way to find a high voltage Module is from
Rechargeable Electric Mosquito Zapper it gives 2000 volts
And some adjusting with variable resistor you can use it
Its called the poor mans Hv😆 you can get it for 10$
Attachments
-16512414741709180076.jpg
1634171217-2032886728.jpg
1634171217-2032886728.jpg (137.54 KiB) Viewed 5671 times
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

Hi:

I was aware of the mosquitoe killing HV source. It is a "Joule Thief" like the one I previously discussed (i.e a blocking oscillator) with added voltage multiplication at the output. Thus, it's noise makes it unsuitable to my needs.
What is the noise in the commercial module you described before?
EDIT: It seems like the different voltages are taking out at different stages of the output multiplier. Can it sustain the current claimed at the latter stages of multiplication?
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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

Post by John Futter »

Cai
most of these can do up to 10 watts of output some a little more
from that you can work it out
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

John:

That seems way too high. Taking the output directly the output at the transformer (thus avoiding any losses in the multiplier) we get a power 1.5 W (the 75V claimed times the *optimistic* 20mA). At 400V that is around 4 mA, which is respectable.
Still, the noise is what worries me the most... It also seems like there is no feedback. The circuit is just a 555 square wave generator and a N-Channel MOSFET! A quick homemade blocking oscillator is cheaper, doesn't have shipping time and should be stiffer. Furthermore, by using a small capacitor between between base and colector (multiplied by Miller Effect) one compromises on the rise time (and thus output voltage) but can significantly reduce noise.
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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

Post by John Futter »

Cai
Both Doug Coulter and myself have used similar bought from Mouser and I got 15 watts max out of mine they are meant to run one or two 5-8 watt flouro tubes as used in laptop LCDs
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post by Cai Arcos »

John:

I think we are talking about different things. You probably reference something like this: https://www.mouser.es/ProductDetail/JKL ... qjc3YDs%3D. Which I have read about in Doug post "Standard HV Supply for detectors". I was talking about the cheapo module referenced above from Aliexpress.
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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

Post 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
Rex Allers
Posts: 570
Joined: Sun Dec 30, 2012 3:39 am
Real name:
Location: San Jose CA

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

Post 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.
Rex Allers
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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

Post 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
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post 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)
Cai Arcos
Posts: 163
Joined: Fri Oct 12, 2018 9:30 am
Real name: Cai Arcos
Location: Barcelona, Spain.

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

Post 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?
Post Reply

Return to “Neutrons, Radiation, and Detection (& FAQs)”