Page 1 of 1

High Voltage Supply for PMT

Posted: Thu Jan 18, 2018 3:27 pm
by Hunter Long
Hi guys,

I don't know of many open source designs for HV PMT power supplies other than the Theremino PmtAdapter: http://www.theremino.com/blog/gamma-spe ... -1?lang=en

So I really want to design an open source, HV, low noise, power supply for a PMT. I would also like it to only use relatively easy to find, low cost components so that anyone could build it. I think these designs by Jim Williams: http://cds.linear.com/docs/en/applicati ... N118fb.pdf look really promising.

However, the component which seems hard to source is the CCFL high voltage transformer and I don't know why. Are they becoming obsolete? The one used in this app note is a CTX210609-R and it is only available from Newark's UK stock meaning there is a $20 fee for any order in the US.

If I can get this power supply working, I'm thinking about selling kits or completed boards. I'd love it if I could keep the cost under ~$50.

Thanks,
Hunter Long

Re: High Voltage Supply for PMT

Posted: Thu Jan 18, 2018 11:33 pm
by Richard Hull
Tons of CCFL transformers are now FREE!!!

CCFL lighting of all sorts is going the way of the dodo bird. Actually, it effectively, died a few years back. Too many would-be electronics builders follow a rigid part numbered scenario rather than build the circuit and shove in a fairly common seeming equivalent type that they obtain for free.

Every single old LCD giant flat screen had 10 to 20 identical, CCFL transformers in them. These are not the exact ones you need, but will function and give output voltages in many circuits up to 2500 volts or more... I have now recovered about 60 of these great little high frequency, high voltage, ferrite transformers.... With the advent of LED flat screens all these free, nice little xfmers will also go the way of the dodo bird.

I have two free sources for these little darlings. Fortunately, no one ever repairs an LCD flat screen, especially one where their idiot kids or pets manage to damage the screen. Smart money goes out and buys a brand new bigger one at one half of what they paid for the old dead one and they pick up a new warranty in the deal. My sources are pals in the dying electronic repair biz who save me the two normal CCFL driver boards scrapped from dead, never reclaimed, flat screens. I was planning on using these to build small GM HV supplies, but Electronic Gold Mine has an occasional sale of their micro-miniature HV transformer at $1.00 each. Buy purchasing just under 100 of them I have designed a nice driver circuit around them on my custom PC board for my GM counters. Whereas, with say 8 of the same CCFLs from a given flat screen I could make 8 supplies and then try and adapt the next 10 (identical), yet different style xfmer to the circuit. Not a great way to mass produce.

Richard Hull

Re: High Voltage Supply for PMT

Posted: Thu Jan 18, 2018 11:36 pm
by John Myers
I think it's an 'economy of scales issue' where it's not really worth it for distributors like Mouser and Newark to sell CCFL transformers anymore. Especially with LED's taking over. You'll likely need to buy straight from the manufacture.
CTX210609-R is obsolete but there may be other similar parts or other brands with similar specs.

Re: High Voltage Supply for PMT

Posted: Fri Jan 19, 2018 4:06 am
by Rex Allers
I've been playing with a TDK CXA-L10A CCFL supply. 5V DC in gives ~ 1kv. I added 3 stages of multiplier and that worked OK. Then I wanted to put voltage feedback around it. Sort of worked but something basic, and strangely wrong in my feedback circuit. Symptoms made no sense to me. I'll get back to it eventually. I keep getting sidetracked and never finishing things.

Anyway, I just looked for one on Mouser to see if they still had it. Obsolete. But they referenced a different one, BXA-601. Oh, hmm, none in stock.

Looked on ebay. Found "Brand New TDK CXA-L10A Inverter USA Seller and Free Shipping". Only $68.95. Yikes! I'm sure I paid under $10 for the few I got.

Ebay has lots under 'CCFL Inverter" but many potted and few I recognized.

Richard's source sounds better and better if you know where to find dead monitors.

Re: High Voltage Supply for PMT

Posted: Fri Jan 19, 2018 5:17 am
by ian_krase
How were you feedbacking it?

Re: High Voltage Supply for PMT

Posted: Fri Jan 19, 2018 6:14 am
by Richard Hull
I only used giant 45-80 inch lcd flat screen TV's and high end 50 inch video monitors. As I noted, these giants have 10 to 20 identical small CCFL transformers spread onto two boards. The later models had only one driver board with 4 or 5 much larger CCFL xfrmers capable of tens of ma. output current, driving several rows of series tubes. The little CCFLs usually fed only 2 tubes, (~8ma). I never fiddle with computer monitors. When I worked up to 2014, my company that installed giant video walls, (10 or more 60" LCDs), would always have a butter figured tech or two drop a 70 inch screen or two on a job from a "johnny lift" 15 feet up to a concrete floor. OOOPs!!

They would hold the busted units in the warehouse for a month or two for insurance inspectors and then throw them away....My way. After retirement I now have two shops handing over boards which are now getting scarce as folks are already ruining and busting up new LED screens which have no CCFL. Virtual CCFL extinction is near. Anti-mercury Nazis are out there beating the drums to kill all fluorescent lighting. A year or so ago, Roto-Metals stopped selling pure cadmium. I am glad I have a reserve... I purchased 40 lbs from them three years ago for my low melting point alloy work.

Richard Hull

Re: High Voltage Supply for PMT

Posted: Fri Jan 19, 2018 8:15 am
by Rex Allers
Ian,
Quick summary of what I tried. Here's a sloppy schematic.
HV Supply schem.png
Big rectangle toward the right is CCFL inverter. Ground between inverter in and out can be broken, and I did. The X3 box is a CW multiplier I built. The HV divider at left is actually physically on the board with the X3 multiplier.

Before any feedback circuit connected I did very simple test. Just put adjustable 0 to 5V into the inverter. HV out varies nicely with over 3 kv out from 5 V in.

So I built the circuit shown on one of those white plastic proto boards. When I tested, turning the HV-Set pot did vary the HV out, but it didn't track as I expected with HV out = 1000 x pot voltage.

Trying to debug I first looked at that 1st Op Amp stage. It's just a simple follower. Idea was so I could measure the HV Monitor point without putting any load on the resistive HV divider at left. So as a check I put two DVMs on the circuit. One on '3V Here' label, and one on HV Mon. As I changed the pot setting the two voltage readings diverged.

Huh?? They should be the same. Not seeing anything wrong in that simple stage, I put it away to revisit later.

No shortage of half-done projects. This is one more.

Re: High Voltage Supply for PMT

Posted: Fri Jan 19, 2018 5:13 pm
by Richard Hull
Rex, we seem to have a lot of stuff partially done, in common. Projects on top of projects.

If I have an idea and build it, no matter what, if it gives me an inordinate amount of difficulty, I will try and make it go at full steam ahead. However, If I am 1. Not totally committed to the project in a special way or... 2. have spent what I feel like is a good first pass attempt to get it right, I often set it aside until I, (supposedly tell myself), that "I shall return" and look at it with a fresh perspective. Yes, sometimes I get around to the fresh look at the problem and master the effort. However the "return-to-finish" ratio is somewhat embarrassing here.

I feel running at a coal face repeatedly with your head is not a good way to mine coal. As such, I will leave the mine for a while and hopefully return with a useful tool, (R&R), to get the job done.....Maybe....I think....I tell myself....

Richard Hull

Re: High Voltage Supply for PMT

Posted: Fri Jan 19, 2018 8:57 pm
by Hunter Long
Thanks for the ideas!!

I called a Coilcraft representative and found a part that looks very similar to the CTX210609-R. It can be found here: https://www.coilcraft.com/ccfl.cfm and is the "FL2015-3L_".

You can purchase directly from Coilcraft and there is no minimum order. I just requested 5 free samples of this part.

Re: High Voltage Supply for PMT

Posted: Fri Jan 19, 2018 9:20 pm
by Jeroen Vriesman
I tried a small royer-like oscillator with 2 TMS93.... CCFL transformers.
These transformers are a bit bigger than the laptop CCFL transformers, which makes the supply a bit more powerful. The transformers are available on aliexpress, inexpensive.
It produced about 2500V at 2mA. About 30kHz.

I didn't try feedback yet, but I connected on the hv side a 47Mohm resistor in series with a small neon light, and a capacitor over the neon light, creating a relaxation oscillator. Frequency between 100Hz and 4kHz.
When shielded from daylight the neon flashes can be detected easily with a bpw34 photodiode.
Next step is making this into a feedback, so the hv can be stabilized, but completely floating.
Maybe some pll with 4046...