5V to 2kV for PMT

Folks,

Id like your advise on an efficient way to boost 5VDC to 2000Vdc for a PMT (20Meg). This will be low pulse rates to the tube current will be dominated by the 20Meg voltage divider. Looking at a 10 stage VM stack and a 220Vp-p signal going in to. The stack is relatively easy but the

200Vp-p from 5V at high efficiency where I'm have lots of options.

1) single inductor boost mode.

2) CT transformer with push pull transistors. (need to watch flux walk) 3) flyback. etc.

designs objectives are:

relatively high efficiency (200mW out, say 400-600mW in) (5V@ ~100mA)

low profile and small footprint. (need to slide in a slot that is 1.3" x 0.5" x 8" deep It cant use much of this depth as there is would like to keep the switching part (without VM) down to

Reply to
Mook Johnson
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Den mandag den 1. september 2014 23.23.03 UTC+2 skrev Mook Johnson:

Photoflash Capacitor Chargers ? linear have several tiny ones

-Lasse

Reply to
Lasse Langwadt Christensen

You can get CCFL inverters for as little as 1$ from China. Normally they run on 12 volts but you could get a boost converter to go from 5 volts. It is AC out so a simple 5 kV diode and a HV cap plus a divider can make for some feedback to the boost regulator to tie it up in a loop. A series L or R plus a cap can lower the noise on the output.

Are you making a scintillation probe for gamma spectrometry?

Reply to
Tom Miller

PMTs are about 10**6 times quieter than APDs for the same sensitive area. They really are magic.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Yup but not spectrometry. just a simple threshold detector.

Reply to
Mook Johnson

My guess would be a 6V CCFL transformer or a transformer pulled from a

240V USB charger. You'd get ~400 volts at 50-80 KHz on the HV side. The driver would be flyback for sure. Probably constant-on, variable-off for efficiency.

You might not need a 10 stage VM. CCFL and strobe trigger transformers can produce well over 1KV for a little while before the insulation goes bad. It might be long enough if your PWM and usage duty cycles aren't too high. Electric fly swatter transformers can make about 1KV at 2KHz for an unknown lifespan.

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Reply to
Kevin McMurtrie

On a sunny day (Mon, 01 Sep 2014 16:23:03 -0500) it happened Mook Johnson wrote in :

Well, you use a voltage divider, that does not always jive with 'high efficiency'.

Anyays I've done it this way:

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And I have done it this way with resistor divider:

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You can get a cheap HV module from ebay too, and control its supply voltag, I have one for 400kV...

It all depends.

Reply to
Jan Panteltje

I would vote for 1) but with the transistor connected to a tap on the inductor (which you might have to wind). Is that the same as 3)? I tend to use a MOSFET with the drain spiking up to maybe 50V at the tap on the inductor, and the end of the inductor spiking up as high as you need it. Having the tap makes the drain capacitance N^2 times less of a pain and lower voltage MOSFETs seem to be better.

I have found it difficult to get low ripple using a micro to control a switching regulator. If you are going for high performance I would suggest either a proper hardware circuit or a micro with dedicated hardware for controlling switchers (fast ADC, very high resolution PWM, etc.).

Chris

Reply to
Chris Jones

I'm seeing mainly few-parts designs; that's probably not perfect (parts are cheap, and robots install 'em). How about integrating a Cockroft-Walton style voltage multiplier with your divider network? Don't just drive the high dynode with 2kv, run taps from CW to intermediate taps on that 20M divider string. The lower-voltage dynode supplies (where the dynodes actually DO draw current) will get the highest regulation, which is just what you want. And, all the capacitors and diodes can be easy-to-get 200V types.

Reply to
whit3rd

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