Low-leakage PNP or PMOS

On Sat, 29 Jan 2022 22:29:02 +0100, Piotr Wyderski
<bombald@protonmail.com> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>
>> You could charge the tube from regulated 400DC through a resistor,
>> which current limits nicely and has low capacitance. Self-quenching.
>> And simple.
>
>This is the traditional way, good for the low dose cases.
>
>> You can get statistics from the discharge frequency. That's the
>> traditional way.
>> 
>> Each shot is the start time for the next time-to-first-count. Given a
>> random pulse, "start time" is anything you want to call it!
>
>It works as long as the tube is not saturated. At high dose rates you 
>stop getting pulses, let alone clear pulses. So the idea is to quench 
>the tube hard by turning off the supply and periodically energize it 
>rapidly. Rumor has it that it allows for 2 more orders of magnitude and 
>I wanted to check it for fun. It might turn out to be simple enough to 
>integrate it into a DIY meter.
>
>OTOH, Phil Hobbs was right. The more I want the more it looks like a 
>scintillation probe. Not giving up yet, though.
>
>	Best regards, Piotr

You could use a half H-bridge to power and quench the tube fast. Like
an IR2213 and a couple of small mosfets and a bit of timing logic.

GM tubes are go or nogo, so can't do spectroscopy. Scintillators and
PMTs are more fun.

 


-- 

I yam what I yam - Popeye

Piotr Wyderski wrote:
> Hi,
> 
> knowing that you often take parts way beyond their specs, I would like 
> to use your wisdom.
> 
> I need a high-side controllable switch capable of charging 5pF to 400V 
> and maintaining most of that charge for a good fraction of a second. Not 
> important if it is a PMOS or a PNP transistor. Could you please 
> recommend me a part known for a particularly low leakage current? Or 
> should I use any transistor and a diode in series with the collector? A 
> diode-connected transistor perhaps?
> 
> T_MAX is, say, 50 degrees Celcius and there will be no self-heating.
> The lower the leakage the better.
> 
>      Best regards, Piotr

Late to the party here, but for one-offs I'd probably use a tube for 
that sort of thing.  (They don't come in P-channel, of course.)

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com