ultra low breakdown voltage gas discharge tube? - Page 1
Forum section: electronics / projects

author: sarepairman2
author_rank: Frequent Contributor
timestamp: February 06, 2016, 04:18:20 pm
content: The lowest I ever found was 90V.Is it possible to engineer a tube that would conduct at a precise LOW voltage to act like the apex circuit protection system?I.e. 5V protection circuit using a gas discharge tube instead of a zener diode.is the issue with this the lack of existence of a zero temperature coefficient of expansion material? or thermal gas conductivity?

author: Kleinstein
author_rank: Super Contributor
timestamp: February 06, 2016, 04:29:19 pm
content: A much lower voltage will likely not work. The limiting factors are the ionization energy in the gas and work function of the electrode material. You just need something like 20-30 V to ionize a noble gas.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 06, 2016, 05:08:45 pm
content: GDTs react kinda slow to turn on so under 90V you are better off with a diode. The time difference is something like 100ns vs 1ns.Also, once fired the GDT will remain on at a much lower voltage than what initially triggered it. So a GDT that fires at 90V would continue to conduct down to 30V or maybe even lower since the spark is practically a short circuit (<1 Ohm). So at very low voltages it might be difficult to extinguish.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: February 06, 2016, 07:29:42 pm
content: you cant make the spacing close enough that time wont matter?Or does the gas behave strangely (microchannel like effects in gas/plasma rather then fluid?) making this unfeasible at small geometries?is this a linear correlation? like bad idea to use a 90v gdt on a 50v circuit?i got my gaseous conductors book now I just need to read it

author: Kleinstein
author_rank: Super Contributor
timestamp: February 06, 2016, 07:48:14 pm
content: There is no simple rule that a small distance causes a low breakdown voltage. Once the distance gets very small or the pressure low, the voltage will go up again. So in vacuum it can help to bring parts closer together to prevent discharge. AFAIR the minimum voltage for air is at about 90V - so no combination of pressure and distance to get a lower voltage. Once you have a spark, making the gas very hot the voltage can drop.So for low voltages diode are definitely the better choice. Also voltage in a gas discharge is not that stable, as temperature and pressure can change it.

author: Someone
author_rank: Super Contributor
timestamp: February 06, 2016, 10:05:43 pm
content: Hopefully this link works:http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.550.7259&rep=rep1&type=pdf"Experimental study of electrical breakdown in MEMS devices with micrometer scale gaps"It has some graphs untangling the pd product and showing V against pressure for different electrode gaps.

author: chris_leyson
author_rank: Super Contributor
timestamp: February 06, 2016, 10:09:39 pm
content: You could maybe trigger the gas by biasing it at it's maximum standoff voltage and then generate the required trigger voltage, but what about drop out voltage. The electron density or electron mobillity is lower in gas than semiconductors. Gas is better suited for valve or tube electronics.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 06, 2016, 10:26:59 pm
content: 2% Thoriated electrodes could lower the voltage significantly. Once that was used in tubeanodescathodes to get them to emit more easily. Today still used in TIG welding electrodes.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: February 07, 2016, 02:31:53 am
content: it is good to explore these avenues so we do not get trapped in a one component world

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 07, 2016, 03:52:13 am
content: Quote from: HAL-42b on February 06, 2016, 10:26:59 pmCathodes. Same function and purpose. They need to be hot to work, so it will have no effect on the breakdown, glow or arc discharge voltages of a completely passive GDT.Quote from: blueskull on February 07, 2016, 02:38:37 amCeria and other rare earths work just as well. Anyway, the amount of Th is small, and almost entirely shielded by a metal more dense than lead...Check your town for a welding supply store, if you're wondering about availability (you might be right that it's restricted, probably more for toxicity than radioactivity).Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 07, 2016, 03:53:59 am
content: Quote from: Kleinstein on February 06, 2016, 04:29:19 pmYeah, you could perhaps replace that with a very low ionization element, like Cs vapor (which will also at least partially coat the electrodes). Probably the leakage current is too high to be useful.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 07, 2016, 04:26:40 am
content: Quote from: blueskull on February 07, 2016, 03:56:49 amAgain, it's hardly double background radiation. Radioactive Kr or Ni is typical for devices that need to fire fast (<< 1us), how much I don't know (uCi??).Tim