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I want to switch a high current/voltage pulse (up to few 10kV, <1kA) from a capacitor as supply. It needs to be cheap and I don't care about efficiency too much yet.

I took a look at using thyristors in series but I think it'll cost too much and could possibly be dangerous as without the correct balancing the thyristors break. I found old Thyratron tubes that I think would work, however I couldn't find them to buy (let alone buying newly made ones that are made for power electronics).

From the search of the vacuum tubes and getting to know all available tech I decided it would be cheapest to use a triggered spark gap.

Do gas discharge tubes (i.e. https://www.littelfuse.com/products/gas-discharge-tubes/high-voltage-gdt/cg3.aspx) work like a spark gap? My idea is to have a high voltage GDT in series with a smaller voltage triggered spark gap (i.e. https://uk.rs-online.com/web/p/gas-discharge-tubes/7606807/ / or homemade). I would then balance the voltage with resistors in parallel. I imagined to have it like this:

enter image description here

(I used a thyristor symbol as I couldn't find any triggered spark gap symbol.)

My thought is that by this arrangement the voltage supplied would divide to ~9 parts over the spark gap and ~1 part to the switch (when it is off). When the switch opens the resistance drops and the voltage over the spark gap rises creating an arc (when the voltage is sufficient). I know the resistance values are too low for above specs but this circuit is only for reference.

Would such approach work for switching an energy pulse of above specs? (I didn't calculate the duration of the pulse yet, but I'd be surprised if the cap held for long as the spark gap would no longer arc at some point.) If not please point out why and maybe guide me in a direction how I could realize this with cheap parts.

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  • \$\begingroup\$ Are you thinking of triggering like a photo flash trigger? Is the voltage AC or DC? Welcome to the form. \$\endgroup\$ – Optionparty Aug 25 '18 at 18:59
  • \$\begingroup\$ DC. There is no other power supply besides the capacitor (sorry maybe i should have used a cap symbol). What is a photo flash trigger? If you mean how i will trigger the switch (thyristor in circuit) i will have to take a look but i think basically its just applying a voltage to the 'gate'(ring?) of the triggered spark gap. \$\endgroup\$ – ShinuSha Aug 25 '18 at 19:07
  • \$\begingroup\$ Updated circuit \$\endgroup\$ – ShinuSha Aug 25 '18 at 19:18
  • \$\begingroup\$ A spark plug as a series switch with an ignition coil trigger might work. \$\endgroup\$ – Sunnyskyguy EE75 Aug 25 '18 at 19:20
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    \$\begingroup\$ A photo-flash trigger transformer, perhaps salvaged from a throw-away (single use) camera, should work. I've used a similar setup to discharge a HV capacitor bank into an inductor, the air-gap made from three screws in a piece of polythene with a 1 cm hole. Use a few megohm HV resistor in parallel with a HV capacitor on the trigger wire to prevent discharge through the transformer. BTW, a triggered air-gap can be very noisy! \$\endgroup\$ – DrMoishe Pippik Aug 26 '18 at 2:27
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Gas discharge tubes work like a spark gap, the difference is they have a gas encapsulated in glass. This lets you determine the breakdown voltage, whereas the breakdown of a spark gap in air would be different depending on conditions such as pressure, humidity, ect.

enter image description here Source: http://g3ynh.info/disch_tube/intro.html

The circuit above may work, but you'd have to get a GDT that would trigger below the 10kV and above the voltage of the resistor divider.

Another option might be a triggered spark gap.

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  • \$\begingroup\$ Thanks for the clarification. I also saw the triggered spark gap you mentioned but couldnt find them to buy (besides from this site and maybe calling them). With my approach I could order the parts from ebay/alibaba and I thought I could minimize the switching voltage needed for a triggered spark gap, so I could use relatively cheap thyristors to do it. Do you think my approach would work in the sense of raising the voltage on the spark gap (-> triggering it) by using a smaller triggered spark gap as a switch? \$\endgroup\$ – ShinuSha Aug 26 '18 at 18:29

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