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Ringing on GDT. Can it be stopped with RC snubber? (no choice but to dupilcate)

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Hazmatt_(The Underdog)

Thu Apr 20 2017, 03:11AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I have had bad luck with the solderable "solder ease" type magnet wire. It tends to break down easily and short.

Any magnet wire that's polyimide, polyester resin, formvar, or enamel coated should work. I think the polyimide (kapton) has an insulation dielectric breakdown voltage of about 2000V, but that would have to be verified by the data sheet for the wire.

Gregary Boyles

Thu Apr 20 2017, 04:48AM

Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117

loneoceans wrote ...

Side note - if done correctly, using magnet wire can yield a good GDT with sufficient isolation between primary and secondary windings. However it's very easy to nick or stress the insulation, which can lead to a short especially with high bus voltages. As a result, I typically prefer using good (but as thin insulation as possible) insulated wire.

I tried ethernet cable wires (with solid cores) but they were too stiff and the resulting windings to loose. Any other suggestions as an alternative to magnet wire?

Gregary Boyles

Thu Apr 20 2017, 04:49AM

Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117

Hazmatt_(The Underdog) wrote ...

I have had bad luck with the solderable "solder ease" type magnet wire. It tends to break down easily and short.

Any magnet wire that's polyimide, polyester resin, formvar, or enamel coated should work. I think the polyimide (kapton) has an insulation dielectric breakdown voltage of about 2000V, but that would have to be verified by the data sheet for the wire.

How do you tell the difference between them?

That magnet wire was from an old cathode ray tv -the coils at the neck of the tube. I can't seem to solder those without stripping the insulation with sand paper. So I have to assume it is not solderease.

teravolt

Thu Apr 20 2017, 07:17PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

do you have a picture if you project on your bench? the measurement that you are making is pausibly induced from your set up or a ground loop. if it were real a 470-50 ohm resistor across your transformer should have a dampening affect at your gate. try moving your test leads away from your project and see what happens. if you plan to do this work you would be happy with a better scope

Gregary Boyles

Thu Apr 20 2017, 11:55PM

Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117

teravolt wrote ...

do you have a picture if you project on your bench? the measurement that you are making is pausibly induced from your set up or a ground loop. if it were real a 470-50 ohm resistor across your transformer should have a dampening affect at your gate. try moving your test leads away from your project and see what happens. if you plan to do this work you would be happy with a better scope

Would love to have a good digital scope but sadly I can't afford several hundred $$$$s at present. So I will have to make do with what I have for the forseeable future.

I got better flat tops to my square wave when I powered my circuit from a plug pack AND after I upped the loops on my GDT from 16 to 25. Apparently there is not enough juice in my ATX power supply (at 12V) to power 3 x 12V fans (one in the ATX itself), and my GDT and all the rest of the electronics.

I have also added an option to power the TC4422's I am using (made my own UCC37422/UCC37421 from 2 x TC4422 and a quad AND gate) from 20V with a 3 pole switch to switch the power between 12V, 20V and 'off'.

Will post some more photos when I am done soldering.

teravolt

Sat Apr 22 2017, 06:34AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

if you have only one type of driver you can try this. the schematic that you picked is old and does not have current monitoring and some other things and this is the more up to date one

1492842880 195 FT179563 Tesla Interupter 1

Gregary Boyles

Sat Apr 22 2017, 02:14PM

Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117

teravolt wrote ...

if you have only one type of driver you can try this. the schematic that you picked is old and does not have current monitoring and some other things and this is the more up to date one

I fried the TC4422s I had. The datasheet says they will run from 20V max so I tried it, but it must have pushed their limits to far and they no longer work.

So I am having a go at creating a darlington H bridge instead, as that will easily take 20V (laptop power supply) and I should get around 16V amplitude on my square wave going through the GDT primary. I am using TIP122/127 and they can take 100V and give me up to 5A. I have a 4.7R resistor in series with the 100nF cap to make sure they don't get over stressed.

I used a half bridge successfully with a plasma globe driver that was some what similar to that schematic just above and with the flyback transformer primary connected between my half bridge and GND.

This H bridge design seem to work in simulation at least:

1492870462 9039 FT0 Capture

Hazmatt_(The Underdog)

Sun Apr 23 2017, 04:13PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

How on earth does that circuit work with no pull-up resistors on the transistor bases?!

There is no way that would work, even if you fixed the open node on L1.

hen918

Sun Apr 23 2017, 04:33PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Hazmatt_(The Underdog) wrote ...

How on earth does that circuit work with no pull-up resistors on the transistor bases?!

There is no way that would work, even if you fixed the open node on L1.

They are BJTs, not MOSFETs. If there is no current flowing through the base they will not be "on". It's quite a clever design, shorting the two bases together through another transistor pulls the lower one up and the top one down, turn them both on. It might not be very efficient though, but that's only due to the use of transistors.

Gregary Boyles

Sun Apr 23 2017, 05:25PM

Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117

OK thanks folks - I will ditch the idea and go back to the TC4422s. Just thought I would try.

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