Author Topic: GDT Experiments  (Read 102 times)

Offline Thunderstruck

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GDT Experiments
« on: March 16, 2019, 06:32:36 AM »
While I'm waiting for some parts to arrive I decided to try and master the dark art of GDT winding. Got some advice on a correct core selection, watched a few videos on the topic and decided to have a go at it.
Well, I wound 5 different cores, and I did not get what I wanted.
I used cores with high AL, Cat5 Network Cable Wire and on one occasion Magnet Wire and got very similar results every time.
I am trying to achieve a good waveform at about 65 - 70kHz

Image 1 - Core specification ( AL5400, T35, 27mm OD )
Image 2 - First attempt
Image 3 - Waveform achieved
Image 4 - Richie Burnett's advice on corrective action for that waveform
Image 5 - He said more  turns  - More turns it is then  ;D
Image 6 - Resulting waveform - Still sloping, and as you can see there is no more room for wire turns

Other attempts had pretty much the same results

I am quite sure that I am not doing something right here - or RS Components sent me wrong cores.




Offline Mads Barnkob

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Re: GDT Experiments
« Reply #1 on: March 20, 2019, 01:06:24 PM »
You did also choose cores with almost identical properties, its not even a 1000 permeability in difference, so you will only see the differences from number of turns and how tight coupled the wires are to eachother/the core.

What kind of test jig did you use? A driver IC --> GDT --> MOSFET gates?

Did you see this practical design guide / experiment? http://thedatastream.4hv.org/gdt_practical.htm
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Offline T3sl4co1l

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Re: GDT Experiments
« Reply #2 on: March 20, 2019, 01:18:29 PM »
The one thing missing from Burnett's advice: reduce the driver impedance.

Was that testing with a function generator (50 ohms)?  Looks about right for it.

Tim

Offline Thunderstruck

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Re: GDT Experiments
« Reply #3 on: March 20, 2019, 09:07:04 PM »
You did also choose cores with almost identical properties, its not even a 1000 permeability in difference, so you will only see the differences from number of turns and how tight coupled the wires are to eachother/the core.

What kind of test jig did you use? A driver IC --> GDT --> MOSFET gates?

Did you see this practical design guide / experiment? http://thedatastream.4hv.org/gdt_practical.htm

Mads, in both cases it was the same core. I did say 5 different cores in my original post, what I wanted to say is 5 different ways ( twisted, straight, trifillar, etc. ). I was expecting to see at least a half decent waveform because it is a high permeability core, especially after watching a few videos.
Test signal was supplied from the FG directly, i do not have a driver circuit to test the GDT with.

I suspected that my FG is not really capable of driving the GDT...
I read that guide a few times, only thing missing is screenshots of waveforms after each attempt.

The one thing missing from Burnett's advice: reduce the driver impedance.

Was that testing with a function generator (50 ohms)?  Looks about right for it.

Tim

Tim, yes I tested the transformer with my FG which is a little bit ancient  :)
« Last Edit: March 20, 2019, 09:14:34 PM by Thunderstruck »

Offline Teravolt

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Re: GDT Experiments
« Reply #4 on: March 20, 2019, 11:15:50 PM »
I dont know if this will help but thare a cuple of articals

http://ferroxcube.home.pl/news/gate%20drive%20trafo.pdf

https://www.coilcraft.com/edu/gate_drive_transformer.cfm

http://seansoleyman.com/solid-state-tesla-coil/

your outputs have good rise time but it looks like they are saturating because the waveform is saging after 7us. usaly your signal generator has a 50 ohm inpedance and may not be able to drive it enough. build a gate driver circuit on a proto board using a mosfet diriving ic or the output of a universal driver. a biger core might help and or using more stacked cores if you had some

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Re: GDT Experiments
« Reply #4 on: March 20, 2019, 11:15:50 PM »

 


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