Kapanadze Cousin - DALLY FREE ENERGY

[verpies]

I think that I've got addicted by gdt's. I need to order some more Toroid's.

FYI: Those ISDN Telco transfomers work very well as GDTs and they are quite cheap where I live.

[AlienGrey]

Hi Carroll.

No problem.

For any newcomers visiting here's my video.

https://www.youtube.com/watch?v=LOqjTHmmumU

I was creating so much RF that this video was the second attempt, it froze the above at the end, just the audio continued to work...

Cheers Graham.

Hi Grumage any idea what the value of the unmarked coil is and or what harmonic it resonates at ?

and what details have got on your advancement on the device, or any one else might have.
Regards AG

[AlienGrey]

FYI: Those ISDN Telco transformers work very well as GDTs and they are quite cheap where I live.

Gate Drive Transformers ? isn't there a factory that makes them, point is can you send some over here ? thanks very much just joking.

AG

[Grumage]

Hi Grumage any idea what the value of the unmarked coil is and or what harmonic it resonates at ?

and what details have got on your advancement on the device, or any one else might have.
Regards AG

Dear Mr AlienGrey.

Are you referring to the schematic perchance?

The inner coil was a guesstimation...... I used 650 turns on a 50 mm plastic former in parallel with the special Aluminium plates that formed an LC circuit. The drive frequency was 9.7 KHz but the inner LC circuit resonated up in the 20.3 KHz area. I used a heavily insulated 10 turn pickup coil for the scope that was indicating nearly 10 KV P/P. I could smell Ozone regularly!

I stopped experimenting because of the expense.... those IGBT's were £13.00 each and I went through quite a few. Hoppy pointed out that my drive circuit had excessively long gate wires that were prone to false triggering, the lack of decent snubbers was another area of concern.

Kind regards, Graham. 

PS. Switch on your Skype !!   

[lost_bro]

Hi lost_bro

I did a mistake on the inductance values. I meant mH instead of uH. So my acoustics driver uses a 6mH, and the fast driver which is for use between 100-300Khz is 2mH.

By coincidence, as a layout I used the first schema of your attached files. Perhaps it is not so a coincidence as I also founded it a very nice single ended approach. See attachment. What resistance value in place of 10Kohm do you suggest for 100-300Khz operation? 10Kohm works nice at 20Khz. I intent to take it down to 5K for the fastest range. As a coupling capacitor I use a tantalum at 2uf for the acoustics range, and 1uF for the faster driver.

I think that I've got addicted by gdt's. I need to order some more Toroid's.

Good evening Jeg

Yes, 2uH would be a very very high frequency GDT

Probably not a coincidence, I would tend to agree with you. I experimented with many different secondary side configurations also.  This design has decent response and a low parts count.  On my 3-switch-flyback, I modded the second scheme listed by placing a reverse parallel 1n4148 diode along side of the Gate resistor.  That helped speed up the *turn off* gate discharge time, but still used the 10Kohm resistor.

"What resistance value in place of 10Kohm do you suggest for 100-300Khz operation? 10Kohm works nice at 20Khz. I intent to take it down to 5K for the fastest range"

Actually I only have used this scheme and the second modded scheme for applications well below 100Khz.

I always use a Double-Ended drive topology (floating a neg. voltage) for any High-Speed, RF applications.
I seem to get faster Rise & Fall time and therefore a cleaner gate drive signal with the Double-Ended approach. I believe the results justify the extra parts count and board real estate for the Double-Ended topo.

If you add the inverted Zener diode (cathode-cathode) with the 1N4148, you can generate a negative voltage at the gate.  Only increases the parts count by one.  You will have to augment your Vcc to your driver IC, as your entire voltage range will be shifted negative by the voltage rating of your zener. So if you want to float -10 volts @ the gate, use a 10Volt Zener and increase your driver voltage by 10 volts to maintain the same Positive voltage.

I am surprised by the distortion on rising edge of your gate drive signal in your last post.  Using the first scheme, you should get a clean well formed rectangular pulse @ the gate.  Like Verpies said, the leakage inductance appears excessive and it could be the coupling between your primary & secondary windings is NOT sufficient.

Try using 30awg magnet wire,  twist or braid about 9-18 strands together to form a single multi-stranded litz-like cable.

Then using your multimeter, pair up the wire ends at both sides after after winding your GDT.  I have found using many pieces of fine, thin gauge wire which is tightly braided/twisted gives a very low leakage inductance and outperforms a single larger gauge every time, especially at RF and renders a very clean gate signal.  Of course this only works for a 1:1 drive ratio. You can configure the same braided/twisted group of wire into a 1:2 drive ratio, but you must set it up like a bifilar between two different pairs within the braid on the secondary.

Good luck.

take care, peace
lost_bro

EDIT: just looked back at your o-scope screenshots............. my bad, 650Khz!!!!!!!!!!!!!  I would definitely try a Double-Ended topology for those frequencies, and braided litz-wire (homemade of course). I would also use a pair of high power drivers with extra pin to pin decoupling and a ground plane (if possible) for the GDT primary.