Re: Toroid cores for GDTs

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Original poster: Skip Malley <skip@xxxxxxxxxxxxxxx>

Steve, I know EXACTLY what you are referring to.  The transformers 
that I am talking to are EXACTLY what you describe.  These are 
trifilar wound with VERY close windings on a ferrite toroid 
core.  See my other reply.  For the switching power supplies I 
designed, I originally used a GDT from Pulse Engineering.  These were 
of the EE core design.  These had occasional problems.  I eventually 
changed to a toroid trifilar wound toroid.  The leakage inductance 
was about 1/10th of the EE core design.  All problems were 
solved.  the ones in my link 
http://www.lse.com.tw/upfiles/spec01125457782.pdf are EXACTLY what 
you and others are describing as the better transformer.

Skip

At 08:03 PM 1/25/2006, you wrote:
> We need to drive several large MOSFETs at high frequency, so we need 
> absolute minimum leakage inductance. We usually get that by 
> forgetting we ever knew about "code" and making the transformer with 
> a multi-filar winding of ordinary PVC insulated wire. If you're a 
> radio ham you might know this as a "Transmission line transformer". 
> You are limited to integer ratios (1:1, 3:2, 4:3, 2:1 etc.) but that 
> is hardly a problem. Finally, using a large toroid core of high 
> permeability ferrite lets you reduce the number of turns, reducing 
> the leakage even further, while keeping the magnetizing current acceptable.