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Registered Member #2655
Joined: Wed Jan 27 2010, 04:09PM
Location: Czech Republic
Posts: 18
Hello, I need to build a DRSSTC GDT, capable of running at +-18V (maybe sometimes I'll decide to overdrive the gates, but not with the current setup), 80-90kHz (but in near future, I want a bigger topload and primary cap, so ability to run at ~70kHz would be nice). The total gate capacitance is 4x30nF=120nF. But the problem is I don't have any suitable core - and I need help with proper core selection. Unfortunately, local supplier (the only one that have any ferrite cores in ~300km range, and I'd like to avoid intl. shipping - I'd pay more shipping cost than the core) does not have a lot of cores to choose from. Anyways, I think FT 140A-75 should be okay. What do you think? Thanks
The main transformer core from an ATX computer PSU is perfect for your frequency range. It is an E I core, or at least all of the ones I took apart were.
Scraping off the glue to minimize the airgap is a good idea. I wrapped mine tightly with electrical tap to clamp it together.
I used one for my half bridge inverter that runs from 42kHz to 138kHz, if memory serves I used about 15 turns. Almost perfect square wave with a little overshoot, 100mV worth with 12 volt supply.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
The ferrites used for interference suppression are designed to be lossy at high frequencies and thus make poor GDTs. You want a high permeability ferrite of the sort used in transformers. I got a pile of Sanlin SL5 T22X14X8 toroids on ebay that work wonderfully. According to the seller "CORE MATERIAL TYPE: SL5 - EQUIV TO FERROXCUBE 3E4, TDK H5B AND SIEMANS EPCOS T65"
I heard someone else had success using the core from the horizontal drive transformer from a TV, hardly surprising since it's doing essentially the same thing. You want an un-gapped core.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Best advice would be to look up the datasheet for the core in question and see what characteristics the material has. Compare it to some of the ferrites known to work well.
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GDT core?
