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Registered Member #4073
Joined: Sun Aug 28 2011, 08:43AM
Location: Australia
Posts: 17
I powered up my first SSTC (based on Steve Ward's MiniSSTC) today, and it looks as though one of the MOSFETS on the half bridge has failed. The secondary resonant freq. is around 380kHz without topload.
I am almost certain it is my GDT. The GDT core was found a long time ago, and I'm not sure it is ferrite as I remembered it was a noise filter in a power supply only after powering it up. The wire was salvaged from a computer (the twisted wire that is used for buttons and led's). All in all, I'm fairly sure this GDT is the cause of the fault.
I included pictures where the gate resistor of the believed faulty mosfet can be seen with damage to it's legs. (sorry, my camera doesn't like to focus on small things)
There is a link to the data sheet on the attatchment.
Would this be a good choice of core? I am planning to wind the core with a similar technique as steve ward, with the CAT-5 cable. If this core is not suitable, what would be a more suitable core (with part number so it can be ordered)?
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
You can test the GDT, just put a test square wave into it (through a cap if it has DC offset), then scope one of the secondary windings. If it's a clean square wave, it's likely fine and proceed to test it with the load of a gate on it. If it's not good, it'll become evident quickly.
There are suggested models if you search old forum posts on the topic.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
2 things I get to check before I can say that my GDT is up to work., first is physically, it should be black semi-magnet appearance / material, and of course my twisted 1 pair wire (24awg) can fit in at least I am targeting about 30 turns.
second is its sound. when supplied by my driver, even w/o feed by signal generator, the "ticks" should be heard and same as the interrupter do so.
also, in the secondary wire of the transformer, I can measure the frequency output liked as on the Interrupter, and the voltage(AC) around 1.5v. (I DON'T KNOW IF MY CRITERIA PROVES ANYTHING, but for me, everytime I seek for a possible GDT, I assure that the GDT passes these tests. And yet IT WORKS!
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MiniSSTC Fet died on start-up; GDT problems?
