Hi Jesse, Have you have a look at Richie's SSTC site ?I would make sure your gate drive has enough "drive" to switch the mosfet on fast. Also make sure you have around 20V driving the msofets. and Also use mosfet drivers which have internal voltage clamps on the output to stop the gate drives being spiking during switching (or use zener diodes on the msofet gates to clamp to say 22V)...
Don't assume larger current mosfets will work, they become slower and harder to turn on the larger the die is, so this could actually make your problem a lot worse!.
a good mosfet is IRL8113 though not sure if these will be high enough voltage, but check out the switch times, rdson, and capacitance figures. as the capacitance figures fall the switchtime should follow and get faster too which means less heat during switching time. then favour rdson. a fast rdson of 0.120ohm can beat a slow 0.001ohm mosfet!
HTH Chris----- Original Message ----- From: "Frosty" <frosty90@xxxxxxxxx>
To: <tesla@xxxxxxxxxx> Sent: Friday, July 25, 2008 4:04 AM Subject: [TCML] sstc
hi all, I've just built my first sstc and it worked pretty much first go. Alas, it no longer works! From what i can tell ive killed the lower two mosfets in the full bridge, but the others seem ok. During operation, the heatsink on these two would get warm (but not hot), but the other two would stay cool. It is a full bridge of IRF740's running off about 300v. Does anyone know what could cause the two lower mosfets only to die? they have transorbs across the gate/source and fast diodes (mur8100e) across the drian/source, and they (the mosfets) seem to have died completely short circuit (gate to source/drain 0 ohms and drain to source about 70 ohms). When i order more mosfets i will probably order bigger ones, but does anyone know what could have killed these? cheers Jesse Frost _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla No virus found in this incoming message. Checked by AVG - http://www.avg.comVersion: 8.0.138 / Virus Database: 270.5.6/1572 - Release Date: 25/07/2008 06:51
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