Re: SSTC probs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jan Florian Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

> Hi guys, this is for the SSTC experts.Ive been using a simple 555 timer and 
> IRF740 MOSFET to run a true tesla coil secondary.I get pretty good output
for 
> the fact its way out of tune.My input power is a 4.5amp variac.When I try to 
> go abouve maybe 70 volts, the MOSFET makes a small little pop noise and 
> output goes to zip...

You have a setup with just one mosfet? Do you have any schematic?
How many primary turns?

The reason the mosfet dies is probably because it get's overvoltage. You
could try an IRFPE50 or other 800V mosfet instead.

(you probably ask now how the heck a 400V fet can fry on 90V... ;o) the
fact is that when the mosfet turns off, the primary coil makes a big
voltage spike accross the drain-source of the mosfet, the larger the more
current had been flowing before turn-off. so if you are particularily
unlucky it goes beyond 90V)

The two diodes won't help, by the way (if your circuit schematic looks
like I think it might look). The diodes only help in half- and full-bridge
SSTC designs.

cheers,
  - Jan

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