Re: It works! Solid state driver

From: 	Scott Stephens[SMTP:stephens-at-enteract-dot-com]
Sent: 	Sunday, December 07, 1997 6:13 PM
To: 	Tesla List
Subject: 	Re: It works! Solid state driver

At 07:09 PM 12/4/97 -0600, you wrote:

>  In my limited experiance the zener fried at low power and took out my
>transistor and driver!

You sure the transient didn't kill the transistor, zener, et? You have to
know the energy of the pulse you wan't to supress.

>I have tried many methods to suppress transients
>but the only thing that seems to protect the transistor at turnoff is a
>capacitor snubber across the drain/source terminals.

I was thinking the resonator capacitor would store the inductive flyback. Or
the FET's integral diode would freewheel. Again, I'll have a better idea
with a good simulation.

>I have also tried
>Mov,s with the same result(the smoke and flame were much more
>spectacular though)!

MOV's arn't designed for repetitive energy. After a couple of hits, they
slowely degrade & die. Transorb's (IIRC), are designed for repitive hits,
energy limits in spec, of course.

>  My secondary is wound directly over the primary to achieve maximum
>coupling. There is a layer of high voltage tape between them rated at

Maximum coupling is a great feature of solid state design with end feeding.
But if you load the secondary (with a white-hot discharge, for instance) the
decreasing load impedance of the secondary will now appear (to the turns
ratio ^2) across your FET's :(

You can then, limit your coupling and your output power, or use dynamic
regulation, or maybe pulsing to give arcs a chance to cool and die out. I
plan all the above :)


A high-speed reverse recovery diode designed to freewheel inductive loads.
Takes some of the reverse recovery time strain off your FET, or BJT. Relying
on a FET's integral diode adds power to be dissipated Realy lowers the
current capability of the device. My thinking is, the resonator capacitor
will do what a snubber will, more efficiently. No doubt, the large primary
cap handling tens of amps, will be its own snubber, I hope they (parallel'd)
don't blow!

>The only simulator I have is Electronics Workbench, but is somewhat

You can do a web search for MicroSim and APLAC. Microsim is has pretty
windows. Kind of like comparing Windows to Unix. Wan't power or a quick
learning curve?

Both are cripple-ware, but sometimes you can rename & edit files, to get by,
until you get rich & famous like Tesla ;)