Re: It works! Solid state driver

From: 	bmack[SMTP:bmack-at-frontiernet-dot-net]
Sent: 	Tuesday, December 09, 1997 7:44 PM
To: 	Tesla List
Subject: 	Re: It works! Solid state driver


Your Pwm had an adjustable "dead time" delay which is supposed
to avoid simultaneous conduction of the power transistors.

Did you set this for the rise/fall spec's of your FET's?

This may be the problem.

Jim McVey

> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-poodle.pupman-dot-com>
> Subject: Re: It works! Solid state driver
> Date: Monday, December 08, 1997 10:17 PM
> From: 	RODERICK MAXWELL[SMTP:tank-at-mail.magnolia-dot-net]
> Reply To: 	tank-at-mail.magnolia-dot-net
> Sent: 	Monday, December 08, 1997 9:03 PM
> To: 	Tesla List
> Subject: 	Re: It works! Solid state driver
> > You sure the transient didn't kill the transistor, zener, et? You have
> > know the energy of the pulse you wan't to supress.
>  The highest wattage/voltage zener I can get my hands on is 5watts/200v 
> > 
> > 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
> > 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,
> > slowely degrade & die. Transorb's (IIRC), are designed for repitive
> > 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
> > >69Kv.
> > 
> > Maximum coupling is a great feature of solid state design with end
> > 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
> > 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.
> > plan all the above :)
> > 
> > >Hexfred??????
> > 
> > A high-speed reverse recovery diode designed to freewheel inductive
> > Takes some of the reverse recovery time strain off your FET, or BJT.
> > on a FET's integral diode adds power to be dissipated Realy lowers the
> > current capability of the device. My thinking is, the resonator
> > will do what a snubber will, more efficiently. No doubt, the large
> > cap handling tens of amps, will be its own snubber, I hope they
> > don't blow!
> > 
> > >The only simulator I have is Electronics Workbench, but is somewhat
> > >limited.
> > 
> > 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?
>   I would love to have ICAP/4 WINDOWS made by Intusoft. Unfortunately
> the list price is over $2500 bucks! And it would probably take 6 months
> to become familiar with the program.
> I have to tell you and the people on Chips list that the circuit has had
> a catasthophic failure due to what Mr. Buylund called "Flux Walking".
> This is a push-pull config. and is prone from what I've read to this
> sort of failure. The circuit is very stable at up to, and including
> 24vdc. But beyond that the power transistors begin to share the current
> unequally. This causes one of the transistors to short out due to
> excessive current draw. The only way to correct this is to use one of
> the bridge configurations, or to use a flyback configuration at lower
> voltage, or duty cycle. I am in the process of rebuliding from the ashes
> at this time! The energy in the shorted transistor was so high it
> actually punched a hole in the metal casing of the transistor the size
> of a pencil lead! It also took out the pwm, and driver.
>                               Frankensteins Helper
>                                       Max