Re: It works! Solid state driver (fwd)
From: Tesla List Owner[SMTP:listown-at-pupman-dot-com]
Sent: Tuesday, December 09, 1997 4:29 PM
Subject: Re: It works! Solid state driver (fwd)
What happened is that you had flux imbalance in the transformer. This is a
common problem with push-pull forward converters or any design when you have no
gap in the core. Air-gapping the core reduces the permeability, and increases the
level of drive you can tolerate before saturation occurs. See any good textbook
on switching power supply desing, such as Abraham Pressman: Switching Power
Supply Design, by McGraw-Hill.
Tesla List wrote:
> 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 to
> > 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 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
> > >69Kv.
> > 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 :)
> > >Hexfred??????
> > 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
> > >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