Re: Zener SSTC?

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

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 07:02 PM 1/15/2004 -0700, you wrote:
>Original poster: Chris Roberts <quezacotl_14000000000000-at-yahoo-dot-com>
>Hi everybody,
>We all know that a conventional tesla coil uses a spark gap that fires and 
>switches the current whenever the voltage builds high enough, but has 
>anybody ever thought about using zener diodes to replace the spark gap? 
>Zeners do the exact same thing, but allow you to fire more reliably, 
>(wouldn't have to worry much about misfires) and I would think that they 
>wouldn't have as many losses related to them either. So has anybody 
>thought about making a "conventional" coil (tank capacitor, primary, etc.) 
>but replacing the sparkgap with zeners? You could also get away with using 
>a really low voltage since you don't need it to break the air gap. Mabye a 
>simpler OLTC? Would you be able to get zeners rated for that kind of 
>thing? Anybody else think that this could work?
>
>
>-Chris
Zeners are very different from a spark gap... After a spark gap fires, the 
voltage drop across the gap is very low (a few hundred volts, at most), so 
the power dissipated in the gap is "reasonable" (10s of watts with a NST 
powered coil).

A zener has constant voltage drop, so after you reached breakdown voltage, 
you'd have the full current * the BIG voltage drop, for kW of dissipation.

A better semiconductor model would be a 4layer diode, like an SCR.  The 
problem is speed, reliability, gradual turn on,etc.  Spark gaps are awfully 
reliable, turn on in nanoseconds, and it's all conducting, almost 
instantly.  SCRs turn on fairly slowly, and the entire junction doesn't 
turn on at once, so it's partially conducting, during which time the power 
dissipation shoots real high.

Perhaps an avalanche transistor or a tunnel diode, but they can't take 10's 
of kV at 10's of Amps.

A thyratron might be comparable, but, when you get right down to it, the 
way a thyratron works isn't all that much different than a spark gap, just 
without the arc.