Re: Thyratron pair (was DC Drive)

To: tesla-at-pupman-dot-com
Subject: Re: Thyratron pair (was DC Drive)
From: Tesla List <mod1-at-pupman-dot-com>
Date: Tue, 14 Oct 1997 13:25:30 -0600 (MDT)
Approved: mod1-at-poodle.pupman-dot-com


---------- Forwarded message ----------
Date: Tue, 14 Oct 1997 08:59:07 +0300 (EET DST)
From: Harri Suomalainen <haba-at-cc.hut.fi>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Thyratron pair (was DC Drive)

On Mon, 13 Oct 1997, Tesla List wrote:
> >The pulse can only rise as fast as the LpCp surge impedance can allow 
> >it to can't it?
> 
> No, fast pulse rise time is basically related to switch turn on time.  
> Spark Gaps and H2 Thyratrons turn on in a few nanoseconds, some newer 
> fast tubes in the 10's of nS, IGBTs in the low 100s nS and older vacuum 
> tubes much slower.  Secondarily, low surge impedance may slow rise time 
> a bit, but fast switch turn on time is most important.

The *driving* waveform can be square with fast switching waveform.
However, as Malcom pointed out the Lp/Cp-system will take energy
as the surge impedance allows. Even with a square wave input the
current in the coil will not rise more than surge impedance allows.
The cap won't charge faster either. It may look nice at the driver
side when scoped but it is still of no use.

If you drive through a primary with *no* cap at all the thing changes
a bit. Even then there is the coil limiting current rise time as drive
voltage indicates (di/dt = U/L where i=current, t=time, U=drive voltage,
L=inductance of primary). Of course secundary will absorb some of that
by mutal inductance but still..

> The faster the rise time the more the wave form resembles a square wave 
> and there are multiple odd harmonics available for the resonator to 
> use.  There is a danger in having too fast of a rise time with a very 
> narrow pulse as the resonator is unable to use the fequency content of 
> the pulse.

The resonator is a high-Q tuned system. If you put square wave in it will
filter quite effectively the harmonics out. Try feeding a coil with a
square wave signal and watch the current draw being fairly pure sine.

I definately fail to see any usefullness of feeding signals in for just
getting filtered off by the coil. I hope I've not misunderstood anything
crusial.
--
"99% of the pain in the world is due to misunderstanding" -M. Jarvelainen

Harri.Suomalainen-at-hut.fi - PGP key available by fingering haba-at-alpha.hut.fi