Re: MOSFET Coil- Ready..Set...

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

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 21:44 06/04/03 -0600, you wrote:
>Original poster: "S Gaeta by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><sgtporky-at-prodigy-dot-net>
>
>
>
>I was also wondering why a feedback winding (coupled to the Tesla coil
>primary) couldn't be used in place of the pick up antenna input where the
>'human touch' is required to start the coil working? Somehow I don't feel
>really comfortable with high impedance inputs on sensitive devices with all
>that high energy noise floating around. If someone else touches the antenna
>while I am playing with the arc, there is the possibility of MOSFET guts
>flying all over the place, along with toasted driver components. I am also
>guessing that the better coupling of a feedback winding might produce a more
>reliable startup, and keep the coil going until you kill the power.

I don't much like the idea of the antenna feedback circuit either, although 
it seems to work fine. But it may not be as simple as just substituting a 
feedback winding. The phase shift with the antenna is probably different to 
what you would get with a feedback winding, so you may need to add an extra 
phase shift somewhere. Besides, you probably want the feedback winding 
coupled to the secondary more than the primary.

I know some SSTCers have successfully used a current sensor in series with 
the secondary ground. You basically put a capacitor (largish, several uf, 
AFAIK) between secondary base and ground, and use the voltage across the 
capacitor in place of the antenna signal. Someone else may be able to give 
more information on this. I've also seen this circuit used in a plasma 
globe that I took apart.

Steve C.