Re: Self-resonant 555 astable conversion?

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

Original poster: "Mercurus2000 by way of Terry Fritz <teslalist-at-qwest-dot-net>" <mercurus2000-at-cox-dot-net>

Are you talking about a 555 timer to power a small magnifier coil?

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, May 17, 2003 6:09 PM
Subject: Re: Self-resonant 555 astable conversion?


 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi Jolyon,
 >
 > It should be possible but take system ground right there off the secondary
 > ground wire too.  The "ground" may have like 10uH of inductance and
 > resistance in it that could cause "sort of high" voltage spikes if the
 > grounds were not all centrally located.  That single ground point thing...
 >
 > I would put it in a small metal box and use those plug in prototyping
 > boards so that circuit changes are easy which will be good when you have
to
 > add that phase correction circuit ;-))  Not that any wire leading from the
 > box is an antenna and possible streamer strike too so add caps or whatever
 > there.  But the environment inside the box should be very quiet really.  I
 > like the heavy cast aluminum boxes from Digi-key and I use 1/4 inch copper
 > tape around the seem.  Nothing gets past that!
 >
 > Cheers,
 >
 >          Terry
 >
 >
 > At 11:02 AM 5/17/2003 +0100, you wrote:
 > >Dear List,
 > >I am enquiring whether it is possible to connect up a 555 as a regular
 > >astable  but with secondary of a small (ferrite bead?) current
transformer
 > >connected between the RC timing network and pins 2 and 6 of the IC
 > >the primary of the CT being connected into the ground wire of the TC
 > >secondary.
 > >
 > >I have used 555 connected as a 50/50 mark-space astable to drive a small
 > >(not very successful) magnifier, but with fixed frequency oscillator in
an
 > >SSTC any changes in the topload-to -ground capacitance will detune the
 > >system; hence I am looking into a way of converting my setup into an
SR-SSTC.
 > >
 > >Protection diodes would of course be connected between the junction of
 > >pins 2 and 6 and the positive and negative rails to the astable, to limit
 > >any excursions to 0.6v above and below the rail voltages.
 > >
 > >This way, the IC would start up as an RC oscillator, turning into a
 > >feedback oscillator as soon as current started to flow in the secondary.
 > >
 > >Would it work and if so, would some form of phase-adjustment be needed to
 > >get the feedback current into the correct phasing to drive the oscillator
 >
 >
 >