Re: Self-resonant 555 astable conversion?

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

Original poster: "Jolyon Vater Cox by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

Yes, I am referring to the use of a 555 astable (with sufficient
amplification) to drive a small magnifier coil.
The setup I am proposing is basically the same as the one I am now using
except there is no current transformer in my present arrangement, frequency
being determined solely by the components in RC
timing network of the astable.

In my proposed assembly, a current transformer  (the secondary of which
would be connected between the RC timing network and Pins 2 & 6 of the IC)
would be used to derive the switching signal for the 555 from the
circulating current in the secondary-tertiary network at resonance.

The trigger input (Pin 2) and the threshold input(Pin 6) of the astable
would be tied together as  normal but the secondary of the  current
transformer would be inserted  between the R-C timing network and the two
pins.

The output of the IC would then be used to drive the primary of a pulse
transformer via a current-boosting stage

and the pulse transformer would be used to derive antiphase signals in order
to switch the transistors of an H-bridge.

The H-bridge would drive the primary of the air-cored transformer, the
secondary of which would be connected the tertiary (or "extra") winding.

Jolyon

Current from  <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, May 18, 2003 1:18 PM
Subject: Re: Self-resonant 555 astable conversion?


 > 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
 >  >
 >  >
 >  >
 >
 >
 >