Re: Self-resonant 555 astable conversion?

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

Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Jolyon (and other picture posters):

On 20 May 2003, at 7:53, Tesla list wrote:

 > Original poster: "Jolyon Vater Cox by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 >
 > I have posted the  diagram of my proposed  setup is at
 > http://hot-streamer-dot-com/temp/555%20sr%20astable.bmp.

Please do us a favour and bottle the pic up either as a zip file or a
jpg. Bitmaps are an incredibly inefficient way of using bandwidth and
time. I'd like to have a look at it but feel uninclined to use
university resources in this manner.

      It'd be great if you would try some of your ideas out and let us
all know which ones actually fly.

Malcolm

 > Looking at the diagram again I am concerned about phasing - should the
 > current transformer should be in one the primary leads from the H-bridge to
 > the step-up transformer, rather than the secondary- this after all, is the
 > position of the current transformer in half-wave converters used in compact
 > flourescent  lamps and electronic halogen transformers -but what is
 > implication of primary current  feedback on the TC frequency distribution/
 > bandpass characteristic?
 >
 >
 > With the current transformer in the secondary lead- isn't there a phase
 > discrepancy between the output of the current transformer and the primary
 > voltage that would need to be corrected in some way e.g by connecting a
 > capacitor in parallel with the secondary of the current transformer,
 > perhaps?
 >
 > What appeared simple at first is now beginning to look rather more
 > complicated...!
 >
 > Jolyon
 >
 > Jolyon  ----- Original Message -----
 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > To: <tesla-at-pupman-dot-com>
 > Sent: Monday, May 19, 2003 2:45 PM
 > Subject: Re: Self-resonant 555 astable conversion?
 >
 >
 >  > Original poster: "Stephen Conner by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >  >
 >  > At 05:36 17/05/03 -0600, you wrote:
 >  > >Original poster: "Jolyon Vater Cox by way of Terry Fritz
 >  > ><teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 >  > >
 >  > >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.
 >  >
 >  > It should be possible, I did something similar for zero-current 
turnoff in
 >  > my OLTC driver circuit. I used a two transistor circuit to amplify the
 >  > collector-emitter volt drop in the IGBT, and coupled the resulting square
 >  > wave into 555 pin 2 using a small capacitor and 1k resistor (the resistor
 >  > isolated pin 2 from the timing capacitor which would otherwise just shunt
 >  > the pulses to ground) In this way the turn-off was locked to the nearest
 >  > negative half-cycle.
 >  >
 >  > If you were to connect a secondary current sensor (probably a capacitor
 >  > would be better than a CT) to the amplifier input, and have the 555
 > running
 >  > at 50% duty cycle at a little below the lowest frequency of interest, it
 >  > would probably lock on.
 >  >
 >  > However I think that better results could be had using a SMPS controller
 >  > chip like the UC3525 that has a sync input pin. Normally used for locking
 >  > multiple SMPSs together to prevent annoying audible beat tones but could
 >  > perhaps be used for feedback. I know the TL494 is popular but I don't
 > think
 >  > it has one of these sync pins.
 >  >
 >  > http://www.scopeboy-dot-com/t3fnq.html
 >  >
 >  > Steve C.
 >  >
 >  >
 >  >
 >  >
 >  >
 >
 >
 >