Re: Sheppard-Talyor circuit up on my website/ low Z construction technique

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

Original poster: "rob by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rob-at-pythonemproject-dot-com>

Tesla list wrote:
> 
> Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jwagner-at-cc.hut.fi>
> 
> > Yes, the normal DC-DC converter has this diode.  However, D24 isolates
> > isolates the new diode from the drain/L node.
> 
> Umm... D24 only helps block positive DC into the xfmr - I mean, the
> positive DC supply voltage coming via L16.
> The diode would clamp the pri voltage to +V_forward, and D24 can be
> neglected here as it won't conduct.

Hi Jan, yes you are correct here.

> 
> Are you running a gapped flyback core? Or "un-gapped"?

Its a huge core out of a 500W flyback SMPS.  It wasn't gapped in the
original circuit.


> 
> Hey, other idea - if you float the circuit, and check the waveform
> directly on the ends of C26, does it rise above input voltage?

I can try that.

> 
> > I found yesterday that with only 30V input my converter produced 400V at
> > the drain/L junction :)   The FREDs got extremely hot and one blew out
> 
> Ouch...
> drain/L junction == L16 & M16 junction?

Yes.

> 
> > (thermally).  Also, for {C} I am now using two 27uF 450V caps in series
> > and these got very hot as well.  I could go back to two 0.056uF 1600V
> > polypropylene caps in parellel for energy storage.  Or I could put one
> > poly cap in parallel with the electrolytics to reduce their dissipation.
> 
> just your paralleled polys are probably better, and I'd suspect
> electrolytics aren't so suitable as the switched/storage cap (low ripple
> current rating, "high"-ESR, etc ?) I already managed to smoke some
> electrolytics forcing them to similar high dI/dt, despite some polys.
> It was a nice-looking swirl of smoke, though! ;o)
> 
> cheers,
> 
>  - Jan
> 
> --
> *************************************************
>  high voltage at http://www.hut.fi/~jwagner/tesla

Yes, I'm sticking with the poly caps.  Rob.

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