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

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

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. 

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

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 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?

> (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

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