Re: Sheppard Taylor Circuit and High Voltage Ceramic Capacitors

["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: "Daniel McCauley by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>
> 
> > 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
> > (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.
> 
> What kind of caps are you using????  You should try to get some ceramic caps
> as these have a very
> low ESR.  Thats why your caps are getting so hot.
> I used a bunch of 1500V ceramics for some high voltage power supplies we
> just built.
> AVX has some very nice high voltage ceramics which are perfect for high
> voltage switchers etc...
> 
> HV06 series has up to 15uF, 1kV which would be perfect for your application.
> Also by putting a 0.1uF cap in parallel should reduce the ESR as well in
> this application.
> 
> However, they sure ain't cheap ! ! ! !  But, they might carry some lower
> cost alternatives, maybe their SMPS series???
> 
> Dan

I have replaced the electrolytics with two 0.056uF 1600V polypropylene
caps.  They stay cool to the touch.  The only reason electrolytics may
be needed is if there is no reservoir cap, i.e. you are running this
converter right off of a rectifier.

Rob.

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