Re: Sheppard Taylor Circuit and High Voltage Ceramic Capacitors

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

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

Hi Rob,

On 3 Jul 2002, at 12:02, Tesla list wrote:

> 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.

Why not use low ESR electrolytics?

Regards,
Malcolm