RE: SSTC - experiments

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

Original poster: Jan Wagner <jwagner-at-cc.hut.fi> 


On Mon, 12 Jan 2004, Tesla list wrote:
 > Original poster: "Steven Ward" <srward16-at-hotmail-dot-com>
 >
 > the only thing we must achieve is pulse-width modulating a square wave
 > (coming from a feedback source).  I havent looked into any ICs about doing
 > this, but it should be possible.  A self-resonant audio based SSTC would be
 > exceptional i think.  When the SSTC is perfectly in tune, it produces very
 > little extra noises.  Maybe i will browse around the TI website and see if
 > i can find a chip that will allow this to happen, it would definately be
 > cool ;D  Also, i never like the idea of losing tune just from moving around
 > the coil.

A simple buck step-down converter in from of the (unmodified!)
self-resonant SSTC will do this. Like TI's UCC3573 which works at max
300kHz => SSTC much lower than this, maybe 150kHz. If it allows to set the
reference voltage externally, use the audio signal, and feedback pin as
in schematic. If it has a fixed internal reference, put on the feedback
pin an error voltage derived from the audio-in and a suitably low-pass
filtered feedback signal (buck output voltage, not TC output).

Designing the buck inductor is a bit trickier. At least, getting the
proper toroidal ferrite core for the inductor is the hardest part. Maybe
digikey has some high-power high freq ferrites?

cheers,
  - Jan

--
****************************************************
  Helsinki University of Technology
  Dept. of Electrical and Communications Engineering
  http://www.hut.fi/~jwagner/ - jwagner-at-cc.hut.fi