Re: Snubbing an IGBT in a sstc

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>

Ref. my drawing 
http://www.pupman.com/current/kcherrick/s-e_nov-snub.jpg.  In my 
posting of 1/28 I'd expressed surprise that the snub primary's 
current was 180 degrees out from the main primary's.  I shouldn't 
have since that's exactly what's wanted.  The snub primary's current, 
derived from the charge in the snub capacitor, acts and should act to 
oppose the main primary's current: in doing so it diminishes the 
current that the main primary draws from the mains supply and thus, 
in effect, "recycles" the snub capacitor's charge back into the mains.

It might be thought that in doing so, the magnetic flux entering the 
secondary is diminished during this process since the two primaries' 
currents oppose...and that is exactly so.  However:  If a) one can 
draw current from the mains up to the limit imposed by the circuit 
breakers; and b) one can draw that current without exceeding the 
capabilities of the driving transistor(s), then...what's the 
problem?  There's relatively little in the circuit to dissipate power 
since the snub capacitor's charge is recycled.  So the major fraction 
of the mains power must be going into the secondary; ...where else?.

And that brings me to a "philosophical" question:  Given the above, 
wherein lies the advantage of a resonant primary in a s. s. t. 
c.?  If criteria a) and b) above were to hold for the resonant case 
on the one hand and for the non-resonant on the other, then--where's 
the advantage of the resonant primary with its added 
complication?  Why not use a non-resonant one, take feedback from the 
secondary, and have the thing always in tune?

It might be thought that the flux from the resonant primary could be 
greater since its inductive reactance is largely "nulled out" by the 
capacitive reactance, so more turns could be employed, carrying the 
same current.  Flux varies as current x turns.  But one still faces 
the limitations of a) and b); if they're the same in both cases, then 
does that matter?  It might seem, in fact, that the added primary 
turns would be detrimental, diminishing as they would the turns-ratio.

Enlighten me, someone.  Perhaps, in my old age, I'm becoming 
forgetful--of basics I should long ago have learned.

KCH