RE: Series connection of Mosfets/IGBTs

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Perhaps I can throw a bit of light on this:

On 18 Feb 2004, at 8:06, Tesla list wrote:

 > Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>
 >
 >  >Series tuned primary, what is that?
 >  >Is it what Marco uses in his SWmode supply? (Series cap resonating
 >  with >leakage inductance) >Does it make the secondary system
 >  invisible to the primary? >If it is good, how do we make it?
 >
 > First of all this is a SSTC thing. Classic coils already have a tuned
 > primary :)
 >
 > Just take a normal SSTC, loosen the coupling a bit, and connect a
 > capacitor in series with the primary, of a value that will resonate
 > with the primary inductance. The capacitor has to be a kind that will
 > stand a high RF current, either a "MMC" of pulse caps in parallel, or
 > a ceramic transmitting type cap.
 >
 > Now stand well back and throw the switch. The series tuned primary
 > seems to boost performance quite drastically, but increases the chance
 > of blowing up your transistors.

What is happening is that the primary is no longer an inductance but
a resistance of very low value at resonance. This allows you to get
more current in. It also allows a high circulating current to build
up.

Malcolm

 > A series tuned SSTC (also known as dual resonant or DRSSTC) also has
 > interesting transient behaviour that lets it generate very high power
 > pulses in the manner of a clasic coil, but with higher efficiency than
 > a solid-state "spark gap replacement". Jimmy Hynes did a lot of work
 > on this and got excellent results, although his setup did have a
 > tendency to explode, throwing little pieces of IGBT all over the
 > garage.
 >
 > http://www.hot-streamer-dot-com/chunkyboy86/ iirc
 >
 > Now that high-speed high-current IGBT modules are getting more common
 > in the surplus market, I reckon the DRSSTC is the future for
 > solid-state coiling. The OLTC is a good way of making use of all those
 > old slow IGBTs though :) besides being a bit easier to build, and
 > arguably less likely to go KaBlooie.
 >
 > Steve Conner
 > Power Electronics Misapplications Dept.
 > scopeboy-dot-com
 >
 >
 >