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SSTC questions



Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

some questions about SSTCs, again. ;o) It's about a full-bridge SMPS.

1) which impedances must be matched, really? someone said that all
should be matched. Does that mean
 a) estimated streamer load input impedance
 => b) secondary output impedance
 => c) secondary unloaded base impedance
 => d) step-up transformer output impedance
 => e) driver input impedance (Uin_min^2/Pin)

This seems like quite much... Ok a) and b) probably will match
themselves "automatically". But for the designing part, wouldn't it be
enough to just match unloaded TC base input Z to the driver input Z
with that step-up transformer?

I figure that the transformer output Z should be equal to the TC base
input Z, right? 

The other option would be narrowband 1/4wave transformer, i.e.
T1_out_Z = SQRT ( Z_pri_in * Z_TC_in ). Intuition tells this might be
the better way.

It'd be a big help if some SSTC-gurus could comment on which method is
the correct one?


2) for a full-bridge, how do I calc the necessary commutating diodes'
current handling capability, repetetive-pulsed, for the case when a
large amount of the stored energy from the secondary is reflected back
into the driver primary side?

3) primary current: the peak (sinusoidal) current is probably equal to
the (square-wave) peak flat-top current?

3) when the worst happens and considerable stored energy is reflected
back to the driver primary and tries to charge the main storage
capacitors, should there be some sort of overvoltage protection
accross the step-up transformer primary winding? Like MOVs/VDRs? Or kW
transient suppressors? Anyone found this to be necessary?


Many thanks!

cheers,
 - Jan