DRSSTC design and improvements

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Original poster: "colin heath" <colin.heath4@xxxxxxxxxxxx>

Hi all,
       well im onto my third drsstc build. the first disaster the second 
wasnt bad giving around 21" with half bridge of the 1n40n60 igbt's. well i 
ran this with 100nf tank cap and a 12" helical primary tapped at 5 turns.
after reading steve wards post im wondering whether to change my design a 
bit. i was currently planning to use 100nf again running the 200khz 
secondary i have. im now thinking that i should be looking at perhaps going 
to a much larger tank cap and less primary inductance to drop the impedance 
and go with a shorter on time. i too was running 300uS on time on previous 
coils.
so in designing the coil should we aim for 100uS on time then leave it 
there and work on things reducing primary losses and larger tank cap rather 
than upping the on time?
cheers
colin heath