you got the classic newbie problem of a resonant loop in the output, Lout, C in the diodes, C in the Tx secondary ( in // with the Lsec ), Cout. All the series C ( two paths as CT output ) plus the wiring L for one and via Lout for the other back to the CT.
Really a full bridge of diodes would have been better here - much less volts everywhere, you could also then use a 2 part choke in the + & - to give some CM filtering.
I assume the blue trace is the pri current - since you sort of mention this.
You should be more worried about the PIV across the diodes - if this is OK - then you don't care too much about the current as long as it does not spike up to ridiculous levels.
Can you show the PIV across the diodes ? use two probes and the subtract function on the scope.
Yes, with a lower Lmag ( very small gap in Tx ) and your series choke on the driving side - you can add some C to the fets to limit the dv/dt at turn off - which will help as the sec side ckt will not then get the same "kick" into ringing.
Alternatively placing snubbers across each diode string ( best ) or across the Tx sec's ( 2nd best ) will solve some of the issue of ringing but not the initial current spike. If the freq was low you could use a ferrite bead ( large ammo bead type thing or power ferrite ) in the sec wdg's to each diode to lessen the hit to the diodes and dissipate some of the ringing energy.
--- Updated ---
100kHz may well be too high for 1200V out - as any snubbers will produce a lot of heat .... esp as you have 2 x the output volts and then some on the sec's and diodes ( Psnub ~ C. V^2 Freq )
--- Updated ---
Also you need at least one extra ckt to stop the converter if the output volts go too high ( i.e. for when the the single extant feedback loop fails for any reason ).
--- Updated ---
p.s. congrats that you got this far.
I can see that pk curr mode control won't work too well if the CT is in series with the Tx
This is one of those occasions where the CT in line with the DC in looks to be a useful change - albeit limiting the max D to allow reset time on said CT.
What is the decoupling like on the pri side 250V rail ?
you are missing the resistors on D25, D26, these are generally considered essential.
--- Updated ---
again, for 1200Vout, a full bridge of diodes seems like a better idea, fully utilised Tx, less turns overall, hence less capacitance
Also - planar are bad for capacitance in general.
--- Updated ---
what is the lowest design operating freq for the 1 : 6+6 ?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?