Can i know what are the information you need to give a explainationfar too little information supplied - to make any useful comment.
No ouput diodes they are replaced by a SRSchematic, Vds waveforms, Vgs waveforms, Vak waveforms of o/p diodes - and what type they are
Doesn't matter - the SR is off - just before the internal diode takes over the current and then has to reverse recover - causing your EMI . ..No ouput diodes they are replaced by a SR
Yes i understand what is the reason for the voltage bump that appears before the FET is actually turns on?This is a thing for the phase shift converter - below a certain load there is no full transition and hence loss of proper soft switching - the shim inductor and diodes lower the level at which proper ZVS is lost - but you still get it below a certain load.
no i do not use a blocking capacitorDo you use a series blocking capacitor?
if you can i will be much obliged. I done a simulation in Matlab to verify the control loop but not in LTspicei will send you a PSFB in LTspice eand you can adapt it to your spec?
the thing i can't understand is whether this voltage waveform is normal or do i need to do something about it. I want to clearly understand why that voltage bump appears in the primary.Absolutely expected...big voltage step input to a high Q series LC resoannt cct...will ring like mad....we cannot stop it...its mother nature.
are you suggesting that the MOSFET is tries to turn on?the volts try to rise - but there is insufficient energy stored - so it goes down again until the gate drive is applied forcing the voltage high.
We don't know if there is any shim inductor, or, how high the pri side leakage is on the Tx - you can see in the waveform ( just - LHS ) that the transition at the end of the power pulse ( some times called the leading leg transition ) IS ZVS, but after the circulating current period there is insufficient energy for ZVS on the passive to active transition ( sometimes called the lagging leg transition ) - this can easily happen at mid load for a given design - and appears to be happening here.From what I understand, that waveform is at medium-load, so one would expect the stored energy to be sufficient to soft switch the bridge completely.
You might be right, but impossible to really tell without seeing Vgs waveforms. Need much more info from OP in general.We don't know if there is any shim inductor, or, how high the pri side leakage is on the Tx - you can see in the waveform ( just - LHS ) that the transition at the end of the power pulse ( some times called the leading leg transition ) IS ZVS
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