I designed 20A charger using tl494 ,the problem mosfet damaged many time one I connect mains rectified DC volt, also IC damaged,
I tried circuit without feedback many time so duty cycle 45% without any problem, I think when duty cycle close to 0 , mosfet bomb ,I think I need some component for protection
The "interlock" diodes D6/D7 look suspicious, not a serious circuit design means.
I don't see what's the specific problem with "duty cycle close to 0", provided the transistors are switching regularly.
There should be RCD snubbers absorbing the drain overvoltage spikes due to transformer leakage, the dimensioning must be checked empirically with loaded output.
By design, the converter has no means to detect flux walking or transistor overcurrent.
The "interlock" diodes D6/D7 look suspicious, not a serious circuit design means.
I don't see what's the specific problem with "duty cycle close to 0", provided the transistors are switching regularly.
There should be RCD snubbers absorbing the drain overvoltage spikes due to transformer leakage, the dimensioning must be checked empirically with loaded output.
By design, the converter has no means to detect flux walking or transistor overcurrent.
with a push pull, all you need is mosfet driver to drive mosfets.
But i done know why you put the pnp turn off circuit in there...that is only needed for hi side drives...pushpull doesnt have hi side drives.
Pushpull is a not that good, there is always not perfect coupling between the primary halves of coils, and you need to quench the leakage spikes.
D6/D7 should be removed. They will push the drivers towards self-oscillation, which you don't want.
Q1 and Q2 are in a fairly standard configuration. Though D4/D5 should not be necessary.
The other major flow is the lack of an energy storage inductor on the secondary side. Without that, it can't even be called a push pull converter. You'll have limited ability to control the average output current/voltage, and you'll get tremendous ripple currents.