MOSFET driver

hi,
Find the attached schematic, i am using this circuit to drive high side n-channel mosfet...
i am feeding the PWM signal from a ATMega 88 controller of 20KHz varing duty cycle from 0-90%.but the driver circuit works till 70% if i try to feed above 70% it is folding back WHAT MIGHT BE THE REASON FOR this behavior what is the solution to come out from this problem...??????? using pulse transformer


Regard's
Pushpa

You can not make a transformer pass 0% (near 0) and 100% (near 100). A transformer can not pass DC or near DC. It works best at 50%. We can extend its range some. If you know much about duty cycle/ transformers/ fly-back voltages etc you will see why the transformer has problems.

Look at LM5104. It will drive from 0% through about 95%. It can not go to 100%

I notice D10 and D11 are shown with opposite polarity. Shouldn't D10 be the other way round?

But if i try to feed pulse from the signal genrator i will work fine......