12v-24v to 230v smps inverter

[thameesha7]

Hi
i need to make 12V-24V DC to 230V DC inverter so i make one like this
i use Push-Pull topology and this circuit for it http://2.bp.blogspot.com/-IGrcj4RjyYs/UOqa9ISSgXI/AAAAAAAAAYY/PpmE6sGtLck/s1600/circuit+50kHz.png
and i use ER35 core
this is my formula Npri http://3.bp.blogspot.com/-vEX8Rr_RdDM/UNdzSMzVsuI/AAAAAAAAATA/Z0WIqaWh2Ow/s1600/turns+calculation.png
i enter my valuve like this Vin(nom) = 24V, F = 50000, Bmax = 1500(guass), Ae = 1.07
then my Npri = 8
and i want output like 230V 25W so i get maximum duty cycle = 98% and my Vin(min) = 11
so 0.98*11=10.78 and i get voltage ratio (secondary : primary) = 250v:10.78 = 23.1
Nsec = N * Npri = 23.1*8 = 184.8
then my Nsec = 185
i get swg 26 as pri and swg 34 as sec

when i supply 12v my FET are not heat and work fine
when i supply 24v inverter work but FET gone heat
what is the wrong in my circuit can someone help me please

(my english knowledge is not good sorry about it)

 

[Tahmid]

What MOSFETs are you using?

By the way, does your inverter need to work over the entire range of 12V to 24V at near maximum capacity?

 

[wally7856]

How did you wind the transformer. Do you know that 8 primary turns = 2 primary windings with 8 turns each.