Solar Freaks

hi, i need help badly. my thesis adviser is on the verge of dropping me from the subject.

Ive been trying to construct a buck converter with the following specs:
Vin(min) = 28V; Vin(max) = 60V; Vout = 24; Iout(min) = 8A; Iout(max) = 10A.

this is my output current target because i need around 200 W power. initially i tried using an LT3845 chip however it seemed my circuit ruined the chip. every time i connected it to a source, the chip started overheating even at no load conditions. so i temporarily switched to constructing a basic buck converter.

the pwm controller im using for the gate drive of the mosfet (top switch) is a uc3843 (or as3843). my inductor is a ferrite core toroid with awg#12 magnet wire. my diode and mosfet are both chosen to be able to withstand high currents.

at no load conditions, the output voltage regulates at around 27V, when i test it on an e-load, however, the voltage stays at 24V only up to 3A constant current load. any higher load than 3A, the supply voltage drops (loading effects?) and seems to get sucked into the circuit. any suggestions of the causes for this kind of behavior or perhaps how i can fix this? thanks so much.

Its really hard tell with so little info.
Post a schematic and ill have a look at it for you.

this is the design using a pulse transformer. my inductance is currently 22uH.
this is the one using the synchronous buck IC. (LT3845)