The 20V Supply voltage drops to low 10V , however if I connect th resistor in place of inductor the supply doesn't drop it remains 20V Anyway my suspection is that there is too much current flowing the inducto and it might be its saturating hence the supply drops.
Its (inductor) design to work from 5-40kHz with maximum curent of 8A an its value is 500uH.
LM3524 is Pulse width Modulator (PWM) is working efficiently,
IR2117 is a mosfet driver is to enable the switching of Mosfet, which I a also not happy with it though, I sometime suspect is not completel switching off, its external components are bootstrapping capacitor an diode
LM7815 is voltage regulator and its supplying the Mosfet Driver
Across the mosfet is snubber circuit Rs & Cs