need help with buck converter

[f1blop]

hi everybody, thanks for reading my post, I hope somebody can help me with this issue.
I'm making a basic 12V to 5V-0.5A-continuos mode-buck converter using SG3524 IC, P-Channel MOSFET, schottky diode, etc. When I test only the pwm and the mosfet it work fine, schitching at the right frequency, but when the rest of the ciruit is implemented and I try to measure the voltage in the diode I can't see the signal I'm expecting to see.
I don't know what's happening because at the output I'am having the right voltage (5V). It could be something related to the operation mode.
I'm forced to use a 20mH inductor.
Please help me

 

[gevy]

Check inductor. May be 20 uH ?

 

[A.Anand Srinivasan]

please post the waveforms you are obtaining so that we can figure out what is the problem....

 

[qa majid]

my project is 48v to 12 v buck converter in continuous conduction mode using matlab simulink.but it is difficult to me to make a simulink model of PWM which hass as out put duty cycle 0.12.can some body help me plz?