Buck converter Basics Notes for Designing and Implementation - PART 2 Simulation

Tried simulating with Qucs

The simulation didn't come of well as I hoped.The Output is showing some kind of  waveform I have no idea of looking at how it became so.

Simulated Circuit using IRF Z44 Mosfet (Now Vishay MOSFET Z44 )

 
 
Simulated Circuit using IRF Z44 MOSFET (Vishay) Waveform I got for Buck Converter Circuit

 
 
Now After trying the same in TINA spice simulator from Texas instruments I couldn't successfully produce an output.As I remember from the "Buck converter demystified" reference the ripple current will be maximum at the 0.5 duty ratio.So I have decided to redesign the parameter values for a different duty ratio of 0.25.
 
New parameters are;
 
 
Duty Ratio : 0.25
 
Period of Switching cycle (SW1) : 20us
 
Time for which SW1 is ON :0.25*20us = 5us
 
Ripple Current : 0.33*0.6 = 0.198A
 
Inductor : 454.54uH
 
Capacitor  at output (@ 100mv overshoot allowed ) : 262.581uF
 
In Qucs I made use of the buckconverter model in the website to obtain the timer for switching the switches ( I loose the MOSFET switches cause I coudn't find the required connection diagram ) and I am now getting the following waveforms.


 
 I think I am getting the required graphs for the buck converter where the output voltage is around 6V whatever the loading in the circuit output I have given.
 
 
  
 
 
If anyone think this is not correct graph do tell me why and how to obtain the correct output.Or else I have to clarify the output with my sir at college when I go back there tommorrow.
 
 FOR DOWNLOADING QUCS (FREE SOFTWARE ) GO TO :
 
Quite Universal Circuit Simulator

 

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