voltage boost in buck converter

[electros6]

Hi guys,
          I designed a buck converte using PMOS . when I simulated it in ltspice I got a weired result , at 10% PWM the voltage is around 8V  with the imput of 12V and I got the same result in hardware and can't go below 6V when it was loaded with 47ohm resistor. can somebody tell what is the problem. I have attached the ltspice file and the waveform at 10% pwm.
                  regards
               N.Baskaran

[SiliconWizard]

Two things at first sight:

• This doesn't look like a proper way of driving the PMOS's gate. This transistor has a relatively high input capacitance. Even with a 1k pull-up, it will still be ON a lot longer than the ON state of your PWM signal, which IMO explains your problem. Take a look at the gate's voltage in LTSPice (or for real on an oscilloscope on the real hardware.) You will need a different way of driving the gate if you want to get a lower output voltage.
• Just a quick side note, I know this is just a simulation here, but you said you built it for real. You should put a series resistor between your PWM signal and the base of the NPN transistor.