What is the source voltage of High side MOSFET in Buck Converter ?

[star_golden]

I am trying to model Buck Converter in Verilog.

MOSFET model which I have designed has 3 inout ports - Source, Gate and Drain.
During charging, High side MOSFET is ON, with the Inductor being charged.
Drain terminal gets input voltage (12V)
I have given PWM to the gate of MOSFET (When High side MOSFET is ON, Low side is off and vice versa).

But I am not able to make out what is the voltage at Source terminal of High side during charging ?
Is the voltage at Source is same as Voltage at the Drain (Input voltage) ?


Please help me to understand the basics.

Thanks and regards,

 

[Audioguru]

The high side N-channel Mosfet drain and source voltages are almost the same when its gate voltage is 10V higher than its power supply voltage. Its gate pulse is bootstrapped to be 10V higher than the power supply voltage. If you do not have a proper buck converter IC and you are feeding a 12V pulse to the gate of the high side Mosfet then its source pulse might be as low as 2V. If you feed the gate a 5V pulse then the source pulse might be almost nothing.