Method of using N-CH MOSFET to control BUCK circuit

In the buck type DC/DC conversion application circuit, the BUCK topology circuit is the most commonly used. However, in the BUCK circuit, the power tube used as a switch must be connected to the positive pole of the input power supply. Since the power tube is used to control the on-off of the positive pole, in the BUCK circuit, this power tube must use a P-CH MOSFET or a PNP transistor as a switch tube.
Since the types of P-CH MOSFETs are fewer than those of N-CH MOSFETs and the prices are relatively high, it is sometimes not easy to find suitable components. Can N-CH MOSFETs be used as the switch tube for positive on-off control? The answer is yes. This article proposes a method of using N-CH MOSFETs to control BUCK circuits.

In the figure above, the PWM signal is generated by a signal generator. The signal used in the simulation is 60kHz, the duty cycle is 50%, and the amplitude is 5V. The 0.22u capacitor in the figure is used as a boost energy storage element and as a power supply for driving the MOSFET. The switching power tube is IRF3205S (N-CH). The entire circuit is a BUCK type step-down DC/DC conversion circuit with an output current of 500mA and an output voltage of 5V. The figure is only to illustrate the working principle of the circuit, so the specific feedback and control circuits are not drawn.