Buck regulator cuts noise, EMI filter requirements

What is a MOSFET?
Metal Oxide Semiconductor Field Effect Transistor, or simply MOSFET, is the most commonly used field effect transistor for both analog and digital circuits. It is composed of two channels: n-type or p-type semiconductor materials, accordingly referred to as NMOSFET and PMOSFET.

What is EMI?
Electromagnetic interference or EMI is an electrical disturbance (interference or noise) in a system due to natural phenomena, low-frequency waves from electromechanical devices or high-frequency waves from ICs and other electronic devices.