FETs, MOSFETs

A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a type of semiconductor switch commonly used to control electrical current in both analog and digital circuits. It operates by applying a voltage to the gate terminal, which regulates current flow between the drain and source terminals. Due to their high efficiency, low power consumption, and fast switching speed, MOSFETs are widely used in power supplies, motor drivers, DC-DC converters, and CMOS logic circuits.

When choosing a MOSFET, it’s important to match its electrical characteristics to your application. Start by checking the Drain-Source Voltage (VDS) to ensure it exceeds the highest voltage your circuit will encounter. Then look at the Gate Threshold Voltage (VGS(th))—if you're using a microcontroller (like 3.3V or 5V logic), you'll need a logic-level MOSFET that turns on fully at those voltages. The Continuous Drain Current (ID) rating must meet or exceed the current your load will draw, and lower on-resistance (RDS(on)) will help minimize heat and power loss.

There are two main types of MOSFETs: n-channel and p-channel, each available in enhancement and depletion mode variants. N-channel enhancement-mode MOSFETs are the most commonly used due to their higher electron mobility, resulting in lower on-resistance and better switching efficiency. While both MOSFETs and BJTs (Bipolar Junction Transistors) function as switches or amplifiers, MOSFETs are voltage-controlled devices, whereas BJTs are current-controlled. This gives MOSFETs a significant advantage in high-speed, low-power, and thermally sensitive applications.