MOSFETs

MOSFETs, also known as MOSFET transistors, stands for ’Metal Oxide Semiconductor Field-Effect Transistors’. MOSFETs are transistor devices which are controlled by a capacitor. The "Field-Effect" means that they are controlled by voltage. The aim of a MOSFET is to control the flow of the current passing through from the source to the drain terminals. It acts very similarly to a switch and is used for switching or amplifying electronic signals.

These semiconductor devices are ICs (integrated circuits) which are mounted onto PCBs. MOSFETs come in a range of standard package types such as DPAK, D2PAK, DFN, I2PAK, SOIC, SOT-223 and TO-220. For more information, please see our guide to MOSFETs.

What are depletion and enhancement modes?

MOSFET transistors have two modes; depletion and enhancement. Depletion MOSFETs work like a closed switch. The current passes through when no current is applied. The current flow will stop if a negative voltage is applied. Enhancement mode MOSFETs are like a variable resistor and are generally more popular than the depletion mode MOSFETs. They come in n-channel or p-channel variants.

How do MOSFETs work?

The pins on a MOSFET package are the Source, Gate and Drain. When a voltage is applied between the Gate and the Source terminals, current can pass through from the Drain to the Source pins. When the voltage applied to the Gate changes, the resistance from the Drain to the Source will change too. The lower the voltage applied, the higher the resistance. As the voltage increases, the resistance from the Drain to Source will decrease. Power MOSFETs are like standard MOSFETs but they are designed to handle a higher level of power.

N-Channel vs. P-Channel MOSFETs

N-Channel MOSFETs contain additional electrons which are free to move around. They are a more popular channel type. N-Channel MOSFETs work when a positive charge is applied to the gate terminal.

P-Channel MOSFETS substrate contains electrons and electron holes. P-Channel MOSFETs are connected to a positive voltage. These MOSFETs turn on when the voltage supplied to the Gate terminal is lower than the Source voltage.