What is an Enhancement-Type MOSFET?

There are two types of MOSFETS: depletion-type MOSFETs and enhancement-type MOSFETs.

Enhancement-type MOSFETS are MOSFETs that are normally off. When you connect an enhancement-type MOSFET, no current flows from drain to source when no voltage is applied to its gate. This is why it is called a normally off device. There is no current flow without a gate voltage.

However, if a voltage is applied to the gate lead of the MOSFET, the drain-source channel becomes less resistive. As the gate-source voltage increases more and more, the current flowing from drain to source increases more and more, until maximum current is flowing from drain to source.

An enhancement-type MOSFET is so named an enhancement device, because as the voltage to the gate increases, the current increases more and more, until at maximum level.

An enhancement-type MOSFET behaves very similar in action to a bipolar junction transistor.

The other type of MOSFET, a depletion-type MOSFET, has the complete opposite behavior. Depletion MOSFETs are normally on devices. They conduct current at maximum level when there is no voltage applied to the gate lead. with a depletion-type MOSFET, as you increase the gate-source voltage, the drain-source channel of the transistor becomes more resistive and the current flowing from drain to source decreases, and if the gate-source voltage reaches the cutoff level, the current completely ceases to flow.