12.17 : MOSFET: エンハンスメントモード

The two modes of p- and n-channel MOSFETs are enhancement and depletion.

Enhancement mode MOSFETs are typically off at zero gate-source voltage, meaning no current flows between the drain and source.

A drain current only flows when a positive voltage is applied to the gate. This creates an electric field that attracts electrons from the substrate to the oxide layer, forming an inversion layer. This forms a conducting channel between the source and the drain, enabling current flow.

Increasing the positive gate voltage increases the drain current through the channel.

Enhancement-mode MOSFETs are excellent electronic switches due to their low ON resistance, high OFF resistance, and high input resistance.

A dimmer switch for LED lights uses an enhancement mode MOSFET to control the brightness.

The gate voltage is adjusted by rotating the knob on the dimmer. When the voltage is zero, the light is off. As the gate voltage increases, more current flows through the LEDs, making them brighter.

Enhancement-mode MOSFETs are used in integrated circuits for producing CMOS-type logic gates and power-switching circuits.