12.17:
MOSFET: Enhancement Mode
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.
12.17:
MOSFET: Enhancement Mode
Enhancement-mode MOSFETs are pivotal components in electronics, distinguished by their capacity to act as highly efficient switches. They are part of the larger family of metal-oxide Semiconductor Field-Effect Transistors (MOSFETs). They are available in two types: p-channel and n-channel, each tailored to specific polarity operations.
In their basic form, enhancement-mode MOSFETs are typically non-conductive when the gate-source voltage (Vgs) is zero. This default 'off' state means no current flows between the drain and source terminals unless a positive Vgs is applied. When this voltage is applied, it generates an electric field that attracts electrons (for n-channel) or holes (for p-channel) towards the oxide layer, effectively creating what is known as an inversion layer. This layer forms a conductive channel between the source and drain, allowing current to flow.
The unique feature of enhancement-mode MOSFETs is their ability to control the magnitude of drain current (id) by adjusting Vgs. Increasing Vgs enhances the conductivity of the channel, thereby allowing more current to pass through. This relationship between Vgs and id makes these devices excellent for precision control applications, such as adjusting the brightness of LED lights through a dimmer switch. Here, rotating the dimmer's knob varies Vgs; at zero voltage, the LEDs are off, and increasing the voltage progressively brightens the LEDs.
Furthermore, enhancement-mode MOSFETs are ideal for power-switching circuits and creating CMOS-type logic gates in integrated circuits due to their high input and low ON resistance. These characteristics enable efficient, high-speed switching with minimal power loss, making enhancement-mode MOSFETs essential in modern electronic design.