Metal-oxide Semiconductor FET (MOSFET)

Metal-oxide semiconductor field-effect transistors (MOSFETs) are electronic switching devices with a conducting channel as the output. An electrode called a gate controls the width of the channel and determines how well the MOSFET conducts. When voltage is applied to the gate, current flows from the drain to the source. A thin layer of oxide insulation keeps current from flowing between the gate and the channel. There are two basic types of metal-oxide semiconductor FETs: n-channel and p-channel. N-channel devices conduct through electrons. P-channel devices conduct through “holes”. Both types of metal-oxide semiconductor FETs provide significantly higher switching speeds than bipolar transistors. In addition, MOSFETs generate little heat, offer excellent linearity, and provide high efficiency and fast reaction times. 

Performance specifications for metal-oxide semiconductor FETs include drain-source breakdown voltage, drain saturation current, gate-source cutoff voltage, common-source forward transconductance, Ohmic resistance, power dissipation, and temperature range. MOSFET operating modes include depletion and enhancement. A MOSFET operating in depletion mode can have its channel decreased or increased by an appropriate gate voltage.  A MOSFET operating in enhancement mode can only increased its channel by an appropriate gate voltage.

Basic IC package types for metal-oxide semiconductor FETs are transistor outline (TO), small outline (SO), and small outline transistor (SOT). For each package type, many variants are available. Transistor outline packages include TO-92, a single in-line package often used for low power devices; TO-220, which is suitable for high power, medium current, and fast-switching power devices; and TO-263, the surface-mount version of the TO-220 package. Small outline transistor packages include SOT23, which is often used in home appliances, office and industrial equipment, personal computers, printers, and communication equipment; SOT89, a plastic, surface mounted package with three leads and a collector pad for good heat transfer; and SOT223, an encapsulated package that provides excellent performance in environments with high temperatures and humidity levels. IC package types for metal-oxide semiconductor FETs also include discrete or deca-watt package (DPAK) and flat package (FPAK).     

Packing methods for metal-oxide semiconductor FETs consist of tape reel, rail, bulk pack, and tube technologies. The tape reel method packs components in a tape system by reeling specified lengths or quantities for shipping, handling, and configuration in industry-standard automated board-assembly equipment. Rail, another standard packing method, is typically used only in production environments. Bulk pack devices are distributed as individual parts, while tray components are shipped in trays. The tube or stick magazine method is used to feed MOSFETs into automatic placement machines for through-hole or surface mounting.

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