The drain and source are heavily doped N+ region and the substrate is p-type. N-Channel MOSFET N-channel MOSFET Enhancement and Depletion Mode The negative gate voltage also attracts holes from the P+ source and drain region into the channel region. When we apply negative gate voltage, the electrons present beneath the oxide layer experience repulsive force and are pushed downward into the substrate, the depletion region is populated by the bound positive charges which are associated with the donor atoms. The current flows due to the flow of positively charged holes, and that’s why known as p-channel MOSFET. The drain and source are heavily doped p+ region and the substrate is in n-type. P-Channel MOSFET P Channel MOSFET Depletion and Enhancement Mode Now with respect to the working principle, MOSFET is classified as follows: The enhancement-mode MOSFET is equivalent to a “Normally Open” switch. The depletion-mode MOSFET is equivalent to a “Normally Closed” switch.Ģ.) Enhancement Mode: The transistor requires a Gate-Source voltage(VGS) to switch the device “ON”. Different Types of MOSFETġ.) Depletion Mode: The transistor requires the Gate-Source voltage (VGS) to switch the device “OFF”. Another synonym is IGFET for the insulated-gate field-effect transistor.

It is insulated from the channel near an extremely thin layer of metal oxide.Ī metal-insulator-semiconductor field-effect transistor or MISFET is a term almost synonymous with MOSFET. The width of the channel is controlled by the voltage on an electrode called Gate which is located between the source and the drain. The charge carriers enter the channel at the source and exit via the drain. It works by varying the width of a channel along which charge carriers flow (electrons or holes). The body (B) is frequently connected to the source terminal, reducing the terminals to three. It is a four-terminal device with S ource (S), D rain (D), Gate (G), and body (B) terminals. The main advantage is that it requires almost no input current to control the load current and that’s why we choose MOSFET over BJT. MOSFETs are particularly useful in amplifiers due to their input impedance being nearly infinite which allows the amplifier to capture almost all the incoming signal. Since they can be made with either p-type or n-type semiconductors, complementary pairs of MOS transistors can be used to make switching circuits with very low power consumption, in the form of CMOS logic. It is used to provide isolation by preventing the direct flow of charges on the gate to the conducting channel.Ī MOSFET is by far the most common transistor in digital circuits, as hundreds of thousands or millions of them may be included in a memory chip or microprocessor. A different transistor's pins may be in the order b, c, e from left to right.The silicon dioxide forms the Gate of the MOSFET. This is especially true for transistors in the plastic TO-92 package.Īs an example, when the KSP2222 (or PN2222) transistor's flat side (the side with the part number printed on it) is facing you with the pins down, the pins are e, b, c (emitter, base, collector) from left to right. transistors with different part numbers) won't necessarily have the pins in the same order. 2N2222, BC107, BC108 and BC109 Transistor Pinout Diagramĭifferent transistors (i.e. The way that a 2N2222, BC107, BC108 and BC109 transistor symbol maps to the physical device is shown in the diagram below. Transistors have three pins called emitter (e), base(b) and collector(c). Metal Can and Plastic Packaged Transistors Transistors Pins The KSP2222 is an equivalent of the 2N2222 but is packaged in a plastic package known as a TO-92 package. The 2N2222 is packaged in a metal can package known as a TO-18 package. They have the part numbers 2N2222 and KSP2222 (also available as PN2222). In the photo below, two different transistors are shown. Transistor Part NumbersĮach transistor has a part number. The bigger the package is, the more power the transistor can handle. These are the names of the packages and not the transistor part numbers. Transistors can be packaged in many different packages, some examples are shown below: Examples of Different Transistors in Different Packagesĭifferent packages have different names, e.g. The symbols used in circuit diagrams for NPN and PNP transistors are shown below: Circuit Diagram Symbols of NPN and PNP Transistors Transistor Packages

There are two types of BJTs, namely NPN and PNP.

Here the BJT (Bi-polar Junction Transistor) is discussed.

There are several kinds of transistors available, e.g.

Transistor definition for dummies