What are Transistors?
MOSFET, Darlington and Bipolar TransistorsA transistor is used to amplify and switch electronic signals and electrical power. They are used in a variety of circuits and they come in many different shapes. You can use a transistor as a switch or you can use a transistor as an amplifier.
MOSFET TransistorsMetal-oxide-semiconductor field-effect transistor is a type of transistor commonly found in digital and analog circuits to amplify or switch electronic signals. The three-terminal device has a source (S), gate (G) and drain (D) and is available in both P-channel (PMOS) and N-channel (NMOS). MOSFETs may also be known as insulated-gate field-effect transistors (IGFET) or metal-insulator-semiconductor field-effect transistor (MISFET). Although similar to a junction field-effect transistor (JFET), on a MOSFET, the gate input is electrically insulated from the main circuit carrying channel.
A MOSFET is available in two basic forms, depletion type and enhancement type. Depletion type is like a "Normally Closed" switch and requires a Gate-Source voltage to turn the device off. Enhancement type is like a "Normally Open" switch and requires a Gate-Source voltage to turn the device on. Typical package types are TO-252, TO-251, TO-247, TO-220, TO-92, SO-8, SPT-23 and SOT-223.
MOSFET Construction and Type
BU Series: Amplifier applications (Includes BUZ series – BUZ77 and BUZ78)
IRF Series: Amplifier applications (Includes IRFP and IRFZ series – IRF540 and IRFP350)
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Darlington TransistorsDarlington transistors are two standard NPN or PNP bipolar transistors that are connected together. The emitter of one transistor is connected to the base of the other to produce a more sensitive transistor with a much larger current gain.
Darlington transistor pairs can be made from two individually connected bipolar transistors or a one single device commercially made in a single package with the standard: base, emitter and collector connecting leads and are available in a wide variety of case styles and voltage (and current) ratings in both NPN and PNP versions.
Also known as a "Darlington pair" or "super-alpha circuit", the transistors are connected together so that the emitter current of the first transistor TR1 becomes the base current of the second transistor TR2.
Basic Darlington Connection
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Bipolar TransistorsThe Bipolar transistor, more commonly known as the bipolar junction transistor (BJT), is a type of transistor that relies on the contact of two types of semiconductors for its operation. They consist of three terminals: collector, base and emitter, which can be arranged as amplifiers or switches. Depending on their polarity, they can be either NPN or PNP.
Bipolar transistors work as current-controlled current regulators. They restrict the amount of current passed according to a smaller, controlling current. They are called bipolar because the controlled current must go through two types of semiconductor material: P and N.
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Other Types of TransistorsGeneral Purpose Transistors
General Purpose SMD Transistors