4.1.2 Transistors Flashcards
Invented by Bell Telephone Laboratories, they abbreviated combination of the words “transconductance” or “transfer”, and “varistor”. The device logically belongs in the varistor family, and has the transconductance or transfer impedance of a device having gain.
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A transistor is a semiconductor device which is used to
amplify or switch electrical signals and power
Transistors are used for a wide variety of digital and analogue functions, including amplifiers, switches, voltage stabilisers, signal modulation, and oscillators. Transistors can be packaged independently or in a very small area, 100s of millions or more transistors can be incorporated into integrated circuits.
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transistors use small digital and analogue signals to control their switching on and off, and the switching speed can be very fast, which can reach 10s or even 100s of MHz.
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Generally, the semiconductor materials used are silicon, germanium, and gallium-arsenide
Transistors are classified depending on their structure
Some transistors are designed primarily for switching purposes. On the other side, some are designed for amplification purposes, and some transistors are designed for both amplification and switching purposes.
Depending on the structure, the transistors are classified into Junction Transistors and Field Effect Transistors.
Junction transistors can be Unijunction Transistors (UJTs), and Bipolar Junction Transistors (BJTs).
Field Effect Transistors (FETs) can be Junction FET (JFET), and Metal Oxide Semiconductor FET (MOSFET)
Photodiodes can be either BJTs or FETs.
The basic transistor is the BJT
Bipolar Junction Transistors
The Field effect devices are those in which current is controlled by the action of an electron field, rather than carrier injection
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A BJT is made up of a sandwich of three parts of P- or N-type semiconductor material
Thus, has two depletion areas.
Field-effect transistors are so named because a weak electrical signal coming in through one electrode creates an electrical field through the rest of the transistor.
The FET was known as a ‘unipolar’ transistor
The term refers to the fact that current is transported by carriers of one polarity (majority),
whereas in the conventional bipolar transistor carriers of both polarities (majority and minority) are involved.
In the BJT current (in mA) is used to control the flow of electrons between the emitter and the collector
In a FET, an electrical field, (voltage rather than current) is used to control the flow of electrons between the Source and the Drain.
A transistor is a type of a semiconductor device that can be used to both conduct and insulate (stop) electric current or voltage. A transistor basically acts as a switch and/or an amplifier. It is a miniature device that is used to control or regulate the flow of electronic signals.
Although Bipolar Junction Transistors (BJTs) can be used in various ways, the most important is for switching and amplification
When a transistor is fully on or saturated, it acts like a switch, with a small input voltage controlling a large current. If the transistor is operating in the region between cut‑off and saturation, it then acts more like an amplifier
biasing transistors
Like a PN Diode, a bipolar transistor must be properly biased to be useful. A BJT has two PN junctions, each must be properly biased for the transistor to function correctly.
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reverse biasing of a transistor
If an external voltage is applied between the base and collector of an NPN transistor, the junction formed between the regions is called the collector-base junction or collector junction. This acts like a reverse-biased PN diode and will not conduct..
forward biasing of a transistor
If the external voltage is now applied between the base and emitter of the transistor, the junction formed between the regions is called the emitter-base junction or emitter junction. This now acts like a forward-biased PN diode and will conduct.
what does BJT stand for
Bipolar Junction Transistor
what does JFET stand for
Junction field effect transistor
what does MOSFET stand for
metal oxide semiconductor field effect transistor
whats the difference between a N and P channel MOFSET
N channel arrow is pointing upwards towards bars and P channel is opposite pointing downwards
whats the difference between an N and P channel JFET
(Gate)
N channel points away from gate
P channel points towards gate
NPN phototransistor arrow points towards (E) emitter
PNP phototransistor arrow points away from (E) Emitter
N channel Unijunction transistor arrow points towards B1
P channel unijunction arrow points away from B1
P-n-P bipolar junction transistor arrow points toward base
n-P-n BJT arrow points away from base
