What is the meaning of the term “alpha” with regard to bipolar transistors? The change of:

Collector current with respect to emitter current.

Two signal diodes joined back-to-back, creating a PN-junction, will have three layers, two junctions, and three terminals, called Bipolar Junction Transistor (BJT).

The value of alpha (α) is determined by the ratio of collector current, or lc to the base current, or lb. Basically, it is the big change in lc as compared with the small change in lb.

The emitter current for a common emitter is defined as le = lc + lb.

For more information, please see Electronics Tutorials site for the article on Bipolar Transistor

And, see Wikipedia's article on Bipolar junction transistor

Last edited by markadlerdallas. Register to edit

Tags: none

What are the three terminals of a bipolar transistor?

Base, collector and emitter.

From kd9fni:

A Bipolar Junction Transistor (BJT) has the base, collector, and emitter terminals. It is controlled by the input current on the base or emitter.

Compare that to a FET, which has the source, gate, and drain and which is controlled by Vgs.

Last edited by markadlerdallas. Register to edit

Tags: none

What is the meaning of the term “beta” with regard to bipolar transistors? The change of:

Collector current with respect to base current.

From wileyj2956:

The Beta of a transistor is a published ratio of the change in collector current that results from a change in base current.

A typical value for a small transistor is 100-150, while "high gain" transistors may have higher beta values.

Power transistors, on the other hand, tend to have a lower value of beta. Beta is also called the "common emitter current gain."

Generally, it is a bad practice to design a transistor circuit that is dependent on beta for biasing or proper function.

For a bipolar junction transistor, beta changes as a function of temperature. Unfortunately, it increases which can lead to a condition known as "thermal runaway".

A mathematical identity is detailed in the Wikipedia's article Bipolar junction transistor

\[\beta=\frac{I_C}{I_B}=\frac{\text{collector current}}{\text{base current}}\]

This is roughly representative of the correct answer in which the beta, or \(\beta\), is the change in collector current with respect to the base current.

See also Electronics Tutorials site for the article Bipolar Transistor

And, Tutorials Point site for the article Bipolar Junction Transistor (BJT) - Theory

Last edited by markadlerdallas. Register to edit

Tags: none

What are the elements of a unijunction transistor?

Base 1, base 2, and emitter.

From Electronics Tutorials article Unijunction Transistor

"Like N-channel FET’s, the UJT consists of a single solid piece of N-type semiconductor material forming the main current carrying channel with its two outer connections marked as Base 2 ( B2 ) and Base 1 ( B1 ).

The third connection, confusingly marked as the Emitter ( E ) is located along the channel. The emitter terminal is represented by an arrow pointing from the P-type emitter to the N-type base."

For more information, please see Wikipedia's article on Unijunction transistor

Last edited by markadlerdallas. Register to edit

Tags: none

The beta cutoff frequency of a bipolar transistor is the frequency at which:

Emitter current gain has decreased to 0.707 of maximum.

From Chegg site, article Alpha Cutoff Frequency

"Alpha cutoff frequency (fα) is a particular frequency, that occurs when the common base DC current gain (α) drops to 0.707 of its low frequency value.

The common base DC current gain is a ratio of the value of transistor's collector current to the value of transistor's emitter current."

Also,

"Similarly, beta cutoff frequency (fβ) is a particular frequency that occurs when the common emitter current gain (β) value drops to 0.707 of its low frequency value.

The common emitter current gain is the ratio of the value of transistor's collector current to the value of transistor base current in a transistor."

Last edited by markadlerdallas. Register to edit

Tags: none

What does it mean for a transistor to be fully saturated?

The collector current is at its maximum value.

At saturation, the maximum collector current is flowing. When a transistor is saturated, it appears that there is a short circuit between the emitter and the collector. At this point, both diodes are in the forward biased mode.

This happens because electrons flow to the base instead of the collector. The base current then is larger than the collector.

For more information, please see Learn Sparkfun site for the article Transistors Operation Modes

Also, All About Circuits site for the article Transistor Ratings and Packages (BJT).

Last edited by markadlerdallas. Register to edit

Tags: none