Bipolar Junction Transistors: Types, Construction, Operation, and Applications - Prof. Bre, Study notes of Electrical and Electronics Engineering

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Bipolar Junction Transistors

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Transistor types

NPN Transistor – A thin, highly dopedp-type region (base) is sandwiched betweentwo n-type regions (emitter and collector).PNP Transistor – A thin, highly dopedn-type region (base) is sandwiched betweentwo p-type regions (emitter and collector).

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Bipolar junction transistor (BJT)

types.

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Transistor construction and

packaging

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ON/OFF switching

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Transistor’s variable resistor

Transistance – The effect of transferring resistance

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Transistor as a digital logic gate

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Transistor as an analog

amplifier

Amplification – Boosting in strength, or increasingamplitude, of an electronic signal.

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Voltage Gain (A

V

) – The ratio of the output signal

voltage change to the input signal voltage change.Output Signal Voltage Change – Change in the outputsignal voltage in response to a change in the inputsignal voltage.Input Signal Voltage Change – The input voltagechange that causes a corresponding change in theoutput voltage.

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Correctly biased NPN transistor

circuit

For normal operation, the NPN transistor’semitter diode junction is forward biased whilethe collector diode or junction is reversebiased.

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Emitter Current (I

E

) – The current at the transistor’s

emitter terminal.Base Current (I

B

) – The relatively small current at

the transistor’s base terminal.Collector Current (I

C

) – The current emerging out

of the transistor’s collector.I

E

= I

B

+ I

C

E

C

I I ≅

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Current-controlled transistor

As I

B

I

C

and

I

E

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Operation in cutoff and

saturation

Cutoff – A transistor is in cutoff when thebias voltage is reduced to a point that it stopscurrent in the transistor.Saturation – A transistor is in saturation whenthe bias voltage is increased to such a pointthat further increase will not cause anyincrease in the current through the transistor.

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Biasing PNP bipolar transistors^ Use negative base voltage.Use negative collector voltage.