Download Bipolar Junction Transistors

Bipolar Junction Transistors
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Transistor types
NPN Transistor – A thin, highly doped
p-type region (base) is sandwiched between
two n-type regions (emitter and collector).
PNP Transistor – A thin, highly doped
n-type region (base) is sandwiched between
two p-type regions (emitter and collector).
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Base, emitter, collector
Base – The region that lies between an emitter
and a collector of a transistor and into which
minority carriers are injected.
Emitter – A transistor region from which
charge carriers are injected into the base.
Collector – A semiconductor region through
which a flow of charge carriers leaves the base
of the transistor.
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Bipolar junction transistor (BJT)
types.
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Transistor construction and
packaging
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Transistor operation
Transistors are basically controlled to operate
as a switch, or are controlled to operate as a
variable resistor.
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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 applications
Digital Logic Gate Circuit
Analog Amplifier Circuit
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Transistor as a digital logic gate
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Transistor as an analog
amplifier
Amplification – Boosting in strength, or increasing
amplitude, of an electronic signal.
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Input-output voltage waveforms
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Voltage Gain (AV) – The ratio of the output signal
voltage change to the input signal voltage change.
Output Signal Voltage Change – Change in the output
signal voltage in response to a change in the input
signal voltage.
Input Signal Voltage Change – The input voltage
change that causes a corresponding change in the
output voltage.
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Correctly biased NPN transistor
circuit
For normal operation, the NPN transistor’s
emitter diode junction is forward biased while
the collector diode or junction is reverse
biased.
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Basic switching regulator action
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Emitter Current (IE) – The current at the transistor’s
emitter terminal.
Base Current (IB) – The relatively small current at
the transistor’s base terminal.
Collector Current (IC) – The current emerging out
of the transistor’s collector.
IE = IB + IC
IC ≅ I E
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Current-controlled transistor
As IB
IC and IE
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Operating a transistor in the
active region
Active Operation – When the base-emitter is
forward biased and the base-collector junction
is reverse biased. In this mode, the transistor
is equivalent to a variable resistor between the
collector and the emitter.
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Operation in cutoff and
saturation
Cutoff – A transistor is in cutoff when the
bias voltage is reduced to a point that it stops
current in the transistor.
Saturation – A transistor is in saturation when
the bias voltage is increased to such a point
that further increase will not cause any
increase in the current through the transistor.
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Biasing PNP bipolar transistors
Use negative base voltage.
Use negative collector voltage.
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Bipolar transistor configurations
Configurations – Different circuit interconnections.
Common – Shared by two or more services, circuits,
or devices. Although the term “common ground” is
frequently used to describe two or more connections
sharing a common ground, the term common alone
does not indicate a ground connection, only a share
connection.
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A correctly biased PNP
transistor circuit
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Common-emitter circuits
Common-Emitter (C-E) Circuits – A configuration in which
the input signal is applied between the base and the emitter
while the output signal appears between the transistor’s
collector and emitter.
Current Gain – The increase in current produced by the
transistor circuit.
Beta (β) – The transistor’s current gain in a common-emitter
configuration.
DC Beta (βDC) – The ratio of a transistor’s dc output current to
its input current.
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Common-emitter circuits (cont.)
AC Beta (βAC) – The ratio of a transistor’s ac output current
to its input current
Voltage Gain:
∆Vout
AV =
∆Vin
Power Gain:
Pout
AP =
Pin
AP = AV × β AC
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Common-emitter circuits (cont.)
Active Region – Flat part of the collector’s
characteristic curve. A transistor is normally operated
in this region, where it is equivalent to a variable
resistor between the collector and emitter.
Quiescent Operating Point (Q-point) – The voltage or
current values that set up the no input signal or
operating point bias voltage.
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Common-emitter circuits (cont.)
Breakdown Region – The point at which the
collector supply voltage will cause a damaging
value of current through the transistor.
Saturation region – The point at which the collector
supply voltage has the transistor operating in
saturation.
Cutoff region – The point at which the collector
supply voltage has the transistor operating in cutoff.
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Common-emitter circuits (cont.)
Input Resistance (Rin) – The amount of opposition offered to
an input signal by the input base-emitter junction (emitter
diode).
Input Impedance (Zin) – The total opposition offered by the
transistor to an input signal.
Output Resistance (Rout) – The amount of opposition offered to
an output signal by the output base-collector junction
(collector diode).
Output Impedance(Zout) – The total opposition offered by the
transistor to the output signal.
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Common-Base (C-B)
configuration
Common-Base Configuration – A configuration in which the
input signal is applied between the transistor’s emitter and
base, while the output is developed across the transistor’s
collector and base.
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Common-Base configuration
(continued)
DC Alpha (αDC) – The ratio for calculation a C-B transistor’s
dc current gain.
I
α DC =
C
IE
AC Alpha (αAC) – The ratio of the input emitter current
change to the output collector current change in a C-B
transistor
∆I
α AC =
C
∆I E
Power gain in a C-B transistor configuration
AP = AV × αAC
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Common-Collector (C-C)
configuration
A configuration in which the input signal is applied between the
transistor’s base and collector, while the output is developed
across the transistor’s collector and emitter.
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C-C (continued)
DC current gain = IE/IB
DC current gain = 1 + βDC
Since βDC = IC/IB
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C-C (continued)
C-C dc current gain
≅
C-E dc current gain (βDC)
AC current gain = ∆I E
∆I B
C-C ac current gain
≅
C-E ac current gain (βAC)
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Degenerative effect
An effect that causes a reduction in the amplification due to
negative feedback.
Emitter-Follower or Voltage-Follower – The C-C circuit in
which the emitter output voltage seems to track or follow the
phase and amplitude of the input voltage.
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C-C as an impedance matching
circuit
Impedance Matching Circuit – A circuit that can
match, or isolate, a high resistance (low current)
source.
Buffer Current Amplifier – The C-C circuit that can
ensure that power is efficiently transferred from the
source to the load.
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Bipolar data sheet
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Testing bipolar junction
transistors
Transistor Tester – A special test instrument
that can be used to test both NPN and PNP
bipolar transistors.
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Using an Ohmmeter to test a
BJT
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Bipolar transistor biasing circuits
Base biasing
Voltage divider biasing
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Base biasing
Base Biasing – A transistor biasing method in which the dc
supply voltage is applied to the base of the transistor via a base
bias resistor
VBE = 0.7V
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DC load line
DC Load Line – A line representing
all the DC operating points of a
transistor for a given load resistance.
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Typical dc load line with
Q point
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Voltage divider biasing
A biasing method used with amplifiers
in which a series arrangement of two
fixed-value resistors is connected
across the voltage source. The result is
that a desired fraction of the total
voltage is obtained at the center of the
two resistors and is used to bias the
amplifier.
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End of Bipolar Junction Transistors
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