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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
Slide - 1
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
chapter 2 transistors (BJT)
2.1 Transistor classification
2.2 Bipolar junction transistors (BJT) construction
2.3 Transistor action and operating
2.4 Quiescent Operating Point
2.5 Bipolar transistor characteristics
2.6 Transistor parameters
2.7 Current gain
2.8 Typical BJT characteristics and maximum ratings
2.9 Transistor operating configurations
Slide - 2
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.1 Transistor classification

 NPN
biplor junction transistor 
PNP





(p-n-p) n-type J.f.e.t.
J.f.e.t.



(n-p-n) p-type J.f.e.t.





transistor 
field effect transistor 



n-type depletion-type m.o.s.f.e.t


depletion-type
m.o.s.f.e.t





p-type depletion-type m.o.s.f.e.t

m.o.s.f.e.t



enhancement-type m.o.s.f.e.t n-type enhancement-type m.o.s.f.e.t





p-type enhancement-type m.o.s.f.e.t




Slide - 3
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2 Bipolar junction transistors (BJT) construction
Bipolar transistors generally comprise n-p-n
or p-n-p junctions of either silicon (Si) or
germanium (Ge) material.
N: phosphorus or arsenic P: boron or gallium
The junctions are, in fact, produced in a
single slice of silicon by diffusing impurities
through a photographically reduced mask.
Silicon transistors are superior when
compared with germanium transistors in the
vast majority of applications
Slide - 4
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
◆The symbols and simplified junction models for n-p-n and p-n-p
transistors are shown in Figure 2.3. It is important to note that the
base region is extremely narrow.
Figure 2.3 The symbols and simplified junction models for n-p-n and p-n-p
transistors
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
E – Emitter
B – Base
C - Collector
Electronics-BTEC
Slide - 6
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.3 Transistor action
◆ In the n-p-n transistor, transistor action is accounted for as follows:
◆ the base-emitter junction is forward biased and the base-collector
junction is reverse biased
◆ Around 99.5% of the electrons leaving the emitter will cross the
Base collector junction and only 0.5% of the electrons will
Recombine with holes in the narrow base region.
Slide - 7
Figure 2.4 Transistor action of n-p-n transistor
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
Slide - 8
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
◆ the base-emitter junction is forward biased and the basecollector junction is reverse biased
Figure 2.5 Transistor action of p-n-p transistor
Slide - 9
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.2 leakage
current
◆ For an n-p-n transistor, the base-collector junction is reversed biased for majority
carriers, but a small leakage current, ICBO , flows from the collector to the base due to
thermally generated minority carriers (holes in the
collector and electrons in the base), being present. The base-collector junction is
forward biased to these minority carriers.
◆ With modern transistors, leakage current is usually very small (typically less than
100nA) and in most applications it can be ignored.
◆ The control of current from emitter to collector is largely independent of the
collector-base voltage and almost wholly governed by the emitter-base voltage.
Slide - 10
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.3 bias and current flow
◆ In normal operation (i.e. for operation as a linear amplifier)
the base-emitter junction of a transistor is forward biased and
the collector-base junction is reverse biased.
◆The current flowing in the emitter circuitis typically 100 times
greater than that flowing in the base.
Figure 2.7 bias and current flow
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.3
bias and current flow
Leakage current ICBO
Slide - 12
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.3
bias and current flow
Slide - 13
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.4 Transistor operating configurations
◆ Three basic circuit configurations are used for transistor amplifiers.
◆ These three circuit configurations depend upon which one of the three
transistor connections is made common to both the input and the output.
◆ In the case of bipolar junction transistors, the configurations are known as
common emitter, common collector (or emitter follower), and common
base.
Figure 2.8 Transistor operating configurations
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.5 bipolar transistor characteristics
◆ The characteristics of a bipolar junction transistor are usually
presented in the form of a set of graphs relating voltage and
current present at the transistors terminals.
Figure 2.9 measurement circuit of bipolar transistor characteristics
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
◆ In this mode, the input
current is applied to the base and
the output current appears in the
collector.
Figure 2.10 Typical input characteristic
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
◆ Each curve corresponds to a different
value of base current. Note the ‘knee’
in the characteristic below VCE =2V.
◆ Also note that the curves are quite flat.
◆ For this reason (i.e. since the collector
current does not change very much as
the collector-emitter voltagechanges)
we often refer to this as a constant
current characteristic.
Figure 2.11 Output characteristics
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
◆ Here IC is plotted against IB for a
small-signal general-purpose
transistor.
◆ The slope of this curve (i.e. the ratio
of IC to IB) is the common-emitter
current gain of the transistor.
Figure 2.12 Transfer characteristic
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
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2.2.6
Bipolar transistor parameters
◆ In particular, the three characteristic graphs can be used to determine the
following parameters for operation in common-emitter mode:
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
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2.2.6
Bipolar transistor parameters
◆ In particular, the three characteristic graphs can be used to determine the
following parameters for operation in common-emitter mode:
Slide - 20
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.6
Bipolar transistor parameters
◆ In particular, the three characteristic graphs can be used to determine the
following parameters for operation in common-emitter mode:
Slide - 21
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.6
Bipolar transistor parameters
Slide - 22
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
Slide - 23
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.7 Current
gain
◆ We use the symbol hFE to represent the static value of common-emitter
current gain.
◆ Similarly, we use hfe to represent the dynamic value of common-emitter
current gain.
◆ Note that hFE is found from corresponding static values while hfe is found
by measuring the slope of the graph.
◆ Furthermore, most transistor parameters (particularly common-emitter
current gain, hfe) are liable to wide variation from one device to the next.
Slide - 24
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.2.8 Typical BJT characteristics and maximum ratings
Table 2.2 Transistor characteristics and maximum ratings
PTOTmax is the maximum device power dissipation.
Slide - 25
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.4 The junction field-effect transistor
Figure 2.13 Conformation of N channel J.F.E.T
Slide - 26
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.4 The junction field-effect transistor
N channel JFET
P channel JFET
Figure 2.14 Symbol of JFET
Slide - 27
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.4 The junction field-effect transistor
Figure 2.15 Operation of N channel JFET
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
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2.5 Metal-oxide-semiconductor field-effect transistor
2.5.1 depletion-type MOS FET
N channel
P channel
Construction of N channel depletion-type MOS FET
Figure 2.16
depletion-type MOS FET
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Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.5 Metal-oxide-semiconductor field-effect transistor
2.5.2 Enhancement-type MOS FET
Construction of N channel enhancement-type MOS FET
Figure 2.16
N channel
P channel
depletion-type MOS FET
Slide - 30
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
2.4 Quiescent Operating Point
Slide - 31
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
Slide - 32
Electronics chapter 2 transistors
Guangdong Institute of Education ---BTEC
electronic
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