electronics principles & applications sixth edition chapter 5 transistors (student version)...
TRANSCRIPT
ElectronicsElectronics
Principles & ApplicationsPrinciples & ApplicationsSixth EditionSixth Edition
Chapter 5Transistors
(student version)
©2003 Glencoe/McGraw-Hill
Charles A. Schuler
• Amplification• Transistors• Characteristic Curves• Transistor Testing• Other Transistor Types• Transistors as Switches
INTRODUCTION
Dear Student:
This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow youto view that segment again, if you want to.
Concept Preview• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the larger currents.
Amplifier Out
InGain =
In
Out
N
P
N
NPN Transistor Structure
The collector is lightly doped. C
The base is thin and is lightly doped.
B
The emitter is heavily doped. E
The C-B junction is reverse biased.
N
P
N
NPN Transistor Bias
C
B
E
No current flows.
The B-E junction is forward biased.
N
P
N
NPN Transistor Bias
C
B
E
Current flows.
When both junctionsare biased....
N
P
N C
B
E
Current flowseverywhere.
Most of the emitter carriersdiffuse through the thin base
region since they are attractedby the collector.
Note that IB is smallerthan IE or IC.
IC
IB
IE
NPN Transistor Bias
N
P
N C
B
E
Although IB is smallerit controls IE and IC.
IC
IB
IE
Note: when the switch opens, all
currents go to zero.
Gain is something smallcontrolling something large
(IB is small).
Transistor Structure and Bias Quiz
The heaviest doping is found in the ___________ region. emitter
The thinnest of all three regions is called the ____________. base
The collector-base junction is ___________ biased. reverse
The base-emitter junction is ____________ biased. forward
The majority of the emitter carriers flow to the ___________. collector
Concept Review• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.
• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the larger currents.
Repeat Segment
Concept Preview• The base to collector gain is called (beta).
• To find divide the collector current by the base current.
• The emitter current is the largest since it is the sum of the base and collector currents.
• PNP transistors have opposite polarity from NPN transistors.
• In an NPN transistor, the major flow is made up of electrons.
• In a PNP transistor, the major flow is made up of holes.
N
P
C
B
E
IC = 99 mA
IB = 1 mA
IE = 100 mA
= IC
IB
The current gain frombase to collector
is called
99 mA
1 mA= 99
N
P
C
B
E
IC = 99 mA
IB = 1 mA
IE = 100 mA
IE = IB + IC
99 mA= 1 mA +
= 100 mA
Kirchhoff’scurrent law:
C
B
E
IC = 99 mA
IB = 1 mA
IE = 100 mA
In a PNP transistor,holes flow from
emitter to collector.
Notice the PNPbias voltages.
Transistor Currents Quiz
is the ratio of collector current to ______ current. base
The sum of the base and collector currents is the __________ current. emitter
In NPN transistors, the flow from emitter to collector is composed of _______. electrons
In PNP transistors, the flow from emitter to collector is composed of _______. holes
Both NPN and PNP transistors show__________ gain. current
Concept Review• The base to collector gain is called (beta).
• To find divide the collector current by the base current.
• The emitter current is the largest since it is the sum of the base and collector currents.
• PNP transistors have opposite polarity from NPN transistors.
• In an NPN transistor, the major flow is made up of electrons.
• In a PNP transistor, the major flow is made up of holes.
Repeat Segment
Concept Preview• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector voltage versus collector current.
• Both dc beta (dc) and ac beta (ac) can be determined from the collector curves.
• The collector circuit of a transistor can be modeled as a resistor, as a closed switch or as an open switch.
• The amount of base current determines which of the three models applies.
Emitter
NPN Schematic Symbol
Base
Collector
Memory aid: NPNmeans Not Pointing iN.
EBC
Collector
Base
Emitter
PNP Schematic Symbol
EBC
IB
IC
VCE
B
C
E
This circuit is used tocollect IC versus
VCE data forseveral values of IB.
0 2 4 6 8 10 12 14 16 18
2468
101214
VCE in Volts
IC in mA
When graphed, the data provide anNPN collector family of curves.
20 A
0 A
100 A
80 A
60 A
40 A
0 2 4 6 8 10 12 14 16 18
2468
101214
VCE in Volts
IC in mA
20 A
0 A
100 A
80 A
60 A
40 A
= IC
IB
= 15040 A
6 mA
100 A
14 mA= 140 This type of gain
is called dc or hFE.
0 2 4 6 8 10 12 14 16 18
2468
101214
VCE in Volts
IC in mA
20 A
0 A
100 A
80 A
60 A
40 A
ac = Another type of gainis called ac or hfe.
IC
IB
= 12520 A
2.5 mA
0 2 4 6 8 10 12 14 16 18
2468
101214
VCE in Volts
IC in mA
20 A
0 A
100 A
80 A
60 A
40 A
IBWith these values of IB:
The C-E model is a resistor.
C
E
0 2 4 6 8 10 12 14 16 18
2468
101214
VCE in Volts
IC in mA
20 A
0 A
100 A
80 A
60 A
40 A
IB When IB >> 100 A
VCE 0
The model is a closed switch.
0 2 4 6 8 10 12 14 16 18
2468
101214
VCE in Volts
IC in mA
20 A
0 A
100 A
80 A
60 A
40 A
IB When IB = 0
IC = 0
The model is an open switch.
Transistor Operating Conditions Quiz
When IB is large and VCE 0, the transistoracts as a ___________ switch. closed
When IB = 0 and IC = 0, the transistoracts as an ___________ switch. open
When IB > 0 and VCE > 0, the transistoracts as a ___________. resistor
Two current gain measures are dc and__________. ac
The symbol hfe is the same as _________. ac
Concept Review• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (dc) and ac beta (ac) can be determined from the collector curves.
• The collector circuit of a transistor can be modeled as a resistor, as a closed switch or as an open switch.
• The amount of base current determines which of the three models applies.
Repeat Segment
Concept Preview
• It is possible to test transistors out-of-circuit using an ohmmeter.
• The E-B and C-B junctions act as diodes during ohmmeter testing.
• The C-E test shows a high resistance because two junctions are involved; one of which is reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in conjunction with the ohmmeter test.
0
The E-B junction is forward biased by the ohmmeter.
V
mA
NPN
E
BC
0
The C-E resistance is very high.
V
mA
NPN
E
BC
0
The meter reading is < 100 kdue to gain.
V
mA
NPN
E
BC
100 k
Concept Review
• It is possible to test transistors out-of-circuit using an ohmmeter.
• The E-B and C-B junctions act as diodes during ohmmeter testing.
• The C-E test shows a high resistance because two junctions are involved; one of which is reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in conjunction with the ohmmeter test.
Repeat Segment
Concept Preview• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled by gate voltage.
• JFETs operate in the depletion mode (as normally on devices).
• Metal oxide semiconductor field effect transistors (MOSFETs) usually operate in the enhancement mode (as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as amplifiers.
Current OutCurrent In CurrentAmplifier
The BJT isa currentamplifier.
Current OutVoltage In VoltageAmplifier
The JFET isa voltage
controlledamplifier.
DrainSource
Drain
Source
Gate
Gate
Structure of anN-channel JFET
P-type substrate
P
N-channel
The channel has carriers so it conducts from source to drain.
DrainSource
Drain
Source
Gate
Gate
P
N-channel
P-type substrate
A negative gate voltagecan push the carriers from
the channel and turn the JFET off.
0VDS in Volts
ID in mA
-4 V
-5 V
0 V
-1 V
-2 V
-3 VVGS
N-channel JFET drain family of characteristic curves
This is known as a depletion-mode device.
n
Source
Gate
Drain
VDD
p
n
It’s possible to make enhancementtype field effect transistors as well.
G
S
D
VGG
Gate bias enhances the channel and turns the device on.
Metaloxide
insulator
N-channelMOSFET
0VDS in Volts
ID in mA
1 V
0 V
5 V
4 V
3 V
2 VVGS
Enhancement mode MOSFET drain family of characteristic curves
Drain
Source
Gate
The IGBT (insulated gate bipolar transistor)
Operation and structuresimilar to a MOSFET
Voltage controlled(like the MOSFET)
Has one more junctionthan a MOSFET
Hole injection reducesthe collector resistance
Faster turn off thanBJTs but not as fast
as MOSFETS
RCE = 8.33 m
Courtesy of Powerex, Inc.
Three major device technologies
hole injection
Extrajunction
Typical IGBT Driver Circuit
IGBT
Typically +15 V for turn on
Typically - 5 to -15 V for turn off
Control signal
Powerex IGBT Module Structure
Powerex high voltage IGBT package
Base 2
Base 1
Emitter
The unijunction transistor fires when its emitter voltage reaches VP.
VP
Emitter current
Em
itte
r vo
ltag
e
Then, the emitter voltagedrops due to its negativeresistance characteristic.
The UJT is not useful as an amplifier.It is used in timing and control applications.
Other Transistor Types QuizBJTs are _________-controlledamplifiers.
current
FETs are __________-controlledamplifiers.
voltage
JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________mode.
enhancement
UJTs are not useful as __________. amplifiers
IGBTs are __________-controlledamplifiers.
voltage
Concept Review• Bipolar junction transistors (BJTs) are controlled by
base current.• Junction field effect transistors (JFETs) are controlled
by gate voltage.• JFETs operate in the depletion mode (as normally on
devices).• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode (as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as amplifiers.
Repeat Segment
Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal switch: off = no current flow and on = no voltage drop.
• MOSFETs can also be used as switches: no gate voltage = switch is off and high gate voltage = switch is on.
How do transistor switches work?How do transistor switches work?Can be viewed as solid state relays:they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on) (or no base current … off)
low resistance from collector to emitter (on)(or very high resistance … off)
low collector dissipation (on or off)PC = VCE x IC
PC = 0 x IC = 0 W (on)(or PC = VCE x 0 = 0 W … off)
LOADLOADLOAD
DRIVER
The driver output is zero volts, IB = 0 and ILOAD = 0The driver output is positive, IB > 0 and the load is onThe driver output is zero volts, IB = 0 and the load is off
RCE RCE 0RCE
NPN SWITCH
LOAD
DRIVER
The driver output is off (high Z): the resistorpulls the base voltage up so that VBE = 0
PNP SWITCH
The driver output goes low: the voltage dropacross the resistor makes VBE negative
The driver output is off (high Z): the resistorpulls the base voltage up so that VBE = 0
LOADLOAD
PNP SWITCH WITH NPN DRIVER
LOADLOADLOAD
NPN SWITCH WITH PNP DRIVER(NEGATIVE POWER SUPPLY)
LOADLOADLOADVBE -0.7 V
VBE +0.7 V
VBE 0 V
VBE 0 V
A
B
C
D
A B C D
STEPPER MOTOR
Enhancement modepower MOSFETsused as switches
Concept Review• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal switch: off = no current flow and on = no voltage drop.
• MOSFETs can also be used as switches: no gate voltage = switch is off and high gate voltage = switch is on.
Repeat Segment
REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches