1. Principles & Applications
Electronics
Principles & Applications
Sixth Edition
Charles A. Schuler
Chapter 5
Transistors
(student version)
© Glencoe/McGraw-Hill

2. INTRODUCTION Amplification Transistors Characteristic Curves
Transistor Testing
Other Transistor Types
Transistors as Switches

3. 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 you
to view that segment again, if you want to.

4. 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.

5. Out In
Amplifier
Out
Gain = In

6. NPN Transistor Structure
The collector is lightly doped. C N
The base is thin and
is lightly doped. B P
The emitter is heavily doped. E N

7. NPN Transistor Bias No current flows. C The C-B junction
is reverse biased. P B N E

8. NPN Transistor Bias C B The B-E junction is forward biased. E
Current flows.

9. NPN Transistor Bias IC Current flows everywhere. C B
Note that IB is smaller
than IE or IC. IC IB IE N C
Most of the emitter carriers
diffuse through the thin base
region since they are attracted
by the collector. P B
When both junctions
are biased.... N E

10. Gain is something small controlling something large
Note: when the
switch opens, all
currents go to zero. IC N C
Although IB is smaller
it controls IE and IC. P B IB N E
Gain is something small
controlling something large
(IB is small). IE

11. 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

12. 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

13. Concept Preview The base to collector gain is called b (beta).
To find b, 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.

14. IC = 99 mA The current gain from base to collector C is called b.
IB = 1 mA P B
99 mA IC N E
b =
= 99 IB
1 mA
IE = 100 mA

15. IC = 99 mA Kirchhoff’s current law: C IB = 1 mA B IE = IB + ICP B
IE = IB + IC
= 1 mA +
99 mA N E
= 100 mA
IE = 100 mA

16. IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector. C
IB = 1 mA B
Notice the PNP
bias voltages. E
IE = 100 mA

17. 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

18. Concept Review The base to collector gain is called b (beta).
To find b, 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

19. 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 (bdc) and ac beta (bac) 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.

20. NPN Schematic Symbol Collector Base Emitter Memory aid: NPN
means Not Pointing iN.

21. PNP Schematic Symbol
Collector E B C
Base
Emitter

22. IC
This circuit is used to
collect IC versus
VCE data for
several values of IB. C IB
VCE B E

23. When graphed, the data provide an NPN collector family of curves.
100 mA 14 12
80 mA 10
60 mA
IC in mA 8
40 mA 6 4
20 mA 2
0 mA 2 4 6 8 10 12 14 16 18
VCE in Volts

24. IC b = IB 100 mA 14 12 80 mA 10 60 mA IC in mA 8 40 mA 6 4 20 mA 22 4 6 8 10 12 14 16 18
VCE in Volts
14 mA IC
6 mA
This type of gain
is called bdc or hFE.
b =
= 140
= 150
40 mA IB
100 mA

25. bac = 100 mA 14 12 80 mA 10 60 mA IC in mA 8 40 mA 6 4 20 mA 2 0 mA 22 4 6 8 10 12 14 16 18
VCE in Volts
2.5 mA
DIC
Another type of gain
is called bac or hfe.
bac =
= 125
20 mA
DIB

26. 100 mA 14 12
80 mA 10
60 mA
IC in mA 8
40 mA 6 4
20 mA 2
0 mA 2 4 6 8 10 12 14 16 18
VCE in Volts
The C-E model is a resistor. C E IB
With these values of IB:

27. 100 mA
VCE @ 0 14 12
80 mA 10
60 mA
IC in mA 8
40 mA 6 4
20 mA 2
0 mA 2 4 6 8 10 12 14 16 18
VCE in Volts IB
When IB >> 100 mA
The model is a closed switch.

28. 100 mA 14 12
80 mA 10
60 mA
IC in mA 8
40 mA 6 4
20 mA 2
0 mA
IC = 0 2 4 6 8 10 12 14 16 18
VCE in Volts IB
When IB = 0
The model is an open switch.

29. Transistor Operating Conditions Quiz
When IB is large and VCE  0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.
open
When IB > 0 and VCE > 0, the transistor
acts as a ___________.
resistor
Two current gain measures are dc and
__________.
ac
The symbol hfe is the same as _________.
ac

30. 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 (bdc) and ac beta (bac) 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

31. 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.

32. The E-B junction is forward biased by the ohmmeter.
NPN V E mA B C
The E-B junction is forward biased by the ohmmeter.

33. The C-E resistance is very high.
NPN V E mA B C
The C-E resistance is very high.

34. The meter reading is < 100 kW due to gain.
NPN V E mA B C
100 kW
The meter reading is < 100 kW due to gain.

35. 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

36. 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.

37. Current Amplifier Current Out Current In The BJT is a current

38. Voltage Amplifier Current Out Voltage In The JFET is a voltage
controlled
amplifier.

39. The channel has carriers so it conducts from source to drain.
Gate
Source
Drain P
N-channel
P-type substrate
Structure of an
N-channel JFET
Drain
Source
Gate
The channel has carriers so it
conducts from source to drain.

40. A negative gate voltage can push the carriers from
Source
Drain P
N-channel
P-type substrate
A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.
Drain
Source
Gate

41. 0 V
-1 V
-2 V
ID in mA
VGS
-3 V
-4 V
-5 V
VDS in Volts
This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

42. It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator
Drain n G S D
VDD
VGG
Gate p n
N-channel
MOSFET
Source
Gate bias enhances the channel and turns the device on.

43. Enhancement mode MOSFET drain family of characteristic curves
ID in mA
VGS
2 V
1 V
0 V
VDS in Volts
Drain
Enhancement mode MOSFET drain family of characteristic curves
Gate
Source

44. The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance
RCE = 8.33 mW
Faster turn off than
BJTs but not as fast
as MOSFETS

45. Three major device technologies
Extra
junction
hole injection
Courtesy of Powerex, Inc.

46. Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off
IGBT
Control signal

47. Powerex IGBT Module Structure
Powerex high voltage IGBT package

48. The unijunction transistor fires when its emitter voltage reaches VP.
Then, the emitter voltage
drops due to its negative
resistance characteristic.
Emitter voltage
Base 2
Emitter current
Emitter
The UJT is not useful as an amplifier.
It is used in timing and control applications.
Base 1

49. Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.
current
FETs are __________-controlled
amplifiers.
voltage
JFETs operate in the __________ mode.
depletion
MOSFETs operate in the __________
mode.
enhancement
IGBTs are __________-controlled
amplifiers.
voltage
UJTs are not useful as __________.
amplifiers

50. 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

51. 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.

52. 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)

53. NPN SWITCH LOAD LOAD LOAD RCE @  W RCE @ 0 W RCE @  W
DRIVER
The driver output is zero volts, IB = 0 and the load is off
The driver output is positive, IB > 0 and the load is on
The driver output is zero volts, IB = 0 and ILOAD = 0

54. PNP SWITCH LOAD LOAD LOAD The driver output goes low: the voltage drop
across the resistor makes VBE negative
The driver output is off (high Z): the resistor
pulls the base voltage up so that VBE = 0
The driver output is off (high Z): the resistor
pulls the base voltage up so that VBE = 0

55. PNP SWITCH WITH NPN DRIVER
LOAD
LOAD
LOAD

56. NPN SWITCH WITH PNP DRIVER (NEGATIVE POWER SUPPLY)
VBE  0 V
VBE  -0.7 V
VBE  +0.7 V
LOAD
LOAD
LOAD

57. Enhancement mode power MOSFETs used as switches STEPPER MOTOR A B C D

58. 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

59. REVIEW Amplification Transistors Characteristic Curves
Transistor Testing
Other Transistor Types
Transistors as Switches