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

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

3. Out In
Amplifier
Out
Gain = In

4. 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

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

6. The B-E junction is forward biased.
NPN Transistor Bias N C P B
The B-E junction
is forward biased. N E
Current flows.

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

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

15. PNP Schematic Symbol
Collector E B C
Base
Emitter

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

17. 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

18. 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

19. 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

20. 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:

21. 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.

22. 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.

23. 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

24. 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.

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

26. 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.

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

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

29. 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.

30. 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

31. 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

32. 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.

33. 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

34. 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

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

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

37. Powerex IGBT Module Structure
Powerex high voltage IGBT package

38. 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

39. 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

40. 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
(or no base current)
low resistance from collector to emitter
(or very high resistance)
low collector dissipation
PC = VCE x IC
PC = 0 x IC = 0 W
(or PC = VCE x 0 = 0 W)

41. 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

42. 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

43. PNP SWITCH WITH NPN DRIVER
LOAD
LOAD
LOAD

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

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

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