CHAPTER
6
Basic Electronics
Instructor Name: (Your Name)
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Learning Objectives
• List the various types of resistors
• Determine whether a diode is forward biased
or reverse biased in a circuit
• Test a diode with a DMM
• Explain the function of a zener diode
• Describe the operation of a bipolar transistor
• Explain the difference between a transistor
being used as an amplifier and a transistor
being used as a relay or a switch
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Learning Objectives (continued)
• Describe the operation of a field effect
transistor (FET)
• Discuss the concept of a high side driver
and a low side driver
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Resistors
•
•
•
•
Limit the current flow through a circuit
Divide voltage
Give off heat
Two main types of resistors; fixed and
variable
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Fixed Resistors and Color Code
Figure 6-1 Fixed-value resistors: physical
size of resistor increases as wattage rating
of resistor increases.
Figure 6-2 Resistor color code.
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Stepped Value Variable Resistor
Figure 6-3 Stepped-value
resistor network.
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Infinitely Variable Resistor
Figure 6-4 Infinitely
variable resistor.
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Potentiometer
Figure 6-7
Potentiometer.
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Semiconductors
• A material that is neither a good nor a poor
conductor
• Silicon is the most common used in
electronics
• Semiconductors usually have a negative
temperature coefficient (NTC)
• Pure silicon has four valence electrons
• Impurities added to silicone is a process
called doping
• Doping with a material that has excessive
electrons creates an N-type junction
• Doping with a material that has excessive
holes creates a P-type junction
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N-Type Semiconductor Doped With Arsenic
Figure 6-9 N-Type
semiconductor doped
with arsenic (As).
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P-Type Semiconductor Doped With Boron
Figure 6-10 P-Type
semiconductor doped
with boron (B).
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Diodes
• Two terminal semiconductor that acts as a
one way check valve to current flow
• The schematic symbol of a diode shows the
direction of current flow through the device
• If a diode is inserted in a circuit so that it
allows current flow it is forward biased
• If a diode is inserted in a circuit so that is
does not allow current flow it is reversed
biased
• The positive terminal of a diode is the anode
• The negative terminal of a diode the cathode
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Diode and Schematic Symbol
Figure 6-15 Stripe indicates cathode end of diode.
Figure 6-12 Diode voltage.
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Diodes (continued)
• Diodes will not permit current flow in the
forward bias direction until 0.7V is dropped
across the diode
• A diode will always drop approximately 0.7V
regardless of the current or voltage in the
circuit
• Diodes have a rated limit to reverse bias
voltage called the inverse voltage rating
• If the inverse voltage rating is exceeded the
diode will be destroyed
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Diode Testing With a DMM
Figure 6-19 Diode testing using DMM.
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Light-Emitting Diodes
Figure 6-21 Schematic symbol for LED.
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Zener Diode
• In the forward biased direction zener
diodes act like a regular diode and allow
current flow
• A zener diode has a rating referred to the
zener voltage
• Once the zener voltage is reached in the
reverse bias direction the zener will switch
on and conduct current in the reversed
bias direction
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Bipolar Transistors
• Bipolar transistors are made up of P-type and
N-type junctions
• There are two major types of bipolar transistors
PNP and NPN
• A PNP type is like a sandwich of N-type material
between two slices of P-type material
• An NPN type is like a sandwich of P-type
material between two slices of N-type material
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NPN Bipolar Transistor
Figure 6-26 NPN bipolar transistor.
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Bipolar Transistors (continued)
• The P-type layer of an NPN transistor is the
base
• One of the N-type layers is called the emitter
• The other N-type layer is called the collector
• The emitter, collector, and base are labeled
E, C, and B
• Transistors amplify low level signals to a
higher level signal
• Transistors act as switches similar to a relay
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Bipolar Transistors (continued)
• The collector of a bipolar transistor is
connected to the positive terminal of the
supply voltage
• The base of a bipolar transistor is connected
to the small signal that will be amplified
• The emitter of a bipolar transistor is
connected to the load device and the load is
connected to the negative terminal of the
supply voltage
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Transistor Amplifying the
Base Current
Figure 6-28 Transistor amplifying the base current.
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NPN Transistor Used As a Switch
Figure 6-29 NPN transistor used as a switch.
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Transistors Connected as a
Darlington Pair
Figure 6-30 Darlington pair permits a very small current to control a very large current.
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Field Effect Transistors (FET)
• FET’s are controlled by voltage not current
• The drain of an FET corresponds to the
collector of a bipolar transistor
• The gate of an FET corresponds to the
base of a bipolar transistor
• The source of an FET corresponds to the
emitter of a bipolar transistor
• The voltage difference between the gate
and the source voltage controls the
resistance between the drain and the
source
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N-Channel JFET Schematic Symbol
Figure 6-31 N-channel
JFET schematic symbol.
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P-Channel JFET
Figure 6-32
P-channel JFET is
similar to a
normally closed
relay.
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Metal Oxide Semiconductor FET
Figure 6-33 Enhancement-mode MOSFET symbols.
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Drivers
• Drivers are transistors used to switch highcurrent devices
• When the transistor is providing a path to
ground it is described as a low side driver
• When a device is providing a path to ground
it is said to be sinking
• When the transistor is providing a path for
positive voltage it is describes as a high side
device
• When a device is providing power it is said to
be sourcing
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Low Side Driver Sinks Current to Ground
Figure 6-34 Low side driver sinks current to ground.
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High Side Driver Sources
Current to the Load
Figure 6-35 High side driver sources current to the load.
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Tech Tip
A device controlled by a low side driver
located inside an electronic control module
will typically be connected to a positive
voltage at one terminal and the electronic
control module on the other. A device
controlled by a high side driver will
typically be connected to ground at one
terminal and the electronic control module
at the other terminal.
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Voltage Dropped Across
Transistor Collector to Emitter
Figure 6-36 Voltage dropped across transistor collector to emitter
indicates transistor is acting as an amplifier.
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Transistor Acting as a Switch
Figure 6-37 Transistor saturated; increasing base current will not result in any additional
collector-emitter current; transistor is acting as a switch in ON position.
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Summary
• Resistors are used for three main purposes;
limit current flow, divide voltage, and give off
heat. Resistors may be fixed or variable
value.
• A rheostat is a two terminal variable resistor.
A rheostat is often used to control the amount
of current flow in a circuit. A wiper moves
over a resistive track, causing a change in
the amount of resistance between two
terminals.
• A potentiometer is a three terminal variable
resistor. A potentiometer is typically used to
divide voltage.
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Summary (continued)
• A diode is a two terminal device that acts as a
one way check valve for current flow. When
current is flowing through the diode, the diode
is said to be forward biased. When the diode
is blocking the flow of current, the diode is
said to be reversed biased.
• Diodes and many other electronic devices
are made of silicon. Silicon mixed with
impurities can form N-type and P-type
semiconductor materials. Placing these two
types of silicon next to each other causes a
junction to form. This PN junction is the basis
of many electronic components.
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Summary (continued)
• The positive end of a diode is known as the
anode; the negative end of a diode is know
as the cathode. A stripe around the girth of a
diode signifies the cathode end of the diode.
• Diodes can be tested outside a circuit using a
DMM or an analog ohmmeter. The diode
should have a very high resistance when
reverse biased by the ohmmeter, and a very
low resistance when forward biased by the
ohmmeter.
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Summary (continued)
• A light emitting diode (LED) is a special diode
that gives off visible light when forward
biased. An LED always requires some sort of
means of limiting current flow through the
LED, unlike standard light bulbs.
• A zener diode is a special diode that acts like
a standard rectifier diode in the forward
biased direction. In the reverse biased
direction, the zener diode will permit current
flow after the zener voltage is reached.
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Summary (continued)
• A transistor is a device that amplifies a small
signal into a large signal. A transistor can be
used as an amplifier in devices such as
radios. A transistor can also be used as a
relay.
• Bipolar transistors are three terminal devices
and contain two PN-type material junctions.
The three terminal are identified as the base,
collector, and emitter. Bipolar transistors are
current controlled devices. Bipolar transistors
can be NPN or PNP type.
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Summary (continued)
• Field effect transistors (FET) are three
terminal devices. The three terminal are
identified as the source, gate, and drain.
FETs are voltage controlled devices.
• Transistors that are used as relays may be
called drivers. Drivers that provide a path
to ground for a device when switched on
are known as low side devices. A low side
driver is said to sink current. Drivers that
supply a positive voltage when switched
on are called high side drivers. A high side
driver is said to source current.
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