Transcript Bill_O_electronics_lecture7

An Introduction to Electronics
by
William O’Shaughnessy
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An Introduction to Electronics
Electronics is the study of the flow of
electrons in an electronic circuit made of
electronic components connected in a
closed path.
An electronic component is something that
affects the flow electrons, by resisting their
flow, creating potentials, or storing them.
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An Introduction to Electronics
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The flow of electrons is called a current
Its mathematical symbol is “I”.
The unit of current flow is the Ampere,
very commonly abbreviated as Amp.
An Amp is the flow of 6.24 * 10^18
electrons past a point in one second.
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An Introduction to Electronics
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Two Things are needed to create a
current flow a source of electrical
potential and a path for the electrons
to flow through
Consider filling this room with water
with the doors sealed. (The water is
the electrons) It can not leave the
room without a hole in the floor.
That hole is the path for the water to
flow.
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An Introduction to Electronics
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Consider filling this room with water
with the doors sealed. (The water is
the electrons) It can not leave the
room without a hole in the floor.
That hole is the path for the water to
flow.
How fast the water hits the next
floors is determined by the height
between floors. This is called
potential or voltage in electricity.
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An Introduction to Electronics
Two Kinds of Current
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Direct Current: Flows only one way
Alternating Current: First flows one way and
then the opposite direction
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How often current changes its direction in
one second is called its frequency.
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The unit of frequency is the Hertz
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Abbreviated Hz = cycles per sec
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Wall Current 60 Hz at 120 volts
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An Introduction to Electronics
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So we have the two most important
characteristics of electronics and the
movement of electrons:
1.) Current: how many are flowing
2.) Voltage: how fast they are
moving or how fast they could move.
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Electronic Components
The Battery
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A battery produces electronic potential
by chemical reactions for example:
 Lead Acid
or Lithium Ion
A battery's greatest potential is called
its voltage
It produces Direct Current
How many electrons it can put out is
called its Amp*hour rating
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Electronic Components
The Resistor
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The resistor is a conductor of electrons
A wire is a resistor with a very low
resistance
The unit of resistance is Ohms,
Its units symbol is 
Its math symbol is R
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Electronic Components
The Resistor
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A conductor can be thought of as a
pipe
The resistance of a wire could be
about .1 ohms; this could be
thought of as a 10 inch diameter
pipe
A resistor of 100 ohms would be like
a pipe of .01 inches diameter
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Electronic Components
The Resistor
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The voltage across a resistor is
proportional the amount of current
that is passing through it.
V = IR This is Ohm's Law. It is
the most important Law of
Electronics
Resistors do not generate potential
Resistors give off heat when they
pass current Pwr = V*I = I^2 R
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Electronic Components
The Capacitor
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A Capacitor is a circuit element that
stores charge, that is electrons.
A capacitor can generate potential.
That potential is proportional to the
charge in the capacitor.
Will accept charge until its potential
equals the potential of the source
A capacitor will not pass DC current
It will pass Alternating Current
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Electronic Components
The Capacitor
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A Capacitor can pass AC current
Small capacitors act as resistors
with high values to AC current.
Its resistance to AC is 1/(2 F C)
Where F is the Frequency of the AC
The unit of capacitance is the Farad
A capacitor of 1 Farad is almost a
battery.
Micro nano pico
More common 1uf, 1nf, 1pf
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Electronic Components
The Inductor
Is coil of wire around an iron core or air
 The inductance, symbol L, is
proportional to the square of the number
of turns of wire
 Its resistance to AC is
2 F L
 Where F is the Frequency of the AC
 The unit of inductance is the Henry
 Common sizes are milli Henries(mH),
microHenries(uH), and nanoHenries(nH)
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Electronic Components
L C Summary
Capacitors in parallel with a voltage source
oppose any change in its potential.
In series capacitors pass AC but not DC.
Inductors in series with a current source oppose
any change in its current.
They pass DC and AC but they delay and
oppose any change in current.
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Electronic Components
The Transformer
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Is two inductors wound around the same core
Is used to multiply an AC voltage by the ratio of the
turns in the two inductors.
If 120 VAC is applied to 4 turns, 60 VAC comes out of
the two turns
If 120 VAC is applied to 2 turns, 240 VAC comes out of
the 4 turns
The coil that gets the voltage is called the “primary”
The other coil is called the “secondary”
Is the primary component in a Wall Wart
(formal name Power Adapter)
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And the biggest thing on an electrical pole.
Electronic Components
The Diode
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Is a semiconductor circuit element that will
pass current only in one direction.
Electrical current flows in the direction of the
arrow, electrons flow in the direction opposite
the arrow.
Is the second major component of a Wall
Wart; the third is a capacitor.
The wire with the bar is the Cathode
The wire with the arrow is the Anode
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Electronic Components
The Diode
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Is a semiconductor circuit element that will
pass current only in one direction.
Electrical current flow in the direction of the
arrow, electrons flow in the direction opposite
the arrow.
Is the second major component of a Wall
Wart; the third is a capacitor.
The wire with the bar is the Cathode
The wire with the arrow is the Anode
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Electronic Components
Bipolar Transistor
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Is a semiconductor circuit element
that amplifies the base to emitter current.
The bar is the base, the arrow is the emitter,
the line is collector
The amplified current flows from the collector to the
emitter in an NPN and from the emitter to the
collector in a PNP transistor.
The amplification factor is called the Beta or h
npn
pnp
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Electronic Components
Field Effect Transistor
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Is a semiconductor circuit element
that switches a current with a voltage
The current goes from a Drain to a Source
(electrons from the Source to the Drain)
Take very, very little current to turn on
They are said to have a high impedance input
n-channel
p-channel
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Rules of Using a
Multimeter
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Never measure current without
the instructors permission (A or ma)
Never measure resistance in a powered on
circuit
Don't touch the metal part of the probe when
measuring in a circuit.
Always measure voltages starting with the
highest scale and work down to smaller
scales
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Soldering
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Always assume all metal parts of
a soldering iron are hot.
First rule of soldering: get the connection hot
before applying solder. (Now obsolete)
New rule: nothing conducts heat like
liquid metal. Have a little liquid solder on the
tip of you soldering iron and use it and
contact pressure to transfer heat from your
iron to the connection before applying solder.
Besure you see solder flow onto the
components. Keep the iron over the bench.
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