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Summary of basic electronic
parameters and components
Voltage: Voltage is the difference in charge between two
points, measured in Volts.
Current: Current is the flow of electrons through a
conductor or semiconductor,measured in Amperes or Amps.
Some materials conduct current better than others; these are
known as conductors, semiconductors, and insulators.
Current flow is from positive to negative.
Power: Power determines how much work a circuit can do.
It is measured in Watts (Watts = Volts * Amps).
Ground: Minimum voltage reference level. True ground
connects to the earth but the circuits we work with may not
actually be connected to the earth, especially if they are battery
powered. Technically this is known as a floating ground.
Resistance: Resistors are measured in Ohm and come
between conductors, which conduct easily and insulators
which don't conduct. The main function of resistors in a circuit
is to control the flow of current and voltage drops to other
components.
For example; if too much current flows through an LED it is
destroyed and will not light, so a resistor is used to limit the
current but not so big as it will limit all the current.
Resistor Colour Code
The resistor colour code is a way of showing the value of a resistor. Instead of
writing the resistance on its body, which would often be too small to read, a colour
code is used. Different colours represent the numbers 0 to 9.
The first two coloured bands on the body are the first two digits of the resistance,
and the third band is the 'multiplier'. Multiplier just means the number of zeroes to
add after the first two digits. Red represents the number 2, so a resistor with red,
red, red bands has a resistance of 2 followed by 2 followed by 2 zeroes, which is
2200 ohms or 2.2 kilo Ohms. The final band is the tolerance (the accuracy ± x %).
All resistors have a tolerance which is shown by the last band.
Color 1st Band 2nd Band 3rd Band 4th Band
Black 0 0 1
Brown 1 1 10
Red 2 2 100
Orange 3 3 1000
Yellow 4 4 10000
Green 5 5 100000
Blue 6 6 1000000
Purple 7 7
Grey 8 8
White 9 9
Red 1%
Gold 5%
Silver 10%
Potentiometer: It is a variable resistor, a
wiper moves between two leads and the
resistance between wiper and lead
determines resistance. Resistance between
leads is maximum resistance of
potentiometer.
Ohms Law: Every circuit has Voltage,
Current and Resistance.
V=IR. Voltage = Current * Resistance.
Circuits: A working circuit must have a closed
loop of current flow through a load. The sum of the
current entering a junction equals the sum of the
current exiting a junction.
Kirchoff's current law is : Iin= Iout.
A circuit with a break in it is called an open circuit.
A circuit without enough resistance in its load is
called a short circuit.
Series Circuits: All components are
connected end to end. Single path for
electrons to flow - all components share the
same current. Total resistance of circuit is
equal to sum of individual resistances. Total
voltage in the circuit is equal to the sum of
individual voltage drops.
Parallel Circuits: All components are connected
in parallel and share the same voltage. The total
resistance of circuit is less than the value after adding
individual resistances. Total current in circuit is equal
to sum of individual branch currents.
Voltage divider: With two resistors in series, the sum of the
voltage drop across each equals the total voltage drop across
both. To determine the voltage between the two resistors, we
use the voltage divider formula; V out = V in * (R2/R1+R2)
Alternating Current: AC Voltage alternates sinusoidal with
time. AC Voltages are specified with a value equal to the DC
voltage capable of doing the same amount of work.
Capacitor Types: Three major types of capacitors are ceramic,
electrolytic, and tantalum.
Semiconductors:
It is probably the most important discovery
in electronics which happened last century.
Without this discovery we wouldn't have
televisions,computers, space rocket, CD
players, etc. Unfortunately it's also one of
the hardest areas to understand in
electronics.
What Are Diodes Made Out Of? What Are Diodes Made Out Of?
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
- Silicon (Si) and Germanium (Ge) are the two most commonSilicon (Si) and Germanium (Ge) are the two most common
single elements that are used to make Diodes. A compound single elements that are used to make Diodes. A compound
that is commonly used is Gallium Arsenide (GaAs), especially that is commonly used is Gallium Arsenide (GaAs), especially
in the case of LEDs because of it’s large bandgap. in the case of LEDs because of it’s large bandgap.
SiSi
+4+
SiSi
+4+
Si Si
+4 +
SiSi
+4+
SiSi
+4+
Si Si
+4 +
SiSi
+4+
SiSi
+4+
Si Si
+4 +
The diagram above shows the 2D The diagram above shows the 2D
structure of the Si crystal. The structure of the Si crystal. The
light green lines represent the light green lines represent the
electronic bonds made when theelectronic bonds made when the
valence electrons are shared. valence electrons are shared.
Each Si atom shares one Each Si atom shares one
electron with each of its fourelectron with each of its four
closest neighbors so that its closest neighbors so that its
valence band will have a full 8 valence band will have a full 8
electrons. electrons.
N-Type Material N-Type Material
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
N-Type Material: N-Type Material:
When extra valence electrons are introduced intoWhen extra valence electrons are introduced into
a material such as silicon an n-type material is a material such as silicon an n-type material is
produced. The extra valence electrons are produced. The extra valence electrons are
introduced by putting impurities into the silicon. introduced by putting impurities into the silicon.
The most commonly used impurities from Group The most commonly used impurities from Group
V are arsenic, antimony and phosphorus. V are arsenic, antimony and phosphorus.
The 2D diagram to the left shows the extra The 2D diagram to the left shows the extra
electron that will be present when a Group V electron that will be present when a Group V
impurity is introduced to a material such as impurity is introduced to a material such as
silicon. This extra electron is very mobile. silicon. This extra electron is very mobile.
+4+4 +4 +
+5 +
+4 +
+4+4 +4+4 +4 +
+4+4 +4 +
