Basic electronics Darya
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Transcript of Basic electronics Darya
Objectives•Define basic components of electricity•Recognize the 3 electrical classifications of materials•Compare and contrast AC vs. DC•Explain the concept of grounding•Use Ohm’s law and Watt’s law to express the relationship between current, voltage, and resistance
Darya Khan Bhutto
Basic Electronics I
What is Electricity
Everything is made of atoms There are 118 elements, an atom is a single part
of an element Atom consists of electrons, protons, and
neutrons
Electrons (- charge) are attracted to protons (+ charge), this holds the atom together
Some materials have strong attraction and refuse to loss electrons, these are called insulators (air, glass, rubber, most plastics)
Some materials have weak attractions and allow electrons to be lost, these are called conductors (copper, silver, gold, aluminum)
Electrons can be made to move from one atom to another, this is called a current of electricity.
Surplus of electrons is called a negative charge (-). A shortage of electrons is called a positive charge (+).
A battery provides a surplus of electrons by chemical reaction.
By connecting a conductor from the positive terminal to negative terminal electrons will flow.
Electricity can be broken down into: Electric Charge
Voltage
Current
Resistance
Negative & Positive Charges What do the effects of electricity in TV, radio, a battery, and
lightening all have in common?
Basic particles of electric charge with opposite polarities.
Electrons
The smallest amount of electrical charge having the quality called negative polarity.
Electrons orbit the center of atoms.
Protons
The proton is a basic particle with positive polarity.
Protons are located in the nucleus of atoms along with neutrons, particles which have neutral polarity.
Electrically, all materials fall into 1 of 3 classifications: Conductors
Insulators
Semi-Conductors
Conductors
Have 1 valence electron
Materials in which electrons can move freely from atom to atom are called conductors.
In general all metals are good conductors.
The purpose of conductors is to allow electrical current to flow with minimum resistance.
Insulators
Have 8 valence electrons Materials in which electrons tend to stay put and do
not flow easily from atom to atom are termed insulators.
Insulators are used to prevent the flow of electricity. Insulating materials such as glass, rubber, or plastic
are also called dielectrics, meaning they can store charges.
Dielectric materials are used in components like capacitors which must store electric charges.
Semi-Conductors
Have 4 valence electronsMaterials which are neither conductors
nor insulators Common semi conductor materials are
carbon, germanium and silicone.Used in components like transistors
The Symbol for Charge
The symbol for charge is Q which stands for quantity.
The practical unit of charge is called the coulomb (C).
One coulomb is equal to the amount of charge of 6.25X1018 electrons or protons stored in a dielectric.
Voltage
Potential refers to the the possibility of doing work. Any charge has the potential to do the work of
attracting a similar charge or repulsing an opposite charge.
The symbol for potential difference is E (for electromotive force)
The practical unit of potential difference is the volt (V) 1 volt is a measure of the amount of work required to
move 1C of charge
Current
When a charge is forced to move because of a potential difference (voltage) current is produced.
In conductors - free electrons can be forced to move with relative ease, since they require little work to be moved.
So current is charge in motion.
The more electrons in motion the greater the current.
Amperes
Current indicates the intensity of the electricity in motion. The symbol for current is I (for intensity) and is measured in amperes.
The definition of current is: I = Q/T Where I is current in amperes, Q is charge
in coulombs, and T is time in seconds.
1 ampere = 1 coulomb per second
Resistance
Opposition to the flow of current is termed resistance. The fact that a wire can become hot from the flow of
current is evidence of resistance.
Conductors have very little resistance.
Insulators have large amounts of resistance.
Ohms
The practical unit of resistance is the ohm designated by the Greek letter omega: Ω
A resistor is an electronic component designed specifically to provide resistance.
Closed Circuits
In applications requiring the use of current, electrical components are arranged in the form of a circuit.
A circuit is defined as a path for current flow.
Common Electronic Component Symbols
A Complex Audio Circuit
Open Circuits
The Circuit is a Load on the Voltage Source The circuit is where the energy of the source (battery) is
carried by means of the current through the the various components.
The battery is the source, since it provides the potential energy to be used.
The circuit components are the load resistance - they determines how much current the source will produce.
Direction of Electron Flow
The direction of electron flow in our circuit is from the negative side of the battery, through the load resistance, back to the positive side of the battery.
Inside the battery, electrons move to the negative terminal due to chemical action, maintaining the potential across the leads.
Electron Flow in a Simple Circuit
DC
Circuits that are powered by battery sources are termed direct current circuits.
This is because the battery maintains the same polarity of output voltage. The plus and minus sides remain constant.
Waveform of DC Voltage
Characteristics of DC
It is the flow of charges in just one direction and...
The fixed polarity of the applied voltage which are characteristics of DC circuits
AC
An alternating voltage source periodically alternates or reverses in polarity.
The resulting current, therefore, periodically reverses in direction.
The power outlet in your home is 60 cycle ac - meaning the voltage polarity and current direction go through 60 cycles of reversal per second.
All audio signals are AC also.
Waveform of AC Voltage
Complex Voltage
This is a more realistic view of what
an audio signal’s voltage would look like
Comparison of DC & ACDC Voltage AC Voltage
Fixed polarity Reverses polarity
Can be steady or vary in magnitude
Varies in magnitude between reversals in polarity
Steady value cannot be stepped up or down by a transformer
Used for electrical power distribution
Electrode voltage for tube and transistor amps
I/O signal for tube and transistor amps
Easier to measure Easier to amplify
Heating Effects the same for both AC and DC current
Many Circuits Include both AC & DC Voltages DC circuits are usually simpler than AC circuits.
However, the principles of DC circuits also apply to AC circuits.
Impedance
Impedance is resistance to current flow in AC circuits and its symbol is .
Impedance is also measured in ohms.
Grounding
In the wiring of practical circuits one side of the voltage source is usually grounded for safety.
For 120 V - ac power lines in homes this means one side of the voltage source is connected to a metal cold water pipe.
For electronic equipment, the ground just indicates a metal chassis, which is used as a common return for connections to the source.
Common Symbols/ Names for Ground in Electric Circuits
Ohm’s Law
The amount of current in a circuit is dependent on its resistance and the applied voltage. Specifically I = E/R
If you know any two of the factors E, I, and R you can calculate the third.
Current I = E/R
Voltage E = IR
Resistance R = E/I
Current is Directly Proportional to Voltage for a Constant Resistance
OHM’s LAW
Current is Inversely Proportional to Resistance for a Constant Voltage
OHM’s LAW
Power
The unit of electrical power is the watt. Power is how much work is done over time. One watt of power is equal to the work done
in one second by one volt moving one coulomb of charge. Since one coulomb a second is an ampere:
Power in watts = volts x amperes P = E x I
3 Power Formulas
P = E x IP = I2 x RP = E2 / R
Conversion FactorsPrefix Symbol Relation to
basic unitExamples
Mega M 1,000,000 or 1x106
5MΩ =5x106 Ω
Kilo k 1,000 or1x103
18kV =18x103 V
Milli m .001 or 1x10-3
48 mA = 48x10-3A
Micro .000001 or1x10-6
15V =15x10-6V
Ohm’s Law
V = I * R !!!!!
V= I * Z !!!!!
DC
An electrical current can flow in either of two directions. If it flows in only one direction, it is called direct current (DC).
A battery is an example of a DC voltage that can supply DC current!
Electrical engineers also use the term DC to refer to an average (or constant part of) a voltage or current signal.
ACA current which alternates in direction or polarity is called an alternating current (AC).
The current flowing from a wall outlet is an example of an AC current!
DC voltage, RMS Voltage, Frequency, Period
Resistors
Resistor Color Code
Kirchoff’s Voltage Law
There must always be a closed path (or loop) for current to flow!
Summation of voltages around any closed loop is 0!
Kirchoff’s Current Law
Summation of currents into a node must equal 0.
Electrons cannot just suddenly appear or disappear!
Voltage Divider
I2= 5 / (15K) = 0.33 mA
I1= VDD / (R1 + R2) = 0.33 mA
I1= 5 / (15K) = 0.33 mA
Vout = [R1 / (R1 + R2)] * VDD
Vout = 5/3 Volts
+VDD =
Use Ohm’s Law, KCL, KVL!
Capacitors
There are many kinds of capacitors but they all do the same thing: store charge.
The simplest kind of capacitor is two conductors separated by an insulating material.
Exercise
• Calculate the total current and voltage drop across each resistor shown in Figure 1
• Build the circuit in Figure 1 on the prototype board
• Measure the total circuit current and voltage drops across each resistor and comparethe calculated and measured values
Capacitance
Battery
Capacitor
Unit = Farad
Pico Farad - pF = 10-12FMicro Farad - uF = 10-6F
A capacitor is used to store charge for a short amount of time
Capacitor Charging
Capacitor Discharge
Inductance
Difference Between R and C
Like resistors, capacitors can impede the flow of current. Unlike resistors, which resist the flow of both DC and AC currents in exactly the same way, capacitors can be used to COMPLETELY BLOCK the flow of DC currents.
As the frequency of the alternations associated with the flow of AC currents increases, capacitors impede the flow of current to a lesser degree!
Low FrequencyHigh Frequency
Inductors (Coils)Inductors are formed by taking a wire and wrapping it as a coil.
Like resistors, inductors can impede the flow of current.
Inductors, however, resist rapid changes in the current flowing through them while freely passing DC currents.
When current is passed through the coil, an electromagnetic field encircles it. The coil can act like a magnet!
High FrequencyLow Frequency
Diodes
A diode is like and electronic one-way valve. It will allow current to flow in only one direction! Clearly, diodes can be used to convert AC currents to DC!
TransistorsTransistors are three terminal devices. A very small current or voltage at one terminal can control a much larger current flowing between the other two leads.
Operational Amplfier
Operational Amplifiers take small voltages and make them MUCH larger.
Golden Rules (Op amp with negative feedback): (1) No-current flows into either (+) or (-) inputs.(2) The (+) and (-) inputs are at the same voltage.
• To measure current, must break circuit and install meter in line.
• Measurement is imperfect because of voltage drop created by meter.
NoiseFiltering not only prevents aliasing but also can be used to remove noise.
All electronics circuits generate small, random electrical currents or voltages. Noise can also enter electronic circuits by means of electromagnetic waves generated by things such as electric motors, radio stations, electric outlets. The HandyBoard digital circuits also serve as a noise source which may corrupt your sensor signals.
Passive, RC, Lowpass Filter
f3dB = 1 / (2pRC)
Basic Electronics Review - 5
R1
Vi
+
A
DR3
R2Vi
+
Req
A
D
Original Circuit Equivalent Circuit
Basic Electronics Review - 6
Power (units are in Watts)– P = I2R = (V/R)2R = V2/R– P = I2R = I2(V/I) = IV
Note: can calculate thepower required for anycircuit by measuring I andV and taking their product R1
R2
R3
Vi
+
A B
C
D
Any circuitI
Capacitor Capacitor– put it in terms that a 6th grader could
understand– “Accumulator”, water tank
Pressure storage. Stores energy in an electric field Voltage across the leads takes time to build up. Units of
capacitance are Farads
+ -
2
21
1
CVE
idtC
V
dtdVCi
dtdQ
CVQ
V
)2cos(2)2sin(()2sin()sin(
ftfCAdt
ftAdCdtdVCi
ftAtAV
pppp
Inductor Inductor – put it in terms that a 6th grader could
understand– “Flywheel, merry-go-round”
An inertia. Stores energy in a magnetic field Tries to oppose changes in current flow. Units of
inductance are Henrys
+ -
i2
21
1
LiE
VdtL
i
dtdiLV
V
)2cos(2)2sin(()2sin()sin(
ftfLAdt
ftAdLdtdiLV
ftAtAi
pppp
The Voltage Divider Consider two resistances in series What is VA in terms of
– Vi, R1 and R2
Vi
+
A
D
R2
R1
VA
So what? Why is this important?
Voltage divider effect occurs whenever one circuit is connected to another
Voltage dividers can be used to set a voltage level somewhere between a given supply voltage and ground If significant current is desired, it is better to use a power supply
or voltage regulator
Parallel Circuit - Example
• Given– Vbattery = 12 V– R1 = 50 W, R2 = 100 W, R3 = 100 W
• Complete the following table:
V = I R
1
2
3
-----------------------------------------------
T
Series Circuit - Example
• Given– Vbattery = 12 V– R1 = 50 W, R2 = 100 W, R3 = 100 W
• Complete the following table V = I R
1
2
3
-----------------------------------------------
T
Parallel Circuit – Pros and Cons
Advantages
The more devices (resistors) in a parallel circuit, does not decrease the current (does not dim bulbs).
If one resistor breaks (a bulb goes out) the rest do not.
Problems
Current doesn’t stay the same for entire circuit– So energy is used up quicker – So the total current increases = faster electrons = hotter
wire = fire?
Basic Laws of CircuitsEquivalent Resistance: Resistors in combination.
Example 5.1: Continued . We start at the right hand side
of the circuit and work to the left.
1 0 W
1 0 W
8 W
2 WR e q
1 0 W
5 WR e q
Figure 5.8: Reduction steps for Example 5.1.
W15eqRAns:
8
Basic Laws of CircuitsEquivalent Resistance: Resistors in combination.
Example 5.2: Given the circuit shown below. Find Req.
c b a
d
R e q4 W
1 2 W
6 W
1 0 W
Figure 5.9: Diagram for Example 5.2.
9
Basic Laws of CircuitsEquivalent Resistance: Resistors in combination.
Example 5.2: Continued.
c b
d , a
R e q4 W
1 2 W
6 W 1 0 W
c b a
d
R e q4 W
1 2 W
6 W
1 0 W
Fig 5.10: Reduction steps.
10
c b
d , a
R e q4 W
1 2 W
6 W 1 0 W
1 2 W6 W4 WFig 5.11: Reduction steps.
Req
10 W resistorshorted out
Basic Laws of CircuitsEquivalent Resistance: Resistors in combination.
Example 5.2: Continued.
11
Basic Laws of CircuitsEquivalent Resistance: Resistors in combination.
Example 5.2: Continued.
4 W4 W
1 2 W6 W4 W
Fig 5.12: Reduction steps.
Req
Req
12