Basic electronics Darya

transcript

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.

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

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

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

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 !!!!!

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

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

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

dtdVCi

)2cos(2)2sin(()2sin()sin(

ftfCAdt

ftAdCdtdVCi

ftAtAV

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

dtdiLV

)2cos(2)2sin(()2sin()sin(

ftfLAdt

ftAdLdtdiLV

ftAtAi

The Voltage Divider Consider two resistances in series What is VA in terms of

– Vi, R1 and R2

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

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Series Circuit - Example

• Given– Vbattery = 12 V– R1 = 50 W, R2 = 100 W, R3 = 100 W

• Complete the following table V = I R

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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.

2 WR e q

5 WR e q

Figure 5.8: Reduction steps for Example 5.1.

W15eqRAns:

Example 5.2: Given the circuit shown below. Find Req.

R e q4 W

Figure 5.9: Diagram for Example 5.2.

Example 5.2: Continued.

R e q4 W

6 W 1 0 W

R e q4 W

Fig 5.10: Reduction steps.

R e q4 W

6 W 1 0 W

1 2 W6 W4 WFig 5.11: Reduction steps.

10 W resistorshorted out

4 W4 W

1 2 W6 W4 W

Fig 5.12: Reduction steps.

Basic electronics Darya

Engineering