JA505 AUTOMOTIVE ELECTRONICS

CHAPTER 1

ELECTRONICS PRINCIPLES

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Basic Electronics Principle

ATOMIC STRUCTURE

We define matter as anything that takes up space and, when subjected to gravity, has weight.

There are many different kinds of matter. copper, iron, gold, and silver. Other elements have been produced only in the laboratory.

Every material we know is made up of one or more elements. Lets say we take a chunk of materiala rock

Some of our pieces would have the characteristics of copper, for example.

Others would show themselves to be carbon, yet others would be iron.

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Atoms If you could keep dividing the material indefinitely, you would

eventually get a piece that only had the characteristics of a single element.

At that point, you would have an atom, which is the smallest particle into which an element can be divided and still have all the characteristics of that element.

An atom is the smallest particle that has the characteristic of the element. An atom is so small that it cannot be seen with a conventional microscope, even a very powerful one.

An atom is itself made up of smaller particles. electrons, protons, and neutrons.

All the atoms of any particular element look essentially the same, but the atoms of each element are different from those of another element. All atoms share the same basic structure. At the center of the atom is the nucleus, containing protons and neutrons, as shown in Figure 2-1.

Orbiting around the nucleus, in constant motion, are the electrons. The exact number of each of an atoms particlesprotons, neutrons,

and electrons depends on which element the atom is from.

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- The simplest atom is that of the element hydrogen. A hydrogen atom (Figure 2-1) contains one proton, one neutron, and one electron.

- Aluminum, by comparison, has 13 protons, 14 neutrons, and 13 electrons.

- These particlesprotons, neutrons, and electronsare important to us Because they are used to explain electrical charges, voltage, and current.

- Electrons orbit the nucleus of an atom in a concentric ring known as a shell.

- The nucleus contains the proton and the neutron, which contains almost all of the mass of the entire atom.

- There are two types of force at work in every atom.

- Normally, these two forces are in balance. One force comes from electrical charges and the other force, centrifugal force, is generated when an object moves in a circular path.

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Electrical Charges Neutrons have no charge, but electrons have a negative

electrical charge. Protons carry a positive electrical charge (Figure 2-2).

Opposite electrical charges always attract one another; so particles or objects with opposite charges tend to move toward each other unless something opposes the attraction.

Like electrical charges always repel; particles and objects with like charges tend to move away from each other unless the repelling force is opposed.

In its normal state, an atom has the same number of electrons as it does protons. This means the atom is electrically neutral or balanced because there are exactly as many negative charges as there are positive charges. Inside each atom, negatively charged electrons are attracted to positively charged protons, just like the north and south poles of a magnet, as shown in Figure 2-3.

Ordinarily, electrons remain in orbit because the centrifugal force exactly opposes the electrical charge attraction. It is possible for an atom to lose or gain electrons.

If an atom loses one electron, the total number of protons would be one greater than the total number of electrons. As a result, the atom would have more positive than negative charges. Instead of being electrically neutral, the atom itself would become positively charged.

The electrons are in different shells or distances from the nucleus. The greater the speed, the higher the energy of the electrons, the further away from the nucleus the electron orbit. All elements are composed of atoms and each element has its own characteristic number of protons with a corresponding equal number of electrons. The term electricity is used to describe the behavior of these electrons in the outer orbits of the atoms.

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Electric PotentialVoltage We noted that a balance (Figure 2-4) between

centrifugal force and the attraction of opposing charges keeps electrons in their orbits.

If anything upsets that balance, one or more electrons may leave orbit to become free electrons. When a number of free electrons gather in one location, a charge of electricity builds up.

This charge may also be called a difference in electric potential.

This difference in electric potential is more commonly known as voltage.

When this potential causes a number of electrons to move in a single direction, the effect is current flow. So the definition of current is the flow of electrons.

Any atom may possess more or fewer electrons than protons. Such an unbalanced atom would be described as negatively (an excess of electrons) or positively (a net deficit of electrons) charged and known as an ion (Figure 2-5).

An ion is an atom that has gained or lost an electron. Ions try to regain their balance of equal protons and electrons by exchanging electrons with nearby atoms.

This is known as the flow of electric current or electricity.

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Valence The concentric orbital paths, or shells, of an atom proceed

outward from the nucleus. The electrons in the shells closest to the nucleus of the atom are held most tightly while those in the outermost shell are held more loosely.

The simplest element, hydrogen, has a single shell containing one electron. The most complex atoms may have seven shells.

The maximum number of electrons that can occupy shells one through seven are, in sequence: 2, 8, 18, 32, 50, 72, 98.

The heaviest elements in their normal states have only the first four shells fully occupied with electrons; the outer three shells are only partially occupied. The outermost shell in any atom is known as its valence ring.

An atom of the element neon with an atomic number of 10 has both a full first and second shell (2 and 8): its second shell is its valence ring (Figure 2-6).

Other more complex atoms that have eight electrons in their outermost shell, even though this shell might not be full, will resemble neon in terms of their chemical inertness.

Valence represents the ability to combine. Remember that an ion is any atom with either a surplus or deficit of electrons.

Free electrons can rest on a surface or travel through matter (or a vacuum) at close to the speed of light. Electrons resting on a surface will cause it to be negatively charged.

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Faradays Law.

Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil.

No matter how the change is produced, the voltage will be generated.

The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc

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Faraday's law is a fundamental relationship which comes from Maxwell's equations. It serves as a succinct summary of the ways a voltage (or emf) may be generated by a changing magnetic environment.

The induced emf in a coil is equal to the negative of the rate of change of magnetic flux times the number of turns in the coil. It involves the interaction of charge with magnetic field.

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Electric Current Electric current is the rate of charge flow past a given point in an

electric circuit, measured in Coulombs/second which is named Amperes.

In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and resistance by Ohm's law.

The standard abbreviations for the units are 1 A = 1C/s.

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Electric Charge The unit of electric charge is the Coulomb (abbreviated C). Ordinary matter is made up of

atoms which have positively charged nuclei and negatively charged electrons surrounding them.

The influence of charges is characterized in terms of the forces between them (Coulomb's law) and the electric field and voltage produced by them.

One Coulomb of charge is the charge which would flow through a 120 watt light bulb (120 volts AC) in one second. Two charges of one Coulomb each separated by a meter would repel each other with a force of about a million tons!

The rate of flow of electric charge is called electric current and is measured in Amperes. In introducing one of the fundamental properties of matter, it is perhaps appropriate to point

out that we use simplified sketches and constructs to introduce concepts, and there is inevitably much more to the story.

No significance should be attached to the circles representing the proton and electron, in the sense of implying a relative size, or even that they are hard sphere objects, although that's a useful first construct.

The most important opening idea, electrically, is that they have a property called "charge" which is the same size, but opposite in polarity for the proton and electron. The proton has 1836 times the mass of the electron, but exactly the same size charge, only positive rather than negative. Even the terms "positive" and "negative" are arbitrary, but well-entrenched historical labels.

The essential implication of that is that the proton and electron will strongly attract each other, the historical archtype of the cliche "opposites attract". Two protons or two electrons would strongly repel each other. Once you have established those basic ideas about electricity, "like charges repel and unlike charges attract", then you have the foundation for electricity and can build from there.

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From the precise electrical neutrality of bulk matter as well as from detailed microscopic experiments, we know that the proton and electron have the same magnitude of charge. All charges observed in nature are multiples of these fundamental charges.

Although the standard model of the proton depicts it as being made up of fractionally charged particles called quarks, those fractional charges are not observed in isolation -- always in combinations which produce +/- the electron charge.

An isolated single charge can be called an "electric monopole". Equal positive and negative charges placed close to each other constitute an electric dipole.

Two oppositely directed dipoles close to each other are called an electric quadrupole. You can continue this process to any number of poles, but dipoles and quadrupoles are mentioned here because they find significant application in physical phenomena.

One of the fundamental symmetries of nature is the conservation of electric charge. No known physical process produces a net change in electric charge.

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Conventional Electric Current Although it is electrons which are the mobile charge

carriers which are responsible for electric current in conductors such as wires, it has long been the convention to take the direction of electric current as if it were the positive charges which are moving.

Some texts reverse this convention and take electric current direction as the direction the electrons move, an obviously more physically realistic direction, but the vast majority of references use the conventional current direction and that convention will be followed in most of this material.

In common applications such as determining the direction of force on a current carrying wire, treating current as positive charge motion or negative charge motion gives identical results. Besides the advantage of agreeing in direction with most texts, the conventional current direction is the direction from high voltage to low voltage, high energy to low energy, and thus has some appeal in its parallel to the flow of water from high pressure to low (water analogy).

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- In a direct current (DC) electrical circuit, the voltage (V in volts) is an expression of the available energy per unit charge which drives the electric current (I in amperes) around a closed circuit.

- Increasing the resistance (R in ohms) will proportionately decrease the current which may be driven through the circuit by the voltage.

- Each quantity and each operational relationship in a battery-operated DC circuit has a direct analog in the water circuit. The nature of the analogies can help develop an understanding of the quantities in basic electric ciruits.

- In the water circuit, the pressure P drives the water around the closed loop of pipe at a certain volume flow rate F. If the resistance to flow R is increased, then the volume flow rate decreases proportionately. You may click any component or any relationship to explore the details of the analogy with a DC electric circuit.

DC Circuit Water Analogy

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Voltage-Pressure Analogy A battery is analogous to a pump in a water circuit. A pump

takes in water at low pressure and does work on it, ejecting it at high pressure. A battery takes in charge at low voltage, does work on it and ejects it at high voltage.

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Electronics Components

Resistor. The electrical resistance of a circuit component or device is defined as

the ratio of the voltage applied to the electric current which flows through it:

R= V/ I If the resistance is constant over a considerable range of voltage,

then Ohm's law, I = V/R, can be used to predict the behavior of the material. Although the definition above involves DC current and voltage, the same definition holds for the AC application of resistors.

Whether or not a material obeys Ohm's law, its resistance can be

described in terms of its bulk resistivity. The resistivity, and thus the resistance, is temperature dependent. Over sizable ranges of temperature, this temperature dependence can be predicted from a temperature coefficient of resistance.

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Resistivity and Conductivity The electrical resistance of a wire would be expected

to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made.

Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as

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The factor in the resistance which takes into account the nature of the material is the resistivity.

Although it is temperature dependent, it can be used at a given temperature to calculate the resistance of a wire of given geometry.

The inverse of resistivity is called conductivity. There are contexts where the use of conductivity is more convenient.

Electrical conductivity = = 1/

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Resistivity Calculation The electrical resistance of a wire would be expected to be

greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made (resistivity).

Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as

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Variable resistor basics

The variable resistor comprises a fixed resistive element along which a slider passes. The variable or adjust able resistor forms a potential divider in which the overall resistance between the two end points remains the same, but the ratio of the two resistors in the legs changes.

In view of the fact that the variable resistor is effectively a potential divider, it is called a potentiometer.

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- Variable resistor symbol The variable resistor symbol used in circuit diagrams indicates its construction.

- Effectively it is a fixed resistor with a slider that can move along the length of the resistive element. In this way it forms a potentiometer as described before.

- The variable resistor symbols depict the current version use din circuit diagrams today and the traditional format that may be seen on older circuit diagrams.

- When a true variable resistor with only two connections is needed, it is common practice to connect the slider to the remote end of the variable resistor as shown below.

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Thermistors Introduction

A thermistor is a specialized resistor, intentionally designed to be thermally sensitive and its primary characteristic is its ability to alter its electrical resistance in response to changes in case temperature.

It can be used to measure temperature, or to sense temperature changes and compensate for the temperature changes.

Thermistor resistance is a function of its absolute temperature. Normally available with accuracy up to 1oC, however, higher accuracy devices are available, but are substantially more expensive.

A time constant characteristic is also specified to signify the response rate to a temperature change (i.e., speed of the thermistor) and is usually expressed in seconds, defined as the time required to change 63.2% of the total difference between initial and final body temperature, when subjected to a step function change in temperature, under zero-power conditions.

The generic relationship between thermistor resistance and temperature is expressed in the equation*:

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- The nature of the p-n junction is that it will conduct current in the forward direction but not in the reverse direction.

- It is therefore a basic tool for rectification in the building of DC power supplies.

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- A bipolar junction transistor consists of three regions of doped semiconductors. - A small current in the center or base region can be used to control a larger

current flowing between the end regions (emitter and collector). The device can be characterized as a current amplifier, having many applications for amplification and switching.

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Transistor Structure

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Constraints on Transistor Operation

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Transformer - A transformer makes use of Faraday's law and the ferromagnetic properties of an

iron core to efficiently raise or lower AC voltages. - It of course cannot increase power so that if the voltage is raised, the current is

proportionally lowered and vice versa.

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Transformer and Faraday's Law

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STEPPER MOTORS - Stepper motors are electromagnetic incremental devices that convert electric pulses

to shaft motion (rotation). These motors rotate a specific number of degrees as a respond to each input electric pulse.

- Typical types of stepper motors can rotate 2, 2.5, 5, 7.5, and 15 per input electrical pulse. Rotor position sensors or sensor less feedback based techniques can be used to regulate the output response according to the input reference command. Stepper motors offers many attractive features such as:

Available resolutions ranging from several steps up to 400 steps (or higher) per revolution.

Several horsepower ratings. Ability to track signals as fast as 1200 pulses per second.

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- Stepper motors, on the other hand, effectively have multiple "toothed" electromagnets arranged around a central gear-shaped piece of iron.

- The electromagnets are energized by an external control circuit, such as a microcontroller To make the motor shaft turn, first, one electromagnet is given power, which makes the gear's teeth magnetically attracted to the electromagnet's teeth. When the gear's teeth are aligned to the first electromagnet, it slightly offset from the next electromagnet.

- The next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one, and from there the process is repeated. Each of those slight rotations is called a "step", with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle

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