Passive Components for Circuit Design (eBook)

Ian Sinclair (Autor)

eBook Download: EPUB | PDF

2000 | 1. Auflage
320 Seiten
Elsevier Science (Verlag)
978-0-08-051359-1 (ISBN)

Infos

Passive Components for Circuit Design is a unique introduction to this key area of analog electronics designed for technician engineers and anyone involved in circuit design. The coverage encompasses all component types capable of power amplification: resistors, capacitors, transformers, solenoids, motors and transducers. The behaviour of the components is explored along with the different types available and the principles of circuit design. Tolerances, stability, variation with temperature, reliability and manufacturing standards are all covered.

Reading this book will improve your skills in component selection and analog circuit design. These are essential skills not only for the analog designer, but for all circuit designers, professional or amateur.



Gain a deeper understanding of using passive components
Understand the range of components and their applications before designing and specifying
Acquire a working knowledge with a minimum of maths

Inhalt

Cover 1
Contents 6
Preface 8
Chapter 1. Fundamentals 10
Chapter 2. Fixed resistors 41
Chapter 3. Variable resistors, potentiometers and diodes 73
Chapter 4. Capacitors 98
Chapter 5. Inductors and inductive components 134
Chapter 6. Inductive devices 167
Chapter 7. Electrochemical cells 199
Chapter 8. Transducing components 223
Chapter 9. Hardware 250
Chapter 10. Computer assistance in electronics 275
Index 296

Textauszug

Chapter 1

Fundamentals

For many decades, engineers have been able to understand and apply electrical principles on the basis of treating electricity as a form of fluid, and quantities such as current remind us of this view. Electronics, however, often forces us to consider in more detail what electric current is as well as what it does. All of the effects that we describe as electrical or electronic depend on units of electrical charge called electrons.

For our purposes we can regard electrons as being particles of unimaginably small size, and all repelling each other. This force of repulsion exists over distances that are large compared to the apparent size of the electron, and we attribute it to a quantity called charge (or electric charge). Each electron appears to carry exactly the same amount of charge, and by convention we take the sign of this charge to be negative for an electron. A charge is positive if it attracts electrons, and the size of any charge is measured by the force which it can exert on another charge at a measured distance. Electrons are the outer parts of any atom, and when an electron is removed from an atom the atom is left with positive charge, as an ion, attracting the electron back to it. These forces are, however, greatly changed when atoms are closely packed together as they are in most metals, and the result is to release electrons, allowing them to take part in carrying current.

Electric current

These materials which conduct electric current well do so because they contain large numbers of electrons which are free to move, and it is this movement of electrons (or any other charged particles) that we call electric current. Conversely, insulators are materials which, although they may contain vast numbers of electrons, retain these electrons strongly bound to the atoms so that none of them is free to move and so carry current.

• Conduction in crystals can also be due to mobile defects in the crystal, called holes, but these exist only within the crystal and cannot have any independent existence.

For any material in which movement of electrons is possible, the number of electrons that passes a fixed point per second is a measure of the strength of the current. To put numbers to this, a current of 1 A is registered when 6.25 × 1012 electrons pass per second – even this very small current demands that 6.25 million million electrons are moving past each second. In a good conductor, such as a metal, which contains vast numbers of free electrons, the average speed of the electrons is very low, of the order of a few centimetres per hour. In a poor conductor, such as a semiconductor material, the speed required for the same current would be considerably higher, measured in many centimetres per second.

• In a vacuum the electron speed is much higher, and it depends on the square root of the accelerating voltage. For example, in a cathode ray tube with accelerating voltage of 10 kV, the speed is around 60 million metres per second, but at 100 V acceleration the speed is around 6 million metres per second.

Since electric current is the movement of any particle that is charged, current flows when electrons move to and fro in a conductor, not only when the movement is in one direction only. Before anything was known of electrons, these two types of current were recognized and given the names AC (alternating current), and DC (direct current). In electronics, AC was at one time vastly more important, since all electronic signals consisted of AC, and DC was an incidental, used mainly for power supplies. Nowadays, many types of electronic signals consist of DC, so that we need to give equal weight to both of these types, although DC is often converted to AC so as to be more easily handled.

All electric current flows in a closed path, so that no atom is ever deprived of an electron because of the flow of electrons. An electron which leaves an atom will be replaced by an electron from another atom, so that electric current consists of a shuffling around of electrons, like musical chairs with no chairs being removed. The closer the chairs the less movement is needed, which is why the speed of electrons in a good conductor is low. Conversely, if the chairs are far apart, high speed is needed for the journey between chairs, corresponding to the high speeds of electrons in poor conductors.

Electrical quantities

The three electrical quantities that are of most interest to us are voltage, current and frequency. Current has been described already; it is the effect of the movement of electrons or other charged particles, and the strength of current is proportional to the amount of charge that passes a point per second. The voltage (more correctly potential, measured in units called volts) at a point is a comparative figure which measures the ‘pressure’ on electrons to move to or from that point to somewhere else. We usually take the potential (voltage) of the surface of the earth (a potential that is fairly constant) as that ‘somewhere else’, the zero level of potential, so that all voltages are measured by comparison to this zero, ground, or earth level. If the voltage of a point is such that electrons will flow to it from the earth, then that point has a positive voltage. Conversely, if electrons will flow from the point to earth, the point has a negative voltage. When the voltage at a point or the current in a circuit (a closed path) reverses at regular intervals then the voltage or the current is alternating, and the number of complete cycles of reversal (positive to negative to positive again, for example) per second is called the frequency.

The frequency of the AC power supply in the UK, and in most of Europe, is 50 Hz, where the hertz (abbreviated to Hz) is the unit of frequency that consists of one complete cycle per second. The standard frequency for North America is 60 Hz, and this has also been adopted for most of the American continent and in Japan.

• When a voltage is steady, it really ought to be referred to as ZF (zero frequency), because the term DC means direct current, and a phrase like DC voltage is really meaningless. A better choice would be constant current, but the use of DC voltage is now so common and so established that it has been followed in this book (and in most others) rather than the more appropriate ZF which could be applied to current or to voltage.

Active and passive components

Electrical/electronic circuits consist of complete closed paths for current, starting at one end with a source of voltage (EMF) which uses energy to pump electrons around the circuit, and ending back at the source. The analogy with a water pumping circuit is very close (Figure 1.1), and extends to the idea that turning off a tap at the tank (breaking the circuit) will make the water level rise, because of the pressure of the pump, in a vertical piece of pipe (the voltage rises when the circuit is disconnected). Inside the source of EMF (electromotive force, an old term) energy of some sort is being used to push electrons around the circuit (when the circuit is connected) or to pile electrons up (when the circuit is disconnected).

Figure 1.1 The similarities between a water circuit and an electrical circuit.

Electronic circuits are built up by connecting components together with conducting paths which can be of metal wire, metal strips, or strips of other conducting materials such as doped silicon. In these paths, signals will be entering components and leaving components, and the power of a signal is measured by its voltage level multiplied by its current level. Electronic components generally are classed as being active or passive according to their effect on the power of signals applied to them. An active component can increase the power of a signal, using energy that is supplied in other ways, usually by a DC supply.

Passive components cannot increase the power of any signals applied to them and will almost inevitably cause power to be lost. Some passive components may increase the voltage of a signal, but this will be at the expense of current so that overall there is no gain of power. This definition is not totally watertight, because of the behaviour of varactor diodes and magnetic amplifiers, but is as near as we can get without becoming too elaborate at this stage.

A truly passive component can be used to reduce the power of a signal (deliberately), to select part of a signal by its voltage, its frequency or its time relationship to another signal, to change the shape of a waveform or to pass a signal from one section of a circuit to another; but in every case the power of the signal is decreased or unchanged, never increased. Resistors, capacitors and inductors are the fundamental passive components. There is a fourth type, however, called the gyrator, which is encountered in microwave circuits and which is of a more specialized nature.

An active component can increase the power of a signal and must be supplied both with the signal and a source of power. In many of the familiar active devices the source of power is a supply of current at a steady voltage, the DC supply, and the signal is fed in at one part of the active component and taken out from another. A few active devices have no separation of input and output, and some...

Produkt-Details

• Erscheint lt. Verlag: 20.11.2000
• Sprache: englisch
• Themenwelt: Kunst / Musik / Theater ► Design / Innenarchitektur / Mode
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• ISBN-10: 0-08-051359-X / 008051359X
• ISBN-13: 978-0-08-051359-1 / 9780080513591