Starting electronics pdf download

Air dielectric is used for the larger capacitance values. Trimmers and smaller variable types use very thin mica or plastic sheets as the dielectric between the plates. Placing capacitors in series effectively increases the thickness of the dielectric, decreases the total capacitance. The total capacitance of capacitors in series is calculated like the total resistance of parallel resistors.

Connecting capacitors together in parallel effectively increases the area of the plates making the total capacitance equal to the sum of the individual capacitances like the total resistance of series resistors. Capacitors in parallel all charge to the same voltage. The voltage, Vs connected across all the capacitors that are connected in parallel is the same.

Then, Capacitors in Parallel have a common voltage supply across them. Then, Capacitors in Series all have the same current so each capacitor stores the same amount of charge regardless of its capacitance. Capacitors connected together in series all have the same amount of charge. The direction of this magnetic field can be thought in terms of a wood screw being screwed into the conductor in the direction of the flow of current, with the head of the wood screw being rotated in the direction of the lines of force.

If we now take this length of wire and form it into a coil of N turns, the magnetic flux surrounding the coil is increased many times over for a given coil of wire compared with the flux produced by a single straight length. Also, if the current which is flowing through the coils conductor is increased in magnitude, the magnetic flux produced around the coil will also increase in value.

However, as the strength of the magnetic flux increases, it induces a secondary An Inductor is a coil of voltage within the coil called a back emf electro-motive force. Then for a coil of wire which opposes the wire, a self-induced voltage is developed across the coil due to the change in flow of current through current flowing through the coil. The polarity of this self-induced voltage produces itself in the form of a a secondary current in the coil that generates another magnetic flux which magnetic field opposes any changes to the original flux.

In other words, the instant the main current begins to increase or decrease in value, there will be an opposing effect trying to limit this change. But because the coil of wire is extremely long, the current through the coil cannot change instantaneously it takes a while for the current to change due mainly to the resistance of the wire and the self-induced effects of the wire coil.

The ability of a coil to oppose any change in current is a result of the self-inductance, L of the coil. This self- inductance, simply called inductance, value of an inductor is measured in Henries, H. Then the greater the inductance value of the coil, the slower is the rate of change of current for a given source voltage.

Then Inductance is the characteristic of an electrical conductor that opposes a change in current flow. An inductor is a device that stores energy within itself in the form of a magnetic field.

This results in a much stronger magnetic field than one that would be produced by a simple coil of wire. Inductors can also be fixed or variable. Inductors are mainly designed to introduce specific amounts of inductance into a circuit. They are formed with wire tightly wrapped around a solid central core which can be either a straight cylindrical rod or a continuous loop or ring to concentrate their magnetic flux. The inductance of a coil varies directly with the magnetic properties of the central core.

Ferrite and powdered iron materials are mainly used for the core to increase the inductance by increasing the flux linking the coil. Increasing levels of inductance can be obtained by connecting the inductors in series, while decreasing levels can be obtained by connecting inductors in parallel. However, there are certain rules for connecting inductors in series or parallel and these are based on the fact that no mutual inductance or magnetic coupling exists between the individual inductors.

In the Resistors in Series tutorial we saw that the different values of the resistances connected together in series just "add" together and this is also true of inductance. Inductors in series are simply "added together" because the number of coil turns is effectively increased, with the total circuit inductance LT being equal to the sum of all the individual inductances added together.

The voltage drop across all of the inductors in parallel will be the same. If the voltage across a resistor varies sinusoidally with respect to time, as it does in an AC circuit, the current flowing through the resistor will also vary. In an AC resistance, the current and voltage are both "in-phase" as there is no phase difference between them. A circuit consisting of reactance inductive or capacitive resistance and a resistance will have an equivalent AC resistance known as Impedance, Z.

Impedance is the phasor sum of the circuit's reactance, X and the resistance, R. Note that although impedance represents the ratio of two phasors, it is not a phasor itself, because it does not correspond to a sinusoidal varying quantity.

Impedance, which is given the letter Z, in a pure ohmic resistance is a complex number consisting only of a real part being the actual AC resistance value, R and a zero imaginary part, j0. Because of this Ohm's Law can be used in circuits containing an AC resistance to calculate these voltages and currents.

As a pure resistor has no reactance, resistance is, for all practical purposes, unaffected by the frequency of the applied sinusoidal voltage or current. In such circuits we can use both Ohms Law and Kirchoff's laws as well as simple circuit rules for calculating the voltage, current, impedance and power as we would in DC circuit analysis. When working with such rules it is usual to use rms values only.

Capacitors oppose these changes in sinusoidal voltage with the flow of electrons through the capacitor being directly proportional to the rate of voltage change across its plates as the capacitor charges and discharges. Unlike a resistor were the opposition to current flow is its actual resistance, the opposition to current flow in a capacitor is called Reactance.

Like resistance, reactance is measured in Ohm's but is given the symbol "X" to distinguish it from a purely resistive ohmic R value and as the component in question is a capacitor, the reactance of a capacitor is called Capacitive Reactance, XC which is also measured in Ohms.

In a pure AC Capacitance circuit, the voltage and current are both "out-of-phase" with the current leading the o o o 5. The effect of a sinusoidal supply produces a phase difference between the voltage and the current waveforms. In an AC circuit, the opposition to current flow through an inductors coil windings not only depends upon the inductance of the coil but also the frequency of the AC waveform.

The opposition to current flowing through a coil in an AC circuit is determined by the AC resistance, more commonly known as Impedance Z , of the circuit. As the component we are interested in is an inductor, the reactance of an For more information visit our website at: www. In other words, an inductors electrical resistance when used in an AC circuit is called Inductive Reactance. Inductive Reactance which is given the symbol XL, and is the property in an AC circuit which opposes the change in the current.

In other words they "filter-out" unwanted signals. Filters are "attenuating" the rest. Then a band pass filter has two corner or cut- off frequencies. The band stop filter blocks rejects or severely attenuates a certain band of frequencies between its two corner frequencies while allowing all those outside of this stop-band to pass.

They neither are not good conductors nor are they good insulators hence their name "semi"-conductors. They have very few "fee electrons" in their valence shell because their atoms are closely grouped together in a tight crystalline pattern called a "crystal lattice".

However, their ability to conduct electricity can be greatly improved by adding certain "impurities" to this crystalline structure thereby, producing more free electrons than holes or vice versa. By controlling the amount of impurities added to the semiconductor material it is possible to control its conductivity. These impurities are called donors or acceptors depending on whether they produce electrons or holes respectively. This process of adding impurity atoms to semiconductor atoms the order of 1 impurity atom per 10 million or more atoms of the semiconductor is called Doping.

Silicon Atom Structure In order for a silicon crystal to conduct electricity, we need to introduce an impurity atom that has five outer electrons in its Co-valent Bonds 4 electrons outermost valence shell to share with its neighbouring atoms.

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The following experiment will show how the current and the voltage are related. The first measurement is the voltage across the forward-biased diode, the second measurement is the current through it.

Each measurement needs to be taken a number of times as the preset is varied in an organized way. Table 6. Do the experiment the following way: 1. Set up the components on the breadboard to measure only the voltage across the diode. The breadboard layout is given in Figure 6. Before you connect your battery to the circuit, make sure the wiper of the preset is turned fully anticlockwise.

Adjust the preset wiper clockwise, until the first voltage in Table 6. Now set up the breadboard layout of Figure 6. Record the value of the current at the voltage of step 2.

Change the position of the meter and its range, and replace the link in the breadboard so that voltage across the diode is measured again. Repeat steps 2—4 with the next voltage in the table. Repeat step 5 until the table shows a given current reading.

Now set the current through the diode to this given value and measure and record the voltage. Set the current to each value given in the table and record the corresponding voltage, until the table is complete. Now plot your results on the graph of Figure 6. My results correct naturally! Repeat the whole experiment again, using the OA47 diode this time. You can put your results in Table 6. Our results are in Table 6. TABLE 6. The only real difference between them is that they change from a level to an extremely steep line at different positions.

The sharp changes in the curves correspond to what are sometimes called transition voltages — the transition voltage for the OA47 is about 0V3; the transition voltage for the 1N is about 0V If similar curves are plotted for different current ranges then slightly different transition voltages will be obtained.

The OA47 diode is made from germanium while the 1N is of silicon construction. All germanium diodes have a transition voltage of about 0V2 to 0V3; similarly all silicon diodes have a transition voltage of about 0V6 to 0V7. But the characteristics we have determined here are really only half the story as far as diodes are concerned. All we have plotted are the forward voltages and resultant forward currents when the diodes are forward biased. If diodes were perfect this would be all the information we need.

So, to get a true picture of diode operation we have to extend the characteristic curves to include reverse-biased conditions. Reverse biasing a diode means that its anode is more negative with respect to its cathode. So by interpolating the x- and y-axes of the graph, we can provide a grid from the diode characteristic that allows it to be drawn in both forward- and reverse-biased conditions.

Whatever type of diode, it will follow a similar curve to that of Figure 6. V1 to the breakdown voltage, there is a more or less constant but small reverse current. The actual value of this reverse current known as the saturation reverse current, or just the saturation current depends on the individual diode, but is generally of the order of microamps. The second distinct part of the reverse-biased characteristic occurs when the reverse voltage is above the breakdown voltage.

The reverse current increases sharply with only comparatively small increases in reverse voltage. Hint The way to remember the zener diode circuit symbol is to note that the bent line representing its cathode corresponds to the electronics breakdown. This analogy turns out to be an apt one, and in fact the electronic diode breakdown voltage is sometimes referred to as avalanche breakdown and the breakdown voltage is sometimes called the avalanche voltage.

Similarly the sharp knee in the curve at the breakdown voltage is often called the avalanche point. Some special diodes, on the other hand, are purposefully manufactured to have a low breakdown voltage, and you can use one of them to study and plot your own complete diode characteristic. Such diodes are named after the American scientist, Zener, who was one of the first people to study electronic breakdown.

The symbol for a zener diode, incidentally, is shown in Figure 6. The procedure is more or less the same as before. The circuit is shown in Figure 6. Complete Table 6. Also use Table 6. Next, plot your complete characteristic on the graph of Figure 6. My results and characteristics are given in Tables 6. Yours should be similar. From the zener diode characteristic you will see that it acts like any ordinary diode. When forward biased it has an exponential curve with a transition voltage of about 0V7 for the current range observed.

Typical maximum ratings of the two ordinary diodes we have looked at, the 1N and the OA47, are listed in Table 6. Chapter 7 Diodes II In the last chapter, we took a detailed look at diodes and their characteristic curves. Figure 7. After all, the curve is merely a graph of the voltage across the component compared to the current through it. To do this we could perform the same experiment we did in the last chapter with the diodes: measuring the voltage and current at a number of points, then sketching the curve as being the line that connects the points marked on the graph.

So resistor characteristic curves are linear too. So, for any value of resistor, we can choose a value for, say, the voltage across it, and hence calculate the current through it. The procedure is simple, just calculate the current at each voltage point for each resistor. Your resultant characteristic curves should look like those in Figure 7.

The equation is thus simplified to be approximately: I I s e40V 1 The exponential factor e40V , of course, confirms what we already knew to be true — that the diode characteristic curve is an exponential curve. Hint But even with this simplified approximation of the characteristic equation, you can appreciate the value of having a characteristic curve in front of you to look at. So, say, if the voltage across the diode whose characteristic curve is shown in Figure 7.

Any change in voltage and current, however, results in a different resistance. Other components, e. It is when designing such circuits and calculating the operating voltages and currents in the circuits that the use of diode characteristic curves really comes in handy. By looking at the circuit we can see that a current will flow. But what is this current? Similarly, if we knew the voltage across the diode we could determine from the characteristic curve the circuit current.

Unfortunately we know neither voltage! Table 7. From Table 7. Because in such a circuit as that of Figure 7. Where the load line and the characteristic curve cross is the operating point. As its name implies, this is the point representing the current through and voltage across the components in the circuit. The slope of the load line and thus the exact position of the circuit operating point depends on the value of the resistor.

What is the new operating point? We already know that diodes may be used in circuits for practical purposes. We already know that diodes allow current flow in only one direction ignoring saturation reverse current and zener current for the time being and this is one of their main uses — to rectify alternating current a. The most typical source of a. Most electronic circuits require d. The part of any electronic equipment — TVs, radios, hi-fis, computers — that rectifies a. We do not look at transformers in detail, it is suffice to know now that a transformer consists essentially of two coils of wire that are not in electrical contact.

The circuit symbol of a transformer Figure 7. The simplest way of rectifying the a. Here a diode simply allows current to flow in one direction to the load resistor, RL , but not in the other direction from the load resistor. The a. The resistor voltage, although in only one direction, is hardly the fixed voltage we would like, but nevertheless is technically a d.

For this reason, the type of rectification shown by the circuit in Figure 7. It would obviously give a much steadier d. We can do this in two ways. First, by using a modified transformer with a center tap to the output or secondary coil and two diodes as in Figure 7. The center tap of the transformer gives a reference voltage to the load, about which one of the two ends of the coil must always have a positive voltage i. The resultant d. Second, an ordinary transformer may be used with four diodes, as shown in Figure 7.

The group of four diodes is often called a bridge rectifier and may consist of four discrete diodes or can be a single device that contains four diodes in its body. Both of these methods give a load voltage where each halfwave of the a. We can reduce the up-and-down variability of the waves by adding a capacitor to the circuit output. If you remember, a capacitor stores charges — so we can use it to average out the variation in level of the full-wave rectified d. This process is referred to as smoothing and a capacitor used to this effect is a smoothing capacitor.

Sometimes the process is also called filtering. You should remember that the rate at which a capacitor discharges is dependent on the value of the capacitor. Nevertheless, a variation in voltage will always occur, and the extent of this variation is known as the ripple voltage, shown in Figure 7. Ripple voltages of the order of a volt or so are common, superimposed on the required d.

In many practical applications such supplies are adequate, but some applications require a much more stable power supply voltage. If such a zener circuit is used at the output of a smoothed power supply say, that of Figure 7. This can be used to demonstrate some of the principles under discussion.

Voltage regulators give an accurate and constant output voltage with extremely small ripple voltages, even with large variations in load current and input voltage. The power supply principle is summarized in Figure 7. This is efficiently done only with the use of diodes in the rectification and stabilization stages.

Build the circuit, as shown in the breadboard layout of Figure 7. The breadboard layout for the circuit is shown in Figure 7. The ripple voltage now increases, causing greater changes in the d. Resistor characteristic curves are: a. Nearly always linear b. Always exponential c. Nearly always exponential d. Rarely drawn e. Diodes are: a. Ohmic b. Non-ohmic c. Linear d. Non-linear e. The voltage across the diode whose characteristic curve is shown in Figure 7.

What is the current through it? It is impossible to say, because diodes are non-ohmic e. Mains voltages are dangerous because: a. They are a. They are d. They are high d. They are not stabilized e. A single diode cannot be used to full-wave rectify an a. For full-wave rectification of an a. A bridge rectifier is always needed b. As few as two diodes can be used c. An IC voltage regulator is essential d. When you use transistors in electronic circuits it is essential that these three terminals are the right way round.

The terminal closest to the tab on the body is the emitter, then in a clockwise direction are the base and the collector terminals. All 2N transistors, however, have the same body type — known as a TO-5 body — and follow the diagram in Figure 8. The many different types of diodes are all formed by combining doped layers of semiconductor material at a junction.

The PN junction as one layer is N-type semiconductor material and the other layer is P-type forms the basis of all other semiconductor-based electronic components. Figure 8. To do the experiment, put a transistor into your breadboard, then use the meter to test the resistance between transistor terminals. Table 8. TABLE 8. Your results should show that low resistances occur in only two cases, indicating forward current flow between base and emitter, and base and collector.

This corresponds, as we would expect, to the diagram of Figure 8. The real-life transistor deals with currents in more than one direction and this confuses the issue. However, all we need to know here thankfully is that the two PN junctions are very close together — so close that, in fact, they affect one another.

From what we know so far, nothing can happen and no current can flow from collector to emitter because between these two terminals two back-to-back PN junctions lie. One of these junctions is reverse biased and so, like a reverse-biased diode, cannot conduct. Now, the lower junction is flooded with charge carriers and because both junctions are very close together, these charge carriers also allow current flow from collector to emitter, as shown in Figure 8.

So, to summarize, a current will flow from collector to emitter of the transistor when the lower junction is forward biased by a small base-to-emitter voltage. When the base-to-emitter voltage is removed the collector-to-emitter current will stop. We can build a circuit to see if this is true, as shown in Figure 8. Note the transistor circuit symbol. Now do the experiment and see what happens. But when the base resistor is connected to positive, the multimeter shows a collector current flow.

So what? What use is this? Not a lot as it stands, but it becomes very important when we calculate the currents involved. And the current through the resistor must be the base current. The resistor voltage is: 9 0. Now we can begin to see the importance of the transistor.

A tiny base current can turn on or off a quite large collector current. This is illustrated in Figure 8. In effect, the transistor is a current amplifier. No matter how small the base current is, the collector current will be much larger. The collector current is, in fact, directly proportional to the base current.

Double the base current and you double the collector current. Halve the base current and the collector current is likewise halved.

We can work out the current gain of a transistor by measuring the collector current, and calculating the base current as we did earlier, and dividing one by the other. For example, the current gain of the transistor we used is: 12 83 10 3 10 6 Yours may be a bit different. The transistor we use here, the 2N, is a fairly common general-purpose transistor. High-power transistors may have current gains more in the region of about 10, while some modern transistors for use in high-frequency circuits such as radio may have current gains around or so.

NPN The 2N transistor is known as an NPN transistor because of the fact that a thin layer of P-type semiconductor material is sandwiched between two layers of N-type semiconductor material. The construction and circuit symbol of an NPN transistor are shown in Figure 8.

The emitter arrow of either symbol indicates direction of base current and collector current flow. So from the circuit symbols we can work out that base current in the NPN transistor flows from base to emitter, while in the PNP transistor it flows from emitter to base. Likewise, collector current flow in the NPN transistor is from collector to emitter and from emitter to collector in the PNP transistor.

Knowing this and comparing the PNP construction to that of the NPN transistor we can further work out that a tiny emitter-tobase current still called the base current, incidentally will cause a much larger emitter-to-collector current still called the collector current.

The ratio of collector current to base current of a PNP transistor is still the current gain. In fact, apart from the different directions of currents, a PNP transistor functions identically to an NPN transistor. Incredibly, at the last count, the number of ways a transistor may be used is — dah, da, dah, dah, dah, da, dah, dah — two! Science fiction? Well, let me tell you that the appliance described here in extremely simple terms already exists, in millions. We call the appliance a computer.

And every computer contains thousands if not millions of transistor electronic switches. The preset should be turned slowly with a fine screwdriver.

We can see the second use of a transistor in the circuit of Figure 8. The breadboard layout of the circuit is shown in Figure 8. Before you connect the battery, make sure the preset variable resistor is turned fully anticlockwise. Now, connect the battery and slowly with a small screwdriver turn the preset clockwise.

Gradually, as you turn the preset, the LED should light up: dim at first, then brighter, then fully bright. So, the other use of a transistor is as a variable control element. These two operational modes of transistors have been given names.

The first, as it switches between two states, one where the Starting Electronics collector current is on or high, the other where it is off or low, is called digital. Any circuit that uses transistors operating in digital mode is therefore called a digital circuit. The other mode, where transistors control, is known as the analog mode, because the collector current of the transistor is simply an analog of the base current.

Any circuit that uses transistors operating in the analog mode is known as an analog circuit. Take Note Sometimes analog circuits are mistakenly called linear circuits. However, this is wrong, because although it might appear that a linear law is followed, this is not so. In an analog circuit, however, transistors are operated over a part of their characteristic curve remember what a characteristic curve is from Chapters 6 and 7?

Yes, like diodes, transistors have characteristic curves too, but as they have three terminals they have correspondingly more curves. In the circuit symbol for an NPN transistor: a. The arrow points out of the base b. The arrow points into the base c. The arrow points out of the collector d. The arrow points into the collector e. In an NPN transistor: a. A small base current causes a large collector current to flow b.

A small collector current causes a large base current to flow c. A small emitter current causes nothing to flow d. Nothing happens e. None of these f. Bigger f. The current gain of a transistor: a. Is equal to the collector current divided by the emitter current b. Is equal to the collector current divided by the base current c. Is equal to the base current divided by the collector current d. The current gain of a transistor has units of: a.

Amps b. Milliamps c. Volts d. This is a trick question, it has no units e. Chapter 9 Analog Integrated Circuits Well, the last chapter was pretty well jam-packed with information about transistors. If you remember, we saw that transistors are very important electronic components. They may be used in one of only two ways: in digital circuits or in analog circuits — although many, many types of digital and analog circuits exist.

In terms of importance, transistors are the tops. Transistors, being active, can control current so that they can be turned into amplifiers or switches depending on the circuit. In order that, say, a transistor can amplify a small signal into a large one, energy has to be added in the form of electricity from a power supply.

The transistor merely controls the energy available from this power supply, creating the amplification effect. They are small! They can be made by mass-production techniques, are almost as small as you can imagine, and certainly many times smaller than you could see with the naked eye.

Now this sort of integration represents the ultimate in human achievement, remember, but processes are being improved every year and integrated circuits with only hundreds of thousands of integrated transistors are now commonplace. So the final chapters of this epic saga are devoted to integrated circuits.

Just as there are analog and digital circuits that transistors are used in, so there are analog and digital ICs. In IC terms the IC in this chapter is a comparatively simple IC, having only around 20 transistors in all; nevertheless, it is an extremely versatile IC and is probably the most commonly used IC of all time. These letters, e.

Other letters printed on the top of the IC refer to other things such as batch number, date of manufacture, etc. Like the , the is housed in an eight-pin DIL dual-in-line body. Other versions of the exist, in different body styles, but the eight-pin DIL version is by far the most popular. Its circuit symbol is shown in Figure 9. Technically speaking these are called the non-inverting and inverting inputs.

The circuit has one output and two inputs for power supply connection. They are not used in every circuit that the is used in. The internal layout of the eight-pin DIL version of the is shown in Figure 9. Now, each input and output of the op-amp is associated with a particular pin of the DlL body.