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Diodes I voltages, reverse currents flow. 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 which allows it to be drawn in both forward and reverse biased conditions. It wouldn’t be possible for you to plot the reverse biased conditions, for an ordinary diode, the way you did the forward biased experiment (we will, however, do it for a special type of diode soon), so instead we’ll make it easy for you and give you the whole characteristic curve. Whatever type of diode, it will follow a similar curve to that of Figure 6.14, where the important points are marked. Figure 6.14 Plotting the reverse bias characteristics for an ordinary diode is not practical, so we give you the characteristic curve here 137
Starting electronics Reverse bias From the curve you can see that there are two distinct parts which occur when a diode is reverse biased. First, at quite low reverse voltages, from about –0.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 in 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. The reason for this is because of electronics breakdown of the diode when electrons gain so much energy due to the voltage that they push into one another just like rocks and boulders rolling down a steep mountainside push into other rocks and boulders which, in turn, start to roll down the mountainside pushing into more rocks and boulders, forming an avalanche. 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. In most ordinary diodes the breakdown voltage is quite high (in the 1N4001 it is well over –50 V), so this is one reason why you couldn’t plot the whole characteristic curve, including reverse biased conditions, in the same experiment — our 138
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Starting Electronics i
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Starting Electronics Keith Brindley
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Contents Contents Preface vi 1. The
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The very first steps 1 The very fir
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The very first steps potential rewa
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The very first steps Photo 1.2 tool
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The very first steps that electrici
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The very first steps Going back to
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The very first steps tially exist.
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The very first steps by a scientist
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The very first steps Hint: Ohm’s
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The very first steps Electronic com
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The very first steps Larger values
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The very first steps Time out That
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On the boards 2 On the boards In th
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On the boards If you are following
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On the boards Hint: The theoretical
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On the boards Photo 2.2 Inside brea
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On the boards Down the edges of the
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On the boards Hint: The multi-meter
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On the boards of leads should be su
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On the boards it gets older and sta
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On the boards Hint: The bands group
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On the boards In practice, you migh
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On the boards called just ohmmeter)
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On the boards ends. We say resistor
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On the boards we would get: and thi
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On the boards Figure 2.9 A comparat
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Measuring current and voltage 3 Mea
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Measuring current and voltage forme
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Measuring current and voltage Netwo
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Measuring current and voltage Netwo
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Measuring current and voltage Did y
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Measuring current and voltage Figur
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Practically there Measuring current
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Measuring current and voltage Take
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Measuring current and voltage Take
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Measuring current and voltage Hint:
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Capacitors 4 Capacitors You need a
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Capacitors Capacitors We’re going
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Capacitors In our experiments in th
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Capacitors Figure 4.4 A simple resi
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Capacitors Time (seconds) 5 10 15 2
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Page 96 and 97: Capacitors In a capacitor circuit l
Page 98 and 99: Capacitors Figure 4.11 An experimen
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Page 104 and 105: Capacitors where ε is the permitti
Page 106 and 107: ICs oscillators and filters 5 ICs,
Page 108 and 109: ICs oscillators and filters Photo 5
Page 110 and 111: ICs oscillators and filters We’ve
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Page 120 and 121: ICs oscillators and filters Value o
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Page 126 and 127: ICs oscillators and filters Figure
Page 128 and 129: ICs oscillators and filters simple
Page 130 and 131: Diodes I 6 Diodes I We’re going t
Page 132 and 133: Diodes I Photo 6.1 A horizontal pre
Page 134 and 135: Diodes I Now, with a resistance of
Page 136 and 137: Diodes I here. We needn’t know an
Page 138 and 139: Diodes I Figure 6.9 The breadboard
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Page 142 and 143: Diodes I Current (mA) Voltage (V) 0
Page 146 and 147: Diodes I battery voltage of 9 V sim
Page 148 and 149: Diodes I Figure 6.17 The circuit, w
Page 150 and 151: Diodes I Figure 6.19 My results fro
Page 152 and 153: Diodes II 7 Diodes II In the last c
Page 154 and 155: Diodes II the same experiment we di
Page 156 and 157: Diodes II We need to draw diode cha
Page 158 and 159: Diodes II Generally, diodes don’t
Page 160 and 161: Diodes II Diode voltage (VD) Resist
Page 162 and 163: Diodes II Diode circuits We’re no
Page 164 and 165: Diodes II Figure 7.9 Waveforms show
Page 166 and 167: Diodes II Filter tips Although we
Page 168 and 169: Diodes II We’ve already seen a de
Page 170 and 171: Diodes II as that from a 230 V a.c.
Page 172 and 173: Diodes II Figure 7.19 The same circ
Page 174 and 175: Transistors 8 Transistors In previo
Page 176 and 177: Transistors Figure 8.1 How to recog
Page 178 and 179: Transistors Black meter lead Red me
Page 180 and 181: Transistors Well, as mentioned earl
Page 182 and 183: Transistors Figure 8.8 A breadboard
Page 184 and 185: Transistors In effect, the transist
Page 186 and 187: Transistors Figure 8.10 transistors
Page 188 and 189: Transistors Hint: Yes, that’s rig
Page 190 and 191: Transistors These two operational m
Page 192 and 193: Analogue integrated circuits 9 Anal
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Analogue integrated circuits circui
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Analogue integrated circuits Figure
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Building on blocs Analogue integrat
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Analogue integrated circuits As the
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Analogue integrated circuits circui
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Analogue integrated circuits an app
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Digital integrated circuits I 10 Di
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Digital integrated circuits I Logic
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Digital integrated circuits I If we
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Digital integrated circuits I Figur
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Digital integrated circuits I It’
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Digital integrated circuits I The t
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Digital integrated circuits I Trans
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Digital integrated circuits I going
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Digital integrated circuits I OR an
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Digital integrated circuits I For t
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Digital integrated circuits II 11 D
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Digital integrated circuits II A se
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Shutting the ’stable gate Digital
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Digital integrated circuits II gate
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Digital integrated circuits II In o
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Digital integrated circuits II Figu
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Digital integrated circuits II Swit
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Digital integrated circuits II The
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Open the black box Digital integrat
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Digital integrated circuits II Ther
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Glossary Glossary 180 ° out-of-pha
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Glossary bode plots method of showi
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Glossary decibels logarithmic units
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Glossary integrated circuit a semic
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Glossary peak voltage the voltage m
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Glossary squarewave a signal which
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Glossary Components used Resistors
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Glossary Index A ampere, 9 AND gate
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