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Transistors Figure 8.8 A breadboard layout for the circuit in Figure 8.7 a collector current of about 12 mA was measured — yours may be a little different. Finally, when the base resistor is returned to zero volts (or simply when it’s disconnected!) the collector current again does not flow. So what? What use is this? Not a lot as it stands, but it becomes very important when we calculate the currents involved. We already know the collector current (about 12 mA in our case) but what about the base-to-emitter current (shortened to base current)? The best way to find this is not by measurement (the meter itself would affect the transistor’s operation!) but by calculation. We know the transistor’s base-to-emitter voltage (shortened to base voltage) and we know the supply voltage. 175
Starting electronics From these we can calculate the voltage across the resistor, and from Ohm’s law we can therefore calculate the current through the resistor. And the current through the resistor must be the base current. The resistor voltage is: So, from Ohm’s law the current is: Not a lot! 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 8.9 and is of vital importance — so remember it! Figure 8.9 current Important: a very small base current can control a large collector 176
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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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Capacitors Time (seconds) 5 10 15 2
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Capacitors In a capacitor circuit l
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Capacitors Figure 4.11 An experimen
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Capacitors Time (seconds) Voltage (
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Capacitors plates of the capacitor
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Capacitors where ε is the permitti
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ICs oscillators and filters 5 ICs,
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ICs oscillators and filters Photo 5
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ICs oscillators and filters We’ve
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ICs oscillators and filters an osci
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ICs oscillators and filters (a) (b)
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ICs oscillators and filters Ouch, t
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ICs oscillators and filters output
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ICs oscillators and filters Value o
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ICs oscillators and filters voltage
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ICs oscillators and filters Value o
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ICs oscillators and filters Figure
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ICs oscillators and filters simple
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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
Page 140 and 141: Diodes I but we never said it was a
Page 142 and 143: Diodes I Current (mA) Voltage (V) 0
Page 144 and 145: Diodes I voltages, reverse currents
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 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
Page 194 and 195: Analogue integrated circuits circui
Page 196 and 197: Analogue integrated circuits Figure
Page 198 and 199: Building on blocs Analogue integrat
Page 202 and 203: Analogue integrated circuits As the
Page 206 and 207: Analogue integrated circuits circui
Page 212 and 213: Analogue integrated circuits an app
Page 214 and 215: Digital integrated circuits I 10 Di
Page 216 and 217: Digital integrated circuits I Logic
Page 218 and 219: Digital integrated circuits I If we
Page 220 and 221: Digital integrated circuits I Figur
Page 222 and 223: Digital integrated circuits I It’
Page 228 and 229: Digital integrated circuits I The t
Page 230 and 231: Digital integrated circuits I Trans
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Digital integrated circuits I Figur
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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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