Electronic Devices and Amplifier Circuits

Chapter 3 Bipolar Junction TransistorsNPNPNPE BE BCathode AnodeAnode CathodeNPNPNPBAnodeCCathodeBCathodeFigure 3.2. Transistors configured as diodesTransistors are used either as amplifiers or more commonly as electronic switches. We will discussthese topics on the next section. Briefly, a typical NPN transistor will act as a closed switch whenthe voltage V BE between its base and emitter terminals is greater than 0.7 V but no greater than5 V to avoid possible damage. The transistor will act as an open switch when the voltage V BE isless than 0.6 V . Figure 3.3 shows an NPN transistor used as an electronic switch to perform theoperation of inversion, that is, the transistor inverts (changes) an input of 5 V to an output of0 V when it behaves like a closed switch as in Figure 3.3, and it inverts an input of 0 V to an outputof 5 V when it behaves like an open switch as in Figure 3.4.CAnodeV CC=5 VV CC=5 VV in= V BE= 5 VBR CCV outV CE 0 VE= =R CV in5 V 0 VFigure 3.3. NPN transistor as electronic closed switch − inverts toLike junction diodes, most transistors are made of silicon. Gallium Arsenide (GaAs) technologyhas been under development for several years and its advantage over silicon is its speed, about sixtimes faster than silicon, and lower power consumption. The disadvantages of GaAs over silicon isthat arsenic, being a deadly poison, requires very special manufacturing processes and, in addition,it requires special handling since it is extremely brittle. For these reasons, GaAs is much moreexpensive than silicon and it is usually used only in superfast computers.3−2Electronic Devices and Amplifier Circuits with MATLAB® / Simulink® / SimElectronics® Examples, Third EditionCopyright © Orchard Publications