PROBLEMS 415
products. Interdisciplinary experts who can blend many different technologies harmoniously are
rather rare.
Let us think for a moment about various electronic and electric systems in an automobile of
today. Only a few of those are listed here:
- Body electronics:Airbags, security and keyless entry, memory seats and mirrors
- Vehicle control:Antilock brakes, traction control, electronic navigation, adaptable suspen-
sion systems
- Power train:Engine and transmission, cruise control, electronic ignition, four-wheel drive
- Instrumentation:Analog/digital dash, computerized performance evaluation and mainte-
nance scheduling, tire inflation sensors
- Communications and entertainment:cellular phone, AM/FM radio, CD/tape player, digital
radio
- Alternative propulsion systemssuch as electric vehicles, advanced batteries, and hybrid
vehicles are being developed. Fiber-optics in communications andelectrooptics, replacing
the conventional wire harness, are already in practice.
In recent years, the conventional electric ignition system has been replaced byelectronic
ignition. Mechanically operated switches, or the so-called points, have been replaced by bipolar
junction transistors (BJTs). The advantages of transistorized ignition systems over the conven-
tional mechanical ones are their greater reliability, durability, and ease of control. The transistor
cycles between saturation (state in which it behaves as a closed switch) and cutoff (state in
which it behaves as an open switch). The ignition spark is produced as a result of rapidly
switching off current through the coil. Modern engine control systems employ electric sensors
to determine operating conditions, electronic circuits to process the sensor signals, and special-
purpose computers to compute the optimum ignition timing.
Automotive electronics has made tremendous advances, and still continues to be one of
the most dominating topics of interest to automotive engineers. Certainly, today’s mechanical
engineers have to be familiar with electronic circuit capabilities and limitations while they try to
integrate them with mechanical design and material science.
Problems
8.1.1A siliconnpnBJT is biased by the method shown
in Figure 8.1.1, withRE= 240 ,R 2 = 3000 ,
andVCC=24 V. The operating point corresponds
toVBEQ= 0 .8V,IBQ= 110 μA,VCEQ=14 V,
andICQ=11 mA. DetermineRCandR 1.
8.1.2By using the rule-of-thumb procedure indicated
in the text, find values of all resistors in the bias
method of Figure 8.1.1 withVCC =10 V for
a siliconnpnBJT for whichβ=100 and the
operating point is given byICQ=5 mA.
8.1.3A fixed-bias method is illustrated in Figure P8.1.3.
AssumingICBOto be small compared toIBQand
ICQ, findRBsuch that the operating point corre-
sponds toICQ=14 mA,VCEQ=7 V, when
VCC=12 V and the silicon BJT has a nominal
β=70. Also determineRC.
*8.1.4Consider the collector–base biasing method
shown in Figure P8.1.4. With the same data as
in Problem 8.1.3, findRBandRC.
8.1.5A BJT is biased by the method shown in Figure
P8.1.5. IfVBEQ= 0 .7V,β=100,VCEQ= 10
V, andICQ=5 mA, findI 1 ,I 2 , andIEQ.
8.2.1For the method of biasing a JFET shown in Figure
8.2.1 of the text, use the design procedure outlined
there to findVG,RS,RD,R 2 , andR 1 , given that
