Page 290 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Electrical systems 273

+
+
+ −
+ − − −
+ − − − − −
+ −

+ −

Figure 3.31 Resistors in use Figure 3.32 Capacitor operation

is for data transmission of between 100 kbits and 1 Mbits per second. It is used
for rapid control devices. The other variation transmits data between 10 kbits and
100 kbits per second. It is used for switching and control operations.

3.1.3 Electronic components

Resistors are probably the most widely used component in electronic circuits
( Fig. 3.31 ). Two factors must be considered when choosing a suitable resistor,
namely the ohmic value and the power rating. Resistors are used to limit current
fl ow and provide fi xed voltage drops. Most resistors used in electronic circuits
are made from small carbon rods; the size of the rod determines the resistance.
A thermistor is a resistor that changes resistance with temperature.
A capacitor is a device for storing an electrical charge ( Fig. 3.32 ). In its simple

form, it consists of two plates separated by an insulating material. One plate can
have excess electrons compared to the other. In vehicles, its main uses are for
reducing arcing across contacts and for radio interference suppression circuits,
as well as in ECUs.
Diodes can be described as one-way valves ( Fig. 3.33 ). For most uses, this is Defi nition
a good description. The diode is made from two types of silicon (N type and P Zener diode
type). Electrons can fl ow from negative (N-type) to positive (P-type) material, but A type of electrical pressure-relief
not the other way. Zener diodes are very similar in operation except that they are valve.
designed to conduct in the reverse direction at a preset voltage. They can be
thought of as a type of pressure-relief valve.
Transistors are the devices that have allowed the development of today’s
complex and small electronic systems ( Fig. 3.34 ). The transistor is used either as
a switch or as an amplifi er. Transistors are constructed from the same materials
as diodes but with three terminals. A small voltage (about 0.7 V) supplied to the
base terminal of a transistor known as an NPN will cause it to fully switch on,
joining the collector and emitter. It is sometimes useful to think of a transistor as
a type of relay. However, with a transistor, a smaller voltage will partially switch
the collector–emitter circuit on and hence the component works as an amplifi er.
Inductors are most often used as part of an oscillator or amplifi er circuit. In
these applications, it is essential for the inductor to be stable and of reasonable
size. The basic construction of an inductor is a coil of wire wound on a former.