Components
Andrew Singmin4.1 Building Block Components .................................................................................
4.1.1 Resistors
The humble resistor is by far the most prolifi c component in use, so it makes a good
starting point. A resistor, as the name implies, serves to provide some form of resistance,
which is measured in ohms. Even the very name resistor already presents an inkling of
what it does. In its very simplest form, as a stand-alone component, a resistor presents a
resistance to the current fl ow that would normally take place when voltage is applied to a
circuit. A high resistance presents more of an “ obstacle, ” so the resulting current fl ow is
relatively small. However, a low resistance allows more current to fl ow. If a resistor were
connected in series with a current source it would be acting as a current limiter. With
resistors you can carry out a lot of simple experiments that are easy to understand and
explain. For instance, put a resistance in series with a voltage source and a light bulb: as
the resistance goes up, the light dims, and as the resistance goes down, the light brightens.
What could be easier to understand?
If limiting current fl ow through a circuit were all there is to a resistor’s function, then we
wouldn’t have much of a range of circuits to play with. But human ingenuity being what
it is, we (electronics designers) have a lot more uses for the resistor. What can we do with
two resistors? As you will soon see, the ingenuity or cleverness of the application is tied
into the situation in which the resistor is being put to use.
The sole function of humble light-emitting diodes (LEDs) is usually no more than to
produce light and to serve as a solid-state indicator lamp. Driven from a low-voltage
source, the LED nevertheless has to have a current-limiting resistor inserted in series
CHAPTER 4