130 Chapter 4
the LM 386 audio power amplifi er on a chip! It’s actually been around for a considerable
number of years, but it is still very widely used. One IC and two capacitors and you’re
in business—wow! The current consumption is pretty good, too. The LM 386 IC is an
example of a special function IC that is designed to deliver (which it does admirably) just
one unique function. The unique one function for the LM 386 IC is as an audio power
amplifi er. It’s hard to believe that a small eight-pin plastic part, a little bigger than one
of the buttons on your TV remote, packs such a technological punch. This particular IC
runs nicely off a regular 9-volt battery—there are no weird dual supplies to worry about.
Many of other higher power ICs require dual supplies, or voltages of 12 volts and higher
(a 12-volt battery that you can’t buy off the shelf and that would fi t in a project case), and
consume masses of current.
Integrated circuits fall into two broad categories: analog and digital. They are very easily
recognized in terms of their functionality and also in terms of the way they’re depicted
in circuit schematics. Analog ICs process mostly AC signals, but they also process DC
signals. The absence of a coupling capacitor at the input would signify that this is a DC
amplifi er we’re looking at. A DC amplifi er has to be capable of amplifying DC signals
as well as AC signals. Analog signals, such as audio signals, require coupling capacitors
at the input and output because only AC signals are allowed to be coupled through
the amplifi er. The presence of coupling capacitors removes the DC components. The
schematic is also drawn in the form of a sideways triangle representing the IC. Input goes
into the wide end on the left and exits as an output from the pointed end on the right. In
essence, all analog IC blocks resemble this basic form. Typical examples of analog ICs
are the LM 741 general-purpose op-amp in an 8-pin DIL package and the LM 324 quad
op-amp package in a 14-pin DIL package. When space is at a premium, the LM 324 is
a superb device; it is especially suited for audio applications and occupies far less board
space than do four separate LM 741s. Analog ICs, incidentally, are also called linear
ICs. Digital ICs only use two voltage states, a logic high (1) and a logic low (0). There
are no capacitors in the signal coupling lines, and the schematics are generally drawn in
the shape of rectangles or squares. Typical examples can be found in the 7400 series of
digital TTL ICs. There are no digital ICs used in this book, but it’s worthwhile to make a
quick mention of them here because they’re such a major portion of the IC family.
The third group of ICs covered in this book are special function ICs, that is, devices
falling into neither the analog nor the digital category. Analog or digital ICs don’t really
do anything by themselves, so to speak. To turn an LM 741 into an amplifi er (which is