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Most electronic circuits
need a DC supply such as
a battery to power them. Since the mains supply
is AC it has to be
converted to DC to be
useful in electronics.
This is what a power
supply does.
First the AC mains
supply passes through an
isolating switch and
safety fuse before it
enters the power supply
unit.
In most cases the high
voltage mains supply is
too high for the
electronic circuitry.
It is therefore stepped
down to a lower value by
means of a Transformer.
The mains voltage can be
stepped up where high DC
voltages are required.
From the transformer the
AC voltage is fed to a
rectifier circuit
consisting of one or
more diodes.
The rectifier converts
AC voltage to DC
voltage.
This DC is not steady as
from a battery. It is
pulsating.
The pulsations are
smoothed out by passing
them through a smoothing
circuit called a filter.
In its simplest form the
filter is a capacitor
and resistor.
Any remaining small
variations can, if
necessary, be removed by
a regulator circuit
which gives out a very
steady voltage.
This regulator also
removes any variations
in the DC voltage output
caused by the AC mains
voltage changing in
value.
Regulators are available
in the form of
Integrated Circuits with
only three connections. |
