A home-made linear power supply (used here to power
amateur radio equipment)
An
AC powered unregulated power supply usually uses a
transformer to convert the voltage from the wall outlet (mains) to a different, nowadays usually lower, voltage. If it is used to produce
DC, a
rectifier is used to convert alternating voltage to a pulsating direct voltage, followed by a
filter, comprising one or more
capacitors,
resistors, and sometimes
inductors,
to filter out (smooth) most of the pulsation. A small remaining
unwanted alternating voltage component at mains or twice mains
power frequency (depending upon whether half- or full-wave rectification is used)—
ripple—is unavoidably superimposed on the direct output voltage.
For purposes such as charging batteries the ripple is not a problem,
and the simplest unregulated mains-powered DC power supply circuit
consists of a transformer driving a single
diode in series with a
resistor.
Before the introduction of
solid-state electronics, equipment used
valves
(vacuum tubes) which required high voltages; power supplies used
step-up transformers, rectifiers, and filters to generate one or more
direct voltages of some hundreds of volts, and a low alternating voltage
for filaments. Only the most advanced equipment used expensive and
bulky regulated power supplies
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