Page 252 - Concise Encyclopedia of Robotics

Power Supply
The voltage regulator
If a special kind of diode,called a Zener diode, is connected in parallel with
the output of a power supply, the diode will limit the output voltage of the
supply by as long as the diode has a high enough power rating. The limiting
voltage depends on the particular Zener diode used. There are Zener diodes
to fit any reasonable power-supply voltage.
When a power supply must deliver high current, a power transistor is
used along with the Zener diode to obtain regulation. A circuit diagram
of such a scheme is shown in Fig. 5.
+
From filter Output
_

Power supply—Fig. 5

In recent years, voltage regulators have become available in integrated-
circuit (IC) form.Such an IC,sometimes along with some external compo-
nents, is installed in the power-supply circuit at the output of the filter.
This provides excellent regulation at low and moderate voltages.

Transients and surges
The AC on the utility line does not have a clean, perfect, constant wave
shape.Sometimes there are “spikes”known as transients. These last for only
a few microseconds, but they can reach peak values of more than 1000 V.
Power surges can also present a problem. In a surge, the voltage rises some-
what above normal for a half-second or so. Without some protection
against the effects of transients and surges, sensitive electronic equip-
ment, such as robot controllers, can malfunction.
The simplest way to get rid of most transients and surges is to use a
commercially made transient suppressor, also called a surge suppressor. A
more sophisticated power-processing device is an uninterruptible power
supply (UPS).These are recommended for serious computer users,because
they can prevent problems that would otherwise result from undervoltage
and blackouts, as well as eliminating the effects of transients and surges.

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