Figure 2. A voltage spike may have a very high
value, up to several thousand volts, but the duration
is on the order of microseconds.
ers or contactors, or from other causes.
Less common sources include short circuits, static electricity, lightning and even
large electromagnetic fields. While spikes
are short, the increased voltage for even
that short time may be enough to damage
a laser’s microelectronic components
and/or to cause malfunctions.
Voltage spikes are counteracted with
surge protection devices (or surge suppressors). Surge protectors typically divert
excess voltage from the protected power
line straight to the ground, although there
are other techniques. There are a variety
of technologies to choose from, each with
advantages for particular power environments.
A voltage spike (Figure 2) may have a
very high voltage value, up to several
thousand volts, but the duration is on the
order of microseconds.
interference is a
broad term covering
multiple causes, the
net effect of which
is that electromagnetic waves of a
wide spectrum of
interference with the
power signal. This
Figure 3. The HighLight
diode laser from
Coherent Inc. requires
a high-capacity PDU
that can be integrated
within the laser control
noise on an AC power line causes deviation in the signal from the desired perfect
EMI can be classified in several ways.
One way is to identify how interference
gets into the power line, which includes
conduction, capacitive coupling and induction. Another way is to address the
frequencies being added to the signal.
Radio-frequency interference (RFI) identi-fies a subset of frequencies common to
communications and other equipment.
A third distinction is identifying common-mode and differential-mode noise.
Common-mode noise manifests identically
on multiple power conductors where the
noise signal flows in the same direction,
in phase, and typically returns through
ground. Differential-mode noise occurs
when the noise on each power line is not
identical. Here, the noise signal flows
through one power line and returns
The primary defense for reducing inducted noise is shielding. This is commonly, but not exclusively, done to mitigate RFI. Cables and components are
encased in metal, and they may require
additional RFI gaskets with significant
design detail to eliminate all air gaps.
The remaining noise types can be re-
duced through EMI filters and isolation
transformers. Filters use a combination
of capacitors and inductors to block or
divert frequencies outside the 50 or 60 Hz
of the power signal. Isolation transform-
ers provide good reduction of
common-mode noise and
allow an isolated ground that
can offer significant bene-
fits in noise reduction on
downstream power lines
connected to the PDU.
devices, EMI filters,
isolation transformers and
shielding are power conditioning strategies well
suited to integration within
PDUs. Adding these capabilities helps isolate sensitive laser equipment connected downstream of the
PDU from the noise created by upstream power
consumers. When an integrated solution is needed,
work with the PDU manufacturer to identify: