medical equipment is in use—the noise generated by a
constantly whirring fan motor is unacceptable for patients
In harsh and rugged conditions, where using fans
to reduce heat is either not practical or unreliable,
designers look for alternative, fanless cooling techniques
to dissipate heat away from the PSU and to improve
potential power conversion capacity, performance, and
component life cycle.
Figure 1, for example, shows how the power output
capacity is derated as ambient temperatures rise.
Designers can employ a range of conductive-cooling
methods, such as heat sinks, heat pipes or cold plates, to
conduct heat through cooler materials and away
from the PSU or other electronic components. A heat
sink consists of a metal attachment connected to the
PSU or another component to conduct the heat away
from its source (see Figure 2). Heat sinks, while simple,
can take up valuable physical space that might be better
used for other purposes while also adding weight to the
Using a heat pipe to conduct heat away involves the use
of a pipe with a circulating liquid. One end of the pipe is
in contact with the hot surface, which vaporizes the liquid.
When the vaporized liquid encounters the cooler surface
in the pipe, it condenses back into a liquid state and
recirculates through the cooling system. Heat pipes can be
effective in carrying heat away from the heat source to a
heat transfer mechanism, yet designers need to cope with
the additional space requirements and the potential for
leaks damaging the electronics.
A third method, a cold plate, relies on a fluid—either
water or some other refrigerant—to remove heat.
Typically, the cold plate has small pipes in metal casings
Figure 2: GE’s CCR0512 fanless PSU employs heat sinks to
dissipate heat. (Source: GE)