MEDICAL ELECTRONICS & DEVICES
THINK AHEAD THERMALLY
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imperative if the end user will be in close contact with the device. In these
cases, you will need to set your requirements to account for safety and comfort
rather than the device’s operating limits.
For example, if a device were to feature a power intensive sensor that comes
into proximity with the patient, heat pipes might be a requirement to quickly
and safely remove the heat from the device, even if the device itself can handle
the heat load.
For higher power electronics, no matter where the heat is being dissipated, one
must account for the user’s safety. If using an enclosure, heat must be
dissipated through one of the sides or through a heat exchanger. The user
should be prevented from contacting these surfaces by use of a guard that still
allows airflow but prevents wayward fingers from contact.
How often and for how long will the equipment be in use?
Equipment use must be carefully considered in conjunction with the device’s rejected heat. Devices that are used for
longer stretches of time or with more frequency will likely need more powerful cooling. Constant use devices are likely
going to need active thermal solutions as the device will consistently be generating heat with little to no cooldown
period. Devices used intermittently but often will have a very different set of thermal requirements; as will devices used
infrequently but with high heat loads that need to be cooled quickly.
With smaller heat loads, even if used regularly, a thermal mass might be all that is necessary to conduct the heat away
from the device and dissipate the heat slowly and naturally. If the heat load is considerable, the device will require a
more complex system to dissipate the heat as quickly as possible. High, instantaneous loads may be too much for a
typical thermal solution to handle before the device reaches maximum junction or case temperatures. Heat pipes or
higher power cooling systems, such as liquid solutions, may be required to safely dissipate these loads.
With intermittent use devices, frequency is also a key consideration. When a device is operated so frequently that it
does not have time to fully cool down
between uses, inconsistent power
dissipation must be taken into account. This
is when the heat essentially adds up over
time, causing a higher average operating
temperature than what the device should
be exposed to. These transient loads are
often overlooked in the design phase and
result in inadequate cooling. Additional
analysis may be required prior to solution
design and product layout if there is the
potential for high transient heat loads. The
final cooling solution may be drastically
different when these are taken into
account.
0
1
2
3
4
5
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8
0 5 10 15 20
Watts or K
Time
Example Temperature Rise Response to Transient Power Loads
Power
Temperature
Rise
Think Ahead Thermally - Medical
www.boydcorp.com/aavid
September 2016