Emphasis On Resistors
If lives are at stake, the choice for custom magnetic
components is Datatronics Romoland, Inc. We’re designed
into implantable pacemakers, portable defibrillators,
pacemaker-defibrillators, brain therapy devices, dental
equipment and more.
Our line of custom magnetic components include:
> Hi-Voltage Transformers
> Power and Swithing Transformers
> Sense Coils
> Fine Wire Magnetics (to 56 AWG)
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to simply decrease the diameter of the wire so
that it is fine enough to handle this new voltage. However, most defibrillators will endure
a voltage of around 2,500 V. At that point, the
diameters required can become restrictive.
In short, it is generally easier to design an
alumina resistor to handle the current pulse
than it is to design a wirewound resistor to
handle the extreme voltages experienced by
defibrillators and their monitoring equipment.
Small Size and Dependability
That same small size that can cause high current pulse handling concerns can also serve as
an asset for alumina substrate-based resistors.
In fact, their small size and resiliency have
actually contributed to advancements in the
medical field. Public access defibrillators, also
known as automated external defibrillators
(AEDs), are designed for use by a layperson
outside of a hospital environment. With the
advent of this technology, victims of cardi-
ac dysrhythmias, ventricular fibrillation, or
pulseless ventricular tachycardia no longer
have to wait until arriving at the hospital for
treatment, and this reduction in wait time
is life-saving. In order for these AEDs to be
viable, however, they need to be miniatur-
ized to a small portable device and withstand
harsher temperatures and humidity than their
counterparts in hospitals.
Alumina substrate based resistors have
provided the miniaturization necessary to
make this possible. As mentioned previously,
with alumina substrate, manufacturers can
print resistors directly onto the surface of
the substrate. These resistors are very thin,
approximately the same height as the copper
conductive traces on a PC board, and can
be fitted into a space-saving planar package.
Manufacturers can also place components directly on top of these resistors while still making conductor traces between them, doubling
the space utilization. While components such
as transistors and diodes must still be surface
mounted on alumina substrate, the space
saved on resistors adds up to big benefits.
Alumina’s ceramic properties also contribute to its compactness. With wirewound
resistors, the entire resistor is wrapped in
conductive wire, so designers must be careful
about placing other elements too close to the
resistor. If a conductive component is placed
too close to the wirewound resistor, it may
arc or cause a fault. Alumina, on the other
hand, will be conductive on one side (the side
where the conductive and resistive pastes
were deposited) and non-conductive on the
other. As a result, designers can place other
elements very close to the backside of the
resistor without worrying about a fault or arc.
Should a fault occur, the failure mode of an
alumina resistor is still an open circuit.
In summary, alumina substrate technology
offers a variety of benefits to medical device
designers and engineers, especially for the optimization of defibrillators and their monitoring equipment. As one of the most commonly
used resistors in the industry, it offers distinct
advantages that include high resistance values,
excellent high voltage handling, small size,
and tight tolerances.
For more information, visit www.ohmite.com.