to be included in the RMF document. Devices
with patient contact (MOPP, means of patient
protection) require two isolation barriers for
electrical safety, an important requirement in
power modules. The first barrier on the supply
side has so far been implemented in a medical
PSU, while reinforced isolated DC/DC converters
provide the second isolation barrier between
the medical electronics and diagnostics tools,
such as endoscopes and ECG electrodes, to
double the safety.
One new feature of the third edition is that it
separates off operator protection; in theory, clear-
ance and creepage distances as defined in
EN60950-1 for electronic equipment are enough
for devices without patient contact intended for
protecting operating staff (MOOP). You might
interpret this as a relief, but the requirement for
very low operating current also needs to be ob-
served according to EN60601, so manufacturers
would be well-advised to limit their possibilities
and use medically isolated converter modules in
MOOP devices as well.
As a leading DC/DC converter manufacturer,
Recom supply a broad range of medical converter
modules certified according to the third edition
with double MOPP for direct patient contact
such as our RxxP, RxxP2, RV, REC3.5 and REC6
(1, 2, 3.5 and 6 watt) lines. Transformer clearance
and creepage distances in these reinforced isolated
converters have to be three times the size as
those used in industrial settings. So far, this has
been implemented with primary and secondary
windings on opposite sides of a toroidal core
separated by a partition wall in the middle. That
deals with the isolation issue, but the magnetic
fields would not be able to overlap due to the
spatial separation between the two windings.
An unpleasant side-effect would be a decrease
in efficiency in the two transformers resulting
in increased heat losses. Recom engineers have
developed a small transformer with primary
and secondary windings interlocked in such a
way as to ensure virtually optimal overlapping
magnetic fields despite the creepage and clearance
distances required for reinforced isolation. The
new converters achieve fifteen to twenty percent
more output in the same casing due to quasi-
resonant circuit topology, and are also approved
for ambient temperatures of up to 85°C – around
15°C more than most transformers with con-
ventional toroidal-core transformers – due to
the low heat loss. Depending on type, we were
able to reduce isolation capacitance to values
down to 1.5pF, ensuring lower leakage current
as required in medical electronics.
A complete generation of highly isolated con-
verters for medical applications has emerged
from this new transformer design, such as in
programming devices for pacemakers, blood gas
analysers and oxi-meters. The RxxP and RxxP2
series cover the 1W and 2W classes and are avail-
able in SIP7 casings. The 2W version is available
as an RV series in DIP24 casings for pin compat-
ibility with legacy designs. The REC3.5 and REC6
series both provide 3.5W and 6W, respectively,
and also come in a DIP24 casing. The models
quoted are available with isolation voltages up to
8kV DC and 10kV DC.
Apart from the reinforced isolated converters
mentioned, there are many other product lines in
the product range approved for medical applica-
tions without patient contact (MOOP) – regulated
and unregulated SMD converters with power rat-
ings from 0.25W to 2W (RxS family) as well as a
wide variety of different converters up to 6W.
n
17
April 2014
P
OWER
M
ODULES
Figure 2. Visual comparison between a reinforced isolated REC3.5 (right) and a single isolation
REC3 that is unsuitable for applications with patient contact (left).
