CIE Sept09 P10-11:Layout 1 07/09/2009 13:17 Page 11
EMC & Circuit Protection
components are contained
within one device.” A
reduced component
Making an MOV
count delivers a number
of cost saving benefits,
Historically, MOVs were high
Ellis noted.
voltage single layer radial leaded
The drawback of TVS
components. Today, they are most
diodes can be clearly
commonly seen in surface mount
seen in the images. Not
form utilising a multilayer Figure 8
only are extra piece
construction. Syfer has taken the
parts required to mount and
technology further to produce
connect the diodes to the pins
multilayer MOVs in planar array and
Testing an MOV
but those extra parts add
discoidal formats. Syfer MOV arrays have been tested to
significant bulk and weight. The
The MOV base material consists of RTCA DO160-E section 22 waveform
varistor planar array can be
zinc oxide, doped with small 4 level 5 and waveform 5 level 3.
manufactured to the same
quantities of bismuth, cobalt and (See Figure 8) 47V and 8V parts were
dimensional specifications and
manganese amongst other metal tested for leakage current, nominal
tolerances as the capacitor planars
oxide additives. It is built up from voltage and clamp voltage. The same
Figure 6
used in the connector. This means
layers of the zinc oxide interleaved parts were then subjected to 500
Figure 6 shows the typical format that adding transient suppression to
with platinum forming the highly pulses at 10s intervals and then
of an MOV protected connector, with a design which already has a
conductive electrodes. re-measured. Failure
the MOV on the left , and the other capacitor planar array, need not have
During firing, the dopants is defined as a
two capacitor planars with ferrite an impact on the size of the
within the dielectric greater than 10%
beads in between forming an connector. See Figure 6.
material migrate to the shift in parameters.
unbalanced Pi filter. In summary, no other transient
grain boundaries and No failures were
The main alternative to MOV voltage suppression technology can
cause each grain to act as observed.
planar arrays is the TVS (transient match the MOV planar when it
a P-N junction with an Testing has also
voltage suppression) diode. Both comes to efficient use of connector
activation voltage of been undertaken in
technologies have their advantages. real estate. The combination of MOV
approximately 3.6 volts. order to demonstrate
“Diodes are available for lower planar and capacitor planar arrays
In order to achieve higher the speed of
working voltages,” Ellis commented, provides sophisticated filtering for
working voltages many
Figure 7
response capabilities.
“and they also have lower leakage low level interference as well as high
layers of ceramic are used, Parts were subjected
and sharper clamping characteristics.” voltage spikes. And prices are
the grains are effectively linked in to a 1MHz 175V square wave with a
He pointed out that MOVs can competitive with alternative
series and parallel creating multiples rise time of less than 400ns. Figure 7
compete on energy and current technologies too!
of their discrete properties. shows the response of a 47V working
capabilities. “But a key advantage is
Syfer’s unique ‘wet-stack’ process planar. Note there is no voltage
that MOVs are considerably more
Syfer Technology Limited
ensures a stress-free component is overshoot present prior to full
volumetrically efficient, as many
| www.syfer.com
produced with mechanical precision. clamping.
www.cieonline.co.uk Components in Electronics September 2009 11
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