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| Key Elements for COTS Transient Energy Mitigation |
Dr. Brett D Robinson EMI Solutions, Inc. Irvine, CA
Any electronic or electrical designed today must address (4) main considerations
before any type of surge protection can be administered.
1) System Signal Stability
2) System Transient Surge Capabilities
3) System Control & Protection Methods
4) System Restoration Capabilities
**Important Note on COTS Equipment
Since the end of the Cold War, reduced budgets have limited the technology
growth in the defense industry. With the DOD representing less than 1% of
electronics industry procurement, the military has recognized that they can no
longer build an infrastructure independent of the commercial industry. This
realization has necessitated the use of Commercial-Off-The-Shelf (COTS)
equipment, being introduced into today’s military electronic systems.
The commercial electronic industry is forced to comply with many of the same
Military and FAA, EMI/EMC requirements. Due to the cost to relay out and
redesign any new PWB and their related sub-components have left the
commercial electronics manufacturers desperate to use what designs they may
have on hand, and still comply with the new SAE and Medical electronic system
EMI compliance standards
Five predominant types of Transient Energy
Listed below are the key element types of energy that can produce severe
transient surges upon critical circuit paths:
a. Electro Static Discharge
b. System Induced Transient Surge
c. Intense Radiated Frequencies
d. Electro Magnetic Pulse
e. Lightning Induced Transients
CHARACTERIZATION OF A LIGHTNING INDUCED EVENT
The typical lightning strike is comprised of three strokes, with the first stroke
surging up to 20,000 amps, & lasting approximately 30 millionths of a second.
Subsequent strokes are about half that intensity, but on strikes like these (also
known as secondary effects); they can be many times more harmful than the
initial strike. Lightning-induced transients are electrical impulses induced onto a
conductor by simply being in the near vicinity of the lightning strike. These
transients can migrate, or travel considerable distances from the physical strike
location especially when other conductors are present. It is these potentially
harmful voltages and currents that we need to suppress for electrical / electronic
circuitry protection. It is also important to remember that the closer the Lightning
strike is to any affected equipment, and the longer the length of the conductors
are in that surrounding area then the greater the induced energy transient can
become.
Since voltage from a lightning strike rises very fast to its peak, (within a few
millionths of a second); the energy must be returned to an earth ground as
quickly as possible, and is performed via a low impedance path; otherwise,
permanent damage to the victim electronic equipment will definitely occur.
ESD
ESD occurs when two objects having different potentials approach close enough
to each other that sparking occurs. This complex event can be easily simplified
by being broken down into four main phases:
1. Electrostatics, the charging and charge distribution prior to the breakdown.
2. Sparking, is the rapid development of the electrical arc.
3. Fast Transients, is the rapid discharge of electromagnetic energy, during the
first phase of the discharge, and is where electromagnetic waves travel onto a
victim, which can be comprised of either equipment or human.
4. Slower Currents and Charge Re-distribution: After the first current energy
transfer; the induced voltages have been reduced by the unit source reflection
via its grounds, and any further dominating frequencies are now low enough,
such that the event can now be treated as being electrically small.
Note: The build-up of electrons onto any electrical system must dissipate quickly
in order to prevent the induced voltages from looping back into the equipment
TRANSIENT ENERGY COUPLING & INDUCED VOLTAGES
The coupling transient mechanism is brought about primarily due to the current
within its energy field; which is dominated by time relative to some moderate
distances of up to 20 cm away. Further, the coupling from the field, to a wire, and
or circuit trace is a function of the rate of change between the electric and the
magnetic fields produced.
This type of transient event will lead to different pulse shapes from the induced
field currents at the discharge point of entry. The induced voltages from the event
couple onto the circuit traces during the test or attachment; and will create some
permanent degradation to the internal victim circuitry.
One type of degradation is called Latch-up, this transient event is an interruption
of logic circuit functions created by a brief energy pulse and that EM generated
noise, can cause electronic systems to upset; which in turn has the potential of
leading to permanent component damage.
WHAT IS A FILTERED and or TVS PROTECTED CONNECTOR ?
Filtered, TVS, and Filtered / TVS combination protective connectors offer
numerous advantages, including better EMI/ESD/EMP/Transient mitigative filter
performance than any equivalent onboard filters, with savings in pc-board real
estate, savings in costly development time, resources, and a reduction in design
implementation time to market.
A filtered connector looks essentially like any other connector, but, additionally
contains integrated C (capacitive), or PI filtering components; and / or are
combined with transient suppression components that suppress and / or
attenuate, unwanted high frequency conducted noise and energy. The mating
capabilities of for these connectors stay identical to those of their non-filtered
counterparts. Filtered connectors are available in D-Sub, Micro-D, Circular and
Custom formats.
The ground plane is the most important part of any filtered connector. Its primary
purpose is to provide a low-impedance path for the filtering elements to " ground "
to the shell of the connector; thus good shielding methodologies must be used to
achieve a complete grounding path from connector to chassis.
The ground plane’s main purpose is to prevent any radiated energy or highfrequency
noise from coupling onto the connector pins; or to the PC board
termination at the engagement ends of the connector. Simply put, the ground
plane essentially acts like an RF barrier that prohibits interference from breaking
through to the opposite end of the connector.
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