voltages and energies vehicle
electronics have to deal with.
Obviously, some of those
transients are pretty severe —
As explained in the
Littelfuse application note,
Suppression of Transients in
an Automotive Environment,
vehicle electronics are already
protected by a central
suppressor in the vehicle,
usually located close to the
master control computer
There are usually
suppressors in other modules around
the vehicle, too. This helps limit the
voltages and energies to which your
gadgets and radios are exposed.
Nevertheless, it’s a good idea to
provide some limited protection by
using protective components on
input and output connections.
Another source of transients —
well-known to inhabitants of areas
with dry weather — is electrostatic
discharge, or ESD. A sudden
discharge of static electricity by a
spark — such as from walking across
a carpet and then touching a
grounded surface — is a typical
example of ESD.
In fact, the standard ESD test
generator uses a finger-shaped probe.
There can be enough energy in an
ESD pulse to destroy semiconductors
or scramble the operation of a circuit.
A typical ESD transient lasts for
less than a microsecond (see Figure
6), but can generate voltages up to
15 kV! ESD transients can appear on
power and signal wiring, connectors,
controls and switches, displays —
anything a finger can touch or
approach ... even metal enclosures.
Because the pulses are short, the
most effective strategy is to use an
RC circuit to slow down the voltage
rise as in Figure 7.
Direct hits from lightning can be
devastating, but even an indirect or
nearby strike can generate pretty
significant transients. These fast-rising
transients have energies equal to or
larger than the automotive inductive
transient, and with voltages nearly as
high as an ESD pulse.
Hams having erected towers and
antennas have out of necessity
developed a wide range of
techniques dealing with lightning’s
effects — ranging from grounding and
bonding techniques through voltage
A number of tutorials and related
articles and standards are available at
Both input and output
connections from your equipment
need protection from lightning and
ESD. Depending on your budget and
the power levels involved, there are a
number of different components you
Low power protection can be as
simple as an RC low pass filter to
damp and absorb transients.
At higher power levels, you’ll
need to use more robust
components and possibly apply
several different techniques to
provide overlapping layers of
protection. It is not unusual to find
clamping diodes, EMI and ESD filter
capacitors, and a beefy MOV all
connected to the same circuit!
The following components give
you several ways to protect
74 November 2015
FIGURE 6. A typical ESD transient
waveform specified by standard IEC
61000- 4-2. Peak voltage from an ESD
transient can reach 50 kV. Pulse voltages
can be either positive or negative
(based on Littelfuse reference 6).
Table 1 — Typical Vehicle Transients.
Type Voltage Energy (Joules) Duration Occurs
Load Dump <125V > 10 J 200-400 msec Infrequently
Field Decay -100V to +40V <1 J 200 msec At turn-off
Inductive -300V to +80V <1 J <320 μsec Often
Mutual Coupling <200V <1 J 1 msec Often
FIGURE 5. The load dump transient that
occurs when the connection between a battery
and the alternator opens during charging. Peak
voltage can be more than 100V and the transient
can last for nearly 1/2 second (based on Littelfuse