eakage Current
I
L
Current passing through the varistor at rated DC voltage at 25°C or any
other specified temperature.
Varistor Voltage
V
N
Voltage across the varistor measured at 1mA of DC current.
Clamping Voltage
V
C
Maximum peak voltage developed across the varistor when passing an 8/20
µs class current pulse.
Class Current
I
C
A peak value of current which is 1/10 of the maximum peak current for 100
pulses at two per minute for the 8/20 pulse.
Voltage Clamping
Ratio
V
C
/

V
APP
A figure of merit measure of the varistor clamping effectiveness as defined
by the symbols V
C
/ V
APP
, where V
APP
= V
RMS
or V
DC
.
Single Pulse
Transient Energy
W
MAX
Energy that may be dissipated for a single 10/1000 µs pulse of a maximum
rated current, with rated AC/DC voltage applied, without causing device
failure.
Load Dump
Transient
W
LD
Load Dump is a transient, which occurs in automotive environment. It is an
exponentially decaying positive voltage that occurs in the event of a battery
disconnect while the alternator is still generating charging current with other
loads remaining on the alternator circuit at the time of battery disconnect.
Single Pulse Peak
Current
I
P
Maximum peak current that may be applied to the varistor for a single 8/20
µs pulse, with line voltage applied, without causing device failure.
Average Power
Dissipation
P
MAX
Maximum average dissipated power at 25°C resulting from a group of pulses
occurring within a specified isolated time period, without causing device
failure.
Capacitance
C
(TYP)
Capacitance between two terminals of the varistor measured at 1 kHz.
Inductance
L
Inductive component of the varistor when measured with a current edge rate
(di/dt) of 100mA/ns. Values are typically measured in nanohenries (nH).
Jump Start Transient
V
JUMP
The jump start transient results from the temporary application of an over-
voltage in excess of the rated battery voltage. The circuit power supply may
be subjected to a temporary over-voltage condition due to the voltage
regulation failing or it may be deliberately generated when it becomes
necessary to boost start the car.
Response Time
The time lag between application of a surge and varistor's "turn-on"
conduction action.
Varistor Voltage
Temperature
Coefficient
(V
N
at 85°C - V
N
at 25°C) / ((V
N
at 25°C) x 60°C) x 100
General Information Varistor Plus
SEI Electronics Inc. P.O. Box 58789 Raleigh, NC 27658-8789 Telephone: (919) 850-9500 FAX: (919) 850-9504
Toll Free: (888) SEI-SEI-SEI www.seielect.com email: marketing@seielect.com ISO 9002 / QS 9000 Registered
2
Single Layer Technology
Varistor Glossary of Terms and Definitions
Term
Symbol
Definition
Insulation
Resistance
IR
Minimum resistance between shorted terminals and varistor surface.
Isolation Voltage
The maximum peak voltage that may be applied under continuous operating
conditions between the varistor terminations and any conducting mounting
surface.
Operating
Temperature
The range of ambient temperature for which the varistor is designed to
operate continuously, as defined by the temperature limits of its climatic
category.
Storage
Temperature
Storage temperature range without voltage applied.
Current/Energy
Derating
Derating of maximum values when operated above 85°C. Varistor Plus
SEI Electronics Inc. P.O. Box 58789 Raleigh, NC 27658-8789 Telephone: (919) 850-9500 FAX: (919) 850-9504
Toll Free: (888) SEI-SEI-SEI www.seielect.com email: marketing@seielect.com ISO 9002 / QS 9000 Registered
3
Single Layer Technology
Overview of Protective Devices (by Varistor Series)