Varistor MOV

Varistor Products Overview
April 7, 2010
CIRCUIT
PROTECTION
SOLUTIONS
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Agenda
1. MOV (Metal Oxide Varistor) fundamentals
- Mechanism of operation
- Electrical Characteristics
2. MOV / MLV (Multi-Layer Varistor) types
and applications
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Transient Surges are Everywhere
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• LOAD DUMP
• INDUCTIVE LOADS
• TRANSIENT BURSTS
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PANELS
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EQUIPMENT
• ESD
HOME
ENTERTAINMENT
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MOV Definition
 An MOV, or Metal Oxide Varistor, is a voltage suppression
device that clamps a transient in an electrical circuit. It is also
called a Varistor , or variable resistor, because its resistance
changes with applied voltage. Sometimes they are referred to
as a VDR, or Voltage Dependant Resistor, by some
manufacturers.
 An MOV is a voltage dependent device which has an electrical
behavior similar to back to back zener diodes.
 When exposed to high voltage transients, the MOV’s resistance
changes from a near open circuit to a very low value, thus
clamping the transient voltage to a safe level.
 The potentially destructive energy of the incoming transient
pulse is absorbed by the Varistor, thereby protecting vulnerable
circuit components.
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Terms




Voltage Transients
Surges
Voltage Spikes
Overvoltage events (short duration)
All mean the same thing.
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Lightning
Transients
70 Volts at 1 mile
10,000 Volts at 500 feet
Underground wires
Electromagnetic coupling into
overhead and buried wires
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ESD Electro-Static Discharge
Walking across a carpet:
35,000 Volts @ RH = 20%
500 Volts @ RH = 65%
Walking across a vinyl floor:
12,000 Volts @ RH = 20%
250 Volts @ RH = 65%
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Clamping action
Transient on
Line
Energy Dissipated
Vline
Vline
Clamp Voltage
Line
MOV
Ground
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MOV Electrical Parameters
Voltage Rating, Energy Peak Current Varistor Voltage
Continuous
at 1mA
VDC
VAC
VDC
Joules
Amps
130
170
100
10000
operating voltage
185 min 225 max
Varistor voltage
1 pulse energy
rating
Clamp Voltage Capacitance
8x20µS
(typical)
Vpeak Amps
pF
340
100
1900
clamp voltage at
specific current
typical
capacitance
1 pulse current
rating
After only 1 hit of these two max limits,
the MOV will need to be replaced.
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V-I curve characteristics
1.
Leakage/Low current region
Acts as a large resistor until
reaching the clamping region.
2.
Clamping Region
Acts as a conductor in this region.
Conducts large amount of current
for a small increase in voltage
3.
High Current/Upturn region
Lower lifetime when used in this
region
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V-I curve characteristics
1.
Leakage/Low current region
Acts as a large resistor until
reaching the clamping region.
2.
Clamping Region
Acts as a conductor in this region.
Conducts large amount of current
for a small increase in voltage
3.
High Current/Upturn region
Lower lifetime when used in this
region
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V-I curve characteristics
1.
Leakage/Low current region
Acts as a large resistor until
reaching the clamping region.
2.
Clamping Region
Acts as a conductor in this region.
Conducts large amount of current
for a small increase in voltage.
3.
High Current/Upturn region
Limited lifetime when used in this
region.
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V-I curve characteristics
For the same MOV
voltage rating:
• Small diameter parts
have a higher clamp
voltage.
• Large diameter parts
have higher current
capability
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Continuous Power Dissipation
MOVs are only used for transient
suppression, and not continuous voltage
regulation. Their power rating for
continuous current is very low. Their
power rating for brief millisecond
transients is very high.
Leakage Current
Leakage current will increase as the
temperature rises.
MOV voltage
MOV Characteristics
MOV current
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Pulse Rating Curve
• Guaranteed lifetime,
meaning less than a 10%
shift in Varistor Voltage.
How many
events before
replacement
• High current events will
rapidly decrease lifetime.
• Wide transients such as
100mS should be avoided.
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MOV selection
1.
Continuous Voltage Rating, RMS or DC, should be >110% of the
maximum expected voltage.
2. Device size depends on the transient energy or current expected or on the
required clamping voltage.
3. Energy and Peak Current ratings are a measure of capability.
4. Max Clamping voltage is a reference point on the V-I curve and is a
measure of the protection level.
5. Varistor voltage can be used for Incoming Inspection and internal
manufacturing test purposes.
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MOV Selection Table
Voltage range
Energy
Normal use
Series
130 - 1000
11 - 360
AC Power Lines
PCB through-hole mounting
LA
CIII
UltraMOV - TMOV
130 - 275
11 - 40
Low Energy
Surface Mount
CH, SM7
130 - 750
270 - 1050
High Energy
Chassis and Board Mount
DA, DB
HA, HB, DHB
130 - 880
450 - 3200
Primary Power Line
Heavy Industrial, Chassis Mount
BA
1100 - 2800
3800 - 10000
Motors, Switch Gear
Heavy Industrial, Chassis Mount
BB
5.5 - 460
.1 - 52
Low Voltage
PCB through-hole mounting
ZA
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MOV Radial Portfolio
5 Series of Leaded MOVs
LA
Lowest energy 130V - 1000V
UltraMOV Medium energy 130V - 625V
C-III
Highest energy 130V - 320V
ZA
Low energy
Low voltage
TMOV
Medium Energy 115 – 750V
Thermally protected
5V – 460V
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MOV Radial Sizes
Disc Diameter (mm)
LA ……………..…… 5 , 7, 10, 14, 20
Diameter
UltraMOV ……….…. 7, 10, 14, 20, 25
C III…………………………………...…14, 20
ZA ……..………….…. 5, 7, 10, 14, 20
TMOV……………..................………14, 20, 25, 34
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MOV Radial Ratings
Peak Current
Series
7mm
10mm
14mm
20mm
25mm
LA
1.2kA
2.5kA
4.5kA
6.5kA
C III
6.0kA
9.0kA
UltraMOV 1.75kA
3.5kA
6.0kA
10.0kA
22kA
ZA
100-1.2kA 250-2.5kA 1- 4.5kA 2- 6.5kA
TMOV
6kA
10kA
20kA
34mm
40kA
Energy
Series
7mm
LA
11-35
C III
UltraMOV 12.5-48
ZA
.4-10
TMOV
10mm
14mm
20-70
38-220
70-360
45-130
90-220
50-200 100-400 230-890
3.5-35
7-52
35-6000 52-480 170-670 235-1050
25-100
.8-18
20mm
25mm
34mm
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TMOV Thermally Protected MOV
What is the TMOVTM Varistor?
•
•
•
The TMOV Varistor is a Metal Oxide Varistor with an
integrated thermally activated element.
The device will automatically and permanently opencircuit when overheating occurs due to certain
sustained over-voltages thereby providing additional
thermal safety for the circuit. The MOV will become
permanently disconnected.
The integrated thermal element means it will not flame,
fragment or scorch when subjected to an abnormal
sustained over-voltage condition defined in UL
Standard 1449.
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TMOV and iTMOV
TMOV
iTMOV
Thermal
Fuse
Monitor Lead
MOV
Line
Line
Neutral
Diode
To Protected Circuit
TMOV
Fuse
LED
Normally On
iTMOV
R
To Protected Circuit
Fuse
Neutral
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TMOVTM Varistor
Typical TMOV body temperature during UL1449 limited current
abnormal overvoltage test
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Application solutions
Typical installation for plug-in
or permanently wired equipment
Equipment
Fuse
AC Power
Input
Washing Machine
Microwave
TV
Set Top Box
Radio
PC
etc
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Application solutions
Typical MOV placement at power supply input
Line
Neutral
Ground
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Application solutions
MOV placement with line-to-ground isolation
Line
Neutral
GDT in series with MOV
Ground
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Set Top Box Power Supply
 Fuse provides overcurrent protection.
 Primary protection provided by MOVs.
 Further protection can be provided by including
additional MOVs on the secondary side.
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MOV Industrial Series
Description
 Leaded and Packaged Devices for Hi Energy
applications.
 Several mounting variations are available.
 Technology is similar to the Radial leaded devices.
 All series are in the range 130VAC and up.
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Industrial Series Summary
Series
CA
HA
HB/DHB
DA/DB
BA
BB
Size
60mm
32mm
40mm
34mm
40mm
60mm
60mm
Voltage
250 - 2800VAC
130 - 750VAC
130 - 750VAC
130 - 750VAC
130 - 750VAC
130 - 880VAC
1100 - 2800VAC
Package
Bare disc
Bolt or thru-slot board mount
Bolt or thru-slot board mount
Box, upright or flat.
Box, upright
Box, upright
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Industrial Series
HA
Series
Solderable contacts
Voltage range
Size (Dia)
130VAC - 750VAC
32 / 40mm
Part Number : V321HA40
VAC where 1 = x10
i.e. 321 = 320VAC
Disc Diameter
A=Bolt on terminal
C= PCB mount
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Industrial Series
HB
Series
Solderable contacts
Voltage range
Size
130VAC - 750VAC
34mm square
Part Number : V321HB34
VAC where 1 = x10
i.e. 321 = 320VAC
Disc Diameter
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Industrial Series
DA/DB
Series
Screw contacts
Voltage range
Size (Dia)
130VAC - 750VAC
40mm
Part Number : V321DA40
Vrms where 1 = x10
i.e. 321 = 320VAC
Disc Diameter
Different box style, A or B
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Industrial Series
BA/BB
Series
Screw contacts
Style
BA
BB
Voltage range
Size (Dia)
130VAC - 750VAC
1100VAC – 2800VAC
60mm
60mm
Part Number : V321BA60
VAC where 1 = x10
2 = x100
i.e. 321 = 320VAC
Disc Diameter
Different box style A and B
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Test Levels
 All standards attempt to apply levels of severity to the described
waveforms, example: ANSI 62/UL1449
Waveform
A
B
0.5ms-150kHz
6kV
200A
6kV
500A
1.2 / 50us
8 / 20us
6kV
3kA
C
10kV
10kA
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Industrial Applications








Industrial Controls
Motor Drives
Generator Protection
Industrial Distribution Panels
Electric Locomotives
Thyristor Power Switching Protection
Din Rail Circuit Breaker Box Protection
Base station protection
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Applications
Motor Drive
Controller
Electric
Motor
Drive
Power
Input
To ensure Input
Power is “clean”
May include
to protect against
transients from the
Motor
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Surface Mount MOVs
7mm and 20mm disc sizes inside.
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Multilayer Varistor
Nicknamed ML or MLV
 Leadless, Surface Mount Chip Form
 Combine Surge, ESD, and Filtering Functions
 Rugged, Robust, Reliable
 Four distinct versions:
ML - supports the broadest application range
MHS - low capacitance, high speed ML
MLE - intended for ESD while providing filter
functions
AUML - automotive load dump
transient protection
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Multilayer Varistors
What is an MLV?
 MLV’s are voltage dependant, non-linear devices
used in overvoltage transient suppression.
 MLV’s are fabricated by wet stack printing layers of
Zinc-Oxide (ZnO) and metal inner electrodes,
sintering, terminating, glassing & finally plating.
 MLV’s are available in sizes 0402 up to 2220
 MLV’s are available in voltages 3.5Vdc up to 120Vdc
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Multilayer Varistor
What does an MLV look like inside?
Fired Zinc Oxide Black Ceramic
End Termination
Standard finish is Tin (Sn)
plated over Nickel (Ni) plated
over Silver (Ag)
Glass is porous and is put on before Ni &
Sn Termination,
Metal Inner Electrodes
Platinum (Pt) or Silver-Palladium (AgPd)
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Multilayer Varistors (MLV)
What does an MLV look like inside? continued
Metal Inner Electrodes
End Termination
(Side view)
(End view)
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MLV Electrical Parameters
Voltage Rating, Energy Peak Current Varistor Voltage
Continuous
at 1mA
VDC
VAC
VDC
Joules
Amps
14
18
0.4
150
operating voltage
22 min
28 max
Varistor voltage
1 pulse energy
rating
Clamp Voltage Capacitance
8x20µS
(typical)
Vpeak Amps
pF
40
10
1100
clamp voltage at
specific current
typical
capacitance
1 pulse current
rating
After only 1 hit of these two max limits,
the MOV will need to be replaced.
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V-I curve characteristics
For the same MOV
voltage rating:
• Smaller parts have a
higher clamp voltage at
a higher currents.
• Larger parts have a
higher energy
capability.
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Multilayer Products
Series
Voltage
Size
 MLA
3.5v – 30VDC
30v – 120VDC
0603 - 1210
1206 - 1210
 MLE
18VDC
0603 - 0805 - 1206
 MHS
9V – 42 VDC
0402 - 0603
 MLN
5.5v – 18VDC
1206 4X array
 AUMLA
18VDC
1206 -1210 - 1812 - 2220
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Multilayer Series
Five Sizes
0805
0603
0402
1mm
1206
1.6mm
2.0mm
1210
3.0mm
3.2mm
.5mm
.8mm
1.3mm
1.5mm
2.5mm
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SurgeArrayTM MLN

A network of four independent multilayer varistors.
in a single 1206 surface mount package.

5.5, 9, 14, 18 VDC available.

The inherent capacitance provides filtering capability to
eliminate the need for an additional capacitor.

Reduces board space and assembly placement cost while
increasing assembly capacity and system reliability.
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Multilayers for Automotive applications
AUMLA
Used to handle load dump requirements
Four sizes
1206
1.6mm
1812
1210
3.2mm
3.2mm
2220
5.7mm
4.5mm
2.5mm
3.2mm
5.0mm
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MLA Performance
ESD Test
Voltage
Peak Clamp Voltage
100
8kV
4kV
V18MLA0805
2kV
1kV
0.5kV
V5.5MLA0805
10
0.1
1.0
10.0
100.0
Peak Impulse Current
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Transient Suppression Performance
Voltage vs Time curves
for contact discharge ESD
8kV
6kV
4kV
2kV
1kV
500V
V18MLA0805
Voltage
80
60
40
20
0
0
10
20
30
40
Nanoseconds
50
60
70
80
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CH Series
Original surface mount Varistor series using Disc Press Technology
 Voltage range 14VAC - 275VAC
 Large 5x8mm package
 Advantage over ML
– Higher voltages to 275VAC
– Higher energy capability
– Higher peak current capability

Standard color is dark blue.
Multilayers are black.
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