Varistors - Fundamentals and Theory
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Transcript of Varistors - Fundamentals and Theory
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Varistors: Ideal solution to surge protection
Electromagnetical Compatibility
Michal JankowWroclaw University of Technology
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Outline
Varistor The Fundamentals & TheoryMetal Oxide Varistor (MOV)Multi Layer Varistor (MLV)Application examplesManufacture’s technical specificationReferences
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Varistor
A varistor is :a variable resistor – a voltage dependent, non-linear device – whose resistance decreases as the voltage applied across the device or terminals increases.
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Varistor
Or it can also be described as a device that:
• At low voltages has an extremely high resistance
• At high voltages has a very low resistance
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Overvoltage Protection Theory
• Under normal operating conditions, the overvoltage device appears as a high impedance device.
• Under overvoltage operating conditions, the overvoltage device appears as a low impedance device
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Varistor – V-I characteristic
The V-I characteristic curve enable varistors to provide fast transient voltage suppression.
I = KVα
V-I characteristic
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What varistors don’t do
Varistors provides no equipment protection from:
Inrush current (during equipment start-up)
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What varistors don’t do
Varistors provides no equipment protection from:
Inrush current (during equipment startup),
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What varistors don’t do
Varistors provides no equipment protection from:
Inrush current (during equipment start-up)
Voltage sags
(also know as a dropout, brownout,
blackout)
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What varistors don’t do
Varistors provides no equipment protection from:
Voltage sags (also know as a brownout),
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What varistors don’t do
Varistors provides no equipment protection from:
Inrush current
Voltage sags
Overcurrent (created by a short circuit)
Varistors neither senses nor controls such
events
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MOV – Metal Oxide Varistor
• MOVs are made of: ZnO, Sik
• Grains form “p-n diode junctions” that allow current to flow in one direction
• Diode junctions they perform like opposing diodes in series.
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MLV – Multi Layer Varistor
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Application
MOVs: Power Supply
Protection
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Application
MOVs: Power Supply
Protection Line Voltage
Protection
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Application
MOVs: Power Supply
Protection Line Voltage
Protection Appliacne
Protection
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Application
MOVs: Power Supply
Protection Line Voltage
Protection Appliacne
Protection Security System
Protection
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Application
MOVs: Power Supply
Protection Line Voltage
Protection Appliacne
Protection Security System
Protection Motor Protection
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Application
MOVs: Power Supply
Protection Line Voltage
Protection Appliacne Protection Security System
Protection Motor Protection Data Line Protection
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Application
MLVs:• Protecting board
level components from ESD damge
• MVLA Series is ideal for low frequency and signal line application
• MVLB Series is optimal for higher freq. Applications
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Technical Specification
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THANK YOU
Varistors: Ideal Solutions to Surge Protection
Electromagnetic CompatilibityMichal Jankow
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Reference
• Free Encyclopedia www.wikipedia.org• Cooper Bussmann www.cooperbussmann.com• Tyco Electronics www.circuitprotection.com• Google Search Engine www.google.com• Digi-Key Corporation
www.parts.digikey.com/1/parts-kws/epcos-inc-va-tvs-varistors-movs
• Littelfusewww.littelfuse.com/company/news-item.html?NewsID=566