Appliance Design - March 2008 - (Page 21)

Combined Protection POWER etal Oxide Varistors (MOVs) are typically used for transient overvoltage suppression in AC line voltage applications. Lightning, inductive load switching, or capacitor bank switching may cause transient over-voltage conditions. In these applications, there also exists the potential for a sustained abnormal over-voltage/ limited-current condition that may cause the MOV to go into thermal runaway, resulting in overheating, out-gassing and possibly fire. New thermally enhanced MOVs help protect a wide variety of low-power systems against damage caused by over-current, overtemperature and over-voltage faults, including lightning strikes, electrostatic discharge (ESD) surges, loss of neutral, incorrect input voltage and power induction. These devices help provide protection in a wide range of AC line applications, including AC mains LED lighting systems, PLC network adapters, cell-phone chargers, AC/DC power supplies (up to 30 VA as input power for 230 VAC input voltage), modem power www.applianceDESIGN.com M supplies, AC panel protection modules, AC power meters, and home appliances. New device helps guard against overcurrent, over-voltage, and over-temperature events. Integrated device Under normal operating conditions the AC line voltage applied to an MOV is not expected to exceed the device’s maximum AC root mean voltage (VACRMS ) rating and, provided that the transient energy does not exceed the MOV’s maximum rating, shortduration transient events are clamped to a suitable voltage level. However, a sustained abnormal over-voltage/limited-current condition, such as a loss of neutral, may cause the MOV to go into thermal runaway. Protecting the MOV from thermal overdissipation is frequently accomplished with a thermal cut-off (TCO) device placed in series with the MOV. A typical line-voltage, transient-protection scheme may also incorporate a thermal-protection element, such as a fuse, to protect the system from damage caused by an over-current condition that exceeds a predetermined level. by philippe di fulvio Philippe Di Fulvio is senior application engineer at Raychem Circuit Protection Products, Tyco Electronics Corp., Menlo Park, Calif. applianceDESIGN March 2008 21 http://www.appliancedesign.com

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Appliance Design - March 2008 Contents Editorial Shipments/Forecasts News Watch A New Appliance is Set to Break into Homes Soon - the Micro CHP Unit, which Generate both Heat and Power. Thermally Enhanced Varistors Help Protect Low-Power Systems Against Damage Caused by Over-Current, Over-Temperature and Over-Voltage Faults. Hybrid Controller Reduces Standby Power Consumption and Improves Active-Mode Efficiency. Battery-Management ICs Solve Design Challenges for Cordless Appliances Using High-Voltage, Lithium-Ion Battery Technology. A Semiconductor Solution Protects the Relay in a Temperature Controller for a Cooking Appliance. New Polyurethane Foam Insulation System Optimizes both Insulation Performance and Productivity. Innovations in Decorative, Pre-Finished Metals Expand Range of Design Options for Appliance Designers. Design Marts Association Report: AHAM Advertiser's Index

Appliance Design - March 2008

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