Appliance Design - March 2008 - (Page 26)

POWER Active Efﬁciency Fig. 1. Flyback converter employing the proposed method. Hybrid controller saves energy in active mode. W by Young-Bae Park and Hang-Seok Choi Young-Bae Park and Hang-Seok Choi are staff engineers at Fairchild Korea Semiconductor, Bucheon-si, Gyeonggi-do, Korea. 26 applianceDESIGN March 2008 hile most domestic appliances and office equipment items are plugged directly into wall outlets and powered from high-voltage alternating current (AC), nearly all of their internal circuitry requires a low-voltage direct current (DC). Accordingly, power supplies are required to convert AC voltage to low DC voltage. According to the research by Ecos Consulting, roughly 3 billion AC/DC power supplies are currently used in the U.S. and about 10 billion are used globally [1, 2]. As power supplies become more pervasive, their impact on the environment in terms of power supply energy efficiency has attracted growing international attention. As a first step, a number of efforts have been made to improve efficiency when the appliance is in standby mode [3,6]. However, many of the technical approaches used to reduce the standby power consumption do not necessarily improve active-mode efficiency. Research by Ecos Consulting shows that about 73 percent of the total energy passing through the power supply occurs when the products are in active mode. This implies that there are more opportunities to save energy in the active mode [1, 2]. Thus, governmental and standardization organizations around the world, committed to protecting natural resources, have endorsed measures to encourage the adoption of energy efficient power supplies. The California Energy Commission (CEC) has proposed mandatory efficiency standards for external power supplies. Other regions of the world, which currently depend on voluntary regulation programs, are also considering mandatory standards to encourage higher efficiency of power supplies [7]. One thing that should be noted in the new CEC standards is that they regulate efficiency at full load and also at partial load. They regulate the average of efficiencies at 25 percent, 50 percent, 75 percent and 100 percent of rated output power, as shown in Table 1. Typically, the efficiency drops as the output load decreases, because the switching loss becomes dominant at a light-load condition, which sometimes becomes an obstacle to meet the active-mode efficiency regulation. The simplest way to reduce the switching loss is to employ a quasi-resonant operation, which is accomplished by operating the converter in the critical conduction mode (CCM), that is, at the boundary of the CCM and discontinuous conduction modes (CCM/DCM). However, the critical conduction mode operation causes www.applianceDESIGN.com 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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