Appliance Design - March 2008 - (Page 28)

POWER off-line flyback converters with different control methods were built and tested according to the specifications shown in Table 2. The same transformer inductance values are used for all cases. For case A, the switching frequency is fixed and the converter operates in CCM for lowline voltage (Vin = 115 VAC) and in DCM for high line voltage (Vin = 230 VAC). Because the switching frequency is fixed, the peak drain currents are almost the same for lowline and high-line voltages. Meanwhile, for case B, the converter always operates in critical conduction mode. The switching frequency decrease for lowline voltage, and therefore its peak drain current, is higher than in the other two cases. This increases the conduction loss, causing a decrease of efficiency at low line. For the proposed control method, the converter operates in CCM with maximum switching frequency at low-line voltage while in valley switching DCM for high-line voltage. Thus, the peak drain current for low line voltage is the same as the case A. Fig. 4 shows the efficiencies of the three prototype converters when input voltages Fig. 3. Narrow switching frequency variation due to the proposed controller. are 115 VAC. As observed, the conventional quasi-resonant operation (case B) shows deteriorated efficiency for a full-load and low-line condition. This is because the reduced switching loss is negligible and increased conduction loss is dominant for full load and low line condition. However, the proposed method shows better efficiency at low-line and full load since it permits quasi-resonant switching only when the converter enters into DCM as the load or input voltage varies. It does not have an increased conduction loss caused by relatively high drain current to guarantee the critical conduction operation over the entire operation range. Fig. 5 shows the efficiencies of the three prototype converters when input voltages are 230 VAC. As can be seen, the proposed method also shows increased efficiency over the other two methods. The conventional quasiresonant operation shows lower efficiency, since the increased switching frequency for high line increases the switching loss. Fig. 4 and Fig. 5 shows that the proposed controller is very effective in improving the active-mode efficiency both in high line and low line conditions. Knowledge is Power. In the dynamic appliance design industry knowledge is a key component of continued success for your business. Market research provides the information needed for a powerful competitive advantage. Clear Seas Research pairs its market research expertise with appliance design industry professionals to ensure a superior information gathering process. Partner with us for a competitive advantage deserving of your brand and maximize your company’s future success. Clear Seas Research Approach to Market Research Customized research: benchmarking, industry trends, brand awareness, positioning, etc. Advanced statistical analysis Quantitative and qualitative research Business-to-business analysis Global capabilities and reach Actionable results Access to industry experts via proprietary databases and industry speciﬁc online communities In the innovative appliance design industry Research to Gain Market Intelligence For more information on our market research services please contact: Phone: 248-362-3700 Email: info@clearseasresearch.com www.clearseasresearch.com 28 applianceDESIGN March 2008 www.applianceDESIGN.com http://www.clearseasresearch.com http://www.clearseasresearch.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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