PFC_Controlled_Power_Supply

PFC_Controlled_Power_Supply - By Dhaval Dalal, Technical...

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Power Electronics Technology February 2005 www.powerelectronics.com 14 Adopting active PFC for harmonic-reduction while making other architectural- and component-level improvements can cost-effectively reduce losses in ATX power supplies. A TX power supplies—the generic name for Intel-specified internal power sup- plies for desktop computers—are de- signed for the lowest cost possible and offer poor active-mode efficiency. As utilities and regulators seek to save energy, manufacturers are finding enhancements to ATX power supplies that are technologically superior and cost effective. For years, the ATX power supplies used in personal com- puters (PCs) have been designed using traditional forward topologies, and there has been little motivation for inno- vation. As a result, their typical efficiency ranges from 65% to 70%, and they require heavy heatsinking and fan cooling for operation. Now, with various degrees of en- ergy concern around the world, utilities and regulatory agencies are looking for any possible way to reduce energy consumption. Consequently, PC power supplies are a prime target. One innovative program will award rebates to manufacturers of computers with power supplies hav- ing efficiency greater than 80% (see www.80plus.org). Going from 67% to 80% efficiency on a typical 300-W ATX power supply can save 75 W at full load. With more than 130 mil- lion PCs sold every year, the poten- tial for energy savings is obviously tremendous. This article identifies the scope for efficiency improvements and the projected impact on global energy re- quirements; provides an overview of existing topological and component approaches to ATX power supplies; and suggests paths for efficiency enhance- Fig. 1. Typical block diagram/structure of an ATX power supply. By Dhaval Dalal , Technical Marketing Director, Power Supplies, ON Semiconductor, Phoenix AC PFC Controller PFC Diode SMPS Controller Bias Output SMPS Regulator Output Rectification SMPS MOSFET Output Circuitry +12 V OUT +5 V OUT Supervisory EMI Filter +3.3 V OUT Post Regulation
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www.powerelectronics.com Power Electronics Technology February 2005 15 POWER SUPPLY EFFICIENCY ments that are technologically superior and cost-effective. Fig. 1 shows a generic block diagram/structure of an ATX power supply. The power supply output ranges from 250 W to 350 W, supplied primarily at three major output voltages—12 Vdc, 5 Vdc and 3.3 Vdc. Any ATX power supply sold in Europe, Japan and some other regions of the world is required to comply with the harmonic cur- rent requirements specified in IEC1000-3-2. As a result, a harmonic reduction front-end in the form of a passive choke or an active power stage (i.e., power factor correc- tion boost) is necessary. The main power conversion stage for this type of sup-
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PFC_Controlled_Power_Supply - By Dhaval Dalal, Technical...

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