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Fig. 4: A short overview of the specific impact on SMPS requirements. density is expected to come mostly from system architecture and power management optimization. For this reason, the digital power management bus has been already standardized by the PMBus Consortium. In addition to PMBus compliance, digital control techniques become increasingly popular in power conversion. Generally, while digital power management can optimize performance at the system level, digital control contributes to optimize the converter-level efficiency in the entire load range by implementing adaptive, load-dependent control algorithms, or phase-shedding in interleaved structures in order to achieve almost flat efficiency plots. In addition, within the digital control, monitoring, protection, and house-keeping features of power are shifted from hardware to software, which significantly shortens product design time, reduces the cost, and also allows for easy adjustment (“tweaking”) of parameters even during the mass production. Regarding the circuital topologies used inside SMPS, the opportunity to significantly reduce the size of power converters by increasing the switching frequency created by the MOSFET technology has focused topologies studies on the reduction of switching losses of the semiconductor devices, which is typically perceived as the major obstacle to maximizing the switching frequency of PWM converters. This has given big emphasis to the resonant power conversion, which led to the development POWER MANAGEMENT of new families of resonant converters, based on the zero-voltage-switching (ZVS), zero-current-switching (ZCS), quasi-resonant (QR) and multi-resonant concepts. From what is mentioned above, the role played in SMPS advancement by semiconductors companies like Infineon looks really crucial: power devices, drivers, ICs, analog and digital controllers, everything inside Infineon portfolio, are all fundamental parts of such a system. For this purpose, figure 5 shows the typical internal structure of a Server AC/DC SMPS and the several families of Infineon components which are used in each of its stages. In fact, the outstanding improvements in SMPS performance achieved in the past 10 years have been primarily brought by the dramatic reduction of the on-resistance achieved in high-voltage MOSFETs using the revolutionary Super Junction principle, introduced by Infineon at the end of the nineties in the CoolMOSTM series and equally impressive improvements in reverse-recovery characteristics of high voltage SiC (Silicon Carbide) diodes. In applications with a low output voltage, further efficiency improvements have been made possible by continuous reduction of on-resistance of low-voltage MOSFETs, like Infineon OptiMOS series, used as synchronous rectifiers. Introduction of innovative devices based on GaN (Gallium Nitride) material promises further revolutionary advancements in this field. An important contribution to the progress of SMPS technology comes in particular from the packaging techniques, having the main goal of minimizing parasitics and improving thermal performances. The need of increased power density has been also triggering more and more advanced component integration: monolithic integration and/or chip co-packaging of semiconductor components such switches, drivers, and control circuits looks promising in order to shrink the system size. For the same reason the use of magnetics with integrated PCB winding(s), allowing more functional integration, will find more extensive use. Unfortunately, it is commonly recognized that the fast progress in semiconductor technologies has been not followed at the same pace by magnetics and capacitors technology. The major effort of magnetics manufacturers has been focused on the optimization of the existing materials in certain frequency ranges and expanding the portfolio of core shapes and sizes, in particular low-profile planar cores, which is surely helpful for the designers. However, more innovative solutions would be needed in order to further minimize the copper losses due to skin and proximity effects, still considered as the actual major trouble in high-frequency applications. Finally, some progresses have been made in the field of low voltage capacitors technology, but no significant changes have been introduced in the high-voltage electrolytic capacitors used as energy-storage (bulk) capacitors: in fact, despite the introduction of some miniaturized series, their typical capacitance/volume ratio is still relatively low. Fig. 5: The typical internal structure of a Server AC/DC SMPS, showing Infineon’s solutions. 24 Electronic Engineering Times Europe March 2014 www.electronics-eetimes.com


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