Analysis of four current switching power supply technology trends.
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The four major trends of today's switching power supply technology

       First, non-isolated DC / DC rapid technological development
       In recent years, non-isolated DC / DC technology is developing rapidly. The current set of electronic equipment or electronic systems because of different load will be required to provide multiple voltage power supply system block level. Such as desktop PC, requires a +12 V, +5 V, +3.3 V,-12V four kinds of voltage and the +5 V standby voltage, the motherboard will need to 2.5V, 1.8V, 1.5V or 1V so. An AC / DC can not give so much in the voltage output, and most are very low supply current, so developed a number of non-isolated DC / DC, they basically can be divided into two categories. Within a class of devices with the power switch, said DC / DC converters. And those without power switch, the need for external power MOSFET, said DC / DC controller. In accordance with the circuit, function, there is relief in the STEP-DOWN, boost the BOOST, there can buck the BUCK-BOOST or SEPIC, as well as positive pressure negative pressure INVERTOR such conversion. The species most of the fastest growing or buck the STEP-DOWN. According to the size of the output current is divided into single-phase, two-phase and polyphase. The way to the main PWM control, a small number of the PFM.
       In the non-isolated DC / DC conversion technology, TI's technology uses the pre-detection gate drive control for synchronization of digital technology, BUCK, using this technology, DC / DC conversion efficiency can reach 97%, which is represented by products such TPS40071. BOOST boost way there have been replaced by MOSFET synchronous BOOST diode products. In the low pressure area to increase the efficiency of large magnitude, and is trying to further eliminate MOSFET body diode conduction and reverse recovery.

       Second, the digital switching power supply blew horn
       Present in the whole system of electronic analog circuits, television, audio equipment, photo processing, communications, networking and so the progressive realization of the digital technology, and the last number of the fortress is Meiyou Dianyuan area of the. In recent years, digital power source continues unabated, more and more results. The power walk at the forefront of digital companies that have TI and Microchip. TI DSP advantages both companies, but also acquired a professional manufacturer UNITRODE PWM IC company, the company has made a communication with TMS320C28F10 output power with a 48V power supply modules, including PFC and PWM section exclusively for digital control. Now, TI has developed a variety of digital PWM control chip. At present mainly UCD7000 series, UCD8000 series and UCD9000 series, they will become the next generation of digital power in the Pathfinder. They generally include both hardware, software programming to be done. Hardware, including the logical part of the PWM clock, amplifier loop ADC, DAC, and digital processing, driven synchronous rectification detection and treatment.
Currently in power in the field of competition is mainly price competition and performance, so digital power still has a long way to go, but the power supply in the field of digital horn has sounded.

       Third, to optimize the primary PWM control IC
       Active clamp technique after enduring more than ten years since the 2002 patent expiration of VICOR company after the lifting of the ban, companies develop a new type of active clamp control IC have sprung up to provide a sufficient choice .
Control of early active clamp control technology TI, not only to maintain the original UCC3580 series, has developed a new and better performance of the UCC2891-94, which uses current-mode control, integrated high-side clamp, low-side clamp two control schemes, given the new control techniques. OnSemi first introduced the low-voltage (100V) active clamp NCP1560 controller chip, then launched a high-voltage applications, control chip NCP1280, both to resolve the LCD TV, plasma TV power supply requirements, and now directed at the next generation of fanless PC unit power. NS company's 5000 United States specifically have a LM5025's active-clamp control IC, with little-known companies gives Semtech active clamp controller chip, the model is the SC4910, visible behind the enormous market opportunities. Until recently, the company launched TI's active clamp control IC UCC2897, has done active clamp PWM control of the perfect. The Taiwanese company is given Fairchild cheapest active clamp control IC, the SD7558 and SD7559.
       In the high-power field, phase shift ZVS full-bridge soft switching technology in the solution contributed to efficiency switching power supply. From TI's UC3875 to the UCC3895, and then from Linear's LTC3722 LTC1922 to increase adaptive testing technology, to make full-bridge phase-shifting technology has reached its peak. However, widely used in synchronous rectification today, it can not achieve the best ZVS synchronous rectification. Because the full-bridge phase-shifting circuit is essentially a non-symmetric, it can not achieve complete ZVS synchronous rectification, due to open on and off the course of its half of the total hard-switching, which compare the efficiency of the ZVS topology symmetric mode synchronous rectification. The latest scientific and technological achievements should be introduced by the company INTERSIL symmetrical full bridge ZVS PWM control IC-ISL6752. It can not only control the primary side of the work of the four MOS switches for the ZVS condition can be predicted accurately control the secondary side synchronous rectifier ZVS work for the state of the drive signal. IC produced by Fengyun 400W of DC / DC power coupled with advanced MOSFET, conversion efficiency up to 95%.
       For low-power switching power supply, they will still flyback PWM control IC, but it must be able to properly solve the secondary side synchronous rectifier control mode. NCP1207 and NCP1377 OnSemi company is high-voltage AC / DC leader in the field. If matched with TI's Synchronous Rectifier Flyback Converter Control IC-UCC27226, while enabling them to become virtually flawless and efficient power supply. Low-voltage DC / DC flyback converters in the field of control IC,, Linear's LTC3806 is the superior of the for. LTC3806 is not only able to control PWM, also gives an accurate secondary synchronous rectification drive signal is low-voltage low-power power supply control IC's masterpiece.
       In summary, switching power supply design can select the best control methods and the best circuit topology. ZVS full-bridge power should be coupled with secondary side synchronous rectification ZVS, the typical control IC is the ISL6752; medium-power to low power should be active clamp ZVS soft-switching forward transformation coupled with the pre-detection of the secondary gate drive technology synchronous rectification; and low-power synchronous rectification should be equipped with a good anti-shock transformation. Of course, there are no absolute limits, but under different conditions should have the appropriate choice.

       4, synchronous rectification for efficient
       From the late 90s of last century since the birth of synchronous rectification, switching power supply technology has been tremendous growth, with IC control technology for synchronous rectifiers have been widely accepted for the R & D engineers, now all synchronous rectification to achieve ZVS, ZCS mode The synchronous rectification.
Galaxy Inc. from the United States in 2002 issued a ZVS synchronous rectification, the now widely used. In this way the secondary side synchronous rectification system skilfully driven synchronous rectification of the pulse signal adjusted to a side than the rising edge of PWM pulse signal ahead, falling backward method to achieve the ZVS synchronous rectification work the way MOS. Last came the two-output type PWM control almost all of the control logic IC to increase the ZVS of the secondary-side synchronous rectification to achieve the control terminal. For example: Linear's LTC3722, LTC3723, INTERSIL ISL6752 and other companies. The IC is not only to solve the primary-side power MOSFET soft switches, and efforts to resolve the secondary side synchronous rectification ZVS mode, the conversion efficiency of up to 94%.
       In the non-symmetrical switching power supply circuit topologies, especially for the good performance of the forward active-clamp forward circuit or circuit, the secondary side synchronous rectification in the way in order to achieve ZVS synchronous rectifier, eliminating MOSFET body diode conduction losses and reverse recovery time of the loss caused, TI's patented technology, "pre-detection gate drive technology," in the control chip adds a number of digital control technology, is excited synchronous rectification control circuitry chip UCC27228 birth to now the efficiency of excitation circuit has reached an unprecedented high efficiency. Together with good primary-side active clamp technique, the making of this new circuit approach focusing both on the primary side did it work the way soft-switching ZVS, but also to solve the core reduction and energy feedback, reducing power MOSFET voltage stress, also be a secondary side synchronous rectifier ZVS best, the integrated use of these two technology small and medium power DC / DC converter, its efficiency is above 94%, power density can reach more than 200W/in.

       5, expert opinion: energy shortages urgently needed energy policy introduced
       Current switching power supply made in China accounted for 80% of the world market, but almost without our high-end market share. China's current energy shortage, and the power industry is a closely related industry, energy consumption, so they need the government and the society in several groups to whom power should be the development of guidance on the direction.
       First of all, TV's no-load power consumption. Many families in the city at night after watching TV, using remote shutdown method shuts down, so that power be consumed. TV's no-load loss over time in more than 3.5W, the European standard is less than 1W, the Japanese standard is less than 0.6W.
       Second, the domestic manufacturers of various household appliances do not ask for power efficiency, only ask the price. For example, DVD producers out with the power adapter, would prefer less than 80% conversion efficiency, load loss of 49 yuan a 1.5W adapter, but not willing to choose more than 90% conversion efficiency, load loss <0.6W The 59 yuan a adapter.

       At present, our country's oil imports have more than 50%, still short of petroleum and power, if more number of private cars, where to go get our oil? Whether the use of laws and policies to encourage businesses and engineers to develop and produce more efficient power supply it?

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