Switching power supplies are now more efficient, smaller, less polluting, and more reliable

First, non isolation DC/DC technology developed rapidly

In recent years, non isolated DC/DC technology has developed rapidly. At present, a set of electronic equipment or electronic system, because of the different load, will require the power supply system to provide more than voltage barrier. Such as desktop PC requires +12V, +5V, +3.3V, -12V four kinds of voltage and standby +5V voltage, the main board requires 2.5V, 1.8V, 1.5V and even 1V. A set of AC/DC is not likely to give so much voltage output, and most of the low-voltage supply currents are very large, so a lot of non isolated DC/DC are developed, and they can be basically divided into two broad categories. A class of internal power switches, called DC/DC converters. Another class of non power switches requires external power MOSFET, called the DC/DC controller. According to the circuit function, there are step-down STEP-DOWN, step-up BOOST, as well as BUCK-BOOST or SEPIC, such as INVERTOR and positive pressure into negative pressure. Among them, the most varieties, the fastest growing or step-down STEP-DOWN. According to the magnitude of the output current, it is divided into single phase, two-phase and multi-phase. The control mode is mainly PWM, and the minority is PFM.

In non isolated DC/DC conversion technology, TI's pre measured gate drive technology uses digital technology to control the synchronization of BUCK, adopting the technology of DC/DC conversion efficiency can reach 97% TPS40071, which are the representative products. The BOOST boost system also produces a synchronous BOOST product using MOSFET instead of diodes. In the field of low voltage, the efficiency is greatly increased, and the problem of conduction and reverse recovery of MOSFET bulk diode is being solved.

Two 、 the switch power blows the digital horn

At present, in the entire electronic analog circuit system, television, audio equipment, photo processing, communications, networks and other digital gradually realized, and the last Digital Fortress is the power sector. In recent years, the research trend of digital power supply has been decreasing, and more and more achievements have been made. In terms of power digitization, companies in front of them are TI and Microchip. TI company has the advantage of DSP, the annexation of the PWM IC professional manufacturer UNITRODE company, the company has made of TMS320C28F10 48V output power supply module for communication, including PFC and PWM as part of fully digital control. Now, TI has developed a number of digital PWM control chips. At present, mainly UCD7000 series, UCD8000 series and UCD9000 series, they will become the next generation of digital power pathfinder. They include both hardware and software programming as a whole. The hardware part includes the logical part of PWM, the clock and amplifier circuit, analog to digital conversion, digital to analog conversion, digital processing, driving, synchronous rectification detection and processing, etc..

At present, the competition in the power field is mainly performance and price competition, so the digital power has a long way to go, but the digital horn in the power supply field has sounded.

Three 、 primary PWM control, IC continuous optimization

The active clamp technique after ten years of enduring, since after the lifting of the ban this patent expires in 2002 VICOR, the company developed a new kind of active clamp control IC such as bamboo shoots after a spring rain like mushrooms, provide adequate choices to the user.

Control of early active clamp TI control technology, not only to maintain the original UCC3580 series, also developed a new and more superior performance of UCC2891-94, it adopts the current control mode, integrated high side and low side clamped clamped two kinds of control scheme are given new control techniques. OnSemi first launched a low voltage (100V) active clamp NCP1560 control chip, then introduced the application of high voltage control chip NCP1280, it can solve the LCD TV plasma TV power requirements, and now at PC power no fan of the next generation. Active clamp control IC 5000 series of special American NS company has a LM5025, even the unknown Semtech also gives active clamp control chip, the model is SC4910, which is behind the huge market opportunities. Until recently, the active clamp control IC UCC2897 introduced by TI has made the PWM control of active clamp perfect. The Taiwanese Fairchild company gives the cheapest active clamp control IC, that is, SD7558 and SD7559.

Control of early active clamp TI control technology, not only to maintain the original UCC3580 series, also developed a new and more superior performance of UCC2891-94, it adopts the current control mode, integrated high side and low side clamped clamped two kinds of control scheme are given new control techniques. OnSemi first launched a low voltage (100V) active clamp NCP1560 control chip, then introduced the application of high voltage control chip NCP1280, it can solve the LCD TV plasma TV power requirements, and now at PC power no fan of the next generation. Active clamp control IC 5000 series of special American NS company has a LM5025, even the unknown Semtech also gives active clamp control chip, the model is SC4910, which is behind the huge market opportunities. Until recently, the active clamp control IC UCC2897 introduced by TI has made the PWM control of active clamp perfect. The Taiwanese Fairchild company gives the cheapest active clamp control IC, that is, SD7558 and SD7559.

For the small power switching power supply, it is still the PWM control IC of the flyback converter, but it must be able to solve the control method of the synchronous rectification of the two side. OnSemi's NCP1207 and NCP1377 are among the best in the field of high voltage AC/DC. If the synchronous rectifier control IC-UCC27226 of TI's flyback converter is added, it will make them an almost perfect high-efficiency power supply. In the flyback converter control in the low voltage DC/DC field, the IC LTC3806 of Linear is excellent. LTC3806 not only can control the PWM, but also give the accurate two side synchronous rectification driving signal. It is the masterpiece of low voltage small power control IC.

To sum up, switching power supply design can choose the best control mode and the best circuit topology. High power should be full bridge ZVS plus two secondary side synchronous rectifier ZVS, typical control IC is ISL6752; medium power low power should be synchronous rectifier active clamp forward converter ZVS soft switch with two side of the pre measured gate drive technology; and small power should be the flyback converter with good synchronization rectification. Of course, there is no absolute limit here, but there are different conditions, there should be the corresponding best choice.

Four 、 synchronous rectification technology to achieve high efficiency

From the last century since the late 90s synchronous rectification technology was born, the switching power supply technology has been greatly developed, synchronous rectification scheme based on IC control technology has been widely accepted as a development engineer, synchronous rectifier technology is now in an effort to achieve synchronous ZVS and ZCS way.

Since 2002, the United States Galaxy Corporation issued ZVS synchronous rectification technology, now it has been widely used. This way the synchronous rectifier cleverly pulse signal two side driven synchronous rectifier is rising ahead signal than a side of the PWM pulse, descent method to achieve the work along the hysteresis synchronous rectifier MOS ZVS. The latest dual output PWM control, IC almost all in the control logic, increased on the two side of the ZVS synchronous rectifier control terminals. For example: Linear's LTC3722, LTC3723, INTERSIL's ISL6752, etc.. These IC not only strive to solve the primary side power MOSFET soft switching, but also strive to solve the two side of the ZVS mode synchronous rectification, conversion efficiency of more than 94%.

In the switching power supply circuit topology is asymmetric, especially for the good performance of the forward circuit or forward active clamp circuit, synchronous rectification in the two side, in order to realize the synchronous rectifier ZVS, eliminating the loss MOSFET body diode conduction loss and reverse recovery time caused by TI's patent "pre measured gate drive technology in the control chip adds a lot of digital control technology, forward converter with synchronous rectifier control chip UCC27228 makes the efficiency of forward circuit reached a hitherto unknown high efficiency. Then with the primary side of the active clamp technique, the circuit model of the latest work done in both soft switching ZVS primary side, and solves the core reset and energy feedback, reduce the voltage stress of the power of MOSFET, but also to achieve the two secondary side synchronous rectifier ZVS best, DC/DC small and medium power converter integrated use of these two technologies, its efficiency is above 94%, the power density can reach more than 200W/in.

Five, experts point of view: energy shortage, the urgent need for energy policy

At present, China made switching power accounts for 80% of the world market, but there is hardly our share in high-end market. Our country is short of energy, and the power industry is closely related to the energy consumption. Therefore, the government and society should guide the development of power supply in several aspects.

First, the no-load power consumption of color TV power supply. In cities, many families turn off the electricity after they watch TV in the evening, so that the power is wasted. At this time, the no-load loss of color TV is more than 3.5W, the European standard is less than 1W, and the Japanese standard is less than 0.6W.

Second, the domestic appliance manufacturers for power efficiency requirements are not high, only asking prices. For example, the DVD manufacturer in external power adapter, choose the conversion efficiency of less than 80%, the no-load loss of 49 yuan of 1.5W an adapter, but not willing to choose more than 90% conversion efficiency, no-load loss of 59 yuan of <0.6W an adapter.

At present, our country's oil imports has more than 50%, is still the lack of big oil, if private cars more, where are we going to get oil? Whether the use of laws and policies to encourage enterprises and engineers to develop and produce high efficiency power?