A communication with the frequency switching power supply technology
        Communication with the high-frequency switching power supply technology is basically embodied in several ways: converter topology, modeling and simulation, digital control and magnetic integration.

        1.1 Converter Topology
        Soft-switch technology, power factor correction technology and multi-level technology is a hot area in recent years, converter topology. Soft-switch technology can effectively reduce the switching losses and switching stress, help converter efficiency; use PFC technology can improve the AC / DC converter input power factor, reducing harmonic pollution on power; and multi-level technology mainly used in communication power three-phase input converter, you can effectively reduce switch voltage stress. Same time, because of high input voltage, the use of appropriate soft-switching technology to reduce switching losses, is a multi-level technology in the future an important research direction.
        To reduce the converter size, need to improve the switching frequency to achieve high power density, smaller size of the magnetic materials must be used and passive components, but will increase the frequency MOSFET switching losses and drive a significant increase in loss, while the soft-switch technology The application can reduce the switching losses. The current most widely used communications power supply project is the active clamp ZVS technology, the early 90s of last century the birth of Phase Shift Full Bridge ZVS technique and the late 90's synchronous rectification.
        1.1.1 ZVS active-clamp
        After three generations of active clamp technique, and to declare the patent. The first companies on behalf of the United States VICOR active clamp ZVS technology, DC / DC operating frequency up to 1 MHZ, the power density close to 200 W/in3, but its conversion efficiency did not exceed 90%. In order to reduce the first generation of active clamp technology costs, IPD company reported a second-generation active-clamp technology patents, the use of P-channel MOSFET, and is used in the transformer secondary side active clamp forward topology, This makes a lot of product cost reduction. But this method the formation of MOSFET ZVS (ZVS) narrow boundary conditions, and the PMOS operating frequency is not satisfactory. In order for magnetic energy in the core reset time is not consumed in vain, a Chinese-American engineer in 2001 for the third generation of active clamp technology patents, which is characterized by active clamp in the second generation will be the basis of core reset the energy released when transferred to the load, so to achieve a higher conversion efficiency. It consists of three circuit: one of the options can be used N channel MOSFET, and therefore a higher operating frequency, using the technology can be ZVS soft switching, synchronous rectification are combined, thus achieving up to 92% of its efficiency and power density of more than 250 W/in3.
        1.1.2 ZVS full-bridge phase shift
        Mid-90s from the 20th century, ZVS full-bridge soft-switching phase-shifting technique has been widely used in the field of power supply. The technology in the MOSFET's switching speed is not ideal, the greater efficiency of the converter play a significant role, but its shortcomings are many. The first one is to add a resonant inductor, which led to a certain size and loss, and the resonant inductor of the electrical parameters of the need to maintain consistency, which in the manufacturing process is more difficult to control; second drawback is the loss of effective duty cycle ratio [1]. In addition, synchronous rectification easier to improve the converter efficiency, phase-shifted full bridge on the secondary side synchronous rectification control performance is not satisfactory. The initial phase PWM ZVS full-bridge controller, UC3875 / 9, and UCC3895 Primary only control, are subject to the logic circuitry to provide accurate time signal pole synchronous rectifier control; today the latest phase full-bridge PWM controllers such as the LTC1922 / 1 , LTC3722-1/-2, despite the increase in secondary synchronous rectification control signal, but still can not effectively achieve the secondary side of the ZVS / ZCS synchronous rectification, but this is to improve the converter efficiency of one of the most effective measures. Another major improvement but LTC3722-1/-2 can reduce the inductance of resonant inductor, resonant inductor not only reduces the size of its loss, the loss of duty cycle also been improved.
        1.1.3 Synchronous Rectification
        Including self-driven synchronous rectification and an external drive. Self-driven synchronous rectification is simple, but the secondary voltage of transformer leakage inductance and so are vulnerable to many factors, resulting in lower volume and less reliable when applied to actual products. For more than 12 V to 20 V output voltage change is about more than using a dedicated external drive IC, it can achieve better electrical performance and greater reliability.
        TI firm has made a forecast-driven strategies of the chip UCC27221 / 2, the dynamic dead-time adjustment to reduce body diode conduction losses. ST companies to design a similar chip STSR2 / 3, not only for anti-shock is also applicable to forward, while improving the continuous and discontinuous conduction mode performance. American Electric Power Electronic Systems Center (CPES) of a variety of resonant driver topologies to reduce drive wear and tear [2], and in 1997 proposed a new type of synchronous rectifier circuit, said subject to a square wave synchronous rectification, synchronous rectification can decrease tube diode conduction losses and reverse recovery loss, and the primary main switch is easy to achieve soft switching [3]. Linear         Technology has introduced LTC3900 synchronous rectifier control chip and the LTC3901 can be better used in forward, push-pull and full-bridge topology.
        ZVS and ZCS synchronous rectification has also started to applications such as active clamp forward circuit of synchronous rectifier drive (NCP1560), two-transistor forward synchronous rectifier drive circuit chip LTC1681 and LTC1698, but have not made symmetrical circuit extension Park ZVS / ZCS synchronous rectification of the good results.

        1.2 Modeling and Simulation
        Switching converters are mainly small-signal and large signal analysis of two models.
        Small signal analysis method: mainly state-space averaging method [4], by the United States California Institute of Technology RDMiddlebrook made in 1976, can say that this is the field of power electronics modeling and analysis of the first major breakthrough in a truly . Subsequently the equivalent circuit such as current injection method, the equivalent controlled source method (the method by the Chinese scholar Zhang column was submitted in 1986), three-terminal switching devices and so on, these are the areas belonging to the circuit averaging method. Average disadvantage is obvious, the signal is the average processing and analysis can not effectively carry out the ripple; is not an accurate stability analysis; of the resonant type converter may not fit; The point is, averaging method derived The model has nothing to do with the switching frequency, and the applicable conditions is in the circuit inductance capacitance resulting natural frequency must be much lower than the switching frequency, the accuracy will be higher.
        Large-signal analysis: are analytic method, phase plane method, large-signal equivalent circuit model method, the switch signal flow method, n harmonic three-port model method, KBM method and the general average. There is also a professor of China's South China University of Technology, Mr. Qiu Shui-sheng made in 1994, equivalent small parameter signal analysis method [5], not only for the PWM converter also applies to the resonant Lei converter, and can carry out analysis of the output ripple .
        The purpose of simulation modeling, then the stability analysis. In 1978, R. Keller for the first time using RDMiddlebrook average state space theory of switching power supply of SPICE simulation [6]. Nearly 30 years, the average switching power supply SPICE modeling, many scholars have established a variety of model theory, to form a variety of SPICE models. Strong points of these models, more representative are: Dr.SamBenYaakov switch inductance model; Dr.RayRidley model; based Dr.VatcheVorperian of Orcad9.1 Pspice model of the average switching power supply; based on Steven Sandler of ICAP4 switch Power average Isspice model; based Dr. VincentG.Bello of Cadence average model of switching power supply and so on. The basis of the use of these models, combined with the main parameters of the macro converter Model, and use the model form of DC / DC converter circuit simulation software in the professional (Matlab, Pspice, etc.) platform DC analysis small-signal analysis and closed-loop large signal transient analysis.
        As the converter topology with each passing day, the development of fast, accordingly, on the converter modeling requirements more stringent. It can be said converter converter topology modeling must catch up the pace of development in order to more accurately applied to engineering practice.

        1.3 Digital Control
        A simple application of digital protection and monitoring circuit is mainly, as well as communication systems, has extensively used in communication power system. It can replace many analog circuits, the completion of the power of starting, input and output of the However, under-voltage protection, output over-current and short circuit protection, and overheat protection, through a specific interface circuit can be completed and the system communication and Display.
        The more advanced digital applications include not only achieve perfect protection and monitoring functions, it can output PWM wave, through the drive circuit to control power switching devices, and to achieve closed-loop control. Currently, TI, ST and Motorola companies, etc, launched a dedicated motor and motion control DSP chip. Digital communication at this stage the main power supply to the combination of analog and digital form, PWM some still use specialized analog chips, DSP chips are involved in the duty cycle control, and frequency settings, output voltage regulation and protection and monitoring.
        In order to achieve faster dynamic response, many advanced control methods have been gradually raised. For example, V2 Semiconductor companies improved control of Intersil companies Active-droop control, Semtech companies charge control, current control Fairchild Valley companies, IR companies to multi-phase control, and the United States, many universities have made a number of other control idea [7,8,9]. Digital control can improve system flexibility, better communication interfaces, fault diagnosis capability, and anti-jamming capability. However, sophisticated communication power, control precision, parameter drift, current sense and average flow, and control delays and other factors will need urgent practical problems.

        1.4 Integrated Magnetic
        With the increase in switching frequency, switching converters be reduced in size, power density has increased substantially, but the switching loss will be increased, and will use more of the magnetic device, which occupy more space.
        Integration technology for magnetic components of foreign research is more mature, some manufacturers have used it to practice communication power. In fact, integration is not a new concept of magnetic early as the late 70s in the 20th century, Cuk Cuk converter in the proposed magnetic integration when the idea had already been presented. Since 1995, the United States and the Centre for Power Electronics Systems (CPES) integration of magnetic devices were a lot of research work, using the concept of multi-phase coupled inductors integrated inductor BUCK made a thorough research [10,11,12], and the application a variety of different types of converters. In 2002, University of Hong Kong Yim-Shu Lee, who also proposed a series of integrated technology for magnetic design [13,14,15].
        Conventional magnetic components design is extremely complicated and need to be considered from different perspectives, such as the core of the size of the choice of materials and windings to determine, and iron loss and copper loss of the assessment. Integrated Magnetics addition, however, must also consider the magnetic flux imbalance, because the flux distribution in the core of each part of the equivalent total flux is different, some parts may be ahead of saturation. Therefore, the magnetic device integrated analysis and research will be more complex and difficult. However, it brings the advantages of high power density, the future communication will be a major development trend of power.

        1.5 Manufacturing Process
        Communication with the high-frequency switching power supply manufacturing process was complex and directly affect the electrical function of the power system, electromagnetic compatibility and reliability, while reliability is the most important indicators of communication power. Manufacturing process of a complete detection means, and complete process control points and anti-static measures such as the use of considerable continuity with the best design product performance, while the extensive use of SMD chip devices will greatly improve the reliability of solder sex. Europe and the United States from 2006 lead-free process requirements for electronic products, which will have the choice of communication power in the device and manufacturing process control, higher, more stringent requirements.
        Present a more attractive technology is American Electric Power Electronic Systems Center (CPEC) made in recent years, integrated power electronic module (IPEM) concept [16], commonly known as "building blocks." Advanced packaging technology reduces the parasitic elements to improve the ringing circuit voltage and efficiency of the drive circuit and power devices are integrated together to improve the driver's speed and thus reduce the switching losses. Power Electronics Integration Technology can not only improve the transient voltage regulator can also improve power density and efficiency of the system. However, this integration module present many challenges, mainly passive and active devices integrated way, and more difficult to achieve the best thermal design. CPEC of the power electronics integration technology research for many years, made many useful methods, structures and models.