【正文】 8 壓由開關(guān)變壓器傳遞，并與后級隔開，返回的取樣電壓由光耦傳遞也與后級隔開，所以前級的市電電壓，是與后級分離的，這就叫冷板，是安全的，變壓器前的電源是獨立的，這就叫開關(guān)電源。斬波器的工作方式有兩種，一是脈寬調(diào)制方式 Ts 不變，改變 ton(通用 )，二是頻率調(diào)制方式， ton 不變，改變 Ts（易產(chǎn)生干擾）。 Boost 電路 —— 升壓斬波器，其輸出平均電壓 開關(guān)電源及電路圖 U0 大于輸入電壓 Ui，極性相同。 Cuk 電路 —— 降壓 或升壓斬波器，其輸出平均電 壓 U0 大于或小于輸入電壓 Ui，極性相反，電容傳輸。 當今軟開關(guān)技術(shù)使得 DC/DC 發(fā)生了質(zhì)的飛躍，美國VICOR 公司設(shè)計制造的多種 ECI 軟開關(guān) DC/DC 變換器，其最大輸出功率有 300W、600W、 800W 等，相應(yīng)的功率密度為 (、 17)W/cm3，效率為（ 80～ 90） %。 AC/DC 變換 AC/DC 變換是將交流變換為直流，其功率流向可以是雙向的，功率流由電源 9 流向負載的稱為“整流”，功率流由負載返回電源的稱為“有源逆變”。 AC/DC 變換按電路的接線方式可分為，半波電路、全波電路。按電路工作象限又可分為一象限、二象限、三象限、四象限。開關(guān)電源模塊作為一種電力電子集成器件，要注意選擇。s work, the relationship of life bee increasingly close, and electronic equipment without reliable power, into the 1980s, puter power and the full realization of the switching power supply, the first to plete the puter Power new generation to enter the switching power supply in the 1990s have entered into a variety of electronic, electrical devices, programcontrolled switchboards, munications, electronic testing equipment power control equipment, power supply, etc. have been widely used in switching power supply, but also to promote the rapid development of the switching power supply technology . Switching power supply is the use of modern power electronics technology to control the ratio of the switching transistor to turn on and off to maintain a stable output voltage power supply, switching power supply is generally controlled by pulse width modulation (PWM) ICs and switching devices (MOSFET, BJT) position. Switching power supply and linear power pared to both the cost and growth with 11 the increase of output power, but the two different growth rates. A power point, linear power supply costs, but higher than the switching power supply. With the development of power electronics technology and innovation, making the switching power supply technology to continue to innovate, the turning points of this cost is increasingly move to the low output power side, the switching power supply provides a broad space for development. The direction of its development is the highfrequency switching power supply, high frequency switching power supply miniaturization, and switching power supply into a wider range of application areas, especially in hightech fields, and promote the miniaturization of hightech products, light of. In addition, the development and application of the switching power supply in terms of energy conservation, resource conservation and environmental protection are of great significance. classification Modern switching power supply, there are two: one is the DC switching power supply。 the other is not isolated as nonisolated DC / DC converter. 12 Isolated DC / DC converter can also be classified by the number of active power devices. The single tube of DC / DC converter Forward (Forward), Feedback (Feedback) two. The doublebarreled doublebarreled DC/ DC converter Forward (Double Transistor Forward Converter), twintube feedback (Double Transistor Feedback Converter), PushPull (Push the Pull Converter) and halfbridge (HalfBridge Converter) four. Four DC / DC converter is the fullbridge DC / DC converter (FullBridge Converter). Nonisolated DC / DC converter, according to the number of active power devices can be divided into singletube, double pipe, and four three categories. Single tube to a total of six of the DC / DC converter, stepdown (Buck) DC / DC converter, stepup (Boost) DC / DC converters, DC / DC converter, boost buck (Buck Boost) device of Cuk the DC / DC converter, the Zeta DC / DC converter and SEPIC, the DC / DC converter. DC / DC converters, the Buck and Boost type DC / DC converter is the basic buckboost of Cuk, Zeta, SEPIC, type DC / DC converter is derived from a single tube in this six. The twintube cascaded doublebarreled boost (buckboost) DC / DC converter DC / DC converter. Four DC / DC converter is used, the fullbridge DC / DC converter (FullBridge Converter). Isolated DC / DC converter input and output electrical isolation is usually transformer to achieve the function of the transformer has a transformer, so conducive to the expansion of the converter output range of applications, but also easy to achieve different voltage output , or a variety of the same voltage output. Power switch voltage and current rating, the converter39。 can be divided into pulsewidthmodulated and pulse 14 amplitude modulated two pulse width modulated control the width of the signal is frequency, pulse amplitude modulation control signal amplitude between the same effect are the oscillation frequency to maintain within a certain range to achieve the effect of voltage stability. The winding of the transformer can generally be divided into three types, one group is involved in the oscillation of the primary winding, a group of sustained oscillations in the feedback winding, there is a group of load winding. Such as Shanghai is used in household appliances art technological production of switching power supply, 220V AC bridge rectifier, changing to about 300V DC filter added to the collector of the switch into the transformer for high frequency oscillation, the feedback winding feedback to the base to maintain the circuit oscillating load winding induction signal, the DC voltage by the rectifier, filter, regulator to provide power to the load. Load winding to provide power at the same time, take up the ability to voltage stability, the principle is the voltage output circuit connected to a voltage sampling device to monitor the output voltage changes, and timely feedback to the oscillator circuit to adjust the oscillation frequency, so as to achieve stable voltage purposes, in order to avoid the interference of the circuit, the feedback voltage back to the os