1、<p>　　Switching Power Supply </p><p>　　Switching power supply is a voltage conversion circuit, the main work is the step-up and step-down, are widely used in modern electronic products. Always work beca

2、use the switching transistor in the "on" and "off" state, so called switching power supply. Switching power supply in real terms is an oscillator circuit, the conversion of electrical energy not only

3、used in power circuit, the circuit in other applications are also common, such as LCD backlight circuits, such as fluorescent lamps. Swit</p><p>　　Talking about switching power supply before you familiar wit

4、h the feedback oscillator circuit transformer, can produce a regular pulse current or voltage of the circuit is called oscillation circuit, transformer feedback oscillator circuit is able to meet these conditions the cir

5、cuit; it in the basic amplifier circuit with a feedback loop composed of C2, L1 election to form a parallel resonant frequency circuit, the instantaneous power in the circuit turn-VT, this time in the C2, L1, composed of

6、</p><p>　　Switching Power Supply vibration by way of sub-swing can be divided into self-excited and it excited the two, since there is no need for plus-excited self-oscillation signal source, since the excit

7、ation can see it as a feedback oscillator circuit transformer, and it is excited is totally dependent on the outside to maintain the oscillation, in the practical application of self-excitation of a comprehensive range o

8、f applications. According to the structure of incentives signal classification; can</p><p>　　Some switching power supply are complex, numerous components, many protection and control circuit, in the absence

9、of technical support, maintenance is a headache with the matter. I face this kind of situation is, first of all, I will find the switch and its participation in the external oscillation circuit, it separated from the cir

10、cuit to see if it met the conditions for oscillation, such as detection bias and whether it is normal, whether positive feedback failure, as well as its own switches,</p><p>　　SMPS developments and trends in

11、 the United States in 1955 Roje (GH.Roger) invention of the self-excited oscillation push redeem transistor single transformer DC converters, high-frequency conversion is the beginning of control circuit, 1957 United Sta

12、tes investigation tournament (Jen Sen) since the invention of the push-pull double Flyback transformers, 1964 American scientists proposes to abolish the frequency transformer series switching power supply scenario, This

13、 power to the right size and </p><p>　　Currently, switching power supply to small, Light volume and the characteristics of high efficiency has been widely used in electronic computer-driven variety of termin

14、al equipment, Communications equipment almost all electronic equipment, the electronic information industry indispensable to the rapid development of a power mode. Currently the market for sale in the switching power sup

15、ply using bipolar transistors made of 100kHz. use made of 500kHz MOS power, though practical, but its frequency </p><p><b>　　開關(guān)電源</b></p><p>　　開關(guān)電源是一種電壓轉(zhuǎn)換電路，主要的工作內(nèi)容是升壓和降壓，廣泛應用于現(xiàn)代電子產(chǎn)品

16、。因為開關(guān)三極管總是工作在 “開” 和“關(guān)” 的狀態(tài)，所以叫開關(guān)電源。開關(guān)電源實質(zhì)就是一個振蕩電路，這種轉(zhuǎn)換電能的方式，不僅應用在電源電路，在其它的電路應用也很普遍，如液晶顯示器的背光電路、日光燈等。開關(guān)源與變壓器相比具有效率高、穩(wěn)性好、體積小等優(yōu)點，缺點是功率相對較小，而且會對電路產(chǎn)生高頻干擾，電路復雜不易維修等?！　≡谡勯_關(guān)電源之前，先熟悉一下變壓器反饋式振蕩電路，能產(chǎn)生有規(guī)律的脈沖電流或電壓的電路叫振蕩電路，變壓器反饋式振蕩電路

17、就是能滿足這種條件的電路；它于基本放大電路與一個反饋回路組成，其中C2、L1組成一個并聯(lián)諧振選頻電路，在電路通電的瞬間VT導通，此時在C2、L1組成的并聯(lián)諧振電路上產(chǎn)生非常豐富的諧波，當外加頻率和并聯(lián)諧振電路的固有頻率相等時,電路進入振蕩狀態(tài)，并通過L3反饋到VT的基極進一步放大，最終形成有規(guī)律的脈沖電流或電壓輸出到負載RL上。開關(guān)電源就是圍繞變壓器反饋式振蕩電路而設(shè)計，只不過在原來的基礎(chǔ)上增加了一些保護和控制電路，我們可以用分析振蕩電

18、路的方法來分析開關(guān)電源?！　￠_關(guān)電源振按</p><p>　　1955年美國羅耶（GH.Roger)發(fā)明的自激振蕩推挽晶體管單變壓器直流變換器，是實現(xiàn)高頻轉(zhuǎn)換控制電路的開端，1957年美國查賽（Jen Sen)發(fā)明了自激式推挽雙變壓器，1964年美國科學家們提出取消工頻變壓器的串聯(lián)開關(guān)電源的設(shè)想，這對電源向體積和重量的下降獲得了一條根本的途徑。到了1969年由于大功率硅晶體管的耐壓提高，二極管反向恢復時間的縮短

19、等元器件改善，終于做成了25千赫的開關(guān)電源。</p><p>　　目前，開關(guān)電源以小型、輕量和高效率的特點被廣泛應用于以電子計算機為主導的各種終端設(shè)備、通信設(shè)備等幾乎所有的電子設(shè)備，是當今電子信息產(chǎn)業(yè)飛速發(fā)展不可缺少的一種電源方式。目前市場上出售的開關(guān)電源中采用雙極性晶體管制成的100kHz、用MOS－FET制成的500kHz電源，雖已實用化，但其頻率有待進一步提高。要提高開關(guān)頻率，就要減少開關(guān)損耗，而要減少開關(guān)

20、損耗，就需要有高速開關(guān)元器件。然而，開關(guān)速度提高后，會受電路中分布電感和電容或二極管中存儲電荷的影響而產(chǎn)生浪涌或噪聲。這樣，不僅會影響周圍電子設(shè)備，還會大大降低電源本身的可靠性。其中，為防止隨開關(guān)啟-閉所發(fā)生的電壓浪涌，可采用R-C或L-C緩沖器，而對由二極管存儲電荷所致的電流浪涌可采用非晶態(tài)等磁芯制成的磁緩沖器。不過，對1MHz以上的高頻，要采用諧振電路，以使開關(guān)上的電壓或通過開關(guān)的電流呈正弦波，這樣既可減少開關(guān)損耗，同時也可控制浪涌