The Research And Solution Of EMI Conducted Noise For Flyback Switched-mode Power Supply

With the improvement of people's material standard of living and the creation of technology,the demand of a variety of multi-functional and intellectual consuming home appliance products grows greater and greater.Nowadays home appliances within 60 W usually use flyback SMPS(switched mode power supply).Any product should get 3C certification before it could be sold in market.Besides national efficiency standards are becoming strict,the high-cost conducted EMI(Electromagnetic Interference)test also becomes a difficult problem for many companies.Firstly,the thesis analyses the principle of the conducted EMI for flyback SMPS,briefly states problems for PWM(pulse width modulation)and QR(quasi-resonant)modes.Then,5 major viewpoints were issued: PCB designing,transformer designing,main components choosing,RCD circuit designing and treatments for partial sensitive circuits.By working out EMI problems occurred in PWM and QR modes,the conclusions could be given out.Finally,after analyzing testing data the countermeasures can be proved effective and useful.Since the thesis focuses on comprehensive researches for flyback SMPS which come from a quantity of practical applications,it has strong applicability for comprehensive experiments.On the other hand,it combines the analysis with designing methods of products,which gives the analysis and countermeasure a starting from the beginning of power design and makes flyback SMPS products pass conducted EMI certification tests more easily.