A Design Of High-performance Fly-back Power Management Chip

With simple structure, lower cost and input-output isolation characteristics,Fly-back Switching Power Supply is widely used in small and medium power AC/DCSwitching Power Supply.Based on the principle of Fly-back Switching Power Supply and active powerfactor correction, this thesis designed a high-performance power management chip. Itsmaximum output power can reach20W, quiescent operating current is below1mA,standard operating frequency is about70kHz. It also achieves a constant output currentwith the feedback signal from the primary coil, and its input power factor can reach0.95or above. The chip also integrated kinds of protection sub-blocks to ensure the safety.This thesis designed these sub-blocks that are relevant to the constant currentcontrol and power factor correction. More specifically, these sub-blocks are zero currentdetection module, current peak detection module, actual current arithmetic module,error comparator and PWM/PFC comparator. The zero current detection module isdesigned to turn on the switch when the current in the secondary winding becomes zero.The equivalent average value of output current can be obtained easily by the analysis ofthe current peak detection module and the actual current arithmetic module, and thiscurrent can be stabled by the high-gain error comparator. The function of PWM/PFCcomparator is to shut off the switch after the peak current of input side reaches thesetting value, and this design can achieved an object that is the same phase of the inputcurrent and input voltage if only we make the phase of the limit voltage be same withthe actual value, thereby realizing the function of the power factor correction.The five sub-blocks above were analyzed in detail. Firstly, Specific design indexeswere made. Secondly, detail circuits were designed. Thirdly, the accuracy of the designwas verified with the result of simulation. Finally, all of sub-blocks were connected andthe circuit with peripheral circuits was simulated.