The Design Of Switching Power Supply With High Power Factor And Load Sharing

This system designs an AC-DC switching power supply consisted of three parts, which are APFC(Active Power Factor Correction), forward converter and load sharing. The input voltage is AC 165~265V,50Hz, and the output is DC 48V,3A. The input stage adopts APFC(Active Power Factor Correct) control system, which was achieved by Boost topology circuit controlled by the chip of UC3854.This design improves the PF(Power Factor) of this power supply ,which achieves at about 97%, and reduces the interfere to the electric nets transmitted by the power supply. The power converter stage which id used the single-ended forward converter as main circuit, and controlled by the chip of UC3842, works in the good condition. The output voltage precision is =1%, and the ripple of full load is =150mV.The output stage adopts the N+1 load sharing controlling system, which is not consisted of UC3907,but a circuit system made up of operators. Tested in the same condition, the load sharing precision of this new system which is ≤3.3% is the same as that of the system made up of the UC3907.This power supply system reduces the costs, and the efficiency of the wholly system is 85.5%.