Design And Implementation Of An AC/DC Regulated Power Supply With High Power Factor

At the input port of switch supply,a lot of harmonic current is contained in the pulse current of the input rectifier and filter circuit.On the one hand,the pulse current can cause pollution to the grid;on the other hand,it can bring damage to electrical equipment.Active power factor correction(APFC)technology is the most effective way to reduce harmonic distortion and improve the power factor.In this paper,a two stage PFC AC/DC regulated power supply with high power factor was designed.And the first stage is Boost converter controlled by UC3854 PFC regulator to correct the power factor,and the second stage is double forward DC/DC converter controlled by STM32 controller to stable the output voltage.In the traditional two-stage PFC circuit,the large volume of the power supply is the main problem to be solved.Towards to this deficiency,a switches synchronous method to decrease the output voltage ripple of the first stage circuit was proposed,which was taking the driving signal's falling edge of the first stage as the trigger signal to control the MOSFET of the second stage circuit conduction.In this method,the energy can be transferred directly to the second stage without though the first filter capacitor,which can reduce the volume of the capacitor.In this paper,the STM32 control chip is as the core,to detect the falling edge of the first stage PWM signal to make the MOSFET conducted of the second stage,at the same time,the output voltage was sampled,combined with the PID algorithm to get the required duty ratio to control the MOSFET closed.Simulation of the overall system was conducted in Matlab/Simulink,the result show the design of control strategy is reasonable,and the power factor,the total harmonic distortion(THD)and output voltage ripple of the first stage are effectively improved.Finally,based on the theoretical analysis,the soft program was written and a two-stage PFC hardware circuit consists of Boost PFC and double forward converter was built.Through debugging the hardware circuit,a two stage PFC circuit was reached.The switch waveform and the output voltage waveform are tested,by the test data,the power supply is above 0.98 of the power supply,and other indicators are achieved basically according to the design requirement.