| Traditionally a large number of application of bridge rectifier and large bulk capacitance of the rectifier circuit, lead the power grid to supply electronic equipment with severe distortion of non-sinusoidal current, low circuit power factor and the harmonic current to pollute the power grid at the same time. In order to reduce the harmonic current of power grid pollution and improve power factor, more and more power supply design has used power factor correction techniques. At home and abroad the corresponding standards have been formulated to limit the input current harmonic. Under the efficiency of small and medium-sized applications, in order to reduce cost and volume, single stage active power factor correction techniques have attracted more and more attention. Single stage flyback APFC converter has some advantages, such as high power factor, harmonic distortion is small, can adjust the output voltage according to the need, output and input isolation, simple structure, high cost performance. Under the efficiency of medium and small sized applications, single stage flyback APFC converter is a preferable solution.This paper is to study under the condition of full voltage input and variable load critical mode the single-stage flyback APFC converter maintaining high power factor, for the purpose of finished work as follows:this paper is to study under the condition of full voltage input and variable load BCM single stage fayback APFC converter maintaining high power factor. The paper completed the work as follows:(1) In the aspect of basic knowledge, this paper firstly introduces the basic concept of power factor correction. The BCM single-stage flyback APFC converter principle is analyzed and the main design of the formula is derived. Finally the paper analyzes the BCM single-stage flyback APFC converter power factor and total harmonic distortion. Then focuses on the ideal switch power supply loop frequency characteristic and the transfer function analysis of the feedback compensation network. Finally analyzed based on the feedback loop PC817 and TL431, involving the transfer function is derived in detail.(2) This paper design a 30W voltage-mode BCM single-stage flyback APFC converter experimental prototype, including the overall structure of converter system, the design of main circuit, PFC control circuit design, the feedback loop design and EMI filter circuit design. Control chip employ Fairchild Semiconductor FAN7930B. FAN7930B is an APFC controller, which use a voltage-mode PWM and operate in BCM. The paper analysis the problem of converter PF that is not stable or even decline seriously under the condition of full voltage and variable load. And for the converter work under the condition of full voltage variable load, the feedback compensation network is proposed to effectively stabilize PF.(3) By making the experimental prototype and debugging prototype, the prototype parameters set the desired parameters, which verify the viability of this converter design. In full load condition,When the input voltage is 90～265V, PF is greater than 0.984, the efficiency is more than equal to 0.90, the total harmonic distortion is less than 12%. In the input voltage of 110V, when the load from 100% load to 20% load, PF is greater than or equal to 0.98. In the input voltage of 220V, when the load from 100% load to 20% load, PF is greater than or equal to 0.925.In the process of data analysis, the paper provide optimized design ideas for different application. The experimental results show that the voltage-mode BCM single stage APFC flyback converter has the characteristics of small size, low cost, high efficiency and achieve high power factor under the condition of full voltage variable load. |
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