Stability Analysis And Design Of Single Stage Buck PFC Converter

With the booming development of electronic power system, electronic electrical equipment has become more and more popular in daily lives, meanwhile it also leads to harmonic pollution to the electricity network. And the power factor correction(PFC) technology is a valid method to improve the power factor of electronic products, decrease harmonic interference, reduce electrical pollution and benefit energy conservation. Therefore it has become one of focuses and important study in electronic field at present that how to improve the power factor(PF) of power IC. The active power factor correction(APFC) technology has been found attractive in most applications not only because it can improve power factor and reduce the total harmonic distortion(THD), but also it has large input voltage range, simple structure and high efficiency. So this paper focuses on tlle design of low cost PFC chip to suit the growing prevalence of small power equipment.It is designed a single stage buck PFC power management IC XD5814 A for LED lighting, and analyzes the loop stability. Firstly this paper introduces the technology and application background of the buck PFC converter. Secondly it describes a description of the definition and control method of power factor correction, and the design and selection principle of the periphery devices are also taken into consideration in this paper. Thirdly, it is to make the Buck topology modeling to analysis of its stability by the state space average method, and improve the system loop stability by analysizing the pole and zero point of transfer function. Finally, some key sub-blocks and whole-chip simulation have been done to verify correction of the above theories. In the view of the shortcoming of the traditional PFC chip in slow transient response for its low band width filter function to reduce the harmonic distortion, the OTA is developed with innovative slew rate enhancement circuits in this PFC. Meanwhile this power chip achieves the higher efficiency in the quasi-resonant(QR) mode and makes the AC input current follow the AC input voltage waveform in the constant on time operation to achieve high power factor. Furthermore, in order to improve of the current controlling precision and achieve the power factor correction, the inductor current sampling circuit of this power IC controls the constant output current by realizing the output current, and improve safety and reliability of this power IC, many protection systems are integrated in it,such as undervoltage lockout(UVLO), open load protection(OLP) and overtemperature protection(OTP) circuit, and reduce the cycle of designing this power IC, testability circuit is also intergrated in it.The input current and voltage can be effectively synchronized the designed APFC controller chip and reduce current distortion, which dramatically optimizes THD. The function described above has been simulated on 0.8μm,5V/30V/600 V BCD process by Hspice. The PFC converter chip works in the condition of the output voltage of 24 V and the output current of 0.3A( 0.1Aout?I ?), and its power factor is 0.977. The total harmonic distortion(THD) is eaual to 0.21, Experimental results show that the performance of XD5814 A is good.