A Study Of Power Factor Improvement Based On Constant On Time

With the development of power electronics technology and innovation, in the regulated power supply, switching power supply instead of linear power supply with its advantages of low power consumption and high efficiency. But there is a common problem in the power factor correction of traditional buck AC/DC switching power supply, the input voltage is sinusoidal AC signal, when the input voltage is smaller than the output voltage, the input current is no longer follows the input voltage waveform,and the input current is approximately zero. This interval is called dead zone and make the improvement of power factor limited.Aiming at this problem, a new power factor correction technology is proposed in this paper, by adding additional auxiliary winding and two switch tubes to improve the peripheral circuit. The circuit improved will be according to the relationship between the input voltage and the output voltage, divide the working state into two modes automatically. When the input voltage is greater than the output voltage, corrector will control the peripheral circuit work in the buck mode. When the input voltage is less than the output voltage, the peripheral circuit works in the buck-boost mode. Then you can eliminate the dead zone, because of the input voltage, input current is not zero, and can follow the input voltage waveform.Work in the buck boost mode, the adjustment of input current waveform is accomplished by the coefficient of K. K is the divide voltage coefficient of the output voltage of internal error amplifier of the correction. It can make a good switch of input current in the two operating mode by setting appropriate K, and will not appear the phenomenon of current pulse. We use quasi resonant technique principle to control external switch turn-on and turn off, to reduce the energy loss of external circuit. It can make the power factor of the circuit close to 1 through the parameters of reasonable setting, and the peripheral circuit of input harmonic component of current can be very good to meet the C standards of IEC61000-3-2, to reduce power waste.The method is based on a buck converter constant on time mode, and the traditional constant on time control is improved and optimized in this paper, with a MOS tube instead of the charge and discharge of the capacitor. Adjust on time according to input voltage automatically. Not only saves chip area, also make the control of on time more accurate, remove the disadvantages of traditional circuit.This paper make a comprehensive analysis of the theory of the improved method,making a theoretically verification of the peripheral circuit by using the software of Matlab, the combination of the peripheral circuit and control circuit are simulated through the software of Cadence and Hspice, the results show that, the circuit that designed achieves the desired results and eliminates the dead zone exists in the switching power supply.