Small signal analysis and design of a single active switch converter providing power factor correction and full regulation

A new mode of operation of a SEPIC-type power factor corrector was analyzed and presented. Compared with the previously known mode it reduces the harmonic distortion by a factor of about 10. In addition, the applied control method provides a well regulated output voltage at no extra cost. Furthermore, the voltage in the energy storage capacitor is no longer load dependent. This improvement is achieved by means of a fast output feedback loop. It is essential to know the small signal behavior of the power cell in order to optimize the control loop. In this paper the small signal equations are derived for two different control modes. As a byproduct, an efficient way of using state space averaging for discontinuous conduction mode is developed. This is particularly useful for circuits with more than one discontinuous state. The paper also includes measurements to confirm the validity of the analysis.