The determination of the boundaries between continuous and discontinuous conduction modes in PWM DC-to-DC converters used as power factor preregulators

The determination of the boundaries between both modes of conduction (continuous and discontinuous) in PWM DC-to-DC switching power converters used as power factor preregulators (PFP) is presented in this paper. When a DC-to-DC switching power converter works as a power factor preregulator, its operating point is constantly changing due to the fact that both the DC voltage conversion ratio and the load “seen” by the power converter are constantly changing in each half-sinusoid of the line voltage (input voltage of the converter). In these conditions, the conduction mode cannot be directly determined. In this paper, the boundaries between both conduction modes in each angle of the half-sinusoidal input voltage have been determined. The conditions to always operate in continuous or in discontinuous conduction modes have been determined as well. Finally, these results have been verified by simulations and experimental results