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 converters used as power factor preregulators is studied. When a DC-to-DC switching converter works as a power factor preregulator, its operation point is constantly changing because both the DC voltage conversion ratio and the load `seen´ by the converter are constantly changing in each half-sinusoid of the line voltage (input voltage of the converter). Under these conditions, the conduction mode cannot be directly determined. The boundaries between both conduction modes in each angle of the half-sinusoidal input voltage are determined. The conditions for always operating in continuous or in discontinuous conduction modes are determined as well. The results have been verified in several prototypes and simulations