In a
power factor corrected AC-to-DC power supply
system, a DC-to-DC power converter is coupled to the output of an AC-to-DC power converter in order to produce a regulated DC output
signal from a rectified AC input
signal. The AC-to-DC power converter and the DC-to-DC power converter each includes a switch for controlling the operation of their respective power converter. The AC-to-
DC converter includes an
inductor. The
system provides
power factor correction for minimizing
harmonic distortion by including a controller that receives the regulated DC output
voltage as a feedback
signal, and in response, produces a series of drive pulses having predetermined constant
duty cycle. These pulses are simultaneously fed to each switch, to operate the respective
converters alternately between ON and OFF states. When the AC-to-
DC converter is driven by a fixed
duty cycle of the series of pulses,
power factor correction is improved since the current flowing through the
inductor is substantially proportional to the waveform of the rectified AC input signal. By preselecting the value of the
inductor, the AC-to-
DC converter is operable in a discontinuous mode when the instantaneous rectified AC input signal is low and in a
continuous mode when the instantaneous rectified AC input signal is high.