A power management unit with integrated stand-by supply for computer motherboards: Control and VLSI design

This paper focuses on the control strategy of a multiple-output active-clamp forward converter devoted to PC power supplies. The primary- and secondary-side switches of the forward converter are driven by dedicated ASIC units. In detail, regulation of the main-switch duty-cycle is achieved by a primary IC implementing feed-forward control, while the outputs of the converter are locally regulated by two ASICs independently from the primary-switch duty-cycle. Since no communication is required during normal mode, the duty cycle is definied by the the primary IC which controls the main switch in such a way that the primary duty-cycle is larger than the secondary one. A peak overall efficiency higher than 90% at 50% load has been obtained in normal operative conditions. During stand-by mode, communication between the primary controller and the secondary ones is however required to increase the low-power-mode efficiency. The working principle of the proposed converter is described in detail both in normal and stand-by mode. Several experimental results are carried out to validate the approach discussed throughout this paper.