Ripple-control Multi-port Step-down Power Converter Design in Outdoor Power Supply Application

Outdoor power supplies have become increasingly popular in recent years owing to the increasing popularity of outdoor camping and hiking. To convert the energy stored in lithium batteries into various portable forms of consumption, many power converter topology and control strategies are being proposed and studied recently. The virtue of lightweight, adaptive, stable should be taken into consideration in power converter design according to special needs of outdoor power supplies. In this paper, a ripple-control multi-port step-down power converter is proposed. The proposed design converts 42V~56V(16xLiFePO4) from lithium battery bank to a 21V~28V first stage output for charge controller (SW3516/SW3526) and a 12V second stage output for cigarette lighter output. The topology incorporates a 2:1 step-down charge pump and introduces a parasitic CCM Buck converter to provide two outputs of different voltage levels without introducing additional active circuitry, thus shrinks the overall solution size, cost and EMI emission. The primary output is optimized for efficiency, while the secondary output is optimized for load regulation. A ripple injection circuit is used to indirectly sense inductor current, which is a Thevenin equivalent of the CF-type3(parallel RC-filter) feedback controller, being capable of effectively predict inductor current. This virtual peak current control method greatly reduces output ripple without introducing resistive losses commonly associated with a true current sensor while preserving transient responsiveness. LTspice simulation is used to compare and analyze the proposed converter topology with a comparison set in terms of ripple injection feedback and loop control in details. Thanks to the superior performance of the proposed power converter, a small 3x2.5 cm² (5cm² excluding connectors) prototype based on GreenPAK programmable CMIC SLG46855 is fabricated, which is capable of delivering up to 288W of output at a relatively high efficiency, performing high coincidence with theory analysis and simulation. This paper not only gives a practical solution for portable outdoor power supply application but also provides compatibility and extensibility for other multi-port ripple-control based converter design.