On Digital Controlled Buck DC-DC Converters

To keep the intelligent terminal units working for a certain period in case of outage, A back-up switching supply based on super capacitor energy storage and buck DC-DC converters is researched. The circuit structure, the selection of the minimum working voltage of the converter and the design considerations of the capacitance of the energy storage capacitor are discussed. Based on the energy balance principle, the lowest output voltage drop and the highest output voltage rise in case of the output current suddenly changing are analyzed, respectively. The design considerations of the output filter capacitor are given. A super capacitor energy storage based back-up supply is used as the example to show the design steps. Experiments are made on the supply, the results of which show that it can meet the requirements of normal working, communication and control, and that the analysis results are in positive to the experiment results.To improve the dynamic behaviour of buck DC-DC converters, a current following digital control approach based on micro-processor is put forward. The output current and the output voltage are measured, based on which, the inductor current to make the output voltage to be the desired value is calculated and is controlled to a narrow range around it. The dynamic performance in case of the load changing and the starting period is analyzed. The design considerations are given. Taking a specific Buck converter as an example, the Simulink simulation results are obtained. Finally a buck DC-DC converter based on current following digital control has been implanted by ARM—LPC2138 and the experiments are made, the results of which show that the proposed approach is feasible, the analysis is correct and the proposed method is with fast responding speed.