Frequency Response Measurements of DC-DC Buck Converter

The key design objective for switched mode power supplies is to achieve stability. The uncompensated system is affected by disturbances appearing at the input voltage as well as in the load current. To mitigate the effect of these disturbances some sort of control scheme is necessary to be added to the system for stable operation and robustness of the system. The introduction of control scheme into the feedback path of the converter system enables it to cope with the issue of disturbances. The frequency domain performance measure parameters i.e. gain margin, phase margin and crossover frequency give fair idea about the stability and overall performance of the system. But the analysis of the system only via simulation is not sufficient for most applications. In many cases the actual circuit is affected by parasitic elements and electromagnetic interference. Therefore measurement of the loop gain of the system is necessary to ensure the system's stable operation. In this work modeling of DC-DC buck converter system is done in Matlab. The results for uncompensated system, controller and compensated system are obtained. Before the implementation of prototype Saber is used for schematic simulation of the system. The simulation in Saber gives a fair idea about the performance of the actual system. Finally based on the system modeled, a prototype is implemented and frequency response measurements are done using network analyzer. The measurement results agree with simulation results and system is able to achieve the targeted values of phase margin and crossover frequency.