DC/DC converters provide stable output voltage and variable output current. It is used to maintain a steady, stable voltage as a power supply for semiconductor devices. DC/DC converters are a necessity for almost all electronic devices and are used to maintain a constant output voltage regardless of minor variations in input voltage or load current. Modeling and simulation is the instrument used to shape the system level analysis and obtain better performance of the converters.A better controller could be obtained if the experimental data is used to determine the load information. The aim of this work is to model the buck converter system of Ericssons BMR450 controller and develop a time-domain based system identification method to identify the capacitive load. The model is implemented in Matlab Simulink and is composed of simple circuits. The system is analyzed through excitation from the command input using binary signal, which include all frequencies of it. The sampled data are analyzed and preprocessed to estimate a mathematical model and validate it. The proposed method is able to identify the load parameter with good accuracy.