DC-DC converters are broadly used in many industries, like electric vehicles, industrial inverters, telecommunications systems, and many others. However, these converters face many challenges when it comes to their performance, particularly when they are used with constant power load (CPL) which has negative-incremental resistance. These loads might lead to instability issues with the converter’s output voltage. This manuscript offers a way out to the above stated challenge, a robust nonlinear control approach has been developed. The control strategy is constructed on passivity-based controller (PBC) and employs a nonlinear-disturbance observer (NDO) to increase controller effectiveness against CPL. The PBC ensures system stability by dissipating transient energy and on the other hand, NDO operates in parallel to compensate for disruptions via a feed-forward channel. This method produces high signal stability and quick recovery performance during load disturbances and uncertainties. The offered strategy to control has been evaluated through simulations using a MATLAB-SIMULINK model. The results showed that this strategy may effectively address instability issues created by CPL.