This paper presents a novel observer-based control scheme for a DC-DC boost converter system using the Lyapunov stability theorem by considering input saturation. To estimate the unavailable state or parameter, a new approach called Immersion and Invariance (I&I) is employed. According to this method, two observers with exponential stability are designed for the unknown input voltage. In addition, the global exponential stability of the system in closed loop with the observer and a control signal is proven. Finally, the effectiveness of this method is validated in practical implementation and the corresponding results confirm the efficiency of the proposed scheme.