This article proposes a current mode control BUCK structure with a fast response and high efficiency by designing a high-speed output detection circuit. When switching between loads, the system loop quickly responds, and the transient bias current rapidly increases, resulting in a smaller transient voltage. The proposed instantaneous gain enhancement path structure is implemented with a TSMC 180-nm process. Simulation results show that in typical applications, when the load current switches between 1 and 1.5 A, the transient output voltage is within 26 mV. The transient voltages of traditional structures with and without feedforward capacitors are 46 and 74 mV, respectively; thus, the proposed system reduces these by approximately 43% and 65%, respectively, and significantly improves transient response speeds. Additionally, the peak efficiency can reach 96%.