The present paper introduces the design and simulation of an op-amp-based PID-controlled DC-DC buck converter to regulate a DC voltage of 12 V to 5 V and support load currents ranging from 1 A to 5 A for automotive applications using LTspice software. The converter operates at a switching frequency of 550 kHz, delivering a regulated output voltage of 5 V for load currents ranging from 1 A to 5 A, with a maximum output voltage ripple of 47.56 mV. The proposed buck converter settles to its regulated value within 943.4 µs at a load current of 1 A, with a peak efficiency of 92.83%. The simulation results of the proposed buck converter response to load current fluctuations show that the buck converter settles to its regulated value in 83.36 µs during a load current change from 1 A to 5 A with an undershoot of 92.62 mV. Conversely, during a load change from 5 A to 1 A, the proposed buck converter recovers from an overshoot of 52.04 mV within 46.32 µs.