This paper presents a simulation of a buck converter using pulse-width modulation (PWM) signal frequencies and duty cycles generated by an Arduino microcontroller for solar panel application. The frequencies used are 23 kHz, 62.5 kHz, 92 kHz, and 186 kHz. A circuit is composed from the results of calculating the buck converter design needed to operate with continuous current mode at minimum value of the component needes. Load used in the circuit is a single Li-ion cell which has a voltage of ~4.2 V, with a simulated panel specifications are 18.36 V and 0.56 A. The I-V characteristics of the converter are studied at input and output in changes of duty cycle and frequency to obtain the overall operating characteristics for each frequency. Overall, the panel current increases before the peak power voltage and decrease after. A peak current of ~1150 mA occurs at frequencies of 23 kHz, 62.5 kHz, 92 kHz, and 186 kHz for duty cycles of 50%, 35%, 35%, and 20%, respectively. Thus, 23 Khz PWM signal is the optimal frequency to drive the circuit beecause of the wide duty cycle operation. In addition, the values of both input current and voltage increase along with the duty cycle rate according to the character of the corresponding I-V curve.