As the maximum power point of a photovoltaic (PV) cell varies mainly with incident illumination and ambient temperature, the PV cell may generate a wide range of voltages and currents at the terminals. As a consequence, the PV cell itself cannot maintain a constant DC voltage and function as a DC voltage power supply source. To overcome this problem, a DC-DC converter with the nonlinear control scheme, sliding mode control (SMC) may be used. In this paper, the SMC is proposed to controlling the output voltage of the DC-DC converter, in order to maintain and stabilize the constant DC-link voltage in both line and load variations. Furthermore, classical controls such as PI and PID are compared with the SMC in the simulation both transient and steady state responses. The results show that the SMC technique is more suitable than those classical controls. It improves the transient response and reduces the steady state error of the DC-link voltage.