A technique to inject fault conditions into a control board of a DC-DC converter and evaluate required functionality by using a hardware-in-the-loop (HIL) simulation is presented in this paper. The power stage of a DC-DC converter and a battery are designed by Xilinx System Generator. Whole models and the special-purpose peripherals between the control board and HIL simulator are all implemented into the FPGA for fault test. The each model on FPGA has a flexible, modular and reusable structure where the designer can customize the hardware model by changing primary parameters. HIL implementation is discussed. Fault injection test based on HIL simulation is shown to explore the useful technique indispensable to validating the predefined protection algorithm at abnormal temperatures and voltages.