Abstract: According to the demand of high power semiconductor laser for high power, low ripple and high reliability constant current driver, a constant current power supply based on four BUCK modules in parallel is designed. The maximum output power is 37.5 kW (250 V×150 A). The conduction time interval of the four modules is T/4 in turn, which weakens the ripple by cancellation between the modules and achieves the output current ripple rate of 0.066%. Using the parallel advantage of FPGA, it can quickly respond to the output protection, and turn off the output within 12.2 μs, so the protection is excellent. The experimental results verify the design, which has been successfully applied in a project.