High temperature gas-cooled reactor (HTR) is a kind of reactor with inherent safety developed by Institute of Nuclear Energy and New Energy Technology of Tsinghua University. In the first circuit, pure helium is used as coolant and the main helium fan is used to promote the coolant circulation. In order to meet the requirements of service environment and performance, the main helium fan adopts the non-lubricant active magnetic bearing (AMB) system as its support system. For the high-speed rotating equipment supported by AMBs, losing power would lead to bearing failure and cause serious damage to the equipment. In this paper, the power supply system of AMBs is optimized. The power supply of AMB system is connected with the DC-link of the motor converter through DC/DC converter. During normal operation, the AMB system is supplied by external power supply, and the DC/DC converter is used as the backup redundant power supply. In the event of a power failure accident, the DC/DC converter is put into operation, converting the remanet kinetic energy of the motor into stable power to maintain the normal operation of the AMB system. The DC/DC converter adopts two-stage topology structure of the former BUCK converter and the later LLC converter, and completes the voltage stabilization control of the latter LLC converter through the digital signal processor (DSP). Experimental results show that this scheme can realize the power loss protection function of the rotating equipment supported by AMBs.