Effective Hold-Up Time Extension Method Using Fan Control in Server Power Systems

This letter proposes a simple and effective hold-up time extension method for server power systems, in which the fan is only turned off during the hold-up time with ac input loss. Due to the elimination of the fan power in the proposed method, the efficiency of the dc–dc converter increases during the hold-up time; thus, the energy stored in the link capacitor decreases less sharply, compared with the conventional method. That is, the hold-up time can be extended without additional devices, volume increase, and operational change of the dc–dc converter, maintaining high efficiency and high power density. The effectiveness of the proposed method is verified by a prototype with 90–264 Vac,rms input, 800 W/12 V output specifications of the server power supply.