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 V_ac,rms input, 800 W/12 V output specifications of the server power supply.