DC POWER SUPPLY

To achieve a stable synchronous rectification to improve a conversion efficiency of a DC power supply without inversely flowing an AC current from an AC power in the case where a power factor improvement is not performed.SOLUTION: A DC power supply which is operated in a first operation mode that performs a power factor improvement of an AC power with a synchronous rectification operation and a second operation mode that executes only a synchronous rectification and does not perform the power factor improvement, comprises: a threshold value storage part that stores positive and negative threshold values in advance. In the case where a polarity of an AC voltage from the AC power is positive, the synchronous rectification is partially inhibited by performing at least a low side opening of a full bridge circuit 4 when the AC current is less than the threshold value of the positive stored in the threshold storage part. In the case where the polarity of the AC voltage from the AC power is negative, the synchronous rectification is partially inhibited by opening at least a high side of the full bridge circuit 4 when the AC current exceeds the negative threshold stored in the threshold storage prat.SELECTED DRAWING: Figure 1 【課題】力率改善を行わない場合にも、交流電源からの交流電流が逆向きに流れることなく、安定した同期整流を実現し、直流電源装置の変換効率を向上する。【解決手段】同期整流動作とともに交流電源の力率改善を行う第一の動作モード及び、同期整流のみを実施し、力率改善を行わない第二の動作モードで動作する直流電源装置において、正と負の閾値を予め記憶させておく閾値記憶部とを備え、前記交流電源からの交流電圧の極性が正の場合に、交流電流が前記閾値記憶部で記憶した正の閾値未満の時には、少なくとも前記フルブリッジ回路４のローサイド開放することで同期整流を部分的に禁止し、前記交流電源からの交流電圧の極性が負の場合に、交流電流が前記閾値記憶部で記憶した負の閾値超過の時には、少なくとも前記フルブリッジ回路４のハイサイドを開放することで同期整流を部分的に禁止する。【選択図】図１