An embodiment of the invention discloses a direct current-direct current converter. The direct current-direct current converter comprises a transformer, wherein the primary side of the transformer is connected with the high voltage power supply; the secondary side of the transformer is connected with a load; the direct current-direct current converter also comprises an electric reactor and a switch circuit; the electric reactor is connected between the primary side of the transformer and the high voltage power supply; the switch circuit is arranged between the secondary side of the transformer and the load; and the switch circuit modulates the output voltage of the secondary side of the transformer into square wave voltage. Compared with the prior art, the applied range of the direct current-direct current converter provided by the invention is enlarged.