A controller for increasing efficiency of a power converter includes a comparison module and a gate signal generation unit. The comparison module is used for generating a detection voltage according to a direct current (DC) input voltage of a primary side of the power converter, and comparing the detection voltage with a predetermined value to generate a comparison result. The gate signal generation unit is used for changing a sink current flowing through a gate pin of the controller according to the comparison result, wherein the gate pin of the controller is coupled to a power switch of the primary side of the power converter.