In general, a zero-voltage switching (ZVS) condition of boost-integrated DC-DC converters is load dependent and lost at a light load due to an insufficient energy stored in a leakage inductor. To extend a ZVS load range without increasing an external leakage inductor at a light load condition, a frequency modulation (FM) control is proposed. By modulating a switching frequency adaptive to a load current at a desired load range, ZVS can be recovered through an energy stored in a boost inductor so that the switching losses can be significantly reduced. Thus, the conversion efficiency at a light load condition can be improved. A ZVS boost integrated flyback (BIF) converter with a voltage doubler rectifier (VDR) is presented to apply the proposed control method as an example. Experimental results from a digitally implemented prototype are shown to demonstrate the proposed work.