A novel passive integrated unit is proposed to increase the power density of a single-stage light-emitting diode (LED) driver in this paper. With the flexible multi-layer foil (FMLF) integration technique, such an integrated unit consists of two transformers, one resonant inductor and two resonant capacitors to reduce the volume of these passive components. The composition principle, flux analysis and parameter design of the proposes integrated device are introduced in detail, respectively. Finally, the validity and feasibility of the proposed ideas are proved by the simulation results of a Maxwell model and a prototype for a 100W-100kHz single-stage LED driver.