This reference design introduces a tiny auxiliary power supply unit (PSU) used to supply automotive insulated-gate bipolar transistor (IGBT) or automotive silicon carbide (SiC) drive. The isolated outputs support three gate controls, each supplied with +21.2V, 2W output. This design uses the planar transformer to reduce the board height and cost. The LM25184-Q1 controller supports primary-side regulation by controlling the flyback voltage from secondary side. There is no need for an additional auxiliary winding. The board maximum efficiency is 89.2%. The design uses six PCB layers, and the temperature rise is just 16°C with full load 6W.