The UCG28826 includes self bias and auxless sensing to eliminate the transformer auxiliary winding. This makes the system design simpler, smaller and cheaper by reducing the auxiliary winding and the associated components.

The self bias feature is especially useful in application like USB-PD chargers with wide output voltage range. Typically in such designs, the aux winding generates device supply voltage (VCC) greater than its UVLO threshold at the minimum V_OUT which is 3.3V. In such case, the voltage on aux winding increases six times when V_OUT = 20V which needs an internal/external power conversion stage to reduce to VCC range, increasing external components and reducing efficiency. The UCG28826's self bias eliminates the need for such additional power conversion stage at the VCC pin thus reducing the number of components and recovering their power losses. The self bias circuit is designed to keep VCC higher than its UVLO threshold throughout the range of operation of the device, given the components around the device are used within the datasheet recommended range. Auxless sensing circuits are connected to the SW pin. The device senses the voltage on SW for valley sensing and various protections.