Number of Electric vehicles (EV) and hybrid electric vehicles (HEV) are constantly growing in automotive sector. A HVLV DCDC converter is one of the significant parts in the overall electronics of the HEVs and EVs, which is primarily used to charge the low voltage battery from the high voltage battery. In the HVLV DCDC circuit design, bias power supply contains a major part. These are used to supply the required power to the gate drivers, microcontrollers and sensors and so forth. There are different possible architectures for the isolated and non-isolated bias power supply of the HVLV DCDC converter. These architectures also influence the choice of the topologies and associated devices in the circuit design.