The numbers of electric vehicles (EV) and hybrid electric vehicles (HEV) in the automotive industry are increasing. An onboard charger is one of the significant parts in the overall electronics of the HEVs and EVs, which is used to charge the high voltage battery. In the onboard charger circuit design, isolated bias power supply contains a major part of the circuit. These chargers are used to supply the required power to the gate drivers. There are several possible architectures for the isolated bias power supply to the gate drivers in the power factor correction (PFC) and DC-DC converter stages of the onboard charger. These architectures also influence the choice of the topologies and related devices used for the isolated bias power supply in the onboard charger.