Low-voltage isolated bias power supply circuits usually have a 12V battery as a power source in HEV and EV. Although there are some systems with 48V as a LV battery, this paper focuses on the 12V battery system. However, these architectures can be still relevant for 48V LV battery designs. In that case, one option is to have a converter to lower the voltage to use the same devices or another option is to have devices supporting an input voltage range designed for a 48V battery.

Considering the state of charge (SOC) of the 12V LV battery, the wider input voltage range needs to be supported by the isolated bias power supply (as an example: 8V–16V). In case of cold crank and load dump scenarios, the input voltage range requirement goes further down and up, respectively. There can be differences in this wide input voltage range of 12V LV battery depending on the OEM. Not all types of topologies and the associated devices can support this wide input voltage range. Therefore, in several designs a pre-regulator is needed between LV battery and isolated bias power supply to regulate the input voltage for the isolated bias power supply device.