In an electric vehicle, truck or bus there is both a high and low voltage power system. The HV system is supplied directly from the traction battery, supplying the motor and other large loads; the cabin and battery heater and A/C compressor. For commercial vehicles this extends to the air compressor and hydraulic pump. The low voltage 12 V or 24V system provides power for all other loads in the vehicle.
The LV battery is charged, and the loads supplied by the main DC-DC converter (1-3 kW) when the vehicle is in use, in the same way the alternator supplies the 12 V system in an ICE vehicle. When the vehicle is off the 12 V is maintained by the LV battery. For passenger vehicles the DC-DC converter is more commonly integrated within the OBC than being a standalone module.
Depending on the specific architecture either reinforced isolated or non-isolated supply rails are required to be created from the HV system voltage which makes the 1000 V input capable solutions from Power Integrations ideal.