A bidirectional power supply system receives power from a low voltage (LV) primary power supply, providing power to a control unit of a LV board net in a first mode of operation. A high voltage (HV) board net is coupled to a HV traction battery. A DC-DC converter, in the first mode, transfers energy from the LV board net to the HV board net to power components of the HV board net via the primary power supply, and, in a second mode of operation, transfers energy from the HV board net to the LV board net to power the control unit via the traction battery. The bidirectional power supply system includes a measurement element to detect whether the primary power supply is lost, and a switching element to switch operation of the DC-DC converter from the first mode to the second mode, when the primary power supply is lost.