Abstract: A method for detecting an insulation fault in a vehicle on-board electrical system having an HV and LV on-board electrical system branches. The LV branch has at least one first LV potential and a second LV potential that differs therefrom and corresponds to a ground potential of the vehicle on-board electrical system. The HV branch has positive HV negative HV potentials. These HV potentials are DC-isolated from the LV branch potentials. An insulation fault between at least one of the HV potentials and the first LV potential is detected by identifying a current flow. The current flow runs through a voltage limiting circuit connected between the ground potential and the first LV potential. This circuit connects the first LV potential, via a plurality of diodes, to a voltage limiting element connected to the ground potential of the vehicle on-board electrical system. A vehicle overvoltage protective circuit is also described.

Abstract: A vehicle on-board electrical system is equipped with a DC voltage charging connection, a non-configurable accumulator, a galvanically isolating DC-DC voltage converter, and an electrical drive. The accumulator is connected to a first side of the DC-DC voltage converter via a switchable connection circuit to which a DC voltage charging connection is connected. The accumulator is connected to the electrical drive and a second side of the DC-DC voltage converter via a drive switch. The connection circuit has a direct connection switch that connects the accumulator to the first side of the DC-DC voltage converter in a switchable manner. The DC voltage charging connection is connected to the direct connection switch via a charging connection switch of the connection circuit.