Patent ID: 7180205

Claim:
A dual-voltage vehicle electric system for a motor vehicle, having a starter (S) which requires a first vehicle electric system voltage, a generator (G) which generates a second vehicle electric system voltage which is higher than the first vehicle electric system voltage, a DC/DC converter ( 1 ), a starter battery (BS), a vehicle electric system battery (BB), a control device ( 2 ), an ignition switch (ZS) and a starter switch (SS) which is closed when the starter is activated, where the starter (S) and the generator (G) are connected to a first terminal of the control device ( 2 ) and first and the second actuation lines (AL 1 , AL 2 ) lead from the control device 2 to the starter (S) and generator (G), wherein the starter battery (BS) and the vehicle electric system battery (BB) have identical rated voltages and are connected in series, a starter commutation device (U) is arranged in connection between the starter battery (BS) and the vehicle electric system battery (BB), the vehicle electric system battery (BB) is connected by one terminal to ground and by the other terminal to a first terminal of the starter commutation device (U), a second terminal of the starter commutation device (U) is connected to a terminal of the starter battery (BS), the other terminal of the starter battery (BS) is also connected to the first terminal of the control device ( 2 ), a series circuit composed of the vehicle electric system battery (BS), starter commutation device (U) and starter battery (BS) is arranged in parallel with the starter (S) or generator (G), the starter commutation device (U) is connected to the control device ( 2 ) via a third actuation line (A 13 ), the terminal of the vehicle electric system battery (BB) which is connected to the commutation device (U) is also connected to a second terminal of the control device ( 2 ) and to a first terminal of the DC/DC converter ( 1 ), the DC/DC converter ( 1 ) is connected by a second terminal to the first terminal of the control device ( 2 ), while a third terminal of the DC/DC converter ( 1 ) is connected to ground, wherein the DC/DC converter ( 1 ) is actuated by means of a fourth actuation line (AL 4 ) of the control device ( 2 ), and in addition the control device ( 2 ) is connected to the ignition switch (SZ) and to the starter switch (SS) via further actuation lines via which the control device ( 2 ) receives information as to whether the ignition switch (ZS) or a the starter switch (SS) have been activated.