On-board electrical system isolating circuit for DC/DC converters, and method for isolating an on-board electrical system from a DC/DC converter
The invention relates to an on-board electrical system supply system ( 1 ), having a DC/DC converter ( 11 ) with at least one semiconductor rectifier element ( 4 ), having two supply connections ( 9 a, 9 b ) for an on-board electrical system, which supply connections are connected at the output end to the DC/DC converter ( 11 ), having an isolating switch ( 5 ) which is coupled between one of the supply connections ( 9 a, 9 b ) and the DC/DC converter ( 11 ), and having an on-board electrical system isolating circuit ( 10 ) which is designed to determine a reverse voltage (U, Ua, Ub) across at least one of the semiconductor rectifier elements ( 4 ), and to actuate the isolating switch ( 5 ), in order to decouple the on-board electrical system from the DC/DC converter ( 11 ), depending on a value of the determined reverse voltage (U, Ua, Ub).
1. An on-board electrical system supply system ( 1 ), comprising:
a DC/DC converter ( 11 ) having at least one semiconductor rectifier element ( 4 );
two supply terminals ( 9 a , 9 b ) for an on-board electrical system, which are coupled to the DC/DC converter ( 11 ) on the output side;
an isolating switch ( 5 ) coupled between one of the supply terminals ( 9 a , 9 b ) and the DC/DC converter ( 11 ); and
an on-board electrical system isolating circuit ( 10 ) configured to measure a reverse voltage (U; Ua; Ub) at at least one of the semiconductor rectifier elements ( 4 ) and to drive the isolating switch ( 5 ) for decoupling the on-board electrical system from the DC/DC converter ( 11 ) depending on a value of the measured reverse voltage (U; Ua; Ub).
2. The on-board electrical system supply system ( 1 ) as claimed in claim 1 , wherein the DC/DC converter ( 11 ) comprises:
a transformer ( 2 ) having a primary side winding ( 2 a ) and a secondary side winding ( 2 b , 2 c ) with a center tap;
an output inductance ( 3 ), which is connected to the center tap and a first of the supply terminals ( 9 a ); and
a rectifier circuit ( 4 ) having two semiconductor rectifier elements ( 4 a , 4 b ), which are respectively connected to the end-side taps of the secondary-side winding ( 2 b , 2 c ) and which are designed for generating a rectified output voltage at a second of the supply terminals ( 9 b ).
3. The on-board electrical system supply system ( 1 ) as claimed in claim 2 , wherein the semiconductor rectifier elements ( 4 a , 4 b ) comprise synchronous rectifier switches.
4. The on-board electrical system supply system ( 1 ) as claimed in claim 2 , wherein the semiconductor rectifier elements ( 4 a , 4 b ) comprise semiconductor diodes.
5. The on-board electrical system supply system ( 1 ) as claimed in claim 1 , furthermore comprising:
an intermediate circuit capacitor ( 8 ) coupled between the two supply terminals ( 9 a , 9 b ).
6. The on-board electrical system supply system ( 1 ) as claimed in claim 1 , wherein the on-board electrical system supply system is for an electric or hybrid vehicle.
7. An on-board electrical system supply system ( 1 ), comprising:
a DC/DC converter ( 11 ) having at least one semiconductor rectifier element ( 4 );
two supply terminals ( 9 a , 9 b ) for an on-board electrical system, which are coupled to the DC/DC converter ( 11 ) on the output side;
an isolating switch ( 5 ) coupled between one of the supply terminals ( 9 a , 9 b ) and the DC/DC converter ( 11 ); and
an on-board electrical system isolating circuit ( 10 ) configured to determine a reverse voltage (U; Ua; Ub) at at least one of the semiconductor rectifier elements ( 4 ) and to drive the isolating switch ( 5 ) for decoupling the on-board electrical system from the DC/DC converter ( 11 ) depending on a value of the determined reverse voltage (U; Ua; Ub),
wherein the on-board electrical system isolating circuit ( 10 ) includes:
a comparator ( 12 a ; 12 b ) configured to determine an undershooting of a first threshold value for the reverse voltage (Ua; Ub) of the semiconductor rectifier elements ( 4 ); and
a flip-flop ( 16 ) configured to output a drive signal for the isolating switch ( 5 ) depending on an output signal of the comparator ( 12 a ; 12 b ).
8. The on-board electrical system supply system ( 1 ) as claimed in claim 7 , wherein the comparator ( 12 a ; 12 b ) is furthermore configured to determine whether the reverse voltage (Ua; Ub) of the semiconductor rectifier elements ( 4 ) exceeds a second threshold value.
9. A method ( 20 ) for isolating an on-board electrical system from a DC/DC converter ( 11 ), comprising the following steps:
converting ( 21 ) a supply voltage into an on-board electrical system voltage by means of a DC/DC converter ( 11 );
measuring ( 22 ) a reverse voltage (U; Ua; Ub) at at least one of the semiconductor rectifier elements ( 4 ) of the DC/DC converter ( 11 ); and
driving ( 24 ) an isolating switch ( 5 ) for decoupling the on-board electrical system from the DC/DC converter ( 11 ) depending on the value of the measured reverse voltage (U; Ua; Ub).
10. The method ( 20 ) as claimed in claim 9 , furthermore comprising the following step:
checking ( 23 a ) whether the measured reverse voltage (U; Ua; Ub) undershoots a first threshold value.
11. The method ( 20 ) as claimed in claim 10 , furthermore comprising the following step:
checking ( 23 b ) whether the measured reverse voltage (U; Ua; Ub) exceeds a second threshold value.
12. The method ( 20 ) as claimed in claim 11 , wherein the isolating switch ( 5 ) is driven to decouple the on-board electrical system when the measured reverse voltage is between the second threshold value and the first threshold value.