Light module for a motor vehicle headlamp and method and electrical circuit for operating same

1. A method for operating a light source of a motor-vehicle headlamp using direct current, wherein the light source was originally provided to be operated with alternating current, includes an inductive load, is arranged between branches of an electric H-bridge circuit with two high-side and two low-side closed semiconductor switches, and is applied with the alternating current in alternating current operation via the H-bridge circuit and each of the high-side switches arranged on top is controlled via a bootstrap circuit with a respective bootstrap capacitor, the method comprising steps of:

in direct current operation, periodically and temporarily disconnecting at least one of the switches for a recharging process;

reconnecting the at least one of the switches at an end of the recharging process; and

concluding the recharging process before current flowing via a branch of the H-bridge circuit reaches a value of about zero amps.

2. The method according to claim 1 , wherein the recharging process lasts fewer than about five microseconds.

3. The method according to claim 1 , wherein a distance between two successive ones of the recharging process is such that, prior to a subsequent one of the recharging process, a load of the bootstrap capacitor is still sufficiently great to safely control at least one of the high-side switches.

4. The method according to claim 3 , wherein the distance is in the millisecond range.

5. The method according to claim 1 , wherein, in the direct current operation for the recharging process, one of the high-side switches and one of the low-side switches is periodically and temporarily disconnected.

6. The method according to claim 1 , wherein, in the direct current operation for the recharging process, one of the high-side switches is periodically and temporarily disconnected.

7. An electric circuit for operating a light source of a motor-vehicle headlamp, wherein the light source was originally provided to be operated with alternating current using direct current and includes a conductive load, the electric circuit comprising:

an electric H-bridge circuit with two high-side and two low-side closed semiconductor switches for supplying the light source with the alternating current in alternating current operation, the light source being arranged between branches of the H-bridge circuit;

bootstrap circuits each of which is provided with a bootstrap capacitor and for controlling one of the high-side switches; and

a recharger for occasionally recharging the bootstrap capacitor by temporarily disconnecting and reconnecting at least one of the switches in direct current operation, a period of the recharging being predetermined such that the recharging is concluded before current flowing via one of the branches of the H-bridge circuit reaches a value of about zero amps.

8. The electric circuit according to claim 7 , wherein the period of the recharging is fewer than about five microseconds.

9. The electric circuit according to claim 7 , wherein a distance between two successive ones of the recharging is such that a load of the bootstrap capacitor is still sufficiently great to safely control at least one of the high-side switches.

10. The electric circuit according to claim 9 , wherein the distance is in the millisecond range.

11. The electric circuit according to claim 7 , wherein, in the direct current operation, one of the high-side switches and one of the low-side switches is periodically and temporarily switched.

12. The electric circuit according to claim 7 , wherein, in the direct current operation for the recharging process, one of the high-side switches is periodically and temporarily switched.

13. A light module of a motor-vehicle headlamp, the light module comprising:

a light source with inductive load; and

a circuit for operating the light source and including:

an electric H-bridge circuit with two high-side and two low-side closed semiconductor switches for supplying the light source with the alternating current in alternating current operation, the light source being arranged between branches of the H-bridge circuit;

bootstrap circuits each of which is provided with a bootstrap capacitor and for controlling one of the high-side switches; and

a recharger for occasionally recharging the bootstrap capacitor by temporarily disconnecting and reconnecting at least one of the switches in direct current operation, a period of the recharging being predetermined such that the recharging is concluded before current flowing via one of the branches of the H-bridge circuit reaches a value of about zero amps.

14. The light module according to claim 13 , wherein the circuit is part of a control unit of the light source.

15. The light module according to claim 13 , wherein the light source is a gas-discharge lamp.

16. A motor-vehicle headlamp comprising:

a housing having a light-emitting aperture that is closed with a transparent cover plate; and

at least one light module arranged in the housing and including a light source with inductive load and a circuit for operating the light source, wherein the circuit has:

an electric H-bridge circuit with two high-side and two low-side closed semiconductor switches for supplying the light source with the alternating current in alternating current operation, the light source being arranged between branches of the H-bridge circuit;

bootstrap circuits each of which is provided with a bootstrap capacitor and for controlling one of the high-side switches; and

a recharger for occasionally recharging the bootstrap capacitor by temporarily disconnecting and reconnecting at least one of the switches in direct current operation, a period of the recharging being predetermined such that the recharging is concluded before current flowing via one of the branches of the H-bridge circuit reaches a value of about zero amps.