Power supply device for light sources, such as halogen lamps, and related method

1. A power supply device for light sources, the device comprising a feed line from mains via a phase-cut dimmer, selectively switchable between a conductive state and a non-conductive state, to permit or interrupt feeding of the device from mains, the device comprising:

a power stage to feed at least one light source from said feed line from mains;

a drive stage for said power stage; and

a supply stage for said drive stage, said supply stage connected to said feed line from mains;

wherein the device further comprises a sensor to detect when said dimmer is non-conductive and when said dimmer is conductive; and

wherein the drive stage is coupled to the sensor to disable driving of said power stage when the sensor indicates that the dimmer is non-conductive, and enable driving of the power stage when the sensor indicates that the dimmer is conductive.

2. The device of claim 1 ,

wherein the drive stage comprises at least one control module switchable between a low-power absorption standby condition when the sensor indicates that the dimmer is non-conductive and an operative drive condition of the power stage when the sensor indicates that said dimmer is conductive.

3. The device of claim 1 ,

wherein the sensor comprises a zero level detector sensitive to the waveform from the dimmer to provide said drive stage a signal indicative that the dimmer is non-conductive.

4. The device of claim 1 ,

wherein the sensor comprises a voltage divider sensitive to the waveform from the dimmer to provide to the drive stage a signal indicative that the dimmer is conductive.

5. The device of claim 4 , further comprising:

a rectifier acting on the waveform from the dimmer; and

wherein the voltage divider is sensitive to the waveform rectified by the rectifier.

6. The device of claim 4 ,

wherein the voltage divider comprises a zener diode to clamp the output voltage from the divider.

7. The device of claim 4 ,

wherein the voltage divider is coupled to an electronic output switch driven by the voltage divider to provide to the drive stage a signal indicative that the dimmer is conductive.

8. The device of claim 1 , further comprising:

a dummy load to be selectively coupled and de-coupled with respect to the output of the dimmer when the sensor indicates that the dimmer is non-conductive and when the sensor indicates that the dimmer is conductive, respectively.

9. The device of claim 8 ,

wherein the dummy load is selectively coupled and de-coupled with respect to the output of the dimmer via the drive stage.

10. The device of claim 1 ,

wherein the supply stage for the drive stage is a buck converter.

11. The device of claim 8 ,

wherein the supply stage for the drive stage is a SEPIC converter with a respective electronic switch interposed between the two inductors of the SEPIC converter, the respective electronic switch adapted to be made conductive by connecting to ground a first inductor in the SEPIC converter when the sensor indicates that the dimmer is non-conductive, thereby realizing the dummy load.

12. A method of operating a power supply device for light sources,

the power supply device comprising:

a power stage to feed at least one light source;

a drive stage for enabling and disabling said power stage; and

a supply stage for said drive stage;

the method comprising:

a phase-cut dimming operation effected by permitting or interrupting feeding of the device from mains, the phase-cut dimming operation comprising:

detecting when the feeding is interrupted or permitted;

disabling driving of the power stage when interruption of the feeding is detected and enabling driving of the power stage when the feeding is detected to be permitted

switching the drive stage to a tow-power absorption standby condition when interruption of the feeding is detected and switching out of said standby condition when the feeding is detected to be permitted.