Driver arrangement for LED lamps

1. A driver arrangement for a LED light source, the arrangement including: a transformer having a primary winding and a secondary winding, said secondary winding connectable to said LED light source to feed power thereto, a first electronic switch to control current flow through said primary winding of said transformer, a sensing resistor coupled to said primary winding of said transformer to produce a sensing signal indicative of the intensity of current flow through said primary winding, a second electronic switch sensitive to said sensing signal to switch off said first electronic switch as said current flow through said primary winding of said transformer reaches a given threshold, whereby said first electronic switch is alternatively turned-on and off in alternating turn-on and switch-off phases to feed power to said LED light source via said secondary winding, wherein said first electronic switch is a field effect transistor, preferably a MOSFET and wherein said sensing resistor is a variable resistor to selectively adjust the duration of said turn-on and switch-off phases to thereby permit controlled dimming of said LED light source.

2. The arrangement of claim 1 , wherein said transformer is a SELV-rated transformer.

3. The arrangement of claim 1 , wherein said primary winding and secondary winding of said transformer have opposite polarities.

4. The arrangement of claim 1 , wherein said secondary winding of said transformer has associated therewith low-voltage rectifier circuitry to feed the power to said LED light source through said low-voltage rectifier circuit.

5. The arrangement of claim 1 , wherein said field effect transistor has its source-drain current path connected in series with said primary winding of said transformer.

6. The arrangement of claim 1 , wherein said sensing resistor is series connected to the source-drain current path through said field effect transistor.

7. The arrangement of claim 1 , wherein said second electronic switch is a transistor.

8. The arrangement of claim 7 , wherein said second electronic switch is a bipolar transistor.

9. The arrangement of claim 8 , wherein said bipolar transistor is connected with its base/emitter junction sensitive to the voltage drop across said sensing resistor.

10. The arrangement of claim 1 , wherein said primary winding of said transformer is fed via a DC bus voltage selectively switched by said first electronic switch.

11. The arrangement of claim 10 , wherein said first electronic switch has a control port fed from said DC bus voltage via a charge circuit that is selectively pinched to ground via said second electronic switch.

12. The arrangement of claim 1 , wherein it includes an auxiliary winding acting as a feedback winding to act on said first electronic switch to speed-up current increase through said primary winding said transformer during said turn-on phases and to short circuit the voltage across said first electronic switch during said switch-off phases.

13. The arrangement of claim 2 , wherein said primary winding and secondary winding of said transformer have opposite polarities.

14. The arrangement of claim 2 , wherein said secondary winding of said transformer has associated therewith low-voltage rectifier circuitry to feed the power to said LED light source through said low-voltage rectifier circuit.

15. The arrangement of claim 3 , wherein said secondary winding of said transformer has associated therewith low-voltage rectifier circuitry to feed the power to said LED light source through said low-voltage rectifier circuit.

16. A driver arrangement for a LED light source, the arrangement including: a transformer having a primary winding and a secondary winding, said secondary winding connectable to said LED light source to feed power thereto, a first electronic switch to control current flow through said primary winding of said transformer, a sensing resistor coupled to said primary winding of said transformer to produce a sensing signal indicative of the intensity of current flow through said primary winding, a second electronic switch sensitive to said sensing signal to switch off said first electronic switch as said current flow through said primary winding of said transformer reaches a given threshold, whereby said first electronic switch is alternatively turned-on and off in alternating turn-on and switch-off phases to feed power to said LED light source via said secondary winding, wherein said first electronic switch is a field effect transistor, preferably a MOSFET wherein said transformer is a SELV-rated transformer and wherein said sensing resistor is a variable resistor to selectively adjust the duration of said turn-on and switch-off phases to thereby permit controlled dimming of said LED light source.

17. A driver arrangement for a LED light source, the arrangement including: a transformer having a primary winding and a secondary winding, said secondary winding connectable to said LED light source to feed power thereto, a first electronic switch to control current flow through said primary winding of said transformer, a sensing resistor coupled to said primary winding of said transformer to produce a sensing signal indicative of the intensity of current flow through said primary winding, a second electronic switch sensitive to said sensing signal to switch off said first electronic switch as said current flow through said primary winding of said transformer reaches a given threshold, whereby said first electronic switch is alternatively turned-on and off in alternating turn-on and switch-off phases to feed power to said LED light source via said secondary winding, wherein said first electronic switch is a field effect transistor, preferably a MOSFET, wherein said primary winding and secondary winding of said transformer have opposite polarities and wherein said sensing resistor is a variable resistor to selectively adjust the duration of said turn-on and switch-off phases to thereby permit controlled dimming of said LED light source.

18. A driver arrangement for a LED light source, the arrangement including: a transformer having a primary winding and a secondary winding, said secondary winding connectable to said LED light source to feed power thereto, a first electronic switch to control current flow through said primary winding of said transformer, a sensing resistor coupled to said primary winding of said transformer to produce a sensing signal indicative of the intensity of current flow through said primary winding, a second electronic switch sensitive to said sensing signal to switch off said first electronic switch as said current flow through said primary winding of said transformer reaches a given threshold, whereby said first electronic switch is alternatively turned-on and off in alternating turn-on and switch-off phases to feed power to said LED light source via said secondary winding, wherein said first electronic switch is a field effect transistor, preferably a MOSFET, said secondary winding of said transformer has associated therewith low-voltage rectifier circuitry to feed the power to said LED light source through said low-voltage rectifier circuit and wherein said sensing resistor is a variable resistor to selectively adjust the duration of said turn-on and switch-off phases to thereby permit controlled dimming of said LED light source.

19. The arrangement of claim 2 , wherein said field effect transistor has its source-drain current path connected in series with said primary winding of said transformer.