CONTROL UNIT FOR LED ASSEMBLY AND LIGHTING SYSTEM

• US 20120223649A1
• Filed: 08/17/2010
• Published: 09/06/2012
• Est. Priority Date: 08/18/2009
• Status: Active Grant

• Current Assignee: eldoLAB Holding B.V. (Acuity Brands, Inc.)
• Original Assignee: eldoLAB Holding B.V. (Acuity Brands, Inc.)
• Inventors: Saes, Marc, Welten, Petrus Johannes Maria
• Granted Patent: US 9,351,365 B2
• Time in Patent Office: Days
• US Class Current: 315/186
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices

Abstract

A lighting system comprising an LED assembly that comprises a first and second LED unit said LED units being serial connected is described. The system comprises; a switched mode power supply for powering the LED assembly; a control unit for controlling the LED assembly the control unit being arranged to: receive an input signal representing a desired output characteristic of the LED assembly, determine a first and second duty cycle for the respective first and second LED units associated with a nominal current of the switched mode power supply, for providing the desired output characteristic, determine the largest of the first and second duty cycles for respective LED units, determine a reduced current based on at least the largest of the duty cycles, adjust the first and second duty cycle for respective LED units based on the reduced current or the largest of the duty cycles, provide output data for the LED assembly and the switched mode power supply based on the adjusted first and second duty cycles and the reduced current. The LED assembly of the system further comprises a capacitor connectable in parallel to the first and second LED units by operating a switch connected in series with the capacitor and wherein the control unit is arranged to control the switch based on at least one of the reduced current and the input signal.

Claims

1. A lighting system comprising

a LED assembly that comprises a first and second LED unit said LED units being serial connected;

a switched mode power supply for powering the LED assembly;

a control unit for controlling the LED assembly the control unit being arranged to;

receive an input signal representing a desired output characteristic of the LED assembly,

determine a first and second duty cycle for the respective first and second LED units associated with a nominal current of the switched mode power supply, for providing the desired output characteristic,

determine the largest of the first and second duty cycles for respective LED units,

determine a reduced current based on at least the largest of the duty cycles,

adjust the first and second duty cycle for respective LED units based on the reduced current or the largest of the duty cycles,

provide output data for the LED assembly and the switched mode power supply based on the adjusted first and second duty cycles and the reduced current.

and wherein the LED assembly further comprises a capacitor connectable in parallel to the first and second LED units by operating a switch connected in series with the capacitor and wherein the control unit is arranged to control the switch based on at least one of the reduced current and the input signal.

2. The lighting system according to claim 1 wherein the reduced current substantially corresponds to the nominal current multiplied with the largest duty cycle.

3. The lighting system according to claim 1 wherein the reduced current is based on a brightness characteristic of the LED unit.

4. The lighting system according to claim 1 wherein the control unit comprises an input port for receiving the input signal.

5. The lighting system according to claim 1 wherein the control unit comprises an output port for providing the output data to the LED assembly and the switched mode power supply.

6. The lighting system according to claim 5 wherein the control unit is arranged to control the switch by providing a control signal to the switch via the output port.

7. The lighting system according to claim 1 wherein the control unit is arranged to control the switched based on the first and/or second duty cycle for respective LED units

27. The lighting system according to claim 1 wherein the switched mode power supply comprises a resonant power converter.

8. A control unit for a LED assembly comprising a first and second LED unit, said LED units being serial connected, the LED assembly, in use, being powered by a switched mode power supply, the control unit being arranged to

receive an input signal representing a desired output characteristic of the LED assembly,

determine a power supply current of the switched mode power supply from the received input signal,

determine a first and second duty cycle for the respective first and second LED units from the determined power supply current and the input signal, the combination of duty cycle and power supply current being set for providing the desired output characteristic,

provide output data for the LED assembly and the switched mode power supply based on the determined first and second duty cycles and the determined power supply current.

9. The control unit according to claim 8, being arranged to control the power supply current to a first value in a first part of a cycle time and to a second value in a second part of the cycle time.

10. The control unit according to claim 8, being arranged to provide the output data such as to sequentially operate the LED units each in a respective part of a cycle time, and to set in each of the parts of the cycle time, the power supply current of the power supply to a value that matches the desired output characteristic of the respective LED unit that is to be operated in that part of the cycle time.

11. A lighting system comprising a LED assembly that comprises a first and second LED unit and a control unit according to claim 8, for controlling the LED assembly.

12. The lighting system according to claim 11, further comprising a feedback circuit to feed a signal representative of the power supply current to a feedback input of the switched mode power supply, the feedback circuit comprising at least one of a digital potentiometer and a digital to analog converter, the control unit having a control output connected to the at least one of the digital potentiometer and the digital to analogue converter, for controlling the potentiometer ratio respectively the digital to analogue converter output, thereby controlling the power supply current.

13. The lighting system according to claim 11, wherein a plurality of parallel branches is provided, each comprising at least one LED unit, a respective switched mode power supply being provided for each of the branches, the control unit being arranged for determining a power supply current for each of the power supplies, depending on the desired output characteristic for the respective LED unit, and for providing output data for each of the power supplies.

14. The lighting system according to claim 11 wherein the LED assembly further comprises a capacitor connectable in parallel to the first and second LED units by operating a switch connected in series with the capacitor and wherein the control unit is arranged to control the switch based on at least one of the determined power supply current and the input signal.

15. The lighting system according to claim 11 wherein the control unit comprises an input port for receiving the input signal and an output port for providing the output data to the LED assembly and the switched mode power supply.

16. The lighting system according to claim 15 wherein the control unit is arranged to control the switch by providing a control signal to the switch via the output port.

17. A lighting system comprising

an LED assembly comprising a first LED unit and a capacitor connectable in parallel to the first LED unit by operating a switch connected in series with the capacitor;

a switched mode power supply for, in use, powering the LED assembly, and

a control unit comprising;

an input port for receiving an input signal;

an output port for providing a control signal to the switched mode power supply and the switch, the control unit being arranged to

receive an input signal representing a desired output characteristic of the LED assembly,

determine a power supply current for the switched mode power supply from the received input signal,

provide, via the output port, a power supply control signal to the switched mode power supply to control the switched mode power supply to provide the power supply current to the LED assembly; and

provide, via the output port, a switch control signal to control the switch based on at least one of the power supply current and the input signal.

18. The lighting system according to claim 17 wherein the control unit is further arranged to

determine a first duty cycle for the first LED unit from the determined power supply current and the input signal, the combination of the first duty cycle and power supply current being set for providing the desired output characteristic, and

provide, via the output port, the switch control signal to control the switch based on the first duty cycle.

19. The lighting system according to claim 17 wherein the LED assembly further comprises a second LED unit;

wherein the capacitor is connectable in parallel to the first and second LED units by operating the switch.

20. The lighting system according to claim 19 wherein the control unit is further arranged to

determine a first duty cycle for the first LED unit from the determined power supply current and the input signal,

determine a second duty cycle for the second LED unit from the determined power supply current and the input signal, the combination of first and second duty cycle and power supply current being set for providing the desired output characteristic, and

provide, via the output port, a switch control signal to control the switch based on the first and/or second duty cycles.

21. The lighting system according to claim 19 wherein the first and second LED units are connected in series.

22. A lighting system comprising

an LED assembly comprising at least one LED illumination device;

a circuit for driving the LED assembly, the circuit comprising

a switch,

an inductor, in a series connection with the switch, the switch to in a conductive state thereof charge the inductor,

a current measurement element to measure a current flowing through at least one of the inductor and the LED illumination device,

the switch, inductor and current measurement element being arranged to establish in operation a series connection with the LED illumination device,

the circuit further comprising;

a reference signal generator for generating a reference signal;

a comparator to compare a signal representing the current measured by the current measurement element with the reference signal, an output of the comparator being provided to a driving input of the switch for driving the switch, and

a controller to control an operation of at least one of the reference signal generator and the comparator and wherein the LED assembly further comprises a capacitor connectable in parallel to the LED illumination device by operating a switch connected in series with the capacitor and wherein the controller is arranged to control the switch based on at least one of the current and the reference signal.

23. The lighting system according to claim 22, wherein the controller is arranged to control the reference signal generator so as to generate a first reference signal value during a first part of a cycle time and a second reference signal value during a second part of the a cycle time.

24. The lighting system according to claim 22, wherein the controller in arranged to disable the comparator during at least a part of the cycle time.

25. The lighting according to claim 24, wherein the controller is arranged to enable the comparator at least once during the cycle time to allow a generation of at least one short current pulse during the cycle time.

26. The lighting system according to claim 22, wherein the controller is arranged to:

provide enable pulses to enable the comparator in at least two cycle time parts of a cycle time;

wherein a pulse length of the enable pulses is varied within each cycle time.