Method and system for driving light emitting elements

• US 8,493,000 B2
• Filed: 12/30/2010
• Issued: 07/23/2013
• Est. Priority Date: 01/04/2010
• Status: Expired due to Fees

• Current Assignee: Cooledge Lighting Inc.
• Original Assignee: Cooledge Lighting Inc.
• Inventors: Jungwirth, Paul
• Primary Examiner(s): VU, DAVID HUNG
• Application Number:
  US12/982,758
• Publication Number:
  US 20110163682A1
• Time in Patent Office: 936 Days
• Field of Search: 315/291, 315/307, 315/308, 315/246, 315/224, 315/185.R, 315/192, 315/193, 315/191, 315/161
• US Class Current: 315/307
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/397 Current mirror circuits
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A system topology and circuit design for efficiently and stably driving currents through strings of solid state light emitting elements by providing current sources that are controlled by a stable voltage reference.

Claims

1. A method for driving light emitting elements, comprising the steps of:

providing a voltage reference to a plurality of parallel-connected current sources;

driving current from each current source through a respective one of a plurality of strings of light emitting elements wherein each current source is connected in series with one of the strings of light emitting elements;

taking up excess voltage not required by any one of the strings of light emitting elements; and

determining the supply voltage for the one or more strings of LEDs by multiplying standard deviations of forward voltages of the LEDs by square root of maximum number of LEDs per string to yield an adjusted standard deviation and then setting the supply voltage equal to the sum of average forward voltage of the LEDs and a multiple of the adjusted standard deviation of the forward voltage.

2. The method of claim 1 further comprising controlling in an analog manner the voltage reference provided to the current sources for controlling on, off and dimming of the light emitting elements in the strings thereof.

3. The method of claim 1 further comprising controlling in a digital manner the voltage reference provided to the current sources for controlling on, off and dimming of the light emitting elements in the strings thereof.

5. The method of claim 1 wherein said providing the voltage reference includes converting a source of voltage supply from AC to DC voltage.

6. The method of claim 1 further comprising bypassing current relative to at least one of the light emitting elements in each of the strings in response to occurrence of an open circuit failure at the at least one of the light emitting elements.

7. The method of claim 1 further comprising providing the strings of light emitting elements on separate circuit boards so as to produce modular configurations thereof.

8. The method of claim 7 further comprising providing a microcontroller for controlling on, off and dimming of the light emitting elements in the strings thereof on the separate circuit boards.

4. A method for driving light emitting elements, the method comprising:

providing a voltage reference to a plurality of parallel-connected current sources;

driving current from each current source through a respective one of a plurality of strings of light emitting elements wherein each current source is connected in series with one of the strings of light emitting elements;

taking up excess voltage not required by any one of the strings of light emitting elements; and

controlling in a digital manner the voltage reference provided to the current sources for controlling on, off and dimming of the light emitting elements in the strings thereof,

wherein said controlling includes producing a delay, in the form of a phase shifted time sequence, of the response of the current sources to the provision of the voltage reference in the digital manner.

9. The method of claim 4 further comprising determining the supply voltage for the one or more strings of LEDs by multiplying standard deviations of forward voltages of the LEDs by square root of maximum number of LEDs per string to yield an adjusted standard deviation and then setting the supply voltage equal to the sum of average forward voltage of the LEDs and a multiple of the adjusted standard deviation of the forward voltage.

19. The method of claim 4 wherein said providing the voltage reference includes converting a source of voltage supply from AC to DC voltage.

20. The method of claim 4 further comprising bypassing current relative to at least one of the light emitting elements in each of the strings in response to occurrence of an open circuit failure at the at least one of the light emitting elements.

21. The method of claim 4 further comprising providing the strings of light emitting elements on separate circuit boards so as to produce modular configurations thereof.

22. The method of claim 21 further comprising providing a microcontroller for controlling on, off and dimming of the light emitting elements in the strings thereof on the separate circuit boards.

10. A system for driving light emitting elements, comprising:

a plurality of strings of light emitting elements;

a plurality of current sources connected in parallel with each other, each of said current sources for providing current to one of said strings of light emitting elements;

a voltage reference connected to said plurality of parallel-connected current sources for driving current from each of said current sources through a respective one of said strings of light emitting elements; and

a plurality of excess voltage take-up elements each connected in series between one of said current sources and one of said strings of light emitting elements,

wherein supply voltage for the one or more strings of LEDs is determined by multiplying standard deviations of forward voltages of the LEDs by square root of the maximum number of LEDs per string to yield an adjusted standard deviation and then setting the supply voltage equal to the sum of the average forward voltage of the LEDs and a multiple of the adjusted standard deviation of the forward voltage.

11. The system of claim 10 further comprising one of an analog control circuit coupled to said voltage reference that control on, off and dimming of the light emitting elements in the strings thereof.

12. The system of claim 10 further comprising one of a digital control circuit coupled to said voltage reference that control on, off and dimming of the light emitting elements in the strings thereof.

14. The system of claim 10 wherein said voltage reference includes a circuit that converts a source of voltage supply from AC to DC voltage.

15. The system of claim 10 further comprising one or more elements coupled in parallel with one or more of the light emitting elements in each of the strings that bypass current relative thereto in response to occurrence of an open circuit failure at the at least one of the light emitting elements.

16. The system of claim 10 wherein said strings of light emitting elements are provided on separate circuit boards so as to produce modular configurations thereof.

17. The system of claim 16 further comprising a microcontroller for controlling on, off and dimming of the light emitting elements in the strings thereof on the separate circuit boards.

13. A system for driving light emitting elements, comprising:

a plurality of strings of light emitting elements;

a plurality of current sources connected in parallel with each other, each of said current sources for providing current to one of said strings of light emitting elements;

a voltage reference connected to said plurality of parallel-connected current sources for driving current from each of said current sources through a respective one of said strings of light emitting elements;

a plurality of excess voltage take-up elements each connected in series between one of said current sources and one of said strings of light emitting elements;

a digital control circuit coupled to said voltage reference that controls on, off and dimming of the light emitting elements in the strings; and

one or more elements coupled to said current sources that produce delay, in the form of a phase shifted time sequence, of the response of the current sources to the provision of the voltage reference in the digital manner.

18. The system of claim 13 wherein supply voltage for the one or more strings of LEDs is determined by multiplying standard deviations of forward voltages of the LEDs by square root of the maximum number of LEDs per string to yield an adjusted standard deviation and then setting the supply voltage equal to the sum of the average forward voltage of the LEDs and a multiple of the adjusted standard deviation of the forward voltage.

23. The system of claim 13 wherein said voltage reference includes a circuit that converts a source of voltage supply from AC to DC voltage.

24. The system of claim 13 further comprising one or more elements coupled in parallel with one or more of the light emitting elements in each of the strings that bypass current relative thereto in response to occurrence of an open circuit failure at the at least one of the light emitting elements.

25. The system of claim 13 wherein said strings of light emitting elements are provided on separate circuit boards so as to produce modular configurations thereof.

26. The system of claim 25 further comprising a microcontroller for controlling on, off and dimming of the light emitting elements in the strings thereof on the separate circuit boards.