Methods and apparatus for controlling respective load currents of multiple series-connected loads

• US 8,736,197 B2
• Filed: 10/08/2008
• Issued: 05/27/2014
• Est. Priority Date: 10/09/2007
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Datta, Michael, Lys, Ihor
• Primary Examiner(s): Cavallari, Daniel
• Assistant Examiner(s): Alaeddini, Borna
• Application Number:
  US12/681,631
• Publication Number:
  US 20110031888A1
• Time in Patent Office: 2,057 Days
• Field of Search: 315/122, 315/119, 315/121, 315/247, 315/246, 315/248, 315/249, 315/260, 315/267, 315/287, 315/185.S, 315/291, 315307-326, 315/294, 315/297, 362/227, 362/230, 362/234, 362/249.01, 362/249.07, 362/249.12, 362/249.13, 362/253
• US Class Current: 315/309
• CPC Class Codes: F21K 9/60 Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H05B 45/28 using temperature feedback
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A lighting apparatus (100) includes one or more first LEDs (202) for generating a first spectrum of radiation (503), and one or more second LEDs (204) for generating a second different spectrum radiation (505). The first and second LEDs are electrically connected in series between a first node (516A) and a second node (516B), between which a series current (550) flows with the application of an operating voltage (516) across the nodes. A controllable current path (518) is connected in parallel with one or both of the first and second LEDs so as to at least partially divert the series current, such that a first current (552) through the first LED(s) and a second current (554) through the second LED(s) are different. Such current diversion techniques may be employed to compensate for shifts in color or color temperature of generated light during thermal transients, due to different temperature-dependent current-to-flux relationships for different types of LEDs.

Claims

1. A lighting apparatus, comprising:

at least one first LED for generating first radiation having a first spectrum;

at least one second LED for generating second radiation having a second spectrum different from the first spectrum, wherein the at least one first LED and the at least one second LED are electrically connected in series between a first node and a second node, and a series current flows between the first node and the second node when an operating voltage is applied across the first node and the second node;

a controllable current path connected in parallel with the at least one second LED, the controllable current path including an energy storage device and a switch; and

a switching power supply for providing power factor correction and the operating voltage, the switching power supply controlling the switch of the controllable current path to selectively divert at least a portion of the series current around the at least one second LED to the energy storage device, such that a first current through the at least one first LED and a second current through the at least one second LED are different,

wherein the energy storage device subsequently provides the diverted portion of the series current to the at least one first LED.

2. The lighting apparatus of claim 1, wherein:

the at least one first LED includes a first number of series-connected red LEDs;

the at least one second LED includes a second number of series-connected white LEDs, wherein the first number and the second number are different; and

the controllable current path is connected in parallel with the second number of series-connected white LEDs.

3. The lighting apparatus of claim 2, wherein the switching power supply controls the controllable current path so as to set a color temperature of light resulting from a mixture of the first radiation and the second radiation.

4. The lighting apparatus of claim 1, further comprising:

at least one temperature sensor for generating a temperature signal, the at least one temperature sensor disposed proximate to and in thermal communication with the at least one first LED and the at least one second LED,

wherein the switching power supply comprises;

a first controller for receiving the temperature signal and providing a first control signal for controlling the controllable current path based at least in part on the temperature signal.

5. The lighting apparatus of claim 4, wherein the first control signal includes a pulse width modulated (PWM) control signal, and wherein the first controller varies a duty cycle of the PWM control signal in response to the temperature signal.

6. The lighting apparatus of claim 5, wherein the first controller determines the duty cycle of the PWM control signal based on a predetermined relationship between the duty cycle and the temperature represented by the temperature signal.

7. The lighting apparatus of claim 6, wherein the predetermined relationship is a linear relationship.

8. The lighting apparatus of claim 4, wherein the switching power supply further comprises:

a power factor correction stage for receiving an A.C. input voltage and providing the power factor correction and the operating voltage; and

a load control stage comprising;

the switch disposed in the controllable current path; and

an integrated circuit (IC) controller coupled to the switch, wherein the IC controller receives the first control signal from the first controller and controls the switch in response to the first control signal.

9. The lighting apparatus of claim 1, wherein the switching power supply comprises:

a power factor correction stage for receiving an A.C. input voltage (514) and providing the power factor correction and the operating voltage; and

a load control stage comprising;

the switch disposed in the controllable current path; and

an integrated circuit (IC) controller coupled to the switch, wherein the IC controller controls the switch using a fixed off time (FOT) control technique, and wherein the IC controller does not have any input that receives a signal relating to the operating voltage.

10. The lighting apparatus of claim 8, wherein the switching power supply further comprises:

a second controller coupled to the power factor correction stage for providing a second control signal to the power factor correction stage so as to control at least one of the operating voltage and a power provided by the power factor correction stage based on at least one voltage or current parameter associated with the power factor correction stage, a frequency of the A.C. input voltage, or an external signal.

19. The lighting apparatus of claim 1, wherein the energy storage device subsequently provides the diverted portion of the series current to the at least one first LED during a next half of a duty cycle of the switch.

11. A method for controlling a color temperature of white light generated by an LED-based lighting apparatus during a thermal transient, the LED-based lighting apparatus comprising at least one first LED for generating first radiation having a first spectrum and at least one second LED for generating second radiation having a second spectrum different from the first spectrum, wherein the white light results from a mixture of the first radiation and the second radiation, and wherein the at least one first LED and the at least one second LED are electrically connected in series between a first node and a second node and a series current flows between the first node and the second node when an operating voltage is applied across the first node and the second node, the method comprising:

A) generating a temperature signal representing a temperature proximate to the at least one first LED and the at least one second LED;

B) controlling, based on the temperature signal, at least one controllable current path connected in parallel with the at least one second LED so as to divert at least a portion of the series current around the at least one second LED, such that a first current through the at least one first LED and a second current through the at least one second LED are different; and

C) recycling the at least a portion of the series current diverted around the at least one second LED back to the at least one first LED.

12. The method of claim 11, wherein B) comprises:

B1) generating a pulse width modulated (PWM) control signal;

B2) varying a duty cycle of the PWM control signal in response to the temperature signal; and

B3) controlling the at least one controllable current path based on the PWM control signal.

13. The method of claim 12, wherein B2) comprises:

B2a) determining the duty cycle of the PWM control signal based on a predetermined relationship between the duty cycle and the temperature represented by the temperature signal.

14. The method of claim 13, wherein the predetermined relationship is a linear relationship.

15. The method of claim 13, wherein B2a) comprises deriving the predetermined relationship by:

B2a-1) measuring the first current and the second current at a plurality of different duty cycles of the PWM control signal;

B2a-2) measuring, at an ambient temperature, a plurality of color temperatures of the white light generated by the lighting apparatus at a plurality of current value pairs for the first current and the second current;

B2a-3) determining an ambient temperature duty cycle for a desired color temperature of the white light based on B2a-1) and B2a-2);

B2a-4) determining a value corresponding to a change in the duty cycle per change in the temperature represented by the temperature signal; and

B2a-5) offsetting the ambient temperature duty cycle by an amount related to the value determined in B2a-4).

16. An apparatus for controlling a color temperature of white light generated by an LED-based light source during a thermal transient, the LED-based light source mounted to a thermally conductive substrate and comprising at least one first LED for generating first radiation having a first spectrum and at least one second LED for generating second radiation having a second spectrum different from the first spectrum, wherein the white light results from a mixture of the first radiation and the second radiation, the thermally conductive substrate having a recess formed therein proximate to the LED-based light source, the apparatus comprising:

a printed circuit board defining a protruding tab for insertion into the recess formed in the thermally conductive substrate;

a temperature sensor disposed on the tab of the printed circuit board, such that when the tab is inserted into the recess formed in the thermally conductive substrate, the temperature sensor is essentially embedded in the thermally conductive substrate proximate to the LED-based light source; and

a plurality of components disposed on the printed circuit board and constituting a switching power supply for providing power factor correction and an operating voltage for the LED-based light source, the switching power supply comprising at least one integrated circuit (IC) controller for controlling flow of a first current through the at least one first LED and flow of a second current through the at least one second LED.

17. The apparatus of claim 16, wherein the at least one first LED and the at least one second LED are electrically connected in series between a first node and a second node and a series current flows between the first node and the second node when the operating voltage is applied across the first node and the second node, and wherein the switching power supply comprises:

at least one controllable current path connected in parallel with the at least one second LED so as to at least partially divert the series current around the at least one second LED, such that the first current through the at least one first LED and the second current through the at least one second LED are different.

18. The apparatus of claim 17, wherein the temperature sensor generates a temperature signal, and wherein the switching power supply further comprises:

a first controller for receiving the temperature signal and providing a first control signal for controlling the at least one controllable current path based at least in part on the temperature signal.