Illumination device and method for avoiding an over-power or over-current condition in a power converter

• US 9,485,813 B1
• Filed: 01/26/2015
• Issued: 11/01/2016
• Est. Priority Date: 01/26/2015
• Status: Expired

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Ketra, Inc. (Lutron Electronics)
• Inventors: Lewis, Jason, Bocock, Ryan Matthew, Savage, Joseph, Luu, Jivan James, Knapp, David
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): Cooper, Jonathan
• Application Number:
  US14/604,870
• Time in Patent Office: 645 Days
• Field of Search: 315148-158
• US Class Current: 1/1
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/18 using temperature feedback
• 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: H05B 45/44 with an active control inside an LED matrix
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs

Abstract

An illumination device and methods are provided herein for avoiding over-current and over-power conditions in one or more power converters included within the illumination device. The illumination device may include at least a plurality of light emitting diode (LED) chains, a driver circuit, at least one power converter, and a control circuit. In some embodiments, the control circuit may be generally configured for determining a maximum safe current level and/or a maximum safe power level attributed to the power converter(s) at a present operating temperature, and for adjusting respective drive currents supplied to the plurality of LED chains by the driver circuit, so as not to exceed the maximum safe current level or the maximum safe power level at the present operating temperature. In some embodiments, a temperature sensor may be included within the illumination device for measuring the operating temperature presently associated with the power converter(s).

Claims

1. An illumination device, comprising:

a plurality of light emitting diode (LED) chains configured to produce illumination for the illumination device;

a driver circuit coupled for generating and supplying a respective drive current to each of the plurality of LED chains;

at least one power converter coupled for supplying power to the driver circuit, wherein the at least one power converter comprises a maximum safe current level or a maximum safe power level, which varies with temperature;

a temperature sensor coupled for measuring a present temperature associated with the at least one power converter; and

a control circuit coupled to the temperature sensor and the driver circuit, wherein the control circuit is configured for;

determining the maximum safe current level or the maximum safe power level of the at least one power converter at the present temperature; and

adjusting the respective drive currents supplied to the plurality of LED chains, so as not to exceed the maximum safe current level or the maximum safe power level at the present temperature;

an interface coupled for receiving a chromaticity setting, and wherein the control circuit is further configured for determining a maximum lumens value that can be safely produced by all LED chains at a predetermined safe temperature to achieve the chromaticity setting; and

wherein the interface is further coupled for receiving a brightness setting, and wherein the control circuit is further configured for determining a target lumens value that can be safely produced by all LED chains at the present temperature to achieve the chromaticity setting without exceeding the maximum safe current level or the maximum safe power level associated with the at least one power converter.

2. The illumination device as recited in claim 1, wherein the control circuit is configured to determine the maximum lumens value by:

determining, for each LED chain, a lumen proportion needed from each LED chain to achieve the chromaticity setting at the predetermined safe temperature;

determining, for each LED chain, a relative lumens needed from the LED chain to achieve the lumen proportion determined for the LED chain, assuming only one of the plurality of LED chains is driven with a maximum drive current;

calculating, for each LED chain, a ratio of the relative lumens determined for the LED chain over a maximum lumen output for the LED chain;

determining, for each LED chain, an actual lumens needed from the LED chain to achieve the chromaticity setting at the predetermined safe temperature by dividing the relative lumens needed from the LED chain by a largest of the calculated ratios; and

summing the actual lumens needed from each LED chain to determine the maximum lumens value that can be produced by all LED chains at the predetermined safe temperature to achieve the chromaticity setting.

3. The illumination device as recited in claim 2, wherein the control circuit is configured to determine the lumen proportions needed from each LED chain to achieve the chromaticity setting at the predetermined safe temperature by:

determining, for each LED chain, chromaticity values that are expected for the LED chain using a forward voltage calibrated for the LED chain at the predetermined safe temperature, the respective drive current supplied to the LED chain, a table of stored calibration values correlating forward voltage and drive current to chromaticity at a plurality of different temperatures, and one or more interpolation techniques; and

calculating the lumen proportions needed from each LED chain to achieve the chromaticity setting at the predetermined safe temperature using the expected chromaticity values.

4. The illumination device as recited in claim 2, wherein the at least one power converter comprises a first power converter coupled for supplying a DC voltage to a plurality of second power converters, each of which are coupled for producing a forward voltage on a respective one of the LED chains, and wherein the maximum safe power level of the first power converter and the maximum safe current levels of the second power converters varies with temperature above the predetermined safe temperature.

5. The illumination device as recited in claim 4, wherein the control circuit is further configured to determine the maximum lumens value by:

determining, for each LED chain, a drive current needed to produce the actual lumens needed from the LED chain to achieve the chromaticity setting at the predetermined safe temperature;

estimating a total power drawn by all LED chains combined at the predetermined safe temperature;

determining the maximum safe power level and the maximum safe current level of the power converters at the predetermined safe temperature;

calculating a ratio of the maximum safe power level at the predetermined safe temperature over the total power estimated at the predetermined safe temperature;

calculating, for each LED chain, a ratio of the maximum safe current level at the predetermined safe temperature over the drive current determined for the LED chain at the predetermined safe temperature;

using a smallest of the calculated ratios to generate a scale factor; and

applying the scale factor to the maximum lumens value.

6. The illumination device as recited in claim 1, wherein the control circuit is configured to determine the target lumens value by:

applying the brightness setting to the maximum lumens value to generate a temporary target lumens value;

determining, for each LED chain, an actual lumens needed from the LED chain to achieve the temporary target lumens value at the present temperature;

determining, for each LED chain, a drive current needed to produce the actual lumens at the present temperature;

estimating a total power drawn by all LED chains combined at the present temperature;

calculating a ratio of the maximum safe power level determined at the present temperature over the total power estimated at the present temperature;

calculating, for each LED chain, a ratio of the maximum safe current level determined at the present temperature over the drive current determined for the LED chain at the present temperature;

using a smallest of the calculated ratios to generate a scale factor; and

calculating the target lumens value by applying the scale factor and the brightness setting to the maximum lumens value.

7. The illumination device as recited in claim 6, wherein the control circuit is configured to determine the actual lumens needed from each LED chain to achieve the temporary target lumens value at the present temperature by:

periodically turning the plurality of LED chains off for short durations of time;

measuring a forward voltage presently developed across each LED chain by applying a non-operative drive current to each LED chain, one chain at a time, during the short durations of time the plurality of LED chains are periodically turned off;

determining chromaticity values that are expected for each LED chain using the forward voltage measured across each LED chain, the respective drive current supplied to each LED chain, a table of stored calibration values correlating forward voltage and drive current to chromaticity at a plurality of different temperatures, and one or more interpolation techniques; and

calculating the actual lumens needed from each LED chain to achieve the temporary target lumens value using the expected chromaticity values and the chromaticity setting.

8. The illumination device as recited in claim 6, wherein the control circuit is configured for adjusting the respective drive currents supplied to the plurality of LED chains, so as to achieve the target lumens value.

9. The illumination device as recited in claim 6, wherein the control circuit is configured for periodically readjusting the respective drive currents supplied to the plurality of LED chains to account for changes in the present temperature by:

measuring a new present temperature;

determining, for each LED chain, an actual lumens needed from the LED chain to achieve the chromaticity setting and the target lumens value at the new present temperature;

determining, for each LED chain, a drive current needed to produce the actual lumens at the new present temperature;

applying the determined drive currents to the LED chains;

determining a total power drawn by all LED chains combined at the new present temperature;

updating the scale factor to account for changes in the maximum safe power level and/or the maximum safe current level of the power converters at the new present temperature;

recalculating the target lumens value using the updated scale factor; and

adjusting the respective drive currents supplied to the plurality of LED chains, so as to achieve the recalculated target lumens value.

10. The illumination device as recited in claim 9, wherein the control circuit is configured for updating the scale factor by:

determining the maximum safe power level and the maximum safe current level of the power converters at the new present temperature;

calculating a ratio of the maximum safe power level at the new present temperature over the total power determined at the new present temperature;

calculating, for each LED chain, a ratio of the maximum safe current level at the new present temperature over the drive current determined for the LED chain;

subtracting 1 from a smallest of the calculated ratios to generate a subtraction result; and

adding the subtraction result to the scale factor to update the scale factor.

11. The illumination device as recited in claim 9, wherein the control circuit is configured for updating the scale factor by:

determining the maximum safe power level and the maximum safe current level of the power converters at the new present temperature;

calculating a ratio of the maximum safe power level at the new present temperature over the total power determined at the new present temperature;

calculating, for each LED chain, a ratio of the maximum safe current level at the new present temperature over the drive current determined for the LED chain;

subtracting 1 from a smallest of the calculated ratios to generate a subtraction result;

multiplying the subtraction result with a coefficient value to generate a multiplication result; and

adding the multiplication result to the scale factor to update the scale factor.

12. A method for controlling a lumen output of an illumination device comprising a plurality of light emitting diode (LED) chains and a plurality of power converters, so as not to exceed a maximum safe power level and a maximum safe current level of the power converters at a present temperature, the method comprising:

measuring a present temperature associated with the at least one power converter;

determining the maximum safe current level and the maximum safe power level of the power converters at the present temperature; and

adjusting drive currents supplied to each of the plurality of LED chains, so as not to exceed the maximum safe current level and the maximum safe power level at the present temperature;

receiving a chromaticity setting and a brightness setting for the illumination device;

determining a maximum lumens value that can be safely produced by all LED chains at a predetermined safe temperature to achieve the chromaticity setting; and

determining a target lumens value that can be safely produced by all LED chains at the present temperature to achieve the chromaticity setting without exceeding the maximum safe current level or the maximum safe power level associated with the power converters.

13. The method as recited in claim 12, wherein said determining a maximum lumens value comprises:

determining, for each LED chain, a lumen proportion needed from each LED chain to achieve the chromaticity setting at the predetermined safe temperature;

determining, for each LED chain, a relative lumens needed from the LED chain to achieve the lumen proportion determined for the LED chain, assuming only one of the plurality of LED chains is driven with a maximum drive current;

calculating, for each LED chain, a ratio of the relative lumens determined for the LED chain over a maximum lumen output for the LED chain;

determining, for each LED chain, an actual lumens needed from the LED chain to achieve the chromaticity setting at the predetermined safe temperature by dividing the relative lumens needed from the LED chain by a largest of the calculated ratios; and

summing the actual lumens needed from each LED chain to determine the maximum lumens value that can be safely produced by all LED chains at the predetermined safe temperature to achieve the chromaticity setting.

14. The method as recited in claim 13, wherein said determining the lumen proportions needed from each LED chain to achieve the chromaticity setting at the predetermined safe temperature comprises:

determining, for each LED chain, chromaticity values that are expected for the LED chain using a forward voltage calibrated for the LED chain at the predetermined safe temperature, the drive current supplied to the LED chain, a table of stored calibration values correlating forward voltage and drive current to chromaticity at a plurality of different temperatures, and one or more interpolation techniques; and

calculating the lumen proportions needed from each LED chain to achieve the chromaticity setting at the predetermined safe temperature using the expected chromaticity values.

15. The method as recited in claim 13, wherein said determining a maximum lumens value further comprises:

determining, for each LED chain, a drive current needed to produce the actual lumens needed from the LED chain to achieve the chromaticity setting at the predetermined safe temperature;

estimating a total power drawn by all LED chains combined at the predetermined safe temperature;

determining the maximum safe power level and the maximum safe current level of the power converters at the predetermined safe temperature;

calculating a ratio of the maximum safe power level at the predetermined safe temperature over the estimated total power;

calculating, for each LED chain, a ratio of the maximum safe current level at the predetermined safe temperature over the drive current determined for the LED chain;

using a smallest of the calculated ratios to generate a scale factor; and

applying the scale factor to the maximum lumens value.

16. The method as recited in claim 12, wherein said determining a target lumens value comprises:

applying the brightness setting to the maximum lumens value to generate a temporary target lumens value;

determining, for each LED chain, an actual lumens needed from the LED chain to achieve the temporary target lumens value at the present temperature;

determining, for each LED chain, a drive current needed to produce the actual lumens at the present temperature;

estimating a total power drawn by all LED chains combined at the present temperature;

calculating a ratio of the maximum safe power level determined at the present temperature over the total power estimated at the present temperature;

calculating, for each LED chain, a ratio of the maximum safe current level determined at the present temperature over the drive current determined for the LED chain at the present temperature;

using a smallest of the calculated ratios to generate a scale factor; and

calculating the target lumens value by applying the scale factor and the brightness setting to the maximum lumens value.

17. The method as recited in claim 16, wherein said determining the actual lumens needed from each LED chain to achieve the temporary target lumens value at the present temperature comprises:

periodically turning the plurality of LED chains off for short durations of time;

measuring a forward voltage presently developed across each LED chain by applying a non-operative drive current to each LED chain, one chain at a time, during the short durations of time the plurality of LED chains are periodically turned off;

determining chromaticity values that are expected for each LED chain using the forward voltage measured across each LED chain, the drive current supplied to each LED chain, a table of stored calibration values correlating forward voltage and drive current to chromaticity at a plurality of different temperatures, and one or more interpolation techniques; and

calculating the actual lumens needed from each LED chain to achieve the temporary target lumens value using the expected chromaticity values and the chromaticity setting.

18. The method as recited in claim 16, further comprising adjusting the drive currents supplied to the plurality of LED chains, so as to achieve the target lumens value.

19. The method as recited in claim 16, further comprising periodically readjusting the drive currents supplied to the plurality of LED chains to account for changes in the present temperature by:

measuring a new present temperature;

determining, for each LED chain, an actual lumens needed from the LED chain to achieve the chromaticity setting and the target lumens value at the new present temperature;

determining, for each LED chain, a drive current needed to produce the actual lumens at the new present temperature;

applying the determined drive currents to the LED chains;

determining a total power drawn by all LED chains combined at the new present temperature;

updating the scale factor to account for changes in the maximum safe power level and/or the maximum safe current level of the power converters at the new present temperature;

recalculating the target lumens value using the updated scale factor; and

adjusting the drive currents supplied to the plurality of LED chains, so as to achieve the recalculated target lumens value.

20. The method as recited in claim 19, wherein said updating the scale factor comprises:

determining the maximum safe power level and the maximum safe current level of the power converters at the new present temperature;

calculating a ratio of the maximum safe power level determined at the new present temperature over the total power determined at the new present temperature;

calculating, for each LED chain, a ratio of the maximum safe current level determined at the new present temperature over the drive current determined for the LED chain at the new present temperature;

subtracting 1 from a smallest of the calculated ratios to generate a subtraction result; and

adding the subtraction result to the scale factor to update the scale factor.

21. The method as recited in claim 19, wherein said updating the scale factor comprises:

determining the maximum safe power level and the maximum safe current level of the power converters at the new present temperature;

calculating a ratio of the maximum safe power level determined at the new present temperature over the total power determined at the new present temperature;

calculating, for each LED chain, a ratio of the maximum safe current level determined at the new present temperature over the drive current determined for the LED chain at the new present temperature;

subtracting 1 from a smallest of the calculated ratios to generate a subtraction result;

multiplying the subtraction result with a coefficient value to generate a multiplication result; and

adding the multiplication result to the scale factor to update the scale factor.