Thermal rollover for life extension of light source controller circuitry

Abstract

Techniques for life extension of light source controller circuitry are described. A thermal rollover algorithm is presented to protect a light source controller mounted on an electronics board from overtemperature caused by the light source. The method includes adjusting dimming of LED modules based on temperature of an electronics board on which control circuitry is mounted.

Description

THERMAL ROLLOVER FOR LIFE EXTENSION OF LIGHT SOURCE CONTROLLERCIRCUITRYBACKGROUND

[0001] Lighting fixtures contain one or more light sources, such as light emitting diodes (LEDs), and the associated components for operation of the one or more light sources within its housing. Some lighting fixtures have an enclosed housing for the one or more light sources, for example, in the form of a molded window, which can provide protection in a variety of environments including hazardous environment. However, enclosing light sources within the lighting fixtures can result in the temperature within the housing to increase to a temperature that adversely affects the lifetime of critical electronic components, such as the controller and memory.

[0002] These heating effects may contribute to dimming of LED-based light sources over time, as well as reliability issues and possible premature failure of the lighting fixtures.BRIEF SUMMARY

[0003] Techniques for life extension of light source controller circuitry are described.

[0004] In some aspects, the techniques described herein relate to a lighting fixture including: LED modules; a dimming control circuit on an electronics board, the dimming control circuit adjusting dimming of the LED modules; a temperature sensor on the electronics board; and a controller with memory storing instructions for a thermal rollover algorithm that controls the dimming control circuit to maintain temperature of the electronics board within safe limits based on temperature of the electronics board detected by the temperature sensor.

[0005] In some aspects, the techniques described herein relate to a method of controlling temperature of control circuitry of a lighting fixture, the method including: adjusting dimming of LED modules based on temperature of an electronics board on which control circuitry is mounted.

[0006] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figures 1A-1D show views of an example lighting fixture.

[0008] Figure 2 shows an example method for life extension of light source controller circuitry.

[0009] Figures 3A and 3B illustrate a thermal rollover algorithm and corresponding state machine diagram, respectively.

[0010] Figure 4 shows a representational diagram of a controller for performing a method for life extension of light source controller circuitry such as the thermal rollover algorithm of Figure 3A.

[0011] Figure 5 shows a graph of a BL653 module temperature vs. dimming details of an example implementation.DETAILED DESCRIPTION

[0012] Techniques for life extension of light source controller circuitry are described. A thermal rollover algorithm is presented to protect a light source controller mounted on an electronics board from overtemperature caused by the light source.

[0013] The thermal rollover algorithm can control the LED temperature, and therefore the temperature of the critical electronic components, by modulating the dimming of the LEDs (based on temperature read from a temperature sensor) such that the temperature is maintained within safe limits for the critical electronic components. Advantageously, suitable temperature of the circuitry can be maintained since temperature adjustments are not required to rely on optimizations of LED temperatures. The temperature is detected at or near the critical electronic components irrespective of the temperature range within the lighting fixture.

[0014] Figures 1A-1D show views of an example lighting fixture. Figure 1A shows a representative diagram of a lighting fixture with life extension of light source controller circuitry. Figure IB shows an example housing 105 for a lighting fixture 100. Figure 1C shows an interior view of the example housing 105. Figure ID shows an LED package 115 and electronics board 130 that may be used in housing 105.

[0015] Referring to Figure 1A, a lighting fixture 100 includes LED modules 110, a dimming control circuit 120 on an electronics board 130, a temperature sensor 140 on the electronics board 130; and a controller 150 with memory storing instructions for a thermal rollover algorithm that controls the dimming control circuit 120 to maintain temperature of the electronics board 130 within safe limits based on temperature of the electronics board 130 detected by the temperature sensor 140. The dimming control circuit 120 adjusts the dimming of the LED modules 110.

[0016] Referring to Figures IB and 1C, housing 105 of a lighting fixture 100A can enclose an LED package 115 and the circuitry for controlling the LED modules, for example behind a molded window 108.

[0017] Referring to Figure ID, in an example implementation, an electronics board 130 is disposed in the housing 105 and connected to the LED package 115 with standoffs 160 and electrically coupled using connectors 170 and wires 180 from a power board (not shown) and controller subassembly (not shown). Controller circuitry, including dimming control circuit (not shown) and a controller (not shown) with memory storing thermal rollover algorithm (see e.g., controller 400 of Figure 4), and a temperature sensor 140 are mounted on the electronics board 130.

[0018] The controller circuitry (e.g., controller 150) on the electronics board 130 can degrade at high temperature, impacting the fixture life. Accordingly, the controller, when executing the thermal rollover algorithm, controls the dimming control circuit so as to maintain the temperature of the electronics board 130 within safe limits based on the temperature of the electronics board 130 detected by the temperature sensor 140.

[0019] Figure 2 shows an example method for life extension of light source controller circuitry. A method of controlling temperature of control circuitry of a lighting fixture involves adjusting dimming of LED modules based on temperature of an electronics board on which control circuitry is mounted. For example, method 200 includes receiving (210) temperature information from a temperature sensor that detects the temperature near the control circuitry. Then, based on the detected temperature, the method 200 includes determining (220), based on the received temperature information, that a temperature of control circuitry is above a first threshold; outputting (230) a control signal to dimming control circuit so as to adjust dimming percentage; and, while the received temperature information indicates the temperature of the control circuitry is above a second threshold that is lower than the first threshold, directing (240) the dimming control circuit to further adjust the dimming percentage in steps. The method can further include allowing (250) the dimming percentage to return to a higher dimming percentage after the received temperature information indicates the temperature of the control circuitry is at or below the second threshold. The control signals are output based on a thermal rollover algorithm.

[0020] For example, as part of the thermal rollover algorithm, when the temperature detected by the temperature sensor is greater than a first threshold, the method includes outputting control signals to the dimming control circuit to begin reducing dimming percentage by a first number of points every first period of time until the temperature reaches a secondthreshold which is a lower temperature than the first threshold; and when the temperature detected by the temperature sensor is equal to or below the second threshold, the method includes outputting control signals to the dimming control circuit to begin returning the dimming percentage by a second number of points every second period of time. The first number of points can be equal to the second number of points or different numbers of points (e.g., first number of points can be 10 points and the second number of points can be 5 points). The first period of time can be equal to the second period of time or be different amounts of time (e.g., 20 minutes for the first period of time and 10 minutes for the second period of time).

[0021] When the temperature is greater than the first threshold and while the temperature is greater than a third threshold, the method can further restrict a maximum dimming percentage to a reduced maximum dimming percentage. The third threshold is a lower temperature than the second threshold. In some cases, when the temperature detected by the temperature sensor is greater than the first threshold, the algorithm reduces a current dimming percentage to the reduced maximum dimming percentage before beginning the reducing of the dimming percentage by the first number of points.

[0022] The thermal rollover algorithm reduces the brightness of the light source through adaptive dimming to counteract the ambient temperature that the light fixture is exposed to. Thus, the internal temperature within the fixture is tracked and the brightness is reduced through adaptive dimming to control the internal temperature. This temperature control is to reduce degradation of the controller for the light source.

[0023] Figures 3A and 3B illustrate a thermal rollover algorithm and corresponding state machine diagram, respectively. Referring to Figures 3A and 3B, the default state after the system power on is Start. During an initial time period (e.g., 1 minute), the change state switches between Start and Idle, and the operations wait for a new dimming command to be received. Once the initial time period passes, the change state is changed from Start to Open. The Open state transitions to Normal, Action, Recovery, and End, based on the temperature information received by the temperature sensor (e.g., “read electronics board temperature” of Figure 3A). A specific implementation is described as follows. It should be noted that the specific increments for adjusting dimming and time periods presented are just one implementation. In addition, the temperature thresholds may also vary depending on the desired lifetime extension for particular circuit components / memory.

[0024] When the temperature is greater than 95 °C, the state is updated to Action. In this state, the thermal rollover active flag is set and recovery flag is reset. The action here is to reduce dimming by 10 points. Once the temperature is above 95 °C and dimming is more than70%, the dimming is set to 70% and after every 20 minutes, the dimming is reduced by steps of 10 points until the temperature reaches 90°C.

[0025] When the temperature is greater than 90°C but less than 95 °C, then the thermal rollover active flag is checked. If the active flag is set, the state is updated to Action. The action here is to reduce dimming by 10 points. If the thermal rollover active flag is not set, check if thermal rollover recovery flag is set. If the thermal rollover recovery flag is set, Update the state to Recovery. The action here is to increase dimming by 10 points.

[0026] If the temperature is greater than or equal to 85°C and less than or equal to 90C, update the state to Recovery. Set the thermal rollover recovery flag and reset the active flag. The current dimming is reduced by a step of 10 points after every 20 minutes. It should be noted that dimming greater than the current dimming is not applied until the temperature reaches below 85°C.

[0027] If temperature is less than 85°C, the state is updated to Normal. At this point, any dimming percent is applicable from 0-100%.

[0028] If none of the above states is true, it can imply that the memory has been corrupted. The action here is to restart the algorithm (“update state to end”, then restart algorithm to begin again at Start).

[0029] As indicated by Figure 3B, the thermal rollover flag sets after every minute. Idle, Action, Normal, Recovery, and Timeout states set the diming. For the Open state, in the thread context, check the thermal rollover flag and temperature to delegate the work. In the Action state, dimming reduction occurs. In the Recovery state, dimming recovery occurs. The Timeout state restricts the LED driver to enter safe mode by applying current dimming.

[0030] The internal temperature within the fixture is tracked by sensing the temperature of the electronics board (e.g., “read electronics board temperature” of Figure 3A). For example, a thermal sensor is connected / mounted on an electronics board (on which the controller is also mounted). The data captured by the thermal sensor is read via I2C protocol (but could be other protocol) from the sensor IC and then this is used by the algorithm on the controller, which then sends a control signal (in digital format) to the driver over, for example, UART protocol.

[0031] It should be understood that other temperature sensors and dimming control algorithms could be included for other purposes while the described thermal rollover algorithm is operating.

[0032] Figure 4 shows a representational diagram of a controller for performing a method for life extension of light source controller circuitry such as the thermal rollover algorithm of Figure 3A. Referring to Figure 4, a controller 400 can include a processor 410, memory 420,and input / output circuitry 430, which can communicate over bus(es) 440 (which can be on- chip or between chips, depending on implementation). The processor can be any suitable processing unit and can include state machine 350 described with respect to Figure 3B. Memory 420 can include, but is not limited to, random access memories (RAMs) such as static random access memory (SRAM) and dynamic random access memory (DRAM), flash, and magnetic memory. Memory 420 stores data and instructions for various operations of controller 400, including instructions for method 200 of Figure 2 and algorithm 300 of Figure 3A. Input / Output circuitry 430 can include signal interfaces suitable for communication with other components on an electronics board (e.g., for receiving input from a temperature sensor on the electronics board and for outputting control signals to a driver). Input / Output circuitry 430 can include wireless interfaces and circuitry such as for BLUETOOTH or near field communication (NFC) protocols.

[0033] Example Operation

[0034] The working functionality of the Thermal Rollover Algorithm was tested in a thermal oven using the BL653 (Nordic nrf52833 controller) and a temperature sensor. The thermal oven temperature was set at 65C. For the thermal rollover algorithm, the upper temperature threshold was set at 95C and the lower temperature threshold was set at 90C.

[0035] Figure 5 shows a graph of a BL653 module temperature vs. dimming details of an example implementation. For the test, software logged the change in the temperature and dimming percentage after every 4 sec. Referring to Figure 5, it can be seen that once the temperature is above 95 C and dimming is more than 70%, the dimming is set to 70% and after every 20 min, the dimming is reduced by steps of 10 points until the temperature reaches 90C. In addition, when the temperature is decreasing such that the range is less than 90C but greater than 85C, current dimming is reduced by a step of 10 points after every 20 minutes. It should be noted that dimming greater than the current dimming is not applied until the temperature reaches below 85C.

[0036] Although the subject matter has been described in language specific to structural features and / or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

Claims

CLAIMSWhat is claimed is:

1. A lighting fixture comprising:LED modules; a dimming control circuit on an electronics board, the dimming control circuit adjusting dimming of the LED modules; a temperature sensor on the electronics board; and a controller with memory storing instructions for a thermal rollover algorithm that controls the dimming control circuit to maintain temperature of the electronics board within safe limits based on temperature of the electronics board detected by the temperature sensor.

2. The lighting fixture of claim 1, wherein the controller comprises a state machine.

3. The lighting fixture of claim 1, wherein the controller is disposed on the electronics board with the dimming control circuit.

4. The lighting fixture of claim 1, wherein the instructions for the thermal rollover algorithm directs the controller to: when the temperature detected by the temperature sensor is greater than a first threshold, output control signals to the dimming control circuit to begin reducing a dimming percentage by a first number of points every first period of time until the temperature reaches a second threshold which is a lower temperature than the first threshold; and when the temperature detected by the temperature sensor is equal to or below the second threshold, output control signals to the dimming control circuit to begin returning the dimming percentage by a second number of points every second period of time.

5. The lighting fixture of claim 4, wherein the instructions for the thermal rollover algorithm further directs the controller to: when the temperature is greater than the first threshold and while the temperature is greater than a third threshold, restrict a maximum dimming percentage to a reduced maximum dimming percentage.

6. The lighting fixture of claim 5, wherein the third threshold is a lower temperature than the second threshold.

7. The lighting fixture of claim 5, wherein the instructions for the thermal rollover algorithm further directs the controller to, when the temperature detected by the temperature sensor is greater than the first threshold, reduce a current dimming percentage to the reduced maximum dimming percentage before beginning the reducing of the dimming percentage by the first number of points.

8. The lighting fixture of claim 4, wherein the first number of points is equal to the second number of points.

9. The lighting fixture of claim 4, wherein the first period of time is equal to the second period of time.

10. A method of controlling temperature of control circuitry of a lighting fixture, the method comprising: adjusting dimming of LED modules based on temperature of an electronics board on which control circuitry is mounted.

11. The method of claim 10, wherein adjusting dimming of LED modules based on temperature of an electronics board on which control circuitry is mounted comprises: receiving temperature information from a temperature sensor detecting the temperature of the electronics board on which the control circuitry is mounted; determining, based on the received temperature information, that a temperature of control circuitry is above a first threshold; outputting a control signal to dimming control circuit so as to adjust a dimming percentage; and while the received temperature information indicates the temperature of the control circuitry is above a second threshold, directing the dimming control circuit to further adjust the dimming percentage in steps.

12. The method of claim 11, wherein outputting the control signal to dimming control circuit so as to adjust dimming percentage; and while the received temperature information indicatesthe temperature of the control circuitry is above the second threshold, directing the dimming control circuit to further adjust the dimming percentage in steps comprises: outputting control signals to the dimming control circuit to begin reducing dimming percentage by a first number of points every first period of time until the temperature reaches a second threshold which is a lower temperature than the first threshold.

13. The method of claim 12, further comprising when the temperature is greater than the first threshold and while the temperature is greater than a third threshold, restricting a maximum dimming percentage.

14. The method of claim 11, further comprising: allowing the dimming percentage to return to a higher dimming percentage after the received temperature information indicates the temperature of the control circuitry is at or below the second threshold.

15. The method of claim 14, wherein allowing the dimming percentage to return to the higher dimming percentage after the received temperature information indicates the temperature of the control circuitry is at or below the second threshold comprises: outputting control signals to the dimming control circuit to begin returning the dimming percentage by a second number of points every second period of time.

Images