Abstract:
Safety improvements to Light Emitting Diodes (LED) are discussed herein. As the LEDs that are part of a luminaire heat up and cool down, the current supplied will be tuned to improve the safety of the luminaire to manage the levels of light and heat produced. At least one thermally active electrical component is incorporated into the LED load of the luminaire, which is communicated to an LED current control to signal when to adjust current levels providing by a driving circuit. Current is reduced when the temperature of the LED load exceeds a threshold, and or returned to an optimal current when the temperature no longer exceeds the threshold.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to Light Emitting Diode (LED) luminares and, more particularly, improving their safety of use. 
       BACKGROUND 
       [0002]    A Light Emitting Diode (LED) is an electrical component that emits light when a suitable voltage is applied across its leads. Luminares may include one or more LEDs in a form factor suitable for various applications. For example, a luminaire may be shaped like an incandescent lightbulb or fluorescent filament to fit the lamps and light fixtures in a home or office. Luminares may also be designed for use in industrial environments, where caustic chemicals, flammable materials, extreme temperatures, or combinations thereof may be present at a greater frequency than in the home or office. Several industrial standards are in place to ensure that the luminaire does not become a danger in various environments (e.g., provide reactants to caustics, become a flashpoint around flammable materials, warp under temperature). These standards often require pass/fail testing when the tested device is initially constructed, but inherent failure modes of some LED devices may result in an unanticipated risks, which may lead to safety related events such as fire and explosion during or after installation. 
       SUMMARY 
       [0003]    The present disclosure is directed to systems, devices, and methods for improving the safety of Light Emitting Diode (LED) luminares through active tuning of the drive current to the LED. By measuring the heat of an LED load with a thermally active electrical component, a current controller may adjust the current running through the components of the LED load, and thereby reduce the heat produced via resistive losses when heat is building up, and allow the LED load to cool to acceptable levels. 
         [0004]    The above summary is not intended to describe each aspect or every implementation. A more complete understanding will become apparent and appreciated by referring to the detailed description in conjunction with the accompanying drawings, and that the scope of the present disclosure is set by the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate various aspects of the present disclosure. The drawings are not necessarily to scale. Like numbers used in the drawings refer to like components, however, it will be understood that the use of a number to refer to a component in a given drawing is not intended to limit the component in anther drawing labeled with the same number. In the drawings: 
           [0006]      FIG. 1A  illustrates an example LED luminaire; 
           [0007]      FIG. 1B  is a circuit diagram for an example tuneback circuit for an LED luminaire; and 
           [0008]      FIG. 2  is a flow chart showing general stages involved in a method for implementing current tuneback in an LED luminaire. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Various examples will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Any examples set forth in this disclosure are not intended to be limiting and merely set forth some of the many possible ways for implementing the broad inventive aspects disclosed herein. 
         [0010]    A Light Emitting Diode (LED) is an electrical component that converts the energy supplied in electrical current into light via electroluminescence. As will be appreciated, as current runs through (non-superconductive) electrical components, such as LEDs, a portion of the energy in the current is converted to heat via the component&#39;s resistance. This heat is radiated to the surrounding components and environment, and may build up in the component, making it hotter, if the energy supplied to the component produces more resistive heat than the component can dissipate in a given period of time. To keep a component within a specified temperature range, heatsinks, fans, cooling ducts, and the like can improve the ability of a component to dissipate heat to the environment, or the current running through a component may be reduced to thereby reduce the heat needed to be dissipated. As will be appreciated, keeping a component or fixture within a given temperature range may improve the safety of the electrical device (e.g., reducing the likelihood that the device may act as an ignition source), the longevity of the components of the fixture (e.g., reducing the likelihood of burning a component out), and help devices meet industrial standards for use in a greater variety of settings (e.g., a luminaire deemed safe for use in a home environment may not meet safety standard for use in a coal mine without additional heat controls). Moreover, depending on the failure mechanism of the luminaire, when a subset of the device (e.g., a die in a multi-die device) fails, current from the failed portions may be driven through the portions that have not yet failed, which can increase the overall heat in the device (or the operable portions thereof) and can lead to accelerated failure of the portions and/or safety hazards. 
         [0011]    To adapt a luminaire to a hazardous environment, the LEDs may be isolated from the environment by an air-tight casing including a non-reactive material (e.g., silicone or glass) through which the LEDs will shine. The casing may be clear or colored, and may be impact resistant or made of a shatter proof material. Additional heatsinks, arc suppression, and interlock features may also be included so that when the luminaire is active in a hazardous environment, no ignition or reaction sources will be exposed to the environment. 
         [0012]      FIG. 1A  illustrates an example LED luminaire  100 . In the example LED luminaire, several components are disposed of on a Printed Circuit Board (PCB)  110 , although one of ordinary skill in the art will appreciate that the components shown may be communicated together without the PCB  110  (e.g., on a breadboard, via direct wiring), and that more or fewer components than illustrated in  FIG. 1  may comprise an LED luminaire  100 , and that different arrangements of components than shown in  FIG. 1  are possible. The example LED luminaire  100  is provided as a non-limiting example. 
         [0013]    The example LED luminaire  100  is illustrated in two sections; the driving circuit  120 , including a current controller  121  and a rectifier  122 , and the LED load  130 , including a temperature sensor  131  and LEDs  132   a - u  (generally, LEDs  132 ). Although both sections are illustrated as being disposed of on the same PCB  110 , one of ordinary skill in the art will recognize that the driving circuit  120  and LED load  130  may be disposed of on separate PCBs  110 , and that a single driving circuit  120  may be communicated to several LED loads  130 . 
         [0014]    The driving circuit  120  includes a current controller  121  and a rectifier  122 . The current controller  121  controls the level of current provided from an alternating current power source (not illustrated), and the rectifier  122  converts alternating current into direct current for use by the LED load  130 . In aspects that use a direct current power source (e.g., a battery) instead of an alternating current power source, the current controller  121  controls the level of current provided from the direct current power source and the rectifier  122  may be omitted or bypassed. In various aspects, the rectifier  122  may be of various configurations and contain components of various values depending on the design specifications and use cases expected of the example LED luminaire  100 , and one of ordinary skill in the art will be familiar with the construction of a rectifier  122  to meet the needs of a given LED luminaire  100 . 
         [0015]    In various aspects, the current controller  121  includes a microprocessor that processes signals according to stored instructions (e.g., burned into the microprocessor, stored as Electrically Erasable Programmable Read-Only Memory (EEPROM)) to affect a level of current provided to the LED load  130 . In other aspects, the current controller  121  includes a series of logic gates that control switches that will open and close in response to signals received from the LED load  130  to raise or lower current levels transmitted to the LED load  130 . Changes to the level of current provided to the LED load  130  may be accomplished with a dimming functionality, allowing the LED load  130  to produce less light with less current, or with a switching functionality, temporarily cutting off current to an LED load  130  or a portion of the LEDs  132  in an LED load  130 . For example, the current controller  121  may temporarily restrict the flow of current to the LEDs  132  (turning them off when current reaches zero or a cutoff for LED operation) until the heat of the LED load  130  drops below a threshold. In another example, a first LED load  130  has its current set to zero until the first LED load  130  cools below a threshold temperature, but a second LED load  130  is provided current. The thresholds may be set via various standards bodies according to various standards (e.g., Underwriters Laboratories (UL), the Institute for Electrical and Electronic Engineers (IEEE), European Conformity (CE), China Compulsory Certificate, (CCC)) for the temperature of the luminaire in-use, which one of ordinary skill in the art will be able to apply. 
         [0016]    The LED load  130  includes at least one temperature sensor  131  and at least one LED  132 . The temperature sensor  131  is communicated with the current controller  121  so that the temperature of the LED load  130  can be reduced via the regulation of current transmitted to the LED load  130 . 
         [0017]    In various aspects, the temperature sensor  131  is a thermistor, a thermocouple, a resistance temperature detector (RTD), or an infrared (IR) photodiode. In some aspects, where the resistance of the temperature sensor  131  changes in relationship with temperature, a reference current of a value known to the current controller  121  is fed through the temperature sensor  131  so that the current controller  121  can measure a change in resistance (via changes in voltage across the temperature sensor  131 ) that indicates a temperature of the LED load  130 . In some aspects, the reference current supplied to the temperature sensor  131  may be the operating current of the LEDs  132  that the current controller  121  adjusts to affect the temperature of the LED load  130 , while in other aspects a separate current is provided so that if the operating current is modified (or set to zero) the reference current will remain constant. 
         [0018]    In aspects where more than one temperature sensor  131  is provided, multiple temperature sensors  131  may be associated with the same LED load  130  or with multiple LED loads  130 . The current controller  121  may average the readings from the multiple temperature sensors  131  or use the maximum value received from a temperature sensor  131  when the multiple temperature sensors  131  are on one LED load  130 , but will treat the readings from multiple temperature sensors  131  from multiple LED loads  130  separately to manage the heat of each LED load  130  separately. Readings may be averaged by using a shared lead of a microprocessor in communication with multiple analog temperature sensors  131  wired in parallel, a bitwise averaging circuit (e.g., an Adder and a bit-shift register) when using digital temperature sensors  131 , or by other means known to those of ordinary skill in the art. Additionally or alternatively, another algorithm besides averaging may be used to collect and smooth cumulative readings over a period of time. Contrarily, readings may be separated by using different leads of a microprocessor (or separate sets of logic gates) to receiving readings. 
         [0019]      FIG. 1B  is a circuit diagram  105  for an example tuneback circuit for use in an LED luminaire  100 . As illustrated, a resistor  160 , representing the resistance of the LED load  130  of at least one LED  132 , and a thermistor  140 , representing a temperature sensor  131  that has different resistances at different temperatures, are in thermal communication with one another. As current flows through the resistor  160 , the thermistor  140  may begin to heat up in response, and its resistance will change. The current controller  121  measures the voltage V T    170  across the thermistor  140  to track the change in resistance corresponding to changes in its temperature. For example, by applying a constant current to the thermistor  140  and comparing V T    170  to a base or a threshold value, the current controller  121  can determine when the thermistor  140  has reached a given resistance (and therefore a given temperature) indicating that the LED load  130  will have similarly reached or exceeded a given temperature threshold. Once the current controller  121  has determined that the LED load  130  has reached or exceeded a temperature threshold via the corresponding changes to V T    170 , the driving circuit  120  will be signaled to adjust the current provided to the LED load  130  to ensure the proper and safe continued operation of the LED luminaire  100 . 
         [0020]    In some aspects, when an overheat threshold is reached, some or all of the LEDs  132  comprising the LED load  130  may be switched off, the current from the AC power source  150  may be reduced, a secondary string of LEDs  132  may be activated instead of a primary string of LEDs  132 , a cooling apparatus (e.g., a fan, a vent, a heat pump) may be provided power, etc. In other aspects, when a cooldown threshold is reached, such as when the actions taken in response to an overheat threshold are deemed effective and the LED luminaire  100  can safely resume normal operations, some or all of the LEDs  132  comprising the LED load  130  may be switched on, a primary string of LEDs  132  may be activated instead of a secondary string of LEDs  132 , the current provided from the power source  150  may be increased (up to a nominal value), a cooling apparatus may be turned off, etc. 
         [0021]      FIG. 2  is a flow chart showing general stages involved in a method  200  for implementing current tuneback in an LED luminaire  100 . Method  200  begins at OPERATION  210 , where a nominal current is provided to the LED load  130  of an LED luminaire  100  when a power source is applied (e.g., a user flips a light switch associated with the LED luminaire  100 ). The nominal current is the current that the LED luminaire  100  is designed to provide to the LED load  130  to produce the requested amount to light from the LEDs  132 . For example, an LED luminaire  100  may be designed to provide 100% of rated light when 50 mA are provided to the LED load  130 , and when a user selects a dimmer function of the LED luminaire  100  for 50% of rated light, 25 mA are provided to the LED load  130 . In the preceding example, the currents of 50 mA and 25 mA are both nominal currents for 100% light rating and 50% light rating respectively, although one of ordinary skill in the art will recognize that the numbers in the above example have been simplified to clearly present the concept of a nominal current. 
         [0022]    Method  200  proceeds to OPERATION  220 , where heat is monitored. Depending on the number and arrangement of temperature sensors  131 , the current controller  121  may measure an average, a maximum, or several temperature readings from the LED load  130 . In various aspects, the temperature readings may be polled from the sensors or received in real-time. To prevent spikes in readings, in various aspects the multiple readings from one temperature sensor  131  (or group of related temperature sensors  131 ) may be averaged over a time period or another algorithm may be applied to adjust the level of current provided to the LED load  130  based on the cumulative temperature data from one or more temperature sensors  131 . 
         [0023]    These temperature readings are compared to a threshold at DECISION  230  to determine whether the temperature exceeds the threshold. When the reading exceeds a threshold, method  200  proceeds to OPERATION  240 . When the reading does not exceed the threshold, method  200  proceeds to DECISION  250 . 
         [0024]    At OPERATION  240 , the operational current is reduced by the current controller  121 . As will be appreciated, when the current controller  121  reduces the operational current in steps (e.g., 100% to 75% to 50% to 25% to 0%), multiple temperature thresholds may exist so that the current controller  121  may adjust the operational current in accordance with the steps. Steps may be even (n % steps), or uneven, or set to grow/shrink (e.g., 100% to 90% to 70% to 40% to 0%). When the current controller  121  adjusts the operational current in a continuum according to the temperature sensor  131  (e.g., an analog reading from the temperature sensor  131  produces an analog reduction in the operational current) the threshold may be a cutoff value (voltage or current) before which no adjustments to the operational current will be made. 
         [0025]    In various aspects, a cutoff value may be supplied by a diode breakdown or avalanche, switches, or the sensitivity of the current controller  121 . Method  200  then returns to OPERATION  220  to continue monitoring the heat of the LED load  130 . 
         [0026]    In aspects where there are multiple temperature sensors  131  associated with different LED loads  130 , the current controller  121  may adjust the current supplied to the LED load(s)  130  so that each LED load  130  is affected individually by an associated temperature sensor  131  (e.g., a first temperature sensor  131  or group thereof affects the current supplied to a first LED load  130 ), is affected mutually by an unassociated temperature sensor  131  (e.g., a second temperature sensor  131  associated with a second LED load  130  may affect the current supplied to a first LED load  130  regardless of what temperature is measured by an associated first temperature sensor  131 ), or is affected in aggregate by multiple temperature sensors  131  (e.g., an average temperature value of the first LED load  130  and the second LED load  130 , as measured by a first temperature sensor  131  and a second temperature sensor  131  respectively, is used to affect the current provided to both LED loads  130 ). Additionally, when there are multiple LED loads  130 , the power supplied to a given LED load  130  may be separately regulated (e.g., the power supplied to first LED load  130  may be different than the power supplied to second LED load  130 ) or commonly regulated (e.g., the power supplied to first LED load  130  is equal to the power supplied to second LED load  130  when power is supplied to both of the LED loads  130 ). 
         [0027]    At DECISION  250 , it is determined whether the operational current is below the nominal current. When the operational current is not below the nominal current, method  200  returns to OPERATION  220  to continue monitoring the heat of the LED load  130  with the present operational current being equal to the nominal current. When the operational current is below the nominal current, method  200  proceeds to OPERATION  260 . 
         [0028]    In various aspects where the operational current is adjusted in steps, the current controller  121  may set a time threshold between the determination in DECISION  230  and the determination in DECISION  250  so that a temperature fluctuating above and below the temperature threshold does not cause the current controller  121  to introduce flicker into the LED luminaire  100  as the operational current is adjusted upward and downward. A time threshold may be set via a number of clock cycles in a microprocessor between performing the operations, via an averaging of temperatures in a register, or the speed of the components in the current controller  121  (e.g., switching delays). 
         [0029]    At OPERATION  260 , the operational current is raised. As will be appreciated, the operational current may be raised in steps (e.g., 0% to 25% to 50% to 75% to 100%) or in a continuum similarly to how the operational current is reduced in OPERATION  240 , but will not be raised to exceed the nominal current. Method  200  then returns to OPERATION  220  to continue monitoring the heat of the LED load  130 . 
         [0030]    Method  200  may conclude when the power source is removed, and may start again when the power source is reapplied. 
         [0031]    Systems, devices or methods disclosed herein may include one or more of the features structures, methods, or combination thereof described herein. For example, a device or method may be implemented to include one or more of the features and/or processes above. It is intended that such device or method need not include all of the features and/or processes described herein, but may be implemented to include selected features and/or processes that provide useful structures and/or functionality. 
         [0032]    Various modifications and additions can be made to the disclosed embodiments discussed above. Accordingly, the scope of the present disclosure should not be limited by the particular embodiments described above, but should be defined only by the claims set forth below and equivalents thereof.