Solid state lighting module, a lighting circuit and lighting control methods

Abstract

A solid state lighting module is disclosed. In one example, the module comprises a light source and a resistor circuit, wherein an output resistance of the resistor circuit is for conveying to a connected driver information on a desired power to be applied to the solid state light source. A control interface is provided for receiving configuration information from an external configuration device and a control circuit configures the resistor circuit thereby to set the output resistance in response to received configuration information. This approach involves integrating the configuration function in the lighting module instead of in the driver. The output resistance can be determined by existing driver architectures without modification, while at the same time the ability of the user to tailor individual lighting modules to their needs is enabled.

Claims

1. A solid state lighting module, comprising: a solid state light source; a resistor circuit, wherein an output resistance of the resistor circuit is for conveying to a connected driver information on a desired power to be applied to the solid state light source; a control interface for receiving configuration information from an external configuration device; and a control circuit for controlling a configuration of the resistor circuit thereby to set the output resistance in response to received configuration information; wherein the output resistance of the resistor circuit is independent of light source drive signals from the connected driver to power the solid state light source, and the control interface comprises a near field communication (NFC) receiver, comprising a near field communication (NFC) antenna and a near field communication (NFC) receiver circuit.

2. A module as claimed in claim 1, further comprising a power supply circuit for generating a power supply for the control circuit from light source drive signals received from the connected driver.

3. The module as claimed in claim 2, wherein the power supply circuit comprises: a transistor circuit having: an output transistor coupled to said light source drive signals and a threshold element applied to the control terminal of the output transistor thereby to set an output voltage of the output transistor as said power supply; or a switch mode power supply circuit; or a voltage line in parallel with a certain number of solid state light sources wherein a forward voltage of said certain number of solid state light sources corresponds to an output voltage as the power supply.

4. The module as claimed in claim 1, wherein the NFC receiver comprises a power harvesting circuit for generating a power supply for the control interface from a wireless signal received from the external configuration device.

5. The module as claimed in claim 4, wherein the output resistance is defined between: a ground terminal of the module and a resistor output terminal; or a light source terminal of the module and a resistor output terminal.

6. The module as claimed in claim 5, wherein the resistor circuit comprises a set of resistor branches, each comprising a resistor and a switch in series, and the branches being in parallel, wherein the control circuit is adapted to control the settings of the switches thereby defining the configuration of the resistor circuit.

7. The module as claimed in claim 5, wherein the resistor circuit comprises first and second terminals for connection to the driver, wherein the resistor circuit comprises: a current sensor for sensing the current flowing between the first and second terminals, a voltage sensor for sensing the voltage between the first and second terminals, and the control circuit comprises: a unit for calculating the equivalent resistance of the resistor circuit according to the sensed voltage and the sensed current, and a switching circuit between the first and second terminals for controlling the equivalent resistance using the configuration information as well as the calculated equivalent resistance.

8. The module as claimed in claim 5, wherein the resistor circuit comprises first and second terminals for connection to the driver and for receiving a voltage, wherein the resistor circuit comprises: a current sensor for sensing the current flowing between the first and second terminals, and the control circuit comprises a current control unit for controlling the current through the resistor circuit using the configuration information as well as feedback of the sensed current.

9. The module as claimed in claim 8, further comprising: a temperature sensor for sensing temperature; wherein the control circuit is adapted for controlling the configuration of the resistor circuit thereby to set the output resistance further in response to the sensed temperature.

10. The module according to claim 1, wherein the control interface is adapted to receive the configuration information before the module is driven by the connected driver.

11. The lighting module system comprising: a lighting module as claimed in claim 10; and a configuration device for sending configuration information to the control interface of the lighting module, thereby to write a desired power setting of the lighting module therein.

12. The lighting circuit according to claim 11, wherein the desired power comprises the rated power of the lighting module.

13. The lighting circuit comprising: a lighting module as claimed in claim 10; and the connected driver, wherein the connected driver comprises: a power unit for providing power to the lighting module; a sensing unit for coupling to the resistor circuit for detecting the output resistance; and a controller for controlling the power applied to the lighting module by the power unit in dependence on the information on the desired power conveyed by the detected output resistance.

14. The lighting circuit according to claim 13, wherein the driver comprises: a feedback loop independent from said resistor network, for sensing the actual light source drive signals provided by the power unit to the lighting module and providing the sensed light source drive signals to the controller, wherein said controller of the driver is further adapted to control the light source drive signals provided by the power unit according to the rated power of the lighting module and the sensed light source drive signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples will now be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a known example of LED module and driver using a current setting resistor in the LED module;

(3) FIG. 2 shows a first example of LED module and driver together with an external interface device;

(4) FIG. 3 shows a second example of LED module and driver;

(5) FIG. 4 shows a first example of power supply circuit;

(6) FIG. 5 shows a second example of power supply circuit;

(7) FIG. 6 shows a first example of resistor circuit;

(8) FIG. 7 shows a second example of resistor circuit; and

(9) FIG. 8 shows a third example of resistor circuit.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(10) The various embodiments provide a solid state lighting module, comprising a solid state light source and a resistor circuit, wherein an output resistance of the resistor circuit is for conveying to a connected driver information on a desired power to be applied to the solid state light source. A control interface is provided for receiving configuration information from an external configuration device; and a control circuit configures the resistor circuit thereby to set the output resistance in response to received configuration information. This approach involves integrating the configuration function in the lighting module instead of in the driver. The output resistance can be determined by existing driver architectures without modification, while at the same time the ability of the user to tailor individual lighting modules to their needs is enabled.

(11) Down lighting and accent lighting solutions are typically based on LED modules, where each module combines a LED light engine and an LED driver. The light engine may for example be based on Chip on Board (CoB) LEDs. Holders are used to mount the CoB LEDs and a cable passes from the holder to the driver. The total system thus consists of a driver, cable and light engine.

(12) As explained above, driver flexibility means that there is a large range of drivers that can drive the same light engine. For instance there are fixed output current drivers, dimming drivers and programmable drivers. There are also different housing types.

(13) It has been proposed to incorporate a small PCB as part of the holder, and the PCB can then include passive current setting components.

(14) Different light engine may require different operation current. The PCB may for example provide a circuit that allows the driver to sense the temperature of the module as well as having a setting resistor used by the driver to know and set the correct current.

(15) A simple schematic of this function is shown in FIG. 1. The LED module 10 comprises the light engine 12 (i.e. the LED string), a current setting resistor 14 and a thermal protection circuit 16. The module 10 connects to a driver 18 using only three terminals. Terminals LED+ and LED− connect to the ends of the LED string 12, and a third terminal LEDset enables the driver 18 to measure the resistance of the current setting resistor 14 by injecting a measurement current Iset. With a certain resistance of the current setting resistor in the LED module, a certain voltage occurs across the setting resistor and is detected by the driver 18, and in turn the driver 18 is aware of how much current/power the LED module requires.

(16) This arrangement does not allow the end user to change the current (and therefore light output flux) of the light module 10. If a different current is needed, the setting resistor 14 needs to be modified.

(17) A customer using the modules to build luminaires may desire to optimize their luminaire light output to their preferences, without being limited to a fixed light output, temperature or power. For instance, their own optical design may require less light output from the module. Alternatively, due to the use of a miniaturized heat sink, a reduced power may be desired to prevent the module reaching too high temperatures.

(18) The desire for the customer to be able to flexibly set the output current has been recognized. For example, a setting resistor may be inserted into the driver by the customer. The driver then uses this setting resistor to define the output current.

(19) An alternative to placing a current setting resistor in a driver is to enable a remotely settable drive current. For example, by using near field communication (NFC) a driver can be programmed using a NFC reader. Philips (Trade Mark) is releasing a system which operates in this way, named the “SimpleSet” (Trade Mark) range. This wireless programming technology allows the luminaire manufacturers to quickly and easily program the LED driver at any stage during the manufacturing process, without a connection to mains power, offering great flexibility.

(20) With this “SimpleSet” system, the driver current is set via the driver and no additional components in the module are required. This approach is thus based on a new and upgraded driver design, and it is therefore particularly suitable for new lighting installations.

(21) There are many existing driver types (fixed output, dimming, DALI dimming, different power levels etc.). It would be desirable in existing installations to be able to use existing drivers to implement the simplified output flux control, for example by changing the lighting module instead of changing the driver.

(22) The invention is based on the integration of configuration functionality in a lighting module (instead of in the driver). For example, a PCB may be provided as part of the LED holder, which implements an NFC antenna and an NFC chip.

(23) FIG. 2 shows a first example of a lighting module coupled to a driver 22, with a first interface type. The driver interface comprises terminals LED+ and LED− for the LED string, and a separate pair of terminals RSET2 and SGND for measuring the external current setting resistor in the light module. This is known as an RSET2 interface.

(24) The driver 22 has a power unit 220 for providing power to the lighting module, and a sensing unit 222 for coupling to the resistor circuit for detecting the output resistance.

(25) A controller 224 is used for controlling the power applied to the lighting module by the power unit 220 in dependence on the desired power conveyed by the detected output resistance. In more detail, the controller 224 should take the information on the desired power as a reference to determine the operation behavior of the power unit 220 to provide actual power in accordance with the desired power. In even more detail, if the driver is a closed loop feedback driver, the controller 224 should sense the actual power provided by the power unit and compare the actual power with the desired power, and in turn the error there between can be used for tuning the power unit 220 so as to reduce the error.

(26) For this purpose, the controller of the driver may comprise a feedback loop independent from said resistor network, for sensing the actual light source drive signals provided by the power unit 220 to the lighting module and providing the sensed light source drive signals to the controller 224. This feedback path includes the current sensor 226 within the light module or alternatively within the driver. The controller 224 of the driver is then further adapted to control the light source drive signals provided by the power unit 220 according to the rated power of the lighting module and the sensed light source drive signals.

(27) This provides a regulation of the power supply delivered to the lighting module.

(28) These elements are standard parts of a conventional driver, and indeed the module of the invention is intended to be connectable to conventional drivers.

(29) The LED module 20 comprises a power supply 23 which provides the power for a microprocessor 24. This power supply is tapped from the LED string. It may be tapped only from a portion of the LED string in order to minimize the power loss from the power supply. Alternatively, this power supply can be a more complicated switch mode power supply or a simple linear power supply.

(30) The microprocessor 24 includes a near field communication integrated circuit (IC), in particular an NFC reader, which translates NFC commands into a signal for controlling a resistor circuit 26. The microprocessor 24 also functions as a control circuit for controlling a configuration of the resistor circuit 26 thereby to set the output resistance. The output resistance is defined between a ground terminal of the module SGND and a resistor output terminal RSET2. The near field communication signal is received using an antenna 28.

(31) The resistor circuit 26 is an electronic circuit which is used to simulate a physical resistor that is used by the LED driver for current setting. The output resistance of the resistor circuit is conveyed to the connected driver 22 and encodes information about the desired power to be applied to the LED string.

(32) The module optionally includes a temperature sensor 29 which may be used for setting a maximum temperature or for controlling the lifetime of the module as discussed below.

(33) The NFC IC functions as a control interface for receiving configuration information from an external configuration device 30. The external configuration device provides configuration information which is received by the microprocessor 24. As shown, the external configuration device 30 comprises an NFC IC 32, in particular an NFC transmitter, and an antenna 34. A user interface 36 enables a user to select a desired output flux which is translated into a corresponding value of the resistor which is to be simulated by the resistor circuit 26.

(34) The output resistance of the resistor network is independent of the light source drive signals from the connected driver 22 used to power the LED string. The desired output may be the rated power of the lighting module.

(35) The control interface (i.e. the NFC receiver of the microprocessor 24) is adapted to receive the configuration information from the external configuration device 30 before the module is driven by the connected driver. This can be carried out by a customer before the lighting system is installed. The NFC communication can be used to set the desired flux lighting to the controller 24 using wireless power transfer from the external configuration device 30, with no other power provided to the module. In a real implementation, the NFC reader may comprise a power harvesting circuit to harvest enough energy to receive the NFC command and store the signal in a non-volatile RAM, even before the LED module is powered by the driver. After the LED module is powered by the driver, the microcontroller reads the signal in the RAM and set the output resistance of the resistor circuit. In this case, only when the driver is powered, does the resistor circuit need to be controlled.

(36) FIG. 3 shows a second example of a lighting module coupled to a driver 22, with a second interface type. The module 20 includes the same components as in FIG. 2 and they are given the same reference numbers. The only difference is that the current setting resistor and the LED string 12 shares a common terminal such as the ground terminal. The temperature sensor is not shown, and the external configuration element is also omitted from FIG. 3.

(37) The LED string is between terminals LED+ and LED−, and the setting resistor is between a light source terminal LED− and a resistor output terminal REST3. This is known as an RSET3 interface. The terminal LED− serves as the ground terminal for the resistor circuit 26.

(38) The same module may function with both RSET2 and RSET3 drivers. For example the module of FIG. 2 with four output terminals may be used with the RSET3 driver of FIG. 3 simply by connecting the LED− and SGND terminals together, i.e. connecting two of the LED module connections to the single LED− driver connection.

(39) The LED module circuit may be implemented in a small space provided by an LED holder.

(40) The circuit is used to mimic a current setting resistor. The module is then programmed with a desired value of the current setting resistor, and it can be connected to any driver that has RSET2 or RSET3 functionality.

(41) The invention enables an existing driver portfolio to be used, whilst still providing a simple user capability to set the desired output of the light engine.

(42) The module may also implement a thermal function by including a temperature sensor which is used to adapt the simulated resistance value in dependence on the temperature level. This may be used to program the module to reduce its desired power to make it stay below a maximum temperature, which may for example enable implementation of a minimum lifetime.

(43) The building blocks used in the module will now be described in further detail.

(44) The power supply 23 is used to generate a power supply for the control circuit 24, such as 5V, from the LED+ and LED− module inputs or from a portion of the LED string. There are various possible circuits.

(45) FIG. 4 shows a first example which comprises a transistor circuit having an output transistor 40 coupled to the light source drive signals and a threshold element 42 in the form of a diode applied to the control terminal of the output transistor 40 thereby to set an output voltage of the output transistor as said power supply. The transistor is turned on and delivers current through a diode 44 to charge an output capacitor 46, until an output voltage is reached corresponding to the threshold element voltage less the base-emitter voltage drop. This embodiment is a typical linear power supply. It should be understood that other types of linear power supply are also applicable.

(46) FIG. 5 shows a second example based on a switch mode power supply circuit. The circuit comprises a switching transistor, an inductor 52 and a diode 54, in this example forming a buck converter. The output is provided across an output capacitor 56. It should be understood that other types of switched mode power supply such as boost and buck boost converter are also applicable.

(47) A third example may be based on a voltage line in parallel with a certain number of solid state light sources. A forward voltage of the set number of solid state light sources then corresponds to a desired output voltage as the power supply. For example, two series 3.3V LEDs may be used to provide a 6.6V supply for the controller.

(48) The resistor circuit comprises an electronic circuit used to generate a controllable output resistance in the view of the connected driver. There are various options for the resistor circuit, some of which are discussed below.

(49) FIG. 6 shows a first example in which the resistor circuit 26 comprises a set of resistor branches 60, 62, 64, each comprising a resistor 60a, 62a, 64a and a switch 60b, 62b, 64b in series. The branches are in parallel. The control circuit 24 is adapted to control the settings of the switches thereby defining the configuration of the resistor circuit.

(50) The example of FIG. 6 gives 8 possible resistor settings.

(51) FIG. 7 shows a second example in which the resistor circuit comprises first and second terminals 70, 72 for connection to the driver, wherein the resistor circuit comprises a current sensor 74 for sensing the current flowing between the first and second terminals (based on the voltage across a sense resistor 75), and a voltage sensor 76 for sensing the voltage between the first and second terminals. The control circuit 24 has a unit for calculating the equivalent resistance of the resistor circuit according to the sensed voltage and the sensed current.

(52) The resistor circuit has a switching element 78 between the first and second terminals for controlling the equivalent resistance using the configuration information as well as the calculated equivalent resistance. The switching element is a transistor which has its output resistance controlled in a dynamic way. The controller 24 provides a desired resistance value 80 based on the current setting value as programmed into it, and a comparator 82 is used to compare this with a value generated by unit 84, to provide feedback control.

(53) This approach is based on simulating the characteristics of a physical resistor. The switching element 78 provides dynamic control of the current and voltage levels so that the equivalent resistor becomes equal to the expected physical resistor.

(54) Unit 84 is a divider element whose function is to provide a value of voltage/current (i.e. resistance). In a digital method, this could be implemented by a microcontroller, so that the unit 84 would not be required as a separate component.

(55) FIG. 8 shows a third example in which the resistor circuit comprises first and second terminals 90, 92 for connection to the driver and for receiving a voltage, wherein the resistor circuit comprises a current sensor 94 for sensing the current flowing between the first and second terminals (based on the voltage across a sense resistor 95). The control circuit comprises a current control unit for controlling the current through the resistor circuit using the configuration information as well as feedback of the sensed current. The current is controlled using a switching element in the form of transistor 96.

(56) This provides a controllable current source, which is specifically the input required by the RSET3 interface. The transistor is dynamically controlled to make the current is equal to that which a physical resistor would insert into the RSET3 port of the driver.

(57) The module may be used with existing types of temperature overload protection. In this case, a thermal component (negative temperature coefficient—NTC) may be connected to the NFC IC. In the event of high temperatures, the circuit will signal to the driver that the module is at too high temperature and the driver can dim or shut down.

(58) As mentioned above, temperature sensing may also be used to enable control of the lifetime of the module. Beyond a certain temperature, a lifetime of less than 50 khrs is predicted. If the customer, building a luminaire using the module, wants to apply the module in a limited heat sink luminaire, the power (current) must be reduced to meet this temperature. Instead of performing extensive testing, the NFC chip may be programmed to a particular lifetime such as 50 khr. The circuit can then internally compare a threshold value with the on-board thermal component, and if it exceeds the maximum temperature a lower drive current can be communicated to the driver.

(59) The invention may be is used in a variety of lighting applications. The lighting modules may be indoor point sources, down lighting units or spot lighting units. The invention can also be used in linear LED applications (as used in offices), and also outdoor lighting for road and streets. In down lighting and office systems, often a well-defined flux is needed making an easy to implement flux setting highly desirable.

(60) The invention has been described in connection with an LED lighting arrangement. However, it can be applied to a driver arrangement for other types of lighting technology. It can be applied to any driver which is adapted to communicate with an external sensing resistor for controlling the driver circuit configuration. For example, other solid state lighting technologies may be used.

(61) The example above uses a NFC system to communicate the desired setting to the lighting module. This provides a convenient wireless operation for the user. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.