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Publication numberWO2013014580 A1
Publication typeApplication
Application numberPCT/IB2012/053681
Publication date31 Jan 2013
Filing date19 Jul 2012
Priority date22 Jul 2011
Publication numberPCT/2012/53681, PCT/IB/12/053681, PCT/IB/12/53681, PCT/IB/2012/053681, PCT/IB/2012/53681, PCT/IB12/053681, PCT/IB12/53681, PCT/IB12053681, PCT/IB1253681, PCT/IB2012/053681, PCT/IB2012/53681, PCT/IB2012053681, PCT/IB201253681, WO 2013/014580 A1, WO 2013014580 A1, WO 2013014580A1, WO-A1-2013014580, WO2013/014580A1, WO2013014580 A1, WO2013014580A1
InventorsAly Aboulnaga
ApplicantKoninklijke Philips Electronics N.V.
Export CitationBiBTeX, EndNote, RefMan
External Links: Patentscope, Espacenet
Light emitting diode driver with non-destructive circuit for indicating fault or outage of light emitting diode load
WO 2013014580 A1
Abstract
A driver (305, 405) supplies power to a load (330, 430) including one or more light- emitting diode (LED) light sources. The driver includes: a rectifier (310, 410) to rectify an AC input voltage; a DC/DC converter (320, 420), including a switching device (424), to convert the rectified AC input voltage into a DC current for driving the load; and a controller (340, 440) to supply a switching control signal to control a switching operation of the switching device. The controller supplies the switching control signal in response to a voltage supplied to a feedback input of the controller. The driver also includes a fault detector (350, 450) to detect whether the load has a fault, such as an open circuit condition or a short circuit condition, and a controller disabler (360, 460) to disable the feedback input of the controller when the fault detector detects a fault.
Claims  (OCR text may contain errors)
CLAIMS:
1. A driver (305, 405) for supplying power to a load (330, 430) including one or more light-emitting diode (LED) light sources, the driver comprising:
a rectifier (310, 420) configured to rectify an AC input voltage;
a DC/DC converter (320, 420) including a switching device (424), the DC/DC converter configured to convert the rectified AC input voltage into a DC current for driving the load; a controller (340, 440) configured to supply a switching control signal to control a switching operation of the switching device of the DC/DC converter, wherein the controller has a zero crossing detection (ZCD) input and supplies the switching control signal in response to a voltage supplied to the ZCD input;
a fault detector (350, 450) configured to detect whether the load (330, 430) has a fault, including detecting when the load (330, 430) has an open circuit condition and detecting when the load (330, 430) has a short circuit condition, and producing a fault detector output signal (355, 455) that indicates whether the load (330, 430) has a fault; and
a controller disabler (360, 460) configured to receive the fault detector output signal (355, 455) and in response thereto to disable the ZCD input of the controller (340, 440) when the fault detector output signal (355, 455) indicates that the load (330, 430) has a fault.
2. The driver (305, 405) of claim 1, wherein when the ZCD input is disabled, then the switching device (424) of the DC/DC converter (420) is turned off.
3. The driver (305, 405) of claim 2, further comprising a pair of input terminals configured to receive the AC input voltage (125), wherein when the switching device (424) of the DC/DC converter (320, 420) is turned on then an input impedance of the driver (305, 405) across the pair of input terminals has a first value, and when the switching device (424) of the DC/DC converter (320, 420) is turned off then the input impedance of the driver (305, 405) has a second value, wherein the second value is substantially greater than the first value.
4. The driver (305, 405) of claim 3, wherein the first value is less than 1 kQ and wherein the second value is greater than 2 kQ.
5. The driver (305, 405) of claim 1, wherein the controller disabler (360, 460) comprises a field effect transistor (Q3) having a first terminal connected to a fixed potential, a second terminal connected to the ZCD input of the controller (340, 440), and a gate connected to receive the fault detector output signal (355, 455) from the fault detector (350, 450).
6. The driver (305, 405) of claim 1, wherein the driver (305, 405) is turned off when the AC input voltage (125) is supplied from a source with a series impedance of about 20 kQ.
7. The driver (305, 405) of claim 6, wherein when the driver (305, 405) is turned off and the fault detector output signal (355, 455) indicates that the load (330, 430) does not have a fault, then the switching device (424) of the DC/DC converter (320, 420) is turned on so as to cause an input impedance of the driver (305, 405) to have a first value less than 1 kQ.
8. The driver (305, 405) of claim 7, wherein when the driver (305, 405) is turned off and the fault detector output signal (355, 455) indicates t hat the load (330, 430) does not have a fault, then the switching device of the DC/DC converter (320, 420) is turned off so as to cause the input impedance of the driver (305, 405) to have a second value greater than 2 kQ.
9. A method of operating a driver (305, 405) for supplying power to a load (330, 430) including one or more light-emitting diode (LED) light sources, the method comprising:
rectifying an AC input voltage (125);
converting the rectified AC input voltage to a DC current for driving the load (330, 430) by performing a DC/DC conversion with a switching device (424);
supplying a switching control signal to the switching device to control a switching operation thereof in response to a zero crossing detection (ZCD) input;
detecting whether the load (330, 430) has a fault, including detecting when the load (330, 430) has an open circuit condition and detecting when the load (330, 430) has a short circuit condition; and
in response to detecting that the load (330, 430) has a fault, disabling the ZCD input so as to disable switching of the switching device (424).
10. The method of claim 9, wherein when the switching device (424) is turned on then an input impedance of the driver (305, 405) across the pair of input terminals has a first value, and when the switching device (424) is turned off then the input impedance of the driver (305, 405) has a second value, wherein the second value is substantially greater than the first value.
11. The method of claim 10, wherein the first value is less than 1 kQ and wherein the second value is greater than 2 kQ.
12. The method of claim 9, further comprising producing a fault detector output signal (355, 455) that indicates whether the load has a fault.
13. The method of claim 12, wherein the driver (305, 405) is turned off when the AC input voltage (125) is supplied from a source with a series impedance of about 20 kQ.
14. The method of claim 13, wherein when the driver (305, 405) is turned off and the fault detector output signal (455) indicates that the load (330, 430) does not have a fault, then the switching device (424) is turned on so as to cause an input impedance of the driver (305, 405) to have a first value less than 1 kQ.
15. The method of claim 14, wherein when the driver (305, 405) is turned off and the fault detector output signal (355, 455) indicates t hat the load (330, 430) does not have a fault, then the switching device (424) is turned off so as to cause the input impedance of the driver (305, 405) to have a second value greater than 2 kQ.
16. A device (300, 400), comprising:
a rectifier (310, 410) configured to rectify an AC input voltage (125);
a DC/DC converter (320, 420) including a switching device (424), wherein the DC/DC converter is configured to convert the rectified AC input voltage into a DC current in response to a switching operation of the switching device, and to supply the current to a load (330, 430) including at least one light-emitting diode (LED) light source;
a controller (340, 440) configured to supply a switching control signal to control the switching operation of the switching device (424) of the DC/DC converter (320, 420) in response to a signal at a feedback input of the controller (340, 440);
a fault detector (350, 450) configured to detect a fault at the load (330, 430), wherein the fault detector (350, 350) produces a fault detector output signal (355, 455) that indicates whether the load (330, 430) has a fault; and
a controller disabler (360, 460) configured to receive the fault detector output signal (355, 455) and in response thereto to disable the input of the controller (340, 440) when the fault detector output signal(355, 455) indicates that the load (330, 430) has a fault.
17. The device of claim 16, further including the load (330, 430).
18. The device of claim 17, wherein the feedback input of the controller (340, 440) is a zero crossing detection (ZCD) input.
Description  (OCR text may contain errors)

Light Emitting Diode Driver With Non-Destructive Circuit For Indicating Fault Or Outage Of Light Emitting Diode Load

Technical Field

[0001] The present invention is directed generally to light emitting diode (LED) based lighting units, and drivers for LED light sources. More particularly, various inventive methods and apparatus disclosed herein relate to a driver for a load of one or more LED light sources that is configured to provide a desired change in its input impedance in response to a fault or outage of the LED load.

Background

[0002] Traffic light systems have existed for nearly 100 years and, over that time, literally millions of traffic light systems have been installed throughout the world. FIG. 1 is a high level block diagram of one example of a traffic light system 100. Traffic light system 100 includes a traffic light controller 110, a traffic lighting unit 120, a 20 kQ load resistor 130 and a relay 140. Although for simplicity of illustration traffic light system 100 is shown in FIG. 1 with one traffic light controller 110 and one traffic lighting unit 120, in some implementations a single traffic light controller 110 may control three or more traffic lighting units 120 (e.g., a red traffic lighting unit 120, a yellow traffic lighting unit 120, and a green traffic lighting unit 120). In traffic light system 100, traffic lighting unit 120 may comprises an incandescent lamp and a color filter to output light of a desired color (e.g., red, yellow, green, white, etc.).

[0003] Various standards have been developed with respect to traffic light systems and their operation.

[0004] In operation, traffic light controller 110 supplies an AC output voltage 115, e.g., nominally 110-120 VAC, which is provided via the parallel combination of load resistor 130 and relay 140 as an AC input voltage 125 to traffic lighting unit 120. In an "ON" mode traffic light controller 110 "turns on" traffic lighting unit 120 by controlling relay 140 to be switched on or connected across load resistor 130. In that case, AC input voltage 125 provided to traffic lighting unit 120 is essentially the same as AC output voltage 115 provided by traffic light controller 110, and the incandescent lamp in traffic lighting unit 120 is lit to produce light. In an OFF mode, controller "turns off" traffic lighting unit 120 by controlling relay 140 to be switched off or disconnected across load resistor 130. In that case, AC output voltage 115 is provided to traffic lighting unit 120 via the 20 kQ load resistor 130 as a series input impedance. As a result, a voltage divider occurs between the impedance of the filament in the incandescent lamp in traffic lighting unit 120, which is normally very low, and the 20 kQ load resistor 130. As a result, input voltage 125 applied across the input of traffic lighting unit 120, and therefore applied to the incandescent lamp in traffic lighting unit 120, is only a few volts at most (e.g., < 10 VAC). Accordingly, the incandescent lamp in traffic lighting unit 120 is not lit and does not produce light.

[0005] The incandescent lamp in traffic lighting unit 120 has a lifetime and eventually the filament will "burn out" and become open so as to no longer cause conduct current and cause the incandescent lamp to produce light. Accordingly, the incandescent lamp will need to be replaced from time to time.

[0006] Toward this end, traffic light controller 110 includes a means for detecting when the incandescent lamp in traffic lighting unit 120 needs to be replaced, in which case, traffic light controller 110 may generate a signal or other indicator that the incandescent lamp in traffic lighting unit 120 requires replacement.

[0007] When the incandescent lamp in traffic lighting unit 120 is working properly, then traffic lighting unit 120 will have a relatively low input impedance ( 20 kQ) set by the low impedance of the filament of the incandescent lamp. In that case, when relay 140 is open so that there is a voltage divider between the impedance of the incandescent lamp (which is quite small) and load resistor 130, only a small percentage of AC output voltage 115 will appear across the input of traffic lighting unit 120 as AC input voltage 125. On the other hand, when the incandescent lamp in traffic lighting unit 120 has burned out, then traffic lighting unit 120 will have a relatively high input impedance (e.g., > 20 kQ) based on the lamp filament being open. In that case, when relay 140 is open so that there is a voltage divider between the impedance of the incandescent lamp and load resistor 130, virtually all, or at least a large percentage, of AC output voltage 115 will appear across the input terminals of traffic lighting unit 120 as AC input voltage 125.

[0008] Accordingly, to determine whether the incandescent lamp in traffic lighting unit 120 needs to be replaced, traffic light controller 110 may measure AC input voltage 125 across the input of traffic lighting unit 120 in the OFF mode where traffic light controller 110 opens relay 140 and turns off traffic lighting unit 120. In particular, if traffic light controller 110 measures AC input voltage 125 in the OFF mode as being less than a predetermined threshold voltage (which may be, for example a voltage between about 10 VAC and 100 VAC) then traffic light controller 110 may determine that the incandescent lamp in traffic lighting unit 120 is working properly. On the other hand, if traffic light controller 110 measures input voltage 125 in the OFF mode as being greater than the predetermined threshold voltage, then traffic light controller 110 may determine that the incandescent lamp in traffic lighting unit 120 has bu rned out. In that case, traffic light controller 110 may generate an alarm signal or other indication (e.g., light an indicator light) that the incandescent lamp in traffic lighting unit 120 requires replacement.

[0009] Semiconductor-based lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum LED light sources that enable a variety of lighting effects in many applications. Some LED-based lighting units embodying these LED light sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Patent Nos. 6,016,038 and 6,211,626.

[0010] Because of the benefits and advantages described above, there continues to be a desire to replace traditional incandescent lamps with LED-based lighting units in traffic light systems and other lighting applications.

[0011] In order to eliminate labor and component costs associated with installing new traffic light controllers, in some cases there is a desire to retrofit an LED-based lighting unit employing LED light sources directly into existing traffic light systems in place of traffic lighting units that employ incandescent lamps. In such cases, the new LED-based lighting units need to behave so that the rest of the traffic light system, including the traffic light controller, is able to function with them in the same way as it functions with traffic lighting units that employ incandescent lamps, without requiring changes or modifications to the rest of the infrastructure of the traffic light system.

[0012] One of the challenges involved in retrofitting an LED-based lighting unit into an existing traffic light system in place of a traffic lighting unit having an incandescent lamp is mimicking the behavior of the incandescent lamp when an LED light source has an open or short defect and needs to be replaced. More specifically, when an LED light source for an LED- based lighting unit has an open-circuit or short-circuit defect, the existing traffic light controller needs to be able to detect this using the same means as it employs to determine that a filament that has burned out in an incandescent lamp.

[0013] In particular, when the LED light source(s) of an LED-based lighting unit is/are working properly, then in an OFF mode where the traffic light controller opens the relay and turns off the LED-based lighting unit, then the LED-based lighting unit needs to present a relatively low input impedance ( 20 kO, e.g., < 1 kO) to the traffic light controller so that the input voltage across the input terminals of the LED-based lighting unit as measured by the traffic light controller is low (e.g., < 10 VAC) and the traffic light controller will conclude that the LED-based lighting unit is working properly. On the other hand, when there is an open circuit or short circuit defect in the LED light source (s), then in an OFF mode where the traffic light controller opens the relay and turns off the LED-based lighting unit, then the LED-based lighting unit needs to present a relatively high input impedance ( 20 kO, e.g., > 200 kO) to the traffic light controller so that the input voltage across the input terminals of the LED-based lighting unit as measured by the traffic light controller is relatively high (e.g., > 100 VAC) and the traffic light controller will determine that the LED-based lighting unit has a defect and one or more LED light source s need to be replaced.

[0014] In addition to the traffic light systems described above, there are other light systems, such as some automotive light systems and emergency light systems, where it is desired to be able to retrofit LED-based lighting units in place of the original incandescent lamps for which the systems were designed, and still to be able to detect a fault or outage in the LED light sources by a particular change in the input impedance of the LED-based lighting unit.

[0015] Thus, there is a need in the art to provide a LED-based lighting unit configured to be retrofit into an existing light system, such as a traffic light system, and an LED driver for one or more LED light sources in such an LED-based lighting unit. In particular, there is a need for an LED-based lighting unit that can mimic the input impedance and voltage behavior of an incandescent lamp in an OFF state when the one or more LED light sources is/are working normally, and when there is an open or short fault in the one or more LED light sources. More specifically, there is a need for such an LED driver whose fault detection may be tested nondestructive^ during manufacturing and while installed, and which is relatively small, inexpensive, and efficient.

Summary

[0016] The present disclosure is directed to inventive methods and apparatus for providing a driver for a load of one or more solid state light sources that is configured to provide a desired change in its input impedance in response to a fault or outage of the load. For example, the present invention provides a solid state lighting unit, and a driver for one or more solid state light sources in a solid state lighting unit, that can permit a traffic light controller to detect a fault in the solid state light sources using the existing means that the traffic light controller already employs to detect when an incandescent lamp in an existing traffic light system needs to be replaced.

[0017] Generally, in one aspect, a driver is provided for supplying power to a load including at least one light-emitting diode (LED) light sources. The driver includes: a rectifier configured to rectify an AC input voltage; a DC/DC converter including a switching device (e.g., a power switching device) for converting the rectified AC input voltage into a regulated DC current for driving the load; and a controller configured to supply a switching control signal to control a switching operation of the switching device of the DC/DC converter. The controller has a zero crossing detection (ZCD) input and supplies the switching control signal in response to a voltage supplied to the ZCD input. The driver also includes a fault detector configured to detect whether the load has a fault, including detecting when the load has an open circuit condition and detecting when the load has a short circuit condition, and producing a fault detector output signal that indicates whether the load has a fault; and a controller disabler configured to receive the fault detector output signal and in response thereto to disable the ZCD input of the controller when the fault detector output signal indicates that the load has a fault.

[0018] In one embodiment, when the ZCD input is disabled (e.g., by driving the ZCD input to control ground), then the switching device of the DC/DC converter is turned off.

[0019] In one version of this embodiment, the driver also includes a pair of input terminals configured to receive the AC input voltage, wherein when the switching device of the DC/DC converter is turned on then an input impedance of the driver across the pair of input terminals has a first value, and when the switching device of the DC/DC converter is turned off then the input impedance of the driver has a second value, wherein the second value is substantially greater than the first value.

[0020] In one embodiment, the controller disabler comprises a field effect transistor having a first terminal connected to fixed potential, a second terminal connected to the ZCD input of the controller, and a gate connected to receive the fault detector output signal from the fault detector.

[0021] In one embodiment, the driver is turned off when the AC input voltage is supplied from a source with a series impedance of about 20 kQ.

[0022] Generally, in another aspect, a method is provided for operating a driver for supplying power to a load including one or more light-emitting diode (LED) light sources. The method comprises: rectifying an AC input voltage; converting the rectified AC input voltage to a regulated DC current for driving the load by performing a DC/DC conversion with a switching device; supplying a switching control signal to the switching device to control a switching operation thereof in response to a zero crossing detection (ZCD) input; detecting whether the load has a fault, including detecting when the load has an open circuit condition and detecting when the load has a short circuit condition; and in response to detecting that the load has a fault, disabling the ZCD input so as to disable switching of the switching device and provide a high input impedance across input terminals of the driver.

[0023] Generally, in yet another aspect, a device includes: a rectifier configured to rectify an AC input voltage; a DC/DC converter including a switching device, wherein the DC/DC converter is configured to convert the rectified AC input voltage into a DC current in response to a switching operation of the switching device, and to supply the current to a load including at least one light-emitting diode (LED) light source; a controller configured to supply a switching control signal to control the switching operation of the switching device of the DC/DC converter in response to a signal at a feedback input of the controller; a fault detector configured to detect a fault at the load, wherein the fault detector produces a fault detector output signal that indicates whether the load has a fault; and a controller disabler configured to receive the fault detector output signal and in response thereto to disable the input of the controller when the fault detector output signal indicates that the load has a fault.

[0024] As used herein for purposes of the present disclosure, the term "LED" should be understood to include any electroluminescent diode or other type of carrier injection/junction- based system that is capable of generating radiation in response to an electric signal. Thus, the term LED includes, but is not limited to, various semiconductor-based structures that produce light in response to current, light emitting polymers, organic light emitting diodes (OLEDs), electroluminescent strips, and the like. In particular, the term LED refers to light emitting diodes of all types (including semi-conductor and organic light emitting diodes) that may be configured to generate radiation in one or more of the infrared spectrum, ultraviolet spectrum, and various portions of the visible spectrum (generally including radiation wavelengths from approximately 400 nanometers to approximately 700 nanometers). Some examples of LEDs include, but are not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs, green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed further below). It also should be appreciated that LEDs may be configured and/or controlled to generate radiation having various bandwidths (e.g., full widths at half maximum, or FWHM) for a given spectrum (e.g., narrow bandwidth, broad bandwidth), and a variety of dominant wavelengths within a given general color categorization.

[0025] For example, one implementation of an LED configured to generate essentially white light (e.g., a white LED) may include a number of dies which respectively produce different spectra of electroluminescence that, in combination, mix to form essentially white light. In another implementation, a white light LED may be associated with a phosphor material that converts electroluminescence having a first spectrum to a different second spectrum. In one example of this implementation, electroluminescence having a relatively short wavelength and narrow bandwidth spectrum "pumps" the phosphor material, which in turn radiates longer wavelength radiation having a somewhat broader spectrum.

[0026] It should also be understood that the term LED does not limit the physical and/or electrical package type of an LED. For example, as discussed above, an LED may refer to a single light emitting device having multiple dies that are configured to respectively produce different spectra of radiation (e.g., that may or may not be individually controllable). Also, an LED may be associated with a phosphor that is considered as an integral part of the LED (e.g., some types of white LEDs). In general, the term LED may refer to packaged LEDs, non-packaged LEDs, surface mount LEDs, chip-on-board LEDs, T-package mount LEDs, radial package LEDs, power package LEDs, LEDs including some type of encasement and/or optical element (e.g., a diffusing lens), etc.

[0027] The term "light source" should be understood to refer to any one or more of a variety of radiation sources, including, but not limited to, LED light sources (including one or more LEDs as defined above), incandescent sources (e.g., filament lamps, halogen lamps), fluorescent sources, phosphorescent sources, high-intensity discharge sources (e.g., sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of electroluminescent sources, pyro-luminescent sources (e.g., flames), candle-luminescent sources (e.g., gas mantles, carbon arc radiation sources), photo-luminescent sources (e.g., gaseous discharge sources), cathode luminescent sources using electronic satiation, galvano-luminescent sources, crystallo- luminescent sources, kine-luminescent sources, thermo-luminescent sources, triboluminescent sources, sonoluminescent sources, radioluminescent sources, and luminescent polymers.

[0028] A given light source may be configured to generate electromagnetic radiation within the visible spectrum, outside the visible spectrum, or a combination of both. Hence, the terms "light" and "radiation" are used interchangeably herein. Additionally, a light source may include as an integral component one or more filters (e.g., color filters), lenses, or other optical components. Also, it should be understood that light sources may be configured for a variety of applications, including, but not limited to, indication, display, and/or illumination. An

"illumination source" is a light source that is particularly configured to generate radiation having a sufficient intensity to effectively illuminate an interior or exterior space. In this context, "sufficient intensity" refers to sufficient radiant power in the visible spectrum generated in the space or environment (the unit "lumens" often is employed to represent the total light output from a light source in all directions, in terms of radiant power or "luminous flux") to provide ambient illumination (i.e., light that may be perceived indirectly and that may be, for example, reflected off of one or more of a variety of intervening surfaces before being perceived in whole or in part).

[0029] The term "spectrum" should be understood to refer to any one or more frequencies (or wavelengths) of radiation produced by one or more light sources. Accordingly, the term "spectrum" refers to frequencies (or wavelengths) not only in the visible range, but also frequencies (or wavelengths) in the infrared, ultraviolet, and other areas of the overall electromagnetic spectrum. Also, a given spectrum may have a relatively narrow bandwidth (e.g., a FWHM having essentially few frequency or wavelength components) or a relatively wide bandwidth (several frequency or wavelength components having various relative strengths). It should also be appreciated that a given spectrum may be the result of a mixing of two or more other spectra (e.g., mixing radiation respectively emitted from multiple light sources).

[0030] For purposes of this disclosure, the term "color" is used interchangeably with the term "spectrum." However, the term "color" generally is used to refer primarily to a property of radiation that is perceivable by an observer (although this usage is not intended to limit the scope of this term). Accordingly, the terms "different colors" implicitly refer to multiple spectra having different wavelength components and/or bandwidths. It also should be appreciated that the term "color" may be used in connection with both white and non-white light.

[0031] The term "lighting unit" is used herein to refer to an apparatus including one or more light sources of same or different types. A given lighting unit may have any one of a variety of mounting arrangements for the light source(s), enclosure/housing arrangements and shapes, and/or electrical and mechanical connection configurations. Additionally, a given lighting unit optionally may be associated with (e.g., include, be coupled to and/or packaged together with) various other components (e.g., control circuitry, which may include one or more drivers) relating to the operation of the light source(s). An "LED-based lighting unit" refers to a lighting unit that includes one or more LED light sources as discussed above, alone or in combination with other non LED light sources.

[0032] The term "driver" is used herein generally to refer to an apparatus for receiving input power for supplying that power in a format to one or more light sources to cause the light source(s) to produce light. In particular, an "LED driver" refers to an apparatus for receiving input power and supplying that power to a load of one or more LED light sources including one or more LEDs as discussed above to cause the one or more LED light sources to produce light.

[0033] The term "controller" is used herein generally to describe various apparatus relating to the operation of one or more light sources. A controller can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein. A "processor" is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein. A controller may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0034] In various implementations, a processor or controller may be associated with one or more storage media (generically referred to herein as "memory," e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM, floppy disks, compact disks, optical disks, magnetic tape, etc.). In some implementations, the storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at least some of the functions discussed herein. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement various aspects of the present invention discussed herein. The terms "program" or "computer program" are used herein in a generic sense to refer to any type of computer code (e.g., software or microcode) that can be employed to program one or more processors or controllers.

[0035] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

Brief Description of the Drawings

[0036] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. [0037] FIG. 1 shows a functional block diagram of a traffic light system.

[0038] FIG. 2 shows one example of an LED-based lighting unit that may be employed, for example, in the traffic light system of FIG. 1.

[0039] FIG. 3 shows a functional block diagram of one embodiment of an LED-based lighting unit that may be employed, for example, in the traffic light system of FIG. 1, while overcoming one or more of the shortcomings of the LED-based lighting unit of FIG. 2.

[0040] FIG. 4 shows a detailed schematic diagram of one embodiment of an LED-based lighting unit that may be employed, for example, in the traffic light system of FIG. 1, with an LED driver whose fault detection may be tested non-destructively.

Detailed Description

[0041] More generally, Applicants have recognized and appreciated that it would be beneficial provide an LED-based lighting unit that can mimic the input impedance and voltage behavior of an incandescent lamp in an OFF state when the LED load is working normally, and when there is an open or short fault in the LED load. More specifically, there is a need for such an LED driver whose fault detection may be tested non-destructively during manufacturing and while installed, and which is relatively small, inexpensive, and efficient.

[0042] In view of the foregoing, various embodiments and implementations of the present invention are directed to an LED-based lighting unit, and an LED driver for an LED-based lighting unit that provides a relatively low input impedance in an OFF state when the LED load is working normally, and provides a relatively high input impedance in an OFF state when there is an open or short fault in the LED load. More specifically, there is a need for such an LED driver whose fault detection may be tested non-destructively during manufacturing and while installed, and which is relatively small, inexpensive, and efficient.

[0043] FIG. 2 shows one example of an LED-based lighting unit 200 that may be employed, for example, in the traffic light system of FIG. 1.

[0044] LED-based lighting unit 200 includes, in pertinent part, a rectifier 210, a DC/DC converter 220, an LED load 230, a controller 240, an outage monitor 250, a switch 260, and a fusistor 270. DC/DC converter 220 includes a flyback transformer 222 and a switching device 224. In the embodiment of FIG. 2, switching device 224 is a first high power Metal Oxide Semiconductor Field Effect Transistor (MOSFET), and switch 260 is a second high power MOSFET. LED load 230 may comprise one or more LED light sources, including one or more LEDs. The portion of LED-based lighting unit 200 excluding LED load 230 is referred to as an LED driver.

[0045] In an example illustrated in FIG. 2, LED-based lighting unit 200 may be installed in a traffic light system, such as the traffic light system 100 of FIG. 1. In particular, LED-based lighting unit 200 may be retrofit in traffic light system 100 as a replacement for a lighting unit that employs incandescent lamps. For example, LED-based lighting unit 200 may be configured to produce light having one of the three traditional traffic light colors: red, amber or green. In some installations a traffic light system may include three LED-based lighting units, one for each of the three traditional traffic light colors all under control of a single traffic light controller. Alternatively, each LED-based lighting unit may be associated with and controlled by its own traffic light controller.

[0046] An operation of LED-based lighting unit 200 will now be explained with respect to an installation in traffic light system 100.

[0047] In operation, traffic light controller 110 controls LED-based lighting unit 200 to be ON or OFF in accordance with a desired traffic light pattern.

[0048] Traffic light controller 110 turns ON LED-based lighting unit 200 by switching relay 140 to be connected across the 20 kO load resistor 130. In that case, all or virtually all of AC output voltage 115 appears as AC input voltage 125 across the input terminals of LED-based lighting unit 200. Rectifier 210 rectifies AC input voltage 125, and DC/DC converter 220 converts the rectified AC input voltage into a desired current and voltage for driving LED load 230. Controller 240 receives a DC supply voltage Vcc from the rectified AC input voltage and in response to a current through switching device 224 sensed at input pin Isen, controls the switching operation of switching device 224 to cause DC/DC converter 220 to provide the desired current and voltage to LED load 230 according to well-known algorithms. The DC current from DC/DC converter 220 causes the LED(s) in LED load 230 to be lit and produce light of a desired color.

[0049] Traffic light controller 110 turns OFF LED-based lighting unit 200 by switching relay 140 to be open across the 20 kQ load resistor 130. In that case, AC output voltage 115 is supplied across the input terminals of LED-based lighting unit 200 as AC input voltage 125 according to a voltage divider:

(1) VAC-IN = VAC-OUT (Z,N /( Z,N + 20 ΚΩ)),

where VA<MN is the voltage of AC input voltage 125, VAC-OUT is the voltage of AC output voltage 115, and Z!N is the input impedance of LED-based lighting unit 200 in the OFF mode.

[0050] Accordingly, the AC input voltage 125, and input current, supplied to LED-based lighting unit 200 is reduced in the OFF mode so as to cause outage monitor 250 to turn on switch 260 and thereby provide a low impedance current path to ground through fusistor 270. Accordingly, the input impedance ZM of LED-based lighting unit 200 in the OFF mode is essentially the impedance of fusistor 270, which for example, may have a nominal impedance of 300 Ω. In that case, from equation (1): VAC-IN ~ 0.015 * VAC-OUT- SO, for example, if VAC-OUT is 110 VAC, then VAC IN would be about 1.6 VAC which would cause LED-based lighting unit 200 to be OFF, and thus the LED(s) in LED load 130 would not produce light.

[0051] Furthermore, when traffic light controller 110 turns OFF LED-based lighting unit 200 by switching relay 140 to be open across the 20 kQ load resistor 130, and there is no fault or outage in LED load 230, then traffic light controller 110 will detect AC input voltage 125 as being about 1.6 VAC as explained above, and therefore below the predetermined threshold voltage level (for example, a voltage between 10 VAC and 100 VAC) for detecting a fault or outage. Accordingly traffic light controller 110 will not generate an alarm signal.

[0052] Now an operation of LED-based lighting unit 200 in the case of an open or short circuit of LED load 230 will be described. [0053] As described above in the "Back ground" section, if there is an outage or fault in LED load 230, then LED-based lighting unit 200 needs to present a high input impedance Zm to traffic light controller 110 in the OFF mode so as to cause the input voltage VAC-IN detected by to be higher than the predetermined threshold voltage (for example, a voltage between 10 VAC and 100 VAC) so that traffic light controller 110 will detect the outage or fault and may generate an alarm signal or other indication that LED-based lighting unit 200, or at least the LED(s) of LED-based lighting unit 200, needs to be replaced.

[0054] Toward this end, when traffic light controller 110 closes relay 140 to cause LED-based lighting unit 200 to be in an ON mode, and outage monitor 250 detects an outage or fault in LED load 230, then outage monitor 250 will turn on switch 260. Since LED-based lighting unit 200 is in the ON mode, the full AC output voltage 115 will appear across the input terminals of LED-based lighting unit 200 as AC input voltage 125, for example 110 VAC. Thus, when outage monitor 250 turns on switch 260, all or almost all of this voltage will appear across fusistor 270, thereby blowing fusistor 270 and causing it to be an open circuit. This in turn produces an open circuit between the rectified AC input voltage from rectifier 110 and the DC supply voltage terminal Vcc of controller 240.

[0055] In that case, when traffic light controller 110 next (and henceforth) opens relay 140 to cause LED-based lighting unit 200 to be in an OFF mode, switching device 224 is turned off and there is no longer a current path through switch 260 to be turned on, so that the input impedance Z|N of LED-based lighting unit 200 in the OFF mode is very high, for example 20 kO and in particular > 200 kO. Accordingly, traffic light controller 110 will measure all, or almost all, of the full AC output voltage 115 across the input terminals of LED-based lighting unit 200 as AC input voltage 125, for example a voltage > 100 VAC, which is greater than the predetermined threshold voltage for detecting an outage or fault. As a result traffic light controller 110 will determine that there is a fault or outage in LED load 230. In that case, traffic light controller 110 may generate an alarm signal or other indication that LED-based lighting unit 200, or at least the LED(s) of LED-based lighting unit 200, needs to be replaced.

[0056] However, the present inventor has determined that there are a number of shortcomings and deficiencies with LED-based lighting unit 200, and particularly the LED driver of LED-based lighting unit 200 with respect to fault or outage detection.

[0057] A first shortcoming of the LED driver of LED-based lighting unit 200 is that when a fault or outage in LED load 230 is detected, fusistor 270 is blown. That means that it is not possible to test the proper operation of the LED driver, including the proper operation of the outage detection, without blowing fusistor 270 and thereby destroying LED-based lighting unit 200.

[0058] A second shortcoming of the LED driver of LED-based lighting unit 200 is that it requires two high power MOSFETS - switching device 224 for DC/DC converter 220, and also switch 260 for blowing the fusistor 270. This adds significantly to the size and cost of the LED driver.

[0059] A third shortcoming of the LED driver of LED-based lighting unit 200 is that outage monitor 250 is always supplied current from the rectified AC input voltage, which contributes to the power loss in the LED driver and thereby decreases its efficiency.

[0060] A fourth shortcoming of the LED driver of LED-based lighting unit 200 is that outage monitor 250 is required to drive a high power MOSFET (switch 260) which complicates the circuitry.

[0061] A fifth shortcoming of the LED driver of LED-based lighting unit 200 is that the high power MOSFET (switch 260) has a large junction capacitance and therefore turns off and on slowly, which tends to overload fusistor 270.

[0062] A sixth shortcoming of the LED driver of LED-based lighting unit 200 is that the voltage measured at the input of LED load 230 in the OFF mode depends on the resistance of fusistor 270. Therefore one or more circuit components of LED-based lighting unit 200 may need to be changed according to AC input voltage levels, for example in different countries.

[0063] To address one or more of these shortcomings, the inventor has conceived off and implemented a new LED driver and an associated new LED-based lighting unit that may be employed, for example, in a traffic light system such as traffic light system 100 of FIG. 1. [0064] FIG. 3 shows a functional block diagram of one embodiment of an LED-based lighting unit 300 that may be employed, for example, in the traffic light system of FIG. 1, while overcoming one or more of the shortcomings described above.

[0065] LED-based lighting unit 300 includes, in pertinent part, a rectifier 310, a DC/DC converter and high/low impedance network 320, an LED load 330, a controller 340, a fault detector 350, and a controller disabler 360. The portion of LED-based lighting unit 300 excluding LED load 330 may be referred to as an LED driver 305.

[0066] In an example illustrated in FIG. 3, LED-based lighting unit 300 may be installed in a traffic light system, such as the traffic light system 100 of FIG. 1. In particular, LED-based lighting unit 300 may be retrofit in traffic light system 100 as a replacement for a lighting unit that employs incandescent lamps. For example, LED-based lighting unit 300 may be configured to produce light having one of the three traditional traffic light colors: red, amber or green. In some installations a traffic light system may include three LED-based lighting units, one for each of the three traditional traffic light colors all under control of a single traffic light controller. Alternatively, each LED-based lighting unit may be associated with and controlled by its own traffic light controller.

[0067] An operation of LED-based lighting unit 300 will now be explained with respect to an installation in traffic light system 100. It should be understood, however, that LED-based lighting unit 300 may be employed in other settings and applications, for example in an automotive lighting system or an emergency lighting system.

[0068] In operation, traffic light controller 110 (not shown in FIG. 3) controls LED-based lighting unit 300 to be ON or OFF in accordance with a desired traffic light pattern.

[0069] Traffic light controller 110 turns ON LED-based lighting unit 300 by switching relay 140 (not shown in FIG. 3) to be connected across 20 kO load resistor 130 (also not shown in FIG. 3). In that case, all or virtually all of AC output voltage 115 of traffic light controller 110 appears as AC input voltage 125 across the input terminals of LED-based lighting unit 300. Rectifier 310 rectifies AC input voltage 125, and DC/DC converter and high/low impedance network 320 converts the rectified AC input voltage into a desired current and voltage for driving LED load 330. Controller 340 controls DC/DC converter and high/low impedance network 320 to provide the desired output signal to LED load 330 according to well-known algorithms. The output signal of DC/DC converter and high/low impedance network 320 causes the LED(s) in LED load 330 to be lit and produce light of a desired color.

[0070] Traffic light controller 110 turns OFF LED-based lighting unit 300 by switching relay 140 (again, not shown in FIG. 3) to be open across the 20 kQ load resistor 130 (also not shown in FIG. 3). In that case, AC output voltage 115 is supplied across the input terminals of LED- based lighting unit 300 as AC input voltage 125 according to the voltage divider relationship of Equation (1).

[0071] Meanwhile, fault detector 350 supplies a fault detector output signal 355 to controller disabler 360 whose operation will be explained below.

[0072] In normal operation, when fault detector 350 does not detect any fault or outage in LED load 330, then fault detector fault detector 350 causes fault detector output signal 355 to have a first level or voltage (e.g., zero volts) which indicates that there is no fault or outage. In response to fault detector output signal 355 having the first level or voltage (e.g., zero volts), controller disabler 360 does not disable controller 340, and therefore controller 340 may operate normally. In that case, in an OFF mode when traffic light controller 110 turns OFF LED- based lighting unit 300, the connection between controller 340 and DC/DC converter and high/low impedance network 320 is maintained to cause DC/DC converter and high/low impedance network 320 to present a low impedance (e.g., < 1 kQ) across the input terminals of LED-based lighting unit 300. Accordingly, traffic light controller 110 determines that there is no fault or outage in LED-based lighting unit 300, so it does not generate an alarm signal.

[0073] On the other hand, when fault detector 350 does detect a fault or outage in LED load 330, then fault detector 350 causes fault detector output signal 355 to have a second level or voltage (e.g., a few volts) which indicates that there is a fault or outage. In response to fault detector output signal 355 having the second level or voltage (e.g., a few volts), controller disabler 360 disables controller 340, for exampling by disabling a feedback input of controller 340 for controlling a switching operation of a switching device in DC/DC converter and high/low impedance network 320. In that case, in an OFF mode when traffic light controller 110 turns OFF LED-based lighting unit 300, the connection between controller 340 and DC/DC converter and high/low impedance network 320 is disabled to cause DC/DC converter and high/low impedance network 320 to present a high impedance (e.g., > 20 kQ, and beneficially > 200 kQ) at the input terminals of LED-based lighting unit 300. Accordingly, traffic light controller 110 determines that there is a fault or outage in LED-based lighting unit 300, and may generate an alarm signal or other indication that LED-based lighting unit 300, or at least the LED(s) of LED- based lighting unit 300, needs to be replaced.

[0074] A more detailed explanation of an operation of an example of embodiment of LED- based lighting unit 300 will now be provided with respect to the schematic diagram FIG. 4.

[0075] FIG. 4 shows a detailed schematic diagram of one embodiment of an LED-based lighting unit that may be employed, for example, in the traffic light system of FIG. 1, with an LED driver whose fault detection may be tested non-destructively. The circuit shown in FIG. 4 may be one embodiment of the LED-based lighting unit 300 of FIG. 3.

[0076] LED-based lighting unit 400 includes, in pertinent part, a rectifier 410, a DC/DC converter and high/low impedance network 420, an LED load 430, a controller 440, a fault detector 450, and a controller disabler 460. DC/DC converter and high/low impedance network 420 includes a flyback transformer 422 and a switching device 424. In the

embodiment of FIG. 4, switching device 424 is a high power Metal Oxide Semiconductor Field effect Transistor (MOSFET). LED load 430 may comprise one or more LED light sources, including one or more LEDs. The portion of LED-based lighting unit 400 excluding LED load 430 is referred to as the LED driver 405. Controller disabler 460 comprises transistor Q3, which is beneficially a small signal MOSFET. Thus in contrast to LED-based lighting unit 200, LED-based lighting unit 400 beneficially includes only a single power MOSFET, switching device 424.

[0077] In an example illustrated in FIG. 4, LED-based lighting unit 400 may be installed in a traffic light system, such as the traffic light system 100 of FIG. 1. In particular, LED-based lighting unit 400 may be retrofit in traffic light system 100 as a replacement for a lighting unit that employs incandescent lamps. For example, LED-based lighting unit 400 may be configured to produce light having one of the three traditional traffic light colors: red, amber or green. In some installations a traffic light system may include three LED-based lighting units, one for each of the three traditional traffic light colors all under control of a single traffic light controller. Alternatively, each LED-based lighting unit may be associated with and controlled by its own traffic light controller.

[0078] An operation of LED-based lighting unit 400 will now be explained with respect to an installation in traffic light system 100. It should be understood, however, that LED-based lighting unit 400 may be employed in other setting and applications, for example in an automotive lighting system or an emergency lighting system.

[0079] In operation, traffic light controller 110 controls LED-based lighting unit 400 to be ON or OFF in accordance with a desired traffic light pattern.

[0080] First, an explanation of the operation LED-based lighting unit 400 will be described in a normal situation where there LED load 430 does not have any open circuit or short circuit fault.

[0081] Traffic light controller 110 turns OFF LED-based lighting unit 400 by switching relay 140 (not shown in FIG. 4) to be open across the 20 kO load resistor 130 (also not shown in FIG. 4). In that case, AC output voltage 115 is supplied across the input terminals of LED-based lighting unit 400 as AC input voltage 125 according to the voltage divider relationship of Equation (1). Resistor R3 of LED-based lighting unit 400 activates switching device 424 to turn on, and the voltage across the input terminals of LED-based lighting unit 400 equals the gate threshold voltage of switching device 424, which is relatively low (e.g., 2-4 volts). With switching device 424 turned on, LED-based lighting unit 400 thereby has an apparent low input impedance (e.g., < 1 kO). The current in switching device 424 is limited by the external 20 ΚΩ load resistor (see FIG. 1). As a result, LED-based lighting unit 400 is OFF, and thus the LED(s) in LED load 430 do not produce light. That is, the low voltage of 2-4 volts across the input terminals of LED-based lighting unit 400 does not trigger any circuitry on LED-based lighting unit 400 other than switching device 424.

[0082] Furthermore, when traffic light controller 110 turns OFF LED-based lighting unit 400 by switching relay 140 to be open across the 20 kQ load resistor 130 and there is no fault or outage in LED load 430, then traffic light controller 110 will detect AC input voltage 125 as being about 2-4 volts as explained above, and therefore less than the predetermined threshold voltage level (for example, a voltage of about 10 VAC or less) for detecting a fault or outage in LED load 430. Accordingly traffic light controller 110 will not generate an alarm signal.

[0083] Traffic light controller 110 turns ON LED-based lighting unit 400 by switching relay 140 (not shown in FIG. 4) to be connected across 20 kQ load resistor 130 (also not shown in FIG. 4). In that case, all or virtually all of AC output voltage 115 of traffic light controller appears as AC input voltage 125 across the input terminals of LED-based lighting unit 400. Rectifier 410 rectifies AC input voltage 125, and DC/DC converter and high/low impedance network 420 converts the rectified AC input voltage into a desired current and voltage for driving LED load 430. Controller 440 receives a DC supply voltage Vcc derived from the rectified AC in put voltage and in response to a zero crossing detection (ZCD) voltage on its ZCD pin, supplies a switching control signal via its CNTL pin to control the switching operation of switching device 424 such that DC/DC converter and high/low impedance network 420 provides the desired DC current to drive LED load 430 according to well-known algorithms. In other words, the ZCD input may be a triggering input for receiving a feedback signal for controlling the switching operation of switching device 424. For example, in some embodiments of controller 440, a ZCD input helps to improve the power factor correction and the total harmonic distortion of the input current waveform. The DC current from DC/DC converter and high/low impedance network 420 causes the LED(s) in LED load 430 to be lit and produce light of a desired color.

[0084] When LED-based lighting unit 400 is turned ON from an OFF state, once AC input voltage 125 goes above 10V, the zener Zl in LED-based lighting unit 400 is activated and the transistor Q7 turns on and discharges the gate voltage of switching device 424. Switching device 424 will remain off until the voltage builds up and controller 440 starts working to control a switching operation of switching device 424. To assure that switching device 424 correctly responds to the switching control signal of controller 440 supplied by the CNTL pin via R7 and Dl, transistor Q6 - which is beneficially a small signal device - also works directly with the gate drive signal. Q6 will always guarantee that the Q7 turns off once the switching control signal from controller 440 becomes high.

[0085] Meanwhile, fault detector 450 supplies a fault detector output signal 455 to controller disabler 460 whose operation will be explained below.

[0086] In normal operation, when fault detector 450 does not detect any fault or outage in LED load 430, then fault detector fault detector 450 causes fault detector output signal 455 to have a first level or voltage (e.g., zero volts) which indicates that there is no fault or outage. In response to fault detector output signal 455 having the first level or voltage (e.g., zero volts), controller disabler 460 does not disable controller 440, and therefore controller 340 may operate normally.

[0087] More specifically, controller disabler 460 comprises a small signal MOSFET Q3 having a first terminal connected to a fixed voltage (in particular, control ground), a second terminal connected to the ZCD input of controller 440, and a gate connected to receive fault detector output signal 455 from fault detector 450. When fault detector 450 does not detect any open circuit or short circuit fault in LED load 430, then fault detector output signal 455 has the first level or voltage (e.g., zero volts) which it supplies to the gate of the MOSFET Q3.. As a result, the MOSFET Q3 is turned off. In that case, with the MOSFET Q3 turned off, controller disabler 460 does not disable or affect the voltage that appears on the ZCD pin of controller 440, and controller 440 operates normally to provide a switching control signal to switching device 424 to control the operation of DC/DC converter and high/low impedance network 420 to supply the desired current and voltage to LED load 430.

[0088] Now an operation of LED-based lighting unit 400 in the case of an open or short circuit of LED load 430 will be described.

[0089] If LED load 430 is open circuited, the output voltage of the LED driver supplied to LED load 430 increases until the zener diode Z4 conducts, causing the fault detector output signal 455 to have a level or voltage of a few volts, which is supplied to the gate of the MOSFET Q3 of controller disabler 460, thereby turning on the MOSFET Q3. Also, if the LED load is shorted, then the output voltage of the LED driver is zero and the drive to transistor Q4 is removed and therefore Q4 is turned off. As a result the fault detector output signal 455 goes to the voltage Vcc (e.g., a few volts), which is supplied to the gate of the MOSFET Q3 of controller disabler 460, again thereby turning on the MOSFET Q3. So it is seen that fault detector 450 is configured to detect when LED load 430 has a fault, including detecting when LED load 430 has an open circuit condition and detecting when LED load 430 has a short circuit condition, and in response thereto causes the fault detector output signal 455 supplied to the gate of the MOSFET Q3 of controller disabler 460 to have a voltage or level of a few volts, which indicates that LED load 430 has a fault. That is, when there is a fault detected (either an open circuit or a short circuit), then fault detector output signal 455 supplies a second level or voltage, particularly a high voltage of a few volts, to the gate of the MOSFET Q3 of controller disabler 460 so that the MOSFET Q3 is turned ON.

[0090] When the MOSFET Q3 of controller disabler 460 is turned ON, it shorts the ZCD pin of controller 440 to the fixed voltage (e.g., control ground) and hence disables the ZCD input to controller 440. This in turn prevents controller 440 from supplying the switching control signal to turn on switching device 424, thereby shutting down the LED driver. As a result, LED-based lighting unit 400 provides a high input impedance (e.g., 20 kO and beneficially > 200 kO) across its input terminals.

[0091] In that case, in an OFF mode when traffic light controller 110 turns OFF LED-based lighting unit 400, traffic light controller 110 measures a larger voltage across the input terminals of LED-based lighting unit 400 greater than the predetermined threshold voltage (for example, a voltage > 10 VAC and beneficially > 70 VAC) for detecting a fault or outage in LED load 430. Accordingly traffic light controller 110 determines that there is a fault or outage in LED-based lighting unit 400, and may generate an alarm signal or other indication that LED-based lighting unit 400, or at least the LED(s) of LED-based lighting unit 400, needs to be replaced.

[0092] Beneficially, LED-based lighting unit 400, and in particular the LED driver of LED- based lighting unit 400, may address one or more of the shortcomings of the LED driver of LED- based lighting unit 200 as described above.

[0093] First the LED driver of LED-based lighting unit 400 does not include a fusistor or other destructive device. So when a fault or outage in LED load 430 is detected, the input impedance of LED-based lighting unit 400 is driven high so as to signal the fault or outage condition, for example to traffic light controller 110, but once the fault or outage is repaired, then the LED driver is able to return to normal operation. That means that it may be possible to test the proper operation of the LED driver, including the proper operation of the outage detection in a factory during manufacturing, and in the filed when it is installed in a traffic light system.

[0094] Also, the LED driver of LED-based lighting unit 400 requires only one high power MOSFET - switching device 424 for DC/DC converter and high/low impedance network 420. This may significantly reduce the size and cost of the LED driver compared to the LED driver for LED-based lighting unit 200.

[0095] Additionally, fault detector 450 is supplied current from the output side of DC/DC converter and high/low impedance network 420, which may reduce the power loss of the LED driver of LED-based lighting unit 400 compared to the LED driver of LED-based lighting unit 200.

[0096] Furthermore, fault detector 450 is only required to drive a small signal MOSFET in controller disabler 460 which may simply the circuitry compared to the outage monitor 250 in LED-based lighting unit 200.

[0097] Moreover, the voltage measured at the input of LED load 230 in the OFF mode depends on the gate junction threshold voltage of switching device 424 which is independent of the AC input voltage level. Therefore the same circuit components for LED-based lighting unit 400 may be employed in applications having different AC input voltage levels, for example in different countries.

[0098] While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0099] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

[00100] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[00101] The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[00102] As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[00103] As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified.

[00104] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts are recited.

[00105] Reference numerals, appearing in parentheses in the claims, if any, are provided merely for convenience and should not be construed as limiting the claims in any way.

[00106] In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

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Classifications
International ClassificationH05B33/08
Cooperative ClassificationH05B33/089, H05B33/0848, H05B33/0893, H05B33/0884, H05B33/0887, H05B33/0824, H05B33/0815
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