WO2016184729A1

WO2016184729A1 - Deep dimming of lighting device with trailing edge phase-cut dimmer

Info

Publication number: WO2016184729A1
Application number: PCT/EP2016/060454
Authority: WO
Inventors: Liang Jia
Original assignee: Philips Lighting Holding B.V.
Priority date: 2015-05-18
Filing date: 2016-05-10
Publication date: 2016-11-24

Abstract

A lighting driver (700, 800) drives an LED-based lighting unit (20, 25). The lighting driver includes: an input (705, 805) configured to receive a trailing edge phase-cut dimming signal produced from an AC line voltage; a rectifier (720, 820) configured to rectify the trailing edge phase-cut dimming signal to produce a rectified trailing edge phase-cut dimming signal; a power stage (730, 830) configured to receive the rectified trailing edge phase-cut dimming signal and in response thereto to drive an LED-based lighting unit: a current sensing trailing edge detector (750, 850) configured to sense an input current supplied to the apparatus via the trailing edge phase-cut dimming signal and in response to the sensed input current to produce a dimming control signal; and a controller (760, 835) configured to control the power stage to adjust a dimming of the LED-based lighting unit in response to the dimming control signal.

Description

DEEP DIMMING OF LIGHTING DEVICE WITH TRAILING EDGE PHASE-CUT DIMMER

Technical Field

[0001] The present invention is directed generally to dimming drivers for LED-based lighting units. More particularly, various inventive methods and apparatus disclosed herein relate to a method for an LED lighting driver to detect the phase-cut angle of a trailing edge phase-cut dimming signal output from an analog phase-cut dimmer at deep dimming levels, and an LED lighting driver which can provide deep dimming with a trailing edge phase-cut dimmer.

Background

[0002] Digital 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 lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these 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, incorporated herein by reference.

[0003] The high cost of energy drives consumers, retailers, and commercial property owners alike to seek out energy-efficient lighting technology, and LEDs have accordingly become increasingly popular. There is little tolerance, however, for energy-efficient products that detract from the look and feel of a lighted space. Dimming is one such lighting feature that can deliver that desired ambiance, as well as delivering even increased energy efficiencies beyond those already attained by the use of more energy efficient technologies such as LEDs.

[0004] Meanwhile, analog phase-cut dimmers are very popular worldwide for incandescent and compact fluorescent light (CFL) indoor lighting applications, their operation and

characteristics are well-known, they are generally inexpensive, and they are already installed in many facilities where it is desired to deploy LED lighting.

[0005] Thus it is often desirable to provide the capability to controllably dim a lighting unit comprising one of more LED light source by means of a conventional analog phase-cut dimmer which is employed for an incandescent light source. For example, it is often desirable to continue to employ an analog phase-cut dimmer which is already installed in a location for controlling one or more lighting units comprising one or more incandescent light sources, when these lighting units are replaced by lighting units which comprise LED light sources.

[0006] A phase-cut dimmer chops the AC voltage at some phase-cut angle (between 0 and 180 degrees), which represents the amount that the light output of the lighting unit should be dimmed, and provides the chopped AC voltage to the lighting unit as an analog phase-cut dimming signal. Because different countries use different AC line voltages (typically between 90 VAC and 300 VAC) and frequencies (typically 50Hz or 60Hz), properties of the phase-cut dimming signal will vary dramatically depending on the locale of the lighting system. When a phase-cut dimmer is connected to a lighting unit having one or more incandescent light sources, it delivers power to the lighting unit which is proportional to the area under the phase- cut dimming signal. Less area means less power, and less power means lower illumination.

[0007] In general phase-cut dimmers are classified into two types: leading edge phase-cut dimmers and trailing edge phase-cut dimmers.

[0008] Leading edge phase-cut dimmers typically employ a TRIAC to phase cut the leading edge of the AC Mains waveform. This often makes it difficult for them to be compatible with LED lighting drivers and LED lighting units, due to the TRIAC fire-on current ringing and spikes and turn-off angle shift due to holding current variation. So an LED lighting driver typically requires special circuitry to deal with these issues, for example, damping and bleeding circuits. Also, a leading edge phase-cut dimmer usually generates audible noise during the dimming process, and the power factor (PF) and total harmonic distortion (THD) are worse than TE dimmers. So in European market, the vast majority of dimmers are trailing edge phase-cut dimmers. [0009] FIG. 1 illustrates an example of an analog phase-cut dimming signal, in particular a trailing edge phase-cut dimming signal 105 (also referred to as a reverse phase-cut dimming signal), wherein the rectified AC line voltage (peak value 109 = 120V) has been cut at a phase- cut angle 107 of 130 degrees until the end of each half cycle (i.e. cut on the right side of the waveform). If phase-cut dimming signal 105 were applied to an incandescent light source, the light output would be approximately 72% of its full intensity. The dimming angle 107 of phase- cut dimming signal 105 is related to the pulse width of the phase-cut AC waveform (i.e., for a reverse phase-cut dimming signal the width of the phase-cut dimming signal between the start of each half cycle and the phase-cut edge). Using this information, phase-cut angle 107 can be calculated using the following equation:

(1) phase_cut_angle (degrees) = (dimming_signal_pulse_width/dimming_signal_period)*180

[0010] Although the compatibility issues for an LED lighting driver and LED-based lighting unit with trailing edge phase-cut dimmers are less than with leading edge phase-cut dimmers, one problem that has persisted when adapting trailing edge phase-cut dimmers to use with LED-based lighting units is the difficulty in providing deep dimming levels. In particular, capacitances in the LED lighting driver convert the sharp falling edge 111 of an ideal trailing edge phase-cut dimming signal 105 into a slowly decaying waveform. This makes it difficult for the LED lighting driver to accurately determine the phase-cut angle 107, particularly when the angle is small. As a result, it is difficult for an LED lighting driver to achieve deep dimming levels, for example dimming levels which are much less than 15% of full power or illumination, and even more particularly dimming levels which are less than 5% of full power or illumination, with a trailing edge phase-cut dimming signal.

[0011] Thus, there is a need in the art for a method for an LED lighting driver to detect the phase-cut angle of a trailing edge phase-cut dimming signal output from an analog phase-cut dimmer at deep dimming levels. There is also a need for an LED lighting driver which can provide deep dimming with a trailing edge phase-cut dimmer. Summary

[0012] The present disclosure is directed to inventive methods and apparatus for detecting the phase-cut angle of a phase-cut dimming signal when applied to an LED lighting driver, and applying the appropriate dimming to a lighting unit. For example, the present disclosure teaches a method of detecting the phase-cut angle of a phase-cut dimming signal based on the input current, rather than the input voltage, and for controlling the dimming level of a lighting unit based on the detected phase-cut angle.

[0013] Generally, in one aspect, a method of dimming a light emitting diode (LED)-based lighting unit comprises: receiving, at an LED lighting driver for driving the LED-based lighting unit, a trailing edge phase-cut dimming signal produced from an AC line voltage; sensing an input current of the trailing edge phase-cut dimming signal and in response to the sensed input current outputting a sensing signal whose waveform follows the input current; generating a dimming control signal having a level which corresponds to an average percentage of time that the sensing signal is greater than a threshold value; and controlling a dimming of the LED-based lighting unit in response to the dimming control signal.

[0014] In some embodiments, the method further comprises rectifying the trailing edge phase-cut dimming signal, wherein sensing an input current of the trailing edge phase-cut dimming signal comprises detecting a current of the rectified trailing edge phase-cut dimming signal.

[0015] In some versions of these embodiments, sensing a current of the rectified trailing edge phase-cut dimming signal comprises detecting a current passing through a sense resistor connected between a rectifier and power ground.

[0016] In some embodiments, generating the dimming control signal includes comparing the sensing signal to the threshold value.

[0017] In some embodiments, generating the dimming control signal comprises: amplifying the sensing signal; comparing the amplified sensing signal to a scaled current threshold and in response thereto generating an output signal; and averaging the output signal to generate the dimming control signal. [0018] In some versions of these embodiments, the output signal has a first voltage when the sensing signal is greater than the threshold value, and has a second voltage less than the first voltage when the sensing signal is less than the threshold value.

[0019] In some versions of these embodiments, the second voltage is a ground voltage..

[0020] In another aspect, an apparatus comprises: an input configured to receive a trailing edge phase-cut dimming signal produced from an AC line voltage; a rectifier configured to rectify the trailing edge phase-cut dimming signal to produce a rectified trailing edge phase-cut dimming signal; a power stage configured to receive the rectified trailing edge phase-cut dimming signal and in response thereto to drive an LED-based lighting unit; a current sensing trailing edge detector configured to sense a rectified input current supplied to the apparatus via the trailing edge phase-cut dimming signal and in response to the sensed input current to produce a dimming control signal; and a controller configured to control the power stage to adjust a dimming of the LED-based lighting unit in response to the dimming control signal.

[0021] In some embodiments, the current sensing trailing edge detector configured to generate the dimming control signal having a level which corresponds to an average percentage of time that the sensed input current is greater than a threshold value.

[0022] In some embodiments, the current sensing trailing edge detector comprises: a current sensing element configured to sense the input current supplied to the apparatus via the trailing edge phase-cut dimming signal and in response thereto to output a sensing signal which varies in correspondence to the input current; and a comparison device configured to compare the sensing signal to the threshold value and in response thereto to generate the dimming control signal.

[0023] In some versions of these embodiments, the current sensing element comprises a resistor connected between the rectifier and power ground.

[0024] In some versions of these embodiments, the comparison device includes: an amplifier configured to amplify the sensing signal; a comparator configured to compare the amplified sensing signal to a scaled current threshold and in response thereto to generate an output signal; and a voltage scaler and averaging circuit configured to scale and average the output signal to generate the dimming control signal.

[0025] In some versions of these embodiments, the output signal has a first voltage when the sensing signal is greater than the threshold value, and has a second voltage less than the first voltage when the sensing signal is less than the threshold value.

[0026] In some versions of these embodiments, the second voltage is a ground voltage.

[0027] In some embodiments, the apparatus further comprises a bus capacitor connected to an output of the rectifier and an input of the power stage.

[0028] In some versions of these embodiments, the input comprises a pair of input terminals, the apparatus further comprising an input electromagnetic compatibility filter having a pair of inductors connected in series with the pair of input terminals, and a capacitor connected in parallel across outputs of the pair of inductors and across an input of the rectifier.

[0029] In yet another aspect, an apparatus comprises: a current sensing element configured to sense an input current of a trailing edge phase-cut dimming signal and in response thereto to output a sensing signal whose waveform follows the input current; a comparison device configured to compare the sensing signal to a threshold value and in response thereto to generate a dimming control signal having a level which corresponds to an average percentage of time that the sensing signal is greater than a threshold value; and a controller configured to receive the dimming control signal and to detect a phase-cut angle of the trailing edge phase- cut dimming signal from the dimming control signal.

[0030] In some embodiments, the comparison device comprises: an amplifier configured to amplify the sensing signal; a comparator configured to compare the amplified sensing signal to a scaled current threshold and in response thereto to generate an output signal; and a voltage scaler and averaging circuit configured to scale and average the output signal to generate the dimming control signal.

[0031] In some versions of these embodiments, the output signal has a first voltage when the sensing signal is greater than the threshold value, and has a second voltage less than the first voltage when the sensing signal is less than the threshold value. [0032] In some versions of these embodiments, the second voltage is a ground voltage.

[0033] 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 emit 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.

[0034] 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 emit 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.

[0035] 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 emit 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.

[0036] 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-based 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.

[0037] 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). [0038] 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) 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- based light sources as discussed above, alone or in combination with other non LED-based light sources.

[0039] 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).

[0040] 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, EEPROM and FLASH memory, 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.

[0041] 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

[0042] 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.

[0043] FIG. 1 illustrates an example of an ideal analog trailing edge, or reverse, phase-cut, dimming signal.

[0044] FIG. 2 is a high level functional block diagram of an example embodiment of a lighting system including an LED lighting driver and an LED-based lighting unit.

[0045] FIG. 3 illustrates an example of a trailing edge detector.

[0046] FIGs 4A and 4B illustrate examples of scaled input signals and output signals of the trailing edge detector of FIG. 3.

[0047] FIG. 5 illustrates an example of a dimming response to a duty cycle of the output signal of the trailing edge detector of FIG. 3.

[0048] FIG. 6 illustrates examples of a voltage waveform and an input current waveform of a trailing edge phase-cut dimming signal applied to an LED lighting driver. [0049] FIG. 7 is a higher level diagram illustrating an example embodiment of a lighting system including a lighting unit and a lighting driver which includes a trailing edge detector for detecting the phase-cut angle of a trailing edge phase-cut dimming signal.

[0050] FIG. 8 is a more detailed diagram illustrating an example embodiment of a lighting system including an LED-based lighting unit and an LED lighting driver which includes a trailing edge detector for detecting the phase-cut angle of a trailing edge phase-cut dimming signal.

[0051] FIG. 9 illustrates a first example of an input current sensed by trailing edge detector of FIG. 8, and a resulting dimming control signal produced by the trailing edge detector.

[0052] FIG. 10 illustrates a second example of an input current sensed by trailing edge detector of FIG. 8, and a resulting dimming control signal produced by the trailing edge detector.

[0053] FIG. 11 illustrates a method of dimming a light source in response to a trailing edge phase-cut dimming signal.

Detailed Description

[0054] Capacitances in an LED lighting driver make it difficult for an LED lighting driver to accurately determine the phase-cut angle of a trailing edge phase-cut dimming signal, particularly when the angle is small. As a result, it is difficult for the LED lighting driver to achieve deep dimming levels, for example dimming levels which are much less than 15%, and even more particularly dimming levels which are less than 5%, with a trailing edge phase-cut dimming signal.

[0055] More generally, the inventor has recognized and appreciated that it would be beneficial to provide an LED lighting driver which can achieve an accurate detection of the phase-cut angle of a trailing edge phase-cut dimming signal, even at low phase-cut angles, so as to achieve deep dimming.

[0056] In view of the foregoing, various embodiments and implementations of the present invention are directed to inventive methods and apparatuses for detecting the phase-cut angle of a trailing edge phase-cut dimming signal. For example, methods and apparatuses are provided for detecting the phase-cut angle of a trailing edge phase-cut dimming signal based on the input current associated with the trailing edge phase-cut dimming signal.

[0057] The difficulty in obtaining deep dimming with an LED lighting driver in conjunction with a trailing edge phase-cut dimming signal will first be explained with respect to FIGs. 2, 3, 4A-4B, and 5.

[0058] FIG. 2 is a high level functional block diagram of an example embodiment of a lighting system 200 including an LED lighting driver 10 and an LED-based lighting unit 20.

[0059] LED lighting driver 10 includes: a pair of input terminals 205; an electromagnetic compatibility (EMC) filter 210; a rectifier 220; a bus capacitor Cbus; and an LED power stage 230. LED-based lighting unit 20 includes one or more LEDs, which may be connected in series, parallel, or a combination of series and parallel, between output terminals of LED power stage 230.

[0060] In operation, LED lighting driver 20 receives at input terminals 205 a trailing edge phase-cut dimming signal, for example trailing edge phase-cut dimming signal 105, produced from an AC line voltage. The trailing edge phase-cut dimming signal passes through EMC filter 210 substantially unattenuated, and is then rectified by rectifier 220 to produce a rectified trailing edge phase-cut dimming signal, Vin. Cbus represents a bus capacitance at the output of the rectifier and input to LED power stage 230. LED power stage 230 receives the rectified trailing edge phase-cut dimming signal and in response thereto supplies an output current to drive LED-based lighting unit 20.

[0061] As explained above, dimming information is included in the trailing edge phase-cut dimming signal as a phase-cut angle where the AC line voltage is cut, and trailing edge detector 300 detects the phase-cut angle.

[0062] FIG. 3 illustrates an example of a trailing edge detector 300 which may be employed with LED lighting driver 10 to detect the phase-cut angle of the trailing edge phase-cut dimming signal applied to input terminals 205 of LED lighting driver 10 so that LED lighting driver 10 can dim LED-based lighting unit 20. In particular, trailing edge detector may be connected to an output terminal of rectifier 220 and an input terminal of LED power stage 230 to receive as its input the rectified trailing edge phase-cut dimming signal, Vin. In response to the rectified trailing edge phase-cut dimming signal, Vin, trailing edge detector 300 may output a dimming control signal Vpav.

[0063] Trailing edge detector 300 operates as follows. The trailing edge phase-cut dimming signal, Vin, is scaled by a factor referred to here as k, which is determined by the values of the resistors Rl, R2, R3 and R4. So long as the scaled trailing edge phase-cut dimming signal, kVin, is greater than the threshold voltage Vz of the Zener diode DZ, the output signal VI at the cathode of the Zener diode is clamped at the Zener breakdown voltage ("Zener voltage") Vz. When the scaled trailing edge phase-cut dimming signal kVin is less than the Zener voltage Vz, then the output signal VI follows the scaled trailing edge phase-cut dimming signal. The trailing edge phase-cut dimming signal, Vin, is periodic, and therefore so is the output signal VI. The periodic output signal VI is integrated of averaged by the capacitor C to produce the dimming control signal Vpav. The level of the dimming control signal Vpav is intended to represent the phase-cut angle of the trailing edge phase-cut dimming signal, Vin.

[0064] FIG. 4A illustrates a first example of a scaled input signal 410 (kVin) and output dimming control signal 430 (Vpav) of trailing edge detector 300. As seen in FIG. 4A, scaled input signal 410 is a periodic signal with a period, T, which is one half of the period 2T of the AC Mains line voltage from which the trailing edge phase-cut dimming signal, and the rectified trailing edge phase-cut dimming signal, Vin, were produced. For example, if the frequency of the AC Mains line voltage is 50 Hz, then the period T would be 10 milliseconds. Here, scaled input signal 410 is a scaled rectified trailing edge phase-cut dimming signal, kVin, which has a phase- cut angle Φ1 of about 90 degrees.

[0065] As seen in FIG. 4A, in practice the trailing edge of the scaled rectified trailing edge phase-cut dimming signal, kVin, does not immediately fall to zero at the phase-cut angle Φ1, as in the ideal signal shown in FIG. 1, but instead slowly decays over a period Δ1, due to the effect of the EMC capacitance Cx and the bus capacitance Cbus which are illustrated in FIG. 2. That is because the voltage across a capacitor cannot change in a step manner. [0066] As a result, the output signal VI does not transition from the Zener voltage (Vz) to the ground at the phase-cut angle Φ1, but instead remains at the Zener voltage Vz for the extra time period Δ1 while the scaled rectified trailing edge phase-cut dimming signal kVin continues to decay to the Zener voltage Vz. That is, for a phase-cut angle of Φ1, within each period T the output signal VI remains at the Zener voltage Vz for a time interval of (Φ1 + Δ1). Due to the capacitor C, the dimming control signal Vpav integrates the output signal VI over several periods T, and represents an average percentage of time in each period that the output signal VI is at the high voltage level (Zener voltage Vz). Meanwhile, FIG. 4B illustrates a case where the scaled input signal 410 is a scaled rectified trailing edge phase-cut dimming signal, kVin, which has a phase-cut angle Φ2 of about 80 degrees. In this case, within each period T the output signal VI remains at the Zener voltage Vz for a time interval of (Φ2 + Δ2).

[0067] In comparing FIG. 4A with FIG. 4B, it is seen that as a result of the decay times Δ1 and Δ2, the output signal VI remains "high" (at the Zener voltage Vz) in each time period T for an extended period of time after the phase cut angle. As a result, the output level of the dimming control signal Vpav does not linearly follow the phase-cut angle, and difference in the level of the dimming control signal Vpav between a phase-cut angle Φ1 of about 90 degrees and a phase-cut angle Φ2 of about 80 degrees is relatively minor. This problem becomes exacerbated at smaller phase-cut angles such that it is no longer possible to detect the phase-cut angle when it becomes too small and to provide effective dimming for small phase-cut angles.

[0068] FIG. 5 illustrates an example of a dimming response to a duty cycle of the output signal of the trailing edge detector of FIG. 3.

[0069] As a result of all of this, in practice LED lighting driver 10 with trailing edge detector 300 is unable to provide deep dimming at dimming levels which are much less than 15% of full power or illumination, and even more particularly dimming levels which are less than 5% of full power or illumination, with a trailing edge phase-cut dimming signal.

[0070] To address these shortcomings, the inventor has contemplated a different approach. [0071] In particular, while it was noted above that the voltage across a capacitor such as Cbus and Cx cannot change very quickly in a step manner, the current through a capacitor can and will change quickly in a step manner. FIG. 6 illustrates examples of a voltage waveform 610 and an input current waveform 620 of a trailing edge phase-cut dimming signal applied to an LED lighting driver. Here it is seen that while the trailing edge 612 of voltage waveform 610 has a slow decay beginning at the phase angle ODIM, the trailing edge 622 of input current waveform 620 falls very quickly to zero with a sharp edge at the phase angle ODIM. The present inventor has appreciated that the sharper slope or decline of the trailing edge 622 of current waveform 620 lends itself to being detected with greater precision and accuracy. This, in turn, permits an LED lighting driver which detects the phase-cut angle from the input current to make more accurate detections of small phase-cut angles and thereby provide deeper dimming of an LED- based light source which it drives.

[0072] FIG. 7 is a higher level diagram illustrating an example embodiment of a lighting system 700 including a lighting unit 25 and a lighting driver 70 which includes a trailing edge detector for detecting the phase-cut angle of a trailing edge phase-cut dimming signal. Lighting driver 70 includes: an input 705; an EMC filter 710; a rectifier stage 720; a power stage 730; a current sensing trailing edge detector 750; and a controller 760.

[0073] In operation, lighting driver 70 receives at its input 705 a trailing edge phase-cut dimming signal, for example trailing edge phase-cut dimming signal 105, produced from an AC line voltage. The trailing edge phase-cut dimming signal passes through EMC filter 710 substantially unattenuated, and is then rectified by rectifier stage 720, which may include a capacitor across its output, to produce a rectified trailing edge phase-cut dimming signal. In some embodiments, EMC filter 710 may be omitted. Power stage 730 receives the rectified trailing edge phase-cut dimming signal and in response thereto drives lighting unit 25. In particular, power stage 730 may supply a current to drive lighting unit 25, and the power consumption and illumination level of lighting unit 25 may be varied by varying the level of the current which power stage 730 supplies to lighting unit 25 to thereby dim lighting unit 25 to a desired level. [0074] Meanwhile, current sensing trailing edge detector 750 includes a current sensing element 752 which senses the input current of the trailing edge phase-cut dimming signal, and in response thereto current sensing trailing edge detector 750 produces a dimming control signal 755 which varies in response to the sensed input current. Significantly, rather than detecting an input voltage provided to power stage 730 or an input or output voltage of rectifier stage 720, which as explained above with respect to FIG. 7 may not cut-off rapidly at the phase-cut angle, current sensing trailing edge detector 750 senses the input current of the trailing edge phase-cut dimming signal, which in general will cut-off rapidly with a sharp trailing edge. In various embodiments, current sensing element 752 may sense the input current of the trailing edge phase-cut dimming signal in a variety of ways, including via a small series resistor, a Hall effect current sensor, a Rogowski coil, or other device which is capable of producing an output which indicates the timing of a sharp edge in the current waveform. In various embodiments, current sensing trailing edge detector 750 may sense the input current of the trailing edge phase-cut dimming signal directly, or indirectly - for example by detecting another current produced from the input current of the trailing edge phase-cut dimming signal and which follows the same waveform, and in particular includes the sharp edges in the waveform of the input current at the phase-cut angle. One example of a current which may be detected to sense the input current may be the output current of rectifier stage 720.

[0075] In some embodiments, dimming control signal 755 has a level which corresponds to an average percentage of time that the sensed input current is greater than a threshold value, which in some embodiments may be set to be slightly above zero current.

[0076] Controller 760 receives dimming control signal 755, and in response to dimming control signal 755 controls power stage 730 to adjust a dimming level of lighting unit 25. In some embodiments, controller 760 may adjust the dimming level of lighting unit 25 in response to the dimming control signal 755 so as to increase the current supplied to lighting unit 25 when the level of dimming control signal 755 is increased, and to decrease the current supplied to lighting unit 25 when the level of dimming control signal 755 is decreased. [0077] Thus lighting driver 70 adjusts the power consumption of lighting unit 25 and the light intensity output by lighting unit 25 in response to the phase-cut angle of a trailing edge of a trailing edge phase-cut dimming signal which is supplied thereto. Because lighting driver 70 includes current sensing trailing edge detector 750 which senses the input current of the trailing edge phase-cut dimming signal, which has a sharp trailing edge in its waveform, lighting driver 70 may be able to detect accurately and respond to small phase-cut angles and provide deep dimming.

[0078] A more concrete example embodiment of lighting driver 70 will now be described with respect to FIG. 8.

[0079] FIG. 8 is a more detailed diagram illustrating an example embodiment of a lighting system including an LED-based lighting unit 20 and an LED lighting driver 80 which includes a trailing edge detector for detecting the phase-cut angle of a trailing edge phase-cut dimming signal. Lighting driver 80 includes: a pair of input terminals 805; an electromagnetic compatibility (EMC) filter 810; a rectifier 820; a bus capacitor Cb_US; an LED power stage 830; a controller 835; and a current sensing trailing edge detector 850.

[0080] Current sensing trailing edge detector 850 includes: a current sensing element (resistor) Rsense; an inverting amplifier comprising U2 and a pair of resistors as shown; a comparator U l; and a voltage scaling/averaging circuit comprising Rl, Rl, R3, and capacitor

[0081] I n operation, LED lighting driver 80 receives across its input terminals 805 a trailing edge phase-cut dimming signal, for example trailing edge phase-cut dimming signal 105, produced from an AC line voltage. The trailing edge phase-cut dimming signal passes through EMC filter 810 substantially unattenuated, and is then rectified by rectifier 820 and filtered by bus capacitor Cbus, to produce a rectified trailing edge phase-cut dimming signal. I n some embodiments, EMC filter 810 may be omitted. LED power stage 830 receives the rectified trailing edge phase-cut dimming signal and in response thereto drives LED-based lighting unit 20. I n particular, power stage 830 may supply a current to drive LED-based lighting unit 20, and the power consumption and illumination level of LED-based lighting unit 20 may be varied by varying the level of the current which LED power stage 830 supplies to LED-based lighting unit 20 to thereby dim LED-based lighting unit 20 to a desired level.

[0082] Meanwhile, current sensing trailing edge detector 850 senses the input current of the trailing edge phase-cut dimming signal via current sensing element Rsense to produce a sensing signal 851 (li_n_seni). The waveform of the sensing signal li_n_seni follows the waveform of the input current of the trailing edge phase-cut dimming signal supplied to LED lighting driver 80. The amplifier comprising U2 receives the sensing signal li_n_seni and outputs an amplified sensing signal Ii_n_sen2. Comparator U l compares the amplified sensing signal Ii_n_sen2 to a scaled current threshold L th and in response thereto generates an output signal VI. Here, it is understood that comparing Ii_n_sen2 to a scaled current threshold li_n_th effectively accomplishes comparing the input current of the trailing edge phase-cut dimming signal to a current threshold.

[0083] Beneficially, as shown in FIG. 6, the trailing edge of the trailing edge phase-cut dimming signal is sharp and declines very quickly. Accordingly, the output signal VI of comparator U l is relatively insensitive to the exact value which is employed for the scaled current threshold li_n_th, so long as it is greater than zero and less than the maximum value of the amplified sensing signal Ii_n_sen2 for a desired lowest detectable phase-cut angle of the trailing edge phase-cut dimming signal. That is, beneficially the scaled current threshold li_n_th may be selected to be a voltage which is slightly above the ground voltage, or slightly greater than zero.

[0084] The voltage scaling circuit comprising Rl, Rl, R3 and capacitor CAVG scales and averages the output signal VI of comparator U l to produce dimming control signal 855 (Vpai) which has a level which corresponds to the trailing edge phase-cut angle (e.g., element 107 in FIG. 1) of the trailing edge phase-cut dimming signal. That is, as the trailing edge phase-cut angle is decreased by the dimmer, the level of dimming control signal 855 also decreases.

Conversely, as the trailing edge phase-cut angle is increased by the dimmer, the level of dimming control signal 855 also increases. Inverting amplifier comprising U2 and its associated resistors, comparator U l, and the voltage scaling/averaging circuit (comprising Rl, Rl, R3, and CAVG) together may be considered to be a comparison device 852 configured to compare sensing signal 851 to a threshold value and in response thereto to generate dimming control signal 855. [0085] FIG. 9 illustrates a first example of an input current 920 produced by a trailing edge phase-cut dimming signal 910 sensed by current sensing trailing edge detector 850 of FIG. 8, the output signal VI 930, and the resultant dimming control signal Vpai 940. Here input current 920 may be an example of the input current sensed by sensing element Rsense in FIG. 8, and dimming control signal 940 may be an example of dimming control signal 855 of FIG. 8.

[0086] In FIG. 9 it is seen that output signal 930 is a periodic signal with a period T and includes voltage pulses whose length and/or timing varies in response to timing of the falling edge of input current 920, and therefore also varies in response to the phase-cut angle of the trailing edge phase-cut dimming signal. Output signal 930 has a first voltage greater than zero when input current 920 is greater than a threshold current lm_th, and a second voltage (e.g., ground voltage) less than the first voltage when input current 920 is less than the threshold current li_n_th- Accordingly, output signal 930 has a duty cycle which follows (and therefore accurately represents) the phase-cut angle ODIMI of trailing edge phase-cut dimming signal 910, even for small angles of ODIMI, for example less than 40 degrees, or in some embodiments less than 30 degrees. Finally, dimming control signal 940 is produced by scaling and averaging output signal 930, in particular by the resistors R3 and R4 and the capacitor CAVG in current sensing trailing edge detector 850 shown in FIG. 8.

[0087] FIG. 10 illustrates a second example of an input current 1020 produced by a trailing edge phase-cut dimming signal 1010 sensed by current sensing trailing edge detector 850 of FIG. 8, the output signal VI 1030, and the resultant dimming control signal Vpai 1040 in a case where the phase-cut angle ODIM2 is smaller than ODIMI. Here, again, input current 1020 may be an example of the input current sensed by sensing element Rsense in FIG. 8, and dimming control signal 1040 may be an example of dimming control signal 855 of FIG. 8. FIG. 10 illustrates that the duty cycle of output signal 1030 follows the (and therefore accurately represents) the relatively small phase-cut angle ODIM2 of trailing edge phase-cut dimming signal 1010. Finally, dimming control signal 1040 is produced by scaling and averaging output signal 1030, in particular by the resistors R3 and R4 and the capacitor CAVG in current sensing trailing edge detector 850 shown in FIG. 8. [0088] For comparison purposes, FIG. 10 also shows examples of an output signal Vz 1050 and a dimming control signal Vpav 1060 which would be produced by a trailing edge detector such as trailing edge detector 300 which operates based on detecting the voltage level of the trailing edge phase-cut dimming signal 1010. As can be seen in FIG. 10, output signal 1030 and dimming control signal 1040 which are produced by sensing input current 1020 do a much better job of accurately representing the phase cut angle ODIM2 of trailing edge phase-cut dimming signal 1010 than do output signal Vz 1050 and a dimming control signal Vpav 1060, which are generated based on sensing the voltage.

[0089] Turning back now to FIG. 8, dimming control signal 855 output by current sensing trailing edge detector 850 is supplied as an input to controller 835. Controller 835 detects the level of dimming control signal 855 and in response thereto controls the level of the output current supplied by LED power stage 830 to LED-based lighting unit 20.

[0090] In some embodiments, controller 835 may include a processor and memory which executes an algorithm which maps the level of dimming control signal 855 to a corresponding current level to be supplied to LED-based lighting unit 20 to achieve a desired power consumption and illumination (or dimming) level. In some embodiments, the algorithm may include referring to a look-up table stored in memory. In other embodiments, controller 835 may include a linear or nonlinear analog control circuit which generates a current control signal which is supplied to LED power stage 830 to adjust or control the output current level of LED power stage 830. For example, in some cases the current control signal may switch a transistor which is included in LED power stage 830 on an off at some frequency (which may be much higher than the frequency of the AC Mains signal) with a duty cycle which is varied to adjust or control the average current level supplied by LED power stage 830 to LED-based lighting unit 20. However other current control techniques are contemplated.

[0091] In some embodiments, controller 835 may be included in LED power stage 830, and may perform one or more control operations for LED power stage 830 in addition to controlling the dimming of LED-based lighting unit 20 by LED power stage 830. [0092] FIG. 11 illustrates a method of dimming a light source in response to a trailing edge phase-cut dimming signal which may be performed by a lighting driver, such as lighting driver 70 and LED lighting driver 80.

[0093] In an operation 1110, a lighting driver receives a trailing edge phase-cut dimming signal produced from an AC line voltage.

[0094] In an operation 1120, the lighting driver senses an input current of the trailing edge phase-cut dimming signal and in response thereto outputs a sensing signal which varies in correspondence to the input current.

[0095] In an operation 1130, the lighting driver generates a dimming control signal having a level which corresponds to an average percentage of time that the sensed input current is greater than a threshold value, which in some embodiments may be set to be slightly above zero current.

[0096] In an operation 1140, the lighting driver controls a power stage to adjust a dimming of a lighting unit in response to the dimming control signal.

[0097] 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.

[0098] 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.

[0099] 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."

[00100] 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.

[00101] 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.

[00102] 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. Thus, as a non-limiting example, "at least one of A and B" (or, eq uivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[00103] 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 of the method are recited.

[00104] I n 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.

Claims

CLAIMS:

1. An apparatus (700, 800), comprising:

an input (705, 805) configured to receive a trailing edge phase-cut dimming signal produced from an AC line voltage;

a rectifier (720, 820) configured to rectify the trailing edge phase-cut dimming signal to produce a rectified trailing edge phase-cut dimming signal;

a power stage (730, 830) configured to receive the rectified trailing edge phase-cut dimming signal and in response thereto to drive an LED-based lighting unit (20, 25);

a current sensing trailing edge detector (750, 850) configured to sense an input current supplied to the apparatus via the trailing edge phase-cut dimming signal (410, 610, 910, 1010) and in response to the sensed input current (620, 920, 1020) to produce a dimming control signal (755, 855); and

a controller (760, 835) configured to control the power stage to adjust a dimming of the LED-based lighting unit in response to the dimming control signal.

2. The apparatus (700, 800) of claim 1, wherein the current sensing trailing edge detector is configured to generate the dimming control signal having a level which corresponds to an average percentage of time that the sensed input current is greater than a threshold value.

3. The apparatus (700, 800) of claim 1, wherein the current sensing trailing edge detector comprises:

a current sensing element (752, R_sen) configured to sense the input current supplied to the apparatus via the trailing edge phase-cut dimming signal and in response thereto to output a sensing signal (851) which varies in correspondence to the input current; and

a comparison device (852) configured to compare the sensing signal to the threshold value and in response thereto to generate the dimming control signal.

4. The apparatus (700, 800) of claim 3, wherein the current sensing element comprises a resistor (R_SEN) connected between the rectifier and power ground.

5. The apparatus (700, 800) of claim 3, wherein the comparison device (852) includes: an inverting amplifier (U2) configured to amplify the sensing signal;

a comparator (Ul) configured to compare the amplified sensing signal to a scaled current threshold and in response thereto to generate an output signal; and

a voltage scaler and filter (R1/R2/R3/CAVG) configured to scale and average the output signal to generate the dimming control signal.

6. The apparatus (700, 800) of claim 5, wherein output signal has a first voltage when the sensing signal is greater than the threshold value, and has a second voltage less than the first voltage when the sensing signal is less than the threshold value.

7. The apparatus (700, 800) of claim 5, wherein the second voltage is a ground voltage.

8. The apparatus (700, 800) of claim 1, further comprising a bus capacitor Cbus connected to an output of the rectifier and an input of the power stage.

9. The apparatus (700, 800) of claim 8, wherein the input comprises a pair of input terminals (805), the apparatus further comprising an input electromagnetic compatibility filter (810) having a pair of inductors (Lc) connected in series with the pair of input terminals, and a capacitor (Cx) connected in parallel across outputs of the pair of inductors and across an input of the rectifier.

10. An apparatus (750, 850), comprising:

a current sensing element (752, R_SEN) configured to sense an input current of a trailing edge phase-cut dimming signal (410, 610, 910, 1010) and in response thereto to output a sensing signal (851) whose waveform follows the input current;

a comparison device (852) configured to compare the sensing signal to a threshold value and in response thereto to generate a dimming control signal (755, 855) having a level which corresponds to an average percentage of time that the sensing signal is greater than a threshold value; and

a controller (760, 835) configured to receive the dimming control signal and to detect a phase-cut angle (ODIM ) of the trailing edge phase-cut dimming signal from the dimming control signal.

11. The apparatus (750, 850) of claim 10, wherein the comparison device comprises: an inverting amplifier (U2) configured to amplify the sensing signal;

12. The apparatus (750, 850) of claim 11, wherein the output signal has a first voltage when the sensing signal is greater than the threshold value, and has a second voltage less than the first voltage when the sensing signal is less than the threshold value.

13. The apparatus (750, 850) of claim 12, wherein the second voltage is a ground voltage.

14. A method (1100) of dimming a light emitting diode (LED)-based lighting unit (20, 25) using an apparatus (700, 800,750, 850) as claimed in any of claims 1-13.