WO2012007798A2

WO2012007798A2 - Bleeding circuit and related method for preventing improper dimmer operation

Info

Publication number: WO2012007798A2
Application number: PCT/IB2010/053614
Authority: WO
Inventors: Zhen Yuan Guan; Haibo Qiao; Chao Peng
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-07-13
Filing date: 2010-08-10
Publication date: 2012-01-19
Also published as: JP2013536544A; BR112013000678A2; CN103004290B; CN103004290A; JP5690930B2; WO2012007798A3; EP2594113A2

Abstract

Disclosed are a method and apparatus for controlling bleed current, to provide the bleed current until ringing of input current at a dimmer has ceased in order to prevent misfiring of a dimmer and flicker of the light source. The return path current to the dimmer is boosted by the bleed current to be at a level greater than the holding current of the dimmer. As a result, the load current of the dimmer is increased to a sufficient minimum so that the dimmer can operate properly.

Description

BLEEDING CIRCUIT AND RELATED METHOD FOR PREVENTING IMPROPER DIMMER

OPERATION

Technical Field

[0001] The present invention is directed generally to control of light sources. More particularly, various inventive methods and apparatus disclosed herein relate to preventing flicker in a light source due to misfiring of a 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.

[0003] Many lighting applications make use of dimmers. Conventional dimmers work well with incandescent (bulb and halogen) lamps. However, problems occur with other types of electronic light sources such as compact fluorescent lamps (CFL), low voltage halogen lamps using electronic transformers, and solid state lighting (SSL) lamps such as LEDs and OLEDs. Conventional dimmers typically chop a portion of each waveform of the input mains voltage signal and pass the remainder of the waveform to the lighting source. A leading edge or triode alternating current (triac) dimmer is a widely used type of dimmer that is of simple circuit design and low cost.

[0004] Fig. 1 is a schematic diagram of a typical lighting system 100 which includes a leading edge triac dimmer 104 coupled to voltage mains 102. Leading edge triac dimmer 104 provides an adjustable voltage signal to lamp 106, to adjustably control the light output by lamp 106. Fig. 2 shows an output waveform of leading edge triac dimmer 104, wherein the leading edge of each waveform is chopped.

[0005] For such a leading edge triac dimmer 104 as shown in Fig. 1, the following

parameters are necessary to enable proper operation. Latching current is the minimum principal current required to maintain a triac in an on state immediately after the triac is switched from an off state to the on state and the triggering signal has been removed. Holding current is the minimum principal current required to maintain the triac in the on state. Holding current is always less than latching current. However, the more sensitive a device, the closer the holding current value approaches the latching current value. Thus, the principal current of the triac should be higher than its latching current immediately after the gating current is removed and always higher than its holding current to maintain conduction of the triac over the entire range of dimming angles. Also, a return path is necessary to ensure proper dimmer operation. If the input impedance of the light source driver is relatively high, the triac will not ignite properly, and ignition timing of the triac will be affected.

[0006] A typical problem of leading edge triac dimmers such as shown in Fig. 1 is ringing. Resonance between inductors within a leading edge triac dimmer and capacitors within a light source driver may result in ringing of the input current provided from voltage mains 102 to dimmer 104. In Fig. 1, the light source driver may be considered as incorporated into lamp 106. Such ringing may typically occur when leading edge triac dimmers are used to dim LED light sources for example. As the ringing becomes large, the resultant minimum input current provided to dimmer 104 will be lower than the holding current necessary to maintain the triac conductive, causing the triac to turn off or misfire. The misfiring causes the lighting current provided from dimmer 104 to lamp 106 to repeatedly spike (multifire) during waveform half cycles, as shown in Fig. 3 for example which illustrates the lighting current C2 of the light source driver and the corresponding input voltage C4 at the light source driver. As a result, the light source driver turns on and off, and lamp 106 consequently flickers on and off. [0007] A known approach to solve this ringing/flicker problem has been to configure resistors in series with the driver capacitors, in an effort to damp the ringing lighting current. This approach however results in increased power consumption, and thus is not an attractive solution.

[0008] Thus, there is a need in the art to provide a circuit and related method that prevents flicker of a light source and that is of simple, low-cost design without excessive power consumption.

Summary

[0009] The present disclosure is directed to inventive methods and apparatus for controlling bleed current, to provide the bleed current until ringing of input current to a dimmer has ceased. Generally, in one aspect, a bleeding circuit is provided that includes a bus configured to provide a voltage signal from a dimmer to adjustably dim light output by a light source. The bleeding circuit includes a detection circuit configured to detect a voltage level of the bus, and to provide a control signal responsive to the detected voltage level. The bleeding circuit also includes a bleeder component configured to provide a bleed current from the bus to the dimmer via a return current path. A delay circuit is further included and is configured to delay the control signal by a predetermined delay and to provide the delayed control signal to the bleeder component, so that the bleeder component provides the bleed current responsive to the delayed control signal until ringing of input current at the dimmer has ceased.

[0010] In another aspect, a system is provided for controlling power delivered to a light source. The system includes a dimmer connected to voltage mains and configured to provide a voltage signal to adjustably dim light output by the light source. The system further includes a rectifier circuit configured to provide a rectified voltage signal to a bus responsive to the voltage signal. Also, a bleeding circuit is included as configured to provide a bleed current to the dimmer via a return current path. A power converter is also included as configured to drive the light source responsive to the rectified voltage signal. The bleeding circuit is further configured to provide the bleed current responsive to a control signal until ringing of input current at the dimmer has ceased. [0011] In yet another aspect, a method is provided for eliminating flicker from light output by a light emitting diode. The method includes providing a voltage signal from a dimmer to adjustably dim light output by the light emitting diode, providing a control signal responsive to a detected voltage level of the voltage signal, providing a bleed current to the dimmer, and delaying the control signal by a predetermined delay to provide a delayed control signal. The bleed current is provided to the dimmer responsive to the delayed control signal until ringing of input current at the dimmer has ceased.

[0012] 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). 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.

[0013] 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.

[0014] 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.

[0015] 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). [0016] The term "lighting fixture" is used herein to refer to an implementation or arrangement of one or more lighting units in a particular form factor, assembly, or package. 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. A "multi-channel" lighting unit refers to an LED-based or non LED-based lighting unit that includes at least two light sources configured to respectively generate different spectrums of radiation, wherein each different source spectrum may be referred to as a "channel" of the multi-channel lighting unit.

[0017] 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).

[0018] 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.

[0019] The term "addressable" is used herein to refer to a device (e.g., a light source in general, a lighting unit or fixture, a controller or processor associated with one or more light sources or lighting units, other non-lighting related devices, etc.) that is configured to receive information (e.g., data) intended for multiple devices, including itself, and to selectively respond to particular information intended for it. The term "addressable" often is used in connection with a networked environment (or a "network," discussed further below), in which multiple devices are coupled together via some communications medium or media.

[0020] In one network implementation, one or more devices coupled to a network may serve as a controller for one or more other devices coupled to the network (e.g., in a master/slave relationship). In another implementation, a networked environment may include one or more dedicated controllers that are configured to control one or more of the devices coupled to the network. Generally, multiple devices coupled to the network each may have access to data that is present on the communications medium or media; however, a given device may be "addressable" in that it is configured to selectively exchange data with (i.e., receive data from and/or transmit data to) the network, based, for example, on one or more particular identifiers (e.g., "addresses") assigned to it.

[0021] The term "network" as used herein refers to any interconnection of two or more devices (including controllers or processors) that facilitates the transport of information (e.g. for device control, data storage, data exchange, etc.) between any two or more devices and/or among multiple devices coupled to the network. As should be readily appreciated, various implementations of networks suitable for interconnecting multiple devices may include any of a variety of network topologies and employ any of a variety of communication protocols.

Additionally, in various networks according to the present disclosure, any one connection between two devices may represent a dedicated connection between the two systems, or alternatively a non-dedicated connection. In addition to carrying information intended for the two devices, such a non-dedicated connection may carry information not necessarily intended for either of the two devices (e.g., an open network connection). Furthermore, it should be readily appreciated that various networks of devices as discussed herein may employ one or more wireless, wire/cable, and/or fiber optic links to facilitate information transport throughout the network.

[0022] 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

[0023] 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.

[0024] Fig. 1 illustrates a schematic diagram of a typical lighting system which includes a leading edge triac dimmer. [0025] Fig. 2 illustrates an output waveform of the leading edge triac dimmer shown in Fig. 1.

[0026] Fig. 3 illustrates input current and voltage waveforms in the typical lighting system as a result of misfiring.

[0027] Fig. 4 illustrates a block diagram of a lighting system of a representative embodiment.

[0028] Fig. 5 illustrates a schematic diagram of a bleeding circuit that may be representative of the bleeding circuit shown in Fig. 4.

[0029] Fig. 6 illustrates input current, bleeding voltage and voltage waveforms in the lighting system of the representative embodiment.

Detailed Description

[0030] Generally, Applicants have recognized and appreciated that it would be beneficial to ensure that the lowest level of the ringing input current at the dimmer be larger than the holding current of the dimmer. By adding DC bias to the resonance wave at the input of the dimmer when the dimmer ignites, the lowest level of the ringing input current can be boosted to a higher level so that the ringing current is kept above the holding current, thus preventing multifiring of the dimmer and the resultant flicker of the light source. In view of the foregoing, various embodiments and implementations of the present invention are directed to a bleeding circuit and method of eliminating flicker, whereby the bleed current is controlled to be maintained on until ringing of the input current at the dimmer has ceased.

[0031] Fig. 4 is a block diagram of a lighting system of a representative embodiment.

Referring to Fig. 4, lighting system 400 includes dimmer 404 connected to voltage mains 402. Voltage mains 402 may provide different unrectified input mains voltage, such as 100 VAC, 120 VAC, 230 VAC and 277 VAC, according to various implementations. Dimmer 404 may be a leading edge triac dimmer, such as leading edge traic dimmer 104 shown in Fig. 1, but however may also be configured in accordance with other types of leading edge triac dimmers, leading edge dimmers, or other types of phase-cutting dimmers such as trailing edge dimmers, as would be understood by one of ordinary skill in the art. Dimmer 404 provides dimming capability by chopping leading edges of a voltage signal waveform from voltage mains 402 in response to setting by the system user. The (dimmed) voltage signal is provided from dimmer 404 to rectifier 406 which provides a rectified voltage signal along the DC bus to DC/DC power converter 410. Power converter 410 outputs a corresponding DC voltage for powering light source 412, which in this example is shown as including LEDs. Bleeding circuit 408 is further included as disposed in parallel with light source 412, and is switchable to draw extra current along with light source 412, to thus increase the load current of dimmer 404 to a sufficient minimum for operation of dimmer 404.

[0032] Fig. 5 is a schematic diagram of bleeding circuit 500, which may be representative of bleeding circuit 408 shown in Fig. 4. Resistors 502, 504 and 506 and Zener diode 508 in Fig. 5 are interconnected and configured as a detector that detects a voltage level of the rectified voltage signal provided to the DC bus by rectifier 406. Resistor 502 includes a first terminal connected to the DC bus. Resistor 504 includes a first terminal connected to a second terminal of resistor 502. Zener diode 508 includes a first anode terminal connected to a second terminal of resistor 504. Resistor 506 includes a first terminal connected to a second cathode terminal of Zener diode 508, and also includes a second terminal connected to ground. A control signal indicative of the voltage level of the rectified voltage signal on the DC bus may be considered as provided at node Nl between Zener diode 508 and resistor 506.

[0033] Bleeding circuit 500 as shown in Fig. 5 further includes diode 524, resistor 526 and capacitor 528 interconnected together to provide a predetermined delay. The first anode terminal of diode 524 is connected to node Nl to receive the control signal. Capacitor 528 includes a first terminal connected to a second cathode terminal of diode 524, and also includes a second terminal connected to ground. Resistor 526 includes first and second terminals respectively connected to the first anode terminal and the second cathode terminal of diode 524. As will be described in further detail subsequently, the resistance R8 of resistor 526 and the capacitance CI of capacitor 528 may be selected as predetermined values, and diode 524 may be selected to delay the control signal at node Nl by a predetermined delay. [0034] Bleeding circuit 500 as shown in Fig. 5 further includes transistor 510 which may be a bipolar transistor having a base or control terminal connected to the delayed control signal at the first terminal of capacitor 528. Transistor 510 includes an emitter or first terminal coupled to ground, and a collector or second terminal connected to node N2. Node N2 is connected to the DC bus via series connected resistors 512 and 514. Resistor 512 includes a first terminal connected to the DC bus. Resistor 514 includes a first terminal connected to the second terminal of resistor 512, and also includes a second terminal connected to node N2. Node N2 is also connected to ground via Zener diode 516. Zener diode 516 includes a first anode terminal connected to node N2, and also includes a second cathode terminal connected to ground.

[0035] Bleeding circuit 500 in Fig. 5 further includes transistor 518 which may be a field effect transistor (FET) for example. A control or gate terminal of transistor 518 is connected to node N2. Transistor 518 includes a first terminal connected to the DC bus, and also includes a second terminal connected to ground through series connected resistors 520 and 522. Resistor 520 includes a first terminal connected to the second terminal of transistor 518. Resistor 522 includes a first terminal connected to the second terminal of resistor 520, and also includes a second terminal connected to ground. Transistor 518 may be characterized as a bleeder component or transistor that is switchably controlled by the voltage level at node N2 to provide a bleed current from the DC bus through resistors 520 and 522 to dimmer 404 via a ground return path. Resistors 520 and 522 limit the current flowing from the DC bus to ground. It should be understood that although transistor 518 is shown as n-type FET including an intrinsic body diode, transistor 518 may be any type of FET, such as a metal oxide semiconductor field effect transistor (MOSFET) or gallium arsenide field effect transistor (GaAs FET), although other types of FETs and/or other types of transistors within the purview of one of ordinary skill in the art may be incorporated, without departing from the scope of the present teachings. Transistor 510 also should not be limited as a bipolar transistor, but similarly may be another type of transistor such as mentioned above.

[0036] The operation of the bleeding circuit of a representative embodiment will now be described with reference to Figs. 4 and 5. In an initial state before dimmer 404 is conductive, bleeding circuit 408 in Fig. 4 is maintained on to draw current. In bleeding circuit 500 shown in Fig. 5, in the initial state before dimmer 404 is turned on to be conductive, resistors 502, 504 and 506 and Zener diode 508 detect the voltage level of the rectified voltage signal on the DC bus as being relatively low. At this time the detected voltage level at node Nl will thus also be correspondingly low, and the voltage level at the control terminal of transistor 510 will also be low. Transistor 510 will be maintained off responsive to the low voltage. As a result, the voltage level at node N2 as applied to the control terminal of transistor 518 will be relatively high, and transistor 518 will be on. Although dimmer 404 is not conductive at this time, the voltage level on the DC bus will be about 5-10V, which maintains bleeding circuit 500 operable. During this period bleeding current is thus provided from the DC bus through transistor 518 and resistors 520 and 522 to dimmer 404 via the return path. The return current path in Fig. 4 is thus maintained at a sufficient minimum so that dimmer 404 can operate properly.

[0037] As the voltage level of the DC bus continues to increase as dimmer 404 becomes conductive to turn light source 412 on, the detected voltage level at node Nl will

correspondingly also increase. Once the voltage level on the DC bus becomes higher than the breakdown voltage of Zener diode 508, capacitor 528 will begin to charge. After the predetermined delay provided by diode 524, resistor 526 and capacitor 528, at a certain point the voltage level at the control terminal of transistor 510 will be high enough to turn transistor 510 on. The voltage level at node N2 will correspondingly drop close to ground level (about 0.3V), and transistor 518 will turn off, so that the bleeding current from the DC bus to the return path is cut off. The predetermined delay provided by diode 524, resistor 526 and capacitor 528 thus delays the time at which the bleeding current is cut off.

[0038] Conventional bleeding circuits are typically designed to switch the bleeding current off when the dimmer circuit is on. In contrast, bleeding circuit 500 of the representative embodiment in Fig. 5 includes diode 524, resistor 526 and capacitor 528 configured to provide a predetermined delay that delays turning off of transistor 510 responsive to the control signal. The amount of delay or delay time provided by diode 524, resistor 526 and capacitor 528 in Fig. 5 is set according to the expected time period or length of ringing of the input current provided to dimmer 404. The predetermined delay time is selected to be longer than the duration of the ringing. The duration of ringing of the input current is normally about 200 - 500 microseconds.

[0039] Transistor 518 is thus controlled to be on to provide bleed current to dimmer 404 via the return current path for a predetermined time after dimmer 404 is on, to boost the input current at the light source for a period of time longer than the duration of the ringing. A bleed current of about a few hundred milliamperes DC current lifts the input current at dimmer 404 to be higher than the holding current of dimmer 404. Dimmer 404 is thus maintained on until after ringing of the input current at dimmer 404 ends. Thus, misfiring of leading edge triac dimmer 404 during half waveform cycles and the resultant flicker of the light source are prevented. This can be understood in view of Fig. 6, which shows lighting current C2 at the light source, bleeding voltage C3 and the input voltage C4 at the DC bus. Lighting current C2 as shown in Fig. 6 is switched on one single time during each respective half waveform cycle, and is not repeatedly switched on and off during half waveform cycles.

[0040] In an example embodiment, if the input voltage at the lighting system described above with respect to Figs. 4 and 5 is 120V/60Hz, resistances Rl and R2 of respective resistors 502 and 504 may both be selected to be about 250kQ, resistance R3 of resistor 506 may be selected to be about lOOkQ, resistance R8 of resistor 526 may be selected to be about 2.2ΜΩ, resistances R4 and R5 of respective resistors 512 and 514 may both be selected to be about 150kQ, and resistances R6 and R7 of respective resistors 520 and 522 may both be selected to be about 680Ω. The capacitance CI of capacitor 528 may be selected to be about lOnF. Diode 524 may be selected to be a 1N4148 diode. The Zener breakdown voltage Zl of Zener diode 508 may be selected to be about 6.8V. The Zener breakdown voltage Z2 of Zener diode 516 may be selected to be about 10V. In accordance with this example, the charging time of capacitor 528 would thus be about 200-500 microseconds so as to maintain bleeding circuit 500 on during an expected time period or length of ringing of the input current at the light source. It should however be understood that the above noted values are given by way of example only, and that various other resistances, capacitances, Zener breakdown voltages and diodes may be selected to meet application specific design requirements of various implementations, as would be apparent to one of ordinary skill in the art.

[0041] 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.

[0042] 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.

[0043] 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."

[0044] It should 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.

[0045] Any reference numerals or other characters, appearing between parentheses in the claims, are provided merely for convenience and are not intended to limit the claims in any way.

[0046] 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.

Claims

What is claimed is:

1. A bleeding circuit comprising:

a bus configured to provide a voltage signal from a dimmer to adjustably dim light output by a light source;

a detection circuit configured to detect a voltage level of the bus, and to provide a control signal responsive to the detected voltage level;

a bleeder component configured to provide a bleed current from the bus to the dimmer via a return current path; and

a delay circuit configured to delay the control signal by a predetermined delay and to provide the delayed control signal to the bleeder component, so that the bleeder component provides the bleed current responsive to the delayed control signal until ringing of input current at the dimmer has ceased.

2. The bleeding circuit of claim 1, wherein the light source comprises at least one light emitting diode.

3. The bleeding circuit of claim 2, wherein the dimmer is a leading edge dimmer.

4. The bleeding circuit of claim 3, wherein the leading edge dimmer comprises a triac.

5. The bleeding circuit of claim 1, wherein the delay circuit comprises a diode and an RC circuit, and the predetermined delay is set in accordance with a time constant of the RC circuit.

6. The bleeding circuit of claim 5, wherein the predetermined delay is within a range of about 20C^sec to 50C^sec.

7. The bleeding circuit of claim 1, wherein the delay circuit comprises:

a diode having a first terminal connected to the detection circuit to receive the control signal, and a second terminal; a resistor having first and second terminals respectively connected to the first and second terminals of the diode; and

a capacitor having a first terminal connected to the second terminal of the diode, and a second terminal connected to the return path,

the delayed control signal is provided from the first terminal of the capacitor to the bleeder component.

8. The bleeding circuit of claim 1, wherein the bleeder component comprises:

a control transistor having a control terminal connected to the delayed control signal, a first terminal connected to a first node, and a second terminal connected to the return path;

a first resistor network having a first terminal connected to the bus, and a second terminal connected to the first node;

a Zener diode having a first terminal connected to the first node, and a second node connected to the return path;

a first transistor having a control terminal connected to the first node, a first terminal connected to the bus, and a second terminal; and

a second resistor network having a first terminal connected to the second terminal of the first transistor, and a second terminal connected to the return path.

9. A system for controlling power delivered to a light source, the system comprising:

a dimmer connected to voltage mains and configured to provide a voltage signal to adjustably dim light output by the light source;

a rectifier circuit configured to provide a rectified voltage signal to a bus responsive to the voltage signal;

a bleeding circuit configured to provide a bleed current to the dimmer via a return current path; and

a power converter configured to drive the light source responsive to the rectified voltage signal, the bleeding circuit further configured to provide the bleed current responsive to a control signal until ringing of input current at the dimmer has ceased.

10. The system of claim 9, wherein the bleeding circuit comprises:

a detection circuit configured to detect a voltage level of the bus, and to provide a first control signal responsive to the detected voltage level;

a bleeder component configured to provide the bleed current from the bus to the dimmer via the return current path; and

a delay circuit configured to delay the first control signal by a predetermined delay and to provide the control signal to the bleeder component, so that the bleeder component provides the bleed current responsive to the control signal until ringing of the input current at the dimmer has ceased.

11. The system of claim 9, wherein the light source comprises at least one light emitting diode.

12. The system of claim 11, wherein the dimmer is a leading edge dimmer.

13. The system of claim 12, wherein the leading edge dimmer comprises a triac.

14. The system of claim 10, wherein the delay circuit comprises a diode and an RC circuit, and the predetermined delay is set in accordance with a time constant of the RC circuit.

15. The system of claim 14, wherein the predetermined delay is within a range of about 200 μsec to 500 μsec.

16. The system of claim 10, wherein the delay circuit comprises:

a diode having a first terminal connected to the detection circuit to receive the first control signal, and a second terminal; a resistor having first and second terminals respectively connected to the first and second terminals of the diode; and

the control signal is provided from the first terminal of the capacitor to the bleeder component.

17. The bleeding circuit of claim 10, wherein the bleeder component comprises:

a control transistor having a control terminal connected to the control signal, a first terminal connected to a first node, and a second terminal connected to the return path;

18. A method for eliminating flicker from light output by a light emitting diode, the method comprising:

providing a voltage signal from a dimmer to adjustably dim light output by the light emitting diode;

providing a control signal responsive to a detected voltage level of the voltage signal;

providing a bleed current to the dimmer; and

delaying the control signal by a predetermined delay to provide a delayed

control signal,

wherein the bleed current is provided to the dimmer responsive to the delayed control signal until ringing of input current at the dimmer has ceased.

19. The method of claim 18, wherein the dimmer is a leading edge dimmer comprising a triac.

20. The method of claim 18, wherein said delaying is provided by a diode and an RC circuit, and the predetermined delay is set in accordance with a time constant of the RC circuit.