Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/10—Controlling the intensity of the light
  • H05B45/18—Controlling the intensity of the light using temperature feedback
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/32—Pulse-control circuits
  • H05B45/325—Pulse-width modulation [PWM]
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/34—Voltage stabilisation; Maintaining constant voltage
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/345—Current stabilisation; Maintaining constant current
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/347—Dynamic headroom control [DHC]
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/37—Converter circuits
  • H05B45/3725—Switched mode power supply [SMPS]
  • H05B45/375—Switched mode power supply [SMPS] using buck topology
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/40—Details of LED load circuits
  • H05B45/44—Details of LED load circuits with an active control inside an LED matrix
  • H05B45/46—Details of LED load circuits with an active control inside an LED matrix having LEDs disposed in parallel lines
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
  • Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Definitions

• This invention relates to the control of lighting systems, for example (but not exclusively) multi-channel lighting systems.
• Multiple channels can for example provide color mixing and color temperature control, although other effects can also be obtained by using multiple light sources.
• LED light sources There are various known multi-channel LED light sources.
• One possible arrangement makes use of different color channels in parallel. Each channel may for example independently provide a different color output.
• different LEDs may be provided in series, and bypass switches can be used to select which LEDs are activated, and thereby control the output color.
• Such a system may generate white light by driving red, green and blue LEDs independently.
• a green LED may make use of a native blue LED and a green phosphor layer.
• White light can be generated with different color temperatures, for example having separate LED strings to generate cold white or warm white from a single luminaire.
• such systems can provide full output color control.
• multi-channel LED drivers are also encountered in LED modules or LED luminaires in which different channels are used to generate separate beams for general lighting and task lighting.
• PWM pulse width modulation
• FIG. 1 shows in schematic form a conventional multi-channel lighting system driver circuit.
• Three LED loads 10,11,12 are shown, which may for example have three different color outputs.
• Each is driven by a respective driver 20,21,22 which essentially comprises a switch mode power supply (SMPS) or linear driver which implements PWM control.
• SMPS switch mode power supply
• the global controller 16 provides commands to the local drivers 20,21,22 to control the operation of the LED loads.
• This approach has a two-stage driver concept.
• One driver stage is to convert the mains voltage to an intermediate DC voltage and the other is to convert the intermediate DC voltage to a LED current.
• the multiple LED channels are then controlled independently from each other.
• FIG 2 shows one example of an implementation of the arrangement shown schematically in Figure 1. It comprises the AC -DC converter 14 which delivers a constant voltage output Vout, and each individual driver is shown as DC current source II to 13, with the channels all in parallel. Each current source has a current sense resistor R1 to R3. The current sources are controlled using pulse width modulation, with control signals PWM1 to PWM3. The current sense resistors are used to set a fixed current level. This is a low cost solution with a linear driver per channel.
• the LED arrangements for example have different color points. They may be different types of white (warm white, cool white, flame white %) or different colors.
• a disadvantage of this arrangement is the efficiency.
• the bus voltage (the output voltage Vout) needs to be higher than the forward voltage of the LED string with the highest forward voltage. This maximum voltage is determined by the voltage bins, the number of LEDs, the drive current and the temperature.
• Losses in each channel are then proportional to the voltage difference between the set bus voltage and the LED (in particular LED string) forward voltage.
• a lighting control circuit for controlling a lighting arrangement, comprising: a power converter for delivering a DC voltage to current driver, wherein the current driver is for connection in series with the lighting arrangement for driving a current through the lighting arrangement, and wherein the power converter has a control loop for controlling the level of the DC voltage;
• a temperature sensing element for sensing a temperature at or near the lighting arrangement
• a feedback circuit for providing a temperature-dependent control input to the control loop of the power converter, such that the DC voltage is adjusted in dependence on a sensed temperature.
• the invention is based on the recognition that the efficiency when using a fixed DC voltage (generally termed the bus voltage) is temperature-dependent.
• the bus voltage should be high enough to guarantee enough voltage headroom for correct operation of the current driver, which may for example comprise a linear current source.
• the headroom will increase the because LED forward voltage decreases and hence the total losses will increase.
• the invention is based on regulating the DC voltage using a feedback circuit in the voltage control loop of the power converter.
• the DC voltage is preferably adjusted inversely with respect to temperature.
• the bus voltage is adjusted to a lower voltage level to increase the efficiency.
• the control loop increases the DC voltage to compensate for the cold LEDs.
• the feedback circuit for example comprises a resistor network, and the temperature sensing element comprises at least one temperature sensitive resistor in the resistor network.
• This provides a simple and low cost way to generate a suitable feedback control signal for controlling the power converter.
• the power converter for delivering a DC voltage for example comprises a switch mode power converter. It may have a voltage regulated output, and may for example have a rectified mains input.
• the power converter for example comprises a buck converter.
• the invention also provides a lighting circuit comprising:
• the current driver and the lighting arrangement, which comprises a light source in series with the current driver, the series combination supplied with the DC voltage, and the light source comprising a LED arrangement through which current is driven by the current driver.
• This provides the combination of the lighting control circuit, and the lighting arrangement (which in this case may be a single LED string light source) and current driver which are driven by the lighting control circuit.
• the invention also provides a lighting circuit comprising:
• the lighting arrangement comprising a set of parallel LED arrangements, wherein each LED arrangement is in series with a respective current driver which drives current through the LED arrangement, and each series combination is supplied with the DC voltage.
• the lighting control circuit is in this case used to control a lighting arrangement comprising a set of at least two light sources (together forming the lighting arrangement) comprising a first light source and a second light source in parallel, wherein the power converter is for delivering a DC voltage to a set of parallel current drivers.
• the DC voltage is the power supply to the current drivers and their associated LED arrangements.
• the current drivers for example each comprise a constant current source circuit.
• the current drivers may each comprise a pulse width modulation control input. In this way, the drive level to the light sources is adapted in a time division manner.
• the frequency of the pulse width modulation is high enough that visible flicker is not perceived, for example in the kHz range (e.g. 500Hz to 10kHz).
• a respective current sense resistor is for example in series with each current driver. This is used to set the current level of the current driver.
• LED arrangements When multiple LED arrangements are used in parallel, they for example have different color points. They may be different types of white (warm white, cool white, flame white %) or different colors.
• the temperature sensing element of the lighting control circuit is preferably in close proximity to one of the LED arrangements or thermally coupled to one of the LED arrangements. This provides optimum operation of the feedback control.
• the one of the LED arrangements is for example the LED arrangement with the largest forward voltage. This is the LED arrangement for which the headroom control is most critical.
• the invention also provides a method of controlling a lighting arrangement, comprising:
• the power converter having a control loop for controlling the level of the DC voltage
• the method is for example for controlling a lighting arrangement comprising a set of at least two light sources comprising a first light source and a second light source in parallel, wherein the method comprises delivering a DC voltage to a set of parallel current drivers using the power converter and driving the light sources using the current drivers.
• the method for example comprises adjusting the DC voltage inversely with respect to temperature.
• Fig. 1 shows in schematic form a known lighting control architecture for driving multiple lighting channels
• Fig. 2 shows one implementation of the lighting control architecture of Fig. 1;
• Fig. 3 shows a lighting control circuit of the invention, applied to the circuit architecture of Fig. 2;
• Fig. 4 shows the efficiency improvements obtained by the circuit of Fig. 3; and Fig. 5 shows a method of controlling a lighting arrangement.
• the invention provides a lighting arrangement such as a LED lamp comprising a light source and associated current driver, or a set of at least two parallel light sources and associated current drivers, supplied by a DC voltage from a voltage-regulated power converter.
• a feedback circuit provides a temperature-dependent control input to a control loop of the power converter, such that the DC voltage used to power the current driver(s) and light source(s) is adjusted in dependence on a sensed temperature. In this way, the voltage headroom required can be reduced, and efficiency gains are made.
• the current sense resistor sets the current making use of an internal reference.
• the light output flux (and hence color point) is set by the PWM signal.
• the current source When the PWM signal is set to zero, the current source is turned off and hence stops generating current.
• the PWM signal is non-zero, the amplitude of the current waveform is set by the current sense resistor and internal reference, whereas the duty cycle, and hence average current, is set by the PWM signal.
• the current sources are linear drivers, by which is meant there is no high frequency switching mode. Instead, they are implemented by a transistor current source circuit, with a sense resistor to set the current.
• a major issue to solve is the temperature dependent efficiency when a fixed bus voltage is used as the voltage source.
• the bus voltage needs to be high enough to guarantee enough headroom (voltage) for correct operation of the current sources.
• the headroom will increase because the LED forward voltage decreases and hence the total losses will increase.
• Figure 3 shows a lighting control circuit in accordance with one example of the invention, applied to the circuit architecture of Figure 2.
• the overall circuit of Figure 3 is a lighting circuit.
• the lighting control circuit of Figure 3 is shown coupled to a single current driver and light source. There may be only a single current driver, or else the lighting control circuit may be implemented as a circuit for controlling a lighting arrangement comprising a set of at least two current drivers comprising a first current driver and a second current driver in parallel.
• the (or each) current driver is connected in series with its associated light source.
• the current driver drives a current through the associated light source.
• the one or more light sources then form the lighting arrangement.
• a power converter delivers a DC voltage Vout to the current driver or the set of parallel current drivers, the power converter having a control loop for controlling the level of the DC voltage Vout.
• the DC voltage Vout is the power supply to the (or each) series- connected current driver and light source.
• the input Vin to the power converter is for example a signal received from a circuit including a full bridge diode rectifier and EMI filter (i.e. the AC/DC converter 14 of Figures 1 and 2).
• a full bridge diode rectifier and EMI filter i.e. the AC/DC converter 14 of Figures 1 and 2.
• the converter circuit as shown typically receives a rectified mains input and is itself a DC/DC converter.
• the rectifier and EMI filter may instead be considered to be part of an overall AC/DC converter architecture.
• the current driver shown in Figure 3 comprises a first current source II and associated first current sense resistor Rl, and the current driver is connected in series with a first light source Dl, which itself is a LED arrangement (represented as a single diode Dl, for simplicity).
• the circuit comprises a constant voltage power converter 30.
• this power converter is implemented as a buck converter.
• the buck converter comprises an energy storage inductor LI, diode dl and storage capacitor Cl.
• a switch SI is provided between the cathode of the diode Dl and the input Vin.
• a voltage feedback point for the control of the switch SI is shown as a control pin Ctrl. It is provided to the power converter controller IC 34, which then controls the timing of operation of the main switch SI to provide the regulated output voltage. The controller 34 implements the control loop of the power converter.
• the switch SI and controller 34 may be part of a power converter integrated circuit, such as a buck PFC constant-voltage regulator circuit.
• the circuit further comprises a feedback circuit 32, in particular in the form of a resistor network R2, R3, R4, RS.
• the resistor RS is a temperature sensing element in particular in the form of a temperature sensitive resistor.
• Resistor RS is the only temperature dependent element, formed as a negative temperature coefficient (NTC) resistor.
• NTC negative temperature coefficient
• the resistors R3, R4 and R2 form a voltage feedback circuit for generating the voltage feedback Ctrl and hence for controlling the output voltage.
• the resistor RS means the control input Ctrl to the controller 34 becomes temperature dependent. Thus, a temperature dependency is added to the control feedback used to control the timing of operation of the power converter main switch SI.
• the feedback resistor circuit is designed such that temperature has the desired influence on the regulated voltage control.
• the control input Ctrl is supplied to the controller 34 and thereby introduced into the control loop of the power converter, such that the DC voltage is adjusted in dependence on the sensed temperature.
• the DC voltage is adjusted inversely with respect to temperature. In this way, at high temperature the bus voltage is adjusted to a lower voltage level to increase the efficiency. At start-up with low temperature, the control loop increases the DC voltage to compensate for the cold LEDs.
• the linear driver II is a fixed current source as explained above, for example with a 1 KHz PWM input. More generally, the current driver or drivers for example each comprise a pulse width modulation control input. In this way, the drive level to the light sources is adapted in a time division manner.
• the frequency of the pulse width modulation is high enough that visible flicker is not perceived, for example in the kHz range (e.g. 500Hz to lOkHz).
• the LED load i.e. the light source Dl
• the LED load is for example a single string of LEDs, such as 6 mid-power LEDs.
• the voltage across the inductor LI at the reverse period is a measure of the output voltage.
• the resistance of RS decreases at higher temperatures and hence the output voltage at the control pin Ctrl will increase. This for example corresponds to a lower output voltage because the reference level of a control pin is reached earlier, giving a shorter conduction period.
• FIG. 4 shows a plot of efficiency versus temperature for the standard approach (plot 40) and for the implementation of Figure 3 (plot 42).
• Figure 3 shows only one current source Dl, but the lighting control circuit may comprise a set of parallel current drivers and associated light sources (as shown in Figure 2), each supplied by the DC voltage.
• the DC voltage is the power supply to the current drivers.
• a respective current sense resistor is for example in series with each current driver.
• the temperature sensing element of the lighting control circuit is preferably in close proximity to one of the LED arrangements or thermally coupled to one of the LED arrangements. This provides optimum operation of the feedback control.
• the one of the LED arrangements is for example the LED arrangement with the largest forward voltage. This is the LED arrangement for which the headroom control is most critical.
• Figure 5 shows a method of controlling a lighting arrangement, which for example comprises a set of at least two light sources comprising a first light source and a second light source in parallel, the method comprising:
• step 50 delivering a DC voltage to the current driver or to the set of parallel current drivers using a power converter, the power converter having a control loop for controlling the level of the DC voltage;
• step 52 sensing a temperature at or near a light source
• step 54 providing a temperature-dependent control input to the control loop of the power converter, such that the DC voltage is adjusted in dependence on a sensed temperature;
• step 56 driving the light source or light sources using the current driver(s).
• the method for example comprises adjusting the DC voltage inversely with respect to temperature.
• the invention is of primary interest for parallel switched current sources. However, it may be applied to a lamp with a single current source such as a one color, white, lamp.

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• Circuit Arrangement For Electric Light Sources In General (AREA)

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• 2020
  • 2020-07-07 US US17/625,014 patent/US11641703B2/en active Active
  • 2020-07-07 EP EP20735434.1A patent/EP3997962B1/en active Active
  • 2020-07-07 JP JP2022501109A patent/JP7509861B2/ja active Active
  • 2020-07-07 CN CN202080049803.XA patent/CN114097305B/zh active Active
  • 2020-07-07 WO PCT/EP2020/069054 patent/WO2021005027A1/en not_active Ceased

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