EP4319488A1 - Fonctionnement d'un moyen d'éclairage à del - Google Patents

Fonctionnement d'un moyen d'éclairage à del Download PDF

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Publication number
EP4319488A1
EP4319488A1 EP22188455.4A EP22188455A EP4319488A1 EP 4319488 A1 EP4319488 A1 EP 4319488A1 EP 22188455 A EP22188455 A EP 22188455A EP 4319488 A1 EP4319488 A1 EP 4319488A1
Authority
EP
European Patent Office
Prior art keywords
time
lighting means
driver unit
pwm modulation
pwm
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22188455.4A
Other languages
German (de)
English (en)
Inventor
András Mozsáry
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Tridonic GmbH and Co KG
Original Assignee
Tridonic GmbH and Co KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tridonic GmbH and Co KG filed Critical Tridonic GmbH and Co KG
Priority to EP22188455.4A priority Critical patent/EP4319488A1/fr
Publication of EP4319488A1 publication Critical patent/EP4319488A1/fr
Pending legal-status Critical Current

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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]
    • H05B45/30—Driver circuits
    • H05B45/32—Pulse-control circuits
    • H05B45/335—Pulse-frequency modulation [PFM]
    • 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]

Definitions

  • the invention relates to a method and driver unit for reducing the effect of bright and dark stripes, which occur when, for example, cameras of smartphones are used to take still pictures or videos inside an area which is illuminated by LED lighting means which are controlled using pulse-width-modulation (PWM).
  • PWM pulse-width-modulation
  • a method for operating a LED based lighting means comprises the steps of: pulse width modulating, PWM, a current through the LED lighting means by a driver unit, such that a long-time average value of a current through the LED based lighting means, as defined by the duty cycle of the PWM set by the driver unit, corresponds to a target value used by a feed-forward or a feedback control unit of the driver unit; and modulating, by the driver unit, this set long time average value by varying: an on-time of the PWM modulation while maintaining a constant off-time of the PWM modulation, in case the PWM duty cycle is more than a given threshold value, or an off-time of the PWM modulation while maintaining a constant on-time of the PWM modulation, in case the PWM duty cycle is less than a given threshold value.
  • the threshold value may be arranged between 25% and 75% PWM duty cycle.
  • the method further comprises: modulating, by the driver unit, the on-time or off-time such that a spectrum of the waveform of the current through the LED based lighting means comprises a DC component as well as an AC component having a frequency greater than 60 Hz, preferably greater than 80 Hz, more preferably greater than 100 Hz, but essentially no component in between.
  • the method comprises: using a sigma-delta modulator for the PWM modulation by the driver unit.
  • the method comprises: performing the PWM modulation such that a long-time average value of the current is constant for a human eye temporal perception.
  • the method further comprises: performing the PWM modulation such that, when a photo or video is taken in an area which is illuminated by the LED based lighting means, no black/white stripes effect occurs in such photos or videos.
  • the method further comprises the step of feeding back a signal to the driver unit representing an actual long-time average value of the current through the LED based lighting means, and performing a feedback-control by comparing, in the driver unit, this actual value with a target (nominal) value, in order to set the duty cycle of the PWM.
  • a driver unit for LED based lighting means comprises: a PWM modulator designed to PWM modulate a current supplied to output terminals for supplying the LED based lighting means; a feed-forward or feedback control unit for generating a long time average value of the PWM modulated current through the LED based lighting means; a modulating unit designed to modulate this given long time average value by cyclically varying: an on-time of the PWM modulation while maintaining a constant off-time of the PWM modulation, in case the PWM duty cycle is more than a given threshold value , or an off-time of the PWM modulation while maintaining a constant on-time of the PWM modulation, in case the PWM duty cycle is less than said given threshold value.
  • the threshold value may be arranged between 25% and 75% PWM duty cycle.
  • the driver unit is configured to: modulate the on-time or off-time such that a spectrum of the current through the LED based lighting means comprises a DC component as well as an AC component having a frequency of greater than 60 Hz, preferably greater than 80 Hz, more preferably greater than 100 Hz.
  • the driver unit is configured to: use a sigma-delta modulator for the PWM modulation.
  • the driver unit is configured to: perform the PWM modulation such that a long-time average value of the current is constant for a human eye temporal perception.
  • the driver unit is configured to: perform the PWM modulation such that, when a photo or video is taken in an area which is illuminated by the LED based lighting means, no black/white stripes effect occurs in such photos or videos.
  • the invention relates to the use of a PWM modulation for varying a frequency of a LED based lighting means by varying the off-time or on-time of the PWM modulation for reducing a black/white stripes effect on photos or videos taken in areas illuminated by the LED based lighting means.
  • FIG. 1 a method 100 for operating a LED based lighting means 202 is shown, according to an embodiment.
  • the method 100 comprises the step of providing 99 a nominal or target value for a long-term average value of a current through the LED lighting means 202.
  • "Long-term average” corresponds to the low pass filtering as effected by the human eye, i.e., a low-pass filtering in the order of 50Hz.
  • This nominal value is either translated, e.g., by mapping or by a function implemented in the diver unit 201, into a duty cycle of a PWM modulation of the current (in case of feedforward control), or it is compared to an actually measured long-term average value of the current through the LED means 202, wherein a feedback control in the driver unit 201 translates any deviation in the comparison to a duty cycle of the PWM modulation.
  • a duty cycle and a set frequency for the PWM modulation are given.
  • the method 100 further comprises pulse width modulating 101, PWM, the current through the LED lighting means 202 by a driver unit 201, such that a long-time average value of the current through the LED based lighting means 202 corresponds to a value set by a feed-forward or a feedback control performed by the driver unit 201.
  • the method 100 comprises modulating 102, by the driver unit 201, this set long-time average value, as expressed by the duty cycle of the PWM, by cyclically varying, with a frequency higher than 50 or 60Hz:
  • the threshold value may be arranged between 25% and 75% PWM duty cycle.
  • both the duty cycle and the frequency of the PWM modulated current through the LED lighting means 202 are cyclically varied.
  • the PWM control of the lighting means 202 is effected with a modulation of the PWM period. In other words, it is no longer a fixed frequency PWM, but a PWM modulation with variable frequency.
  • the period is modulated by varying the on-time of the PWM while maintaining a constant off-time, provided that the PWM duty cycle is greater than a given threshold which is preferably within the range of between 25% to 75%. Otherwise, i.e. if the PWM duty cycle is lower than said given threshold, a varying off-time and a constant on-time comes is applied.
  • the modulation can be made such that in a long-time average the duty cycle of the PWM modulation is constant. Especially, the duty cycle should be constant in view of the time resolution of the human eye. Therefore, “long-time average” is meant to be within range of human eye temporal perception, while “short-time fluctuations" are those beyond the speed of human eye.
  • the resulting spectrum of the modulation should be such that there is no spectrum contribution in a non-zero frequency area, which is resolvable to the human eye.
  • the modulation is done such that the resulting frequency spectrum has only the DC components as well as AC components higher than for example 100 Hz.
  • the method 100 may further comprise the step of using a sigma-delta modulator for the PWM modulation by the driver unit 201.
  • the method 100 may comprise the step of feeding back a signal 203 to the driver unit 201 representing an actual long time average value of the current through the LED based lighting means 202 (see also Fig. 2 ).
  • Fig. 2 shows an embodiment of a driver unit 201 for LED based lighting means 202.
  • the driver unit 201 for LED based lighting means 202 comprises:
  • the LED based lighting means 202 can be a device which comprises one or more LEDs.
  • the driver unit 201 can be configured to provide a nominal or target value for the long-term average value of the current through the LED lighting means 202.
  • the driver unit 201 can be configured to translate this nominal value, e.g., by mapping or by a function implemented in the diver unit 201, into a duty cycle of a PWM modulation of the current (in case of feedforward control). Alternatively or additionally, the driver unit 201 can be configured to compare the nominal value to an actually measured long-term average value of the current through the LED lighting means 202. The driver unit 201 can further comprise a feedback control unit configured to translate any deviation in this comparison to a duty cycle of the PWM modulation. Thus, in both cases, a duty cycle and a set frequency for the PWM modulation are given.
  • the driver unit 201 in particular the modulating unit 201e, can be configured to modulate the on-time or off-time such that a spectrum of the current through the LED based lighting means 202 comprises both a DC and an AC component.
  • the AC component can have a frequency of greater than 60 Hz, preferably greater than 80 Hz, more preferably greater than 100 Hz. In this way, flickering effects visible to the human eye can be avoided, as explained above.
  • the PWM modulator 201c of the driver unit 201 can be a sigma-delta modulator.
  • black/white stripes or similar effects can be avoided in photos or videos which are captured in an area which is illuminated by the LED based lighting means 202.
  • the photos or videos can be captured by a camera of a smartphone.
  • the LED based lighting means 202 can be installed in the area, e.g. to provide an ambient illumination of the area.

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  • Circuit Arrangement For Electric Light Sources In General (AREA)
EP22188455.4A 2022-08-03 2022-08-03 Fonctionnement d'un moyen d'éclairage à del Pending EP4319488A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP22188455.4A EP4319488A1 (fr) 2022-08-03 2022-08-03 Fonctionnement d'un moyen d'éclairage à del

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP22188455.4A EP4319488A1 (fr) 2022-08-03 2022-08-03 Fonctionnement d'un moyen d'éclairage à del

Publications (1)

Publication Number Publication Date
EP4319488A1 true EP4319488A1 (fr) 2024-02-07

Family

ID=82786466

Family Applications (1)

Application Number Title Priority Date Filing Date
EP22188455.4A Pending EP4319488A1 (fr) 2022-08-03 2022-08-03 Fonctionnement d'un moyen d'éclairage à del

Country Status (1)

Country Link
EP (1) EP4319488A1 (fr)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180084616A1 (en) * 2016-09-16 2018-03-22 Lutron Electronics Co., Inc. Load Control Device for a Light-Emitting Diode Light Source Having Different Operating Modes

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180084616A1 (en) * 2016-09-16 2018-03-22 Lutron Electronics Co., Inc. Load Control Device for a Light-Emitting Diode Light Source Having Different Operating Modes

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