JP2024137009A - Lighting equipment - Google Patents

Abstract

To provide a lighting device with improved noise resistance.SOLUTION: A lighting device includes a light source and a lighting circuit that supplies a drive current to the light source. The lighting circuit includes a control unit that controls a drive current, and the control unit outputs a pulse-width modulated lighting control signal to control the drive current. The lighting control signal is generated such that the frequency of the pulse-width modulation decreases as a duty ratio, which is a ratio of a pulse width to a period in the pulse-width modulation, decreases.SELECTED DRAWING: Figure 3

Description

An embodiment of the present invention relates to a lighting device.

The lighting device includes, for example, a light source including a plurality of light-emitting diodes (LDEs) and a lighting circuit that supplies a driving current to the light source. The lighting circuit increases or decreases the driving current by changing the duty ratio of a pulse-width modulated lighting control signal, thereby dimming the light source. It is desirable that the frequency of the lighting control signal is higher than the frequency of human hearing so as not to generate a sound that is recognized as noise or noise. However, if the duty ratio is reduced without changing the frequency of the lighting control signal in order to reduce the brightness of the lighting device, the pulse width becomes narrower and the noise resistance of the lighting circuit decreases.

JP 2014-157784 A

The embodiment provides a lighting device with improved noise resistance.

The lighting device according to the embodiment includes a light source and a lighting circuit that supplies a drive current to the light source. The lighting circuit has a control unit that controls the drive current, and the control unit outputs a pulse-width modulated lighting control signal to control the drive current. The lighting control signal is generated such that the frequency of the pulse-width modulation decreases as the duty ratio, which is the ratio of the pulse width to the period in the pulse-width modulation, decreases.

According to the embodiment, it is possible to provide a lighting device with improved noise resistance.

1 is a block diagram showing a lighting device according to an embodiment; 1 is a circuit diagram showing a lighting circuit of a lighting device according to an embodiment. 5 is a graph showing the operation of a lighting circuit in the lighting device according to the embodiment. FIG. 11 is a schematic diagram showing a lighting control signal in a lighting device according to a comparative example. FIG. 4 is a schematic diagram showing a lighting control signal in the lighting device according to the embodiment. 11 is a schematic diagram showing another lighting control signal in the lighting device according to the embodiment. FIG.

The following describes the embodiments with reference to the drawings. Identical parts in the drawings are given the same numbers, and detailed descriptions thereof are omitted as appropriate, while different parts are described. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, and the like are not necessarily the same as in reality. Even when the same parts are shown, the dimensions and ratios between them may be different depending on the drawing.

Figure 1 is a block diagram showing a lighting device 1 according to an embodiment. The lighting device 1 is a lighting device for use in directing, which is installed in, for example, a studio or a stage.

As shown in FIG. 1, the lighting device 1 includes a light source 2 and a lighting circuit 3. The light source 2 is, for example, a light-emitting diode 10. The light source 2 is, for example, composed of a plurality of light-emitting diodes 10.

The lighting circuit 3 includes, for example, an A/D conversion unit 20, a D/D conversion unit 30, and a control unit 40. The lighting circuit 3 is driven, for example, by an external AC power source AC. The A/D conversion unit 20 converts the AC current supplied from the AC power source AC into DC and supplies it to the D/D conversion unit 30.

The D/D conversion unit 30 converts the direct current input from the A/D conversion unit 20 into a drive current Id for the light emitting diode 10 and supplies it to the light source 2. The control unit 40 receives a control input input from the outside and generates a lighting control signal to be supplied to the D/D conversion unit 30. The D/D conversion unit 30 outputs a drive current Id corresponding to the lighting control signal input from the control unit 40. In other words, the control unit 40 adjusts the light source 2 via the D/D conversion unit 30.

Figure 2 is a circuit diagram showing the lighting circuit 3 of the lighting device 1 according to the embodiment. Figure 2 shows a schematic diagram of the circuit configuration of the D/D conversion unit 30. The D/D conversion unit 30 includes, for example, a switching element 31, a diode 33, an inductor 35, a capacitor 37, and a resistor 39.

The D/D conversion unit 30 has, for example, a first input terminal 30a, a second input terminal 30b, a first output terminal 30c, and a second output terminal 30d. The output of the A/D conversion unit 20 (see FIG. 1) is connected to the first input terminal 30a and the second input terminal 30b. The light source 2 is connected to the first output terminal 30c and the second output terminal 30d.

As shown in FIG. 2, the D/D conversion unit 30 includes a so-called step-down chopper circuit. The step-down chopper circuit is composed of a switching element 31, a diode 33, an inductor 35, and a capacitor 37. The switching element 31 is, for example, an N-channel MOSFET.

The drain 31a of the switching element 31 is connected to the first input terminal 30a. The source 31b of the switching element 31 is connected to the cathode of the diode 33 and the inductor 35. The source 31b of the switching element 31 is also connected to the first output terminal 30c via the inductor 35. The switching element 31 is controlled to be turned on and off by a lighting control signal input to the gate 31c from the control unit 40.

The capacitor 37 is connected to the first output terminal 30c and the second output terminal 30d. In other words, the capacitor 37 is connected in parallel to the light source 2.

The resistor 39 is connected to the second input terminal 30b and the second output terminal 30d. The resistor 39 is also connected to the anode of the diode 33. The second input terminal 30b and the anode of the diode 33 are connected to the capacitor 37 and the second output terminal 30d via the resistor 39. The end of the resistor 39 on the second output terminal 30d side is connected to the control unit 40.

The DC current input to the first input terminal 30a of the D/D conversion unit 30 is converted to a pulse current by the switching element 31. That is, the DC current input to the switching element 31 is converted to a pulse current by, for example, a lighting control signal. The lighting control signal is, for example, pulse width modulated (PWM). The pulse current output from the switching element 31 is smoothed by a low-pass filter composed of an inductor 35 and a capacitor 37, and is supplied to the light source 2 as the drive current Id.

The D/D conversion unit 30 converts a direct current into a pulse current by a lighting control signal input from the control unit 40. As a result, the D/D conversion unit 30 controls the drive current Id and dims the light source 2. The resistor 39 is provided to monitor the drive current Id returning from the light source 2 to the second input terminal 30b. In other words, the control unit 40 is configured to detect a change in the drive current Id by monitoring the voltage drop in the resistor 39 and feed it back to the lighting control signal.

Figure 3 is a graph showing the operation of the lighting circuit 3 in the lighting device 1 according to the embodiment. The horizontal axis is the dimming degree (%) of the light source 2. The vertical axis is the frequency (kHz) of the lighting control signal output from the control unit 40. The dimming degree corresponds to the duty ratio of the lighting control signal. In other words, as the duty ratio of the lighting control signal increases, the dimming degree also increases.

As shown in FIG. 3, the frequency of the lighting control signal increases as the dimming level increases. For example, the frequency of the lighting control signal is 50 kHz when the dimming level is 50%, and is maintained at 50 kHz even when the dimming level exceeds 50%. In other words, at dimming levels of 50% or less, the lighting control signal is generated such that the frequency of the pulse width modulation decreases as the dimming level decreases.

For example, the human audible frequency is between 20 Hz and 20 kHz. In this example, when the dimming level is 36% or less, the frequency of the lighting control signal falls within the audible frequency band. For example, the frequency of the lighting control signal at a dimming level of 30% is within the human audible frequency band, and the lighting control signal has a first duty ratio corresponding to a dimming level of 30%. Furthermore, the frequency of the lighting control signal at a dimming level of 40% is higher than the audible frequency band, and the lighting control signal has a second duty ratio that is greater than the first duty ratio.

Figure 4 is a schematic diagram showing a lighting control signal in a lighting device according to a comparative example. Figure 4 shows three lighting control signals LCS1, LCS2, and LCS3 corresponding to different dimming levels.

In this example, the pulse width modulation period Tm1 is constant and does not depend on the dimming level. The period Tm1 is set, for example, so that the frequencies of the lighting control signals LCS1 to LCS3 are higher than the human audible frequency.

The control unit 40 adjusts the dimming of the light source 2 by changing the duty ratio (the ratio of the pulse width Wp to the period Tm1) of the lighting control signal. The lighting control signal LCS1 has a period Tm1 and a pulse width Wp1. The lighting control signal LCS2 has a period Tm1 and a pulse width Wp2, and the lighting control signal LCS3 has a period Tm1 and a pulse width Wp3. The pulse widths Wp1, Wp2, and Wp3 have a relationship of Wp1<Wp2<Wp3, and the lighting control signals LCS1 to LCS3 correspond to low dimming, medium dimming, and high dimming, respectively.

In this example, when the control unit 40 (see FIG. 2) controls the light source 2 to a low dimming level, the pulse width Wp1 of the lighting control signal LCS1 becomes narrow. When the pulse width Wp1 reaches a level where noise caused by the frequency components of the AC power supply cannot be ignored, for example, the dimming of the light source 2 becomes unstable. In other words, the noise resistance of the lighting circuit 3 decreases.

Figure 5 is a schematic diagram showing the lighting control signals in the lighting device 1 according to the embodiment. Figure 5 shows three lighting control signals LCS4, LCS5, and LCS6 corresponding to different dimming levels.

In this example, the pulse width Wp1 of the lighting control signals LCS4 to LCS6 is constant and does not depend on the dimming level. The pulse width Wp1 is set to a level that does not reduce the noise resistance of the lighting circuit 3.

The lighting control signal LCS4 has a period Tm1 and a pulse width Wp1. The lighting control signal LCS5 has a period Tm2 and a pulse width Wp1, and the lighting control signal LCS6 has a period Tm3 and a pulse width Wp1. The periods Tm1, Tm2, and Tm3 have a relationship of Tm1>Tm2>Tm3, and the lighting control signals LCS4 to LCS6 are set to have duty ratios corresponding to the respective dimming levels.

For example, when the control unit 40 (see FIG. 2) controls the light source 2 to a low dimming level, the period Tm1 becomes longer. As a result, the modulation frequency of the lighting control signal LCS4 falls within the human audible frequency range (see FIG. 3), but the driving current Id controlled by the lighting control signal LCS4 becomes a low level. As a result, noise in the audible frequency range caused by the lighting control signal LCS4 is suppressed to a level that is not recognized as noise, for example.

Figure 6 is a schematic diagram showing another lighting control signal in the lighting device 1 according to the embodiment. Figure 6 shows three lighting control signals LCS7, LCS8, and LCS9 corresponding to different dimming levels.

The lighting control signal LCS7 has a period Tm1 and a pulse width Wp1, and has a duty ratio corresponding to a low dimming level. The modulation frequency of the lighting control signal LCS7 is within the human audible range (see FIG. 3), but the noise of the lighting circuit 3 is suppressed because the duty ratio is small. The pulse width Wp1 is set wider than the level that reduces the noise resistance of the lighting circuit 3.

The lighting control signal LCS8 has a period Tm2 and a pulse width Wp2, and the lighting control signal LCS9 has a period Tm3 and a pulse width Wp3. The duty ratio (Wp2/Tm2) of the lighting control signal LCS8 is greater than the duty ratio (Wp1/Tm1) of the lighting control signal LCS7. In addition, the duty ratio (Wp2/Tm2) of the lighting control signal LCS8 is less than the duty ratio (Wp3/Tm3) of the lighting control signal LCS9.

The periods Tm1, Tm2, and Tm3 of the lighting control signals LCS7 to LCS9 have a relationship of, for example, Tm1>Tm2>Tm3. The pulse widths Wp1, Wp2, and Wp3 have a relationship of, for example, Wp1<Wp2<Wp3.

In order to generate the lighting control signals shown in Fig. 5 and Fig. 6, the control unit 40 (see Fig. 2) holds, for example, a table that specifies the period Tm and the pulse width Wp corresponding to the dimming level. Table 1 is an example of such a table.

According to an embodiment, the relationship of each period Tm is Tm1>Tm1a>Tm1b>Tm1c>Tm1d>Tm1e>Tm2>Tm2a>Tm3. The pulse widths Wp1, Wp1a, Wp1b, Wp1c, Wp1d, Wp1e, Wp2, Wp2a, Wp3, Wp4, and Wp5 are set to have a duty ratio (Wp/Tm) corresponding to each dimming level.

Table 1 is stored, for example, in a storage device of the control unit 40 (see FIG. 2). The control unit 40 reads, for example, the period Tm and pulse width Wp corresponding to the dimming level specified by an external control input, and generates the lighting control signals LCS7 to LCS9.

For example, when lowering the dimming level of the light source 2 from 50% to 30%, the control unit 40 outputs lighting control signals corresponding to dimming levels of 45%, 40%, and 35% in sequence before outputting a lighting control signal corresponding to a dimming level of 30% to the D/D conversion unit 30. In this way, by gradually lowering the dimming level of the light source 2, the lighting circuit 3 can be operated stably. Note that, although the example shown in Table 1 shows an example in which the dimming level is changed in steps of 5%, the embodiment is not limited to this. For example, the dimming level may be changed in steps of 1% or 2%.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

(Appendix 1)
A light source;
A lighting circuit for supplying a driving current to the light source;
Equipped with
The lighting circuit has a control unit that controls the drive current,
The control unit outputs a pulse-width modulated lighting control signal to control the driving current;
The lighting device according to claim 1, wherein the lighting control signal is generated such that a frequency of the pulse width modulation decreases as a duty ratio, which is a ratio of a pulse width to a period in the pulse width modulation, decreases.
(Appendix 2)
The lighting device described in Appendix 1, characterized in that the lighting control signal has a first duty ratio when the frequency of the pulse width modulation is in the human audible frequency band, and has a second duty ratio greater than the first duty ratio when the frequency of the pulse width modulation is higher than the human audible frequency band.
(Appendix 3)
3. The lighting device according to claim 2, wherein a pulse width at the first duty ratio is the same as a pulse width at the second duty ratio.
(Appendix 4)
The lighting device described in Appendix 2, characterized in that a frequency of the pulse width modulation at a third duty ratio greater than the second duty ratio is higher than a frequency of the pulse width modulation at the second duty ratio and is the same as a frequency of the pulse width modulation at a fourth duty ratio greater than the third duty ratio.
(Appendix 5)
5. The lighting device according to claim 1, wherein the pulse width in the pulse width modulation is greater than a predetermined value.
(Appendix 6)
6. The lighting device according to claim 1, wherein the control unit sequentially outputs a plurality of lighting control signals in which the frequency of the pulse modulation is changed in a stepwise manner.

REFERENCE SIGNS LIST 1... Illumination device, 2... Light source, 3... Lighting circuit, 10... Light-emitting diode, 20... A/C conversion section, 30... D/D conversion section, 31... Switching element, 31a... Drain, 31b... Source, 31c... Gate, 33... Diode, 35... Inductor, 37... Capacitor, 39... Resistor, 40... Control section, AC... AC power source, Id... Drive current, LCS1 to LCS9... Lighting control signal

Claims (6)

A light source;
A lighting circuit for supplying a driving current to the light source;
Equipped with
The lighting circuit has a control unit that controls the drive current,
The control unit outputs a pulse-width modulated lighting control signal to control the driving current;
The lighting device according to claim 1, wherein the lighting control signal is generated such that a frequency of the pulse width modulation decreases as a duty ratio, which is a ratio of a pulse width to a period in the pulse width modulation, decreases. The lighting device according to claim 1, characterized in that the lighting control signal has a first duty ratio when the frequency of the pulse width modulation is within the human audible frequency band, and has a second duty ratio greater than the first duty ratio when the frequency of the pulse width modulation is higher than the human audible frequency band. The lighting device according to claim 2, characterized in that the pulse width at the first duty ratio is the same as the pulse width at the second duty ratio. The lighting device according to claim 2, characterized in that the frequency of the pulse width modulation at a third duty ratio greater than the second duty ratio is higher than the frequency of the pulse width modulation at the second duty ratio and is the same as the frequency of the pulse width modulation at a fourth duty ratio greater than the third duty ratio. The lighting device according to claim 1, characterized in that the pulse width in the pulse width modulation is greater than a predetermined value. 2. The lighting device according to claim 1, wherein the control unit sequentially outputs a plurality of lighting control signals in which the frequency of the pulse modulation is changed in a stepwise manner.

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