Light source dimmer

Abstract

To prevent a problem such as flickering of illumination light and non-lighting even when a dimming rate is extremely low in a light source dimmer that controls an ON time per hour of a pulsed current.SOLUTION: A light source dimmer 1 that supplies a pulsed current S5 for burst dimming to a light source 2 to control an ON time of the pulsed current S5 on the basis of a dimming ratio signal uses a pulsed current whose pulse width is made large enough not to cause unstable lighting of the light source 2 as the pulsed current S5. Then, the dimmer 1 changes the duty ratio of the pulsed current S5 according to the dimmer rate in a range where the dimmer rate is higher than a predetermined boundary value, and changes the dimmer rate by thinning out the pulses of the pulsed current S5 while keeping the duty ratio of the pulsed current S5 constant in a range where the dimmer rate is equal to or lower than the boundary value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dimming device that changes the dimming rate of a light source such as a fluorescent lamp or an LED, and more particularly to a dimming device for a light source that performs burst dimming of the light source. [Background technology]

[0002] There is a widespread demand for changing the illuminance of light sources such as fluorescent lamps and LEDs when they are turned on and driven. For example, Patent Documents 1 and 2 disclose dimming devices that change the dimming rate (ratio to maximum illuminance) of a light source to meet such demands. More specifically, Patent Document 2 discloses burst dimming of a light source by controlling the pulsed drive current applied to the light source using PWM (pulse width modulation), that is, by controlling the ON time per unit time of the pulsed drive current. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-078857 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-138279 Summary of the Invention [Problem to be solved by the invention]

[0004] When performing burst dimming as shown in Patent Document 1, the duty ratio of the pulsed drive current must be significantly reduced to achieve a very low dimming rate. However, doing so can disrupt the pulse waveform at the rising and falling edges of the drive current, which can lead to problems such as flickering or non-lighting of the illumination light.

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a dimming device for a light source that controls the ON time per unit time of a pulsed current, which does not cause problems such as flickering or non-lighting of the illumination light even when the dimming rate is set very low. [Means for solving the problem]

[0006] The light source dimming device according to the present invention comprises: 1. A light source dimming device that supplies a pulsed current for burst dimming to a light source and controls an ON time per unit time of the pulsed current based on a dimming rate signal, As the pulsed current, a pulsed current having a pulse width of 1.5 μs or more is used, Dimming rate About 3 to 5% Higher all In the range, the duty ratio of the pulsed current is changed according to the dimming rate, and 3 to 5% below all In this range, the dimming rate is changed by thinning out the pulses of the pulsed current while keeping the duty ratio of the pulsed current constant. It is characterized by the following.

[0007] In the dimming device of the present invention having the above configuration, the pulse width of the pulsed current is, for example, about 1.5 μs or more (when the burst period is 50 μs and the dimming rate is 3% or more). Also, the boundary value of the dimming rate is, for example, about 3 to 5%. [Effects of the Invention]

[0008] According to the inventor's research, the reason why the pulse waveform of the drive current becomes distorted when the dimming ratio is set very low is because the pulse width of the drive current becomes very small when the duty ratio of the pulsed drive current is significantly reduced, resulting in a distorted pulse waveform. Therefore, the dimming device of the present invention uses a pulsed current with a large pulse width that does not cause unstable lighting of the light source. When the dimming ratio is higher than a predetermined boundary value, the duty ratio of the pulsed current is changed according to the dimming ratio. When the dimming ratio is below the boundary value, the dimming ratio is changed by thinning out the pulses of the pulsed current while keeping the duty ratio of the pulsed current constant. Therefore, with the dimming device of the present invention, even when the dimming ratio is set very low, the pulse width of the drive current becomes very small, preventing the pulse waveform from becoming distorted, thereby preventing problems such as flickering or non-lighting of the illumination light. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit diagram of a light control device according to a first embodiment of the present invention; [Figure 2] 5 is a schematic diagram showing the waveform of the light source drive current in the above-mentioned dimming device for each dimming rate. [Figure 3] Schematic diagram explaining the waveform distortion of the light source driving current [Figure 4] Schematic diagram showing waveforms of various signals in the above-mentioned dimming device. [Figure 5] Schematic diagram showing waveforms of various signals in the above-mentioned dimming device. [Figure 6] A schematic diagram showing waveforms of various signals in a dimmer device different from that shown in FIG. [Figure 7] 1 is a circuit diagram of a light control device according to a second embodiment of the present invention; [Figure 8] A schematic diagram showing the waveforms of the various signals mentioned above, along with the numerical values ​​that define the waveforms. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating the circuit configuration of a light source dimming device according to a first embodiment of the present invention. The dimming device 1 of this embodiment drives and dims a plurality of LEDs 2a, 2b, 2c, etc. that make up an LED module 2, and in this example, is provided separately from a lighting drive circuit 3 for the LED module 2. The lighting drive circuit 3 has an input filter unit 5 connected to an AC power source 4 via input terminals 5a, 5b, and an AC / DC converter 6. The AC / DC converter 6 converts the AC output of the input filter unit 5 into a constant-voltage DC output.

[0011] The dimming device 1 includes a dimming signal input unit 10 that receives a dimming signal S1 from input terminals 10a and 10b, a pulse width modulator 11, an AND circuit 12, a switching element drive unit 13 that receives an output S4 of the AND circuit 12, and a MOS FET 14 that is driven by the switching element drive unit 13 to turn on / off the drive current applied to the LEDs 2a, 2b, 2c, etc. of the LED module 2. The dimming device 1 further includes a D-type flip-flop 15a that receives the output signal S3 of the pulse width modulator 11, a plurality of D-type flip-flops 15a, 15b, 15c, etc. (up to eight stages are shown in the figure) connected in series, a square wave / triangular wave conversion unit 16, an operational amplifier 17 that adjusts the potential of the output signal S2 of the dimming signal input unit 10 to an appropriate potential and outputs it as a dimming instruction signal S8, and a comparator 18 that compares this dimming instruction signal S8 with the output signal S9 of the square wave / triangular wave conversion unit 16.

[0012] Dimming control by the dimming device 1 having the above configuration will be described below with reference to Fig. 2. Fig. 2 also shows the waveform of the output current S5 (which corresponds to the waveform of the light output of the LED module 2) applied to the LED module 2 via the MOS FET 14 in Fig. 1 at (1) to (7) for each set dimming rate. When the LED module 2 is burst dimmed, that is, when this output current S5 is applied to the LED module 2 in pulses as a drive current, the waveform of this output current S5 will be as shown in more detail in Fig. 3 (1) and (2), for example.

[0013] (1) and (2) in Figure 3 show the cases where the dimming ratio is set relatively high, e.g., 50%, and the case where the dimming ratio is set relatively low, e.g., 5%, respectively. In both cases, ideally, the pulse waveform would be treated as a rectangular wave (ideal waveform) indicated by the dashed line in the figure. However, in reality, time delays occur at the rising and falling edges of the pulse, resulting in the waveform (actual waveform) indicated by the solid line in the figure. In this example, even if the actual waveform is like that shown in (1) or (2) in Figure 3, it has been confirmed that there is no practical problem with the relationship between the current applied to the LED module 2 and its light output. However, if the dimming ratio is set significantly lower than the case of (2) above, e.g., less than 5%, the applied current value may not rise to the predetermined value, resulting in problems such as flickering or non-illumination of the LED module 2. The dimming device 1 of this embodiment is designed to prevent this problem by using a configuration described in detail below. This point will be explained below.

[0014] A dimming level setting signal S1 indicating a dimming level is input from input terminals 10a and 10b to a dimming signal input unit 10 of a dimming device 1, and the dimming signal input unit 10 outputs a dimming signal S2 corresponding to the dimming level setting signal S1. The dimming signal S2 is, for example, an analog voltage signal of 0 to 1 V. A pulse width modulator 11, which is, for example, a silicon oscillator, is controlled by the dimming signal S2 and outputs a Tmain signal S3, which is a pulse signal having a duty ratio corresponding to the voltage of the dimming signal S2. The duty ratio D of the pulse signal is D = pulse width t / pulse period T, as shown in FIG. 2 (3). The pulse period T is generally set to approximately 2 ms (milliseconds) or less.

[0015] Although the Tmain signal S3 has been collectively referred to as a "pulse signal" for convenience, the duty ratio Dmain of the Tmain signal S3 is in the range of 0.05≦Dmain≦1. When Dmain=1, the Tmain signal S3 is a continuous signal with a uniform output level and, strictly speaking, is not a pulse signal. However, the term "pulse width modulation" generally includes the case where the duty ratio is 1, and will be treated as such in this disclosure. As described above, the pulse width modulator 11 sets the minimum value of the duty ratio Dmain of the Tmain signal S3 to 0.05. In other words, when the dimming rate indicated by the dimming signal S2 is lower than 5%, the pulse width modulator 11 outputs a Tmain signal S3 with a duty ratio Dmain fixed at 0.05.

[0016] The Tmain signal S3 is input to the AND circuit 12, which outputs an AND output S4, which is the logical product of the Tmain signal S3 and the output signal S10 of the comparator 18. The AND output S4 is input to the switching element driver 13, and a MOS FET 14 serving as a switching element is driven based on the output S5 of the switching element driver 13. The output S5 of the switching element driver 13 has a current value increased to a level capable of driving the MOS FET 14, and its waveform is the same as the waveform of the AND output S4.

[0017] As mentioned above, the drive current applied to the LEDs 2a, 2b, 2c, etc. of the LED module 2 is turned on / off by the MOS FET 14, so the relationship shown in Figure 2 also shows the waveform of the AND output S4 for each dimming rate. In this dimming device 1, when the dimming rate is gradually reduced from 100% as shown in Figure 2 (1) to (2) or below, the duty ratio of the Tmain signal S3 is reduced according to the dimming rate to be set. For example, if a dimming rate of 50% is desired, the duty ratio of the Tmain signal S3 is set to 0.5 as shown in Figure 2 (3).

[0018] As described above, if the duty ratio of the Tmain signal S3 is changed between 1 (state shown in (1) of the figure) and 0.05 (state shown in (5) of the figure), the dimming ratio can be set to a desired value between 100% and 5% without any problems. However, if the dimming ratio is set to less than 5%, for example 2.5%, in order to light the LED module 2 at an even lower illuminance, and the duty ratio of the Tmain signal S3 is set to 0.025 as shown in (6) of the figure, this may cause problems such as flickering or failure to light the LED module 2, as previously explained with reference to (2) of Figure 3.

[0019] Therefore, in the dimming device 1 of this embodiment, when the dimming ratio is set to less than 5%, the duty ratio of the pulsed Tmain signal S3 is fixed to 0.05, and the Tmain signal S3 is thinned out by the AND circuit 12 at a thinning ratio corresponding to the dimming ratio, and input as the AND output S4 to the switching element driver 13. That is, as an example, when the dimming ratio is set to 2.5%, as shown in (7) of FIG. 2, the pulsed Tmain signal S3 is thinned out so that only 1 / 2 remains, and input as the AND output S4 to the switching element driver 13. Also, when the dimming ratio is set to 1%, the pulsed Tmain signal S3 is thinned out so that only 1 / 5 remains, and input as the AND output S4 to the switching element driver 13. More specifically, if the desired dimming ratio is 1 / n of 5%, the Tmain signal S3 is thinned out so that only 1 / n remains.

[0020] Therefore, the AND output S4, which has an even smaller pulse width than the actual waveform shown in Fig. 3(2), will not be input to the switching element drive unit 13. In other words, the MOS FET 14 will no longer turn on / off the LEDs 2a, 2b, 2c, etc. with such a small pulse width (during the ON time), and as a result, problems such as flickering or non-lighting of the LED module 2 will be prevented.

[0021] Hereinafter, a detailed configuration for fixing the duty ratio of the Tmain signal S3 to 0.05 and thinning out the Tmain signal S3 as described above will be described in detail with reference to FIGS. 1, 4, and 5. In (7) of FIG. 2, an example was shown in which the Tmain signal S3 is thinned out every other pulse to clearly explain leaving only half of the pulse-like Tmain signal S3. However, in the dimming device 1 of FIG. 1, if three stages of D-type flip-flops 15a, 15b, and 15c are provided, for example, four consecutive pulses of the Tmain signal S3 are basically left as they are, and the following four (=8-4) pulses are thinned out, as shown in FIGS. 4 and 5, which will be described in detail later. If eight stages of D-type flip-flops 15a to 15h are provided, 128 consecutive pulses of the Tmain signal S3 are left as they are, and the following 128 (=256-128) pulses are thinned out. In the present invention, when only half of the Tmain signal S3 is to be retained, either of the two types of thinning methods described above may be applied.

[0022] Furthermore, the thinning rate of the Tmain signal S3 is not limited to 1 / 2. Generally speaking, N consecutive pulses (2≦N) of the Tmain signal S3 may be left as they are, and one pulse following them may be thinned out. Conversely, one pulse of the Tmain signal S3 may be left as it is, and the following N consecutive pulses (2≦N) may be thinned out. In the present invention, "thinning out pulses" includes all of the above-mentioned embodiments. Furthermore, the thinning rate is not limited to 1 / 2, and other thinning rates such as 1 / 4, 1 / 3, 2 / 3, etc. may also be used.

[0023] 1, a portion of the Tmain signal S3 is branched off before being input to the AND circuit 12, as described above, and input to the first-stage D-type flip-flop 15a. The D-type flip-flop outputs a pulse whose H / L level changes in response to the rising edge of the input pulse, so the waveform of the Tmain signal S3 changes as shown in (1) to (4) of FIG. 4 as it passes through the multiple D-type flip-flops 15a, 15b, 15c, and so on, and is finally output as the pulse signal S6.

[0024] In this example, three D-type flip-flops are used. (1) in FIG. 4 shows the Tmain signal S3 before being input to the first-stage D-type flip-flop 15a. (2) in FIG. 4 shows the pulse signal after passing through the first-stage D-type flip-flop 15a. (3) in FIG. 4 shows the pulse signal after passing through the second-stage D-type flip-flop 15b. (4) in FIG. 4 shows the pulse signal 6 after passing through the third-stage D-type flip-flop 15c. The pulse signal 6 determines the period of the triangular wave S9 generated by the square wave / triangular wave converter 16 shown in FIG. 1, as shown in (4) in FIG. 1. To compare the period of this triangular wave S9 with that of the Tmain signal S3, (1) in FIG. 4 also shows the triangular wave S9. In this embodiment, the pulse width of the Tmain signal S3 is, for example, 50 μs.

[0025] The triangular wave S9 is input to the comparator 18 in FIG. 1 and compared with the dimming instruction signal S8 output from the operational amplifier 17. As a result, as shown in FIG. 5(1), the comparator 18 outputs a pulse signal S10 that rises in a range where the triangular wave S9 is lower than the dimming instruction signal S8. This pulse signal S10 is input to the AND circuit 12 in FIG. 1, and as shown in FIG. 5(2), the AND circuit 12 outputs an AND output S4 (see FIG. 5(3)) that is an AND of the pulse signal S10 and the Tmain signal S3. As can be seen by comparing this AND output S4 with FIG. 5(2), four consecutive pulses of the Tmain signal S3 remain intact, and the four pulses following them are thinned out.

[0026] 1 and lighting the LED module 2 based on the output S5 (whose waveform is the same as that of the AND output S4) of this switching element driver 13, it becomes possible to light the LED module 2 at a lower dimming rate than when lighting the LED module 2 based on the Tmain signal S3. Furthermore, the duty ratio of the pulsed AND output S4 is 0.05, which is the same as the duty ratio of the Tmain signal S3, so problems such as flickering or non-lighting of the LED module 2 do not occur.

[0027] In addition, the operational amplifier 17 adjusts the dimming instruction signal S8 based on the dimming signal S2 so that the signal levels (voltages) of the dimming instruction signal S8 and the triangular wave S9 are always S8>S9 in the region where the duty ratio is 0.05 or more. Therefore, the pulse signal S10 output from the comparator 18 is always at H level in the region where the duty ratio is 0.05 or more. Therefore, in this region, the AND output S4 from the AND circuit 12 is not thinned out as described above, and becomes the Tmain signal S3 itself.

[0028] In the above example, the pulse signal S10 output from the comparator 18 in FIG. 1 is referred to as the Tsub signal, and its duty ratio is referred to as Dsub. The duty ratio Dmain of the Tmain signal S3, as well as the values ​​of Dmain and Dsub for each dimming ratio that is set, and the number of pulses of the Tmain signal and Tsub signal are summarized in Table 1 below.

[0029] [Table 1]

[0030] In the example described above, since the triangular wave S9 is used, the pulsed AND output S4 is in an incomplete state at the start of dimming control, as shown in (3) of Figure 5. To eliminate this state, a sawtooth wave S19 as shown in (1) of Figure 6 can be used instead of the triangular wave S9. (1), (2), and (3) of Figure 6 correspond to (1), (2), and (3) of Figure 5, respectively.

[0031] Furthermore, instead of the dimmer 1 shown in FIG. 1 used in this embodiment, a dimmer 101 as shown in FIG. 7 can be applied. In FIG. 7, elements equivalent to those in FIG. 1 described above are assigned the same numbers, and their description will be omitted unless particularly necessary. The dimmer 101 of FIG. 7, which is a second embodiment of the present invention, uses a microcomputer 102 including an A / D converter 103, a program processor 104, etc. The program processor 104 generates a Tmain signal S103 similar to the Tmain signal S3 described above and a Tsub signal S110 similar to the Tsub signal S10 through predetermined program processing. The Tmain signal S103 and the Tsub signal S110 are input to an AND circuit 105, and an output S104 obtained by ANDing these signals is input from the AND circuit 105 to the switching element driver 13.

[0032] Here, specific numerical examples of the pulse width, pulse period, etc. of the pulsed current described above will be described with reference to the waveform diagram shown in FIG. 8. The example in FIG. 8 assumes that dimming control is performed by the dimming device 1 of FIG. 1, and that the generation timing of the Tsub signal S10 relative to the start of dimming control is set as shown in (3) of FIG. 6. In the example in FIG. 8, the pulse period T of the Tmain signal S3 is 50 μs, the pulse width t is 2.5 μs, and the pulse period of the Tsub signal S10 is 800 μs. Note that since the relationship between the pulse waveform and elapsed time is difficult to see from the graph in FIG. 8, the relationship is shown numerically in Tables 2 to 4 for some periods (elapsed times 0 to 1600 μs). In these numerical tables, "1" and "0" shown in the "Out" columns of the Tmain signal S3 and the Tsub signal S10 indicate states in which the pulse is rising and not rising, respectively.

[0033] [Table 2]

[0034] [Table 3]

[0035] [Table 4]

[0036] In (1) of FIG. 8, the duty ratio D=2.5 / 50=0.05, i.e., the dimming rate is 5%. On the other hand, (2) and (3) of FIG. 8 show the case where the thinning rate of the Tmain signal S3 is set to 1 / 2, resulting in a dimming rate of 2.5%. In (3) of FIG. 8, eight consecutive pulses of the Tmain signal S3 are left as they are, and the following eight pulses are thinned out. This thinning can be performed in the same manner as described in the first embodiment, using the Tsub signal S10, as shown in (4) of the same figure (see FIG. 6).

[0037] On the other hand, (2) in Figure 8 shows a case where the Tmain signal S3 is thinned out every other pulse. In the present invention, as described above, the Tmain signal S3 may be thinned out in this manner, or the Tmain signal S3 may be thinned out every other pulse as described above. However, the method of using the Tsub signal S10 as described above cannot be applied to thinning out the Tmain signal S3 every other pulse. Therefore, when thinning out in this manner, it is desirable to perform the thinning through program processing using, for example, the dimmer 101 shown in Figure 7 described above.

[0038] When the Tmain signal S3 is thinned out by multiple pulses using the Tsub signal S10, the period of the Tsub signal S10 must be an integer multiple of the period of the Tmain signal S3. In this case, the dimming ratio of the Tmain signal S3 after thinning out is essentially (y / Y) compared to the dimming ratio of the Tmain signal S3 before thinning out. Here, y and Y are both integers, 0≦y≦Y, and y varies depending on the Tsub signal S10. Meanwhile, Y is a value of 2 to the nth power, i.e., 2, 4, 8, or 16, where n is the number of stages in the D-type flip-flops 15a. Specifically, when Y=2 and y=0, 1, or 2, assuming the number of stages in the D-type flip-flops 15a is 1, the dimming ratios are 0% (all S3 is thinned out), 2.5% (half S3 is thinned out), and 5% (no thinning out), respectively. Furthermore, when the number of stages of D-type flip-flops 15a is 2, Y=4, and y=0, 1, 2, 3, and 4, the dimming ratios are 0% (all S3 thinned out), 1.25% (S3 thinned out by 3 / 4), 2.5% (S3 thinned out by half), 3.75% (S3 thinned out by 1 / 4), and 5% (no thinning out), respectively. In contrast, when thinning is performed by the above program processing, there are no such restrictions and it is possible to freely achieve a low dimming ratio.

[0039] In the dimming device 1 of FIG. 1, the more stages of the D-type flip-flops 15a..., the more precisely the dimming rate can be set in the range of 5% or less. For example, if the number of stages is 4, the dimming rate can be changed in 0.3125% increments (16 steps) in the range of 5% or less. If the number of stages is 8, the dimming rate can be changed in 0.0195% increments (256 steps) in the range of 5% or less. However, if the number of stages is too large, the difference in the periods of the Tmain signal S3 and the Tsub signal S10 becomes too large (the period of the Tmain signal S3 is too short, the period of the Tsub signal S10 is too long, or both), making it difficult to set the circuit operation.

[0040] If the period of the Tmain signal S3 is lengthened, single burst dimming (i.e., using only the Tmain signal S3) allows smooth dimming down to a dimming rate of 5% or less, but there is a risk of abnormal noise from the device. The region where the pulse period T of the Tmain signal S3 is ≥ 50 μs corresponds to a frequency of 20 kHz or less, which is in the audible frequency band. Setting the period longer (lower frequency) than this may cause problems with light source flickering. Therefore, to eliminate the risk of abnormal noise, the pulse period T of the Tmain signal S3 must be shortened to less than 50 μs. According to the present invention, by shortening the pulse period T of the Tmain signal S3 to this extent, abnormal noise can be prevented, and dimming down to a dimming rate of 5% or less is possible. [Explanation of symbols]

[0041] 1, 101 dimmer 2 LED modules 3 Lighting drive circuit 4 AC power supply 5 Input filter section 6 AC / DC conversion section 10. Dimming signal input section 11 Pulse Width Modulator 12 AND Circuit 13 Switching element driver 14 MOS FETs 15a, 15b, 15c... D-type flip-flop 16 Square wave / triangle wave conversion section 17 Operational Amplifiers 18 Comparator 102 Microcomputer 103 A / D conversion section 104 Program Processing Section 105 AND circuit

Claims

[Claim 1] 1. A light source dimming device that supplies a pulsed current for burst dimming to a light source and controls an ON time per unit time of the pulsed current based on a dimming rate signal, As the pulsed current, a pulsed current having a pulse width of 1.5 μs or more is used, A light source dimming device configured to change the duty ratio of the pulsed current in accordance with the dimming ratio over the entire range where the dimming ratio is higher than approximately 3 to 5%, and to change the dimming ratio by thinning out the pulses of the pulsed current while keeping the duty ratio of the pulsed current constant over the entire range where the dimming ratio is 3 to 5% or less.

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