JP2022117849A - light source dimmer - Google Patents

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

The present invention relates to a light control device for changing the dimming rate of a light source such as a fluorescent lamp or an LED, and more particularly to a light source light control device for performing burst light control of the light source.

2. Description of the Related Art There is a wide demand for changing the illuminance of a light source such as a fluorescent lamp or an LED. For example, Patent Documents 1 and 2 disclose light control devices that change the light control rate (ratio to maximum illuminance) of a light source in order to meet such demands. More specifically, in Patent Document 2, a pulsed drive current applied to a light source is PWM (pulse width modulated) controlled, that is, the ON time per unit time of the pulsed drive current is controlled to perform burst modulation of the light source. shown to glow.

JP-A-2000-078857 JP 2012-138279 A

When performing burst dimming as disclosed in Patent Document 1, the duty ratio of the pulsed drive current must be significantly reduced to make the dimming ratio very low. However, in doing so, the pulse waveform is disturbed at the rising and falling edges of the driving current, which may cause problems such as flickering of the illumination light and non-lighting.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. To provide a light control device which does not cause problems such as lighting.

The light source dimmer according to the present invention comprises:
A light source dimming device that supplies a pulsed current for burst dimming to a light source and controls the ON time of the pulsed current per hour based on a dimming rate signal,
As the pulse-like current, a pulse-like current with a pulse width that is large enough not to cause unstable lighting of the light source is used,
In a range where the dimming rate is higher than a predetermined boundary value, the duty ratio of the pulse-shaped current is changed according to the dimming rate, and in a range where the dimming rate is equal to or lower than the boundary value, the duty ratio of the pulse-shaped current is The light control rate is changed by thinning out the pulses of the pulsed current while keeping it constant,
It is characterized by

In the light control device of the present invention having the above configuration, the pulse width of the pulsed current is, for example, approximately 1.5 μs or more (when the burst period is 50 μs and the dimming rate is 3% or more). Further, the boundary value of the dimming ratio is set to, for example, about 3 to 5%.

According to research by the present inventor, the reason why the pulse waveform of the drive current is disturbed when the dimming ratio is extremely low is that when the duty ratio of the pulse-shaped drive current is significantly reduced, the pulse width of the drive current becomes extremely small. It was found that this was caused by the disturbance of the pulse waveform. Therefore, in the dimming device of the present invention, a pulsed current with a pulse width that is large enough not to cause unstable lighting of the light source is used. The duty ratio of the pulse-shaped current is changed according to the dimming rate, and in the range where the dimming rate is equal to or lower than the above boundary value, the duty ratio of the pulse-shaped current is kept constant and the pulses of the pulse-shaped current are thinned out for dimming. I am trying to change the rate. Therefore, in the light control device of the present invention, even if the light control rate is very low, the pulse width of the driving current becomes very small and the pulse waveform is not disturbed. problem can be prevented.

1 is a circuit configuration diagram of a light control device according to a first embodiment of the present invention; FIG. Schematic diagram showing the waveform of the light source drive current for each dimming rate in the dimming device Schematic diagram explaining waveform disturbance of light source driving current Schematic diagram showing waveforms of various signals in the light control device Schematic diagram showing waveforms of various signals in the light control device Schematic diagram showing waveforms of various signals in a dimming device different from that of FIG. FIG. 2 is a circuit configuration diagram of a light control device according to a second embodiment of the present invention; A schematic diagram showing the waveforms of the various signals mentioned above, along with the numerical values that define the waveforms.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing the circuit configuration of a light source dimming device according to a first embodiment of the present invention. As an example, the light control device 1 of the present embodiment drives a plurality of LEDs 2a, 2b, 2c, . It is provided separately from the drive circuit 3 . The lighting drive circuit 3 has an input filter section 5 connected to an AC power source 4 from input terminals 5a and 5b, and an AC/DC conversion section 6. As shown in FIG. The AC/DC conversion section 6 converts the AC output of the input filter section 5 into a constant voltage DC output.

The dimming device 1 includes a dimming signal input section 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 driving section 13 that receives an output S4 of the AND circuit 12, It also has a MOS·FET 14 as a switching element that is driven by the switching element driving section 13 to turn on/off the drive current applied to the LEDs 2a, 2b, 2c, . . . of the LED module 2. The light control device 1 further includes a plurality of D-type flip-flops 15a, 15b, 15c, . rectangular wave/triangular wave converter 16, an operational amplifier 17 that adjusts the potential of the output signal S2 of the dimming signal input part 10 to a proper potential and outputs it as a dimming instruction signal S8, and this dimming It has a comparator 18 for comparing the instruction signal S8 and the output signal S9 of the rectangular wave/triangular wave converter 16. FIG.

Light control by the light control device 1 having the above configuration will be described below with reference to FIG. 2 shows the waveform of the output current S5 applied to the LED module 2 via the MOS FET 14 in FIG. are shown in (1) to (7). When the LED module 2 is subjected to burst dimming, that is, when the output current S5 is applied to the LED module 2 in a pulse form as a drive current, the waveform of the output current S5 is as shown in FIG. It becomes as shown in (1) and (2).

(1) and (2) of FIG. 3 respectively show a case where the dimming rate is set relatively high, for example 50%, and a case where the dimming rate is set relatively low, for example 5%. there is In either case, ideally, the pulse-shaped waveform is treated as a rectangular wave (ideal waveform) indicated by the dashed line in the figure. The waveform (actual waveform) is indicated by a solid line inside. In this example, even if the actual waveforms are as shown in (1) and (2) of FIG. I have confirmed that this does not occur. However, if the dimming rate is set to be less than 5%, which is significantly lower than the above case (2), the applied current value will not rise to the predetermined value, and problems such as flickering and non-lighting of the LED module 2 will occur. I may invite The light control device 1 of the present embodiment can prevent this problem from occurring with a configuration that will be described in detail later. This point will be described below.

A dimming signal input section 10 of the dimming device 1 receives a dimming level setting signal S1 indicating a dimming level from input terminals 10a and 10b. A corresponding dimming signal S2 is output. This dimming signal S2 is, for example, an analog voltage signal of 0 to 1V. A pulse width modulator 11 made of, for example, a silicon oscillator is controlled by the dimming signal S2 to output a pulse signal Tmain signal S3 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 (3) of FIG. In general, the pulse period T is set to approximately 2 ms (milliseconds) or less.

Further, although the term “pulse signal” is collectively used here for convenience, the duty ratio Dmain of the Tmain signal S3 is in the range of 0.05≦Dmain≦1, and when Dmain=1, the Tmain signal S3 outputs only one signal. It is a continuous signal with a similar level and, strictly speaking, it is not a pulse signal. However, since the term "pulse width modulation" is usually used to include the case where the duty ratio is 1, it is treated as such in the present disclosure. Further, the pulse width modulator 11 sets the minimum value of the duty ratio Dmain of the Tmain signal S3 to 0.05 as described above. That is, when the dimming rate indicated by the dimming signal S2 is lower than 5%, the Tmain signal S3 with the duty ratio Dmain fixed at 0.05 is output.

The Tmain signal S3 is input to the AND circuit 12, and the AND circuit 12 outputs an AND output S4, which is the AND of the Tmain signal S3 and the output signal S10 of the comparator 18. FIG. This AND output S4 is input to the switching element driving section 13, and based on the output S5 of this switching element driving section 13, the MOS-FET 14 as a switching element is driven. The output S5 of the switching element driving section 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.

As described above, the drive currents applied to the LEDs 2a, 2b, 2c, . It is also shown for each dimming rate. In this light control device 1, when the light control rate is sequentially decreased from 100% shown in FIG. Lower. For example, when the dimming rate is desired to be 50%, the duty ratio of the Tmain signal S3 is set to 0.5 as shown in (3) in FIG.

As described above, if the duty ratio of the Tmain signal S3 is changed between 1 (state (1) in the figure) and 0.05 (state (5) in the figure), the dimming ratio is set to the desired value between 100% and 5% without problems. However, if an attempt is made to set the dimming rate to less than 5%, for example 2.5%, in order to light the LED module 2 at a lower illuminance, the duty ratio of the Tmain signal S3 is set to 0 as shown in (6) in FIG. If it is set to 0.025, problems such as flickering and non-lighting of the LED module 2 may occur, as described above with reference to FIG. 3(2).

Therefore, in the light control device 1 of the present embodiment, when the light control rate is set to less than 5%, the duty ratio of the pulse-like Tmain signal S3 is fixed at 0.05, and the Tmain signal S3 is output by the AND circuit 12 as Thinning is performed at a thinning rate corresponding to the value of the dimming rate, and the result is input to the switching element driving section 13 as an AND output S4. That is, when the light control rate is set to 2.5% as an example, as shown in FIG. Input to the switching element drive unit 13 . When the dimming rate is set to 1%, the pulse-like Tmain signal S3 is thinned out so as to leave only ⅕, and is input to the switching element driving section 13 as an AND output S4. More specifically, if the dimming rate desired to be set is 1/n of 5%, the Tmain signal S3 is thinned out to leave only 1/n.

Therefore, the AND output S4 having a pulse width that is even smaller than the actual waveform shown in FIG. In other words, the MOS-FET 14 does not turn ON/OFF the LEDs 2a, 2b, 2c, ... with such a very short pulse width (in the ON time), and as a result, the LED module 2 flickers or does not light up. Problems are prevented.

Hereinafter, a detailed configuration for fixing the duty ratio of the Tmain signal S3 to 0.05 and thinning out the Tmain signal S3 will be described in detail with reference to FIGS. 1, 4, and 5. FIG. Note that in (7) of FIG. 2, an example of thinning out the Tmain signal S3 every other pulse is shown in order to clearly explain that only 1/2 of the pulse-shaped Tmain signal S3 is left. In the dimming device 1, for example, when three stages of D-type flip-flops 15a, 15b and 15c are provided, as shown in FIGS. Leave them as they are and decimate the 4 (=8-4) pulses that follow them. When 8 stages of D-type flip-flops 15a to 15h are provided, 128 continuous 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 1/2 of the Tmain signal S3 is left, any of the above two forms of thinning may be applied.

Furthermore, the thinning rate of the Tmain signal S3 is not limited to 1/2. Generally speaking, the continuous N pulses (2≤N) of the Tmain signal S3 may be left as they are and the following one pulse may be thinned. On the other hand, one pulse of the Tmain signal S3 may be left as it is and the following N consecutive pulses (2.ltoreq.N) may be thinned out. In the present invention, "pulse thinning" includes all of the forms described above. Also, the thinning rate is not limited to 1/2, and other thinning rates such as 1/4, 1/3, and 2/3 may be used.

The Tmain signal S3 output from the pulse width modulator 11 shown in FIG. 1 is partially branched before being input to the AND circuit 12 as described above, and is input to the first-stage D-type flip-flop 15a. be. Since the D-type flip-flop outputs a pulse whose H/L level changes in response to the rise of the input pulse, the Tmain signal S3 passes through a plurality of D-type flip-flops 15a, 15b, 15c, . , the waveform changes as shown in (1) to (4) in FIG. 4, and is finally output as a pulse signal S6.

In this example, it is assumed that there are three stages of D-type flip-flops, and (1) in FIG. FIG. 4(3) shows the pulse signal after passing through the first-stage D-type flip-flop 15a, and FIG. 4(4) shows the pulse signal after passing through the second-stage D-type flip-flop 15b. It 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 rectangular wave/triangular wave converter 16 shown in FIG. 1, as indicated by (4) in FIG. In order to compare the period of this triangular wave S9 with the period of the Tmain signal S3, the triangular wave S9 is also shown in (1) of FIG. In this embodiment, the pulse width of the Tmain signal S3 is 50 μs as an example.

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 within a range in which the triangular wave S9 has a lower value than the dimming instruction signal S8. This pulse signal S10 is input to the AND circuit 12 in FIG. 1, and from the AND circuit 12, as shown in FIG. It is output (see (3) in FIG. 5). This AND output S4 is obtained by leaving four continuous pulses of the Tmain signal S3 as they are and thinning out the following four pulses, as can be seen from a comparison with (2) in FIG.

The AND output S4 as explained above is inputted to the switching element driving section 13 of FIG. is turned on, it becomes possible to turn on the LED module 2 at a lower dimming rate than when the LED module 2 is turned on based on the Tmain signal S3. The duty ratio of the pulse-like AND output S4 is 0.05, which is the same as the duty ratio of the Tmain signal S3.

In addition, based on the dimming signal S2, the operational amplifier 17 instructs dimming so that the signal levels (voltages) of the dimming instruction signal S8 and the triangular wave S9 are always S8>S9 in a region where the duty ratio is 0.05 or more. Signal S8 is adjusted. 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 as described above, but becomes the Tmain signal S3 itself.

Here, in the example described above, the pulse signal S10 output from the comparator 18 in FIG. 1 is called a Tsub signal, and its duty ratio is called Dsub. and Dsub, and the number of pulses of the Tmain and Tsub signals are summarized in Table 1 below.

In the example described above, since the triangular wave S9 is used, the pulse-shaped AND output S4 is in an incomplete state at the start of the dimming control, as shown in FIG. 5(3). . In order to eliminate this state, a sawtooth wave S19 as shown in FIG. 6(1) may be used instead of the triangular wave S9. (1), (2) and (3) in FIG. 6 correspond to (1), (2) and (3) in FIG. 5, respectively.

Further, a light control device 101 as shown in FIG. 7 can be applied instead of the light control device 1 shown in FIG. 1 used in this embodiment. In this FIG. 7, elements equivalent to those in FIG. 1 described previously are assigned the same numbers, and description thereof will be omitted unless particularly necessary. A light control device 101 of FIG. 7, which is a second embodiment of the present invention, uses a microcomputer 102 having an A/D conversion unit 103, a program processing unit 104, and the like. By program processing, a Tmain signal S103 similar to the Tmain signal S3 and a Tsub signal S110 similar to the Tsub signal S10 are generated. These Tmain signal S 103 and Tsub signal S 110 are input to AND circuit 105 , and output S 104 obtained by ANDing these signals is input to switching element driving section 13 .

Here, specific numerical examples of the pulse width, pulse period, etc. of the pulse-shaped current described above will be described with reference to the waveform diagram shown in FIG. In the example of FIG. 8, it is assumed that dimming control is performed by the dimming device 1 of FIG. It is set to be the case. In the example of FIG. 8, the Tmain signal S3 has a pulse period T=50 μs and a pulse width t=2.5 μs, and the Tsub signal S10 has a pulse period=800 μs. Since it is difficult to understand the relationship between the pulse waveform and the elapsed time in the graph of FIG. 8, Tables 2 to 4 show the relationship numerically for some periods (elapsed time 0 to 1600 μs). In this numerical table, "1" and "0" shown in the "Out" column of the Tmain signal S3 and Tsub signal S10 respectively indicate the state in which the pulse has risen and the state in which the pulse has not risen.

In (1) of FIG. 8, the duty ratio D=2.5/50=0.05, that is, 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 and the dimming rate is set to 2.5%. In (3) of FIG. 8, 8 consecutive pulses of the Tmain signal S3 are left as they are, and the following 8 pulses are thinned out. Such thinning out can be performed in the same manner as described in the first embodiment using the Tsub signal S10 as shown in (4) of FIG. 6 (see FIG. 6).

On the other hand, (2) of FIG. 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 way, or the Tmain signal S3 may be thinned out by a plurality of continuous pulses as described above. However, the method of using the Tsub signal S10 as described above cannot be applied to thin out the Tmain signal S3 every other pulse. Therefore, when such thinning is performed, it is desirable to perform thinning by program processing using the above-described light control device 101 of FIG. 7, for example.

When thinning out the Tmain signal S3 by a plurality of pulses using the Tsub signal S10, the period of the Tsub signal S10 must be an integral multiple of the period of the Tmain signal S3. In this case, the light control rate of the Tmain signal S3 after thinning is basically (y/Y) with respect to the light control rate of the Tmain signal S3 before thinning. Here, 0.ltoreq.y.ltoreq.Y where y and Y are both integers, and y varies according to the Tsub signal S10. On the other hand, when the number of stages of the D-type flip-flops 15a is n, Y is the n-th power of 2, that is, 2, 4, 8, 16, . Specifically, when the number of stages of the D-type flip-flops 15a is 1, Y=2, and y=0, 1, 2, the dimming rate is 0% (all S3 thinning), 2.5% (half thinning of S3), and 5% (no thinning). Also, when the number of stages of the D-type flip-flops 15a is 2, Y=4, and y=0, 1, 2, 3, 4, the dimming rate is 0% (S3 is all thinned out). , 1.25% (3/4 thinning of S3), 2.5% (half thinning of S3), 3.75% (1/4 thinning of S3), and 5% (no thinning). On the other hand, when thinning is performed by the above program processing, it is possible to freely achieve a low dimming rate without being subject to such restrictions.

In the light control device 1 of FIG. 1, the more the number of stages of the D-type flip-flops 15a . For example, if the number of stages is 4, the dimming rate can be changed stepwise in increments of 0.3125% (16 steps) in a region where the dimming rate is 5% or less. Further, when the number of steps is 8, the dimming rate can be changed in steps of 0.0195% (256 steps) in the region where the dimming rate is 5% or less. However, if the number of stages is too large, the difference between the periods of the Tmain signal S3 and the Tsub signal S10 becomes too large (either 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 up the operation of the circuit.

If the cycle of the Tmain signal S3 is lengthened, single burst dimming (that is, only the Tmain signal S3) enables smooth dimming down to a dimming rate of 5% or less, but abnormal noise is generated from the device. There is a risk of The region of the pulse period T≧50 μs of the Tmain signal S3 has a frequency of 20 kHz or less, which is an audible frequency band. If the period (lower frequency) is longer than this, the problem of flickering of the light source may occur. Therefore, in order to eliminate the possibility of noise generation, it is necessary to shorten the pulse period T of the Tmain signal S3 to less than 50 μs. According to the present invention, the pulse period T of the Tmain signal S3 can be shortened to that extent to prevent the occurrence of abnormal noise, and the dimming can be performed up to a dimming rate of 5% or less.

Reference Signs List 1, 101 light control device 2 LED module 3 lighting drive circuit 4 AC power supply 5 input filter section 6 AC/DC conversion section 10 light control signal input section 11 pulse width modulator 12 AND circuit 13 switching element drive section 14 MOS-FET
15a, 15b, 15c... D-type flip-flop 16 rectangular wave/triangular wave converter 17 operational amplifier 18 comparator 102 microcomputer 103 A/D converter 104 program processor 105 AND circuit

Claims (1)

A light source dimming device that supplies a pulsed current for burst dimming to a light source and controls the ON time of the pulsed current per hour based on a dimming rate signal,
As the pulse-like current, a pulse-like current with a pulse width that is large enough not to cause unstable lighting of the light source is used,
In a range where the dimming rate is higher than a predetermined boundary value, the duty ratio of the pulse-shaped current is changed according to the dimming rate, and in a range where the dimming rate is equal to or lower than the boundary value, the duty ratio of the pulse-shaped current is A dimming device for a light source configured to change the dimming rate by thinning out the pulses of the pulsed current while keeping it constant.

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