Power supply device for solid-state light source

Abstract

To provide a power supply device for a solid-state light source that can restrain occurrence of flickering of light emitted from the solid-state light source even when the illuminance of the solid-state light source set by a dimmer is low.SOLUTION: A power supply device (21) for a solid-state light source supplies power to a solid-state light source (22) based on an output of a dimmer (10), the device including an effective voltage detection unit (33) that receives the output of the dimmer, detects an effective voltage of the output, and outputs the value of the effective voltage, a low-pass filter (35) using a Bessel filter provided on the output side of the effective voltage detection unit, a cut-off frequency change unit (34) that changes the cut-off frequency of the low-pass filter, a PWM unit (36) that generates a pulse-width modulated signal based on the output of the low-pass filter, and a lighting unit (28) that generates a pulsed direct current according to the output of the PWM unit based on the output of the dimmer, and supplies the pulsed direct current to the solid-state light source.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a power supply device for a solid state lighting (SSL) such as a light emitting diode (LED) or an electroluminescence (EL). [Background technology]

[0002] In recent years, lighting fixtures using energy-efficient SSL have come into widespread use as part of the climate change (global warming) countermeasures required by the SDGs and other goals. For example, in the lighting of studios and stages, dimmers that use commercial power phase control have traditionally been widely used, and lighting fixtures connected to such conventional dimmers are increasingly being converted to SSL (especially LEDs). SSLs have an extremely fast response speed compared to incandescent bulbs such as tungsten bulbs, so they are prone to the so-called "flickering" phenomenon, in which the brightness changes when the voltage fluctuates in a short period of time due to noise, etc. In particular, in the lighting of studios and stages, there are many opportunities to reduce the illuminance to achieve a dim brightness for production purposes, and when SSL is connected to a conventional dimmer, the flickering becomes noticeable when such a dim brightness is achieved.

[0003] Patent Document 1 describes an LED lighting device used to prevent flickering of the light emitted by such an LED (SSL). This lighting device branches the phase-controlled power output from a dimmer and inputs it to a power supply circuit and a control circuit. The power supply circuit converts the input power into DC using a rectifier circuit and a smoothing circuit, and inputs the DC power into a conversion circuit. The conversion circuit includes a switching element, and is ON / OFF controlled by the control circuit described below. The control circuit converts the input power into a digital signal at a predetermined sampling interval (e.g., 185.12 microseconds), calculates a moving average value for the digital values ​​of a predetermined number of samples (e.g., within a range of 4 to 30), and outputs a PWM (pulse width modulation) signal having a duty ratio corresponding to the obtained calculation result to the conversion circuit. The conversion circuit turns on / off the DC power input from the power supply circuit using the duty ratio of the PWM signal input from the control circuit, thereby lighting the LED at an illuminance (light output, brightness) corresponding to the duty ratio. Here, by setting the illuminance using the moving average value of the sampled digital signal of the analog power output from the dimmer, rather than using it as is, it is possible to suppress fluctuations in illuminance when short-term fluctuations occur in the output voltage of the dimmer, thereby suppressing flickering. In Patent Document 2, the sampling interval is shorter (10 microseconds) than in Patent Document 1, and the time interval for calculating the moving average value is longer (250 milliseconds), which further suppresses fluctuations in illuminance due to short-term fluctuations in the output voltage of the dimmer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-207364 A [Patent Document 2] JP 2017-220438 A Summary of the Invention [Problem to be solved by the invention]

[0005] The dimmer devices described in Patent Documents 1 and 2 can prevent flickering when the output voltage of the dimmer device (i.e., the illuminance of the LED (SSL) set by the dimmer device) is relatively high, but flickering occurs when this voltage is reduced.

[0006] An object of the present invention is to provide a power supply device for an SSL that can suppress flickering in the light emitted by the SSL even when the illuminance set by the dimmer is low. [Means for solving the problem]

[0007] The power supply device for a solid-state light source according to the present invention, which has been made to solve the above problems, is a device that supplies power to a solid-state light source based on the output of a dimmer device, a) an effective voltage detection unit which receives an output of the dimmer device, detects an effective voltage of the output, and outputs a value of the effective voltage; b) a low-pass filter using a Bessel filter provided on the output side of the effective voltage detection unit; c) a cutoff frequency changing unit that changes a cutoff frequency of the low-pass filter in accordance with the effective voltage detected by the effective voltage detection unit; d) a PWM unit that generates a pulse width modulation signal based on an output of the low pass filter; e) a lighting unit that generates a pulsed direct current according to an output of the PWM unit from an output of the dimmer device and supplies the pulsed direct current to the solid-state light source; Equipped with.

[0008] The solid-state light source power supply device according to the present invention can be used by connecting it to a voltage control type dimmer or a phase control type dimmer.

[0009] As shown in Fig. 1, the output of a dimmer is supplied to a lighting device including a solid-state light source. The power supply device for a solid-state light source according to the present invention is disposed between the output of the dimmer and the solid-state light source in the lighting device, and divides the output of the dimmer into a power portion and a control portion, which are processed by an input unit and a control unit, respectively. The effective voltage detection unit in the control unit receives the output of the dimmer device, detects the effective voltage of the output, and outputs the value at a predetermined cycle. This detection of the effective voltage can be performed, for example, based on the output obtained by analog-to-digital (A / D) conversion of the voltage output from the dimmer device (Fig. 2(a)). Alternatively, a zero-cross detector or the like can be used to measure the conductive period or non-conductive period of the output voltage of the dimmer device, and the effective voltage can be calculated (detected) based on the values ​​of the conductive period or non-conductive period (Fig. 2(b)). The effective voltage detection unit converts the detected effective power value into a pulse and outputs it to a low-pass filter (LPF).

[0010] The period in which the effective voltage detector outputs the effective voltage value is longer than half the period of the commercial power supply, and more specifically, is preferably about 2 to 4 times the period of the commercial power supply. That is, when the commercial power supply frequency is 50 Hz, the output frequency of the effective voltage detector is 25 Hz to 12.5 Hz, and when the commercial power supply frequency is 60 Hz, the output frequency is about 30 Hz to 15 Hz.

[0011] The low-pass filter removes components with frequencies higher than the cutoff frequency from the output of the effective voltage detector, and outputs the resultant output, which is provided to the PWM unit. The cut-off frequency changer (cut-off f) changes the cut-off frequency of this low-pass filter. This change in cut-off frequency is performed automatically according to the value of the effective voltage from the dimmer detected by the effective voltage detector. Figures 2(a) and 2(b) show examples of a circuit that automatically changes the cut-off frequency according to the value of the effective voltage from the dimmer detected by the effective voltage detector.

[0012] The PWM unit generates a pulse width signal having a duty ratio corresponding to the output of the low-pass filter. The frequency of this pulse width modulation signal is set to a high frequency (e.g., 200 Hz) so that humans cannot perceive the flicker. The lighting section generates a pulse current based on the pulse signal from the PWM section from the DC current generated by the input section and supplies it to the solid-state power source, causing the solid-state light source to emit light at an illuminance that corresponds to the output of the dimmer.

[0013] According to the power supply device for a solid-state light source of the present invention, the cutoff frequency changing unit changes the cutoff frequency of the low-pass filter, thereby suppressing flickering of the solid-state light source according to the degree of flickering. As described above, the cutoff frequency is automatically changed according to the effective voltage (dimming level) output by the dimmer.

[0014] Low-pass filters include Bessel filters, Butterworth filters, Chebyshev filters, etc., and any of them can be used in the power supply device for solid-state light sources according to the present invention. However, for the following reasons, it is preferable to use a Bessel filter, and it is particularly preferable to use a second-order Bessel filter.

[0015] The Bessel filter has the advantage that the attenuation near the cutoff frequency is relatively gradual, while the flatness in the passband is better than that of other low-pass digital filters. The inventor measured the time change in illuminance when a voltage V1 was applied to a tungsten light bulb, which is a heat-generating light bulb, from a state in which no voltage was applied to a certain time (time t=0) and the voltage was changed in a stepwise manner. It was found that the change in illuminance (transient response) from time t=0 until the illuminance of the tungsten light bulb reaches a constant value at which it is at its maximum, is similar to the step response function of a Bessel filter (especially a second-order Bessel filter). Here, the step response function is a function of time obtained by performing an inverse Laplace transform on a transfer function, which is a function of frequency that indicates the characteristics of the filter, and includes a cutoff frequency as a constant. By setting the cutoff frequency of the step response function for each voltage V1 applied to the tungsten light bulb, the transient response and the step response function at each voltage V1 can be approximated. As a result, by setting the cutoff frequency so that the step response function matches the transient response of a tungsten light bulb, it is possible to achieve dimming of a solid-state light source that has dynamic characteristics equivalent to those of a tungsten light bulb and suppresses the occurrence of flicker.

[0016] When the low-pass filter is a second-order Bessel filter, the cutoff frequency changer preferably changes the cutoff frequency so that the cutoff frequency is proportional to the effective voltage of the output of the dimmer with a positive proportionality coefficient, thereby making it possible to set a digital filter that is closer to the transient response of a tungsten light bulb.

[0017] The present invention can further be configured such that the effective voltage detection unit has a spike noise removal filter that removes spike noise contained in the output of the dimmer (FIG. 2(a)). This makes it possible to remove the effect of spike noise on the digital signal output by the effective voltage detection unit, thereby more reliably suppressing flickering of the solid-state light source. The spike noise removal filter can be, for example, one that takes a moving average of the intensity values ​​of the digital signal obtained by A / D converting the output of the dimmer, or one that takes the average by excluding the maximum and / or minimum values ​​of the intensity values ​​when taking such a moving average. Effect of the Invention

[0018] According to the present invention, even when the illuminance set by the dimmer is low, flickering in the light emitted from the solid-state light source can be suppressed. [Brief description of the drawings]

[0019] [Figure 1] 1 is a block diagram showing the configuration of a power supply device which is an embodiment of a power supply device for a solid-state light source (SSL) according to the present invention; [Diagram 2] 1A and 1B are functional block diagrams of two examples of control units in the power supply device of this embodiment, where (a) detects effective voltage by A / D conversion, and (b) measures effective voltage by measuring conductive / non-conductive periods. [Diagram 3] A graph showing the transient response of illuminance when a voltage of 100V is applied from a state of 0 voltage for a PAR64 tungsten bulb (500W) and its replacement LED light. [Figure 4] A graph showing the transient response of illuminance when a voltage of 100V is applied and then cut off for a PAR64 tungsten bulb and its replacement LED light. [Diagram 5] A graph showing the transient response of illuminance when a voltage of 100V is applied from a state of 0 voltage for a PAR36 tungsten bulb (300W) and its replacement LED light. [Figure 6]A graph showing the transient response of illuminance when a voltage of 100V is applied and then cut off for a PAR36 tungsten bulb and its replacement LED light. [Figure 7] A graph showing the transient response of the illuminance when different voltages (100V, 40V, 20V) are applied to a PAR64 tungsten lamp and the corresponding transient response of a second-order Bessel filter. [Figure 8] This is a graph showing the actual measured values ​​and their linear approximation showing the relationship between the applied voltage and the cutoff frequency of a second-order Bessel filter for a PAR64 type tungsten lamp. [Figure 9] This is a graph showing the actual measured values ​​and their linear approximations showing the relationship between the applied voltage and the cutoff frequency of a second-order Bessel filter for a PAR36 tungsten lamp. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An LED power supply device, which is one embodiment of a power supply device for a solid-state light source (SSL) according to the present invention, will be described with reference to Figures 1 to 9. The configuration of this embodiment can also be applied when using other solid-state light sources such as EL.

[0021] 1 is a block diagram showing an electrical structure of a lighting system 1 including an LED lighting device 20 including a power supply device 21 according to an embodiment of the present invention, and a dimmer 10. The power supply device 21 of this embodiment receives power from the dimmer 10 and lights an LED 22 as a solid-state light source at an illuminance set by the dimmer 10. The power supply device 21 includes an input unit 23, a control unit 27, a lighting unit 28, etc., and the input unit 23 includes a power factor correction circuit. The control unit 27 is configured by a CPU.

[0022] An AC voltage having an effective voltage corresponding to the illuminance specified therein is input from the phase control dimmer 10. The input from the dimmer 10 is converted to a DC voltage by a power factor improvement circuit in the input unit 23. Based on this DC voltage, the control power supply unit 25 generates a voltage of about 5V for operating the control unit 27. It is desirable for the input unit to incorporate a large-capacity capacitor 24 in order to hold the energy required to increase the time constant when the power is turned off, which will be described later. Similarly, it is desirable for the control power supply unit 25 to have a storage function such as a small supercapacitor so that it can maintain control for the required time when the power is turned off.

[0023] The control unit 27 steps down the AC voltage output from the dimmer 10 using a voltage divider circuit 26, and performs the signal processing described below. There are two types of control units 27. One, as shown in Fig. 2(a), digitally calculates the effective voltage by high-speed sampling of the output of the dimmer 10 using A / D conversion, and the other, as shown in Fig. 2(b), uses a zero-cross converter to measure the conductive period and non-conductive period of the output of the dimmer, and calculates the effective voltage based on the measured period.

[0024] Hereinafter, the type of A / D conversion will be described. In this type of control section, the output from the dimmer 10 is input to the A / D converter 31, where the voltage value is converted into a digital signal at a predetermined sampling frequency. The sampling frequency is, for example, about 256 times the power supply frequency. That is, if the power supply frequency is 60 Hz, the sampling frequency is about 15.36 kHz, and if the power supply frequency is 50 Hz, the sampling frequency is about 12.80 kHz. The effective voltage of the output of the dimmer is detected by performing a process such as a moving average method on the sampled digital signal in this way (effective voltage detection section 33). The moving average method process here also serves to reduce the effect of spike-like noise contained in the output of the dimmer. Furthermore, when calculating the effective voltage, the spike-like noise may be more reliably removed by performing a process of removing the maximum and / or minimum values ​​of the digital signal input from the A / D converter 31 and then taking the average (noise removal circuit 32).

[0025] The effective voltage of the output of the dimmer obtained in this manner is filtered by a low-pass filter (LPF) 35. Here, the cut-off frequency (cut off f) 34 of the low-pass filter 35 is changed according to the effective voltage detected in advance. In this embodiment, the cut-off frequency is changed according to the magnitude of the effective voltage.

[0026] The PWM generator 36 generates a pulse signal of a predetermined frequency (e.g., 200 Hz) and sets the duty ratio of the signal to a value corresponding to the output of the low-pass filter 35. In this way, a PWM signal having a duty ratio corresponding to the effective voltage of the output from the dimmer 10, i.e., the illuminance value set by the dimmer, is input to the lighting unit 28, which pulses the direct current from the input unit 23 based on the signal and supplies it to the LED 22. In this way, the LED 22 lights up at an illuminance corresponding to the illuminance setting in the dimmer 10, and the low-pass filter 35 removes sudden changes in the power supply voltage, providing lighting with little flicker.

[0027] Hereinafter, the filtering process executed in the LED power supply device 21 of this embodiment will be described with reference to Figs. 3 to 9. Figs. 3 to 9 are graphs showing the results of an experiment for determining the type of digital filter and the cutoff frequency used in the filtering process executed in this embodiment. In this experiment, the time change (transient response) of illuminance was obtained when a voltage of a predetermined magnitude was applied to a tungsten light bulb, which is an incandescent light bulb (not an SSL such as an LED), from a state of zero voltage, and when the voltage was cut off (the voltage was set to zero) from a state in which a voltage of a predetermined magnitude was applied. In addition, the transient response of illuminance was obtained similarly for LED lights replacing these tungsten light bulbs when a similar voltage was applied and cut off without filtering.

[0028] First, the results of measuring the transient response of illuminance for a PAR64 tungsten light bulb with a power consumption of 500W and its substitute LED light when an effective voltage of 100V is applied from a voltage of 0 (Fig. 3) and when the voltage application is cut off (to 0 voltage) from a voltage of 100V applied (Fig. 4) are shown. In addition, the results of measuring the transient response of illuminance for a PAR36 tungsten light bulb with a power consumption of 300W and its substitute LED light when the same voltage is applied (Fig. 5) and cut off (Fig. 6) are shown. In both measurement results, it can be seen that the LED light has a more rapid change in illuminance than the tungsten light bulb. This rapid change in illuminance is one of the reasons why LEDs are prone to change in illuminance (flickering) when instantaneous voltage fluctuations such as noise occur. Therefore, in LEDs, flickering can be suppressed by controlling the change in illuminance that occurs when the voltage fluctuates in the same way as in tungsten light bulbs to be gentle.

[0029] Therefore, in this embodiment, the control unit 27 performs digital signal processing using a low-pass filter 35 to suppress abrupt changes in illuminance. Various types of low-pass filters such as a Bessel filter, a Butterworth filter, and a Chebyshev filter can be used for the low-pass filter 35. In this embodiment, the following experiment was performed to identify a filter that can provide an output closest to the transient response of a tungsten light bulb. In this experiment, experimental values ​​of the transient response were obtained when three different effective voltages, 100V, 40V, and 20V, were applied from a voltage 0 state to each of PAR64 type and PAR36 type tungsten light bulbs, and the experimental values ​​were compared with the calculated values ​​obtained from the low-pass filter calculation formula.

[0030] Figure 7 shows the experimental values ​​for the three effective voltages mentioned above for a PAR64 tungsten lamp, and the calculated values ​​obtained using a second-order Bessel filter. As in this example, the formula for calculating the second-order Bessel filter in the step response, which shows the response when the input (voltage) is changed in a stepwise manner from 0 to a specified value, is the transfer function G(s) shown below.

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[0031] Figure 8 shows a graph of the cutoff frequency of the second-order Bessel filter for each effective voltage applied to the PAR64 tungsten lamp obtained in Figure 7. As shown in Figure 8, the cutoff frequency is proportional to the effective voltage. A similar experiment was also performed on a PAR36 tungsten lamp to determine the cutoff frequency for each effective voltage. As shown in Figure 9, the cutoff frequency is proportional to the effective voltage (with a proportionality coefficient different from that of the PAR64 type).

[0032] So, the cutoff frequency ω c , the effective voltage V in and ω using a positive proportionality coefficient A determined for each tungsten lamp. c =AV inThat is, the cutoff frequency changer 34 changes the effective voltage V in The smaller the cutoff frequency ω of the low-pass filter 35, c Set (change) it so that it becomes small. In this case, the transfer function G(s) is

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[0033] In conventional SSL power supply devices, noise removal processing is performed under the same conditions (sampling intervals) regardless of the illuminance value indicated by the dimmer. Therefore, when the illuminance value indicated is small, flickering cannot be sufficiently suppressed. In contrast, in this embodiment, the cutoff frequency ω of the low-pass filter 35 becomes lower as the illuminance value indicated by the dimmer 10 becomes smaller. c Since the value of the illuminance is set small, flickering can be effectively prevented even when the illuminance indication value is small, which was a problem in the past when flickering was likely to occur.

[0034] Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above embodiment and various modifications are possible. [Explanation of symbols]

[0035] 1. Lighting system 10...Light control device 20...LED lighting device 21…Power supply device 22...LED 23...Input section 24…Capacitor 25…Control power supply section 26…Voltage divider circuit 27...Control section 28…Lighting section 31...A / D converter 32...Noise elimination circuit 33...Effective voltage detection section 34…Cutoff frequency change section 35...Low pass filter 36…PWM generator

Claims

1. An apparatus for supplying power to a solid-state light source based on an output of a dimmer, comprising: a) an effective voltage detection unit which receives an output of the dimmer device, detects an effective voltage of the output, and outputs a value of the effective voltage; b) a low-pass filter using a Bessel filter provided on the output side of the effective voltage detection unit; c) a cutoff frequency changing unit that changes a cutoff frequency of the low-pass filter in accordance with the effective voltage detected by the effective voltage detection unit; d) a PWM unit that generates a pulse width modulation signal based on an output of the low pass filter; e) a lighting unit that generates a pulsed direct current according to an output of the PWM unit from an output of the dimmer device and supplies the pulsed direct current to the solid-state light source; A power supply device for a solid-state light source comprising:

2. 2. The power supply device for a solid-state light source according to claim 1, wherein the effective voltage detection section detects the effective voltage based on an output obtained by inputting a voltage output from a dimmer and performing analog-to-digital conversion.

3. 2. The power supply device for a solid-state light source according to claim 1, wherein the effective voltage detection unit detects a current-carrying period or a non-current-carrying period of a phase-controlled voltage output from the dimmer device, and detects the effective voltage based on the current-carrying period or the non-current-carrying period.

4. 2. The power supply device for a solid-state light source according to claim 1, wherein the low-pass filter is a second-order Bessel filter.

5. 5. The power supply device for a solid-state light source according to claim 4, wherein the cutoff frequency changing section changes the cutoff frequency so that the cutoff frequency is proportional to the effective voltage detected by the effective voltage detection section with a positive proportionality coefficient.

6. 2. The power supply device for a solid-state light source according to claim 1, wherein the effective voltage detection section detects the effective voltage after performing a process to remove spike noise contained in the output of the dimmer.

7. 7. A lighting device comprising: the solid-state light source power supply device according to claim 1; and a solid-state light source connected to an output side of the lighting unit.

8. A lighting system comprising: the lighting device according to claim 7; and a dimmer connected to an input side of the effective voltage detector.

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