LED drive device and stage lighting light

Abstract

To provide an LED drive device and a stage lighting light that both suppress flickers and improve the ease of dimming control.SOLUTION: Provided is an LED drive device comprising a computation control unit and a converter circuit, and performing light emission drive of an LED on the basis of a dimming control signal. The LED drive device is characterized in that the converter circuit includes a switching element, a smoothing inductor, and a smoothing capacitor, the smoothing capacitor being constituted by a first capacitor connected to the power supply side and a second capacitor connected to the smoothing inductor side that are connected in series, and the second capacitor being a capacitance variable capacitor having such a characteristic that the electrostatic capacitance gradually decreases as the voltage between both ends rises.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention mainly relates to an LED driving device mounted on a lighting fixture for stage lighting used in places such as a theater stage or a television studio, and a lighting fixture for stage lighting provided with the LED driving device.

Background Art

[0002] A lighting device using an LED as a light source is widely used as a lighting fixture for stage lighting in a theater stage, a television studio, an arena, etc. In order to obtain a high-quality production effect, in the lighting device, it is essential to take measures against so-called flicker, that is, the fluctuation of the light output caused by the pulsating current flowing through the LED (see Patent Document 1). In the lighting device described in Patent Document 1, by appropriately setting the ripple rate of the output current, the change in the light emission amount at a level visible to the user is suppressed, and the flicker in a high-brightness environment is reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] FIG. 6 shows an example of a conventionally known LED driving device that is mounted on a lighting fixture for stage lighting. As shown in FIG. 6, when supplying a DC current to an LED using a buck chopper circuit, a smoothing capacitor is connected in parallel with the LED. In order to suppress flicker even at high output, it is effective to increase the capacitance. However, if the capacitance is increased, when dimming is performed, especially when gradually increasing the output from a state where the lighting output is completely off, the LED starts lighting after the charging of the capacitor is completed, resulting in a delay in operation and a sudden increase in the dimming output, deteriorating the operability. That is, it is desirable to have as little capacitance as possible for improving the operability of dimming. Thus, measures against flicker and improvement of the operability of dimming are in an antinomic relationship.

[0005] Also, even if an attempt is made to adopt a small capacitance within a practical range, capacitors with a small capacitance that can withstand a smoothing current are few in variety and difficult to obtain. Even if they can be obtained, such capacitors are often expensive, and an increase in cost is inevitable.

[0006] An object of the present invention is to address such problems and to provide an LED driving device and a lighting fixture for stage lighting that can achieve both suppression of flicker and improvement of the operability of dimming.

Means for Solving the Problems

[0007] In order to achieve such an object, the technical means according to the present invention is an LED driving device that at least includes the following configuration.

[0008] An LED driving device comprising an arithmetic control unit and a converter circuit, which performs light emission driving of an LED based on a dimming control signal, wherein the converter circuit has a switching element, a smoothing inductor, and a smoothing capacitor, and the smoothing capacitor is configured by serially connecting a first capacitor connected to the power supply side and a second capacitor connected to the smoothing inductor side, and the second capacitor is a variable capacitance capacitor having a characteristic that its capacitance gradually decreases as the voltage across its terminals increases.

[0009] In order to achieve such an object, a lighting device for stage lighting according to the present invention comprises at least the following configuration.

[0010] A lighting device for stage lighting having an arithmetic control unit and a converter circuit, and comprising an LED driving device that performs light emission driving of an LED based on a dimming control signal, wherein the converter circuit has a switching element, a smoothing inductor, and a smoothing capacitor, and the smoothing capacitor is configured by serially connecting a first capacitor connected to the power supply side and a second capacitor connected to the smoothing inductor side, and the second capacitor is a variable capacitance capacitor having a characteristic that its capacitance gradually decreases as the voltage across its terminals increases.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the configuration of the LED driving device according to the embodiment of the present invention will be described with reference to the drawings. In the following description, the same reference numerals in different figures indicate parts having the same function, and duplicate descriptions in each figure are omitted as appropriate.

[0013] 〔First Embodiment〕 (Circuit Configuration of LED Driving Device) FIG. 1 is a circuit configuration diagram of the LED driving device A according to the first embodiment of the present invention. As shown in FIG. 1, the LED driving device A includes a microcomputer 1A and a converter circuit 2A. A control signal output from the microcomputer 1A is input to the switching element Tr1, and the converter circuit 2A is driven by PWM control to perform dimming control of the LED1. Although not shown, the LED driving device A is mounted on an LED profile spotlight, which is one of the lights for stage lighting.

[0014] The microcomputer 1A functions as a control circuit (arithmetic control unit) that receives a dimming control signal such as DMX from a console (not shown) and generates a PWM control signal with a different pulse width modulation rate according to a desired illuminance. However, as the control circuit (arithmetic control unit), instead of a microcomputer, it may be constructed with an FPGA, an ASIC, etc., and the control for controlling the illuminance may also be PFM control instead of PWM control.

[0015] As shown in FIG. 1, the converter circuit 2A uses a step-down chopper type, and as a control method, a discontinuous current mode is used. To simplify the explanation, in FIG. 1, only one LED, LED1, is shown, but actually, the converter circuit 2A is composed of a plurality of circuits (first converter circuit, second converter circuit, third converter circuit...) corresponding to the number of a plurality of LEDs.

[0016] As shown in FIG. 1, in the converter circuit 2A, an output terminal to which LED1 is connected, a smoothing capacitor Cs, and a freewheeling diode D1 are connected in parallel to a 54V power supply Vin. Between the connection point of the output terminal on the non-power supply side and the smoothing capacitor Cs, and the anode of the freewheeling diode D1, a current detection sensor CT1 for temperature correction and a smoothing inductor L1 for current smoothing are inserted.

[0017] Regarding the smoothing capacitor Cs, in order to improve the dimming operability, it is preferable that the capacitance is as small as possible at the start of LED lighting, and in order to suppress flicker, the capacitance is as large as possible at the rated output of the LED. To realize such voltage-capacitance characteristics, the smoothing capacitor Cs is constructed by connecting a first capacitor C1 connected to the power supply side and a second capacitor C2 connected to the smoothing inductor L1 side in series, as shown in FIG. 1. As the first capacitor C1, An electrolytic capacitor with a capacitance of 150 μF (manufactured by Panasonic, EEHZS1J151P) was used. As the second capacitor C2, three multilayer ceramic capacitors (ferroelectric capacitors) with a capacitance of 22 μF (manufactured by Murata Manufacturing Co., Ltd., GRT21BR61E226ME13L) were connected in parallel so that the combined capacitance as C2 was 66 μF. Here, the three capacitors are connected in parallel for capacitance adjustment and convenience of component procurement. Of course, in principle, one ferroelectric capacitor with a capacitance of 66 μF could be used. That is, as long as there is one ferroelectric capacitor with an appropriate capacitance, the number of elements can be reduced. Conversely (regardless of the number of elements), in addition to the three parallel capacitors, a Zener diode for overvoltage protection may also be connected in parallel.

[0018] Figure 2 is a graph showing the voltage-capacitance characteristics of the electrolytic capacitor, which is the first capacitor in the LED driving device A according to the first embodiment of the present invention, and the ferroelectric capacitor, which is the second capacitor. However, this is for explanatory purposes to understand the principle of the invention and does not show actual measurement data itself. The electrolytic capacitor has a constant capacitance until the voltage changes from 0% to 100% of the rated voltage, while the ferroelectric capacitor has a characteristic that its capacitance gradually decreases as the voltage increases. Such characteristics are not preferable because they cause distortion in the voltage and current passing through the capacitor when used in an electronic circuit and increase the pulsating current during smoothing. However, since they are small in size and can provide a large capacitance, they are actually widely used.

[0019] For the first capacitor C1 and the second capacitor C2, the resistance values of the first resistor R1 and the second resistor R2 connected in parallel to each of them are preferably selected so that the voltage across the first capacitor C1 becomes the maximum output voltage of the LED1 at the rated output of the LED1. Here, R1 = 33 kΩ and R2 = 20 kΩ. Also, in order to cope with individual differences in LED characteristics, the second resistor may be configured as a series connection of two resistors, a variable resistor and a fixed resistor, and the variable resistor may be arranged on the first resistor side.

[0020] (Circuit characteristics of the LED driving device) The circuit characteristics of the LED driving device A according to the first embodiment of the present invention will be described. FIG. 3 is a circuit configuration diagram for explaining the circuit operation of the LED driving device A according to the first embodiment of the present invention, and FIG. 4 is a graph showing the voltage-capacitance characteristics of the smoothing capacitor in the LED driving device A according to the first embodiment of the present invention.

[0021] As described in the above explanation of the circuit configuration and as shown in FIG. 3, the LED driving device A has a configuration in which two types of capacitors are connected in series and a voltage dividing circuit is connected. The electrolytic capacitor as the first capacitor C1 has a larger capacitance than the ceramic capacitor as the second capacitor C2, and the total capacitance is set to be approximately only C2. When charging C1 by the voltage dividing circuit, the voltage dividing circuit is adjusted so that the voltage across C1 becomes the same as the voltage across LED1 at the maximum output. As can be understood from the voltage-capacitance characteristics in FIG. 4, the voltage Vc2 across C2 is the voltage obtained by subtracting the voltage Vc1 of C1 from the voltage Vled across LED1. When the voltage across LED1 is low at the time of turning off the light or starting dimming, the capacitance Cs as the combined capacitance decreases, so the rising characteristic at the start of dimming is good. As the output is increased and the voltage Vled across LED1 rises, the voltage Vc2 across C2 decreases according to its voltage-capacitance characteristics, while the capacitance of C2 increases. At the maximum output, the voltage Vc2 across C2 approaches 0V and the capacitance is also maximum, so flicker can be sufficiently reduced.

[0022] [Second Embodiment] (Circuit configuration of the LED driving device) FIG. 5 is a circuit configuration diagram of the LED driving device B according to the second embodiment of the present invention. As shown in FIG. 5, the LED driving device B includes a microcomputer 1B and a converter circuit 2B. A control signal output from the microcomputer 1B is input to a switching element Tr1, and the converter circuit 2B is driven by PWM control to perform dimming control of the LED1. In the first embodiment, the load current was monitored for thermal correction, but in the second embodiment, the voltage value of the LED output is monitored so that the bias voltage can be adjusted from the microcomputer as a control circuit (arithmetic control unit).

[0023] Using the first embodiment, it was explained that the capacitance of the smoothing capacitor can be made variable. However, in actual implementation, there is a problem that the range of the variable amount changes depending on the characteristics of the LED used and the characteristics of the capacitor itself. For this reason, when implementing, it is necessary to adjust the voltage dividing circuit or change the capacitor according to the LED to be used. Also, when replacing the board for maintenance or the like, adjustment and confirmation are required, which increases the amount of work. Therefore, in order to eliminate such manual adjustment, the bias voltage is automatically adjusted by the microcomputer.

[0024] Specifically, a control current for a bias voltage that gives the optimum capacitance of the smoothing capacitor from the monitored output voltage and the output setting to the LED is output via a microcomputer and a DA converter, and the control current is input to the base of a bipolar transistor and automatically adjusted by the microcomputer so that an appropriate bias voltage is generated. In this way, by adopting a configuration in which the bias voltage can be changed from the microcomputer and adjusted to the optimum capacitance, it becomes possible to handle LEDs with different voltages at the time of lighting without manual adjustment. Also, when using an LED with a small difference in voltage between the off state and the on state, it becomes possible to continuously change the bias voltage from the microcomputer during lighting, so that it is possible to handle multiple types of LEDs without changing parts. Note that the control circuit (arithmetic control unit) may be constructed of an FPGA, an ASIC, etc. instead of a microcomputer, the monitoring target may be the output voltage and the output setting, and further, both the voltage and the current may be monitored. Also, the amplifier using a bipolar transistor may be composed of a unipolar transistor (such as a field effect transistor) or an operational amplifier.

[0025] According to the description of the embodiments so far, it is considered that the specific effect of the LED driving device of the embodiment, which can achieve both flicker suppression and improvement of dimming operability, can be understood. In addition to this, the LED driving device of the embodiment is also advantageous in terms of component procurement. In the prior art, when using a single capacitor for smoothing, a capacitor with a large capacitance is used in advance considering a decrease in capacitance, or a capacitor with a high withstand voltage is selected for use at a voltage with little change in capacitance. However, in any case, multiple capacitors are connected in series or in parallel and used, or a large capacitor is used, resulting in an increase in cost and difficulty in obtaining. Although ferroelectric capacitors are not inexpensive, they are still less costly and easier to obtain than selecting a single capacitor that meets the above conditions.

[0026] As described above, the LED driving device and the lighting fixture for stage lighting according to the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and design changes and the like within the scope not departing from the gist of the present invention are also included in the present invention. For example, although the object on which the LED driving device is mounted has been described as an LED profile spotlight, the present invention is also applicable to other lighting fixtures for stage lighting such as LED border lights and LED horizon lights. Further, although the inventor is not well-informed and does not know, assuming that there is, or has been developed, a capacitor having a characteristic that its capacitance gradually increases as the voltage increases, which is in line with the technical idea of the present invention, it will be possible to realize an LED driving device that is in line with the present invention with such a single capacitor having such characteristics.

[0027] In addition, unless there are particular contradictions or problems in the purpose, configuration, etc. of the above-described embodiments, it is possible to cross-use and combine their technologies with each other.

Explanation of Reference Numerals

[0028] A…………LED driving device 1A………Microcomputer 2A………Converter circuit Vin……Power supply Cs………Smoothing capacitor C1………First capacitor C2………Second capacitor L1………Smoothing inductor D1………Freewheeling diode B…………LED driving device 1B………Microcomputer 2B………Converter circuit

Claims

1. An LED driving device including an arithmetic control unit and a converter circuit, which performs light emission driving of an LED based on a dimming control signal, The converter circuit has a switching element, a smoothing inductor, and a smoothing capacitor, The smoothing capacitor is configured by connecting a first capacitor connected to the power supply side and a second capacitor connected to the smoothing inductor side in series, The second capacitor is a variable capacitance capacitor having a characteristic that its capacitance gradually decreases as the voltage across both ends increases An LED driving device characterized by this.

2. The variable capacitance capacitor is a ferroelectric capacitor The LED driving device according to claim 1, characterized by this.

3. The first capacitor is an electrolytic capacitor The LED driving device according to claim 1, characterized by this.

4. The capacitance of the first capacitor and the capacitance of the second capacitor are selected so that the combined capacitance of the smoothing capacitor is optimal both at the start of lighting of the LED and at the rated output of the LED. The LED driving device according to claim 1, characterized by this.

5. The combined capacitance of the smoothing capacitor is set to be sufficiently small to improve dimming operability at the start of lighting of the LED, and to be sufficiently large to suppress flicker at the rated output of the LED. The LED driving device according to claim 1, characterized by this.

6. An amplifier for varying the bias voltage applied to the variable capacitance capacitor is provided, The voltage value of the LED output is input to the arithmetic control unit, The arithmetic control unit outputs a bias control signal for adjusting the bias voltage applied to the variable capacitance capacitor in order to obtain an optimal capacitance according to the output of the LED, The bias control signal is input to the amplifier The LED driving device according to claim 1, characterized by this.

7. Equipped with the LED driving device according to any one of claims 1 to 6 A lighting fixture for stage lighting characterized by this.

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