JP2019125446A - Led drive circuit, led lighting device, led lighting system, and led driving method - Google Patents

Abstract

To provide an LED drive circuit capable of dimming the output light of an LED element and capable of easily changing the wavelength of the output light of the LED element.SOLUTION: An LED drive circuit that controls the brightness and emission wavelength of output light of an LED element includes an NPN transistor 10 in which a collector terminal C is connected to the cathode side of the LED element and an emitter terminal E is grounded via a current control resistor 20, and a PWM signal generation circuit 30 that generates a PWM signal to be input to a base terminal B of the NPN transistor 10. The PWM signal generation circuit 30 includes a CPU 31 having a pulse signal generation unit that generates a pulse signal whose voltage waveform changes in a rectangular shape and a PWM control unit that controls a duty ratio of the pulse signal, and a voltage increase/decrease circuit 32 and a switching resistor unit 33 as a voltage control unit for controlling the signal strength of the pulse signal.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an LED drive circuit, an LED illumination device, an LED illumination system, and an LED drive method, and more specifically, controls the brightness of output light of the LED element and controls the color of output light of the LED element The present invention relates to an LED driving circuit, an LED lighting device, an LED lighting system, and an LED driving method that can be performed.

  In recent years, various lighting devices using LED (light emitting diode) elements as a light source are in widespread use. Furthermore, even in illumination devices that require high-intensity illumination light such as performance illumination devices used in theaters and studios, LED elements are used instead of light bulbs such as halogen lamps as light sources It is coming. LED devices have the advantage of consuming very little power and generating heat compared to conventional light sources such as halogen lamps.

  Further, Patent Document 1 describes a lighting device that dims LED elements by PWM (Pulse Width Modulation) control so that the color of the irradiation light does not change.

JP, 2015-144080, A

By the way, since a conventional light bulb such as a halogen lamp has a broad emission wavelength spectrum, in a lighting device for effect using such a light source, a color filter is used to obtain a desired color.
On the other hand, since the LED element has the emission wavelength spectrum of the bright line spectrum, for example, the desired color is obtained by adjusting the balance of the emission intensities of the three types of LED elements respectively corresponding to the three primary colors. Specifically, a color within a range surrounded by triangles connecting three points on the chromaticity diagram respectively corresponding to the three primary colors outputted by the LED element can be obtained as a mixed color.

  However, in a lighting device using three types of LED elements, it is difficult to obtain a color corresponding to the area outside the triangle on the chromaticity diagram. For example, it is difficult to obtain both blue-green and yellow-green colors with only three LED elements corresponding to three primary colors. Specifically, in order to obtain a bluish green color, a bluish green color can be obtained by using a green LED element having a higher peak wavelength of output light, ie, a green color LED element that outputs bluish green color. It becomes difficult to obtain yellowish green. Conversely, yellow green can be obtained by using a green LED element having a lower peak wavelength of output light, that is, a green LED element that outputs yellowish green, but this time to obtain blue green. Is difficult.

  On the other hand, lighting devices for stage effects and the like are required to represent a wide range of colors including bluish green and yellowish green. For example, Horizon Lights, which is a type of lighting equipment for presentation, can be used to represent various sky colors, such as dusk at dusk and dusk twilight, as well as daytime blue sky, in the stage background. Required Such an empty color has an important effect in stage production, so that horizon lights using LED elements as light sources can also represent a wide range of colors, similar to horizon lights using conventional halogen lamps as light sources. Is required.

In addition, if the kind of luminescent color of a LED element is increased, the range of the color which can be output can be expanded. For example, if a total of four types of LED elements, that is, a green LED element that outputs bluish green and a green LED element that outputs yellowish green are provided in addition to red and blue LED elements, bluish A green LED element that outputs a hazy green color can be turned on to generate a bluish green color, and a green LED element that outputs a yellowish green color can be turned on to generate a yellow-green color.
However, increasing the type of color of the LED element is not preferable because it increases the manufacturing cost of the lighting device.

  The present invention has been made in view of the above circumstances, and can control the light output from the LED element and can easily change the wavelength of the output light from the LED element, LED lighting An object of the present invention is to provide an apparatus, an LED lighting system and an LED driving method.

  As a result of repeated studies and experiments, the inventor of the present invention has focused on the characteristics of the LED element that the color of the output light may change when the driving current of the LED element is changed. Although such characteristics of the LED element are generally considered to be undesirable, the present inventors have completed the present invention by taking advantage of such characteristics.

  The LED drive circuit of the present invention is an LED drive circuit that controls the brightness and emission wavelength of the output light of the LED element, and the first terminal is connected to the cathode side of the LED element, and the second terminal is a current control resistor. And a PWM signal generation circuit for generating a PWM signal input to a control terminal of the bipolar transistor, the PWM signal generation circuit comprising: a pulse signal whose voltage waveform changes in a rectangular shape And a PWM control unit for controlling the duty ratio of the pulse signal, and a voltage control unit for controlling the signal intensity of the pulse signal.

  According to the LED drive circuit of the present invention, the output light of the LED element can be dimmed by PWM control, and the signal strength of the pulse signal is controlled to control the drive current of the LED element. The wavelength of the output light of the element can be easily changed.

  Further, the LED lighting device of the present invention comprises at least three types of LED elements outputting light of different wavelengths, and the LED driving circuit of the present invention driving at least one type of the at least three types of LED elements. It is characterized by being equipped.

  According to the LED lighting device of the present invention, since the light emission wavelength of at least one type of LED element can be changed by the LED driving circuit of the present invention, the color range of mixed light output from the LED lighting device is expanded. be able to.

  In the LED lighting system of the present invention, the LED lighting device of the present invention, the light control signal for controlling the brightness of the output light of the LED element, and the emission wavelength of the output light of the LED element The PWM control unit of the LED drive circuit controls the duty ratio of the pulse signal according to the dimming signal, and the PWM control unit of the LED drive circuit The voltage control unit controls the signal strength of the pulse signal in accordance with the color adjustment signal.

  According to the LED lighting system of the present invention, by inputting the light control signal and the color adjustment signal from the operation unit to the LED lighting device, the output light of the LED element is easily dimmed, and the output light of the LED element is The wavelength can be easily changed

  Further, according to the LED driving method of the present invention, the PWM signal is input to the base terminal of the NPN transistor whose collector terminal is connected to the cathode side of the LED element and whose emitter terminal is grounded via the current control resistor. In the LED driving method for driving the LED element, a pulse signal is generated, and a duty ratio of the pulse signal is controlled to control brightness of the LED element and control a signal voltage of the pulse signal. Thus, the emission wavelength of the LED element is controlled.

  According to the LED driving method of the present invention, the output light of the LED element can be easily dimmed by PWM control, and the light emission wavelength of the LED element can be easily changed by controlling the signal voltage of the pulse signal. can do.

  According to the LED driving circuit, the LED lighting device, the LED lighting system, and the LED driving method of the present invention, it is possible to easily dim the output light of the LED element and to easily change the wavelength of the output light of the LED element it can.

It is a block diagram of the LED lighting system concerning a 1st embodiment of the present invention. It is a circuit diagram of the LED drive circuit concerning a 1st embodiment of the present invention. It is a chromaticity coordinate explaining the color range of the output light of the LED lighting apparatus which concerns on 1st Embodiment of this invention, and an LED lighting system. It is a time chart of the LED drive circuit concerning a 1st embodiment of the present invention. It is a circuit diagram of the LED drive circuit concerning a 2nd embodiment of the present invention. It is a time chart of the LED drive circuit concerning a 2nd embodiment of the present invention. It is a block diagram of the LED lighting system which concerns on 3rd Embodiment of this invention. It is a circuit diagram of the LED drive circuit concerning a 3rd embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First Embodiment
FIG. 1 shows a block diagram of an LED lighting system according to a first embodiment of the present invention. As shown in the figure, the LED lighting system is configured of an LED lighting device 2 including an LED drive circuit 1 for driving LED elements, and an operation unit (console) 3.

The LED lighting device 2 according to the present embodiment includes, for example, three types of LED elements that constitute a horizon light and output three primary colors of red, green, and blue. The red LED element has a peak wavelength in the wavelength range of, for example, 570 to 690 nm, the green LED element has a peak wavelength in the wavelength range of, for example, 460 to 620 nm, and the blue LED element has, for example, 420 to 530 nm It has a peak wavelength within the wavelength range. Here, the peak wavelength of the LED element refers to the wavelength at which the emission intensity is maximum among the emission spectrum of the LED element.
Although the three types of LED elements are driven by separate LED drive circuits 1, FIG. 1 shows only one block of the three LED drive circuits 1 as a representative.

  Further, the operation unit 3 is provided with means for adjusting the brightness of the LED element and means for adjusting the color of the LED element. These adjustment means can be configured by a slide bar, a rotary knob, or a toggle switch or other mechanism.

  The operation unit 3 controls the light adjustment signal for controlling the brightness of the output light of the LED element as an external signal to each of the three LED drive circuits 1 of the LED lighting device 2 and the emission wavelength of the output light of the LED element The toning signal to be input is input. Each LED drive circuit 1 controls the brightness and the color of the LED element as described below. The external signal may be a DMX signal.

  FIG. 2 shows a circuit diagram of the LED drive circuit 1. The LED drive circuit shown in the figure includes an NPN transistor 10 (TR1), a current control resistor 20 (1 LIMIT), and a PWM signal generation circuit 30. In the NPN transistor 10, a collector terminal C is connected to the cathode side of the LED element D1 as a first terminal, and an emitter terminal E is grounded via a current control resistor 20 as a second terminal. Further, a DC constant voltage (DC +) is applied to the anode side of the LED element D3.

  The PWM signal generation circuit 30 combines a pulse signal generation unit that generates a pulse signal whose voltage waveform changes in a rectangular shape and a PWM control unit that controls the duty ratio of the pulse signal; And a switching resistance unit 33 as a voltage control unit for controlling the wave height of

The CPU 31 controls the duty ratio of the PWM signal in accordance with the dimming signal as an external signal input from the operation unit 3 to the CPU 31. Further, the CPU 31 outputs a resistance switching signal to the switching resistor unit 33 according to the color adjustment signal as an external signal. In response to the switching signal, the switching resistor unit 33 switches a resistor (not shown) to control the signal strength of the PWM signal input to the voltage increase / decrease circuit 32. In the example shown in FIG. 1, while the wave height of the voltage waveform of the PWM signal input to the voltage increase / decrease circuit 32 is VA (for example, VA = 1.0 V), the PWM signal output from the voltage increase / decrease circuit 32 The wave height of the voltage waveform is amplified to VB (e.g., VB = 1.1 to 5.0 V).
The voltage increase / decrease circuit 32 can also make the output PWM signal strength lower than the signal strength of the input PWM signal.
Thus, the PWM signal generation circuit 30 controls the duty ratio of the PWM signal and controls the signal strength of the PWM signal.

  In addition, in order to facilitate reproduction of a desired color, when the external signal input to the CPU 31 disappears, a stored signal is output from the CPU 31 to the switching resistance unit 33, and the switching resistance unit 33 stores the immediately preceding resistance. Is preferred.

  The PWM signal generated by the PWM signal generation circuit 30 is input to the base terminal B of the NPN transistor 10 via the current limiting resistor R1. Therefore, the wave height VB of the PWM signal generated by the PWM signal generation circuit 30 becomes the base voltage VB of the NPN transistor 10.

  The NPN transistor 10 functions as a switching element in PWM control. The NPN transistor 10 turns on when the voltage level of the voltage waveform of the PWM signal input to the base terminal B is intermittently “high” according to the duty ratio, and causes the LED drive current IF to flow. . Thus, the lower the duty ratio, the darker the LED element, while the higher the duty ratio of the PWM signal, the brighter the LED element. Therefore, the brightness of the LED element is controlled by controlling the duty ratio of the PWM signal.

By the way, in the case of normal PWM control, the NPN transistor 10 merely functions as a switching element as described above.
However, in the present embodiment, the NPN transistor 10 functions not only as a simple switching element, but also as a current control element that reflects the signal strength of the PWM signal on the magnitude of the LED drive current IF as described below. Do.

Generally, the voltage between the base B and the emitter E of the NPN transistor is substantially constant (for example, about 0.7 V). Therefore, when the base voltage VB rises, the emitter voltage VE also rises.
For example, when base voltage VB = 1.0 V, emitter voltage VE = 1-0.7 = 0.3 V, while when base voltage VB = 5.0 V, emitter voltage VE = 5-0. .7 = 4.3V.

  The emitter current IE at the emitter voltage VE is a value obtained by dividing the emitter voltage VE by the current control resistor 20 (1 (Ω) LIMIT). Furthermore, the emitter current IE is substantially equal to the drive current IF of the LED element that is the collector current IC (for example, the collector current IC is 95 to 99% of the emitter current IE).

Therefore, the drive current IF of the LED element is expressed as a function of the signal strength VB of the PWM signal, which is the base voltage VB, as shown in equation (1).
IF (A) ≒ (VB−0.7 (V)) ÷ 1 (Ω) LIMIT (1)
And, as apparent from the equation (1), when the base voltage B rises, the LED
The drive current IF of the element also rises.

  In order to keep the collector voltage VC higher than the emitter voltage VE, the base voltage VB should be controlled in a range satisfying VC−0.7 ≧ VB. The collector voltage VC is a value obtained by subtracting the voltage drop of the LED element from the DC constant voltage (DC +) applied to the LED element.

  In the LED element, the light emission wavelength may become longer as the drive current IF becomes smaller, and the light emission wavelength may become shorter as the drive current IF becomes larger. Therefore, as apparent from the above equation (1), the lower the signal intensity VB of the PWM signal generated by the voltage control unit 32, the longer the light emission wavelength of the LED element, and the higher the signal intensity VB. The emission wavelength of the LED element is shortened. Therefore, by controlling the signal intensity VB of the pulse signal, the emission wavelength of the LED element, that is, the tint is controlled.

  The light emission intensity of the LED element is determined by both the duty ratio of the PWM signal and the LED drive current IF. Therefore, when the LED drive current IF is increased in order to change the color of the LED elements, the duty ratio of the PWM signal may be reduced in order to maintain the LED elements at a desired brightness. Also, conversely, when the LED drive current IF is reduced to change the color of the LED element, the duty ratio of the PWM signal may be increased to maintain the LED element at a desired brightness. Similarly, in the other embodiments, it is preferable to control both the duty ratio of the PWM signal and the LED drive current IF.

Next, with reference to the chromaticity diagram of FIG. 3, the relationship between the signal strength of the PWM signal and the mixed color output from the LED lighting device 2 will be described.
First, the color of the output light of the red LED element is indicated by a point R, and the color of the output light of the blue LED element is indicated by a point B on the XY coordinates of the chromaticity diagram.

Furthermore, the signal intensity of the PWM signal is low, the emission wavelength of the green LED element is long, and the color of the output light of the green LED element when the yellowish green light is output is indicated by a point G1.
At this time, the LED lighting device 2 can express the color in the range surrounded by the solid triangle with the points R, B, and G1 as the apex as a mixed color. This range includes yellowish green corresponding to a region indicated by a broken line circle yg in the chromaticity diagram. Therefore, when the signal strength of the PWM signal is low, yellowish green can be expressed.

The point G2 indicates the color of the output light of the green LED element when the bluish green light is output because the signal strength of the PWM signal is high and the emission wavelength of the green LED element is shortened.
At this time, the LED lighting device 2 can express the color in the range surrounded by the dashed triangle with the points R, B, and G2 as vertices as a mixed color. This range includes a blue-green color corresponding to the area indicated by the broken line circle gb in the chromaticity diagram. Therefore, when the signal strength of the PWM signal is low, bluish green can be expressed.
In any case, white corresponding to a region indicated by a broken circle w in the chromaticity diagram of FIG. 3 can be expressed as a mixed color of three primary colors.

Therefore, when expressing yellowish green, a color adjustment signal for reducing the signal strength of the PWM signal is input as an external signal from the operation unit 3 to the CPU 31 of the LED drive circuit 1 of the green LED element of the LED lighting device 2 It is good to do.
On the other hand, when expressing blue-green, the color adjustment signal for increasing the signal intensity of the PWM signal as an external signal from the operation unit 3 to the CPU 31 of the LED drive circuit 1 of the green LED element of the LED lighting device 2 It is good to input
Thus, the LED lighting device 2 and the LED lighting system of the present embodiment can expand the range of expressible colors without increasing the types of LED elements.

Next, with reference to a time chart shown in FIG. 4, an operation example of the LED drive circuit 1 for driving the green LED element will be described.
The upper part of the time chart represents the PWM signal output from the CPU 31, the middle part represents the resistance switching signal output from the CPU 31 to the switching resistor unit 33, and the lower part represents the PWM signal output from the voltage increase / decrease circuit 32. .

  As shown in the upper timing chart, the PWM signal starts from a duty ratio of 0% (off state), gradually increases the duty ratio to 100% (full light state), and again gradually increases the duty ratio to 0%. Is decreasing.

At time t1, the resistance switching signal remains L, and the signal strength of the PWM signal output from the voltage increase / decrease circuit 32 and input to the base terminal B of the NPN transistor 10 remains low. At this time, the color of the output light of the green LED element is yellowish green, and corresponds to point G1 on the chromaticity diagram of FIG.
Therefore, from the start to t2, the green LED gradually increases in brightness with yellowish green output light.

  Next, at time t2, the resistance switching signal switches from L to H. As a result, the signal strength of the PWM signal output from the voltage adjusting circuit 32 is increased. At this time, the color of the output light of the green LED element changes to bluish green, and changes from point G1 to point G2 on the chromaticity diagram of FIG. 3.

Then, from t2 to t3, the green LED is a bluish green output light, and the brightness is gradually increased to the full light state.
Further, after t3, the green LED is a bluish green output light, and the brightness gradually decreases from t4 to t2 from the full light state to the off state.

When the LED lighting device 2 is a horizon light, for example, the background is gradually brightened in yellowish green and changed to bluish green at time t2 by combining the operation of the green LED element described above with the red and blue LED elements It is possible to turn on all the light at time t3, and then to turn it dark and gradually turn blue and green.
In addition, in the operation unit 3 of the LED illumination system, for example, the above-described effect can be expressed by switching the color adjustment signal at time t2 while performing the light adjustment operation.
As described above, according to the LED lighting device 2 and the LED lighting system of the present embodiment, even if there are only three types of LED elements corresponding to three primary colors, a wide range of colors can be expressed.

Second Embodiment
FIG. 5 shows a circuit diagram of an LED drive circuit according to a second embodiment of the present invention.
In addition, in this embodiment, the same code | symbol is attached | subjected to the component same as the LED drive circuit of 1st Embodiment, and the detailed description is abbreviate | omitted.
Further, by incorporating the LED drive circuit of the present embodiment instead of the LED drive circuit of the first embodiment, the LED lighting device and the LED lighting system of the present invention can be configured as in the first embodiment. .

As shown in the figure, the LED drive circuit of the second embodiment adds a second current control resistor 22 and changes the combined resistance of the current control resistor 20 and the second current control resistor 22. It is provided.
In the adjustment circuit 20a, the second current control resistor 22 is grounded via the second NPN transistor 12 (TR2). The ON / OFF state of the second NPN transistor 12 is controlled by the pulse current adjustment signal input from the CPU 31 to the base terminal B, and the second NPN transistor 12 functions as a switching element of the emitter current flowing through the second NPN transistor 12.

  When the second NPN transistor 12 is in the OFF state, the emitter current flows only through the first current control resistor 20. On the other hand, when the second NPN transistor 12 is in the ON state, the emitter current flows through both the first current control resistor 20 and the second current control resistor 22 connected in parallel thereto. In this case, since the combined resistance of the first and second current control resistors 20 and 22 is smaller than that of the first current control resistor 20 alone, the emitter current is increased. As a result, the LED drive current IF also increases, and the emission wavelength of the LED element becomes shorter.

Next, with reference to a time chart shown in FIG. 6, an operation example of the LED drive circuit according to the second embodiment for driving the green LED element will be described.
The first stage from the top of the time chart represents the PWM signal output from the CPU 31, the second stage represents the resistance switching signal output from the CPU 31 to the switching resistor unit 33, and the third stage represents the adjustment circuit from the CPU 31 The fourth stage represents the PWM signal output from the voltage increase / decrease circuit 32, and the fifth stage represents the LED drive current IF.

  As shown in the time chart of the first stage, the PWM signal starts from a duty ratio of 0% (off state) and gradually increases to 100% (full light state) as in the time chart of the first embodiment. Again, the duty ratio is gradually reduced to 0%.

From the start to t5, the resistance switching signal remains L, and the signal strength of the PWM signal output from the voltage increase / decrease circuit 32 and input to the base terminal B of the NPN transistor 10 remains low. At this time, the color of the output light of the green LED element is yellowish green, and corresponds to point G1 on the chromaticity diagram of FIG.
Therefore, from the start to t5, the green LED gradually increases in brightness with yellowish green output light.

  Next, at time t5, the resistance switching signal switches from L to H. As a result, the signal strength of the PWM signal output from the voltage increase / decrease circuit 32 is increased, and the LED drive current IF is increased. At this time, the color of the output light of the green LED element changes to bluish green, and changes from point G1 to point G2 on the chromaticity diagram of FIG. 3.

  Then, from t5 to t6, the green LED is a bluish green output light, and the brightness is gradually increased to the full light state.

  Next, at time t6, the pulse current adjustment signal switches from L to H. As a result, the LED drive current IF is further increased. At this time, the color of the output light of the green LED element changes to a more bluish green color, and on the chromaticity diagram of FIG. 3, the point G2 further changes to the left side of the drawing.

  Furthermore, after t6, the green LED is a more bluish green output light, and gradually reduces the brightness from the all-light state to the light-off state.

When the LED lighting device 2 is a horizon light, for example, the background is gradually brightened yellow green from the start by combining the above operation of the green LED element with the red and blue LED elements, and at time t2, it turns blue green. It is possible to change the state to a full light state at t6 and to change to a bluish bluish green color, and then to gradually darken and turn off the bluish bluish green color.
In addition, in the operation unit 3 of the LED lighting system, for example, while performing a light control operation, the toning signal is switched at time t5, and further, the pulse current adjustment signal is switched at time t6 to express the above effect can do.
As described above, according to the LED lighting device 2 and the LED lighting system of the present embodiment, even if there are only three types of LED elements corresponding to three primary colors, a wider range of colors can be expressed.

Third Embodiment
FIG. 7 shows a circuit diagram of an LED drive circuit according to a third embodiment of the present invention.
In addition, in this embodiment, the same code | symbol is attached | subjected to the component same as the LED drive circuit of 1st Embodiment, and the detailed description is abbreviate | omitted.
Further, by incorporating the LED drive circuit of the present embodiment instead of the LED drive circuit of the first embodiment, the LED lighting device and the LED lighting system of the present invention can be configured as in the first embodiment. .

  As shown in the drawing, in the LED drive circuit of this embodiment, a PNP transistor 10a (TR3) is provided as a transistor element in place of the NPN transistor 10 of the first embodiment. In the PNP transistor 10a, an emitter terminal E is connected to the cathode side of the LED element D1 as a first terminal, and a collector terminal C is grounded via a current control resistor 20 as a second terminal.

  The PNP transistor 10a is turned on when the base voltage VB1 applied to the base terminal B is lower than the emitter voltage VE by a predetermined value (for example, about 0.7 V) or more. Therefore, in the present embodiment, in accordance with the light adjustment signal as the external signal input to the CPU 31, the CPU 31 duty ratio of the low (L) section, not the high (H) section of the pulse waveform of the PWM signal. Control as a ratio.

Furthermore, the voltage increase / decrease circuit 32 controls the signal strength of the PWM signal as a potential difference between the high interval of the pulse waveform of the PWM signal and the low interval. In the example shown in FIG. 7, the wave height of the voltage waveform of the PWM signal input to the voltage increase / decrease circuit 32 is VA (for example, VA = 5.0 V), while the PWM signal output from the voltage increase / decrease circuit 32 The wave height of the voltage waveform is changed to VB (for example, VB = 0.0 to 5.0 V) which is smaller than VA by W.
The voltage increase / decrease circuit 32 can also make the output PWM signal strength higher than the signal strength of the input PWM signal.

  Then, the lower the VB, the larger the potential difference (VB1-VB) across the resistor R3 connected to the base terminal B, and the base current IB = ((VB1-VB) / R3). As a result, ((VB1) −VB) / R3) × hFE = 1 (Ω) The current flowing through the LIMIT1 resistor 20 ≒ the LED current IF is increased. "HFE" represents the current amplification factor of the PNP transistor 10a. Also, conversely, the higher the VB, the smaller the LED current IF. Therefore, also in the present embodiment, the emission wavelength of the LED element, that is, the tint is controlled by controlling the signal intensity VB of the pulse signal.

Next, with reference to a time chart shown in FIG. 8, an operation example of driving a green LED element by the LED drive circuit of the present embodiment will be described.
The first stage from the top of the time chart represents the PWM signal output from the CPU 31, the second stage represents the resistance switching signal output from the CPU 31 to the switching resistor unit 33, and the third stage represents the voltage increase / decrease circuit 32. The fourth stage represents the base current IB flowing through the base terminal B of the PNP transistor 10a, and the fifth stage represents the pulse current waveform of the LED drive current IF.

As shown in the upper timing chart, the PWM signal starts from a duty ratio of 0% (off state), gradually increases the duty ratio to 100% (full light state), and again gradually increases the duty ratio to 0%. Is decreasing.
Before t7, the resistance switching signal remains L, and the VB of the PWM signal output from the voltage increase / decrease circuit 32 and input to the base terminal B of the PNP transistor 10a remains low, and the green LED element The color of the output light remains yellowish green.

Next, at time t7, the resistance switching signal switches from L to H. As a result, the signal strength of the PWM signal output from the voltage adjusting circuit 32 is increased. As a result, the color of the output light of the green LED element changes to bluish green.
Then, from t7 to t8, the green LED is a bluish green output light, and the brightness is gradually increased to the full light state. Furthermore, after t8, the green LED is a bluish green output light, and gradually reduces the brightness from the all-light state to the light-off state.
As described above, also in the present embodiment, the brightness and the color of the green LED element can be controlled as in the first embodiment.

Although the embodiments of the present invention have been described above, the present invention can be variously modified and modified.
In the embodiment described above, the signal strength of the PWM signal is switched by switching the switching resistor. However, in the present invention, the method of switching the signal strength of the PWM signal is not limited to this. Also, the signal strength of the PWM signal may be switched in multiple steps or may be changed continuously.

  In the embodiment described above, an example is described in which the LED drive circuit of the present invention drives the three types of LED elements that respectively output the three primary colors, but in the LED lighting system and the LED lighting device of the present invention It is not necessary to drive the LED element of the present invention with the LED drive circuit of the present invention. For example, only one type of LED element may be driven with the LED drive circuit of the present invention.

  In the above-described embodiment, the transistor element in the LED drive circuit is formed of an NPN type or PNP type bipolar transistor. However, in the present invention, the transistor element is not limited to the bipolar transistor. May be composed of FETs (Field Effect Transistors). For example, an enhancement type MOS (Metal Oxide Semiconductor) -FET is also preferable as a transistor element because the drain current can be controlled by changing the gate voltage strength. In particular, if the transistor element is an N-channel MOS-FET, the light control and emission wavelength of the LED can be obtained by inputting a pulse signal having the same signal waveform as that of the first embodiment in which the transistor element is an NPN transistor. Changes can be made.

  In the embodiment described above, an example in which only three types of LED elements for outputting each of the three primary colors are provided has been described, but in the LED lighting device and the LED lighting system of the present invention, four or more types of LED elements are provided. May be For example, in addition to the three primary color LED elements, an LED element that outputs white light may be provided.

  The present invention can be applied to drive circuits of various LED elements, LED lighting devices, and LED lighting systems, and is particularly suitable for application to lighting devices and lighting systems for effects used in studios or stages. .

10 (First) NPN transistor (TR1)
12 (Second) NPN transistor (TR2)
20 (first) current limiting resistor (1 LIMIT)
20a Adjustment circuit 22 (second) current limiting resistor 30 PWM signal generation circuit 31 CPU
32 Voltage adjustment circuit 33 Switching resistor section

Claims (7)

An LED drive circuit for controlling the brightness and emission wavelength of output light of an LED element, comprising:
A transistor element whose first terminal is connected to the cathode side of the LED element and whose second terminal is grounded via a current control resistor;
A PWM signal generation circuit that generates a PWM signal to be input to the control terminal of the transistor element;
Equipped with
The PWM signal generation circuit
A pulse signal generation unit that generates a pulse signal whose voltage waveform changes in a rectangular shape;
A PWM control unit that controls a duty ratio of the pulse signal;
A voltage control unit that controls the signal strength of the pulse signal;
LED drive circuit characterized by having. The LED drive circuit according to claim 1, further comprising a regulator circuit that changes a combined resistance value of the current control resistor. The transistor element is an NPN transistor,
The first terminal is a collector terminal,
The second terminal is an emitter terminal,
The LED drive circuit according to claim 1, wherein the control terminal is a base terminal. The transistor element is a PNP transistor,
The first terminal is an emitter terminal,
The second terminal is a collector terminal,
The LED drive circuit according to claim 1, wherein the control terminal is a base terminal. At least three types of LED elements that output light of different wavelengths,
The LED lighting device, comprising: the LED drive circuit according to any one of claims 1 to 4, which drives at least one of the at least three types of LED elements. The LED lighting device according to claim 5;
The LED lighting apparatus further includes an operation unit for inputting a light adjustment signal for controlling the brightness of the output light of the LED element and a color adjustment signal for controlling the emission wavelength of the output light of the LED element.
The PWM control unit of the LED drive circuit controls a duty ratio of the pulse signal according to the dimming signal.
The LED lighting system, wherein the voltage control unit of the LED drive circuit controls the signal strength of the pulse signal in accordance with the color adjustment signal. The LED driving method is to drive the LED element by inputting a PWM signal to a control terminal of a transistor element whose first terminal is connected to the cathode side of the LED element and whose second terminal is grounded via a current control resistor. ,
Generate a pulse signal,
The brightness of the LED element is controlled by controlling the duty ratio of the pulse signal,
And controlling an emission wavelength of the LED element by controlling a signal voltage of the pulse signal.

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