JP2002134284A - Driver of white light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driver of a white light emitting diode equipped with an adjustment means, by which color temperature and luminosity can be adjusted with simple composition. SOLUTION: The driver of the white light emitting diode 23, which changes a luminescence light of an excitation element (LED tip) of blue luminescence to white light with a fluorescent substance, and emits it, is constituted that a drive circuit equipped with a pulse oscillation circuit 31, which controls a transistor T1 prepared in a drive current way of the white light emitting diode 23 and while driving the white light emitting diode 23 with the pulse current by this drive circuit, by changing the average current value of the pulse current and the duty ratio, the color temperature and luminosity of the light to emit are adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a white light emitting diode used as a lighting fixture, a display, a backlight of a display, a light source for a sensor, and the like.
In particular, the driving device is provided with adjusting means for adjusting the color temperature and the luminance.

[0002]

2. Description of the Related Art High-brightness single quantum well structure InGaN
With the development of blue and green light emitting diodes,
Light emitting diodes have come to be used in a wide range of fields, such as point light sources used for button illumination of mobile phones, liquid crystal backlights, tabletop illumination, and scanners for image reading scanners. One of the reasons is that a white light emitting diode can be realized.

The white light emitting diode is realized by the following method. It is composed of a blue light-emitting excitation element and a phosphor that converts light emitted from the excitation element into white light. It is constituted by using a blue light emitting diode and a light emitting diode having a complementary color relationship with the light emission. It is constructed using three colors of light emission of a red light emitting diode, a green light emitting diode and a blue light emitting diode.

In addition to the above, blue-green emission of an excitation element using CdZnSe / ZnSe and PL (Photo Lumi)
There is a configuration using yellow-orange light emission based on the above-described light emission, and a configuration using a combination of an excitation element that emits ultraviolet light and a phosphor that excites red, green, and blue colors with ultraviolet light.

In particular, since a white light emitting diode having a combination of a blue light emitting excitation element and a phosphor has been proposed, this light emitting diode is a light source using a conventional CFL or a flat cold cathode tube. As a result, it has come to be used in place of a bulb light source.

FIGS. 13 to 15 show an example of a white light emitting diode comprising a combination of a blue light emitting excitation element and a phosphor. FIG. 13 shows a configuration example of an InGaN blue light emitting device having a single quantum well structure, 11 is a sapphire substrate, 12 is an n-type semiconductor (n-type GaN), and 13 is a P-type semiconductor (P-type G
aN) and 14 are n-electrodes and 15 is a P-electrode.

The white light emitting diode 20 is constructed as shown in FIGS. 14 and 15 by using the above blue light emitting element as an excitation element (LED chip) 16. That is, the excitation element 16 is die-bonded to the insulating substrate 17 on which the anode and cathode lead electrodes are formed, and n-
The electrode 14 and the P-electrode 15 are connected to the extraction electrode by a gold wire.

[0008] A transparent epoxy resin 18 mixed with a YAG: Ce phosphor is provided integrally with the insulating substrate 17 so as to cover the excitation element 16. In the white light emitting diode 20 thus configured, the blue light emitted from the excitation element 16 is absorbed by the phosphor, and the white light having a peak near 460 nm is emitted from the epoxy resin 18 as shown in FIG. Irradiated through.

FIG. 16 shows an emission spectrum when light is emitted at an ambient temperature Ta = 25 ° C. and a drive current IF = 20 mA. Further, the white light emitting diode 20 has a structure of MID (Molded Interconnect).
on Device).

[0010]

SUMMARY OF THE INVENTION Excitation element 1 for emitting blue light
White light-emitting diode 2 composed of a combination of phosphor 6 and phosphor
In the case of 0, the white light distribution becomes wide due to the amount of the phosphor, the variation in the excitation wavelength of the phosphor, and the like, in addition to the variation in the output and the wavelength of the excitation element 16.

FIG. 17 is a diagram showing a white color distribution of the white light emitting diode 20 on a color temperature diagram, and a0, b1, b2, and c0 shown in the color temperature diagram are combined with luminance by the discriminator. The area of the color temperature that can be selected is shown. In the discriminator, the luminance is divided into three stages for every √2 times, and is managed in 12 combinations in combination with the color temperature selection.

However, in practice, variations between color rods and variations in luminance occur. In particular, when a plurality of white light emitting diodes are provided in the same device, the device quality deteriorates due to the variation in the color temperature and luminance of the adjacent light emitting diodes, and the specifications are satisfied both as a display and a sensor. May be defective.

[0013] In order to reduce variations in color temperature and luminance, the selection width of the sorting machine can be set to be narrow, but this is not an effective means when considering the cost up based on the capacity of the sorting machine and the sorting time.

In a sorter, a drive current of 20 mA is usually passed for sorting. However, a white light emitting diode actually incorporated in a device is not driven at 20 mA, but the drive current is often changed according to the device. . For this reason, as shown in FIG. 18, the color temperature is dependent on the driving current, and the color temperature varies.

In order to prevent such a variation in color temperature, a light-emitting diode must be provided in the apparatus, and the screen must be sorted by a screener for each current to be driven. This screening method requires a wide variety of setting conditions. Not realistic.

As a result, a white light emitting diode selected with a drive current of 20 mA was used, and some of the devices did not satisfy the specifications in the final inspection process of the device, and were treated as defective products. For this reason, as a method of eliminating defects in the final inspection step, a method of adjusting the color temperature and the luminance without using a sorting machine has been required.

In view of the above-mentioned circumstances, the present invention provides a white light emitting diode in which the color temperature and the luminance can be adjusted by simple components, and the variation in the color temperature and the luminance can be minimized. The purpose is to propose a drive.

[0018]

In order to achieve the above object, according to the present invention, as a first invention, light emitted from an excitation element that emits blue light or ultraviolet light is converted into white light by a phosphor and emitted. A driving device for driving with a pulse current, and changing an average current value and / or a duty ratio of the pulse current.
Adjusting means for adjusting color temperature and / or luminance of emitted light.
We propose a driving device for

According to a second aspect of the present invention, there is provided a driving apparatus for driving a white light emitting diode which emits light emitted from a plurality of excitation elements having different emission colors by converting white light into white light by a phosphor, Adjusting means for adjusting the color temperature and / or brightness of emitted light by changing the average current value and / or duty ratio of the pulse current. A driving device is proposed.

According to a third aspect of the present invention, in the first or second aspect, one LED lamp having a plurality of white light emitting diodes is provided, and each of the white light emitting diodes is supplied with a pulse current. , And adjusting means for changing the average current value and / or duty ratio of the pulse current and adjusting the color temperature and / or luminance of the emitted light. A driving device for a white light emitting diode is proposed.

[0021]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front view implemented as a diffused light source device, and FIG.

In this diffused light source device, as shown, a light guide plate 21 is arranged in a case 22 and a white light emitting diode is provided at a position in the case 22 which is a side portion of the light guide plate 21.
23 is arranged. The white light emitting diode 23
Is similar to the light emitting diode 20 shown in FIGS.

A diffusion sheet 24 is provided on the surface of the light guide plate 21, a reflection sheet 25 is provided on the lower surface thereof, and a cover 27 having a window 26 is covered on the case 22. There is a configuration. The lead wire connected to the lead electrode of the white light emitting diode 23 is led out through the case 22.

When the white light emitting diode 23 emits light, the light emitted from the light source enters the light guide plate 21 and is reflected and refracted by the light guide plate 21, so that the diffusion sheet 2 is formed.
4 causes diffusion. Thus, the diffused light is reflected by the reflection sheet 25.
And is radiated through the window 26.

The above diffused light source device drives the white light emitting diode 23 with a pulse current to emit light, and furthermore, an average current value or a duty ratio of the pulse current.
actor) to adjust the color temperature and the luminance.
That is, the adjustment is performed by changing the average current value or the duty ratio of the pulse current according to the adjustment of the color temperature and the adjustment of the luminance.

FIG. 3 is a diagram showing an example of a circuit for driving the white light emitting diode 23. This drive circuit includes a pulse oscillation circuit 31 composed of an IC. The pulse oscillation circuit 31 controls a transistor T1 for a switching operation in accordance with the set values of resistors R1, R2 and a capacitor C1, and drives the white light emitting diode 23. The pulse width and frequency of the driving pulse current are changed, and the current value (pulse amplitude) of the pulse current is changed according to the set value of the resistor R3.

That is, the pulse width and the frequency are changed while changing the resistance R3, and the color temperature is changed while keeping the brightness constant, or the brightness is changed while keeping the color temperature constant, and the color temperature and the brightness are changed. Can be adjusted.

The oscillation frequency (f) at this time is as follows. The duty ratio (D) is as follows.

At this time, the average current value (I) flowing through the white light emitting diode 23 is expressed as follows. V _F : forward voltage of white light emitting diode V _BE : base-emitter voltage of transistor T1

Although the above-described driving circuit has a configuration in which a pulse current is output by the pulse oscillation circuit 31 and the transistor T1, a configuration in which a transistor, an op-amp, and the like are controlled using an unstable multivibrator or a CR oscillator. can do. That is, any circuit can be used as long as it can drive the white light emitting diode 23 with a pulse current.

FIGS. 4 and 5 are current-color temperature graphs showing the change in color temperature when the measurement is performed while changing the frequency. The duty ratio of the pulse current is 50%.
In this measurement, the frequency F1 = 50 Hz and F2 = 1k
Hz, F3 = 10 kHz, and F4 = 100 kHz. As can be seen from this graph, the color temperature changes in proportion to the average current value of the pulse current.

FIG. 6 is a graph showing the measured values of the color temperature according to the difference in the average current value of the pulse current on the XY color temperature coordinates. As shown in the drawing, it is clear that the color temperature is divided into groups for each current value, and that the color temperature changes in proportion to the current, and it does not depend on the frequency.

FIG. 7 is a graph showing the relationship between the duty ratio and the color temperature. The measurement conditions in this case are a frequency of 100 kHz, an average pulse current of 10 mA,
The duty ratio of the pulse current is 10%, 25%, 50%,
Changed to 100%. As described above, when the average current is constant, the color temperature is proportional to the duty ratio.

As described above, since the color temperature changes even when the radiance is constant, the luminance changes due to the relative luminous efficiency. FIG. 8 is a graph showing the relationship. The horizontal axis (X axis) of this graph is represented by a logarithmic scale, and it can be seen that the luminance is proportional to the duty ratio.

As can be seen from this graph, there is no problem even if the luminance changes by about 35%, and when the color temperature is severe, the color temperature can be adjusted by the duty ratio with the current kept constant.

Next, FIG. 9 shows the measurement results when the average current value and the duty ratio of the pulse current are changed so as to make the luminance constant. In this case, the resistance R
3, the current value for the white light emitting diode 23 is changed, and the color temperature is changed so as to keep the luminance constant. The measurement condition at this time is a frequency of 100 kHz. When the luminance is fixed and the duty ratio is changed, the color temperature changes in proportion to the current value.

FIG. 10 shows the average current value changed in this measurement. In the graph of FIG. 10, since the average current value is 1 / duty ratio on the X axis,
This average current value is inversely proportional to the duty ratio when the luminance is constant.

FIG. 11 is a graph showing the relationship between the average current value and the luminance. From this graph, it is understood that the average current value and the luminance do not depend on the frequency, but are proportional to only the current.

As a result, the luminance L is expressed as follows. L = aI + ba a: proportional constant b: intercept I: average current value

The color temperature T is expressed as follows. T = mI / D + n m: proportionality constant n: intercept D: duty ratio

From the above relationship, it is possible to adjust the color temperature while keeping the luminance constant, and to adjust the luminance while keeping the color temperature constant. It is also possible to simultaneously adjust the color temperature and the luminance.

FIG. 12 is a circuit diagram showing an embodiment of the drive circuit. In this figure, the same components as those shown in FIG. 3 are denoted by the same reference numerals.

As shown in the figure, in this drive circuit, a transistor T2 for amplifying operation is provided in the input circuit (R1, R2, C2) of the pulse oscillation circuit 31, and this transistor T2
Are controlled by a color temperature adjustment signal SC, a transistor T3 for amplifying operation is provided in a drive current path of the white light emitting diode 23, and the transistor T3 is controlled by a brightness adjustment signal SO.

The color temperature adjustment signal SC is output as follows. That is, the color temperature of the white light emitting diode 23 is measured, an adjustment value is obtained based on the measured value, and the adjustment value is set by the color temperature adjustment value setting circuit 32.

Then, an adjustment signal output circuit 33 for inputting a setting signal from the setting circuit 32 inputs an adjustment signal SC to the base of the transistor T2 in accordance with the set adjustment value.
The transistor T2 is controlled according to the adjustment of the color temperature.

As a result, the pulse signal output from the pulse oscillating circuit 31 has a pulse width and a frequency including the adjustment value of the color temperature, and this pulse signal causes the transistor T1
Is controlled, and the color temperature of light emission of the white light emitting diode 23 is adjusted.

On the other hand, the luminance adjustment signals SO1 and SO2 are
Output as follows. That is, a light receiving device 34 for receiving the light emitted from the white light emitting diode 23 is provided, and a light receiving signal (photoelectric conversion signal) of the light receiving device 34 is input to a luminance adjustment value calculation circuit 35 to calculate the adjustment value.

The arithmetic circuit 35 calculates a luminance adjustment value from the predetermined luminance expected value and the light receiving signal, and sends this arithmetic signal to the adjustment signal output circuit 36. Thus, the adjustment signal output circuit 36 inputs the adjustment signal SO1 corresponding to the operation signal to the base of the transistor T3, and controls the transistor T3 in accordance with the brightness adjustment value.

As a result, the driving current of the white light emitting diode 23 is controlled according to the luminance adjustment value, and the luminance is adjusted.

A manual setting circuit 37 for manually setting the brightness adjustment value is provided. The manual setting circuit 37 sets an arbitrary brightness. When a setting signal of the setting circuit 37 is input to the adjustment signal output circuit 36, the output circuit 3
6 shuts off the input of the operation signal from the operation circuit 35 and outputs the luminance adjustment signal SO2 according to the manually set signal. As a result, the brightness of the white light emitting diode 23 is adjusted by manual setting.

Therefore, according to this drive circuit, the pulse signal of the pulse width and the frequency according to the color temperature adjustment value set by the adjustment value setting circuit 32 is supplied to the pulse oscillation circuit 3.
1, the transistor T1 is controlled by this pulse signal, and the color temperature of the white light emitting diode 23 is adjusted.

When the color temperature is adjusted as described above, the luminance adjustment value is set by the manual setting circuit 37, and the transistor T3 is controlled by the luminance adjustment signal SO2, whereby the pulse current flowing through the white light emitting diode 23 is obtained. (Average current) and the color temperature can be adjusted while keeping the luminance constant.

In a state where the adjustment setting by the adjustment value setting circuit 32 is constant and the color temperature of the white light emitting diode is constant, the luminance adjustment signal SO1 based on the operation signal or the luminance adjustment signal based on the manual setting is set. If the transistor T3 is controlled by SO2, the brightness can be adjusted while keeping the color temperature constant.

The drive circuit can simultaneously adjust the color temperature and the luminance by outputting both the color temperature adjustment signal SC and the luminance adjustment signal SO1 or SO2.

Although an example in which the present invention is applied to a diffused light source device has been described above, the present invention is not limited to the diffused light source device, and the color temperature and luminance are adjusted similarly for one light emitting diode. In addition, even when a plurality of light emitting diodes are configured as one light source unit, each light emitting diode may be configured to change the average current value and / or the duty ratio of the pulse current for driving each light emitting diode. The color temperature and brightness of the light emitting diode can be adjusted.

In practicing the present invention, In
Not only a white light emitting diode composed of a blue light emitting excitation element (LED chip) having a GaN active layer and a phosphor, but also other light emitting wavelength systems of InGaN type, silicon carbide type, GaAlAs type, GaAssp type In addition to the above, it can be constituted by an excitation element using another compound semiconductor and a phosphor, and when a material causing upconversion is used, and when a plurality of excitation elements are combined, the same operation as described above is performed. can do.

[0057]

As described above, according to the present invention, the color temperature and the luminance of the emitted light are changed by driving the white light emitting diode with the pulse current and changing the average current value and / or the duty ratio of the pulse current. Since the adjustment is made, the color temperature and the brightness can be adjusted even after the white light emitting diode is incorporated in the device, and even when a plurality of white light emitting diodes are incorporated in the same device. Since the light emitting diode can be adjusted, defective products of the apparatus can be reduced as much as possible.

[Brief description of the drawings]

FIG. 1 is a front view of a diffused light source device showing one embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is a diagram showing an example of a circuit for driving a white light emitting diode.

FIG. 4 is a graph showing a relationship of a color temperature (X) when measured while changing a frequency.

FIG. 5 is a graph showing a relationship between color temperature (Y) when measurement is performed while changing frequency.

FIG. 6 is a diagram showing color temperatures based on differences in average current values of pulse currents on XY color temperature coordinates.

FIG. 7 is a graph showing a relationship between a duty ratio of a pulse current and a color temperature.

FIG. 8 is a graph showing a relationship between a duty ratio of a pulse current and relative luminance.

FIG. 9 is a graph showing a change in color temperature when the duty ratio of a pulse current driven to make the luminance constant is changed.

FIG. 10 is a graph showing that the average current value of the pulse current is inversely proportional to the duty ratio.

FIG. 11 is a graph showing a relationship between an average current value of a pulse current and luminance.

FIG. 12 is a circuit diagram showing an embodiment of a drive circuit.

FIG. 13 is a configuration diagram showing a blue light emitting excitation element (LED chip).

FIG. 14 is a front view of a white light emitting diode.

FIG. 15 is a side view of a white light emitting diode.

FIG. 16 is a view showing an emission spectrum of the above-mentioned white light emitting diode.

FIG. 17 is a diagram showing a white color distribution of a white light emitting diode on a color temperature diagram.

FIG. 18 is a graph showing that the color temperature changes by changing the drive current.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Light guide plate 22 Case 23 White light emitting diode 24 Diffusion sheet 25 Reflection sheet 26 Window 27 Cover 31 Pulse oscillation circuit

Claims (3)

[Claims] 1. A driving device for driving a white light emitting diode which emits blue light or ultraviolet light from an excitation element which emits blue light or ultraviolet light by converting it into white light by means of a phosphor. A driving device for a white light emitting diode, comprising: adjusting means for changing an average current value and / or a duty ratio of a current to adjust a color temperature and / or a brightness of emitted light. . 2. A driving apparatus for driving a white light emitting diode which emits light emitted from a plurality of excitation elements having different emission colors by converting white light into white light by means of a phosphor, comprising: a driving means driven by a pulse current; A driving device for a white light emitting diode, comprising: adjusting means for changing the average current value and / or the duty ratio to adjust the color temperature and / or the brightness of emitted light. 3. The driving device according to claim 1, further comprising a single LED lamp having a plurality of white light emitting diodes, and driving each of the white light emitting diodes with a pulse current. And an adjusting means for changing the average current value and / or the duty ratio of the pulse current to adjust the color temperature and / or luminance of the emitted light. Drive unit.