Patent Grant
8188670
The present invention is related to a light emitting device and a method for driving a light emitting device.
Priority is claimed on Japanese Patent Application No. 2007-003253, filed Jan. 11, 2007, the content of which is incorporated herein by reference.
Hitherto, a light emitting diode driving circuit is known, which consists of a parallel circuit in which each of a pair of light emitting diodes are connected to each other by reverse polarity, and an AC power supply which applies an alternating current to the parallel circuit (for example, the following Patent documents 1 and 2).
In the conventional light emitting diode driving circuit, a pair of light emitting diode emit light alternately by applying an alternating current.
However, in the conventional light emitting diode driving circuit such as Patent document 1, synthesized color light is often obtained, which consists of blue and another color other than blue, by using blue light emitting diode for a first light emitting diode, and using a color light emitting diode other than blue for the second light emitting diode. It has not been examined at all with respect to color temperature of light emitting diode. The present invention was made in view of the above circumstances and it is an object of the present invention to provide a light emitting device which can emit light of an arbitrary color temperature and driving method of a light emitting device.
The present invention adopts the following constitution to achieve the object.
According to the present invention, a light emitting device and a process for driving the light emitting device are provided, which can emit light of an arbitrary color temperature.
With reference to drawings, an explanation of an embodiment of the present invention will be given below.
As shown in
The first and the second light emitting diode devices 2 and 3 are connected in parallel so as to have opposite polarities. Each of the first and the second light emitting diode devices 2 and 3 is constituted from a plurality of light emitting diodes which are connected in series. In
Each of the light emitting diodes 2a to 2c and 3a to 3c is approximately constituted from a semiconductor light emitting element having a p-n junction and a transparent resin body for covering the semiconductor light emitting element not illustrated in the drawing. The transparent resin body contains fluorescent powder, for example, a semiconductor light emitting element which emits blue light contains yellow fluorescent substance solely or a mixture of green and red fluorescent substances. By varying the content of each color of the fluorescent substances to the output of the semiconductor light emitting element, light of various color temperatures can be emitted.
It should be noted that the color temperature of each of the light emitting diodes 2a to 2c which constitute the first light emitting diode device 2 is preferably identical. Similarly, the color temperature of each of the light emitting diodes 3a to 3c which constitute the second light emitting diode device 3 is preferably identical.
The color temperature of the light emitted from the first and the second light emitting diode devices 2 and 3 preferably ranges from 2000K to 12000K.
In addition, the color temperature of the light emitted from the first light emitting diode device 2 is preferably higher than the color temperature of the light emitted from the second light emitting diode device 3. As the color temperature of the first and the second light emitting diode devices 2 and 3, 6500K for providing daylight, 3000K for providing bulb color, 5000K for providing neutral white, 4200K for providing white, and 3500K for providing warm are exemplary. As the combination of the color temperatures of the first and the second light emitting diode devices 2 and 3, a combination of a first light emitting diode device 2 having a color temperature of 6500K and a second light emitting diode device 3 having a color temperature of 3000K, a combination of a first light emitting diode device 2 having a color temperature of 10000K and a second light emitting diode device 3 having a color temperature of 2500K, and a combination of a first light emitting diode device 2 having a color temperature of 5000K and a second light emitting diode device 3 having a color temperature of 2500K are exemplary.
Next, as for the power supply unit 4, whatever power supply unit can be used that can apply alternating current or direct current freely to each of the light emitting diode devices 2 and 3, and that can arbitrarily invert the direction of direct current, i.e. which can freely invert the polarity. A pulse power supply which can freely change pulse width and the duty ratio of an applied current is more preferable.
An example of a constant current power supply unit 4 is shown in
A pair of the switching devices 4c and 4d is constructed so that they can be switched arbitrarily by a non-illustrated control means.
A pair of the switching devices 4c and 4d should alternately be turned on/off to generate an alternating current in the constant current power supply unit 4 shown in
In addition, an alternating current with an irregular and rectangular wave as shown in
It should be noted that the brightness can be controlled by varying the value (so-called duty ratio) defined by the formula: t2/(t2+t3).
In addition, the switching device 4d among a pair of switching devices is always turned on while the switching device 4c is always turned off to generate a direct current in the constant current power supply unit 4 shown in
On the other hand, the switching device 4c among a pair of switching devices is always turned on while the switching device 4d is always turned on, so a direct current flows in a clockwise direction (direction indicated by an arrow B) as shown in
Either in alternating current or direct current, the electrical current flowing in the direction shown by the arrow A drives the second light emitting diode device 3 which is in a sequential polarity to the direction shown by the arrow A. The electrical current flowing in the direction shown by the arrow B drives the first light emitting diode device 2 which is in a sequential polarity to the direction shown by the arrow B. In this way, it becomes possible to arbitrarily emit any one of the first and the second light emitting diode devices 2 and 3 by controlling the direction of an electric current.
For example, in the case in which an alternating current as shown in
In the case in which an alternating current shown in
The power supply frequency is, as mentioned above, preferably 100 Hz or more, and more preferably ranges from 100 Hz to 10 kHz. The electrical current preferably ranges from −20 mA to 20 mA in the case of, for example, a light emitting diode chip of 350 μm square.
In addition, in the case in which a direct current flows along the direction shown by the arrow A, only the second light emitting diode device 3 emits a light having a color temperature T2.
In addition, in the case in which a direct current flows along the direction shown by the arrow B, only the first light emitting diode device 2 emits a light having a color temperature of T1.
In addition, in the case in which a pulse electric current as shown in
In addition, when the first light emitting diode device 2 or the second light emitting diode device 3 is driven by a direct current, there is a case that an electric current (reverse overvoltage) flows in a reverse direction through a circuit of the light emitting diode 1 momentarily against a direct current, due to the influence of, for example, static electricity. In such a case, when a reverse overvoltage is generated during, for example, a direct current flowing in the direction “A” in order to drive the second light emitting diode device 3, the overvoltage electrical current flows through the first light emitting diode device 2, and as a result, the first light emitting diode device 2 serves as a protection circuit for the second light emitting diode device 3. Similarly, when a reverse overvoltage is generated during flowing a direct current in the direction “B” in order to drive the first light emitting diode device 2, the overvoltage electrical current flows through the second light emitting diode device 3, and as a result, the second light emitting diode device 3 serves as a protection circuit for the first light emitting diode device 2.
A parallel circuit consisting of the first and the second light emitting diode devices 2 and 3 of this embodiment can be realized, for example, by a lamp, as shown in
Each of the first and the second light emitting diode devices 52A and 52B is constituted from non-illustrated three pieces of light emitting diodes each of which is connected in series. In each of the light emitting diode device 52A and 52B, three pieces of light emitting diodes connected in series are sealed by a transparent resin. As a light emitting diode, a semiconductor light emitting element having a p-n junction is exemplary. In addition, into the transparent resin, a fluorescent powder is mixed. For example, a light emitting diode which emits blue light contains only a yellow fluorescent substance or a mixture of green and red fluorescent substances.
In addition, each of the first and the second light emitting diode device 52A and 52B is combined to emit light having different color temperatures.
In addition, the package 53 is approximately constituted from a metal substrate (not shown) made of, for example, aluminum; an insulate resin film (not shown) formed on one surface of the metal substrate; and a copper foil (not shown) formed on the insulate resin film. The copper foil is patterned into a predetermined pattern shape, thereby forming a electrode pattern (not shown) which corresponds to the first and the second light emitting diode devices 52A and 52B, and a wiring pattern (not shown) for connecting to outside circuits.
Next, as shown in
In addition, the circuit as shown in
As explained above, an alternating current or a direct current is generated from the constant current power supply unit 4, and each of the first and the second light emitting diode devices 2 and 3 is driven by the resultant electrical current, thereby emitting light which exhibits an arbitrary color temperature.
In addition, since each of the first and the second light emitting diode devices 2 and 3 serves as a protection circuit for another light emitting diode device when reverse direction overvoltage is generated, it is possible to prevent breakage of the first and the second light emitting diode devices 2 and 3.
On a printed circuit board, the first light emitting diode device 2 having a color temperature of 6500K of daylight and a chip resistance 5 for adjusting electric current were connected in series. In addition, the second light emitting diode device 3 having a color temperature of 3000K of electric bulb color were connected in series. In addition, each of the first and the second light emitting diode devices 2 and 3 were connected together in parallel to have opposite polarities. A light emitting device as shown in
It should be noted that to each of a pair of switching devices 4c and 4d disposed to the constant electrical current power supply 4, a hand-operated switching unit is installed as a controlling means. The hand-operated switching unit is equipped with a change-over switch which changes three modes of off mode, daylight mode and electric bulb color mode.
Here, the off mode is a mode in which both the switching devices 4c and 4d in
In addition, a light emitting device having the constitution above was incorporated into a side of a mirror installed in the sunshade of an automobile.
When the light emitting diode is turned on, the hand-operated change-over switch should be changed to an arbitrary mode. That is, when the change-over switch is set to be in the daylight mode, the switching device 4c is turned on, and the switching device 4d is turned off to allow a direct current to flow in the direction indicated by the arrow B in
In addition, when the change-over switch is set to be the electric bulb mode, the switching device 4c is turned off, and the switching device 4d is turned on to allow a direct current to flow in the direction indicated by the arrow A in
A light emitting device of Example 2 was produced in the same way as in Example 1, with the exception of an automatic switching unit being disposed instead of the hand-operated switching unit in Example 1.
The automatic switching unit disposed in the light emitting device automatically controls the switching devices of the constant current power supply unit to generate an alternating current having a rectangular wave as shown in
In the light emitting device with the constitution above, when the pulse width t2 was set to be 0.5 milliseconds, and the pulse width t3 was set to be 0.5 milliseconds, the driving time of the first light emitting diode device 2 was identical with the driving time of the second light emitting diode device 3, thereby emitting a synthesized light having a color temperature of 4700K.
In addition, in the light emitting device with the constitution above, when the pulse width t2 was set to be 0.67 milliseconds, and the pulse width t3 was set to be 0.34 milliseconds, a synthesized light having a color temperature of 5300K is thereby emitted.
Also, in the light emitting device with the constitution above, when the pulse width t2 was set to be 0.34 milliseconds, and the pulse width t3 was set to be 0.67 milliseconds, a synthesized light having a color temperature of 4000K was emitted.
Additionally, in the light emitting device with the constitution above, when the pulse width t2 was set to be 0 seconds, and the pulse width t3 was set to be an arbitrary time to drive only the second light emitting diode device 3, t a single color light having a color temperature of 3000K was emitted.
In addition, in the light emitting device with the constitution above, when the pulse width t2 was set to be an arbitrary time, and the pulse width t3 was set to be 0 seconds to drive only the first light emitting diode device 2, a single color light having a color temperature of 6500K was emitted.
Thus, according to the light emitting device of Example 2, a light having an arbitrary color tone of a color temperature ranging from 6500K to 3000K can be emitted by freely varying the pulse width of an alternating current.
It should be noted that the technical scope of the present invention is not limited to the above embodiments, and that various changes may be added. For example, the number of light emitting diode chips sealed in each light emitting diode device is not limited to three, may be one or more, and the upper limit thereof is not limited. In addition, not all of the light emitting diode chips sealed in each light emitting diode device need to be connected in series, and some of them may be connected in parallel. In addition, the number of light emitting diode devices is not limited to two, and may be three or more. That is, it is possible to connect a plurality of light emitting diode devices in series, and the resultant light emitting diode devices are prepared by two or more, and these light emitting diode devices connected in series are further connected in parallel, and then the resultant light emitting diode devices may be connected to the power supply.
In such a case, the driving electrical current for driving each of the light emitting diode devices may be varied to every light emitting diode device, for example, by changing the limiting resistor.
In addition, it is also possible to materialize the present invention, by connecting the light emitting diode chips in parallel so that they have opposite polarities, and then covering each of the light emitting diode devices with transparent resin which contains various amounts of fluorescent substances, in the light emitting diode devices.
[Industrial Applicability]
The present invention is applicable to a light emitting device and a driving method thereof, which can emit light having an arbitrary color temperature.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-003253 | Jan 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/050022 | 1/7/2008 | WO | 00 | 5/19/2009 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2008/084771 | 7/17/2008 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4949066 | Reinhardt | Aug 1990 | A |
| 20060202915 | Chikugawa | Sep 2006 | A1 |
| 20060221637 | Chikugawa et al. | Oct 2006 | A1 |
| 20080054814 | Deppe et al. | Mar 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| 59-171361 | Nov 1984 | JP |
| 02-154481 | Jun 1990 | JP |
| 08-265129 | Oct 1996 | JP |
| 2001-332765 | Nov 2001 | JP |
| 2005-101296 | Apr 2005 | JP |
| 2006-253215 | Sep 2006 | JP |
| 2006-286935 | Oct 2006 | JP |
| 253184 | Dec 2004 | TW |
| 200624707 | Jul 2006 | TW |
| Number | Date | Country | |
|---|---|---|---|
| 20100066258 A1 | Mar 2010 | US |
