Light emitting device and illumination device

To provide an illumination device that has light emitting diodes as light sources and is capable of switching emission colors and of performing dimming in each of the emission colors, an illumination device includes plural light emitting units in which at least one light emitting diode is disposed, the other light emitting units than the light emitting unit whose forward voltage is a maximum are provided with a switching element that is connected in series with the light emitting diode, and the other light emitting units than the light emitting unit whose forward voltage is a minimum are provided with an element that is connected in series with the light emitting diode and has a resistance.

TECHNICAL FIELD

The present invention relates to a light emitting device that includes a light emitting element such as a light emitting diode (LED) and an illumination device that uses a light emitting device.

BACKGROUND ART

In recent years, a light emitted diode (LED) with low power consumption and long life has been attracting attention, and an illumination device which has an LED as a light source has often been used instead of an illumination device in related art that has an incandescent light bulb as a light source. In the illumination device that has an LED as the light source, an illumination device has been suggested which is capable of dimming for changing beams and of toning for changing emission colors (for example, see PTLs 1 to 4 and so forth).

In an illumination device of PTL 1, current is supplied from a power source unit to plural light sources (white light and incandescent-lamp color light) with different emission colors, in the power source unit, two step-down chopper circuits are connected in parallel with an output end of a boost chopper circuit, and an LED unit of white light and an LED unit of incandescent-lamp color light are respectively connected with the step-down choppers. In addition, a current is independently supplied to each of the LED unit of the white color light and the LED unit of the incandescent-lamp color light, and dimming and toning are thereby performed.

A light emitting device in PTL 2 includes a first LED and a second LED that have different emission colors and are connected in parallel with each other, and a resistance which is in series connected with the first LED is provided. In addition, the voltage is changed by using differences in the change characteristic between a forward current of the first LED and the forward current of the second LED in a case where a power source voltage is changed, the ratio between a beam emitted from the first LED and a beam emitted from the second LED in all the beams is thereby changed, and dimming and toning are simultaneously performed.

An illumination device of PTL 3 includes a first light emitting unit and a second light emitting unit with different emission colors and includes a switching element that is disposed in series with the second light emitting unit on a second current path through which current flows to the second light emitting unit. In addition, ON and OFF of the switching element are switched in accordance with a signal from a selection control circuit, and to which of the first light emitting unit and the second light emitting unit the current flows is thereby selected. Accordingly, toning is performed.

An LED illumination device of PTL 4 includes plural LED groups in which plural LEDs are directly connected together in a forward direction. The plural LED groups have different total forward voltages, which are the totals of forward voltages of the plural LEDs. In the LED groups other than the LED group that has the maximum total forward voltage, a switching element connected in series is connected in series with the plural LEDs. In addition, the switching element is turned ON or OFF by a control signal from a control unit, and the current is thereby selectively caused to flow through any of the plural LED groups. Accordingly, dimming or toning is performed.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in a case of a light emitting device disclosed in PTL 2, the ratios of a beam of a first light emitting diode and a beam of a second light emitting diode to all beams change in accordance with the change in voltage, and a color temperature simultaneously changes in accordance with the change in the beams. That is, dimming may not be performed with respect to each color temperature.

In the illumination device disclosed in PTL 2, beams of an LED unit of white light and an LED unit of incandescent-lamp color light are individually adjustable, and such a configuration is capable of toning and dimming. However, a step-down chopper circuit is requested for each of the LED units, the circuit configuration is complicated, and costs become high. Further, size reduction is difficult.

Illumination devices disclosed in PTL 3 and PTL 4, a switching element is disposed in order to supply a current to each light source unit, the beam of each of the light source units is adjusted by ON or OFF of the switching element, and dimming is thereby performed. However, a control unit for outputting a control signal to the switching element is requested, the circuit configuration of a power source unit is complicated, and costs become high. Further, size reduction is difficult.

Accordingly, an object of the present invention is to provide an illumination device that has a light emitting diode as a light source, is small in size with a simple configuration, is capable of switching emission colors, and is capable of performing dimming in each emission color.

Solution to Problem

To achieve the above object, a light emitting device according to the present invention includes plural light emitting units in which at least one light emitting diode is disposed. The plural light emitting units respectively have different emission colors and forward voltages. The other light emitting units than the light emitting unit whose forward voltage is a maximum are provided with a switching element that is connected in series with the light emitting diode, and the other light emitting units than the light emitting unit whose forward voltage is a minimum are provided, on a negative electrode side, with an element that is connected in series with the light emitting diode and has a resistance. The switching element is an element that includes a first terminal, a second terminal, and a third terminal, causes the first terminal and the second terminal to turn into a conducting state by applying a prescribed voltage to the third terminal, and subsequently retains the conducting state in a case where a voltage of the third terminal is within a specific range. A terminal on a positive electrode side of the element that has the resistance is electrically connected with the third terminal of the switching element that is provided to the light emitting unit whose forward voltage is highest among the light emitting units whose forward voltages are lower than the light emitting unit that is provided with the element which has the resistance.

Such a configuration turns ON the switching element by changing the supplied current, thereby switches light emission by the light emission units, and adjusts the beams, that is, performs dimming by fluctuating the current in a range in which the switching element is not turned ON. Then, after the switching element is turned ON, the switching element is not turned OFF unless current supply is stopped. Thus, the supplied current value is appropriately adjusted, and it is thereby possible to arbitrarily change the emission colors of light emission and to perform dimming in each of the emission colors. Accordingly, a control circuit for switching the light emission and dimming is not requested, and it is thereby possible to make the light emitting device have a simple configuration. In addition, the simple configuration enables size reduction and weight saving and enables costs to be lowered.

At least one of the switching elements may be configured to include a thyristor. In such a configuration, the switching element may be provided as one element, and it is thus possible to reduce an installation area and to increase the degree of freedom of wiring.

In the above configuration, at least one of the switching elements may include a PNP junction bipolar transistor and an NPN junction bipolar transistor, a base and a collector of the PNP junction bipolar transistor may respectively be connected with a collector and a base of the NPN junction bipolar transistor, an emitter terminal of the PNP junction bipolar transistor may be the first terminal, an emitter terminal of the NPN junction bipolar transistor may be the second terminal, and a base terminal of the NPN junction bipolar transistor may be the third terminal.

In the above configuration, at least one of the plural light emitting units may include a light emitting diode group in which plural light emitting diodes are connected in series, and the light emitting unit whose forward voltage is low may have a small number of light emitting diodes that are connected in series in the light emitting diode group compared to the light emitting unit whose forward voltage is high. Because the forward voltage may be adjusted by the number of light emitting diodes, an element for adjusting the forward voltage is not requested.

In the above configuration, at least one of the plural light emitting units may include the plural light emitting diode groups, and the plural light emitting diode groups may be connected in parallel. The number of light emitting diodes that are connected in series in the light emitting diode group and the number of the light emitting diode groups that are connected in parallel are adjusted, the number of light emitting diodes of each of the light emitting units may thereby be made the same number, and the forward voltage is adjustable.

In the above configuration, the light emitting unit that includes the plural light emitting diode groups may be dividedly arranged so as to include at least one of the light emitting diode groups, and at least one of the light emitting diode groups of the different light emitting unit may be arranged between the divided light emitting units. In such a manner, the light emitting unit is dividedly arranged as individual or plural light emitting diode groups, the light emitting diode group of the other light emitting unit is arranged between the divided light emitting units, and unevenness of arrangement of the light emitting diodes of the light emitting units may thereby be suppressed. Note that the light emitting unit may be divided into individual light emitting diode groups, and between those, the light emitting diode group of the different light emitting unit may thereby be arranged. The light emitting unit may be divided so as to include plural light emitting diode groups, and between those, individual or plural light emitting diode groups of the different light emitting unit may thereby be arranged.

In the above configuration, each of the plural light emitting units includes the light emitting diode group in which a same number of light emitting diodes are connected series, at least one of the light emitting diode groups includes one or plural diodes that are connected in series with the light emitting diode, and the light emitting unit whose forward voltage is high has a large number of the connected diodes compared to the light emitting unit whose forward voltage is low. Consequently, the number of light emitting diodes of each of the light emitting units is made the same number, and the forward voltage may thereby be changed with the same or substantially same beam amount. Thus, it becomes possible to switch the emission colors and to perform dimming in each of the emission colors in a simple configuration.

In the above configuration, at least one of the elements that have the resistance may have a characteristic in which a resistance value becomes low in response to a temperature rise. In such a configuration, in a case where the voltage value at which the switching element is turned ON becomes low due to the temperature rise, the change in the voltage value due to the current may likewise be made small. Accordingly, the fluctuation in the current value at which the switching element is turned ON may be suppressed even if the temperature changes, and it is possible to make the width of dimming in each of the emission colors the same or substantially same.

The above configuration may further include: a substrate on which the plural light emitting units, the switching element, and the element which has the resistance are mounted; and land units that are respectively connected with positive electrode sides and negative electrode sides of the plural light emitting units. In such a manner, an integrated configuration in one substrate enables size reduction.

Advantageous Effects of Invention

The present invention may provide an illumination device that has a light emitting diode as a light source, is small in size with a simple configuration, is capable of switching emission colors, and is capable of performing dimming in each emission color.

DESCRIPTION OF EMBODIMENTS

First Embodiment

FIG. 1is a diagram that illustrates one example of an illumination device according to the present invention. As illustrated inFIG. 1, an illumination device A includes a current source Pi and a light emitting device Op. The light emitting device Op includes a first light emitting unit1and a second light emitting unit2, and the first light emitting unit1and the second light emitting unit2are connected in parallel with the current source Pi.

The current source Pi is a power source that may supply a direct current to a connected circuit. The current source Pi has a configuration that is capable of changing a flowing current value and is also capable of keeping supplying a current of an arbitrary current value. Similarly to a common power source, the current source Pi has a configuration that may apply a voltage to a connected circuit. The current source Pi includes a positive electrode Pi1and a negative electrode Pi2. It is assumed that in the illumination device A according to the present invention, the negative electrode Pi2is grounded inside the current source Pi.

The first light emitting unit1includes plural (here, five) light emitting diodes11(hereinafter referred to as LED11) and a resistance12. Note that the number of LEDs11is not limited to five. For example, the number of LEDs11is also decided in accordance with the demanded beam amount (brightness) of the light emitting device Op, and the upper limit of the number of LEDs11that are connectable in series is decided in accordance with the voltage applied from the current source Pi. Further, as the resistance12included in the first light emitting unit1, a resistor (resistance element) may be raised. However, the resistance12is not limited to a resistor. An element that has an electrical resistance (for example, a FET, a Zener diode, or the like) may be used. In the following description, simply expressed “resistance” is not limited to a resistor but includes “an element that has a (electrical) resistance”. In the first light emitting unit1, five LEDs11are connected in series in a forward direction. The five LEDs11that are connected in series in the forward direction are recognized as one set, and this one set is defined as a first LED group10. Note that in the following description, in a case of a configuration in which the first light emitting unit1has one LED11and the resistance12, the first LED group10will be interpreted as the LED11.

The first LED group10is the LEDs11that are connected in series in the forward direction and thus has polarity, that is, has a positive electrode (anode) terminal101and a negative electrode (cathode) terminal102. The positive electrode terminal101is connected with a first connection terminal31that is connected with the positive electrode Pi1of the current source Pi. Further, the negative electrode terminal102is connected with a second connection terminal32that is connected with the negative electrode Pi1of the current source Pi via the resistance12.

Given that forward voltages of the LEDs11are Vf11 to Vf15, because the five LEDs11of the first LED group10are connected in series in the forward direction, a total forward voltage SVf1 of the first LED group10, which is the total of the forward voltages of all the LEDs11, may be obtained by the following formula.
SVf1=Vf11+Vf12+Vf13+Vf14+Vf15
Note that in a case where all the forward voltages of the LEDs11are equivalent (Vf1),
SVf1=5×Vf1.

The resistance12is disposed between the negative electrode terminal102of the first LED group10and the second connection terminal32. That is, the current that flows through the first LED group10passes through the resistance12and flows to the second connection terminal32.

The second light emitting unit2includes plural (here, five) light emitting diodes21(hereinafter referred to as LED12) and a thyristor22that is a switching element. Note that the number of LEDs21is not limited to five. For example, the number of LEDs21is also decided in accordance with the demanded beam amount brightness) of the light emitting device Op, and the upper limit of the number of LEDs21that are connectable in series is decided in accordance with the voltage applied from the current source Pi. In the second light emitting unit2, five LEDs21are connected in series in the forward direction. The five LEDs21that are connected in series in the forward direction are recognized as one set, and this one set is defined as a second LED group20. Note that in the following description, in a case of a configuration in which the second light emitting unit2has one LED21and the thyristor22, the second LED group20will be interpreted as the LED21.

The second LED group20is the LEDs21that are connected in series in the forward direction and thus has polarity, that is, has a positive electrode (anode) terminal201and a negative electrode (cathode) terminal202. The positive electrode terminal201is connected with the first connection terminal31that is connected with the positive electrode Pi1of the current source Pi. Further, the negative electrode terminal202is connected with the second connection terminal32that is connected with the negative electrode Pi2of the current source Pi via the thyristor22.

Given that forward voltages of the LEDs21are Vf21 to Vf25, because the five LEDs21of the second LED group20are connected in series in the forward direction, a total forward voltage SVf2 of the second LED group20, which is the total of the forward voltages of all the LEDs21, may be obtained by the following formula.
SVf2=Vf21+Vf22+Vf23+Vf24+Vf25
Note that in a case where all the forward voltages of the LEDs21are equivalent (Vf2),
SVf2=5×Vf2.

The light emitting device Op of the present invention causes the first light emitting unit1and the second emitting unit2to emit light while switching those, thereby switches emission colors, and performs adjustment of the beam in the switched emission color, that is, dimming. Thus, the LED11used for the first light emitting unit1and the LED21used for the second light emitting unit2are LEDs of different emission colors. For example, the LED11emits light in a first emission color (for example, neutral white: color temperature of approximately 5000 K), and the LED21emits light in a second emission color (for example, incandescent-lamp color: color temperature of approximately 3000 K). Note that the first emission color and the second emission color are examples, and emission colors are not limited to those. Further, in this embodiment, the first LED group10and the second LED group20are respective groups in which the LEDs which emit light at the same color temperature are connected in series in the forward direction, but LED groups are not limited to those. For example, LEDs of plural kinds of color temperatures are combined, and an LED group that emits light at different color temperatures may thereby be configured.

The thyristor22corresponds to “switching element” in claims. The thyristor21has an anode221, a cathode222, and a gate223. The anode221corresponds to “first terminal” in claims, the cathode corresponds to “second terminal”, and the gate223corresponds to “third terminal”.

As illustrated inFIG. 1, the anode221of the thyristor22is connected with the negative electrode terminal202of the second LED group20, and the cathode222of the thyristor22is connected with the second connection terminal32that is connected with the negative electrode Pi2of the current source Pi. Further, the gate223of the thyristor22is connected with the negative electrode terminal102of the first LED group10of the first light emitting unit1and the resistance12. In other words, the gate223is connected with the second connection terminal32that is connected with the negative electrode Pi2of the current source Pi via the resistance12.

The current flows from the anode to the cathode in the thyristor22by applying a voltage (referred to as trigger voltage) that is a prescribed voltage or more to the gate223(between the gate and the cathode) in a state where a forward voltage is applied between the anode221and the cathode222. That is, the thyristor22turns from a non-conducting state to a conducting state, and this state change will be referred to as being turned ON. Then, the thyristor22that is turned ON maintains an ON state even when the voltage of the gate223becomes low, and the current keeps flowing.

That is, the thyristor22is a switching element that is turned ON when the trigger voltage is applied to the gate223and retains the forward current regardless of the voltage of the gate223after being turned ON. Then, the thyristor22returns to the non-conducting state in a case where the voltage between an anode211and the cathode222becomes the voltage for retaining conduction or less or a case where the forward current becomes “0”. This state change will be referred to as being turned OFF.

As illustrated inFIG. 1, for an easy description, a reference point S0, a first connection point S1, and a second connection point S2are set. The reference point S0is at a reference voltage, is a ground point in the present invention, and is provided on wiring that is connected with the second connection terminal32. The cathode222of the thyristor22is connected with the reference point S0. The point at which the gate223of the thyristor22is connected with the negative electrode terminal102of the first LED group10is set as the first connection point S1. The first connection point S1is connected with the reference point S0via the resistance12.

For example, in a case where the current flows through the resistance12, the first connection point S1is at a higher voltage than the reference point S0only by the product of the resistance value of the resistance12and the flowing current value. In addition, because the cathode222of the thyristor22is connected with the reference point S0and the gate223is connected with the first connection point S1, a voltage is generated between the gate223and the cathode222when the current flows through the resistance12. Note that in this embodiment, because the reference point S0is set as the ground point and the voltage of the cathode222is “0”, the voltage between the gate223and the cathode222may simply be referred to as gate voltage. Further, the positive electrode terminal101of the first LED group10and the positive electrode terminal201of the second second LED group20are set as a second connecting point S2, and the second connection point S2is connected with the first connection terminal31.

The light emitting device Op uses above-described characteristics of the thyristor22. Details of the light emitting device Op will be described.FIG. 2is a diagram in which the thyristor in an OFF state is replaced by a switch in a circuit diagram of the illumination device illustrated inFIG. 1.FIG. 3is a diagram in which the thyristor in the ON state is replaced by a switch in the circuit diagram of the illumination device illustrated inFIG. 2. Note that inFIG. 2andFIG. 3, the current flow is indicated by arrows.

First, in a state where power is not supplied from the current source Pi (state inFIG. 1), the current does not flow through either the first light emitting unit1or the second light emitting unit2, and light is not emitted. As illustrated inFIG. 2, the thyristor22is turned OFF. In this state, when power starts being supplied from the positive electrode Pi1of the current source Pi to the first connection terminal31, the whole supplied current flows to the first LED group10of the first light emitting unit1. Note that it is assumed that in a case where the current is supplied from the current source Pi, the voltage that is the total forward voltage SVf1 or more but less than the upper limit value is applied to the second connection point S2.

Given that the current value of the current supplied from the current source Pi is a current value Ia and the current value of the current that flows through the first LED group10of the first light emitting unit1is a current value IL1, Ia=IL1holds. Then, given that the resistance value of the resistance12is a resistance value RL, because direct current flows between the first LED group10and the resistance12, the current that flows through the first LED group10flows through the resistance12without any change, that is, a current of the current value IL1flows through the resistance12. As described above, the negative electrode Pi2of the current source Pi is grounded, and the voltage of the reference point S0, which is a point on the wiring which is connected with the second connection terminal32connected with the negative electrode Pi2, is “0”. Then, because the current of the current value IL1flows through the resistance12, a voltage Vg of the first connection point S1may be obtained by the following formula.
Vg=IL1×RL

That is, the voltage of the first connection point S1is decided in accordance with the current value IL1of the current which flows through the first LED group10(here, similar to the current value Ia of the current supplied from the current source Pi) and the resistance value RL of the resistance12. Further, as illustrated inFIG. 1, the cathode222of the thyristor22is at the same potential as the reference point S0, and the gate223is at the same potential as the first connection point S1. That is, the gate voltage of the thyristor22in a case where the current of the current value IL1flows through the first LED group10is the voltage Vg.

As described above, the thyristor22is turned ON by applying the trigger voltage to the gate. Given that the voltage value at which the thyristor22is switched from OFF to ON is a voltage value Vgt, the thyristor22Keeps being turned OFF in the light emitting device Op while Vg<Vgt, and the current does not flow through the second LED group20of the second light emitting unit2. In other words, in a case where the current value IL1of the current that flows through the first LED group10satisfies IL1<Vgt/RL, the LEDs11of the first LED group10are lit. The beam amount of light in a case where the LED emits light changes in accordance with the current value. Thus, a current IL1that flows through the first LED group10is fluctuated in the range of IL1<Vgt/RL and the beam amount of light emitted from each of the LEDs11is thereby adjusted, that is, dimming of the first light emitting unit1is possible.

In addition, when the thyristor22is turned OFF, the current value Ia of the current supplied from the current source Pi is the same as the current value IL1of the current that flows through the first LED group10of the first light emitting unit1. Thus, in the illumination device A, the current value Ia that is supplied at a start of an action (that is, a power supply stopped state is fluctuated in the range of Ia<Vgt/RL, and the beam amount of light emitted from the LEDs11of the first LED group10is thereby adjusted, that is, dimming is possible. Because the LED11is an LED that emits the light in the first emission color, the illumination device A may emit light in the first emission color while performing dimming.

When the current value Ia of the current supplied from the current source Pi becomes Ia>Vgt/RL, the voltage Vg of the first connection point S1becomes higher than Vgt, and the thyristor22is turned ON. When the thyristor22is turned ON, the illumination device A has a circuit illustrated inFIG. 3. That is, the first light emitting unit1and the second light emitting unit2are in parallel connected with the current source Pi. Here, given that the current value of the current that flows through the second LED group20of the second light emitting unit2is a current value IL2, the relationship with the current value Ia of the current supplied from the current source Pi and the current value IL1of the current that flows through the first LED group10of the first light emitting unit1becomes as follows.
Ia=IL1+IL2

That is, the current (current value Ia) supplied from the current source Pi are divided at the second connection point S2into the current (current value IL1) that flows through the first light emitting unit1and the current (current value IL2) that flows through the second light emitting unit2. Accordingly, the LEDs11of the first LED group10of the first light emitting unit1and the LEDs21of the second LED group20of the second light emitting unit2emit light.

When the current value Ia of the current supplied from the current source Pi becomes Ia>Vgt/RL, because the current flows through the second light emitting unit2, the current value IL1of the current that flows through the first LED group10of the first light emitting unit1becomes small. Accordingly, the voltage value Vg (=RL×IL1) of the first connection point S1decreases and becomes lower than the voltage Vgt that turns ON the thyristor22. Once the thyristor22is turned ON, even if the voltage applied to the gate223fluctuates, the current flows between the anode and the cathode. Thus, even if the current IL1that flows through the first LED group10, that is, the resistance12decreases and the voltage value Vg, of the first connection point S1decreases, the thyristor22maintains the ON state, and the current of the current value IL2flows through the second LED group20of the second light emitting unit2.

Here, a description will be made about the relationship between the current value IL1and the current value IL2in a case where the thyristor22is turned ON. As illustrated inFIG. 3, when the thyristor22is turned ON, the first light emitting unit1and the second light emitting unit2become parallel. Here, the current supplied from the current Source Pi flows more through the first LED group10or the second LED group20, whose total forward voltage is lower. For example, in a case where the total forward voltage is in the relationship of SVf1>SVf2, the current values of the currents that flow through the LED groups are IL1<IL2.

In the light emitting device Op according to the present invention, the total forward voltage SVf1 of the first LED group10and the total forward voltage SVf2 of the second LED group20are decided such that SVf1>SVf2 and SVf1−SVf2>Th1. Here, Th1 is a threshold value and is a predetermined value. The total forward voltage SVf1 of the first LED group10and the total forward voltage SVf2 of the second LED group20are decided in such a manner, and the current value IL1of the current that flows through the first light emitting unit1and the current value IL2of the current that flows through the second light emitting unit become IL1<<IL2when the thyristor22is turned ON. Note that the threshold value Th1 is decided in accordance with the used LED.

In the illumination device A that includes the light emitting device Op in the above configuration, when the thyristor22is turned OFF, the current supplied from the current source Pi flows through the first light emitting unit1. Accordingly, the LEDs11which are included in the first light emitting unit1and whose emission color is the first emission color emit light. The thyristor22is controlled so as to be turned ON by the current supplied to the first light emitting unit1. Thus, in the illumination device A, the current supplied to the first light emitting unit1, that is, the current value Ia of the current supplied from the current source Pi is fluctuated at less than the current value (Vgt/RL) that turns ON the thyristor22, and it is thereby possible to dim the light in the first emission color (daylight color).

Further, when the thyristor22is turned ON, most of the current supplied from the current source Pi flows through the second light emitting unit2. Accordingly, the LEDs21which are included in the second light emitting unit2and whose emission color is the second emission color emit light. Here, although the current also flows through the first light emitting unit1, the current value IL1is very small, and the beam amount of light emission of the LEDs11is thus a slight amount. That is, when the thyristor22is turned ON, the second light emitting unit2that includes the LEDs21whose emission color is the second emission color mainly emits light. Although the first light emitting unit1that includes the LEDs11whose emission color is first emission light light emit light, an influence on the emission color of the light emitted from the second light emitting unit2is suppressed.

Once the thyristor22is turned ON, the thyristor22is not turned OFF unless the voltage becomes the voltage for retaining conduction between the anode and the cathode or less or the current is blocked. Thus, after the thyristor22is turned ON, the current value Ia. of the current supplied from the current source Pi is fluctuated in a range in which the voltage does not become the voltage for retaining conduction between the anode and the cathode or less, and it is thereby possible to dim the light in the second emission color (incandescent-lamp color).

Usually, as for an LED, a forward current value If is predetermined, and in a light emitting device, a circuit is designed such that a current of the forward current value If or less is caused to flow through the LED. A description will be made about a case of using the resistance12with the resistance value RL that makes the voltage of the first connection point S1become Vgt in a case where the forward current values of the LED11and the LED21are the same If and where the current of the forward current value If flows through the resistance12. In this case, in the illumination device A, when the current of the forward current value If flows through the first light emitting unit1, the voltage of the first connection point S1becomes Vgt, and the thyristor22is turned ON.

That is, because the total forward voltage SVf1 of the first LED group10of the first light emitting unit1is higher than the total forward voltage SVf2 of the second LED group20of the second light emitting unit2, it becomes difficult to cause the forward current value If to pass through. Thus, in the actual light emitting device Op, the resistance value RL of the resistance12is preferably set such that the voltage of the first connection point S1becomes below the voltage value Vgt that turns ON the thyristor22when the forward current value If flows. That is, it is preferable that RL<Vgt/If holds. However, causing a current that largely exceeds the forward current value If to flow through the LED results in failure such as malfunction. Thus, the resistance12preferably includes the resistance value RL that makes the voltage of the first connection point S1become Vgt when the current exceeds the forward current value If in a safe range for an LED10.

In addition, when the thyristor22is turned ON, the current value Ia of the current supplied from the current source Pi is larger than a forward current If. Thus, when the emission color of emitted light is switched from the first emission color to the second emission color, a current close to the forward current If flows through the second light emitting unit2. For example, depending on a using method, it is desirable to initially dim the light in the second emission color from a start of an operation. In this case, the voltage value of the first connection point S1is instantly raised to Vgt in a short period that a user may not recognize, the thyristor22is to ON, and dimming may thereafter be performed by adjusting the current source Pi. In the actual light emitting device Op, light in the first emission color is emitted from the first light emitting unit1. However, because the light is emitted in a short time, the user may not recognize the light in the first emission color. Thus, the user recognizes that the light in the second emission color is emitted from the start of the operation of the illumination device A to dim the light.

In the light emitting device Op according to this embodiment, the number of LEDs11of the first LED group10of the first light emitting unit1is the same as the number of LEDs21of the second LED group20of the second light emitting unit2. Thus, the LED11with a forward voltage Vf1 and the LED21with a forward voltage Vf2 are employed, with which the difference between the total forward voltage SVf1 of the first LED group10and the total forward voltage SVf2 of the second LED group20becomes the threshold value Th1 or more.

A specific example of the light emitting device Op that has a circuit configuration as descried above will be described with reference to the drawings.FIG. 4is a diagram that illustrates an outline configuration of the light emitting device according to the present invention. As illustrated inFIG. 4, the light emitting device Op is provided with a substrate Ed and printed wiring Ph that is formed on an upper surface of the substrate Bd. The printed wiring Ph has a first path Ph1for connecting the five LEDs11of the first LED group10of the first light emitting unit1in series and a second path Ph2for connecting the five LEDs21of the second LED group20of the second light emitting unit2in series.

End portions of the first path Ph1and the second path Ph2on positive electrode sides are connected together at one point. In addition, the printed wiring Ph includes the first connection terminal31that extends from a connecting point on the positive electrode side to an end portion of the substrate Bd. Further, end portions of the first path Ph1and the second path Ph2on negative electrode sides are connected together at one point. In addition, the printed wiring Ph includes the first connection terminal31that extends from a connecting point on the negative electrode side to the end portion of the substrate Bd. Note that as illustrated inFIG. 1and so forth, the positive electrode Pi1of the current source Pi and the negative electrode Pi2of the current source Pi are respectively connected with the first connection terminal31and the second connection terminal32.

As illustrated inFIG. 4, the first path Ph1and the second path Ph2are in shapes in which protrusion portions are inserted in respective recess portions. In addition, the LEDs11and the LEDs21are mounted on the respective protrusion portions. Mounting in such a manner makes the LEDs11and the LEDs21be aligned at regular intervals in a linear manner. Alignment in such a manner enables beams of light emitted from the illumination device A to be made uniform when the LEDs11of the first LED group10emit light or when the LEDs21of the second LED group20emit light.

In the illumination device A of the present invention, the thyristor22may be turned ON or OFF by fluctuating the current value Ia of the current supplied from the current source Pi. In addition, the current value Ia of the current supplied from the current source Pi is fluctuated, and it is thereby possible to switch the emission color of light emitted from the illumination device A into the first emission color (here, neutral white) or the second emission color (here, incandescent-lamp color) and to perform dimming in each of the emission colors.

In the illumination device A according to the present invention, as described above, the thyristor22may be turned into the OFF state or the ON state by adjusting the current value of the current supplied from the current source Pi. Thus, a control unit is not requested which generates and outputs a control signal for controlling the thyristor. Accordingly, the number of components may be decreased, and the costs requested for manufacture may be reduced. Further, because the number of components is lessened, size reduction and weight saving are easy.

The illumination device A according to the present invention has a configuration in which the thyristor22or a switching element23is connected with the negative electrode terminal202of the second LED group20. However, the configuration is not limited to this, but the thyristor22or the switching element23may be connected with the positive electrode terminal201. In this case, the anode221of the thyristor22is connected with the second connection point S2, and the cathode222is connected with the positive electrode terminal201of the second LED group20. Further, the gate223of the thyristor22is connected with the first connection point S1. In such a configuration, because the current flows from the anode to the cathode when the thyristor22is turned ON, the current flows through the second LED group20. Further, the thyristor22may be attached among the plural LEDs21of the second LED group20.

The thyristor22used for the illumination device A according to the present invention is a semiconductor element, and the voltage at which the thyristor22is turned ON changes in accordance with the change in temperature.FIG. 5is a diagram that illustrates a temperature characteristic of the thyristor. In a graph illustrated inFIG. 5, the vertical axis represents the voltage value (V) at which the thyristor22is turned ON, and the horizontal axis represents the temperature of the thyristor22.

As described above, the thyristor22is turned ON in accordance with the magnitude of the current IL1that flows through the first light emitting unit1. That is, when the relationship of IL1Vgt/RL holds among the current that flows through the first light emitting unit1, a gate voltage Vgt, and a resistance R, the thyristor22is turned ON. Meanwhile, as illustrated inFIG. 5, the voltage value Vgt of the gate voltage for turning ON the thyristor22becomes low due to a temperature rise of the thyristor. For example, in a case where the resistance value RL of the resistance12is a fixed value, when the voltage value Vgt becomes small, the thyristor22is switched ON even if the current that flows through the first light emitting unit1is small. In the illumination device A, as the temperature of the thyristor22rises more, the thyristor22is turned ON at the smaller current value IL1, and the range of dimming in the first emission color becomes narrower.

In order to handle such a change, due to the temperature of the thyristor22, in the gate voltage Vgt at which the thyristor22is turned ON, it is preferable to use a resistance, which has a characteristic in which the resistance value becomes small in response to the temperature rise (negative resistance), as the resistance12of the first light emitting unit1. Because the current does not flow when the thyristor22is turned OFF, a main cause of the temperature rise of the thyristor22is heat generation by the LEDs11of the first LED group10. The heat of the LEDs11is transmitted to the resistance12, and the temperature of the resistance12also rises. In a case where the resistance12has the negative resistance, a gate voltage value Vgt at which the thyristor22is turned ON becomes low, and the resistance value RL of the resistance12also becomes low. Thus, the change in the current value IL1that flows through the first light emitting unit1in a case where the thyristor22is turned ON may be made small. Accordingly, in the illumination device A, even if the temperature of the thyristor22, that is, the temperature on the inside of the device changes, the range of dimming of the light in the first emission color may be inhibited from changing.

Note that as a resistance that has the negative resistance, ceramics in which oxides of metal such as manganese (Mn), nickel (Ni), and cobalt (Co) are fired, semiconductors that use silicon (Si), germanium (Ge), gallium nitride (GaN), gallium arsenide (GaAs), and indium gallium nitride (InGaN), and so forth may be raised. A material of the resistance12is selected in accordance with the change, due to the temperature, in the gate voltage Vgt at which the thyristor22is turned ON, and the range of dimming of the light in the first emission color may be inhibited from changing due to the temperature.

Modification Example

In this embodiment, a configuration is provided which includes the thyristor22in series with the second LED group20of the second light emitting unit2. Embodiments are not limited to the thyristor. For example, a switching element in a configuration illustrated inFIG. 6may be used instead of the thyristor22.FIG. 6is a diagram that illustrates the switching element which is used instead of the thyristor. Note thatFIG. 6illustrates a configuration that uses two bipolar transistors. Here, the configuration will be described as the switching element23.

The switching element23illustrated inFIG. 6is an equivalent circuit to the thyristor, in which a PNP bipolar transistor231and an NPN bipolar transistor232are combined. The switching element23connects a base terminal of the PNP bipolar transistor231with a collector terminal of an NPN bipolar transistor. Further, a collector terminal of the PNP bipolar transistor231is connected with a base terminal of the NPN bipolar transistor. In addition, an emitter terminal of the PNP bipolar transistor231of the switching element23is connected with the negative electrode terminal202of the second LED group20of the second light emitting unit2. Further, an emitter terminal of the NPN bipolar transistor232is connected with the reference point S0. In addition, a base terminal of the NPN bipolar transistor232is connected with the first connection point S1.

In the switching element23in such a configuration, a voltage is applied to the base terminal of the NPN bipolar transistor232, a current thereby flows from an emitter to a base of the PNP bipolar transistor231, and the current flows from a collector to an emitter of the NPN bipolar transistor232. Further, a base of the NPN bipolar transistor232is at the same voltage as a collector voltage of the PNP bipolar transistor231. Thus, because a state where the voltage for conduction between the collector and the emitter of the NPN bipolar transistor is retained even if the voltage at the first connection point S1, the switching element23retains the ON state.

It is possible to perform a similar action to the thyristor22by using such a switching element23.

Second Embodiment

Another example of the illumination device according to the present invention will be described with reference to the drawings.FIG. 7is a diagram that illustrates another example of the illumination device according to the present invention. An illumination device B illustrated inFIG. 7has the same configuration as the illumination device A except that a first light emitting unit1bis different. Thus, the same portions of the illumination device B as the illumination device A are provided with the same reference characters, and detailed descriptions of the same portions will not be made.

The relationship of Vf1>Vf2 is present between the forward voltage Vf1 of the LED11and the forward voltage Vf2 of the LED21, which are used in the illumination device A. Thus, the total forward voltage SVf1 of the first LED group10in which the five LEDs11are connected in series becomes large compared to the total forward voltage SVf2 of the second LED group20in which the five LEDs21are connected in series in the same manner.

Meanwhile, there may be a case where the forward voltage Vf1 of the LED11is the same as the forward voltage Vf2 of the LED21. In this case, the total forward voltage SVf1 of the first LED group10becomes the same value as the total forward voltage SVf2 of the second LED group20. In the illumination device B, in order to accurately switch the first emission color and the second emission color, the total forward voltage SVf1 and the total forward voltage SVf2 are set such that SVf1 SVf2>Th1 holds. In a case of Vf1=Vf2, the number of LEDs11is made more than the number of LEDs21, and it thereby becomes possible to obtain a configuration that satisfies the above-described condition.

In the illumination device, there may be a case where the beam amount of the light in the first emission color is set to the same beam amount as the beam amount of the light in the second emission color. In a case where the beam amounts of light emitted by the LED11and the LED21are the same, it is difficult to provide different numbers of LEDs11and LEDs21. Thus, in the illumination device B, the first light emitting unit in includes a diode13that is disposed in series with the first LED group10. The diode13is arranged between the negative electrode terminal102of the first LED group10and the first connection point S1. In such a manner, the forward voltage of the diode13that is connected in series with the first LED group10of the first light emitting unit1is adjusted, and a total forward voltage SVf1b of the first LED group10that includes the diode13may thereby be set such that SVf1b−SVf2>Th1 holds.

Accordingly, in the illumination device A, when the thyristor22is turned OFF, the current supplied from the current source Pi flows through the first light emitting unit1b, and the light in the first emission color is emitted from the LEDs11of the first LED group10. Further, when the thyristor22is turned ON, most of the current supplied from the current source Pi flows through the second light emitting unit2, and the light in the second emission color is emitted from the LEDs21of the second LED group20.

As discussed above, in the illumination device13, the diode13is connected in series with the first LED group10, and it is possible to adjust the total forward voltage SVf1b by a simple configuration. Note that in this embodiment, a description is made on an assumption that all the forward voltages of the used LEDs are the same. However, embodiments are not limited to this. For example, in order to adjust the difference between the total forward voltage of the first LED group10of the first light emitting unit1band the total forward voltage of the second LED group20of the second light emitting unit2, a diode may be connected in series. Note that in this embodiment, it is assumed that the diode is connected in series with an LED group of a first light emitting unit. However, embodiments are not limited to this. For example, in a case where the difference between the total forward voltages is too large, the diode may be connected in series with the LED group of the second light emitting unit2. Further, diodes with different forward voltages may respectively be connected in series with the LED groups of both of the light emitting units, and the difference between the total forward voltages may thereby be adjusted. Further, the number of connected diodes is not limited to one, but plural diodes may be connected.

Third Embodiment

Still another example of the illumination device according to the present invention will be described with reference to the drawings.FIG. 8is a diagram that illustrates still another example of the illumination device according to the present invention. As for an illumination device C illustrated inFIG. 8, in a first light emitting unit1c, three first LED groups10cin which plural (here, five) LEDs11are connected in series are connected in parallel. Further, in a second light emitting unit2c, five second. LED groups20cin which plural (here, three) LEDs21are connected in series are connected in parallel. The other portions than those are the same as the illumination device A of the first embodiment. Thus, in a configuration of the illumination device C, substantially same portions as the illumination device A are provided with the same reference characters, and detailed descriptions of the same portions will not be made.

A current flows through an LED by applying a voltage that is a predetermined voltage or more in the forward direction in other words, for the LED, the voltage that is the predetermined voltage or more has to be applied in the forward direction. Thus, there is an upper limit for the number of LEDs that are connectable in series in accordance with the applied voltage and the characteristics of the LED. In the illumination device C, depending on the demanded beam amount, more LEDs than the number of LEDs connectable in series may be requested. Thus, in the illumination device C, the plural LED groups, in which a less number of LEDs than the upper limit of the number of LEDs connectable in series are connected in series, are connected in parallel, and the demanded numbers of LEDs are thereby mounted.

As illustrated inFIG. 8, in the illumination device C, the first light emitting unit1cincludes the three first LED groups10cin which the five LEDs11are connected in series. In addition, the three first LED groups10care connected in parallel. That is, the three first LED groups10care connected in parallel with respect to the current source Pi. In the first light emitting unit1c, the first LED groups10care connected in parallel, and a total forward voltage SVf1c of the first light emitting unit1cis the same as a total forward voltage of the first LED groups10c, that is, SVf1c=5×Vf1 holds. Further, the resistance12is connected in series with the first LED groups10cthat are connected in parallel.

As illustrated inFIG. 8, in the illumination device C, the second light emitting unit2cincludes the five second LED groups20cin which the three LEDs21are connected in series. In addition, the five second LED groups20care connected in parallel. That is, the five second LED groups20care connected in parallel with respect to the current source Pi. In the second light emitting unit2c, the second LED groups20care connected in parallel, and a total forward voltage SVf2c of the second light emitting unit2cis the same as a total forward voltage of the second LED groups20c, that is, SVf2c−3×Vf2 holds. Further, the thyristor22is connected in series with the second LED groups20cthat are connected in parallel.

In the illumination device C, the first light emitting unit1cincludes15LEDs11, and the second light emitting unit2cincludes15LEDs21. Thus, it is possible to make the beam amounts of light emitted from the illumination device C the same or substantially same between the light in the first emission color and the light in the second emission color.

In addition, in a case where the forward voltages of the LEDs11and21are the same, that is, Vf1=Vf2 holds, the number of LEDs connected in series in the first light emitting unit1cis large compared to the second light emitting unit2c, and thus SVf1c>SVf2c holds. Note that in the illumination device C according to the present invention, because the number of LEDs is 15 for each of the first light emitting unit1cand the second light emitting unit2c, the selection ranges of the number of LEDs aligned in series and the number of LEDs in parallel are narrow. However, in a case where much more LEDs are used, more combinations of LEDs in series and in parallel are provided. Among the combinations, the first light emitting unit1cand the second light emitting unit2care formed in the combination that makes SVf1c−SVf2c>Th1 hold. Accordingly, the illumination device C is capable of switching the emission color of emitted light to the first emission color or the second emission color by turning ON or OFF the thyristor22.

In such a manner, in the illumination device C, the number of LEDs connected in series and the number of parallel connections of the LEDs connected in series may be adjusted, and it is possible to switch the emission colors and to perform dimming in each of the emission colors by a simple configuration. The other characteristics than those are the same as the first embodiment and the second embodiment.

In a configuration in which plural LEDs are connected in series and the LEDs connected in series are connected in parallel, work for connection is likely to become troublesome. Thus, one chip may be formed as a light emitting device Opc.FIG. 9is a diagram that illustrates an outline configuration of a light emitting device according to the present invention.

As illustrated inFIG. 9, the light emitting device Opc has the substrate Bd, a first wiring pattern Pt1, a second wiring pattern Pt2, a third wiring pattern Pt3, the resistance12, the thyristor22, a first land unit Ld1, a second land unit Ld2, a first sealing unit Cv1, and a second sealing unit Cv2. The resistance12and the thyristor22are the same as those described above, and details will thus not be described.

In the light emitting device Opc of this embodiment, the first wiring pattern Pt1, the second wiring pattern Pt2, and the third wiring pattern Pt3are arcs which are formed on a circumference with the same center and radius and whose central angles are different. In addition, the second wiring pattern Pt2and the third wiring pattern. Pt3are formed while neighboring each other, and the first wiring pattern Pt1is formed to be opposed to the second wiring pattern Pt2and the third wring pattern Pt3. In the light emitting device Opc illustrated inFIG. 9, the first light emitting unit1cthat includes plural first LED groups10cand the second light emitting unit2cthat includes plural second LED groups20care arranged in a circular portion that is surrounded by the first wiring pattern Pt1, the second wiring pattern Pt2, and the third wiring pattern Pt3. Note that in a state illustrated inFIG. 9, the first light emitting unit1cis arranged in a lower half of the light emitting device Opc, and the second light emitting unit2cis arranged in an upper half.

The first light emitting unit1cincludes plural first LED groups10c, and the plural first LED groups10care connected in parallel. The first LED group10cuses a LED chip11cformed as a chip. In the first LED group10c, plural LED chips11care connected in series by using wires Wr. Note that in consideration of viewing easiness of the drawing, in the light emitting device Opc illustrated inFIG. 9, three first LED groups10cin which four LED chips11care connected in series are connected in parallel in the first light emitting unit1c. Further, similarly to the first light emitting unit1c, the second light emitting unit2cincludes plural second LED groups20c, and the plural second LED groups20care connected in parallel. Similarly to the first LED group10c, the second LED group20calso uses a LED chip21cformed as a chip. In the second LED group20c, plural LED chips21care connected in series by using wires Wr. Note that in consideration of viewing easiness of the drawing, in the light emitting device Opc illustrated inFIG. 9, four second LED groups20cin which three LED chips21care connected in series are connected in parallel in the second light emitting unit2c. The first light emitting unit1cincludes12LED chips11c, and the second light emitting unit2cincludes12LED chips21c. That is, in the light emitting device Opc illustrated inFIG. 9, the numbers of LED chips11cand21cthat are respectively included in the first light emitting unit1cand the second light emitting unit2care the same numbers. However, the numbers are not limited to the same numbers but may be different numbers.

The first wiring pattern Pt1is printed wiring that is formed on the substrate Bd. Positive electrodes of the first LED groups10cand positive electrodes of the second LED groups20care connected with the first wiring pattern Pt1. That is, the first wiring pattern Pt1is a common wiring pattern to both of the first light emitting unit1cand the second light emitting unit2c. The first wiring pattern Pt1is connected with the first LED groups10cand the second LED groups20cby the wires Wr.

The first wiring pattern Pt1is connected with the first land unit Ld1via a wiring pattern. A first land Ld1is a terminal with which the positive electrode Pi1of the current source Pi is connected and is the first connection terminal31.

Negative electrodes of the first LED groups10care connected with the second wiring pattern Pt2. The second wiring pattern Pt2is connected with a second land Ld2via a resistance. The second land Ld2is a terminal with which the negative electrode Pi2of the current source Pi is connected and is the second connection terminal32. That is, the three first LED groups10care connected with the first wiring pattern Pt1on their positive electrode sides, are connected with the second wiring pattern Pt2on their negative electrode sides, and are thereby connected in parallel.

Negative electrodes of the second LED groups20care connected with the third wiring pattern Pt3. The third wiring pattern Pt3is connected with the second land unit Ld2via the thyristor22. The anode221of the thyristor22is connected with the third wiring pattern Pt3, the cathode222is connected with the second land Ld2, and the gate223is connected with the second wiring pattern Pt2. That is, the second LED groups20care connected with the first wiring pattern Pt1on their positive electrode sides, are connected with the third wiring pattern Pt3on their negative electrode sides, and are thereby connected in parallel.

The light emitting device Opc includes the first sealing unit Cv1that seals a portion between the first wiring pattern Pt1and the second wiring pattern Pt2of the substrate Bd by a resin and the second sealing unit Cv2that seals a portion between the first wiring pattern Pt1and the third wiring pattern Pt3by a resin. The first sealing unit Cv1seals the first light emitting unit1cthat includes the three first LED groups10c, and the second sealing unit Cv2seals the second light emitting unit2cthat includes the four second LED groups20c.

The first sealing unit Cv1and the second sealing unit Cv2have a sealing resin layer that uses a transparent resin such as a silicone resin or an epoxy resin. The first sealing unit Cv1and the second sealing unit Cv2are provided for purposes such as protection of the LED chips11c, the LED chips21c, and the wires Wr, an improvement in light-output efficiency, changes in light distribution characteristics, and further retainment of a phosphor that converts the emission colors. Note that in a configuration in which the characteristics of the sealing units are the same, for example, the emission colors of the LED chips are used without any change, that is, in a case where conversion of the emission colors are not requested or the substances that convert light are the same, the first sealing unit Cv1and the second sealing unit Cv2may be integrated into one sealing unit and may thereby seal the whole.

As discussed above, the light emitting device Opc may be formed as a chip on board (COB) in which plural LED chips11cand plural LED chips21care mounted on a surface of the substrate Bd. In such a manner, size reduction is possible by integrating plural LED chips into one chip. Further, only two pieces of wiring for current supply are used, and costs may thus be lowered. Moreover, because the LED chips are dealt with as one light source by devising the sealing unit, it is possible to inhibit production of plural shadows of an object that is irradiated with light or blurriness and to cause the user not to experience an uncomfortable feeling.

Note that in this embodiment, the first wiring pattern Pt1, the second wiring pattern Pt2, and the third wiring pattern Pt3are arc shapes. However, embodiments are not limited to this. Note that in this embodiment, the different sealing units seal the three first LED groups10cand the four second LED groups20c. However, in a configuration in which the emission colors of the LED chips are used without any change, that is, in a case where conversion of the emission colors is not requested or the substances that convert the emission colors are the same, one sealing unit may seal the whole. In this case, a connected body in which the plural LED chips11care connected in series and a connected body in which plural LED chips21care connected in series may be disposed alternately in parallel directions.

In this embodiment, the resistance12and the thyristor22are arranged on the substrate Bd. However, in addition to direct mounting, a land for connection is prepared on the substrate Bd, and the resistance12separately provided from the substrate Bd may be connected with the thyristor22through the land.

Modification Example 1

Still another example of the light emitting device according to this embodiment will be described with reference to the drawings.FIG. 10is a diagram that illustrates still another example of the Light emitting device which configures the illumination device of the third embodiment. Members that configure a light emitting device Opc1illustrated inFIG. 10are the same as the light emitting device Opc illustrated inFIG. 9. Thus, the members that configure the light emitting device Opc1are provided with the same reference characters as the light emitting device Opc.

In the light emitting device Opc1illustrated inFIG. 10, the first wiring pattern Pt1and the second wiring pattern Pt2are arc shapes which are formed on a circumference with the same center and radius. Note that in a state illustrated inFIG. 10, the first wring pattern Pt1is arranged on the left, and the second wiring pattern Pt2is arranged on the right. In addition, the third wiring pattern Pt3is an arc shape which is formed on a circumference with the same center as the first wiring pattern Pt1and the second wiring pattern Pt2and with a larger radius than those. The third wiring pattern Pt3is arranged on the outside of the second wiring pattern Pt2. That is, the first wiring pattern. Pt1and the second wiring pattern Pt2are opposed to each other. In addition, the third wiring pattern Pt3is arranged on the outside of the second wiring pattern Pt2.

As illustrated inFIG. 10, the light emitting device Opc1has the first light emitting unit1cthat includes plural (here, three) first LED groups10cand the second light emitting unit2cthat includes plural (here, four) second LED groups20c. The first light emitting unit1cthat includes the three first LED groups10cis arranged in a central portion in an up-down direction between the first wiring pattern Pt1and the second wiring pattern Pt2. That is, the three first LED groups10care collectively arranged in the central portion in a crossing (orthogonal) direction with respect to an alignment direction of the first wiring pattern Ph1and the second wiring pattern Pt2.

Further, the two second LED groups20cas a set are collectively arranged in each of higher and lower portions than a portion, in which the first light emitting unit1cis arranged, between the first wiring pattern Pt1and the second wiring pattern Pt2. In the light emitting device Opc1, as for the second light emitting unit2c, the two second LED groups20cas a set are arranged in each of the higher and lower portions, dividedly. That is, in the light emitting device Opc1, the first light emitting unit1cthat includes the three first LED groups10cis arranged between the second light emitting units2cthat are dividedly arranged.

In addition, in the light emitting device Opc1, the first wiring pattern Pt1is connected with the positive electrodes of the first LED groups10cand the second LED groups20c. The first wiring pattern Pt1is connected with the first LED groups10cand the second LED groups20cby the wires Wr. The first wiring pattern Pt1is a common wiring pattern that are connected with both of the first LED groups10cand the second LED groups20c.

The second wiring pattern Pt2is connected with the negative electrodes of the first LED groups10c. The second wiring pattern Pt2is connected with the first LED groups10cby the wires Wr. The third wiring pattern Pt3is connected with the negative electrodes of the second LED groups20c. The third wiring pattern Pt3is connected with the second LED groups20cby the wires Wr.

The light emitting device Opc1has the first sealing unit Cv1and plural (here, two) second sealing units Cv2. The first sealing unit Cv1seals the three first LED groups10c. Further, the two second sealing units Cv2seal the respective sets of the two second LED groups20cthat are arranged across the three first LED groups10c. Note that to facilitate viewing of the drawing, the first sealing unit Cv1is hatched.

Note that in this embodiment, the two second sealing units Cv2are divided but may be coupled together at end portions. Further, in a configuration in which the characteristics of the sealing units are the same, for example, the emission colors of the LED chips are used without any change, that is, in a case where conversion of the emission colors are not requested or the substances that convert light are the same, the first sealing unit Cv1and the second sealing units Cv2may be integrated into one sealing unit and may thereby seal a whole portion in which the LED chips are arranged.

As illustrated inFIG. 10, in the light emitting device Opc1, in a region in which the LED chips are arranged, that is, a portion between the first wiring pattern Pt1and the second wiring pattern Pt2, the LED chips11care evenly or substantially evenly arranged in the central portion. That is, plural LED chips11care arranged in the central portion between the first wiring pattern Pt1and the second wiring pattern Pt2in a well-balanced manner in up-down and left-right directions.

Further, in the light emitting device Opc1, plural LED chips21care evenly or substantially evenly arranged across the first light emitting unit1c. That is, the plural LED chips21care arranged in the portion between the first wiring pattern Pt1and the second wiring pattern Pt2in a well-balanced manner in up-down and left-right directions.

That is, viewing the light emitting device Opc1illustrated inFIG. 10, the LED chips11cand the LED chips21care arranged line-symmetrically or substantially line-symmetrically to a first line L1that extends in the alignment direction of the first wiring pattern Pt1and the second wiring pattern Pt2and to a second line L2that is orthogonal to the first line L1. That is, the LED chips11cand the LED chips21care arranged line-symmetrically or substantially line-symmetrically to each of two orthogonal lines (L1and L2).

The plural LED chips11cand the plural LED chips21care arranged in a state with low unevenness. Accordingly, unevenness of the beams in a case where the LED chips11cemit light may be lessened. Accordingly, when the LED chips21cemit light, unevenness of the beams may be lessened with respect to light that is irradiated with light.

Based on the above description, the light emitting device Opc1of this modification example is used, and it is thereby possible to irradiate an irradiation target with the light in the first emission color and the light in the second emission color with less unevenness.

Modification Example 2

Another example of the light emitting device according to this embodiment will be described with reference to the drawings.FIG. 11is a diagram that illustrates another example of the light emitting device which configures the illumination device of the third embodiment. Members that configure a light emitting device Opc2illustrated inFIG. 11are the same as the light emitting device Opc illustrated inFIG. 9. Thus, the members that configure the light emitting device Opc2are provided with the same reference characters as the light emitting device Opc. Note that to facilitate viewing of the drawing, the first sealing units Cv1are hatched.

As illustrated inFIG. 11, in the light emitting device Opc2, the first light emitting unit1cthat includes three first LED groups10cand the second light emitting unit2cthat includes four second LED groups20care arranged in a portion between the first wiring pattern Pt1and the second wiring pattern Pt2. In the light emitting device Opc2, the first LED groups10cand the second LED groups20care, arranged alternately. That is, in the light emitting device Opc2, as for the first light emitting unit1c, the first LED groups10care arranged one by one dividedly. In addition, the second LED groups20cof the second light emitting unit2care arranged one by one among the first light emitting units1cthat are dividedly arranged. In other words, in the light emitting device Opc2, as for the second light emitting unit2c, the second LED groups20care arranged one by one dividedly. In addition, the first LED groups10cof the first light emitting unit1care arranged one by one among the second right emitting units2cthat are dividedly arranged.

The light emitting device Opc2has plural (here, three) first sealing units Cv1and plural (here, four) second sealing units Cv2. The three first sealing units Cv1respectively seal the first LED groups10c. Further, the four second sealing units Cv2respectively seal the second LED groups20c. That is, the three first sealing units Cv1and the four second sealing units Cv2are arranged alternately. Note that in this embodiment, the first sealing units Cv1are divided so as to be capable of sealing the respective first LED groups10c. However, embodiments are not limited to this. For example, the first sealing units Cv1may be coupled together on the first wiring pattern Pt1side. Similarly, the second sealing units Cv2are divided but may be coupled together on the opposite side to the first sealing units Cv1. Further, in a configuration in which the characteristics of the sealing units are the same, for example, the emission colors of the LED chips are used without any change, that is, in a case where conversion of the emission colors are not requested or the substances that convert light are the same, the first sealing units Cv1and the second sealing units Cv2may be integrated into one sealing unit and may thereby seal a whole portion in which the LED chips are arranged.

In the light emitting device Opc2, the first LED groups10cand the second LED groups20care arranged alternately. In the light, emitting device Opc2, such a configuration lessens unevenness of arrangement of plural LED chips11c. That is, the plural LED chips11care arranged in the portion between the first wiring pattern Pt1and the second wiring pattern Pt2in a well-balanced manner.

Further, in the light emitting device Opc2, unevenness of arrangement of plural LED chips21cis lessened. That is, the plural LED chips21care arranged in the portion between the first wiring pattern Pt1and the second wiring pattern Pt2in a well-balanced manner.

That is, viewing the emitting device Opc2illustrated inFIG. 11, the LED chips11cand the LED chips21care arranged line-symmetrically or substantially line-symmetrically to the first line L1that extends in the alignment direction of the first wiring pattern Pt1and the second wiring pattern Pt2and to the second line L2that is orthogonal to the first line L1. That the LED chips11cand the LED chips21care arranged line-symmetrically or substantially line-symmetrically to each of the two orthogonal lines (L1and L2).

In the light emitting device Opc2, the plural LED chips11cand the plural LED chips21care arranged in a state with low unevenness. Accordingly, unevenness of the beams of light emitted from the first light emitting unit1cmay be lessened. Further, unevenness of the beams of light emitted from the second light emitting unit2cmay be lessened.

Based on the above description, the light emitting device Opc2of this modification example is used, and it is thereby possible to irradiate an irradiation target with the light in the first emission color and the light in the second emission color with low unevenness. Note that in the above-described light emitting units, the LED groups in which plural LEDs are connected in series in the forward direction are connected in parallel. However, embodiments are not limited to this. For example, in a case of a configuration that is capable of emitting light with sufficient beams, individual LEDs may be connected in parallel.

Fourth Embodiment

Yet another example of the illumination device according to the present invention will be described with reference to the drawings.FIG. 12is a diagram that illustrates yet another example of the illumination device according to the present invention. An illumination device D illustrated inFIG. 12includes a light emitting device Opd that is capable of switching n (n≥3) emission colors and of performing dimming in each of the emission colors.

As illustrated inFIG. 12, the light emitting device Opd includes a first light emitting unit O1of a first emission color to an nth light emitting unit Onof an nth emission color. The first emitting unit O1to the nth light emitting unit On are connected in parallel. In each of those, a positive electrode side is connected with the first connection terminal31, and a negative electrode side is connected with the second connection terminal32. The first light emitting unit O1includes a first LED group Lt1in which plural (here, five) LEDs L1of the first emission color are connected in series and a resistance R1. Note that for convenience of description, the LED is denoted with L1, the first LED group is denoted with Lt1, and the resistance is denoted with R1. However, those are the same as the LED11, the first LED group10, and the resistance12, respectively.

Making a description about a kth light emitting unit Okthat is the kth (k=2, 3, . . . , n−1) light emitting unit as an example, in the kth light emitting unit Ok, a kth LED group Ltkin which plural (here, five) LEDs Lkof the kth emission color are connected in series, a thyristor Sck, and a resistance Rkare connected in series. As for the thyristor Sckof the kth light emitting unit Ok, an anode is connected with the kth LED group Ltk, and a cathode is connected with the second connection terminal3via the resistance Rk. Further, a base terminal is connected with a terminal on a positive electrode side (in other words, a high voltage side) of a resistance Rk-1of a k−1th light emitting unit Ok-1.

Moreover, in the nth light emitting unit Onthat is the nth light emitting unit, an nth LED group Ltnin which plural (here, five) LEDs Lnof the nth emission color are connected in series and a thyristor Scnare connected in series. As for the thyristor Scnof the nth light emitting unit On, the anode is connected with the nth LED group Ltn, and the cathode is connected with the second connection terminal32. Further, the base terminal is connected with the terminal on the positive electrode side (in other words, the high voltage side) of a resistance Rn-1of an n−1th light emitting unit On-1.

A description will be made about a light emitting action of the illumination device D that includes this light emitting device Opd. In the light emitting device Opd in a state where power is not supplied, all thyristors are in the OFF state. In this state, when a higher voltage than a total forward voltage is applied to each LED group and power is supplied. Accordingly, a current first flows through the first LED group Lt1of the first light emitting unit O1, and the five LEDs L1emit light. Accordingly, the light in the first emission color is emitted. In addition, the voltage of the resistance R1on the positive electrode side is expressed by the product of a resistance value RL1of the resistance R1and a flowing current value IL1. When the voltage of the resistance R1on the positive electrode side is the gate voltage of a thyristor Sc2disposed for a second light emitting unit O2and the gate voltage exceeds a specific voltage, the thyristor Sc2is turned ON. That is, the current flows through a second LED group Lt2.

The thyristor Sc2is turned ON, and most of the current supplied from the current source Pi thereby flows through the second LED group Lt2, and LEDs L2emit light. The current supplied from the current source Pi is changed in this state, and it is thereby possible to perform dimming in a second emission color. In addition, the current that flows through the second LED group Lt2flows through the resistance R2, and the voltage of the resistance R2on the positive electrode side is expressed by the product of a resistance value RL2of the resistance R2and a flowing current value IL2. In addition, the voltage of the resistance R2on the positive electrode side is the gate voltage of a thyristor Sc3of a third light emitting unit O3. When the gate voltage exceeds a specific value, a thyristor Sc3is turned ON, the current flows through a third LED group Lt3of the third light emitting unit O3, and LEDs L3emit light.

Note that in order to cause most of the current supplied from the current source Pi to flow through the light emitting unit that includes the thyristor when the concerned thyristor is turned ON, the total forward voltage of the LED group has to be higher than the LED group of the light emitting unit whose thyristor is turned ON immediately before the concerned thyristor. That is, given that the total forward voltage of the kth LED group Ltkof the kth light emitting unit Okis SVf-k, the total forward voltage SVf-kof the kth LED group Ltkis decided such that the relationship of SVfk-1−SVfk>Thkholds. Note that the kth LED group Ltkis the LED group whose total forward voltage is the maximum among the LED groups whose total forward voltages are lower than a k−1th LED group Ltk-1. In addition, Thkmay be a value that varies in accordance with a variable k or may be a common value.

In such a configuration, the illumination device D is capable of emitting light in plural emission colors and of performing dimming in each of the emission colors.

In the above-described embodiments, the thyristor is used as the switching element. However, embodiments are not limited to this. For example, a gate turn off (GTO) thyristor may be used. The GTO thyristor causes a current to flow from a cathode to a gate, that is, makes the gate voltage lower than the cathode and may thereby stop the current that flows from an anode to the cathode. The GTO thyristor is used, and it thereby becomes possible to turn OFF the thyristor without stopping the current supplied from the current source and to perform more kinds of control. Note that in a case where the GTO thyristor is used, in addition to the above-described circuit that applies the voltage by using the resistance, a circuit, an element, or the like that applies a lower voltage than the cathode to the gate is included.

In the above-described embodiments, as a light emitting device, a substrate on which LEDs, a thyristor, and a resistance are mounted is described. However, a light emitting device is not limited to this. The light emitting device may include a configuration for connection with a separately prepared power source device (for example, a connector or the like). Moreover, the light emitting device may have configuration in which a substrate which includes the above-described circuit together with a heat dissipation tool or an optical tool such as a lens is incorporated in a housing. For example, the light emitting device is usable as a spotlight, a ceiling light, or an LED light bulb. That is, the light emitting device may be an apparatus on which LEDs are mounted and which is connected with a separately prepared power source and emits light by being supplied with power (current) from the power source.

In the foregoing, the embodiments of the present invention have been described. However, the present invention is not limited to those contents. Further, various modifications may be applied to the embodiments of the present invention without departing from the gist of the present invention.

A light emitting device according to the present invention, which is described in the foregoing, includes plural light emitting units in which at least one light emitting diode is disposed. The plural light emitting units respectively have different emission colors and forward voltages, the other light emitting units than the light emitting unit whose forward voltage is a maximum are provided with a switching element that is connected in series with the light emitting diode, and the other light emitting units than the light emitting unit whose forward voltage is a minimum are provided, on a negative electrode side, with a resistance that is connected in series with the light emitting diode. The switching element is an element that includes a first terminal, a second terminal, and a third terminal, causes the first terminal and the second terminal to turn into a conducting state by applying a prescribed voltage to the third terminal, and subsequently retains the conducting state in a case where a voltage of the third terminal is within a specific range. A terminal of the resistance on a positive electrode side is electrically connected with the third terminal of the switching element that is provided to the light emitting unit whose forward voltage is highest among the light emitting units whose forward voltages are lower than the light emitting unit that is provided with the resistance.

Consequently, the switching element is turned ON by changing the supplied current, light emission by the light emission units are thereby switched, and adjustment of the beams, that is, dimming is performed by fluctuating the current in a range in which the switching element is not turned ON. Then, after the switching element is turned ON, the switching element is not turned OFF unless current supply is stopped. Thus, the supplied current value is appropriately adjusted, and it is thereby possible to arbitrarily change the emission colors of light emission and to perform dimming in each of the emission colors. Accordingly, a control circuit for switching the light emission and dimming is not requested, and it is thereby possible to make the light emitting device have a simple configuration. In addition, the simple configuration enables size reduction and weight saving and enables costs to be lowered.

In the above-described light emitting device, at least one of the switching elements may be configured to include a thyristor. In such a configuration, one element may be used as the switching element, and it is thus possible to reduce a ground contact area and to increase the degree of freedom of wiring.

In the above-described light emitting device, at least one of the switching elements may include a PNP junction bipolar transistor and an NPN junction bipolar transistor, a base and a collector of the PNP junction bipolar transistor may respectively be connected with a collector and a base of the NPN junction bipolar transistor, an emitter terminal of the PNP junction bipolar transistor may be the first terminal, an emitter terminal of the NPN junction bipolar transistor may be the second terminal, and a base terminal of the NPN junction bipolar transistor may be the third terminal.

In the above-described light emitting device, at least one of the plural light emitting units may include a light emitting diode group in which plural light emitting diodes are connected in series, and the light emitting unit whose forward voltage is low may have a small number of emitting diodes that are connected in series in the light emitting diode group compared to the light emitting unit whose forward voltage is high. Because the forward voltage may be adjusted by the number of light emitting diodes, an element for adjusting the forward voltage is not requested.

In the above-described light emitting diode, at least one of the plural light emitting units may include the plural light emitting diode groups, and the plural light emitting diode groups may be connected in parallel. The number of light emitting diodes that are connected in series in the light emitting diode group and the number of the light emitting diode groups that are connected in parallel are adjusted, the number of light emitting diodes of each of the light emitting units may thereby be made the same number, and the forward voltage is adjustable.

In the above-described light emitting device, the light emitting unit that includes the plural light emitting diode groups may be dividedly arranged so as to include at least one of the light emitting diode groups, and at least one of the light emitting diode groups of the different light emitting unit may be arranged between the divided light emitting units. In such a manner, the light emitting unit is dividedly arranged as individual or plural light emitting diode groups, the light emitting diode group of the other light emitting unit is arranged between the divided light emitting units, and unevenness of arrangement of the light emitting diodes of the light emitting units may thereby be suppressed. Note that the light emitting unit may be divided into individual light emitting diode groups, and between those, the light emitting diode group of the different light emitting unit may thereby be arranged. The light emitting unit may be divided so as to include plural light emitting diode groups, and between those, individual or plural light emitting diode groups of the different light emitting unit may thereby be arranged.

In the above-described light emitting device, each of the plural light emitting units includes the light emitting diode group in which a same number of light emitting diodes are connected in series, at least one of the light emitting diode groups includes one or plural diodes that are connected in series with the light emitting diode, and the light emitting unit whose forward voltage is high has a large number of the connected diodes compared to the light emitting unit whose forward voltage is low. Consequently, the number of light emitting diodes of each of the light emitting units is made the same number, and the forward voltage may thereby be changed with the same or substantially same beam amount. Thus, it becomes possible to switch the emission colors and to perform dimming in each of the emission colors in a simple configuration.

In the above-described light emitting device, at least one of the resistances may have a characteristic in which a resistance value becomes low in response to a temperature rise. In such a configuration, in a case where the voltage value at which the switching element is turned ON becomes low due to the temperature rise, the change in the voltage value due to the current may likewise be made small. Accordingly, the fluctuation in the current value at which the switching element is turned ON may be suppressed even if the temperature changes, and it is possible to make the width of dimming in each of the emission colors the same or substantially same.

The above-described light emitting device may include: a substrate on which the plural light emitting units, the switching element, and the resistance are mounted; and land units that are respectively connected with positive electrode sides and negative electrode sides of the plural light emitting units. In such a manner, an integrated configuration in one substrate enables size reduction.

REFERENCE SIGNS LIST

A to D illumination device

1first light emitting unit

10first LED group

2second light emitting unit

20second LED group

31first connection terminal

32second connection terminal

Bd substrate

Ph printed wiring

Bd substrate

Ld1first land unit

Ld2second land unit

Pi current source (power source)