Light emitting element driving semiconductor integrated circuit, light emitting element driving device, light emitting device, and vehicle

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2016-098858 filed in Japan on May 17, 2016, the entire contents of which are hereby incorporated by reference.

The present invention relates to a light emitting element driving semiconductor integrated circuit. In addition, the present invention relates to a light emitting element driving device, and a light emitting device and a vehicle each using the same.

There are general structural examples of a light emitting device that lights a plurality of light emitting elements as illustrated in FIGS. 10 and 11 .

The light emitting device illustrated in FIG. 10 includes a plurality of light emitting diodes 101 , and a driving circuit 102 that drives the plurality of light emitting diodes 101 .

The light emitting device illustrated in FIG. 11 includes at least one light emitting diode 101 A belonging to a first system, a driving circuit 102 A that drives the at least one light emitting diode 101 A, at least one light emitting diode 101 B belonging to a second system, a driving circuit 102 B that drives the at least one light emitting diode 101 B, at least one light emitting diode 101 C belonging to a third system, and a driving circuit 102 C that drives the at least one light emitting diode 101 C.

The plurality of light emitting diodes 101 disposed in the light emitting device illustrated in FIG. 10 have different life periods due to production tolerance or the like. Therefore, when life of a light emitting diode having the shortest life period ends due to occurrence of a short-circuit abnormality, remaining light emitting diodes that are still alive are driven (lighted) by current output from the driving circuit 102 . However, because the number of lighted light emitting diodes is decreased by one in this lighted state, the luminance is insufficient so that sufficient luminance for securing safety may not be obtained.

The light emitting device illustrated in FIG. 11 has the three systems. Therefore, even if the number of lighted light emitting diodes is decreased in one of the three systems, light emitting diodes in remaining two systems are normally lighted. However, because the number of lighted light emitting diodes is decreased in this lighted state, the luminance is insufficient so that sufficient luminance for securing safety may not be obtained.

Therefore, it is possible to adopt the structure illustrated in FIG. 12 as a countermeasure against the above, in which a plurality of light emitting diodes 101 ′ and a driving circuit 102 ′ that drives the plurality of light emitting diodes 101 ′ are added as a backup to the light emitting device illustrated in FIG. 10 , and the light emitting diode and the driving circuit to be used are switched to the backup when the number of lighted light emitting diodes 101 is decreased. Similarly, it is possible to adopt the structure illustrated in FIG. 13 , in which at least one light emitting diode 101 D and a driving circuit 102 D that drives the at least one light emitting diode 101 D are added as a backup to the light emitting device illustrated in FIG. 11 , and when the number of lighted light emitting diodes in one circuit is decreased, the backup is used instead of the one circuit.

However, there is a problem that the structure illustrated in FIG. 12 causes more number of components than the structure illustrated in FIG. 10 , and hence power consumption and cost are increased. Similarly, there is a problem that the structure illustrated in FIG. 13 causes more number of components than the structure illustrated in FIG. 11 , and hence power consumption and cost are increased.

Note that JP-A-2015-79566 proposes a light source control device that can provide appropriate luminance even if a short-circuit breakdown occurs in one of light sources. However, the light source control device proposed in JP-A-2015-79566 controls the plurality of light sources that are connected in parallel, and uses a switch to cut off current supply to the light emitting diode that is short-circuited and broken, so that the light emitting diodes that are not short-circuited can be prevented from being turned off. The light emitting device illustrated in FIG. 10 and the light emitting device illustrated in FIG. 11 do not have the structure in which the light emitting diodes are connected in parallel. Therefore, even if the above-mentioned technique proposed in JP-A-2015-79566 is applied to the light emitting device illustrated in FIG. 10 and the light emitting device illustrated in FIG. 11 , occurrence of insufficient luminance due to a decrease in the number of lighted light emitting diodes cannot be prevented.

It is an object of the present invention to provide a light emitting element driving semiconductor integrated circuit that can suppress occurrence of insufficient luminance when a plurality of light emitting elements are partially broken down so that the number of lighted light emitting elements is decreased. In addition, in view of the situation described above, it is an object of the present invention to provide a light emitting element driving device, and a light emitting device and a vehicle each using the light emitting element driving device, which can prevent occurrence of insufficient luminance when a plurality of light emitting elements are partially broken down so that the number of lighted light emitting elements is decreased.

An example of the light emitting element driving semiconductor integrated circuit disclosed in this specification, which constitutes at least a part of a light emitting element driving device arranged to drive a series connection unit including a plurality of light emitting elements, includes a single-element short-circuit detection unit arranged to detect that one of the plurality of light emitting elements is short-circuited, and a control unit arranged to control a power element of the light emitting element driving device so that current supplied from the light emitting element driving device to the series connection unit is increased, when the single-element short-circuit detection unit detects that one of the plurality of light emitting elements is short-circuited.

Another example of the light emitting element driving semiconductor integrated circuit disclosed in this specification, which constitutes at least a part of a light emitting element driving device arranged to drive at least one light emitting element, includes a determining unit arranged to determine whether or not luminance of the at least one light emitting element is decreased due to a decrease in the number of lighted elements in the at least one light emitting element, a transmitting unit arranged to transmit a notification signal to another light emitting element driving semiconductor integrated circuit, when the determining unit determines that luminance of the at least one light emitting element is decreased due to a decrease in the number of lighted elements in the at least one light emitting element, a receiving unit arranged to receive another notification signal transmitted from another light emitting element driving semiconductor integrated circuit, and a control unit arranged to control a power element of the light emitting element driving device. When the determining unit determines that luminance of the at least one light emitting element is decreased due to a decrease in the number of lighted elements in the at least one light emitting element, the control unit controls the power element to stop current supply from the light emitting element driving device to the at least one light emitting element. When the receiving unit receives the another notification signal, the control unit controls the power element so that current supplied from the light emitting element driving device to the at least one light emitting element is increased.

Still another example of the light emitting element driving semiconductor integrated circuit disclosed in this specification, which constitutes at least a part of a light emitting element driving device arranged to supply respective currents to a plurality of systems each including at least one light emitting element, includes a determining unit arranged to determine whether or not luminance of one system is decreased due to a decrease in the number of lighted elements in the one system, and a control unit arranged to control a plurality of power elements of the light emitting element driving device. When the determining unit determines that luminance of the one system is decreased due to a decrease in the number of lighted elements in the one system, the control unit controls the power element corresponding to the one system to stop current supply from the light emitting element driving device to the one system, and controls at least one power element corresponding to a system other than the one system so that current supplied from the light emitting element driving device to the system other than the one system is increased.

An example of the light emitting element driving device disclosed in this specification, which drives a series connection unit including a plurality of light emitting elements, includes a power element, a single-element short-circuit detection unit arranged to detect that one of the plurality of light emitting elements is short-circuited, and a control unit arranged to control the power element so that current supplied from the light emitting element driving device to the series connection unit is increased, when the single-element short-circuit detection unit detects that one of the plurality of light emitting elements is short-circuited.

Another example of the light emitting element driving device disclosed in this specification, which supplies respective currents to a plurality of systems each including at least one light emitting element, includes a plurality of power elements, a determining unit arranged to determine whether or not luminance of one system is decreased due to a decrease in the number of lighted elements in the one system, and a control unit arranged to control the plurality of power elements. When the determining unit determines that luminance of the one system is decreased due to a decrease in the number of lighted elements in the one system, the control unit controls the power element corresponding to the one system to stop current supply from the light emitting element driving device to the one system, and controls at least one power element corresponding to a system other than the one system so that current supplied from the light emitting element driving device to the system other than the one system is increased.

A light emitting device disclosed in this specification includes a plurality of light emitting elements, and the light emitting element driving device according to any one of the structures described above arranged to drive the plurality of light emitting elements.

A vehicle disclosed in this specification includes the light emitting device having the structure described above.

The meanings and effects of the present invention will become more apparent from the description of an embodiment given below. However, the embodiment described below is merely an embodiment of the present invention, and meanings of the present invention and terms of structural components are not limited to those described in the following embodiment.

FIG. 1 is a diagram illustrating a first structural example of a light emitting device.

FIG. 2 is a diagram illustrating a second structural example of the light emitting device.

FIG. 3 is a diagram illustrating one structural example of a driving circuit.

FIG. 4 is a diagram illustrating a third structural example of the light emitting device.

FIG. 5 is an external view (front) of a vehicle equipped with the light emitting device.

FIG. 6 is an external view (rear) of the vehicle equipped with the light emitting device.

FIG. 7 is an external view of an LED head light module.

FIG. 8 is an external view of an LED turn lamp module.

FIG. 9 is an external view of an LED rear lamp module.

FIG. 10 is a diagram illustrating a general structural example of a light emitting device that lights a plurality of light emitting elements.

FIG. 11 is a diagram illustrating another general structural example of the light emitting device that lights a plurality of light emitting elements.

FIG. 12 is a diagram illustrating a structure in which backup components are added to the light emitting device illustrated in FIG. 10 .

FIG. 13 is a diagram illustrating a structure in which backup components are added to the light emitting device illustrated in FIG. 11 .

First Structural Example

FIG. 1 is a diagram illustrating a first structural example of a light emitting device. The light emitting device illustrated in FIG. 1 is equipped with a light emitting element driving device including a light emitting element driving IC 10 , a coil L 1 , an output capacitor C 1 , a sense resistor Rs, and a capacitor C 2 . In addition, the light emitting device illustrated in FIG. 1 includes light emitting diodes Z 1 to Z 3 to be driven by the light emitting element driving device. Note that, in the structural example of FIG. 1 , the number of the light emitting diodes and the number of short-circuit detection circuits disposed in the light emitting element driving IC 10 are each three, but the number may be two or more without limiting to three.

The light emitting element driving IC 10 is a semiconductor integrated circuit device (so-called LED driver IC), in which N-channel MOS field-effect transistors 1 H and 1 L (hereinafter referred to as an upper transistor 1 H and a lower transistor 1 L), an upper driver 2 H and a lower driver 2 L, a diode D 1 , a control unit 3 , an amplifier 4 , and short-circuit detection circuits 5 A to 5 C are integrated. In addition, the light emitting element driving IC 10 has external terminals T 1 to T 13 arranged to establish external electrical connections.

Outside the light emitting element driving IC 10 , the external terminal T 1 is connected to an application terminal of an input voltage Vi. The external terminal T 2 is connected to a first terminal of the coil L 1 . A second terminal of the coil L 1 (application terminal of an output voltage Vo) is connected to a first terminal of the sense resistor Rs. A second terminal of the sense resistor Rs is connected to the anode of a series connection unit including the light emitting diodes Z 1 to Z 3 . The cathode of the series connection unit including the light emitting diodes Z 1 to Z 3 is connected to a ground terminal. A first terminal of the output capacitor C 1 is connected to the second terminal of the coil L 1 . A second terminal of the output capacitor C 1 is connected to the ground terminal. The external terminal T 3 is connected to the ground terminal. The external terminal T 4 is connected to the first terminal of the coil L 1 via the capacitor C 2 . The external terminal T 5 is connected to the first terminal of the sense resistor Rs. The external terminal T 6 is connected to the second terminal of the sense resistor Rs. The external terminal T 7 is connected to the ground terminal via a resistor R 1 . The external terminal T 8 is connected to the ground terminal via a resistor R 2 . The external terminal T 9 is connected to the anode of the light emitting diode Z 1 . The external terminal T 10 is connected to the cathode of the light emitting diode Z 1 and the anode of the light emitting diode Z 2 . The external terminal T 11 is connected to the cathode of the light emitting diode Z 2 and the anode of the light emitting diode Z 3 . The external terminal T 12 is connected to the cathode of the light emitting diode Z 3 .

Inside the light emitting element driving IC 10 , the drain of the upper transistor 1 H is connected to the external terminal T 1 . The source of the upper transistor 1 H is connected to the external terminal T 2 . The gate of the upper transistor 1 H is connected to the output terminal of the upper driver 2 H. The drain of the lower transistor 1 L is connected to the external terminal T 2 . The source of the lower transistor 1 L is connected to the external terminal T 3 . The gate of the lower transistor 1 L is connected to the output terminal of the lower driver 2 L. In other words, the upper transistor 1 H and the lower transistor 1 L are connected in series between an application terminal of the input voltage Vi and the ground terminal, and the connection node therebetween (application terminal of a switch voltage Vsw) is connected to the output capacitor C 1 via the coil L 1 .

The upper driver 2 H generates a control signal GH for the upper transistor 1 H based on an instruction from the control unit 3 . The upper transistor 1 H is turned on when the control signal GH is high level, and it is turned off when the control signal GH is low level. The lower driver 2 L generates a control signal GL for the lower transistor 1 L based on an instruction from the control unit 3 . The lower transistor 1 L is turned on when the control signal GL is high level, and it is turned off when the control signal GL is low level.

The diode D 1 and the capacitor C 2 externally connected to the light emitting element driving IC 10 constitute a bootstrap circuit. The bootstrap circuit generates a boost voltage Vbst. The anode of the diode D 1 is connected to an application terminal of a constant voltage Vreg. The cathode of the diode D 1 is connected to the external terminal T 4 .

A first power supply terminal of the upper driver 2 H and a first power supply terminal of the control unit 3 are connected to the external terminal T 4 (application terminal of the boost voltage Vbst). A second power supply terminal of the upper driver 2 H is connected to the external terminal T 2 (application terminal of the switch voltage Vsw). Therefore, high level of the control signal GH applied to the gate of the upper transistor 1 H is the boost voltage Vbst, and low level of the control signal GH is the switch voltage Vsw.

A first power supply terminal of the lower driver 2 L is connected to the application terminal of the constant voltage Vreg. A second power supply terminal of the lower driver 2 L is connected to the external terminal T 3 (application terminal of the ground voltage GND). Therefore, high level of the control signal GL applied to the gate of the lower transistor 1 L is the constant voltage Vreg, and low level of the control signal GL is the ground voltage GND.

An operation of the bootstrap circuit having the structure described above is described. When the upper transistor 1 H is turned off while the lower transistor 1 L is turned on so that the switch voltage Vsw is low level (GND), current flows from the application terminal of the constant voltage Vreg to the capacitor C 2 via the diode D 1 so as to charge the capacitor C 2 . In this case, the boost voltage Vbst is substantially the constant voltage Vreg (more correctly a value (Vreg−Vf) obtained by subtracting a forward drop voltage Vf of the diode D 1 from the constant voltage Vreg).

On the other hand, when the upper transistor 1 H is turned on while the lower transistor 1 L is turned off in the state where the capacitor C 2 is charged so that the switch voltage Vsw is increased from low level (GND) to high level (Vi), the boost voltage Vbst is increased to a value (Vi+Vreg) higher than high level (Vi) of the switch voltage Vsw by the charge voltage of the capacitor C 2 (substantially Vreg). Because this boost voltage Vbst is applied to the first power supply terminal of the upper driver 2 H, the upper transistor 1 H can be securely driven to be turned on and off.

The control unit 3 generates a PWM signal inside and drives the upper driver 2 H and the lower driver 2 L so as to turn on and off the upper transistor 1 H and the lower transistor 1 L in accordance with a feedback voltage Vfb in an on period (high level period) of the PWM signal. On the other hand, the control unit 3 drives the upper driver 2 H and the lower driver 2 L so as to stop generation of the output voltage Vo in an off period (low level period) of the PWM signal.

The amplifier 4 amplifies a voltage applied between a noninverting input terminal (+) and an inverting input terminal (−), which is a voltage across both ends of the sense resistor Rs, so as to generate the feedback voltage Vfb. Therefore, the feedback voltage Vfb is a voltage signal that increases or decreases in accordance with an output current Io flowing in the sense resistor Rs.

Note that the upper transistor 1 H, the lower transistor 1 L, the upper driver 2 H, the lower driver 2 L, the control unit 3 , and the amplifier 4 constitute an output voltage generating unit, which generates the output voltage Vo from the input voltage Vi so that the output current Io flowing in the light emitting diodes Z 1 to Z 3 coincides with a target value in the on period of the PWM signal generated by the control unit 3 , and stops the generation of the output voltage Vo in the off period of the PWM signal generated by the control unit 3 .

The short-circuit detection circuit 5 A checks whether or not an anode-cathode voltage of the light emitting diode Z 1 (voltage between the external terminal T 9 and the external terminal T 10 ) is substantially zero. If it is substantially zero, a short-circuit of the light emitting diode Z 1 is detected, and a low level signal is output. If a short-circuit of the light emitting diode Z 1 is not detected, a high level signal is output. The short-circuit detection circuit 5 B detects a short-circuit of the light emitting diode Z 2 in the same manner, and the short-circuit detection circuit 5 C detects a short-circuit of the light emitting diode Z 3 in the same manner.

If none of the short-circuit detection circuits 5 A to 5 C detects a short-circuit of the light emitting diode, i.e., if all the short-circuit detection circuits 5 A to 5 C output the high level signal, the control unit 3 generates the PWM signal having an on-duty corresponding to a resistance value of the resistor R 1 connected to the external terminal T 7 . On the other hand, if one of the short-circuit detection circuits 5 A to 5 C detects a short-circuit of the light emitting diode, i.e., if one of the short-circuit detection circuits 5 A to 5 C outputs the low level signal while other two short-circuit detection circuits output the high level signal, the control unit 3 generates the PWM signal having an on-duty corresponding to a resistance value of the resistor R 2 connected to the external terminal T 8 . The on-duty corresponding to the resistance value of the resistor R 2 is set to a larger value than the on-duty corresponding to the resistance value of the resistor R 1 .

In addition, if one of the short-circuit detection circuits 5 A to 5 C detects a short-circuit of the light emitting diode, i.e., if one of the short-circuit detection circuits 5 A to 5 C outputs the low level signal while other two short-circuit detection circuits output the high level signal, the control unit 3 outputs to the external terminal T 13 an abnormality notification signal S 1 indicating that there is an unlighted light emitting diode.

According to the light emitting device illustrated in FIG. 1 described above, when life of a light emitting diode having the shortest life period among the light emitting diodes Z 1 to Z 3 ends due to occurrence of a short-circuit abnormality, current flowing in the remaining two light emitting diodes that are still alive becomes larger than usual based on the PWM signal having a larger on-duty. Thus, even if the number of lighted light emitting diodes is decreased by one, insufficient luminance can be prevented.

In addition, because the light emitting device illustrated in FIG. 1 can prevent insufficient luminance even if the number of lighted light emitting diodes is decreased by one, a user hardly notices that one light emitting diode is short-circuited. However, because the light emitting device illustrated in FIG. 1 outputs the abnormality notification signal S 1 externally from the external terminal T 13 when one light emitting diode is short-circuited, it is possible to readily urge the user to have the light emitting device illustrated in FIG. 1 repaired, by using the abnormality notification signal S 1 .

In addition, it is possible to adopt the following structure different from the above-described structure. If none of the short-circuit detection circuits 5 A to 5 C detects a short-circuit of the light emitting diode, the control unit 3 sets a target value of the output current Io corresponding to the resistance value of the resistor R 1 connected to the external terminal T 7 . On the other hand, if one of the short-circuit detection circuits 5 A to 5 C detects a short-circuit of the light emitting diode, the control unit 3 sets a target value of the output current Io corresponding to the resistance value of the resistor R 2 connected to the external terminal T 8 . The target value of the output current Io corresponding to the resistance value of the resistor R 2 is set to a larger value than the target value of the output current Io corresponding to the resistance value of the resistor R 1 . With this structure, even if the number of lighted light emitting diodes is decreased by one, insufficient luminance can be prevented. Note that this structure is particularly preferred when the on-duty of the PWM signal generated by the control unit 3 is close to 100% in a normal state (where a short-circuit does not occur in the light emitting diode).

Further, it is possible to combine the structure described above and the variation described above to make the following structure. If none of the short-circuit detection circuits 5 A to 5 C detects a short-circuit of the light emitting diode, the control unit 3 generates the PWM signal having the on-duty corresponding to the resistance value of the resistor R 1 connected to the external terminal T 7 , and sets a target value of the output current Io corresponding to the resistance value of a current setting resistor connected to a current setting external terminal provided additionally. On the other hand, if one of the short-circuit detection circuits 5 A to 5 C detects a short-circuit of the light emitting diode, the control unit 3 generates the PWM signal having the on-duty corresponding to the resistance value of the resistor R 2 connected to the external terminal T 8 , and sets a target value of the output current Io corresponding to the resistance value of another current setting resistor connected to another current setting external terminal provided additionally.

Second Structural Example

FIG. 2 is a diagram illustrating a second structural example of the light emitting device. The light emitting device illustrated in FIG. 2 include at least one light emitting diode 11 A belonging to a first system, a driving circuit 12 A that drives the at least one light emitting diode 11 A, at least one light emitting diode 11 B belonging to a second system, a driving circuit 12 B that drives the at least one light emitting diode 11 B, at least one light emitting diode 11 C belonging to a third system, and a driving circuit 12 C that drives the at least one light emitting diode 11 C. The driving circuits 12 A to 12 C have a structure enabling mutual communication with each other.

The driving circuits 12 A to 12 C have the same structure, and hence a structural example of the driving circuit 12 A is described as a typical one among the driving circuits 12 A to 12 C. FIG. 3 is a diagram illustrating one structural example of the driving circuit 12 A. Note that at least one light emitting diode 11 A connected to the driving circuit 12 A is also shown in FIG. 3 . In addition, in FIG. 3 , the same part as in FIG. 1 is denoted by the same numeral, and detailed description thereof is omitted.

The driving circuit 12 A as the structural example illustrated in FIG. 3 is constituted of a light emitting element driving IC 13 and external components. The light emitting element driving IC 13 includes a determining unit constituted of comparators 14 A and 14 C, reference voltage sources 14 B and 14 D, and an OR gate 14 E. In addition, the light emitting element driving IC 13 includes a communication unit 15 .

The comparator 14 A compares a voltage of the external terminal T 6 with a first reference voltage V REF1 output from the reference voltage source 14 B, and outputs a high level signal if the voltage of the external terminal T 6 is equal to or higher than the first reference voltage V REF1 . The comparator 14 C compares the voltage of the external terminal T 6 with a second reference voltage V REF2 (lower than the first reference voltage V REF1 ) output from the reference voltage source 14 D, and outputs a high level signal if the voltage of the external terminal T 6 is lower than the second reference voltage V REF2 . When at least one of output signals of the comparators 14 A and 14 C is high level, the OR gate 14 E outputs a high level signal to the control unit 3 and the communication unit 15 .

The first reference voltage V REF1 is set to a value higher than a total forward voltage of the light emitting diode 11 A, for example, which is a threshold value for determining whether or not there is a malfunction that the light emitting diode 11 A is not lighted because of a breakage. The second reference voltage V REF2 is set to a value lower than a forward voltage of one element in the light emitting diode 11 A, for example, which is a threshold value for determining whether or not there is a malfunction that the light emitting diode 11 A is not lighted because of a ground fault. Thus, the determining unit can determine whether or not luminance of the light emitting diode 11 A is decreased due to a decrease in the number of lighted elements in the light emitting diode 11 A. If the determining unit determines that luminance of the light emitting diode 11 A is decreased due to a decrease in the number of lighted elements in the light emitting diode 11 A, it outputs a high level signal.

When receiving the high level signal from the OR gate 14 E, the communication unit 15 outputs a notification signal to an external terminal T 14 , so as to supply the notification signal to the external terminals T 14 of the other light emitting element driving ICs connected to the external terminal T 14 of the light emitting element driving IC 13 (the light emitting element driving IC constituting a part of the driving circuit 12 B and the light emitting element driving IC constituting a part of the driving circuit 12 C).

In addition, the communication unit 15 receives the notification signals, which are transmitted from the external terminals T 14 of the other light emitting element driving ICs (the light emitting element driving IC constituting a part of the driving circuit 12 B and the light emitting element driving IC constituting a part of the driving circuit 12 C), and are input to the external terminal T 14 of the light emitting element driving IC 13 .

If the OR gate 14 E outputs the low level signal and the communication unit 15 does not receive the notification signal, the control unit 3 generates the PWM signal having the on-duty corresponding to the resistance value of the resistor R 1 connected to the external terminal T 7 . On the other hand, if the OR gate 14 E outputs the low level signal and the communication unit 15 receives the notification signal, the control unit 3 generates the PWM signal having the on-duty corresponding to the resistance value of the resistor R 2 connected to the external terminal T 8 . The on-duty corresponding to the resistance value of the resistor R 2 is set to a larger value than the on-duty corresponding to the resistance value of the resistor R 1 . In addition, If the OR gate 14 E outputs the high level signal, the control unit 3 set the on-duty of the PWM signal to 0% so as to stop the switching control.

Further, when the OR gate 14 E outputs the high level signal, the control unit 3 outputs the abnormality notification signal S 1 indicating that there is an unlighted light emitting diode to the external terminal T 13 .

According to the light emitting device illustrated in FIG. 3 described above, if luminance of the light emitting diode in one of the three systems decreases because of a decrease in the number of lighted light emitting diodes in the one system, current flowing in the light emitting diodes in the remaining two systems is increased based on the PWM signal having a larger on-duty than usual. In this way, even if luminance of the light emitting diode is decreased in one system, insufficient luminance can be prevented.

In addition, in the light emitting device illustrated in FIG. 3 , because insufficient luminance can be prevented even if luminance of the light emitting diode is decreased in one system, the user hardly notices that luminance of the light emitting diode is decreased in one system due to a decrease in the number of lighted light emitting diodes in the one system. However, when luminance of the light emitting diode is decreased in one system due to a decrease in the number of lighted light emitting diodes in the one system, the light emitting device illustrated in FIG. 3 outputs the abnormality notification signal S 1 externally from the external terminal T 13 of the light emitting element driving IC in the one system, and hence it is possible to readily urge the user to have the light emitting device illustrated in FIG. 3 repaired, by using the abnormality notification signal S 1 .

In addition, it is possible to modify this structural example too, in the same manner as the variation of the first structural example described above.

Third Structural Example

FIG. 4 is a diagram illustrating a third structural example of the light emitting device. The light emitting device illustrated in FIG. 4 has a structure in which the three light emitting element driving ICs disposed respectively for the three systems in the light emitting device illustrated in FIG. 3 are combined into one light emitting element driving IC 16 . In other words, the light emitting element driving IC 16 includes a second system circuit 17 and a third system circuit 19 , and second system external components 18 and third system external components 20 are externally connected to the light emitting element driving IC 16 . The communication unit 15 used in the light emitting device illustrated in FIG. 3 is eliminated because it is not necessary to communicate among the light emitting element driving ICs in the light emitting device illustrated in FIG. 4 .

The external terminal of the light emitting element driving IC 16 connected to the application terminal of the input voltage Vi, the external terminal of the light emitting element driving IC 16 connected to the ground terminal, and the like can be shared by the first to third systems, and hence it is preferred to share them.

Control of the output currents Io of the first to third systems in the light emitting device illustrated in FIG. 4 is basically the same as the control of the output currents Io of the first to third systems in the light emitting device illustrated in FIG. 3 , and hence detailed description thereof is omitted. The light emitting device illustrated in FIG. 4 achieves the same effect as the light emitting device illustrated in FIG. 3 .

<Application>

The light emitting device described above can be used appropriately as illustrated in FIGS. 5 and 6 , for example, as a headlight of a vehicle X 10 (appropriately including a high beam, a low beam, a small lamp, a fog lamp, or the like) X 11 , a day and night running (DRL) light source X 12 , a tail lamp (appropriately including a small lamp, a back lamp, or the like) X 13 , a stop lamp X 14 , a turn lamp X 15 , or the like.

Note that the light emitting device described above may be provided as a module (such as an LED head light module Y 10 of FIG. 7 , an LED turn lamp module Y 20 of FIG. 8 , or an LED rear lamp module Y 30 of FIG. 9 ). In addition, it may be provided as a driving device having a function of controlling the number of light emitting elements, which is a semifinished product in which the light emitting diode and the external components of the light emitting element driving IC are eliminated from the light emitting device described above.

In addition, the light emitting device described above can be used as a backlight of a display device, for example.

<Other Variations>

Note that the embodiment described above exemplifies the structure in which the light emitting diode is used as the light emitting element, but the present invention is not limited to this structure. For example, it is possible to use an organic electro-luminescence (EL) element as the light emitting element.

In addition, other than the embodiment described above, various technical features disclosed in this specification can be variously modified within the scope without deviating from the spirit of the technical invention. For example, the embodiment described above uses the switching regulator as the light emitting element driving device that drives the light emitting element, which performs switching control of the power elements (the upper transistor 1 H and the lower transistor 1 L) so that the output current Io coincides with the target value. However, it is possible to use a linear regulator instead of the switching regulator, which controls on resistance of the power element so as to coincide with a target value. In addition, it is possible to implement a combination of the first structural example and the second structural example, for example. Similarly, it is possible to implement a combination of the first structural example and the third structural example. In other words, the embodiment described above is merely an example in every aspect and should not be interpreted as a limitation. The technical scope of the present invention is defined not by the above description of the embodiment but by the claims, and should be understood to include all modifications within meaning and scope equivalent to the claims.

The light emitting element driving semiconductor integrated circuit of the first structure described above, which constitutes at least a part of a light emitting element driving device arranged to drive a series connection unit including a plurality of light emitting elements, includes a single-element short-circuit detection unit arranged to detect that one of the plurality of light emitting elements is short-circuited, and a control unit arranged to control a power element of the light emitting element driving device so that current supplied from the light emitting element driving device to the series connection unit is increased, when the single-element short-circuit detection unit detects that one of the plurality of light emitting elements is short-circuited.

The light emitting element driving semiconductor integrated circuit of the second structure described above, which constitutes at least a part of a light emitting element driving device arranged to drive at least one light emitting element, includes a determining unit arranged to determine whether or not luminance of the at least one light emitting element is decreased due to a decrease in the number of lighted elements in the at least one light emitting element, a transmitting unit arranged to transmit a notification signal to another light emitting element driving semiconductor integrated circuit, when the determining unit determines that luminance of the at least one light emitting element is decreased due to a decrease in the number of lighted elements in the at least one light emitting element, a receiving unit arranged to receive another notification signal transmitted from another light emitting element driving semiconductor integrated circuit, and a control unit arranged to control a power element of the light emitting element driving device. When the determining unit determines that luminance of the at least one light emitting element is decreased due to a decrease in the number of lighted elements in the at least one light emitting element, the control unit controls the power element to stop current supply from the light emitting element driving device to the at least one light emitting element. When the receiving unit receives the another notification signal, the control unit controls the power element so that current supplied from the light emitting element driving device to the at least one light emitting element is increased.

The light emitting element driving semiconductor integrated circuit of the third structure described above, which constitutes at least a part of a light emitting element driving device arranged to supply respective currents to a plurality of systems each including at least one light emitting element, includes a determining unit arranged to determine whether or not luminance of one system is decreased due to a decrease in the number of lighted elements in the one system, and a control unit arranged to control a plurality of power elements of the light emitting element driving device. When the determining unit determines that luminance of the one system is decreased due to a decrease in the number of lighted elements in the one system, the control unit controls the power element corresponding to the one system to stop current supply from the light emitting element driving device to the one system, and controls at least one power element corresponding to a system other than the one system so that current supplied from the light emitting element driving device to the system other than the one system is increased.

In addition, the light emitting element driving semiconductor integrated circuit having one of the first to third structures may further include an external output unit arranged to externally output an abnormality notification signal indicating that there is an unlighted light emitting element, when the single-element short-circuit detection unit detects that one of the plurality of light emitting elements is short-circuited, or when the determining unit determines that luminance of the at least one light emitting element is decreased due to a decrease in the number of lighted elements in the at least one light emitting element, or when the determining unit determines that luminance of the one system is decreased due to a decrease in the number of lighted elements in the one system (fourth structure).

The light emitting element driving device having the fifth structure described above, which drives a series connection unit including a plurality of light emitting elements, includes a power element, a single-element short-circuit detection unit arranged to detect that one of the plurality of light emitting elements is short-circuited, and a control unit arranged to control the power element so that current supplied from the light emitting element driving device to the series connection unit is increased, when the single-element short-circuit detection unit detects that one of the plurality of light emitting elements is short-circuited.

The light emitting element driving device of the sixth structure described above, which supplies respective currents to a plurality of systems each including at least one light emitting element, includes a plurality of power elements, a determining unit arranged to determine whether or not luminance of one system is decreased due to a decrease in the number of lighted elements in the one system, and a control unit arranged to control the plurality of power elements. When the determining unit determines that luminance of the one system is decreased due to a decrease in the number of lighted elements in the one system, the control unit controls the power element corresponding to the one system to stop current supply from the light emitting element driving device to the one system, and controls at least one power element corresponding to a system other than the one system so that current supplied from the light emitting element driving device to the system other than the one system is increased.

In addition, the light emitting element driving device having the fifth or sixth structure described above may further include an external output unit arranged to externally output an abnormality notification signal indicating that there is an unlighted light emitting element, when the single-element short-circuit detection unit detects that one of the plurality of light emitting elements is short-circuited, or when the determining unit determines that luminance of the one system is decreased due to a decrease in the number of lighted elements in the one system (seventh structure).

The light emitting device described above includes a plurality of light emitting elements, and the light emitting element driving device having any one of the fifth to seventh structures arranged to drive the plurality of light emitting elements (eighth structure).

In addition, in the light emitting device having the eighth structure described above, the light emitting element may be a light emitting diode or an organic EL element (ninth structure).

In addition, in the light emitting device having the eighth or ninth structure described above, the light emitting device may be used as an in-vehicle lamp (tenth structure).

In addition, in the light emitting device having the tenth structure described above, the light emitting device may be mounted in a vehicle as a headlight module, a turn lamp module, or a rear lamp module (eleventh structure).

The vehicle described above includes the light emitting device having the tenth or eleventh structure described above (twelfth structure).

In addition, in the vehicle having the twelfth structure, the light emitting device may be used as at least one of a headlight, a day and night running light source, a tail lamp, a stop lamp, and a turn lamp (thirteenth structure).