Light-emitting element driving device, light-emitting device, and vehicle

Abstract

A light-emitting element drive device (5) comprises: a first external terminal (SET terminal) connectable to a first setting resistor (Rset); a second external terminal (SET_TH terminal) connectable to a first thermistor (TH1) of a negative characteristic disposed near a light-emitting element light source (10); a current setting unit (2) that generates setting current (Iset) on the basis of a resistance value of the first setting resistor; a current addition unit (3) that generates additional current (Iadd) of a negative characteristic with respect to a resistance value of the first thermistor; and a current driver (1) that is connected between the ground terminal end and the application terminal end of a power supply volage (Vin) and that generates, on the basis of reference current (Iref) which is a sum total of the setting current and the additional current, output current (Iout) flowing to the light-emitting element light source.

Description

[Technical Field]

[0001] The present disclosure relates to a light emitting element driving device. [Background technology]

[0002] 2. Description of the Related Art Various light emitting element driving devices for driving light emitting elements such as LEDs (light emitting diodes) have been developed.

[0003] A conventional LED driver is disclosed in, for example, Patent Document 1. The LED driver in Patent Document 1 has a current setting unit. An output current supplied to the LED is generated according to a reference current generated by the current setting unit. The current setting unit is connected to a setting resistor and a negative temperature coefficient thermistor that are externally attached to the LED driver. The current setting resistor and the negative temperature coefficient thermistor are connected in parallel. The current setting characteristic realized by the current setting unit is a positive characteristic (the higher the resistance value of the current setting resistor, the higher the reference current). As a result, the reference current can be reduced as the temperature around the thermistor increases, making it possible to perform temperature derating of the output current.

[0004] Furthermore, a conventional light-emitting element driving device is disclosed in, for example, Patent Document 2. The light-emitting element driving device of Patent Document 2 includes a current driver that generates an output current flowing in a light-emitting element light source connected between a power supply voltage application terminal and a ground terminal, and a bypass function unit that bypasses at least one of a plurality of light-emitting elements that constitute the light-emitting element light source when the power supply voltage drops, thereby reducing the number of series stages of light-emitting elements through which the output current flows. This makes it possible to maintain the lighting of the light-emitting element light source even when the power supply voltage drops. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-71712 [Patent Document 2] International Publication No. 2019 / 187279 Summary of the Invention [Problem to be solved by the invention]

[0006] However, LEDs have the characteristic that their brightness drops significantly as the ambient temperature rises. Conventional LED driver temperature derating reduces the output current as the temperature rises, leaving room for improvement in terms of LED brightness control.

[0007] In view of the above circumstances, a first object of the present disclosure is to provide a light emitting element driving device that can suppress changes in luminance of a light emitting element due to temperature changes.

[0008] In addition, in the above-described conventional light-emitting element driving device, when the power supply voltage is turned on, the bypass function unit performs bypassing when the power supply voltage is low, and then the bypass is released when the power supply voltage becomes high. However, if an open circuit occurs in a light-emitting element to be bypassed, current flows to light-emitting elements other than the bypassed element when the light-emitting element is bypassed, causing the light-emitting element to light up. However, when the bypass is subsequently released, current stops flowing to the light-emitting element, causing the light-emitting element to turn off. This undesirably causes the light-emitting element to appear to light up momentarily and then turn off when the power supply voltage is turned on.

[0009] In view of the above situation, a second object of the present disclosure is to provide a light-emitting element driving device having a bypass function that effectively suppresses abnormal lighting of light-emitting elements caused by an open circuit. [Means for solving the problem]

[0010] For example, a light emitting element driving device according to an aspect of the present disclosure may include: a first external terminal connectable to a first setting resistor; a second external terminal connectable to a first thermistor with a negative coefficient arranged around the light-emitting element light source; a current setting unit that generates a set current based on the resistance value of the first setting resistor; a current adding unit that generates an additional current with a negative characteristic with respect to the resistance value of the first thermistor; a current driver that generates an output current flowing through the light-emitting element light source connected between a power supply voltage application terminal and a ground terminal, based on a reference current that is the sum of the set current and the additional current; The configuration has the following.

[0011] Furthermore, for example, a light emitting element driving device according to an aspect of the present disclosure includes: a current driver that generates an output current flowing through a light-emitting element light source connected between a power supply voltage application terminal and a ground terminal; a first external terminal connectable to a node to which a high potential side light source and a low potential side light source included in the light-emitting element light source are connected in series; a bypass control unit that draws the output current from the first external terminal and controls a conduction state of a path that bypasses the low potential side light source in accordance with the power supply voltage; a constant current source and a switch provided between the power supply voltage application terminal and the first external terminal; a comparator that compares the voltage of the first external terminal with an open circuit detection threshold voltage and outputs a detection signal; a UVLO (Under Voltage Lock Out) unit that compares the power supply voltage with a UVLO threshold voltage and outputs a UVLO detection signal; a variable setting unit that variably sets the open detection threshold voltage and the UVLO threshold voltage in conjunction with each other; and When the power supply voltage is started up, the bypass control unit keeps the path in an off state, and if the UVLO detection signal indicates that UVLO has been released, switches the switch to an on state, and if the detection signal indicates that the voltage of the first external terminal is higher than the open detection threshold voltage, determines that an open has occurred on the lower potential side of the node, and maintains the path in an off state. [Effects of the Invention]

[0012] According to the light emitting element driving device according to the present disclosure, it is possible to suppress changes in the luminance of the light emitting element due to temperature changes.

[0013] Furthermore, according to the light-emitting element driving device of the present disclosure, in a light-emitting element driving device having a bypass function, an effective configuration can be implemented to suppress abnormal lighting of light-emitting elements caused by an open circuit. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the overall configuration of an LED light emitting device according to an exemplary embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a specific internal configuration of each of the current setting unit and the current adding unit. [Figure 3] FIG. 3 is a graph showing an example of the relationship between the ambient temperature of a red LED and the luminance. [Figure 4] FIG. 4 is a graph showing an example of the relationship between the ambient temperature of the LED light source and the combined resistance value of the set resistor Rset_th and the thermistor TH1. [Figure 5] FIG. 5 is a graph showing an example of the relationship between the ambient temperature of the LED light source and the additional current Iadd, corresponding to FIG. [Figure 6] FIG. 6 is a graph showing an example of the relationship between the ambient temperature of the LED light source and the reference current Iref, corresponding to FIGS. [Figure 7] FIG. 7 is a plan view showing an example of a socket-type LED module. [Figure 8] FIG. 8 is an external view (front view) showing an example of a vehicle on which an LED driving device is mounted. [Figure 9] FIG. 9 is an external view (rear view) showing an example of a vehicle on which an LED driving device is mounted. [Figure 10] FIG. 10 is a diagram showing the overall configuration of an LED light emitting device according to an exemplary embodiment. [Figure 11] FIG. 11 is a diagram illustrating an example of the internal configuration of the CR timer. [Figure 12]FIG. 12 is a diagram showing a case where no open circuit occurs on the lower potential side of node Nx. [Figure 13] FIG. 13 is a diagram showing a case where an open circuit occurs on the lower potential side of node Nx. [Figure 14] FIG. 14 is a diagram showing the operation when no open circuit occurs on the lower potential side of node Nx. [Figure 15] FIG. 15 is a diagram showing the operation when an open circuit occurs on the lower potential side of node Nx. [Figure 16] FIG. 16 is a diagram showing the first output current and the second output current. [Figure 17] FIG. 17 is a diagram illustrating a first configuration example of the variable setting section. [Figure 18] FIG. 18 is a diagram illustrating a second configuration example of the variable setting section. [Figure 19] FIG. 19 is a plan view showing a configuration example of a socket-type LED module. [Figure 20] FIG. 20 is an enlarged view of an example of a wiring pattern on a substrate. [Figure 21] FIG. 21 is an enlarged view of another example of a wiring pattern on a substrate. [Figure 22] FIG. 22 is an external view (front) showing an example of a vehicle on which an LED driving device is mounted. [Figure 23] FIG. 23 is an external view (rear view) showing an example of a vehicle on which an LED driving device is mounted. DETAILED DESCRIPTION OF THE INVENTION

[0015] <<First Technical Disclosure>> The first technical disclosure will be described below.

[0016] <1. LED light emitting device> FIG. 1 is a diagram showing the overall configuration of an LED light emitting device X1 according to an exemplary embodiment. The LED light emitting device X1 is an in-vehicle lamp that is turned on by receiving a power supply voltage Vin from a battery B. Examples of the LED light emitting device X1 include a headlamp, a daytime running lamp, a tail lamp, a stop lamp, and a turn lamp. The battery is the power source for the vehicle in which the LED light emitting device X1 is mounted, and a lead-acid battery, a lithium-ion battery, or the like is preferably used.

[0017] As shown in FIG. 1, the LED light emitting device X1 includes an LED driving device 5 and an LED light source 10, as well as various discrete components externally attached to the LED driving device 5, such as setting resistors Rset and Rset_th and thermistors TH1 and TH2.

[0018] The LED driving device 5 is a semiconductor integrated circuit device (so-called LED driver IC) that operates by receiving a power supply voltage Vin from a battery B and generates an output current Iout to be supplied to the LED light source 10.

[0019] The LED driver 5 has external terminals for establishing electrical connection with the outside, including a VIN terminal, an OUT terminal, a THD terminal, a SET terminal, a SET_TH terminal, and a GND terminal. The VIN terminal is connected to an application terminal of the power supply voltage Vin. That is, the LED driver 5 receives the power supply voltage Vin via the VIN terminal.

[0020] The LED light source 10 is an LED string made up of multiple LED chips (light-emitting elements) connected in series. The LED light source 10 may be made up of a single LED, or may be made up of LED chips connected in series and parallel.

[0021] The LED driving device 5 has an internal configuration in which a current driver 1, a current setting section 2, a current adding section 3, and a constant current source 4 are integrated.

[0022] Note that FIG. 1 shows only a part of the internal configuration of the LED driving device 5, and in addition to the configuration shown in FIG. 1, the LED driving device 5 also has a control logic unit, a dimming unit that performs PWM (Pulse Width Modulation) dimming of the LED light source 10, various abnormality detection units, an abnormality notification unit that notifies the outside of an abnormality, an internal power supply circuit that generates an internal voltage, and a UVLO (Under Voltage Lock Out) unit.

[0023] The current driver 1 is provided between the VIN terminal and the OUT terminal. The anode of the LED light source 10 is connected to the OUT terminal. The cathode of the LED light source 10 is connected to the ground terminal. The current driver 1 generates an output current Iout that flows through the LED light source 10 that is connected between the application terminal of the power supply voltage Vin and the ground terminal.

[0024] The current driver 1 performs constant current control of the output current Iout so that the output current Iout matches a predetermined target value. Although not shown in FIG. 1, the current driver 1 may include, for example, an output transistor provided on a current path through which the output current Iout flows, a sense resistor that converts the output current Iout into a feedback voltage, and an error amplifier that linearly drives the output transistor so that the feedback voltage matches a reference voltage. The target value of the output current Iout can be set arbitrarily according to a reference current Iref, which will be described later.

[0025] The current setting unit 2 generates a set current Iset. The set current Iset is used to generate a reference current Iref. That is, the current setting unit 2 generates the set current Iset for setting a target value of the output current Iout. The set current Iset can be adjusted by adjusting the resistance value of a setting resistor Rset externally connected to the SET terminal.

[0026] A constant current source 4 is provided between the application terminal of the internal voltage Vreg and the THD terminal. A thermistor TH2 is externally connected to the THD terminal. The thermistor TH2 is a negative temperature coefficient thermistor. A negative temperature coefficient thermistor has a characteristic that its resistance value decreases as the temperature increases. The thermistor TH2 is arranged around the LED light source 10. The constant current source 4 flows a constant current Ithd to the thermistor TH2 via the THD terminal, generating a terminal voltage Vthd at the THD terminal. The current setting unit 2 adjusts the set current Iset based on the terminal voltage Vthd. This performs temperature derating, which adjusts the output current Iout according to the ambient temperature of the LED light source 10.

[0027] The current adding unit 3 generates the additional current Iadd. The reference current Iref is generated by combining (summing) the setting current Iset and the additional current Iadd. Outside the LED driving device 5, a setting resistor Rset_th and a thermistor TH1 are connected in series between the SET_TH terminal and the ground terminal. The thermistor TH1 is a negative temperature coefficient thermistor and is arranged around the LED light source 10. The current adding unit 3 adjusts the additional current Iadd based on the resistance values ​​of the setting resistor Rset_th and the thermistor TH1 (i.e., the combined resistance value of the setting resistor Rset_th and thermistor TH1) and the terminal voltage Vthd. Therefore, the current adding unit 3 adjusts the output current Iout in accordance with the ambient temperature of the LED light source 10, thereby controlling the brightness and temperature derating of the LED light source 10.

[0028] <2. How to adjust the output current> FIG. 2 is a diagram showing a specific example of the internal configuration of each of the current setting unit 2 and the current adding unit 3. As shown in FIG.

[0029] The current setting unit 2 has an output transistor 2A and an error amplifier 2B. The output transistor 2A is arranged in a path through which the set current Iset flows, and is configured by an NMOS transistor (N-channel MOSFET). The source of the output transistor 2A is connected to the SET terminal. The node connecting the output transistor 2A and the SET terminal is connected to the inverting input terminal (-) of the error amplifier 2B. The non-inverting input terminal (+) of the error amplifier 2B is connected to the THD terminal. The output terminal of the error amplifier 2B is connected to the gate of the output transistor 2A.

[0030] The current adding unit 3 has an output transistor 3A and an error amplifier 3B. The output transistor 3A is arranged in a path through which the additional current Iadd flows, and is composed of an NMOS transistor. The drain of the output transistor 3A is connected to the drain of the output transistor 2A. The source of the output transistor 3A is connected to the SET_TH terminal. A node connecting the output transistor 3A and the SET_TH terminal is connected to the inverting input terminal (-) of the error amplifier 3B. The non-inverting input terminal (+) of the error amplifier 3B is connected to the THD terminal. The output terminal of the error amplifier 3B is connected to the gate of the output transistor 3A.

[0031] With the configuration of the current setting unit 2 as described above, the voltage at the SET terminal is controlled to coincide with the terminal voltage Vthd, and the set current Iset is expressed by the following equation. Iset=Vthd / Rset However, Vthd = TH2 x Ithd (TH2: resistance value of thermistor TH2)

[0032] Therefore, the set current Iset has a negative characteristic with respect to the set resistor Rset (the larger the resistance value of the set resistor Rset, the smaller the set current Iset) and a positive characteristic with respect to the thermistor TH2 (terminal voltage Vthd) (the larger the resistance value of the thermistor TH2 (the higher the terminal voltage Vthd), the larger the set current Iset).

[0033] Furthermore, with the above-described configuration of the current adding unit 3, the voltage at the SET_TH terminal is controlled to match the terminal voltage Vthd, and the additional current Iadd is expressed by the following equation. Iadd=Vthd / (Rset_th+TH1) (TH1: resistance value of thermistor TH1)

[0034] Therefore, the additional current Iadd has a negative characteristic with respect to the resistance value of thermistor TH1 (the larger the resistance value of thermistor TH1, the smaller the additional current Iadd) and a positive characteristic with respect to thermistor TH2 (terminal voltage Vthd) (the larger the resistance value of thermistor TH2 (the higher the terminal voltage Vthd), the larger the additional current Iadd).

[0035] In addition, the reference current Iref is Iref=Iset+Iadd The target value of the output current Iout is set to be larger as the reference current Iref is larger (positive characteristic with respect to the reference current Iref).

[0036] As a result, when the ambient temperature of the LED light source 10 rises and the resistance value of thermistor TH1 decreases, the additional current Iadd increases. Note that when the ambient temperature of the LED light source 10 rises and the resistance value of thermistor TH2 decreases, the additional current Iadd decreases, but since the increase in the additional current Iadd due to thermistor TH1 is greater than the decrease in the additional current Iadd, the additional current Iadd increases as the temperature rises.

[0037] FIG. 3 shows an example of the relationship between the LED ambient temperature (horizontal axis) and brightness (vertical axis) for a red LED (assuming the LED current is a predetermined constant value). Note that brightness on the vertical axis is shown as a ratio to brightness at 20°C. Characteristics vary depending on the LED used, and FIG. 3 shows two example characteristics using solid and dashed lines. As such, LEDs have the characteristic of significantly decreasing brightness as temperature rises. Therefore, by increasing the additional current Iadd as the ambient temperature of the LED light source 10 increases as described above, the reference current Iref and therefore the output current Iout can be increased, thereby suppressing the decrease in brightness.

[0038] 4 shows an example of the relationship between the ambient temperature of the LED light source 10 (LED ambient temperature) and the combined resistance of the set resistor Rset_th and thermistor TH1. As shown, the higher the temperature, the smaller the combined resistance. However, by connecting the set resistor Rset_th, which is a fixed resistor, in series with the thermistor TH1, the change in the combined resistance at high temperatures can be suppressed. This makes it possible to prevent the additional current Iadd from becoming excessive at high temperatures.

[0039] FIG. 5 shows an example of the relationship between the LED ambient temperature and the additional current Iadd, corresponding to FIG. 4. As shown, at low temperatures, the additional current Iadd increases as the temperature increases. However, at high temperatures, the change in the combined resistance value is suppressed as shown in FIG. 4, so the influence of the thermistor TH2 (terminal voltage Vthd) becomes greater, and the additional current Iadd decreases as the temperature increases. As a result, at high temperatures, the reference current Iref, and therefore the output current Iout, can be reduced as the temperature rises, thereby suppressing heat generation from the LED light source 10. This allows the LED light source 10 to have a longer life.

[0040] FIG. 6 shows an example of the relationship between the LED ambient temperature and the reference current Iref, corresponding to FIGS. 4 and 5. The higher the LED ambient temperature, the smaller the resistance value of the thermistor TH2, and the smaller the set current Iset. The increasing change in the additional current Iadd due to an increase in the LED temperature is greater than the decreasing change in the set current Iset, so the reference current Iref increases. However, when the LED ambient temperature is high, the additional current Iadd decreases as the temperature increases, as shown in FIG. 5, and the reference current Iref decreases significantly along with the decrease in the set current Iset. This reduces the output current Iout when the LED ambient temperature is high, making it possible to suppress heat generation from the LED light source 10.

[0041] Note that the non-inverting input terminal (+) of the error amplifier 3B in the current adding unit 3 is not limited to being connected to the THD terminal, but may instead be connected to, for example, an application terminal for a fixed internal voltage. In this case, the additional current Iadd does not decrease when the LED ambient temperature is high, but the use of the setting resistor Rset_th suppresses the increase in the additional current Iadd.

[0042] <3. Socket-type LED module> FIG. 7 is a plan view showing a socket-type LED module Y as an example of the LED light-emitting device X1 described above. The socket-type LED module Y of this configuration example is, for example, an in-vehicle lighting fixture, and includes a substrate 300, an LED chip 400, a white resin 480, a reflector 600, an LED driving device 5, and a socket 900. Note that, although the LED chips 400 shown in FIG. 7 correspond to the example of FIG. 1 and include three LED chips constituting the LED light source 10, the number of LED chips is not limited to this. Also, in FIG. 7, electronic components externally attached to the LED driving device 5 are omitted for convenience.

[0043] The substrate 300 has a base material and a wiring pattern formed on it (see the hatched area in this figure). The base material is rectangular and made of, for example, glass epoxy resin. The wiring pattern is a conductive member laid on the surface of the base material to mount the LED chip 400 and various electronic components, and is made of a metal such as Cu or Ag. The upper surface of the substrate 300 is mounted with an LED driver 5 and various external components. The electronic components are connected by the wiring patterns laid on the upper and lower surfaces of the substrate 300 to form a circuit that lights up the LED chip 400 in the desired light emission state.

[0044] The reflector 600 is made of, for example, a white resin and is fixed to the central region of the substrate 300 so as to surround the LED chip 400. The reflector 600 reflects light emitted laterally from the LED chip 400 upward. A reflective surface 601 is formed on the reflector 600. The reflective surface 601 surrounds the LED chip 400. Although it is difficult to see in FIG. 7 , the reflective surface 601 is inclined in the thickness direction of the substrate 300 so that the farther the reflective surface 601 is from the substrate 300, the farther it is from the LED chip 400 in a direction perpendicular to the thickness direction of the substrate 300. In other words, the reflective surface 601 has a tapered shape in which the cross section perpendicular to the thickness direction of the substrate 300 becomes larger toward the opening side of the reflector 600.

[0045] White resin 480 is made of a white resin material that does not transmit light from LED chip 400, and corresponds to an example of an opaque resin. As can be seen from Fig. 7, white resin 480 surrounds LED chip 400, and its outer periphery reaches reflective surface 601 of reflector 600. Therefore, in Fig. 7, the area extending from LED chip 400 to reflective surface 601 in the vertical and horizontal directions in the figure is filled with white resin 480.

[0046] The socket 900 is a component for mounting the substrate 300 and attaching it to, for example, an automobile. The socket 900 is made of, for example, synthetic resin and is formed by, for example, injection molding. The socket 900 includes a mounting portion 910 for mounting the substrate 300 and an attachment portion for attaching it to, for example, an automobile. The mounting portion 910 has a cylindrical shape with one open end, and the substrate 300 is mounted on the inner bottom surface of the mounting portion 910. A heat sink 950, which is, for example, a circular plate made of aluminum, is fixed to the inner bottom surface of the mounting portion 910. The substrate 300 is mounted on the mounting portion 910 of the socket 900 by adhering the bottom surface of the substrate 300 to the upper surface of the heat sink 950 with an adhesive.

[0047] The white resin 480 covers the entire annular region extending from the support substrate of the LED chip 400 to the reflective surface 601 of the reflector 600. Therefore, the region surrounded by the reflective surface 601 is covered with the white resin 480 except for the region occupied by the LED chip 400. This makes it possible to reflect more light from the semiconductor layer of the LED chip 400. This is suitable for increasing the brightness of the socket-type LED module Y. Furthermore, there is no need to apply a separate treatment to the region surrounded by the reflective surface 601 of the substrate 300 to favorably reflect light.

[0048] By providing the reflector 600 having the reflective surface 601, the area directly above the socket type LED module Y can be illuminated more brightly.

[0049] In particular, when an LED chip 400 (LED light source 10) is provided in such a socket-type LED module Y, the ambient temperature of the LED light source 10 is likely to rise. Therefore, it is important to suppress the decrease in brightness that accompanies an increase in the ambient temperature of the LED by performing brightness control as in the LED driving device 5 of this embodiment. Furthermore, it is important to suppress the heat generation of the LED light source 10 by performing temperature derating, which reduces the output current Iout when the ambient temperature of the LED is high, as in the LED driving device 5 of this embodiment.

[0050] <4.Applications> The LED driving device 5 described so far can be incorporated into light-emitting devices such as headlamps (including high beams, low beams, small lamps, fog lamps, etc., as appropriate) X11, daytime running lamps (DRLs) X12, tail lamps (including small lamps or back lamps, etc., as appropriate) X13, stop lamps X14, and turn lamps X15 of a vehicle X10, as shown in Figures 8 and 9.

[0051] The LED driving device 5 may be provided as a module (such as the aforementioned socket-type LED module Y) together with the LED light source 10 to be driven, or may be provided as a standalone IC independent of the LED light source 10.

[0052] <5.Other> Although exemplary embodiments have been described above, the embodiments can be modified in various ways within the spirit and scope of the present invention.

[0053] For example, in the above embodiment, an example was given of a configuration using an LED as the light-emitting element, but the configuration of the present invention is not limited to this, and light-emitting elements other than LEDs that have the characteristic of decreasing brightness as the temperature rises may also be used.

[0054] Furthermore, in the above embodiment, an example was given in which the current driver 1 is of a current source type (= an output format in which the output current Iout flows from the power supply terminal to the anode of the LED light source 10), but the configuration of the LED driving device 5 is not limited to this in any way, and the current driver 1 may be of a current sink type (= an output format in which the output current Iout is drawn from the cathode of the LED light source 10 toward the ground terminal).

[0055] <6. Notes> As described above, for example, the light emitting element driving device (5) according to the present disclosure: a first external terminal (SET terminal) connectable to a first setting resistor (Rset); a second external terminal (SET_TH terminal) connectable to a first thermistor (TH1) with a negative characteristic that is arranged around the light-emitting element light source (10); a current setting unit (2) that generates a set current (Iset) based on the resistance value of the first set resistor; a current adding unit (3) that generates an additional current (Iadd) with a negative characteristic with respect to the resistance value of the first thermistor; a current driver (1) that generates an output current (Iout) flowing through the light-emitting element light source connected between an application terminal of a power supply voltage (Vin) and a ground terminal, based on a reference current (Iref) that is the sum of the set current and the additional current; (first configuration).

[0056] In addition, in the above first configuration, a second setting resistor (Rset_th) connected in series with the first thermistor (TH1) can be connected to the second external terminal (SET_TH terminal), and the current adding unit may be configured to generate the additional current having a negative characteristic with respect to the combined resistance value of the first thermistor and the second setting resistor (second configuration).

[0057] In addition, the second configuration may further include a third external terminal (THD terminal) connectable to a second thermistor (TH2) with negative characteristic arranged around the light-emitting element light source, and a constant current source (4) connected to the third external terminal, and the current adding unit may be configured to generate the additional current with positive characteristic with respect to the terminal voltage (Vthd) of the third external terminal (third configuration).

[0058] In the third configuration, the current setting section may generate the set current having a positive characteristic with respect to the terminal voltage (fourth configuration).

[0059] Furthermore, in the above fourth configuration, the current setting unit may be configured to have a first error amplifier (2B) including: a first output transistor (2A) arranged in a path through which the set current flows; a first input terminal connected to a first node to which a first terminal of the first output transistor and the first external terminal (SET terminal) are connected; a second input terminal connected to an application terminal of the terminal voltage (Vthd); and an output terminal connected to a control terminal of the first output transistor (fifth configuration).

[0060] Furthermore, in any of the first to fifth configurations, the current adding unit may be configured to have a second output transistor (3A) arranged in a path through which the additional current flows, and a second error amplifier (3B) including a first input terminal connected to a second node to which a first terminal of the second output transistor and the second external terminal (SET_TH terminal) are connected, a second input terminal connected to an application terminal of a reference voltage (Vthd), and an output terminal connected to a control terminal of the second output transistor (sixth configuration).

[0061] In addition, the sixth configuration may further include a third external terminal (THD terminal) connectable to a second thermistor (TH2) with negative characteristics arranged around the light-emitting element light source, and a constant current source (4) connected to the third external terminal, and a second setting resistor (Rset_th) connected in series with the first thermistor can be connected to the second external terminal (SET_TH terminal), and the reference voltage may be the terminal voltage (Vthd) of the third external terminal (seventh configuration).

[0062] Furthermore, the light emitting device (X1) according to the present disclosure is configured to have a light emitting element driving device (5) having any one of the first to seventh configurations described above, and the light emitting element light source (10) (eighth configuration).

[0063] In the eighth configuration, the light-emitting element light source may be an LED light source (ninth configuration).

[0064] In addition, the eighth or ninth configuration may further include a substrate (300) having a wiring pattern for mounting the light-emitting element light source and the light-emitting element driving device, and a socket (900) for mounting the substrate (tenth configuration).

[0065] A vehicle (X10) according to the present disclosure is configured to include a light emitting device configured as any one of the eighth to tenth aspects above.

[0066] <<Second Technical Disclosure>> The second technical disclosure will be described below. In the following description, the reference numerals indicating the components and signals will be treated as having no relation to the first technical disclosure.

[0067] <1. LED light emitting device> FIG. 10 is a diagram showing the overall configuration of an LED light emitting device X1 according to an exemplary embodiment. The LED light emitting device X1 is an in-vehicle lamp that is lit by receiving a power supply voltage Vin from a battery (not shown). Examples of the LED light emitting device X1 include a headlamp, a daytime running lamp, a tail lamp, a stop lamp, and a turn signal lamp. The battery is a power source for the vehicle in which the LED light emitting device X1 is mounted, and a lead-acid battery, a lithium-ion battery, or the like is preferably used.

[0068] 10, the LED light emitting device X1 includes an LED driving device 15 and an LED light source 200. The LED driving device 15 is a semiconductor integrated circuit device (so-called LED driver IC) that operates by receiving a power supply voltage Vin from the battery and generates an output current Iout to be supplied to the LED light source 200.

[0069] The LED driver 15 has external terminals for establishing electrical connection with the outside, including a VIN terminal, an OUT terminal, an ISINK terminal, a CRT terminal, a DISC terminal, and a CNT terminal. The VIN terminal is connected to an application terminal of the power supply voltage Vin. That is, the LED driver 15 receives the power supply voltage Vin via the VIN terminal.

[0070] The LED light source 200 is an LED string consisting of multiple LED chips (light-emitting elements) connected in series. The LED light source 200 is divided into a high-potential side LED 201 (high-potential side light source) and a low-potential side LED 202 (low-potential side light source).

[0071] The high-potential side LED 201 is composed of at least one LED chip. In the example shown in Fig. 10, the high-potential side LED 201 is composed of two LED chips connected in series. The anode of the high-potential side LED 201 is connected to the OUT pin (=output terminal of the output current Iout) of the LED driver 15.

[0072] The low-potential side LED 202 is composed of at least one LED chip. In the example shown in Fig. 10, the low-potential side LED 202 is composed of two LED chips connected in series. The cathode of the low-potential side LED 202 is connected to the ground terminal. On the other hand, the node Nx, to which the cathode of the high-potential side LED 201 and the anode of the low-potential side LED 202 are connected, is connected to the ISINK terminal, the reason for which will be described later.

[0073] The LED driving device 15 has an internal configuration that integrates a current driver 1, a UVLO unit 2, a control logic unit 3, a bypass control unit 4, a constant current circuit 5, a comparator 6, a constant current source 7, a switch 8, a CR timer 9, and a variable setting unit 10.

[0074] 10 shows only a part of the internal configuration of the LED driver 15, and in addition to the configuration shown in Fig. 10, the LED driver 15 also has various abnormality detection units, an abnormality notification unit for notifying the outside of an abnormality, an output current setting unit for setting the output current Iout, etc. The abnormality detection units include an LED open detection unit for detecting an open circuit in the LED light source 200 based on the voltage of the OUT terminal, an output ground fault detection unit for detecting a ground fault in the OUT terminal based on the voltage of the OUT terminal, a thermal protection circuit (TSD), etc.

[0075] The current driver 1 performs constant current control of the output current Iout flowing through the LED light source 200 so that the output current Iout matches a predetermined target value. The current driver 1 has an error amplifier 1A, a sense resistor 1B, and a PMOS transistor 1C. One end of the sense resistor 1B is connected to a terminal to which a power supply voltage Vin is applied. The other end of the sense resistor 1B is connected to an inverting input terminal (-) of the error amplifier 1A and to the source of the PMOS transistor 1C. A non-inverting input terminal (+) of the error amplifier 1A is connected to a terminal to which a reference voltage is applied. The output terminal of the error amplifier 1A is connected to the gate of the PMOS transistor 1C. The drain of the PMOS transistor 1C is connected to an OUT terminal.

[0076] The UVLO (Under Voltage Lock Out) unit 2 is a circuit that detects a reduced voltage of the power supply voltage Vin. The UVLO unit 2 compares the power supply voltage Vin with a UVLO threshold voltage Vin_UVLO, and outputs a UVLO detection signal Suvlo as the comparison result.

[0077] The control logic unit 3 is the main body that comprehensively controls the operation of the entire LED driving device 15. For example, the control logic unit 3 performs control to stop the output current Iout according to the detection results obtained by various abnormality detection units (LED open detection unit, output ground fault detection unit, temperature protection circuit, etc.), and causes the abnormality notification unit to notify the outside.

[0078] <2.CR Timer> The CR timer 9 will now be described with reference to Fig. 11. Fig. 11 is a diagram showing an example of the internal configuration of the CR timer 9. The CR timer 9 is configured to enable PWM dimming by connecting external components (a capacitor Ccrt and a resistor Rcrt) to the CRT terminal and the DISC terminal.

[0079] As shown in FIG. 11, the CRT timer 9 has a constant current source 9A, a switch 9B, a comparator 9C, a comparator 9D, a NOR circuit 9E, an NMOS transistor 9F, and an NMOS transistor 9G.

[0080] One end of a capacitor Ccrt is externally connected to the CRT terminal, and one end of a resistor Rcrt is also connected to the CRT terminal, with the other end of the resistor Rcrt being connected to the DISC terminal.

[0081] A comparator 9C compares the voltage at the CRT terminal with a reference voltage Vcrt_dis1. A constant current source 9A and a switch 9B are provided between the application terminal of the internal voltage Vreg and the CRT terminal. The internal voltage Vreg is generated by an internal voltage source (not shown) based on the power supply voltage Vin. The switch 9B is turned on and off according to the output of the comparator 9C.

[0082] The comparator 9D compares the voltage of the CRT terminal with a reference voltage Vcrt_dis2 (>Vcrt_dis1). One input terminal of the NOR circuit 9E is connected to the output terminal of the comparator 9C. The other input terminal of the NOR circuit 9E is connected to the output terminal of the comparator 9D.

[0083] The drain of the NMOS transistor 9F is connected to the DISC terminal, the source of the NMOS transistor 9F is connected to the ground terminal, and the gate of the NMOS transistor 9F is connected to the output terminal of the NOR circuit 9E.

[0084] The drain of NMOS transistor 9G is connected to the DISC terminal. The source of NMOS transistor 9G is connected to the ground terminal. The gate of NMOS transistor 9G is connected to the output terminal of comparator 9D.

[0085] Also, a switch SWdc is arranged between the battery B that generates the power supply voltage Vin and the CRT terminal. When used in the PWM dimming mode, the switch SWdc is turned off. In this case, a triangular wave is generated at the CRT terminal.

[0086] Specifically, first, when the voltage at the CRT terminal is lower than the reference voltage Vcrt_dis1, the output of comparator 9C is at the High level, switch 9B is on, and capacitor Ccrt is charged by the constant current source 9A via the CRT terminal. When the voltage at the CRT terminal rises due to charging and exceeds the reference voltage Vcrt_dis1, the output of comparator 9C switches to the Low level and switch 9B is turned off. At this time, since the outputs of comparators 9C and 9D are both at the Low level, the output of NOR circuit 9E becomes the High level and NMOS transistor 9F is turned on. Therefore, capacitor Ccrt is discharged via the DISC terminal. Also, when the output of comparator 9C switches to the Low level as described above, the reference voltage switches from Vcrt_dis1 to Vcrt_cha (<Vcrt_dis1).

[0087] When the voltage at the CRT terminal drops due to discharge and falls below the reference voltage Vcrt_cha, the output of comparator 9C switches to the High level and switch 9B is turned on. At this time, the charging of capacitor Ccrt starts and the reference voltage of comparator 9C switches from Vcrt_cha to Vcrt_dis1. By repeating such operations, a triangular wave is generated at the CRT terminal.

[0088] When a triangular wave is generated, the PWM dimming signal Spwm output from the comparator 9C is generated in a pulsed form. The control logic unit 3 generates an LED-on signal Sled_on based on the PWM dimming signal Spwm, and controls the current driver 1 to turn on and off. During the rising period of the triangular wave (= the high-level period of Spwm), the current driver 1 (i.e., the output current Iout) is in the off state, and during the falling period of the triangular wave (= the low-level period of Spwm), the current driver 1 (i.e., the output current Iout) is in the on state. The frequency and on-duty of the PWM dimming can be set as desired by adjusting the resistance value of the resistor Rcrt and the capacitance value of the capacitor Ccrt.

[0089] On the other hand, when used in DC dimming mode, the switch SWdc is turned on and the power supply voltage Vin is applied to the CRT terminal. As a result, when the voltage at the CRT terminal exceeds the reference voltage Vcrt_dis1, the PWM dimming signal Spwm is fixed at a low level and the current driver 1 is maintained in the on state.

[0090] Furthermore, when the voltage at the CRT terminal exceeds Vcrt_dis2, the output of the comparator 9D goes high, and the state changes from NMOS transistor 9F on and NMOS transistor 9G off to NMOS transistor 9F off and NMOS transistor 9G on. Because the NMOS transistor 9G has a higher on-resistance than the NMOS transistor 9F, it is possible to reduce the current flowing into the DISC terminal and thereby suppress the power consumption of the IC.

[0091] When using only DC dimming mode, short the CRT terminal to the VIN terminal and leave the DISC terminal open.

[0092] <3. Bypass function> 10, a description will be given of the bypass function provided in the LED driver 15. As described above, the node Nx to which the high potential side LED 201 and the low potential side LED 202 are connected is connected to the ISINK terminal.

[0093] The bypass control unit 4 and the constant current circuit 5 constitute a bypass function unit. The constant current circuit 5 has an error amplifier 5A, an NMOS transistor 5B, and a sense resistor 5C. The drain of the NMOS transistor 5B is connected to the ISINK terminal. The source of the NMOS transistor 5B is connected to one end of the sense resistor 5C. The other end of the sense resistor 5C is connected to the ground terminal. The node where the NMOS transistor 5B and the sense resistor 5C are connected is connected to the inverting input terminal (-) of the error amplifier 5A. The non-inverting input terminal (+) of the error amplifier 5A is connected to the terminal to which a reference voltage is applied. With this configuration, the constant current circuit 5 performs constant current control of the current drawn from the ISINK terminal.

[0094] The bypass control unit 4 controls the on / off of the constant current circuit 5. When the constant current circuit 5 is in the on state, the output current Iout flows through the high potential side LED 201 and is drawn into the constant current circuit 5 from the ISINK terminal. In other words, the low potential side LED 202 is bypassed. As a result, when the power supply voltage Vin is low, by bypassing the low potential side LED 202, the number of series-connected LED chips through which the output current Iout flows is reduced, and the total forward voltage of the LED light source 200 is reduced, so that the LED light source 200 can be kept lit.

[0095] When the power supply voltage Vin is high, the constant current circuit 5 is turned off, so that the output current Iout flows sequentially through the high-potential side LED 201 and the low-potential side LED 202, and all the LED chips in the LED light source 200 are lit.

[0096] <4. Open detection function> When the power supply voltage Vin rises (when the power supply voltage Vin is started), the constant current circuit 5 is turned on while the power supply voltage Vin is low, thereby bypassing the low-potential side LED 202 and lighting the high-potential side LED 201. Thereafter, when the power supply voltage Vin increases, the constant current circuit 5 is controlled to be switched off. However, if an open circuit occurs on the lower potential side of node Nx (including an open circuit in the low-potential side LED 202), if the constant current circuit 5 is off, the output current Iout will not flow, and the high-potential side LED 201 will be turned off. In such a case, to the human eye, the LED light source 200 will be turned on momentarily and then turned off. Therefore, the LED driving device 15 according to this embodiment is provided with a function (open detection function) for detecting the occurrence of an open circuit on the lower potential side of node Nx.

[0097] The comparator 6 is provided for the open circuit detection function as described above. The non-inverting input terminal (+) of the comparator 6 is connected to the ISINK terminal. The inverting input terminal (-) of the comparator 6 is connected to the application terminal of the open circuit detection threshold voltage Vth_op. The comparator 6 compares the voltage of the ISINK terminal with the open circuit detection threshold voltage Vth_op, and outputs a detection signal Sdet as the comparison result to the bypass control unit 4.

[0098] A constant current source 7 and a switch 8 are also provided for the open detection function. The constant current source 7 and the switch 8 are provided between the application terminal of the power supply voltage Vin and the ISINK terminal.

[0099] Here, the operation of the open circuit detection function when the power supply voltage Vin rises will be described. When the power supply voltage Vin rises from 0 V, the bypass control section 4 keeps the constant current circuit 5 in the off state.

[0100] Then, when the power supply voltage Vin rises and exceeds the UVLO threshold voltage Vin_UVLO, a UVLO signal Suvlo indicating UVLO release is output from the UVLO unit 2. When the UVLO signal Suvlo indicates UVLO release and the LED on signal Sled_on indicates on, the bypass control unit 4 switches the switch 8 to the on state.

[0101] 12, if no open circuit has occurred on the lower potential side of node Nx, a constant current Imoni (broken arrow) flows through the low potential side LED 202 via the on-state switch 8 and the ISINK terminal. At this time, the voltage of the ISINK terminal becomes close to the total forward voltage of the low potential side LED 202, so the open circuit detection threshold voltage Vth_op is set to a voltage higher than the voltage of the ISINK terminal. As a result, the comparator 6 determines that the voltage of the ISINK terminal is lower than the open circuit detection threshold voltage Vth_op and outputs a low-level detection signal Sdet indicating that no open circuit has occurred.

[0102] In this case, the bypass control unit 4 switches the constant current circuit 5 to the ON state. As a result, the low potential side LED 202 is bypassed, the output current Iout is drawn from the high potential side LED 201 to the ISINK terminal, and the high potential side LED lights up. After that, when the power supply voltage Vin increases, the bypass is released by the bypass control unit 4 switching the constant current circuit 5 to the OFF state, and the output current Iout flows through the high potential side LED 201 and the low potential side LED 202, and all the LED chips in the LED light source 200 light up.

[0103] On the other hand, when the switch 8 is turned on as described above, if an open circuit occurs on the lower potential side of the node Nx, as shown in FIG. 13, the constant current Imoni charges the parasitic capacitance Cled of the high-potential side LED 201 and the external capacitive element Csink via the ISINK terminal. The capacitive element Csink is an element externally connected to the ISINK terminal to counter EMC (Electromagnetic Compatibility) testing. The EMC test is a BCI (Bulk Current Injection) test that injects noise into the power line, and the capacitive element Csink is provided to suppress voltage fluctuations at the ISINK terminal during the test. The voltage at the ISINK terminal generated by the charging is compared with the open circuit detection threshold voltage Vth_op by the comparator 6. Because the voltage at the ISINK terminal is higher than the open circuit detection threshold voltage Vth_op, the comparator 6 outputs a high-level detection signal Sdet indicating the occurrence of an open circuit.

[0104] Here, the open circuit detection threshold voltage Vth_op must be equal to or lower than the UVLO threshold voltage Vin_UVLO. In DC dimming mode, the level of the PWM dimming signal Spwm output from the CR timer 9 is fixed, and the LED-on signal Sled_on indicates ON when UVLO is released, so the bypass control unit 4 immediately turns on the switch 8. However, since the voltage at the ISINK terminal does not exceed the power supply voltage Vin, if the open circuit detection threshold voltage Vth_op is higher than the UVLO threshold voltage Vin_UVLO, the voltage at the ISINK terminal will be lower than the open circuit detection threshold voltage Vth_op, and the comparator 6 may erroneously detect that no open circuit has occurred.

[0105] Furthermore, the bypass control unit 4 must wait for the waiting time required for the voltage at the ISINK terminal to become higher than the open detection threshold voltage Vth_op through charging, from when the switch 8 is turned on, until it determines whether or not there is an open circuit based on the detection signal Sdet output from the comparator 6. The required waiting time Twait must satisfy the condition of the following equation (1). Vth_op < Imoni×Twait / C (1) where C=Cled+Csink

[0106] The bypass control unit 4 waits for the waiting time Twait before determining whether the terminal is open, and if it is open (if Sdet=High), it maintains the off state of the constant current circuit 5. This makes it possible to avoid the high potential side LED 201 from momentarily lighting up due to the occurrence of an open circuit.

[0107] Here, with reference to Figs. 14 and 15, the operation at the time of rising of the power supply voltage Vin will be described. In the timing charts shown in Figs. 14 and 15, the waveforms of the power supply voltage Vin, the constant current Imoni, the voltage Vsink of the ISINK terminal, the output current Iout, the first output current Ia, and the second output current Ib are shown from the top to the bottom. As shown in Fig. 16, the first output current Ia is the output current flowing through a path from the node Nx to the ISINK terminal, and the second output current Ib is the output current flowing through a path from the node Nx to the low-potential side LED 202. Also, as shown in Figs. 14 and 15, the open-circuit detection threshold voltage Vth_op is equal to or lower than the UVLO threshold voltage Vin_UVLO.

[0108] Fig. 14 is a diagram showing the operation when no open circuit occurs on the lower potential side of node Nx. Fig. 14 and Fig. 15, which will be described later, show the case of DC dimming mode.

[0109] 14, when the power supply voltage Vin rises from 0 V and becomes equal to or greater than the UVLO threshold voltage Vin_UVLO (at timing t1), the UVLO is released and the LED on signal Sled_on indicates on, so the switch 8 is immediately switched on. As a result, the constant current Imoni rises and the voltage Vsink reaches a value close to the total forward voltage Vf of the low-potential side LEDs 202. The voltage Vsink is lower than the open-circuit detection threshold voltage Vth_op.

[0110] The bypass control unit 4 waits for the waiting time Twait from the timing t1 and then determines that no open circuit has occurred based on the detection signal Sdet (timing t2). As a result, the bypass control unit 4 turns off the switch 8 and switches on the constant current circuit 5. As a result, the first output current Ia (=Iout) is drawn from the ISINK terminal, and the high-side LED 201 lights up.

[0111] After that, when the power supply voltage Vin becomes sufficiently high, the bypass control unit 4 switches the constant current circuit 5 to the off state (timing t3). As a result, the second output current Ib (=Iout) flows through the low potential side LED 202. Therefore, all the LED chips in the LED light source 200 light up.

[0112] On the other hand, Fig. 15 shows the operation when an open circuit occurs on the lower potential side of node Nx. As shown in Fig. 15, when the power supply voltage Vin rises from 0 V and becomes equal to or higher than the UVLO threshold voltage Vin_UVLO (timing t11), the UVLO is released and the LED on signal Sled_on indicates on, so that the switch 8 is immediately switched on.

[0113] As a result, the constant current Imoni rises, and the constant current Imoni charges the parasitic capacitance Cled and the capacitive element Csink, causing the voltage Vsink to rise. At timing t12, which is the waiting time Twait after timing t11, Vsink exceeds the open circuit detection threshold voltage Vth_op. As a result, the bypass control unit 4 determines that an open circuit has occurred based on the detection signal Sdet, turns off the switch 8, and maintains the constant current circuit 5 in the off state. As a result, the output current Iout does not flow, and the high-side LED 201 does not light up.

[0114] <5. Variable setting function> Next, the variable setting unit 10 will be described.

[0115] The number of LED chips constituting the low potential side LED 202 may vary. For example, while the number is two in FIG. 1, it may be three, for example. In this case, the total forward voltage of the low potential side LED 202 varies depending on the number. Here, as described above, the open circuit detection threshold voltage Vth_op needs to be set higher than the total forward voltage of the low potential side LED 202, so the open circuit detection threshold voltage Vth_op needs to be changed depending on the number of LED chips constituting the low potential side LED 202.

[0116] Furthermore, as described above, since the UVLO threshold voltage Vin_UVLO needs to be equal to or higher than the open circuit detection threshold voltage Vth_op, the open circuit detection threshold voltage Vth_op also needs to be changed in accordance with the change in the open circuit detection threshold voltage Vth_op as described above.

[0117] Furthermore, from the above formula (1), the waiting time Twait also needs to be changed according to the change in the open detection threshold voltage Vth_op. Note that the capacitive element Csink is not essential and may not be provided. In this case, the waiting time Twait may be a fixed value.

[0118] Therefore, in the LED driving device 15, the variable setting unit 10 variably sets the open detection threshold voltage Vth_op, the UVLO threshold voltage Vin_UVLO, and the waiting time Twait in the bypass control unit 4 in conjunction with each other according to the number of LED chips that make up the low potential side LED 202. The variable setting unit 10 performs the variable setting using the CNT terminal.

[0119] The variable setting unit 10 detects, for example, two patterns of open / GND (ground potential) application to the CNT terminal, and performs variable setting according to the detection result.

[0120] Furthermore, the variable setting unit 10 detects, for example, three patterns of application of power supply voltage Vin / open / GND to the CNT terminal, and performs variable setting according to the detection result.

[0121] 17 is a diagram showing an example of the configuration of the variable setting section 10 configured to be able to detect the above three patterns. In the configuration shown in Fig. 17, the variable setting section 10 has comparators 10A, 10B, and 10C, and a constant current source 10D.

[0122] The non-inverting input terminal (+) of comparator 10A is connected to the CNT terminal. The inverting input terminal (-) of comparator 10A is connected to the application terminal of reference voltage V1. The inverting input terminal (-) of comparator 10B is connected to the CNT terminal. The non-inverting input terminal (+) of comparator 10B is connected to the application terminal of reference voltage V2. The inverting input terminal (-) of comparator 10C is connected to the CNT terminal. The non-inverting input terminal (+) of comparator 10C is connected to the application terminal of reference voltage V3. A constant current source 10D is provided between the application terminal of internal voltage Vdd and the CNT terminal.

[0123] Here, reference voltage V1 is set to a voltage value slightly higher than 0V (for example, 0.6V). Reference voltage V2 is set to a voltage value slightly higher than internal voltage Vdd (for example, 3.0V if Vdd=2.5V). Reference voltage V3 is set to a voltage slightly lower than power supply voltage Vin (for example, VIN-1V).

[0124] In this case, the CNT terminal = power supply voltage Vin is detected by the output of comparator 10C being at a low level. The CNT terminal = open is detected by the output of comparator 10B being at a low level and the output of comparator 10C being at a high level. The CNT terminal = GND is detected by the output of comparator 10A being at a low level.

[0125] In addition, in the case of a configuration that detects two patterns of open / GND application to a CNT terminal as described above, for example, in the configuration of FIG. 17, the comparators 10B and 10C may be omitted, or the comparators 10A and 10C may be omitted.

[0126] Fig. 18 is a diagram showing another example configuration of the variable setting section 10. In the configuration shown in Fig. 18, the variable setting section 10 has a constant current source 10E. The constant current source 10E is provided between the application terminal of the internal voltage Vdd and the CNT terminal. A setting resistor Rcnt is externally connected to the CNT terminal.

[0127] With this configuration, the voltage Vcnt of the CNT terminal is Vcnt=Icnt×Rcnt (Icnt: constant current value by the constant current source 10E), and the voltage Vcnt can be changed by changing the resistance value of the external setting resistor Rcnt. The variable setting unit 10 performs variable setting according to the voltage Vcnt. This allows for more flexible variable setting.

[0128] <6. Socket-type LED module> Fig. 19 is a plan view showing a socket-type LED module Y as an example of the LED light-emitting device X1 described above. The socket-type LED module Y of this configuration example is, for example, an in-vehicle lighting fixture, and includes a substrate 300, an LED chip 400, a white resin 480, a reflector 600, an LED driving device 15, and a socket 900. For convenience, the LED chips 400 shown in Fig. 19 are shown as three LED chips constituting the LED light source 200, but the number of LED chips is not limited to this (the number of LED chips is four in the example of Fig. 1). Furthermore, in Fig. 19, electronic components externally attached to the LED driving device 15 are omitted for convenience.

[0129] The substrate 300 has a base material and a wiring pattern formed on it (see the hatched area in this figure). The base material is rectangular and made of, for example, glass epoxy resin. The wiring pattern is a conductive member laid on the surface of the base material to mount the LED chip 400 and various electronic components, and is made of a metal such as Cu or Ag. The upper surface of the substrate 300 is mounted with an LED driver 15 and various external components. The electronic components are connected by the wiring patterns laid on the upper and lower surfaces of the substrate 300 to form a circuit that lights up the LED chip 400 in the desired light emission state.

[0130] The reflector 600 is made of, for example, a white resin and is fixed to the central region of the substrate 300 so as to surround the LED chip 400. The reflector 600 reflects light emitted laterally from the LED chip 400 upward. A reflective surface 601 is formed on the reflector 600. The reflective surface 601 surrounds the LED chip 400. Although it is difficult to see in FIG. 16 , the reflective surface 601 is inclined in the thickness direction of the substrate 300 so that the farther the reflective surface 601 is from the substrate 300, the farther it is from the LED chip 400 in a direction perpendicular to the thickness direction of the substrate 300. In other words, the reflective surface 601 has a tapered shape in which the cross section perpendicular to the thickness direction of the substrate 300 becomes larger toward the opening side of the reflector 600.

[0131] White resin 480 is made of a white resin material that does not transmit light from LED chip 400, and corresponds to an example of an opaque resin. As can be seen from Fig. 19, white resin 480 surrounds LED chip 400, and its outer edge reaches reflective surface 601 of reflector 600. Therefore, in Fig. 19, the area extending from LED chip 400 to reflective surface 601 in the vertical and horizontal directions in the figure is filled with white resin 480.

[0132] The socket 900 is a component for mounting the substrate 300 and attaching it to, for example, an automobile. The socket 900 is made of, for example, synthetic resin and is formed by, for example, injection molding. The socket 900 includes a mounting portion 910 for mounting the substrate 300 and an attachment portion for attaching it to, for example, an automobile. The mounting portion 910 has a cylindrical shape with one open end, and the substrate 300 is mounted on the inner bottom surface of the mounting portion 910. A heat sink 950, which is, for example, a circular plate made of aluminum, is fixed to the inner bottom surface of the mounting portion 910. The substrate 300 is mounted on the mounting portion 910 of the socket 900 by adhering the bottom surface of the substrate 300 to the upper surface of the heat sink 950 with an adhesive.

[0133] The white resin 480 covers the entire annular region extending from the support substrate of the LED chip 400 to the reflective surface 601 of the reflector 600. Therefore, the region surrounded by the reflective surface 601 is covered with the white resin 480 except for the region occupied by the LED chip 400. This makes it possible to reflect more light from the semiconductor layer of the LED chip 400. This is suitable for increasing the brightness of the socket-type LED module Y. Furthermore, there is no need to apply a separate treatment to the region surrounded by the reflective surface 601 of the substrate 300 to favorably reflect light.

[0134] By providing the reflector 600 having the reflective surface 601, the area directly above the socket type LED module Y can be illuminated more brightly.

[0135] In particular, automotive lamps are required by law to remain lit even when the power supply voltage Vin drops. In light of this, LED driver 15 with a bypass function is highly suitable as a main driver for automotive lamps.

[0136] 20 is an enlarged view of an example of a wiring pattern on the substrate 300. The wiring pattern shown in FIG. 20 includes a ground wiring 301 that forms a so-called solid ground, and a plurality of terminal wirings 302 that are arranged around the ground wiring 301.

[0137] With the LED driver 15 mounted on the substrate 300, the heat dissipation pad 150 formed on the underside of the LED driver 15 is electrically connected to the ground wiring 301. Furthermore, each external terminal of the LED driver 15 is electrically connected to each terminal wiring. The terminal wiring 302A shown in Fig. 20 is electrically connected to the CNT terminal of the LED driver 15. The terminal wiring 302A is integrated with the ground wiring 301, and it becomes possible to apply GND to the CNT terminal.

[0138] 21 is an enlarged view of another example of the wiring pattern on the substrate 300. The wiring pattern shown in FIG. 21 includes terminal wiring 302B and terminal wiring 302C. Terminal wiring 302C is not a terminal wiring adjacent to terminal wiring 302B. Terminal wiring 302B is electrically connected to the CNT terminal of the LED driver 15. Terminal wiring 302C is electrically connected to the VIN terminal of the LED driver 15.

[0139] As shown in Fig. 21, in order to apply a power supply voltage Vin to the CNT terminal, the terminal wiring 302B is connected to the terminal wiring 302C by a connection wiring 302D. The connection wiring 302D extends in the horizontal direction in which the terminal wirings 302 (external terminals of the LED driving device 15) are arranged. However, in the socket type LED module Y, the size of the substrate 300 is small, and there is a possibility that a component P (such as a resistor) is arranged in the location where the connection wiring 302D is to be provided, and there is a possibility that the connection wiring 302D cannot be provided. In other words, there is a possibility that the power supply voltage Vin cannot be applied to the CNT terminal.

[0140] 20, even if the size of the substrate 300 is small, it is easy to integrate the terminal wiring 302A for GND with the ground wiring 301. Therefore, in the socket-type LED module Y, it is particularly easy to apply the LED driving device 15 provided with the variable setting unit 10 configured to detect the two patterns of open / GND application to the CNT terminals described above.

[0141] In addition, when the variable setting unit 10 is configured to detect the three patterns of application of the power supply voltage Vin / open / GND to the CNT terminal as described above, it may be difficult to apply the power supply voltage Vin to the CNT terminal as described above, so for example, depending on the number of LED chips (number of series stages) constituting the low potential side LED 202, GND may be applied to the CNT terminal when the number is most frequently used (for example, 1), open when the number is second most frequently used (for example, 2), and the power supply voltage Vin when the number is least frequently used (for example, 3).

[0142] <7.Applications> The LED driving device 15 described so far can be incorporated into light-emitting devices such as headlamps (including high beams, low beams, small lamps, fog lamps, etc., as appropriate) X11, daytime running lamps (DRLs) X12, tail lamps (including small lamps or back lamps, etc., as appropriate) X13, stop lamps X14, and turn lamps X15 of a vehicle X10, as shown in Figures 22 and 23.

[0143] The LED driving device 15 may be provided as a module (such as the aforementioned socket-type LED module Y) together with the LED light source 200 to be driven, or may be provided as a standalone IC independent of the LED light source 200.

[0144] <8.Other> Although exemplary embodiments have been described above, the embodiments can be modified in various ways within the spirit and scope of the present invention.

[0145] For example, in the above embodiment, a configuration using a light-emitting diode as the light-emitting element has been described as an example, but the configuration of the present invention is not limited to this, and for example, an organic EL (electro-luminescence) element can also be used as the light-emitting element.

[0146] Furthermore, in the above embodiment, an example was given in which the current driver 1 is of a current source type (= an output format in which the output current Iout flows from the power supply terminal to the anode of the LED light source 200), but the configuration of the LED driving device 15 is not limited to this in any way, and the introduction of the above bypass function is also effective when the current driver 1 is of a current sink type (= an output format in which the output current Iout is drawn from the cathode of the LED light source 200 toward the ground terminal).

[0147] <9. Notes> As described above, for example, the light-emitting element driving device (15) according to the present disclosure: a current driver (1) for generating an output current (Iout) flowing through a light-emitting element light source (200) connected between an application terminal of a power supply voltage (Vin) and a ground terminal; a first external terminal (ISINK terminal) connectable to a node (Nx) at which a high potential side light source (201) and a low potential side light source (202) included in the light-emitting element light source are connected in series; a bypass control unit (4) that draws the output current from the first external terminal and controls the conduction state of a path that bypasses the low potential side light source according to the power supply voltage; a constant current source (7) and a switch (8) provided between the power supply voltage application terminal and the first external terminal; a comparator (6) that compares the voltage of the first external terminal with an open circuit detection threshold voltage (Vth_op) and outputs a detection signal; a UVLO unit (2) that compares the power supply voltage with a UVLO (Under Voltage Lock Out) threshold voltage (Vin_UVLO) and outputs a UVLO detection signal (Suvlo); a variable setting unit (10) that variably sets the open detection threshold voltage and the UVLO threshold voltage in conjunction with each other; and When the power supply voltage is started up, the bypass control unit keeps the path in the off state, and if the UVLO detection signal indicates that UVLO has been released, switches the switch to the on state, and if the detection signal indicates that the voltage of the first external terminal is higher than the open detection threshold voltage, determines that an open has occurred on the lower potential side of the node, and maintains the path in the off state (twelfth configuration).

[0148] In addition, in the above twelfth configuration, the variable setting unit may be configured to variably set a waiting time (Twait) that the bypass control unit waits after switching the switch to the on state and before making an open circuit determination in conjunction with the open circuit detection threshold voltage and the UVLO threshold voltage (thirteenth configuration).

[0149] In the thirteenth configuration, the waiting time may be set in consideration of the capacitance of a capacitive element (Csink) for EMC test countermeasures that can be externally connected to the first external terminal (fourteenth configuration).

[0150] In addition, in any of the above-mentioned configurations 12 to 14, the bypass control unit may be configured to switch the switch to the on state when the UVLO detection signal indicates that UVLO has been released and the light-emitting element on signal (Sled_on) indicates that the light-emitting element light source is on (configuration 15).

[0151] In addition, in the fifteenth configuration, a capacitor (Ccrt) and a resistor (Rcrt) can be externally connected, and a CR timer (9) is further provided which generates a triangular wave and a PWM dimming signal (Spwm) which is a pulse signal corresponding to the triangular wave based on charging of the capacitor and discharging from the capacitor through the resistor, The current driver is controlled to be turned on and off based on the PWM dimming signal, the light-emitting element on signal is a signal based on the PWM dimming signal, The CR timer may be configured to be capable of generating the PWM dimming signal with a fixed level in a DC dimming mode (sixteenth configuration).

[0152] Furthermore, in any of the above 12th to 16th configurations, a second external terminal (CNT terminal) may be further provided, and the variable setting unit may be configured to perform variable setting in response to application of a signal to the second external terminal (17th configuration).

[0153] In addition, in the above-mentioned 17th configuration, the variable setting unit may be configured to detect two patterns, open / GND (ground potential) application, to the second external terminal and perform variable setting according to the detection result (18th configuration).

[0154] In addition, in the above-mentioned 17th configuration, the variable setting unit may be configured to detect three patterns of application of the power supply voltage / open / GND (ground potential) to the second external terminal, and perform variable setting according to the detection result (19th configuration).

[0155] Furthermore, in the above-mentioned seventeenth configuration, the variable setting unit may have a constant current source (10E) and perform variable setting based on the voltage generated at the second external terminal by passing a constant current (Icnt) from the constant current source through a setting resistor (Rcnt) that can be externally connected to the second external terminal (twentieth configuration).

[0156] Furthermore, the light-emitting device (X1) according to the present disclosure is configured to include a light-emitting element driving device (15) having any one of the first to ninth configurations described above, and the light-emitting element light source (200) (21st configuration).

[0157] In the twenty-first configuration, the light-emitting element light source may be an LED light source (twenty-second configuration).

[0158] Furthermore, in the above-mentioned 21st or 22nd configuration, the configuration may further include a substrate (300) having a wiring pattern for mounting the light-emitting element light source and the light-emitting element driving device, and a socket (900) for mounting the substrate (23rd configuration).

[0159] In addition, in the twenty-third configuration, the light-emitting element driving device has a second external terminal (CNT terminal) and a heat dissipation pad (150) provided on a lower surface, the wiring pattern includes a terminal wiring (302A) electrically connected to the second external terminal, and a ground wiring (301) integrated with the terminal wiring and electrically connected to the heat dissipation pad; The variable setting unit may be configured to detect two patterns of open / ground potential application to the second external terminal, and perform variable setting in accordance with the detection result (24th configuration).

[0160] A vehicle (X10) according to the present disclosure is configured to include a light emitting device (X1) configured as any one of the twenty-first to twenty-fourth configurations described above. [Industrial Applicability]

[0161] The present disclosure can be used, for example, in a light emitting element driving device for use in a vehicle. [Explanation of symbols]

[0162] 1 Current Driver 2 Current setting section 2A output transistor 2B Error Amplifier 3 Current addition section 3A output transistor 3B Error Amplifier 4 constant current source 5 LED driver 10 LED light sources 300 boards 400 LED chips 480 White resin 600 Reflector 601 Reflective surface 900 sockets 910 Mounting section 950 Heat sink B Battery Rset, Rset_th setting resistor TH1, TH2 thermistor X1 LED light source X10 vehicle X11 Headlamp X12 Daytime Running Lamps X13 tail lamp X14 Stop lamp X15 Turn Lamp Y-socket type LED module

Claims

1. a first external terminal connectable to a first setting resistor; a second external terminal connectable to a first thermistor with a negative coefficient arranged around the light-emitting element light source; a current setting unit that generates a set current based on the resistance value of the first setting resistor; a current adding unit that generates an additional current with a negative characteristic with respect to the resistance value of the first thermistor; a current driver that generates an output current flowing through the light-emitting element light source connected between a power supply voltage application terminal and a ground terminal, based on a reference current that is the sum of the set current and the additional current; A light emitting element driving device having the above structure.

2. a second setting resistor connected in series with the first thermistor can be connected to the second external terminal; 2. The light-emitting element driving device according to claim 1, wherein the current adding section generates the additional current having a negative characteristic with respect to a combined resistance value of the first thermistor and the second set resistor.

3. a third external terminal connectable to a second thermistor with a negative coefficient arranged around the light-emitting element light source; a constant current source connected to the third external terminal; and The light-emitting element driving device according to claim 2 , wherein the current adding section generates the additional current having a positive characteristic with respect to the terminal voltage of the third external terminal.

4. The light-emitting element driving device according to claim 3 , wherein the current setting section generates the set current having a positive characteristic with respect to the terminal voltage.

5. The current setting unit a first output transistor disposed in a path through which the set current flows; a first error amplifier including: a first input terminal connected to a first node where a first terminal of the first output transistor and the first external terminal are connected; a second input terminal connected to an application terminal of the terminal voltage; and an output terminal connected to a control terminal of the first output transistor; The light emitting element driving device according to claim 4 , further comprising:

6. The current adding unit a second output transistor disposed in a path through which the additional current flows; a second error amplifier including: a first input terminal connected to a second node to which a first terminal of the second output transistor and the second external terminal are connected; a second input terminal connected to an application terminal of a reference voltage; and an output terminal connected to a control terminal of the second output transistor; The light emitting element driving device according to claim 1 , further comprising:

7. a third external terminal connectable to a second thermistor with a negative coefficient arranged around the light-emitting element light source; a constant current source connected to the third external terminal; and a second setting resistor connected in series with the first thermistor can be connected to the second external terminal; 7. The light-emitting element driving device according to claim 6, wherein the reference voltage is a terminal voltage of the third external terminal.

8. A light emitting device comprising: the light emitting element driving device according to claim 1; and the light emitting element light source.

9. The light emitting device according to claim 8 , wherein the light emitting element light source is an LED light source.

10. a substrate provided with a wiring pattern for mounting the light-emitting element light source and the light-emitting element driving device; a socket for mounting the substrate; The light emitting device according to claim 8 or claim 9, further comprising:

11. A vehicle comprising the light emitting device according to any one of claims 8 to 10.

12. a current driver that generates an output current flowing through a light-emitting element light source connected between a power supply voltage application terminal and a ground terminal; a first external terminal connectable to a node to which a high potential side light source and a low potential side light source included in the light-emitting element light source are connected in series; a bypass control unit that draws the output current from the first external terminal and controls a conduction state of a path that bypasses the low potential side light source in response to the power supply voltage; a constant current source and a switch provided between the power supply voltage application terminal and the first external terminal; a comparator that compares a voltage of the first external terminal with an open circuit detection threshold voltage and outputs a detection signal; a UVLO (Under Voltage Lock Out) unit that compares the power supply voltage with a UVLO threshold voltage and outputs a UVLO detection signal; a variable setting unit that variably sets the open detection threshold voltage and the UVLO threshold voltage in conjunction with each other; and When the power supply voltage is started up, the bypass control unit keeps the path in an off state, and if the UVLO detection signal indicates that UVLO has been released, switches the switch to an on state, and if the detection signal indicates that the voltage of the first external terminal is higher than the open detection threshold voltage, determines that an open has occurred on the lower potential side of the node, and maintains the path in an off state.

13. The light-emitting element driving device according to claim 12, wherein the variable setting unit variably sets the waiting time that the bypass control unit waits after switching the switch to the on state and before making an open determination in conjunction with the open detection threshold voltage and the UVLO threshold voltage.

14. The light-emitting element driving device according to claim 13 , wherein the waiting time is set in consideration of a capacitance of a capacitive element for EMC testing that can be externally connected to the first external terminal.

15. The light-emitting element driving device according to any one of claims 12 to 14, wherein the bypass control unit switches the switch to an on state when the UVLO detection signal indicates that UVLO has been released and when a light-emitting element on signal indicates that the light-emitting element light source is on.

16. a CR timer to which a capacitor and a resistor can be externally connected, which generates a triangular wave and a PWM dimming signal that is a pulse signal corresponding to the triangular wave based on charging of the capacitor and discharging of the capacitor through the resistor; The current driver is controlled to be turned on and off based on the PWM dimming signal; the light-emitting element on signal is a signal based on the PWM dimming signal, 16. The light-emitting element driving device according to claim 15, wherein the CR timer is capable of generating the PWM dimming signal with a fixed level in a DC dimming mode.

17. It further has a second external terminal, 17. The light-emitting element driving device according to claim 12, wherein the variable setting section performs variable setting in response to application of a signal to the second external terminal.

18. 18. The light-emitting element driving device according to claim 17, wherein the variable setting section detects two patterns of open and application of GND (ground potential) to the second external terminal, and performs variable setting in accordance with the detection result.

19. 18. The light-emitting element driving device according to claim 17, wherein the variable setting unit detects three patterns of application of the power supply voltage / open / GND (ground potential) to the second external terminal, and performs variable setting according to the detection result.

20. 18. The light-emitting element driving device according to claim 17, wherein the variable setting unit has a constant current source and performs variable setting based on a voltage generated at the second external terminal by flowing a constant current from the constant current source through a setting resistor that can be externally connected to the second external terminal.

21. A light emitting device comprising: the light emitting element driving device according to any one of claims 12 to 20; and the light emitting element light source.

22. 22. The light emitting device according to claim 21, wherein the light emitting element light source is an LED light source.

23. a substrate provided with a wiring pattern for mounting the light-emitting element light source and the light-emitting element driving device; a socket for mounting the substrate; 23. The light emitting device according to claim 21 or claim 22, further comprising:

24. the light-emitting element driving device has a second external terminal and a heat dissipation pad provided on a lower surface, the wiring pattern includes a terminal wiring electrically connected to the second external terminal, and a ground wiring integrated with the terminal wiring and electrically connected to the heat dissipation pad; 24. The light emitting device according to claim 23, wherein the variable setting section detects two patterns, open and application of GND (ground potential), to the second external terminal, and performs variable setting in accordance with the detection result.

25. A vehicle comprising the light emitting device according to any one of claims 21 to 24.

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