Light-emitting element drive device, and light emission system

Abstract

A light-emitting element drive device (201) is equipped with an overcurrent detection unit (6) which is configured so as to detect an overcurrent of the current flowing to light-emitting element units (41-44) of one or more channels, and so as to be capable of connecting to one or more current detection resistors (R1) provided between the positive electrodes of the light-emitting element units and an end for application of a power supply voltage (Vout) for driving said light-emitting element units.

Description

Light-emitting element driving device and light-emitting system

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

[0002] Conventionally, LEDs (light-emitting diodes) have been used for various purposes due to their low power consumption and long life. LEDs are an example of light-emitting elements. A conventional example of an LED driver for driving an LED is disclosed in Patent Document 1.

[0003] The LED driver of Patent Document 1 is provided with an LED terminal, which is an external terminal for connecting the cathode of the LED to an external device. The LED driver is also provided with a function for detecting a ground fault in the cathode of the LED by monitoring the voltage of the LED terminal. A ground fault in the cathode of an LED causes the LED to emit abnormally bright light, which can make driving difficult for the vehicle driver, particularly in automotive applications. Therefore, detecting a ground fault and providing protection when detected are important. Furthermore, a ground fault in the cathode of an LED can cause a current exceeding its tolerance to flow through the LED, potentially shortening the LED's lifespan.

[0004] International Publication No. 2020 / 054096

[0005] However, in the method of monitoring the voltage at the LED terminal as described above, depending on the impedance state at the time of a ground fault, the voltage at the LED terminal may not drop low enough to detect an abnormality, making it impossible to detect the abnormality, and the LED may continue to emit abnormal light.

[0006] In view of the above circumstances, an object of the present disclosure is to provide a light emitting element driving device that can effectively detect abnormal light emission of a light emitting element.

[0007] An exemplary light-emitting element driving device of the present disclosure includes an overcurrent detection unit configured to be connectable to at least one current detection resistor provided between an application terminal of a power supply voltage for driving at least one channel of a light-emitting element unit and the positive electrode of the light-emitting element unit, and configured to detect an overcurrent in a current flowing through the light-emitting element unit.

[0008] According to the exemplary light-emitting element driving device of the present disclosure, abnormal light emission of a light-emitting element can be effectively detected.

[0009] FIG. 1 is a diagram showing the configuration of a light-emitting system according to a comparative example. FIG. 2 is a diagram showing the configuration of a light-emitting system according to a first embodiment of the present disclosure. FIG. 3 is a diagram showing the configuration of a light-emitting system according to a second embodiment of the present disclosure. FIG. 4 is a diagram showing the configuration of a light-emitting system according to a third embodiment of the present disclosure. FIG. 5 is a diagram showing the configuration of a light-emitting system according to a fourth embodiment of the present disclosure. FIG. 6 is a diagram showing the configuration of a light-emitting system according to a fifth embodiment of the present disclosure. FIG. 7 is a diagram showing the configuration of a light-emitting system according to a sixth embodiment of the present disclosure. FIG. 8 is a diagram showing the configuration of a light-emitting system according to an eighth embodiment of the present disclosure. FIG. 9 is a diagram showing an example of the configuration of a backlight device. FIG. 10 is a diagram showing an example of an in-vehicle display.

[0010] Comparative Example Here, a comparative example will be described first for comparison with the embodiment of the present disclosure. By describing the comparative example, the problem will become clearer.

[0011] Fig. 1 is a diagram showing the configuration of a light emitting system 50 according to a comparative example. The light emitting system 50 shown in Fig. 1 includes an LED driving device (light emitting element driving device) 20, an output stage 30, and LED arrays 41 to 44.

[0012] The LED driving device 20 drives LED arrays (light emitting element units) 41 to 44 on a plurality of channels (four channels in this embodiment, for example).

[0013] The LED driving device 20 is a semiconductor device that integrates a minimum voltage selection unit 1, a DC / DC control unit 2, a constant current driver 3, an output discharge unit 4, and an output short circuit protection circuit 5 (SCP (short circuit protection)).

[0014] The LED driver 20 also has an OUTL terminal, a VDISC terminal, and LED1 to LED4 terminals as external terminals for establishing electrical connection with the outside. Note that the configuration of the LED driver 20 shown in Fig. 1 shows only a portion of the configuration for convenience, and in reality, the LED driver 20 has other external terminals such as a VCC terminal as external terminals, and is also internally provided with an internal voltage generator (VREG) and various protection circuits such as UVLO (Under Voltage Lock Out).

[0015] An output stage 30 is arranged outside the LED driver 20 to generate an output voltage Vout from an input voltage Vin by DC / DC conversion and supply the output voltage Vout to the anodes (positive electrodes) of the LED arrays 41 to 44. The output stage 30 has a switching element N1, a diode D1, an inductor L1, and an output capacitor Co. The switching element N1 is driven and controlled by the LED driver 20, thereby controlling the output stage 30. The output stage 30 and the LED driver 20 form a DC / DC converter. In this embodiment, a step-up DC / DC converter is particularly configured as the DC / DC converter.

[0016] The application terminal of the input voltage Vin is connected to one terminal of the inductor L1. The other terminal of the inductor L1 is connected to the anode of the diode D1 and the drain of the switching element N1, which is composed of an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET). The source of the switching element N1 is connected to the ground terminal. The gate of the switching element N1 is connected to the OUTL terminal. The cathode of the diode D1 is connected to one terminal of the output capacitor Co. The other terminal of the output capacitor Co is connected to the ground terminal. An output voltage Vout is generated at one terminal of the output capacitor Co.

[0017] The switching element N1 may be included in the LED driving device 20.

[0018] The anodes of the LED arrays 41 to 44 are connected to one end of an output capacitor Co, which generates an output voltage Vout. Each of the LED arrays 41 to 44 is made up of a plurality of LEDs connected in series. The cathodes of the LED arrays 41 to 44 are connected to the LED1 terminal to the LED4 terminal, respectively.

[0019] The LED arrays 41 to 44 are not limited to being connected in series, but may be configured with LEDs connected in series and parallel, or may be configured with only one LED. The number of drivable LED arrays (number of channels) is also not limited to four, but may be, for example, six.

[0020] Next, the internal configuration of the LED driving device 20 will be described.

[0021] LED terminal voltages Vled1 to Vled4 are applied to the LED1 to LED4 terminals as the cathode voltages of the LED arrays 41 to 44. The minimum voltage selector 1 selects the lowest voltage from the LED terminal voltages Vled1 to Vled4.

[0022] The DC / DC control unit 2 has an error amplifier 21. The non-inverting input terminal (+) of the error amplifier 21 is connected to the output terminal of the minimum voltage selection unit 1. The inverting input terminal (-) of the error amplifier 21 is connected to the application terminal of the reference voltage Vref. The DC / DC control unit 2 also has, for example, a slope generation unit, a PWM comparator, a driver, and other components (not shown) in addition to the error amplifier 21, and generates a gate signal GS by PWM control based on an error signal between the output of the minimum voltage selection unit 1 and the reference voltage Vref, output from the error amplifier 21. The generated gate signal GS is applied to the gate of the switching element N1 via the OUTL terminal, thereby controlling the on / off of the switching element N1. As a result, the output voltage Vout is controlled so that the lowest voltage among the LED terminal voltages Vled1 to Vled4 matches the reference voltage Vref.

[0023] The constant current driver 3 has four channels of constant current circuits 31 arranged between each of the LED1 terminal to LED4 terminal and the ground terminal. The constant current value of the current flowing through the constant current circuit 31 can be set by an LED current setting unit (not shown).

[0024] The VDISC terminal is connected to the output discharge unit 4. The VDISC terminal is connected to one end of the output capacitor Co, which generates the output voltage Vout. If the converter is started up with a remaining charge in the output capacitor Co, the LED may flicker. Therefore, it is desirable that no charge remains in the output capacitor Co at startup. Therefore, the output discharge unit 4 discharges the residual charge in the output capacitor Co. This discharge is performed when the DC / DC converter is turned off (when the signal applied to the enable terminal, not shown, falls, or during protection).

[0025] An output short circuit protection circuit (SCP) 5, which is provided as one of the protection functions, has ground fault detection comparators 5A to 5D provided corresponding to each channel of the LED arrays 41 to 44. The ground fault detection comparators 5A to 5D have a non-inverting input terminal to which each of the LED terminal voltages Vled1 to Vled4 is applied, and an inverting input terminal to which a reference voltage Vref_sht for ground fault detection is applied.

[0026] When the ground fault detection comparators 5A to 5D detect that any of the LED terminal voltages Vled1 to Vled4 falls below 0.3 V, for example, the output short-circuit protection circuit 5 starts counter operation, and after about 13 ms, for example, a latch is activated and all circuits other than the internal voltage generation unit (not shown) are shut down.

[0027] For example, if the cathode of LED array 44 (channel 4) has a ground fault as shown in Figure 1, the LED terminal voltage Vled4 will be the lowest compared to the other LED terminal voltages, causing the DC / DC converter to perform a boost operation. However, because the LED terminal voltage Vled4 does not rise, the output short-circuit protection circuit 5 stops the operation of the DC / DC converter, and no current flows to the LED arrays 41 to 44. Therefore, the LED arrays 41 to 44 are turned off.

[0028] However, depending on the impedance state at the time of the ground fault (for example, a pull-down of 1 kΩ relative to the ground terminal), the LED terminal voltage of the channel in which the ground fault occurred may not drop low enough to be detected by the ground fault detection comparators 5A to 5D. In this case, ground fault protection is not activated, the DC / DC converter continues to operate, and a current greater than normal flows through the LED array of the channel in which the ground fault occurred due to the current path from the cathode to the ground terminal formed by the ground fault.

[0029] For example, when the light-emitting system 50 according to the comparative example is installed in the backlight of an in-vehicle display device, the display device may shine brighter than the set brightness, which may obstruct the driver's view in some cases. In addition, excessive current flowing through the LED increases the load on the components in the DC / DC converter, requiring the components to have excess withstand capability.

[0030] In view of the above, the inventors of the present invention have conducted extensive research into a technology that can more reliably detect abnormal light emission from the LED arrays 41 to 44 (light-emitting element units) as follows.

[0031] <First embodiment> The configuration of a light-emitting system 501 according to a first embodiment of the present disclosure is shown in Fig. 2. The configuration shown in Fig. 2 differs from the comparative example (Fig. 1) in that a current detection resistor R1 is provided outside the LED driving device 201, and further in the configuration of the LED driving device 201 and an MCU (microcomputer) 25. That is, the light-emitting system 501 has a current detection resistor R1 and an MCU 25.

[0032] A first terminal of the current detection resistor R1 is connected to the terminal to which the output voltage Vout is applied, and a second terminal of the current detection resistor R1 is connected to the anodes of the LED arrays 41 to 44. In other words, the current detection resistor R1 is provided after the output stage 30.

[0033] The LED driving device 201 has an overcurrent detection unit 6 and an OCD terminal (overcurrent detection terminal) as an external terminal for connecting to a current detection resistor R1.

[0034] The overcurrent detection unit 6 has an amplifier 61 and a comparator 62. The inverting input terminal of the amplifier 61 is connected to a first terminal of the current detection resistor R1 via a VDISC terminal. The non-inverting input terminal of the amplifier 61 is connected to a second terminal of the current detection resistor R1 via an OCD terminal. The inverting input terminal of the comparator 62 is connected to an output terminal of the amplifier 61. The non-inverting input terminal of the comparator 62 is connected to an application terminal of a reference voltage Va for overcurrent detection.

[0035] With this configuration, the total current Ia, which is the sum of the currents flowing through the channels of the LED arrays 41 to 44, is converted into a current / voltage by the current detection resistor R1. The converted voltage appears across the current detection resistor R1 and is amplified by a predetermined gain factor by the amplifier 61. The amplified voltage is compared with a reference voltage Va by the comparator 62, and the comparison result is output as a flag signal Flg.

[0036] This allows the comparator 62 to detect an overcurrent in the total current Ia, for example, when a ground fault occurs in the cathode of the LED arrays 41 to 44. In other words, the overcurrent detection unit 6 can detect an overcurrent in the current flowing through the LED arrays 41 to 44 (light-emitting element units).

[0037] In this embodiment, the LED driver 201 has an FG terminal (flag terminal) and an EN terminal (enable terminal) as external terminals. The MCU 25 is externally connected to the FG terminal and the EN terminal. The flag signal Flg output from the comparator 62 is input to the MCU 25 via the FG terminal. The MCU 25 can output an enable signal Eb via the EN terminal to an internal voltage generator 7 provided in the LED driver 201. The internal voltage generator 7 generates an internal power supply voltage Vreg based on a power supply voltage applied to a VCC terminal (not shown) provided in the LED driver 201. The internal power supply voltage Vreg is generated when the enable signal Eb is in an enable state and is used as a power supply voltage for the internal circuitry of the LED driver 201.

[0038] If the flag signal Flg is at a level indicating an overcurrent abnormality, the MCU 25 disables the enable signal Eb. This stops the operation of the internal voltage generator 7, causing the internal power supply voltage Vreg to drop. The UVLO unit 8 provided in the LED driver 201 detects the drop in the internal power supply voltage Vreg and commands the DC / DC control unit 2 to stop the operation of the DC / DC converter. This stops the switching of the switching element N1, stops current from flowing to the LED arrays 41 to 44, and releases the abnormal light emission state.

[0039] Second Embodiment Fig. 3 is a diagram showing the configuration of a light-emitting system 502 according to a second embodiment of the present disclosure. The difference between the configuration shown in Fig. 3 and the first embodiment (Fig. 2) is the configurations of the LED driver 202 and the MCU 25.

[0040] In this embodiment, the LED driving device 202 has an LED current setting unit 9 and a communication unit 10. Note that the LED current setting unit 9 is also provided in the first embodiment in the same manner.

[0041] The communication unit 10 is configured to communicate with the MCU 25, for example, by SPI (Serial Peripheral Interface). The communication unit 10 includes a register 10A. Various types of information are stored in the register 10A.

[0042] The LED driver 202 has an ADIM terminal (dimming terminal) as an external terminal. The MCU 25 can dim the LED arrays 41 to 44 by outputting a dimming signal Dm to the LED current setting unit 9 via the ADIM terminal. This type of dimming is called DC dimming.

[0043] The LED current setting unit 9 has an error amplifier 91 and an output transistor 92. The non-inverting input terminal of the error amplifier 91 is connected to an application terminal of a reference voltage Vref_led for setting the LED current. The output terminal of the error amplifier 91 is connected to the gate of an output transistor 92 configured by an n-channel MOSFET. The source of the output transistor 92 is connected to the inverting input terminal of the error amplifier 91. The LED driver 202 has an ISET terminal (current setting terminal) as an external terminal. A first terminal of a setting resistor Reset is externally connected to the ISET terminal. The ISET terminal is connected to the source of the output transistor 92.

[0044] As a result, the voltage at the ISET terminal is controlled to match the reference voltage Vref_led, and a current flows to the ISET terminal at a current value determined by the voltage at the ISET terminal and the setting resistor Reset. A current proportional to the current flowing through the ISET terminal flows to each constant current circuit 31. The reference voltage Vref_led is variable according to the dimming signal Dm, and the LED current can be set by the dimming signal Dm.

[0045] When the output of the comparator 62 in the overcurrent detection unit 6 reaches a level indicating an overcurrent abnormality, information indicating the abnormality is written to the register 10A. When the MCU 25 reads the information indicating the abnormality from the register 10A through communication with the communication unit 10, the MCU 25 changes the reference voltage Vref_led to be lower than normal using the dimming signal Dm. This reduces the current flowing through the LED arrays 41 to 44, and prevents the LED arrays 41 to 44 from emitting abnormally bright light. This allows the LED arrays 41 to 44 to be protected without being turned off.

[0046] As a modification of this embodiment, when the MCU 25 reads information indicating the above-mentioned abnormality from the register 10A through communication with the communication unit 10, the operation of the DC / DC converter may be stopped by disabling the enable signal Eb, as in the first embodiment.

[0047] Furthermore, as a modification of this embodiment, the communication unit 10 may not be provided, and when the MCU 25 receives a flag signal Flg indicating an abnormality from the FG terminal, as in the first embodiment, dimming may be performed to reduce the brightness of the LED using the dimming signal Dm.

[0048] 4 is a diagram showing the configuration of a light-emitting system 503 according to a third embodiment of the present disclosure. The difference between the configuration shown in FIG. 4 and the second embodiment (FIG. 3) is the configuration of the LED driver 203.

[0049] More specifically, the LED driver 203 has a flag output unit 11. In addition to the output Cp1 of the comparator 62 in the overcurrent detection unit 6, the flag output unit 11 also receives outputs from various protection circuits 12 (SCP, TSD (thermal shutdown), UVLO, etc.) (not shown). The flag output unit 11 outputs a flag signal Flg from a FLG terminal to the MCU 25 based on Cp1 and the outputs from the various protection circuits 12. Specifically, if any one of the outputs including Cp1 indicates an abnormality, the flag signal Flg becomes a level indicating an abnormality.

[0050] When the MCU 25 receives the flag signal Flg at a level indicating an abnormality, it communicates with the communication unit 10 to read the register 10A to determine the specific type of abnormality. The register 10A stores information indicating which abnormality has been detected by the overcurrent detection unit 6 and the various protection circuits 12. When the MCU 25 reads the register 10A and determines that an overcurrent abnormality has been detected by the overcurrent detection unit 6, the MCU 25 performs dimming to reduce the brightness of the LEDs using the dimming signal Dm, as in the second embodiment. Note that the MCU 25 may also stop operation of the DC / DC converter using the enable signal Eb if, for example, the overcurrent detection unit 6 detects an overcurrent abnormality and the output short-circuit protection circuit (SCP) detects a ground fault at the cathode of the LED.

[0051] <Fourth embodiment> Fig. 5 is a diagram showing the configuration of a light-emitting system 504 according to a fourth embodiment of the present disclosure. The configuration shown in Fig. 5 differs from that of the first embodiment (Fig. 2) in that current detection resistors Ra to Rd are provided. That is, the light-emitting system 504 has current detection resistors Ra to Rd.

[0052] The current detection resistors Ra to Rd are provided corresponding to the channels of the LED arrays 41 to 44. Specifically, first terminals of the current detection resistors Ra to Rd are commonly connected to an application terminal of the output voltage Vout. Second terminals of the current detection resistors Ra to Rd are connected to the anodes of the LED arrays 41 to 44, respectively.

[0053] In this embodiment, the LED driver 204 includes overcurrent detection units 6A to 6D and OCD1 to OCD4 terminals. The overcurrent detection units 6A to 6D are provided corresponding to the channels of the LED arrays 41 to 44. Each of the overcurrent detection units 6A to 6D includes an amplifier 61 and a comparator 62. More specifically, a first end of a current detection resistor Ra is connected to the inverting input terminal of the amplifier 61 of the overcurrent detection unit 6A, and a second end of the current detection resistor Ra is connected to the non-inverting input terminal of the amplifier 61 of the overcurrent detection unit 6A via the OCD1 terminal. Similarly, both ends of resistors Rb, Rc, and Rd are connected to the input terminals of the amplifier 61 of the overcurrent detection units 6B to 6D.

[0054] The LED driving device 204 has terminals FG1 to FG4 corresponding to the overcurrent detection units 6A to 6D. The flag signals Flg1 to Flg4 output from the comparators 62 of the overcurrent detection units 6A to 6D are sent to the MCU 25 via the terminals FG1 to FG4, respectively.

[0055] With this configuration, the overcurrent detectors 6A to 6D can detect overcurrent for each channel of the LED arrays 41 to 44. Therefore, the MCU 25 can determine in which channel an overcurrent abnormality is occurring, based on the flag signals Flg1 to Flg4.

[0056] In this embodiment, the LED driver 204 has LED current setting units 9A to 9D. The LED current setting units 9A to 9D are provided corresponding to the channels of the LED arrays 41 to 44. Each of the LED current setting units 9A to 9D has an error amplifier 91 and an output transistor 92. The setting resistor Reset may be shared by the LED current setting units 9A to 9D, or may be provided for each of the LED current setting units 9A to 9D.

[0057] The LED driver 204 has ADIM1 terminals to ADIM4 terminals corresponding to the LED current setting units 9A to 9D. The MCU 25 outputs dimming signals Dm1 to Dm4 to the LED current setting units 9A to 9D via the ADIM1 to ADIM4 terminals, respectively. The dimming signal Dm1 varies the reference voltage Vref_led1 in the LED current setting unit 9A, enabling dimming of the LED array 41 (first channel). Similarly, the dimming signals Dm2 to Dm4 vary the reference voltages Vref_led2 to Vref_led4 in the LED current setting units 9B to 9D, respectively, enabling dimming of the LED arrays 42 to 44 (second to fourth channels).

[0058] The MCU 25 determines which channel is experiencing an overcurrent abnormality based on the flag signals Flg1 to Flg4, and performs dimming to reduce the brightness of the LEDs using the dimming signals Dm1 to Dm4 corresponding to the determined channel. For example, if an overcurrent abnormality occurs in the LED array 44 of the fourth channel, the flag signal Flg4 detects the overcurrent abnormality, and the dimming signal Dm4 changes the reference voltage Vref_led4 in the LED current setting unit 9D so that it is lower than normal. This suppresses abnormal light emission in the fourth channel.

[0059] As described above, according to this embodiment, an overcurrent abnormality can be detected for each channel and only the abnormal channel can be dimmed, so that protection can be achieved without reducing the brightness of the LED arrays 41 to 44 as a whole.

[0060] As a modification of this embodiment, the FG1 to FG4 terminals may not be provided, but a communication unit 10 may be provided, and the output states of the overcurrent detection units 6A to 6D may be stored in a register 10A of the communication unit 10, and the MCU 25 may read the register 10A via communication. This also allows the MCU 25 to determine in which channel an overcurrent abnormality has occurred.

[0061] 6 is a diagram showing the configuration of a light-emitting system 505 according to a fifth embodiment of the present disclosure. In the light-emitting system 505 of this embodiment, a current detection resistor Ra is provided corresponding to the pair of LED arrays 41 and 42 (channels 1 and 2), and a resistor Rb is provided corresponding to the pair of LED arrays 43 and 44 (channels 3 and 4). More specifically, first terminals of the current detection resistors Ra and Rb are commonly connected to the application terminal of the output voltage Vout, a second terminal of the current detection resistor Ra is connected to the anodes of the LED arrays 41 and 42, and a second terminal of the resistor Rb is connected to the anodes of the LED arrays 43 and 44.

[0062] In the LED driver 205 of this embodiment, overcurrent detection units 6A and 6B and OCD1 and OCD2 terminals are provided corresponding to the current detection resistors Ra and Rb. Correspondingly, the LED driver 205 is provided with FG1 and FG2 terminals as flag terminals, ADIM1 and ADIM2 terminals as dimming terminals, and LED current setting units 9A and 9B. The LED current setting units 9A and 9B correspond to the set of LED arrays 41 and 42 and the set of LED arrays 43 and 44, respectively.

[0063] With this configuration, it is possible to detect an overcurrent abnormality and adjust the light intensity for each pair of LED arrays 41 and 42 and each pair of LED arrays 43 and 44. This makes it possible to reduce the number of external terminals in the LED driving device while achieving the same effects as in the fourth embodiment.

[0064] 7 is a diagram showing the configuration of a light-emitting system 506 according to a sixth embodiment of the present disclosure. This embodiment does not use an MCU as in the first to fifth embodiments. An LED driver 206 according to this embodiment includes a dimming control unit 13. The dimming control unit 13 variably controls the reference voltage Vref_led in the LED current setting unit 9.

[0065] When the output signal Cp1 output from the comparator 62 of the overcurrent detection unit 6 indicates an abnormality, the dimming control unit 13 changes Vref_led in the LED current setting unit 9 to be lower than normal. This reduces the currents flowing through the LED arrays 41 to 44, thereby providing protection. According to this embodiment, protection can be achieved by feedback to the LED current setting unit 9 within the LED driver 206, without using an MCU.

[0066] By applying the fourth or fifth embodiment to this embodiment, a plurality of overcurrent detection units 6 and a plurality of LED current setting units 9 may be provided corresponding to the channels of the LED arrays 41 to 44, and the LED current setting unit 9 corresponding to the channel in which an overcurrent abnormality is detected may be controlled by the dimming control unit 13. This makes it possible to obtain the same effect as the fourth or fifth embodiment without using an MCU.

[0067] Seventh Embodiment In the first to sixth embodiments, the reference voltage Va for overcurrent detection may be variable. For example, the reference voltage Va may be variable based on a setting resistor Reset externally connected to the ISET terminal (current setting terminal). In this case, the overcurrent threshold value can be set according to the LED current setting.

[0068] Eighth Embodiment Fig. 8 is a diagram showing the configuration of a light-emitting system 507 according to an eighth embodiment of the present disclosure. In the light-emitting system 507 shown in Fig. 8, a p-channel MOSFET 35 is provided in addition to a current detection resistor R1.

[0069] More specifically, a first end of the current detection resistor R1 is connected to a terminal to which the output voltage Vout is applied. A second end of the current detection resistor R1 is connected to a source of the p-channel MOSFET 35 at a node N1. A drain of the p-channel MOSFET 35 is connected to each anode of the LED arrays 41 to 44.

[0070] The LED driver 207 of this embodiment includes an overcurrent detection unit 14. The LED driver 207 also includes a PGT terminal (gate connection terminal) as an external terminal. The overcurrent detection unit 14 includes a current limiting unit 141 and a comparator 142. The current limiting unit 141 includes an amplifier 141A. The inverting input terminal of the amplifier 141A is connected to a node N1 via an OCD terminal. A voltage that is lower than the output voltage Vout by a reference voltage Vb1 is applied to the non-inverting input terminal of the amplifier 141A. The output terminal of the amplifier 141A is connected to the gate (control terminal) of the p-channel MOSFET 35 via the PGT terminal.

[0071] Since the voltage drop across the current detection resistor R1 due to the total current Ia flowing through the current detection resistor R1 during normal operation is small, the voltage at the OCD terminal is high and the output of the amplifier 141A is low, thereby keeping the p-channel MOSFET 35 in a fully on state.

[0072] On the other hand, when the total current Ia increases due to an overcurrent generated in the LED arrays 41 to 44, the voltage drop across the current detection resistor R1 increases. When this voltage drop exceeds the reference voltage Vb1, that is, when the voltage at node N1 falls below Vout-Vb1, the amplifier 141A controls the gate voltage of the p-channel MOSFET 35 to increase. This increases the impedance between the drain and source of the p-channel MOSFET 35. This then reduces the total current Ia, suppressing the current flowing through the LED arrays 41 to 44.

[0073] It is desirable that the reference voltage Vb1 in the current limiting unit 141 be a voltage value corresponding to a current setting value greater than the maximum value of the total current Ia due to current value variations in the constant current driver 3.

[0074] The non-inverting input terminal of the comparator 142 is connected to the PGT terminal. The inverting input terminal of the comparator 142 is connected to the terminal to which the reference voltage Vb2 is applied. As a result, the comparator 142 outputs the result of comparing the gate voltage of the p-channel MOSFET 35 with the reference voltage Vb2. By using such a comparator 142, it is possible to notify an MCU of an overcurrent abnormality, for example.

[0075] <Application to Backlight Device> A backlight device will be described as an example of an application of the LED driving device according to the embodiment described above. An example configuration of a backlight device to which the LED driving device can be applied is shown in Fig. 9. Note that the configuration shown in Fig. 9 is of a so-called edge light type, but is not limited to this, and a direct type configuration may also be used.

[0076] The backlight device 70 shown in FIG. 9 is an illumination device that illuminates a liquid crystal panel 81 from the back. The backlight device 70 includes an LED light source device 71, a light guide plate 72, a reflector 73, and optical sheets 74. The LED light source device 71 includes an LED and a substrate on which the LED is mounted. Light emitted from the LED light source device 71 enters the interior through the side of the light guide plate 72. The light guide plate 72, which is made of, for example, an acrylic plate, totally reflects the light that enters the interior and guides it throughout the entire interior, causing it to exit as planar light from the side on which the optical sheets 74 are arranged. The reflector 73 reflects light that leaks from the light guide plate 72 and returns it to the interior of the light guide plate 72. The optical sheets 74 are made of a diffusion sheet, a lens sheet, etc., and are intended to uniformize and improve the brightness of the light illuminating the liquid crystal panel 81. The LED light source device 71 can be any of the light-emitting systems described above.

[0077] <Regarding In-Vehicle Displays> The backlight device to which the LED driving device according to the above-described embodiment is applied is particularly suitable for installation in in-vehicle displays.

[0078] An in-vehicle display is provided on the dashboard in front of the driver's seat of a vehicle, such as an in-vehicle display 85 shown in FIG. 10 . The in-vehicle display 85 can display various images, such as car navigation information, captured images of the area behind the vehicle, a speedometer, a fuel gauge, a fuel consumption meter, and a shift position, and can convey various information to the user. Such an in-vehicle display is also called a cluster panel or a center information display (CID). Alternatively, the in-vehicle display may be a rear entertainment device disposed behind the driver's seat or passenger seat, for example.

[0079] <Others> Although exemplary embodiments have been described above, the embodiments can be modified in various ways within the scope of the spirit of the present invention.

[0080] <Additional Notes> As described above, for example, the light-emitting element driving device (201) according to the present disclosure is configured to be connectable to at least one current detection resistor (R1) provided between an application terminal of a power supply voltage (Vout) for driving at least one channel of light-emitting element unit (41 to 44) and the positive electrode of the light-emitting element unit, and to include an overcurrent detection unit (6) configured to detect an overcurrent of a current flowing in the light-emitting element unit (first configuration).

[0081] In addition, in the above first configuration, the overcurrent detection unit (6) may be configured to include an amplifier (61) having an input terminal configured to be connected to the current detection resistor (R1), and a first comparator (62) configured to compare the output of the amplifier with a first reference voltage (Va) (second configuration).

[0082] Furthermore, in the second configuration, the device may be configured to include a constant current driver (3) that can be connected to the negative electrode of the light-emitting element portion, a current setting terminal (ISET terminal) that is an external terminal that can be connected to a setting resistor (Reset), and a current setting unit (9) that is configured to set the current value of the constant current driver based on the setting resistor, and the first reference voltage (Va) may be configured to be variably set based on the setting resistor (third configuration).

[0083] In addition, any of the first to third configurations may be configured to include an external terminal (FG terminal) for outputting the detection result of the overcurrent detection unit (6) to the outside (fourth configuration).

[0084] In the fourth configuration, the external terminal may be configured to be connectable to an external MCU (25) (fifth configuration).

[0085] Furthermore, the fourth or fifth configuration may be configured to include at least one protection circuit (12); and a flag output unit (11) configured to generate a flag signal (Flg) based on the detection result and the abnormality detection result by the protection circuit and output the flag signal via the external terminal (sixth configuration).

[0086] Furthermore, in any of the above first to sixth configurations, the configuration may be such that it has a register (10A) capable of storing the detection result of the overcurrent detection unit as information, and is provided with a communication unit (10) configured to be able to communicate with an external MCU (25) (seventh configuration).

[0087] Furthermore, in any of the first to seventh configurations, the light emitting element may be configured to include a constant current driver (3) that is connectable to the negative electrode of the light emitting element unit, a current setting unit (9) that is configured to set the current value of the constant current driver, and a dimming control unit (13) that is configured to cause the current setting unit to set the current value lower than normal when an overcurrent abnormality is detected by the overcurrent detection unit (6) (eighth configuration).

[0088] In addition, in any of the first to eighth configurations, the current detection resistors (Ra to Rd) may be provided for each of the multiple channels, and the overcurrent detection units (6A to 6D) may be provided for each of the multiple current detection resistors (ninth configuration, Figure 5).

[0089] In addition, in any of the first to eighth configurations, the current detection resistors (Ra, Rb) may be provided for each of a plurality of groups consisting of a plurality of the channels, and the overcurrent detection units (6A, 6B) may be provided for each of a plurality of the current detection resistors (tenth configuration, Figure 6).

[0090] Furthermore, a light-emitting system (501) according to one aspect of the present disclosure includes a light-emitting element driving device (201) of any one of the first to tenth configurations described above, the current detection resistor (R1), an MCU (25), and a DC / DC converter configured to generate the power supply voltage (Vout), and when an overcurrent abnormality is detected by the overcurrent detection unit (6), the MCU is configured to instruct the light-emitting element driving device to stop operation of the DC / DC converter (eleventh configuration).

[0091] Furthermore, a light-emitting system (502) according to one aspect of the present disclosure comprises a light-emitting element driving device (202) of any one of the first to tenth configurations described above, the current detection resistor (R1), and an MCU (25), wherein the light-emitting element driving device (202) has a constant current driver (3) configured to be connectable to the negative electrode of the light-emitting element unit, and a current setting unit (9) configured to set the current value of the constant current driver, and when an overcurrent abnormality is detected by the overcurrent detection unit (6), the MCU is configured to send a dimming signal (Dm) to the light-emitting element driving device so as to cause the current setting unit to set the current value lower than normal (twelfth configuration).

[0092] Furthermore, a light-emitting system (507) according to one aspect of the present disclosure comprises a light-emitting element driving device (207) of any one of the first to tenth configurations described above, the current detection resistor (R1), and a transistor (35) connected between the current detection resistor and the positive electrode of the light-emitting element unit, wherein the overcurrent detection unit (14) has a current limiting unit (141) configured to limit the current flowing through the current detection resistor by controlling the control terminal of the transistor, and is configured to detect the overcurrent based on the voltage of the control terminal (thirteenth configuration).

[0093] Furthermore, in the above-mentioned thirteenth configuration, the current limiting unit (141) may be configured to have an amplifier (141A) including a first input terminal configured to be connectable to a node (N1) to which the current detection resistor (R1) and the transistor (35) are connected, a second input terminal configured to be connected to an application terminal of a voltage that is lower than a predetermined voltage (Vout) by a second reference voltage (Vb1), and an output terminal configured to be connectable to the control terminal (fourteenth configuration).

[0094] Furthermore, in the above-mentioned 13th or 14th configuration, the overcurrent detection unit (14) may be configured to have a third comparator (142) including a first input terminal configured to be connected to the control terminal and a second input terminal configured to be connected to an application terminal of a third reference voltage (Vb2) (15th configuration).

[0095] In any of the thirteenth to fifteenth configurations, the transistor (35) may be a p-channel MOSFET (sixteenth configuration).

[0096] Furthermore, an illumination device (70) according to one aspect of the present disclosure includes a light-emitting element driving device having any one of the first to tenth configurations described above, or a light-emitting system having any one of the eleventh to sixteenth configurations described above (seventeenth configuration).

[0097] Moreover, an in-vehicle display device (85) according to one aspect of the present disclosure includes the lighting device of the seventeenth configuration (eighteenth configuration).

[0098] The present disclosure can be used, for example, as a driving means for an LED for use in a vehicle.

[0099] 1 Minimum voltage selection unit 2 DC / DC control unit 3 Constant current driver 4 Output discharge unit 5 Output short circuit protection circuit 5A to 5D Ground fault detection comparator 6 Overcurrent detection unit 6A to 6D Overcurrent detection unit 7 Internal voltage generation unit 8 UVLO unit 9 LED current setting unit 9A to 9D LED current setting unit 10 Communication unit 10A Register 11 Flag output unit 12 Protection circuit 13 Dimming control unit 14 Overcurrent detection unit 141 Current limiting unit 141A Amplifier 142 Comparator 20 LED driver 21 Error amplifier 30 Output stage 31 Constant current circuit 35 p-channel MOSFET 41 to 44 LED array 50 Light emitting system 61 Amplifier 62 Comparator 70 Backlight device 71 LED light source device 72 Light guide plate 73 Reflector 74 Optical sheets 81 Liquid crystal panel 85 In-vehicle display 91 Error amplifier 92 Output transistor 201 to 207 LED driver 501 to 507 Light-emitting system Co Output capacitor D1 Diode L1 Inductor N1 Switching element R1 Current detection resistor Ra to Rd Current detection resistor Reset Setting resistor

Claims

1. A light-emitting element driving device comprising an overcurrent detection unit configured to be connectable to at least one current detection resistor provided between an application terminal of a power supply voltage for driving at least one channel of a light-emitting element unit and a positive electrode of the light-emitting element unit, and configured to detect an overcurrent of a current flowing in the light-emitting element unit.

2. 2. The light-emitting element driving device according to claim 1, wherein the overcurrent detection unit includes an amplifier having an input terminal configured to be connected to the current detection resistor, and a first comparator configured to compare the output of the amplifier with a first reference voltage.

3. a constant current driver configured to be connectable to a negative electrode of the light emitting element portion; a current setting terminal which is an external terminal connectable to a setting resistor; a current setting unit configured to set a current value of the constant current driver based on the setting resistor; Equipped with 3. The light-emitting element driving device according to claim 2, wherein the first reference voltage is variably set based on the setting resistor.

4. The light-emitting element driving device according to claim 1 , further comprising an external terminal for outputting a detection result of said overcurrent detection section to an external device.

5. The light-emitting element driving device according to claim 4 , wherein the external terminal is configured to be connectable to an external MCU.

6. at least one protection circuit; 5. The light-emitting element driving device according to claim 4, further comprising a flag output section configured to generate a flag signal based on the detection result by the protection circuit in addition to the detection result, and output the flag signal via the external terminal.

7. 2. The light-emitting element driving device according to claim 1, further comprising a communication section configured to communicate with an external MCU, the communication section having a register capable of storing a detection result of the overcurrent detection section as information.

8. a constant current driver configured to be connectable to a negative electrode of the light emitting element portion; a current setting unit configured to set a current value of the constant current driver; a dimming control unit configured to cause the current setting unit to set the current value lower than a normal current value when an overcurrent abnormality is detected by the overcurrent detection unit; The light emitting element driving device according to claim 1 .

9. the current detection resistor is provided for each of the plurality of channels, The light-emitting element driving device according to claim 1 , wherein the overcurrent detection unit is provided for each of the plurality of current detection resistors.

10. The current detection resistor is provided for each of a plurality of groups each composed of a plurality of the channels, The light-emitting element driving device according to claim 1 , wherein the overcurrent detection unit is provided for each of the plurality of current detection resistors.

11. A light emitting element driving device according to any one of claims 1 to 10, the current detection resistor, an MCU, and a DC / DC converter configured to generate the power supply voltage, When an overcurrent abnormality is detected by the overcurrent detection unit, the MCU commands the light-emitting element drive device to stop operation of the DC / DC converter.

12. A light emitting element driving device according to any one of claims 1 to 10, the current detection resistor, and an MCU, the light-emitting element driving device includes a constant current driver configured to be connectable to a negative electrode of the light-emitting element unit, and a current setting unit configured to set a current value of the constant current driver; When an overcurrent abnormality is detected by the overcurrent detection unit, the MCU sends a dimming signal to the light-emitting element drive device to cause the current setting unit to set the current value lower than normal.

13. 2. A light emitting element driving device comprising: the light emitting element driving device according to claim 1; the current detection resistor; and a transistor connected between the current detection resistor and the positive electrode of the light emitting element portion, A light-emitting system, wherein the overcurrent detection unit has a current limiting unit configured to limit the current flowing through the current detection resistor by controlling the control end of the transistor, and is configured to detect the overcurrent based on the voltage of the control end.

14. The light-emitting system of claim 13, wherein the current limiting unit has an amplifier including a first input terminal configured to be connectable to a node to which the current detection resistor and the transistor are connected, a second input terminal configured to be connected to an application terminal of a voltage that is lower than a predetermined voltage by a second reference voltage, and an output terminal configured to be connectable to the control terminal.

15. The light-emitting system according to claim 13 or claim 14, wherein the overcurrent detection unit has a third comparator including a first input terminal configured to be connected to the control terminal and a second input terminal configured to be connected to an application terminal of a third reference voltage.

16. 15. A light emitting system according to claim 13 or claim 14, wherein the transistor is a p-channel MOSFET.

17. A lighting device comprising the light-emitting element driving device according to any one of claims 1 to 10 or the light-emitting system according to any one of claims 11 to 16.

18. An in-vehicle display device comprising the lighting device according to claim 17.