LED driver, LED light source device, and in-vehicle display device

Abstract

An LED drive device (30) has a plurality of LED terminals (LED1 terminal–LED6 terminal) for connecting the cathodes of LEDs (41–46) of a plurality of systems, a minimum voltage input terminal (MINSELIN terminal), a minimum voltage output terminal (MINSELOUT terminal), and a selector (10). When the minimum voltage input terminal is used, the selector selects the lowest voltage from among the voltages of the plurality of LED terminals and the voltage of the minimum voltage input terminal and causes the lowest voltage to be outputted from the minimum voltage output terminal. When the minimum voltage input terminal is not used, the selector selects the lowest voltage from among the voltages of the plurality of LED terminals and causes the lowest voltage to be outputted from the minimum voltage output terminal.

Description

[Technical Field]

[0001] The present disclosure relates to an LED driving device. [Background technology]

[0002] 2. Description of the Related Art LEDs (light emitting diodes) have been used in a variety of applications due to their low power consumption and long lifespan. A conventional example of an LED driving device for driving an LED is disclosed in Patent Document 1.

[0003] The LED driver in Patent Document 1 has a DC / DC controller that controls an output stage to generate an output voltage from an input voltage and supply it to the LEDs, and a constant current driver that generates an output current that flows through the LEDs, and drives multiple systems of LEDs. Each system is composed of LEDs connected in series, and the LEDs in each system are connected in parallel.

[0004] The DC / DC controller has an error amplifier that compares the lowest voltage among the cathode voltages of multiple LED systems with a reference voltage, and a PWM comparator that compares the output of the error amplifier with a slope signal to generate an internal PWM signal.

[0005] The constant current driver is turned on and off based on an external PWM signal input to the PWM terminal, thereby performing PWM dimming control. While the constant current driver is on, the error amplifier and PWM comparator PWM-drive the switching element in the output stage with switching pulses so that the minimum voltage of the cathode voltages mentioned above matches the reference voltage. This controls the output voltage (LED anode voltage) to a voltage value obtained by adding the reference voltage to the maximum voltage among the forward voltages of the LEDs in multiple systems. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-21117 Summary of the Invention [Problem to be solved by the invention]

[0007] With the LED driving device described above, the cathode voltage of the LED in the system with the maximum forward voltage is controlled to the reference voltage, and the cathode voltages of the LEDs in the other systems are controlled to voltages equal to or higher than the reference voltage.

[0008] Recently, there has been a demand for an increased number of LEDs in order to increase the display area, for example in in-vehicle display devices. As a result, the problem of heat generation from the LED driver becomes a problem when the number of parallel connections (number of systems) of LEDs increases. To address this problem, a method of driving LEDs using multiple LED drivers has been considered to suppress heat generation from the LED driver. However, this method requires an output stage (consisting of coils, transistors, etc.) for each LED driver, which leads to the problem of an increased number of parts (increased costs, etc.).

[0009] In view of the above circumstances, an object of the present disclosure is to provide an LED driving device that can drive multiple systems of LEDs while suppressing an increase in the number of components. [Means for solving the problem]

[0010] For example, an LED driving device according to the present disclosure includes a plurality of LED terminals for connecting cathodes of LEDs in a plurality of systems, a minimum voltage input terminal, a minimum voltage output terminal, and a selector; When the minimum voltage input terminal is used, the selector selects the lowest voltage from among the voltages of the plurality of LED terminals and the voltage of the minimum voltage input terminal, and outputs the selected voltage from the minimum voltage output terminal; When the minimum voltage input terminal is not used, the selector selects the minimum voltage from among the voltages of the plurality of LED terminals and outputs it from the minimum voltage output terminal. [Effects of the Invention]

[0011] According to the LED driving device of the present disclosure, it is possible to drive multiple systems of LEDs while suppressing an increase in the number of parts. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an LED driving device according to an exemplary embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of an LED light source device made up of two LED driving devices. [Figure 3] FIG. 3 is a timing chart showing an example of the on / off states of the six constant current circuits in the LED driver (slave) and the on / off state signals output from the PWMOUT terminal. [Figure 4] Figure 4 is a timing chart showing an example of the on / off states of the six constant current circuits in the LED driving device (master), the on / off state signals input to the PWMIN terminal, and the DC / DC control state in the LED driving device (master). [Figure 5] FIG. 5 is a diagram showing an example of the configuration of a slave-dedicated LED driving device. [Figure 6] FIG. 6 is a diagram showing an example of the configuration of an LED light source device when an LED driving device dedicated to a slave is used. [Figure 7] FIG. 7 is a diagram illustrating an example of the configuration of a backlight device. [Figure 8] FIG. 8 is a diagram showing an example of an in-vehicle display. DETAILED DESCRIPTION OF THE INVENTION

[0013] <1. LED driver configuration> Fig. 1 is a diagram showing the configuration of an LED driving device 30 according to an exemplary embodiment. The LED driving device 30 shown in Fig. 1 drives multiple systems (six systems in this embodiment, as an example) of LED arrays 41 to 46. Note that Fig. 1 shows a configuration in which LEDs are driven using a single LED driving device 30, and as will be described later, it is also possible to configure a system in which multiple systems of LEDs are driven using multiple LED driving devices 30.

[0014] The LED driving device 30 is a semiconductor device that integrates an internal voltage generating unit 1, a current detecting unit 2, an oscillator unit 3, a slope generating unit 4, a PWM comparator 5, a DC / DC control logic unit 6, a driver 7, an output discharge unit 8, an error amplifier 9, a selector 10, a reference voltage generating unit 11, a protection circuit unit 12, a logic unit 13, an LED current setting unit 14, a Schmitt trigger 15, and a constant current driver 16.

[0015] Furthermore, the LED driving device 30 has external terminals for establishing electrical connection with the outside, including a VCC terminal, a VREG terminal, a CSH terminal, an SD terminal, a VDISC terminal, an OUTL terminal, a CSL terminal, LED1 terminals to LED6 terminals, a MINSELOUT terminal, a MINSELIN terminal, a PWMIN terminal, an OVP terminal, a GND terminal, a PWMOUT terminal, an ISET terminal, a PWM terminal, FAIL1 terminals to FAIL3 terminals, a COMP terminal, and an EN terminal. Note that, as will be described later, when a communication function for communicating with an external microcomputer is enabled in the LED driving device 30, the FAIL1 terminal functions as an SDO terminal, the FAIL2 terminal functions as an SDI terminal, and the FAIL3 terminal functions as an SCK terminal.

[0016] An output stage 35 is arranged outside the LED driver 30 to generate an output voltage Vout from an input voltage Vin by DC / DC conversion and supply the output voltage Vout to the anodes of the LED arrays 41 to 46. The output stage 35 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 30, thereby controlling the output stage 35. The output stage 35 and the LED driver 30 form a DC / DC converter. In this embodiment, a step-up DC / DC converter is particularly configured as the DC / DC converter.

[0017] The input voltage Vin is applied to one end of capacitor Cvcc, the VCC terminal, and one end of resistor Rcsh. The other end of capacitor Cvcc is connected to ground. The other end of resistor Rcsh is connected to the CSH terminal and the source of transistor M1, which is a p-channel MOSFET. The drain of transistor M1 is connected to one end of inductor L1. The gate of transistor M1 is connected to the SD terminal. The other end of inductor L1 is connected to the anode of diode D1 and the drain of switching element N1, which is an n-channel MOSFET. The source of switching element N1 is connected to ground via resistor Rcsl. The gate of switching element N1 is connected to the OUTL terminal. The cathode of diode D1 is connected to one end of output capacitor Co. The other end of output capacitor Co is connected to ground. An output voltage Vout is generated at one end of output capacitor Co.

[0018] The switching element N1 and the resistor Rcsl may be included in the LED driving device 30.

[0019] The anodes of the LED arrays 41 to 46 are connected to one end of the output capacitor Co, which generates the output voltage Vout. Each of the LED arrays 41 to 46 is made up of a plurality of LEDs connected in series. The cathodes of the LED arrays 41 to 46 are connected to the LED1 terminal to the LED6 terminal, respectively.

[0020] The LED arrays 41 to 46 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 systems) is also not limited to six, but may be, for example, four.

[0021] Next, the internal configuration of the LED driving device 30 will be described.

[0022] When an enable signal Ven input to an EN terminal is High, the internal voltage generator 1 generates an internal voltage Vreg (for example, 5 V) from an input voltage Vin applied to a VCC terminal and outputs it from a VREG terminal. The internal voltage Vreg is used as a power supply voltage for an internal circuit included in the LED driving device 30. A capacitor Cvg is connected to the VREG terminal.

[0023] The current detection unit 2 is connected to a CSH terminal and an SD terminal.

[0024] The oscillator 3 generates a predetermined clock signal and outputs it to the slope generator 4 .

[0025] The slope generating unit 4 generates a slope signal (triangular wave signal) Vslp based on the clock signal input from the oscillator 3 and outputs this to the PWM comparator 5. The slope generating unit 4 also has a function of providing an offset to the slope signal Vslp in accordance with the CSL terminal voltage obtained by converting the current flowing through the switching element N1 using the resistor Rcsl.

[0026] The PWM comparator 5 compares the error signal Verr input to the non-inverting input terminal (+) with the slope signal Vslp input to the inverting input terminal (-) to generate an internal PWM signal pwm, which is output to the DC / DC control logic unit 6.

[0027] The DC / DC control logic unit 6 generates a drive signal for the driver 7 based on the internal PWM signal pwm.

[0028] Based on the drive signal input from the DC / DC control logic unit 6, the driver 7 generates a gate voltage of the switching element N1 in a pulsed manner between the internal voltage Vreg and the ground voltage.

[0029] The switching element N1 is turned on / off based on a gate voltage input from the driver 7.

[0030] LED terminal voltages Vled1 to Vled6 are applied to the LED1 terminal to the LED6 terminal as the cathode voltages of the LED arrays 41 to 46, respectively. The selector 10 selects the lowest voltage among the LED terminal voltages Vled1 to Vled6 and outputs it to one inverting input terminal (-) of the error amplifier 9. As will be described later, when the MINSELIN terminal is used, the selector 10 selects the lowest voltage among the LED terminal voltages Vled1 to Vled6 and the MINSELIN terminal voltage.

[0031] The other inverting input terminal (-) of the error amplifier 9 is applied with the OVP terminal voltage obtained by dividing the output voltage Vout using voltage dividing resistors Rovp1 and Rovp2. A reference voltage Vref generated by a reference voltage generator 11 is applied to the non-inverting input terminal (+) of the error amplifier 9. The error amplifier 9 outputs an error amplifier output current (source current or sink current) that corresponds to the difference between the lower of the voltages applied to the two inverting input terminals (-) and the reference voltage Vref. Feedback control based on the OVP terminal is performed only at startup to speed up startup, and feedback control based on the output of the selector 10 is performed after startup.

[0032] The output terminal of the error amplifier 9 is connected to the COMP terminal. The COMP terminal is connected to the ground terminal via an external resistor Rpc and capacitor Cpc connected in series. An error voltage Verr is generated at the COMP terminal. The error voltage Verr is applied to the non-inverting input terminal (+) of the PWM comparator 5.

[0033] The protection circuit unit 12 includes a TSD unit, a TSDW (thermal warning) unit, an OCP unit, an OVP unit, an LED open detection circuit (OPEN), an LED short detection circuit (SHORT), an output short circuit protection circuit (SCP), and a UVLO unit.

[0034] The TSD unit shuts down circuits other than the internal voltage generation unit 1 when the junction temperature of the LED driver 30 reaches, for example, 175°C or higher. The TSD unit restores circuit operation when the junction temperature of the LED driver 30 reaches, for example, 150°C. The TSDW unit issues a warning when the junction temperature of the LED driver 30 reaches, for example, 140°C or higher.

[0035] The OCP unit monitors the CSL terminal voltage (input current detection voltage), which is the current flowing through the switching element N1 detected as a voltage signal by resistor Rcsl, and activates overcurrent protection when the CSL terminal voltage exceeds, for example, 0.3 V. When activating overcurrent protection, the OCP unit turns off DC / DC switching.

[0036] The SD terminal is connected to the gate of the transistor M1. When the current detection unit 2 detects an overcurrent flowing through the resistor Rcsh (an overcurrent flowing through the inductor L1), it turns off the transistor M1 and cuts off the path from the application terminal of the input voltage Vin to the inductor L1.

[0037] The OVP unit monitors the OVP terminal voltage and activates overvoltage protection when the OVP terminal voltage exceeds, for example, 1.0 V. When overvoltage protection is activated, DC / DC switching is turned off.

[0038] In the LED open detection circuit (OPEN), when any of the LED terminal voltages Vled1 to Vled6 is, for example, 0.3 V or less and the OVP terminal voltage is, for example, 1.0 V or more, LED open detection is activated and only the LED array detected as open is latched off (the constant current circuit 161 of the corresponding system in the constant current driver 16 is turned off).

[0039] In the LED short detection circuit (SHORT), when any of the LED terminal voltages Vled1 to Vled6 is, for example, 4.5V or higher, the built-in counter starts operating, and after approximately 13 ms, the circuit is latched and only the LED array for which a short has been detected is latched off (the constant current circuit 161 of the corresponding system in the constant current driver 16 is turned off).

[0040] In the output short-circuit protection circuit (SCP), when the OVP terminal voltage falls below 0.25V, for example, or when any of the LED terminal voltages Vled1 to Vled6 falls below 0.3V, for example, a built-in counter starts operating and latches after approximately 13 ms has elapsed, shutting down circuits other than the internal voltage generator 1. The output short-circuit protection circuit also provides ground fault protection in both cases where a ground fault occurs on the anode side (DC / DC output terminal side) of the LED arrays 41 to 46, and on the cathode side of the LED arrays 41 to 46.

[0041] The UVLO unit shuts down circuits other than the internal voltage generating unit 1 when the input voltage Vin falls to, for example, 2.8 V or less, or when the internal voltage Vreg falls to, for example, 2.7 V or less.

[0042] The protection circuit unit 12 outputs an abnormality detection signal from the FAIL1 terminal to the outside based on the abnormality detection state of the TSDW unit. The FAIL1 terminal is connected to the VREG terminal via a resistor Rf1. When the TSDW unit detects an abnormality, the protection circuit unit 12 turns on a transistor (not shown) connected to the FAIL1 terminal, causing the FAIL1 terminal to output a low level.

[0043] Furthermore, the protection circuit unit 12 outputs an abnormality detection signal from the FAIL2 terminal to the outside based on the abnormality detection states of the LED open detection circuit, the LED short detection circuit, and the output short-circuit protection circuit (SCP). The FAIL2 terminal is connected to the VREG terminal via a resistor Rf2. When any of the TSD unit, the OCP unit, the LED open detection circuit, the LED short detection circuit, and the output short-circuit protection circuit (SCP) detects an abnormality, the protection circuit unit 12 turns on a transistor (not shown) connected to the FAIL2 terminal, causing the FAIL2 terminal to output a low level.

[0044] The Schmitt trigger 15 transmits a PWM dimming signal input from an external device to the PWM terminal to the logic unit 13. The PWM dimming signal is input as a pulse signal. The logic unit 13 sends a PWM dimming command to the constant current driver 16 based on the PWM dimming signal. This causes the LED to be PWM dimmed.

[0045] The LED current setting unit 14 sets, in the constant current driver 16, a constant current value according to the resistance value of a resistor Riset connected to an ISET terminal (current setting terminal).

[0046] The constant current driver 16 has six constant current circuits 161 arranged between each of the LED1 terminal to LED6 terminal and a GND terminal connected to the ground terminal. The logic unit 13 controls the on / off of the constant current circuit 161 according to the duty of the PWM dimming signal. Specifically, the constant current circuit 161 is turned on during an LED current on period according to the on duty of the PWM dimming, and is turned off during an LED current off period according to the on duty of the PWM dimming. When the constant current circuit 161 is turned on, an LED current ILED flows at a constant current value set by the LED current setting unit 14.

[0047] The logic unit 13 instructs the DC / DC control logic unit 6 to perform DC / DC operation when the constant current circuits 161 of at least any system are in the ON state, and instructs the DC / DC control logic unit 6 to stop DC / DC operation when the constant current circuits 161 of all systems are in the OFF state. This is because if the DC / DC operation is stopped when the constant current circuits 161 of at least any system are in the ON state, the output capacitor Co will discharge, the output voltage Vout will drop, and there is a risk of malfunction in lighting the LED.

[0048] The VDISC terminal is also connected to the output discharge unit 8. The VDISC terminal is connected to one end of the output capacitor Co, which generates the output voltage Vout. If the device is started up while there is still charge in the output capacitor Co, there is a possibility that the LED will flicker. For this reason, the output capacitor Co needs to be discharged at startup, but since it may take a long time to discharge the charge using only the discharge paths such as the OVP setting resistors Rovp1 and Rovp2, the output discharge unit 8 discharges the residual charge in the output capacitor Co. This discharge is performed when the DC / DC converter is turned off (when the enable signal Ven applied to the EN terminal falls or during protection).

[0049] The LED driving device 30 also has a communication function for communicating with an external microcomputer. For example, I2C communication or SPI communication can be used as the communication function. When the communication function is enabled, the FAIL1 to FAIL3 terminals are connected to an external microcomputer (not shown). In this case, the FAIL1 terminal functions as an SDO terminal (data output terminal), the FAIL2 terminal functions as an SDI terminal (data input terminal), and the FAIL3 terminal functions as an SCK terminal (clock terminal). The communication function can be enabled or disabled by whether or not to pull up the FAIL1 to FAIL3 terminals.

[0050] When the communication function is enabled, the logic unit 13 controls the on / off of the constant current circuit 161 for each system according to the PWM dimming setting (on-duty setting) for each system set by the external microcomputer. This allows PWM dimming for each LED system to be performed. Note that when the communication function is enabled, the protection circuit unit 12 notifies the external microcomputer of an abnormality using communication.

[0051] The MINSELIN terminal, MINSELOUT terminal, PWMIN terminal, and PWMOUT terminal are not used when the LED driving device 30 is used alone as shown in FIG. 1, but are used when multiple LED driving devices 30 are used as described below, and details of these terminals will be described later.

[0052] 2. DC / DC controller Next, the DC / DC controller 301 (a circuit block including the oscillator 3, slope generator 4, PWM comparator 5, DC / DC control logic unit 6, driver 7, and error amplifier 9) of the LED driver 30 will be described in detail.

[0053] The error amplifier 9 generates an error amplifier output current according to the difference between the reference voltage Vref and the lower of the minimum value of the LED terminal voltages Vled1 to Vled6 selected by the selector 10 and the OVP terminal voltage. The error amplifier output current is a source current when the lower voltage is lower than the reference voltage Vref, and is a sink current when the lower voltage is higher than the reference voltage Vref.

[0054] The PWM comparator 5 compares the error voltage Verr with the slope signal Vslp to generate an internal PWM signal pwm. The internal PWM signal pwm goes high if the error voltage Verr is higher than the slope signal Vslp, and goes low if the error voltage Verr is lower than the slope signal Vslp.

[0055] The control logic unit 6 controls the on / off of the switching element N1 based on the internal PWM signal pwm. Specifically, the control logic unit 6 turns on the switching element N1 when the internal PWM signal pwm is at a high level. Conversely, the control logic unit 6 turns off the switching element N1 when the internal PWM signal pwm is at a low level.

[0056] As a result, the feedback control unit, which is made up of the error amplifier 9, PWM comparator 5, control logic unit 6, and driver 7, performs feedback control to output a switching pulse from the OUTL terminal to the switching element N1 so as to match the minimum value of the LED terminal voltages Vled1 to Vled6 with the reference voltage Vref. In other words, the DC / DC controller 301 has the above-mentioned feedback control unit.

[0057] When the switching element N1 is turned on, a current flows from the input voltage Vin application terminal through resistor Rcsh, transistor M1, inductor L1, and switching element N1 to the ground terminal, and energy is stored in inductor L1. At this time, diode D1 is in a reverse bias state, so no current flows from output capacitor Co to switching element N1. If charge has accumulated in output capacitor Co, an LED current ILED will flow from output capacitor Co to the anodes of LED arrays 41-46.

[0058] When the switching element N1 is turned off, the energy stored in the inductor L1 is released, and the current flows into the LED arrays 41 to 46 as the LED current ILED, and also flows into the output capacitor Co, charging the output capacitor Co.

[0059] By repeating the above operation, the output voltage Vout obtained by boosting the input voltage Vin is supplied to the anodes of the LED arrays 41 to 46. At this time, the cathode voltage of the LED array in the system with the highest forward voltage is controlled to the reference voltage Vref, and the cathode voltages of the LED arrays in the other systems are controlled to voltages equal to or higher than the reference voltage Vref.

[0060] <3. Using multiple LED drivers> Using multiple LED drivers 30 with the above-described configuration makes it possible to drive multiple systems of LEDs. Fig. 2 is a diagram showing an LED light source device 50 made up of two LED drivers 30. The LED light source device 50 shown in Fig. 2 has a master LED driver 30m, a slave LED driver 30s, an output stage 35, a master-side LED light source 40m, and a slave-side LED light source 40s.

[0061] The LED light source 40m is composed of six LED arrays. The number of LED arrays constituting the LED light source 40m is not limited to six (the same applies to the LED light source 40s). The cathodes of the LED arrays constituting the LED light source 40m are connected to the LED1 terminal to the LED6 terminal of the LED driver 30m, respectively. The output voltage Vout generated at one end of the output capacitor Co in the output stage 35 is supplied to the anodes of the LED arrays constituting the LED light source 40m.

[0062] The LED light source 40s is composed of six LED arrays. The cathodes of the LED arrays constituting the LED light source 40s are connected to the LED1 terminal to the LED6 terminal of the LED driving device 30s, respectively. One end of the output capacitor Co in the output stage 35 is connected to the anode of each LED array constituting the LED light source 40s. This makes it possible to supply the output voltage Vout to the anode of the LED light source 40s.

[0063] The slave LED driver 30s does not use the DC / DC controller 301. Therefore, the OUTL terminal and the CSL terminal of the LED driver 30s are unused.

[0064] Furthermore, the OVP terminal of the slave LED driver 30s is connected to the OVP terminal of the master LED driver 30m, which allows overvoltage protection by the OVP unit and ground fault protection by the output short-circuit protection circuit (SCP) to be implemented in both the master and slave.

[0065] 2, the MINSELOUT terminal of the LED driver 30s is connected to the MINSELIN terminal of the LED driver 30m. The selector 10 (FIG. 1) in the LED driver 30 outputs the minimum voltage of the terminal voltages of the LED1 to LED6 terminals and the terminal voltage of the MINSELIN terminal from the MINSELOUT terminal. When the MINSELIN terminal is unused, as in the LED driver 30s in FIG. 2, the minimum voltage of the terminal voltages of the LED1 to LED6 terminals is output from the MINSELOUT terminal.

[0066] In addition, in the master LED driving device 30m, the minimum voltage among the terminal voltages of the LED1 to LED6 terminals and the terminal voltage of the MINSELIN terminal is selected by the selector 10 and input to the error amplifier 9, and is used for DC / DC control by the DC / DC controller 301.

[0067] As a result, the minimum voltage (hereinafter referred to as the slave-side minimum voltage) among the terminal voltages of the LED1 terminal to the LED6 terminal in the LED driver 30s is output from the MINSELOUT terminal of the LED driver 30s shown in Fig. 2. Then, in the LED driver 30m, the selector 10 selects the minimum voltage among the terminal voltages of the LED1 terminal to the LED6 terminal in the LED driver 30m and the slave-side minimum voltage input to the MINSELIN terminal, and outputs it to the error amplifier 9.

[0068] Therefore, the DC / DC controller 301 and output stage 35 of the LED driver 30m generate the output voltage Vout so that the minimum voltage among the cathode voltages of the 12 systems (6 systems × 2) of LED arrays that make up the LED light sources 40m and 40s matches the reference voltage Vref. As a result, the LED terminal voltage (cathode voltage) corresponding to the LED array with the largest forward voltage among the 12 systems is controlled to the reference voltage Vref, and the other LED terminal voltages are controlled to voltages equal to or higher than Vref.

[0069] As shown in FIG. 2, the PWMOUT terminal of the LED driver 30s is connected to the PWMIN terminal of the LED driver 30m.

[0070] Here, the logic unit 13 (FIG. 1) of the LED driving device 30 outputs an on / off state signal of a first logic level (e.g., high level) indicating the on state from the PWMOUT terminal when at least any of the six constant current circuits 161 is in the on state or when the on / off state signal input to the PWMIN terminal indicates the on state. On the other hand, when all of the six constant current circuits 161 are in the off state and the on / off state signal input to the PWMIN terminal indicates the off state, the logic unit 13 outputs an on / off state signal of a second logic level (e.g., low level) indicating the off state from the PWMOUT terminal.

[0071] When the PWMIN terminal is unused, the signal input to the PWMIN terminal is not taken into consideration and output from the PWMOUT terminal is performed.

[0072] Furthermore, in the master LED driver 30m, if at least any of the six constant current circuits 161 is in the on state or the on / off state signal input to the PWMIN terminal indicates the on state, the logic unit 13 commands the DC / DC control logic unit 6 to turn on DC / DC control, and if all of the six constant current circuits 161 are in the off state and the on / off state signal input to the PWMIN terminal indicates the off state, the logic unit 13 commands the DC / DC control logic unit 6 to turn off DC / DC control. When DC / DC control is in the on state, the DC / DC controller 301 and output stage 35 generate the output voltage Vout, and when DC / DC control is in the off state, the generation of the output voltage Vout is stopped.

[0073] In the configuration shown in FIG. 2, the PWMIN terminal is unused in the LED driver 30s, and therefore an on / off state signal corresponding to the on / off state of the six constant current circuits 161 in the LED driver 30s is output from the PWMOUT terminal.

[0074] Here, Fig. 3 shows an example of the on / off states of the constant current circuits 161 of six systems (CH1 to CH6) in the LED driving device 30s (slave), and the on / off state signals output from the PWMOUT terminal. Note that Fig. 3 shows an example in which the communication function for communicating with the external microcomputer as described above is enabled, and PWM dimming settings are performed for each system through communication (this also applies to Fig. 4, which will be described later). This allows the on-duty to be different for each system, as shown in Fig. 3. Also, in Fig. 3, the timing at which the six systems switch from the off state to the on state is the same, but this does not necessarily have to be the same (this also applies to Fig. 4, which will be described later).

[0075] As shown in Figure 3, when at least one of the six constant current circuits 161 is in the on state, the on / off state signal is at the first logic level (on level), and when all of the six constant current circuits 161 are in the off state, the on / off state signal is at the second logic level (off level).

[0076] In this way, the on / off state signal output from the PWMOUT terminal in LED driver 30s is input to the PWMIN terminal in LED driver 30m. Here, Fig. 4 shows an example of the on / off state of the six constant current circuits 161 (CH1 to CH6) in LED driver 30m (master), the on / off state signal input to the PWMIN terminal (i.e., the same as PWMOUT in Fig. 3), and the state of DC / DC control in LED driver 30m.

[0077] As shown in FIG. 4, when at least one of the six constant current circuits 161 is in the on state or the on / off state signal is in the on state, the DC / DC control is in the on state, and when all of the six constant current circuits 161 are in the off state and the on / off state signal is in the off state, the DC / DC control is in the off state.

[0078] As a result, if at least one of the 12 constant current circuits 161 on the master side and the slave side is in the on state, the DC / DC controller 301 and the output stage 35 in the master LED driving device 30m generate the output voltage Vout, and if all of the 12 constant current circuits 161 are in the off state, the generation of the output voltage Vout is stopped.

[0079] In this way, by using the MINSELOUT and MINSELIN terminals, information on the minimum LED terminal voltage can be transmitted from the slave side to the master side. Furthermore, by using the PWMOUT and PWMIN terminals, information on the on / off state of the constant current circuit 161 can be transmitted from the slave side to the master side. Therefore, the DC / DC controller 301 and output stage 35 on the master side can control the output voltage Vout supplied to the LEDs of all systems in the master and slave. This eliminates the need to provide an output stage 35 for each of the multiple LED driving devices 30, thereby minimizing the increase in the number of components. This, in turn, reduces costs and circuit area.

[0080] Furthermore, since information on the on / off state of the constant current circuit 161 is transmitted from the slave side to the master side, the slave side can set PWM dimming for each system without relying on the master side, thereby improving the degree of freedom in dimming.

[0081] If a ground fault occurs in the cathode of the LED array in the slave LED light source 40s, 0V is output from the MINSELOUT terminal of the LED driver 30s. If the output short-circuit protection circuit (SCP) in the master LED driver 30m monitors the MINSELIN terminal in addition to the LED terminal voltages Vled1 to Vled6, it is possible to shut down circuits other than the internal voltage generator 1 in the LED driver 30m when 0V is applied to the MINSELIN terminal. This makes it possible to stop the generation of the output voltage Vout even if a ground fault occurs in the cathode of the slave LED light source 40s.

[0082] Furthermore, if a short circuit occurs in the LED array of the slave LED light source 40s, the MINSELOUT terminal of the LED driver 30s cannot notify the LED driver 30m of this. However, in this case, the LED short detection circuit (SHORT) in the LED driver 30s turns off only the constant current circuit 161 corresponding to the LED that was detected as shorted, so there is no problem in continuing to generate the output voltage Vout. This allows the LED to remain lit, for example, as a function related to functional safety.

[0083] 2, two LED driving devices 30 are used, but three or more may be used. In this case, two or more LED driving devices 30s as slaves are connected in order downstream of the LED driving device 30m as a master.

[0084] In this case, in the LED driving devices 30s acting as slaves except for the last one, the MINSELOUT terminal of the LED driving device 30 at the next stage is connected to the MINSELIN terminal, and the MINSELOUT terminal of the LED driving device 30 at the previous stage is connected to the MINSELIN terminal. Also, in the LED driving devices 30s acting as slaves except for the last one, the PWMOUT terminal of the LED driving device 30 at the next stage is connected to the PWMIN terminal, and the PWMIN terminal of the LED driving device 30 at the previous stage is connected to the PWMOUT terminal. In the LED driving device 30s at the last stage, the MINSELIN terminal and PWMIN terminal are not used.

[0085] <4. Modifications> When using multiple LED drivers, it is possible to use a slave-only LED driver 30X as shown in Fig. 5. The LED driver 30X shown in Fig. 5 differs from the previously described LED driver 30 (Fig. 1) in that it does not have a DC / DC controller 301. In other words, the LED driver 30X is an IC device dedicated to a constant current driver. This allows the size of the LED driver 30X to be smaller than that of the LED driver 30.

[0086] 6 is a diagram showing the configuration of an LED light source device 50X when such a slave-only LED driver 30X is used. In the LED light source device 50X shown in FIG. 6, the LED driver 30 is used as the master. The MINSELOUT terminal of the LED driver 30X is connected to the MINSELIN terminal of the LED driver 30, and the PWMOUT terminal of the LED driver 30X is connected to the PWMIN terminal of the LED driver 30. As a result, as in the previously described embodiment, information on the minimum LED terminal voltage and information on the on / off state of the constant current circuit 161 can be transmitted from the slave side to the master side.

[0087] Such an LED light source device 50X requires only one output stage 35, and the use of a small-sized LED driver 30X allows for a further reduction in circuit area. However, in the LED light source device 50 (FIG. 2) described above, the same LED driver 30 can be used as both a master and a slave, making it easier to manage the LED driver 30.

[0088] <5. Application to backlight devices> 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 of the configuration of a backlight device to which the LED driving device can be applied is shown in Fig. 7. Note that the configuration shown in Fig. 7 is of a so-called edge light type, but is not limited to this, and a direct type configuration may also be used.

[0089] The backlight device 70 shown in FIG. 7 is an illumination device that illuminates a liquid crystal panel 81 from behind. 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 LEDs and a substrate on which the LEDs are 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, made of, for example, an acrylic plate, totally reflects the light that enters the interior and guides it throughout the interior, where it is emitted 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, which are made of a diffusion sheet, lens sheet, etc., aim to uniformize and improve the brightness of the light illuminating the liquid crystal panel 81. The LED light source device 71 can be, for example, the LED light source devices 50 and 50X described above. This allows for a larger liquid crystal panel 81.

[0090] <6. About in-vehicle displays> The backlight device to which the LED driving device according to the embodiment described above is applied is particularly suitable for installation in an in-vehicle display.

[0091] 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. 8. 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 a variety of 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.

[0092] <7.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.

[0093] <8. Notes> As described above, for example, the LED driving device (30) according to the present disclosure includes a plurality of LED terminals (LED1 terminal to LED6 terminal) for connecting the cathodes of a plurality of systems of LEDs (41 to 46), a minimum voltage input terminal (MINSELIN terminal), a minimum voltage output terminal (MINSELOUT terminal), and a selector (10), When the minimum voltage input terminal is used, the selector selects the lowest voltage from among the voltages of the plurality of LED terminals and the voltage of the minimum voltage input terminal, and outputs the selected voltage from the minimum voltage output terminal; When the minimum voltage input terminal is not used, the selector is configured to select the minimum voltage from among the voltages of the plurality of LED terminals and output it from the minimum voltage output terminal (first configuration).

[0094] In addition, in the first configuration, the power supply further includes a DC / DC controller (301) that controls an output stage (35) that generates an output voltage (Vout) from an input voltage (Vin) and supplies the output voltage to the anodes of the LEDs of the plurality of systems, The DC / DC controller may be configured to perform control so that the lowest voltage selected by the selector from the voltages of the plurality of LED terminals and the voltage of the lowest voltage input terminal matches a reference voltage (Vref) (second configuration).

[0095] Furthermore, the second configuration may further include a ground fault protection circuit (SCP) that stops operation of the DC / DC controller when a cathode ground fault of the LED is detected based on the voltage of the minimum voltage input terminal (third configuration).

[0096] In any one of the first to third configurations, each of the LEDs of the plurality of systems a constant current circuit (161) for supplying a current to the The configuration may further include an LED short detection circuit (SHORT) that turns off the constant current circuit corresponding to the detected LED when a short circuit of the LED is detected based on the voltage of the LED terminal (fourth configuration).

[0097] In any one of the first to fourth configurations, the LED display device further includes a constant current circuit (161) that supplies current to each of the plurality of systems of LEDs, an on / off state input terminal (PWMIN terminal), an on / off state output terminal (PWMOUT terminal), and an on / off state signal output unit (logic unit 13), When the on / off state input terminal is used, the on / off state signal output unit: when at least one of the constant current circuits is in an ON state or when an ON / OFF state signal input to the ON / OFF state input terminal indicates an ON state, the ON / OFF state signal indicating an ON state is output from the ON / OFF state output terminal; When all of the constant current circuits are in the off state and the on / off state signal input to the on / off state input terminal indicates the off state, the on / off state signal indicating the off state is output from the on / off state output terminal; When the on / off state input terminal is not used, the on / off state signal output unit: When at least one of the constant current circuits is in an ON state, the ON / OFF state signal indicating the ON state is output from the ON / OFF state output terminal; When all of the constant current circuits are in the off state, the on / off state signal indicating the off state may be output from the on / off state output terminal (fifth configuration).

[0098] In addition, in the fifth configuration, the power supply further includes a DC / DC controller (301) that controls an output stage (35) for generating an output voltage (Vout) from an input voltage (Vin) and supplying the output voltage to the anodes of the LEDs of the plurality of systems, and a DC / DC operation on / off control unit (logic unit 13), The DC / DC operation on / off control unit is causing the DC / DC controller to perform a DC / DC operation when at least one of the constant current circuits is in an ON state or when an ON / OFF state signal input to the ON / OFF state input terminal indicates an ON state; A sixth configuration may be adopted in which, when all of the constant current circuits are in the off state and the on / off state signal input to the on / off state input terminal indicates the off state, the DC / DC controller is caused to stop DC / DC operation.

[0099] In the fifth or sixth configuration, the constant current circuit may be controlled to be turned on and off based on a PWM dimming setting for each system through communication with an external device (seventh configuration).

[0100] The LED light source device (50) according to the present disclosure includes an output stage (35) that generates an output voltage (Vout) from an input voltage (Vin); an LED driving device (30m) as a master of any one of the first to seventh configurations, having a DC / DC controller (301) that controls the output stage; At least one LED driver (30s) as a slave of any one of the first to seventh configurations; a first LED light source (40m) provided corresponding to the master LED driving device; a second LED light source (40s) provided corresponding to the slave LED driving device; and the output voltage is supplied to an anode of the first LED light source and an anode of the second LED light source; the LED driving device as the slave is connected to the LED driving device as the master in order from the downstream side; The minimum voltage output terminal (MINSELOUT terminal) of the LED driving device as the slave is connected to the minimum voltage input terminal (MINSELIN terminal) of the LED driving device as the slave or master on the preceding stage (eighth configuration).

[0101] In the eighth configuration, the LED driving device (30X) as the slave may not have a DC / DC controller (ninth configuration).

[0102] Furthermore, in the eighth or ninth configuration, the master LED driving device and the slave LED driving device may both have an overvoltage detection terminal (OVP terminal) and an open protection unit (OPEN) that performs LED open protection based on the voltage of the overvoltage detection terminal, and the overvoltage detection terminal of the slave may be connected to the overvoltage detection terminal of the master (tenth configuration).

[0103] An illumination device (70) according to the present disclosure has an LED light source device having any one of the eighth to tenth configurations (eleventh configuration).

[0104] Moreover, the in-vehicle display device 85 according to the present disclosure has a configuration including the lighting device of the eleventh configuration. [Industrial Applicability]

[0105] The present disclosure can be used, for example, as a driving means for an LED for use in a vehicle. [Explanation of symbols]

[0106] 1 Internal voltage generator 2 Current detection section 3 Oscillator 4 Slope generation section 5 PWM Comparator 6 DC / DC control logic section 7 Drivers 8 Output discharge section 9 Error Amplifier 10 Selectors 11 Reference voltage generation unit 12 Protection circuit section 13 Logic section 14 LED current setting section 15 Schmitt trigger 16 Constant Current Driver 30,30X LED driving device 30m,30s LED drive device 35 output stage 40m,40s LED light source 50,50X LED light source device 70 Backlight device 71 LED light source device 72 Light guide plate 73 Reflector 74 Optical sheets 81 LCD panel 85 In-vehicle display 161 Constant current circuit 301 DC / DC Controller Co Output Capacitor D1 Diode L1 inductor N1 switching element

Claims

1. a plurality of LED terminals for connecting the cathodes of the plurality of LEDs; a minimum voltage input terminal; a minimum voltage output terminal; A selector, and When the minimum voltage input terminal is used, the selector selects the lowest voltage from among the voltages of the plurality of LED terminals and the voltage of the minimum voltage input terminal, and outputs the selected voltage from the minimum voltage output terminal; When the minimum voltage input terminal is not used, the selector selects the minimum voltage from among the voltages of the plurality of LED terminals and outputs it from the minimum voltage output terminal.

2. a DC / DC controller that controls an output stage for generating an output voltage from an input voltage and supplying the output voltage to the anodes of the LEDs of the plurality of systems; 2. The LED driving device according to claim 1, wherein the DC / DC controller performs control so that the lowest voltage selected by the selector from the voltages of the plurality of LED terminals and the voltage of the lowest voltage input terminal is equal to a reference voltage.

3. 3. The LED driving device according to claim 2, further comprising a ground fault protection circuit that stops operation of said DC / DC controller when a cathode ground fault of an LED is detected based on the voltage of said minimum voltage input terminal.

4. a constant current circuit that supplies current to each of the plurality of LEDs; 2. The LED driving device according to claim 1, further comprising an LED short detection circuit that turns off the constant current circuit corresponding to the detected LED when a short circuit of the LED is detected based on the voltage of the LED terminal.

5. a constant current circuit that supplies current to each of the plurality of LEDs; an on / off state input terminal; an on / off state output terminal; an on / off state signal output unit; and When the on / off state input terminal is used, the on / off state signal output unit: when at least one of the constant current circuits is in an ON state or when an ON / OFF state signal input to the ON / OFF state input terminal indicates an ON state, the ON / OFF state signal indicating an ON state is output from the ON / OFF state output terminal; When all of the constant current circuits are in the off state and the on / off state signal input to the on / off state input terminal indicates the off state, the on / off state signal indicating the off state is output from the on / off state output terminal; When the on / off state input terminal is not used, the on / off state signal output unit: When at least one of the constant current circuits is in an ON state, the ON / OFF state signal indicating the ON state is output from the ON / OFF state output terminal; 2. The LED driving device according to claim 1, wherein when all of the constant current circuits are in the off state, the on / off state signal indicating the off state is output from the on / off state output terminal.

6. a DC / DC controller that controls an output stage for generating an output voltage from an input voltage and supplying the output voltage to the anodes of the LEDs of the plurality of systems; a DC / DC operation on / off control unit; and The DC / DC operation on / off control unit is causing the DC / DC controller to perform a DC / DC operation when at least one of the constant current circuits is in an ON state or when an ON / OFF state signal input to the ON / OFF state input terminal indicates an ON state; 6. The LED driving device according to claim 5, wherein when all of the constant current circuits are in the off state and the on / off state signal input to the on / off state input terminal indicates the off state, the DC / DC controller is caused to stop DC / DC operation.

7. 6. The LED driving device according to claim 5, wherein the constant current circuit can be controlled to be turned on and off based on a PWM dimming setting for each of the systems via communication with an external device.

8. an output stage for generating an output voltage from an input voltage; The LED driving device as a master according to any one of claims 1 to 7, which has a DC / DC controller for controlling the output stage; At least one LED driver as a slave according to any one of claims 1 to 7; a first LED light source provided corresponding to the master LED driving device; a second LED light source provided corresponding to the slave LED driving device; and the output voltage is supplied to an anode of the first LED light source and an anode of the second LED light source; the LED driving device as the slave is connected to the LED driving device as the master in order from the downstream side; The LED light source device, wherein the minimum voltage output terminal of the LED driving device as the slave is connected to the minimum voltage input terminal of the LED driving device as the slave or master on the preceding stage.

9. The LED light source device according to claim 8 , wherein the slave LED driver does not include a DC / DC controller.

10. each of the master LED driver and the slave LED driver has an overvoltage detection terminal and an open protection unit that performs LED open protection based on a voltage of the overvoltage detection terminal; The LED light source device according to claim 8 , wherein the overvoltage detection terminal of the slave is connected to the overvoltage detection terminal of the master.

11. An illumination device comprising the LED light source device according to claim 8.

12. An in-vehicle display device comprising the lighting device according to claim 11.

Images