LED driving device, LED light source device, and vehicle-mounted display device

Abstract

The present invention provides an LED driver, an LED light source, and an in-vehicle display device. The LED driver (30) includes: a plurality of LED terminals (LED1 to LED6) for connecting the cathodes of multiple channels of LEDs (41 to 46), a minimum voltage input terminal (MINSELIN), a minimum voltage output terminal (MINSELOUT), and a selector (10). When the minimum voltage input terminal is used, the selector selects the lowest voltage among the voltages of the plurality of LED terminals and the voltage of the minimum voltage input terminal and outputs it from the minimum voltage output terminal. When the minimum voltage input terminal is not used, the selector selects the lowest voltage among the voltages of the plurality of LED terminals and outputs the minimum voltage from the minimum voltage output terminal.

Description

[0001] This case is a divisional application of the patent application filed on May 2, 2022, with application number 2022800369288 and invention title "LED driving device, LED light source device and vehicle display device". Technical Field

[0002] This disclosure relates to LED driver devices. Background Technology

[0003] Traditionally, LEDs (light-emitting diodes) have been used in various applications due to their low power consumption and long lifespan. Patent Document 1 discloses a conventional example of an LED driving device for driving LEDs.

[0004] The LED driver device of Patent Document 1 includes: a DC / DC controller that controls an output stage for generating an output voltage based on an input voltage and supplying it to the LED; and a constant current driver that generates an output current flowing through the LED. This LED driver device drives LEDs in multiple channels. Each channel includes multiple LEDs connected in series, and LEDs in different channels are connected in parallel.

[0005] The DC / DC controller includes: an error amplifier that compares the lowest voltage among the cathode voltages of LEDs in multiple channels with a reference voltage; and a PWM comparator that compares the output of the error amplifier with a ramp signal to generate an internal PWM signal.

[0006] The constant current driver is turned on and off based on an external PWM signal input to the PWM terminal. This enables PWM dimming control. During the constant current driver's conduction period, the error amplifier and PWM comparator operate as follows: PWM driving of the switching elements of the output stage via switching pulses ensures that the minimum cathode voltage equals the reference voltage. Consequently, the output voltage (the anode voltage of the LED) is controlled to be equal to the sum of the maximum forward voltage among the LEDs in the multiple channels and the reference voltage.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-21117 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] With the LED driving device described above, the cathode voltage of the LED with the highest forward voltage in the channel is controlled to be equal to the reference voltage, and the cathode voltage of the LEDs in other channels is controlled to be a voltage higher than the reference voltage.

[0012] Recently, in applications such as automotive displays, there has been a desire to increase the number of LEDs to increase the display area. However, if the number of LEDs connected in parallel (the number of channels) increases, the heat generated by the LED driver becomes a problem. Therefore, to suppress the heat generated by the LED driver, the use of multiple LED drivers to drive the LEDs has been considered. However, this method requires setting up an output stage (composed of coils and transistors, etc.) for each LED driver, resulting in an increase in the number of components (and thus increased costs).

[0013] In view of the above, the object of this disclosure is to provide an LED driver device that enables the driving of multi-channel LEDs while suppressing the increase in the number of components.

[0014] Methods for solving problems

[0015] For example, according to one aspect of this disclosure, an LED driver includes: a plurality of LED terminals for connecting the cathodes of LEDs in a plurality of channels; a minimum voltage input terminal; a minimum voltage output terminal; and a selector.

[0016] When using the lowest voltage input terminal, the selector selects the lowest voltage among the voltages of the plurality of LED terminals and the voltage of the lowest voltage input terminal, and outputs the lowest voltage from the lowest voltage output terminal.

[0017] Without using the lowest voltage input terminal, the selector selects the lowest voltage among the voltages of the plurality of LED terminals and outputs the lowest voltage from the lowest voltage output terminal.

[0018] Invention Effects

[0019] According to the LED driving device disclosed herein, it is possible to drive multi-channel LEDs while suppressing the increase in the number of components. Attached Figure Description

[0020] Figure 1 This is a diagram illustrating the structure of an LED driver device according to an exemplary embodiment.

[0021] Figure 2 This is a diagram showing an example of the structure of an LED light source device consisting of two LED driver devices.

[0022] Figure 3 This is an example of the on / off state of a 6-channel constant current circuit in an LED driver (slave device), and a timing diagram of the on / off state signal output from the PWMOUT terminal.

[0023] Figure 4This is a timing diagram showing the on / off state of a 6-channel constant current circuit in an LED driver (main control device), the on / off state signal input to the PWMIN terminal, and the state of DC / DC control in the LED driver (main control device).

[0024] Figure 5 This is a diagram illustrating a structural example of an LED driver device specifically designed for subordinate devices.

[0025] Figure 6 This is a diagram illustrating a structural example of an LED light source device using a dedicated LED driver for a slave device.

[0026] Figure 7 This is a diagram showing an example of the structure of a backlight device.

[0027] Figure 8 This is an example of a vehicle-mounted display. Detailed Implementation

[0028] <1. Structure of LED Driver Device>

[0029] Figure 1 This is a diagram showing the structure of an LED driver 30 according to an exemplary embodiment of this disclosure. Figure 1 The LED driver 30 shown drives an LED array 41-46 with multiple channels (6 channels in this embodiment). Furthermore, Figure 1 The diagram shows a structure using a single LED driver 30 to drive an LED. As described later, it is also possible to construct a system using multiple LED driver 30 to drive multi-channel LEDs.

[0030] The LED driver 30 is a semiconductor device that integrates an internal voltage generation unit 1, a current detection unit 2, an oscillation unit 3, a ramp generation 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 generation 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.

[0031] In addition, the LED driver 30 has VCC terminal, VREG terminal, CSH terminal, SD terminal, VDISC terminal, OUTL terminal, CSL terminal, LED1 to LED6 terminals, MINSELOUT terminal, MINSELIN terminal, PWMIN terminal, OVP terminal, GND terminal, PWMOUT terminal, ISET terminal, PWM terminal, FAIL1 to FAIL3 terminals, COMP terminal, and EN terminal as external terminals for establishing electrical connections with the outside. Furthermore, as described later, when the communication function for communicating with an external microcomputer in the LED driver 30 is active, 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.

[0032] An output stage 35 is disposed outside the LED driver 30. This output stage 35 is used to generate an output voltage Vout from the input voltage Vin via DC / DC conversion and supply it to the anode of the LED arrays 41-46. The output stage 35 includes 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 the output stage 35 is controlled by the LED driver 30. The output stage 35 and the LED driver 30 form a DC / DC converter. Furthermore, in this embodiment, the DC / DC converter is specifically configured as a boost DC / DC converter.

[0033] 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.

[0034] In addition, the switching element N1 and the resistor Rcsl can also be included in the LED driver 30.

[0035] The anodes of LED arrays 41 to 46 are connected to one end of the output capacitor Co that generates the output voltage Vout. Each of the LED arrays 41 to 46 is composed of multiple LEDs connected in series. Each of the cathodes of LED arrays 41 to 46 is connected to terminals 1 to 6 of LEDs, respectively.

[0036] Furthermore, the LED arrays 41-46 are not limited to being connected in series; for example, they can be composed of LEDs connected in series and parallel, or they can be composed of only one LED. In addition, the number of LED arrays (channels) that can be driven is not limited to 6; for example, it can also be 4, etc.

[0037] Next, the internal structure of the LED driver 30 will be described.

[0038] When the enable signal Ven input to the EN terminal is high, the internal voltage generation unit 1 generates an internal voltage Vreg (e.g., 5V) based on the input voltage Vin applied to the VCC terminal and outputs it from the VREG terminal. The internal voltage Vreg is used as the power supply voltage for the internal circuitry included in the LED driver 30. The capacitor Cvg is connected to the VREG terminal.

[0039] The CSH and SD terminals are connected to the current sensing unit 2.

[0040] The oscillation unit 3 generates a specified clock signal and outputs it to the ramp generation unit 4.

[0041] The ramp generation unit 4 generates a ramp signal (triangular wave signal) Vslp based on the clock signal input from the oscillation unit 3, and outputs it to the PWM comparator 5. In addition, the ramp generation unit 4 has the function of imparting an offset to the ramp signal Vslp according to the CSL terminal voltage, which is obtained by converting the current flowing through the switching element N1 through the resistor Rcsl.

[0042] The PWM comparator 5 compares the error signal Verr input to the non-inverting input terminal (+) with the ramp signal Vslp input to the inverting input terminal (-) to generate an internal PWM signal pwm, and outputs it to the DC / DC control logic unit 6.

[0043] The DC / DC control logic unit 6 generates the drive signal for the driver 7 based on the internal PWM signal pwm.

[0044] The driver 7 generates a pulse-shaped gate voltage of the switching element N1 that oscillates between the internal voltage Vreg and the ground voltage based on the drive signal input from the DC / DC control logic unit 6.

[0045] The switching element N1 is turned on / off based on the gate voltage input from the driver 7.

[0046] LED terminal voltages Vled1 to Vled6 are applied to LED1 to LED6 respectively as the cathode voltages of LED arrays 41 to 46. Selector 10 selects the lowest voltage among LED terminal voltages Vled1 to Vled6 and outputs it to an inverting input (-) of error amplifier 9. Furthermore, as described later, when using the MINSELIN terminal, selector 10 selects the lowest voltage among LED terminal voltages Vled1 to Vled6 and the MINSELIN terminal voltage.

[0047] The OVP terminal voltage, obtained by dividing the output voltage Vout using voltage divider resistors Rovp1 and Rovp2, is applied to the other inverting input terminal (-) of error amplifier 9. A reference voltage Vref generated by reference voltage generation unit 11 is applied to the non-inverting input terminal (+) of error amplifier 9. The error amplifier output current (source current or sink current) corresponds to the difference between the lower of the voltages applied to the two inverting input terminals (-) and the reference voltage Vref. To accelerate startup, feedback control based on the OVP terminal is performed only during startup; feedback control based on the output of selector 10 is performed after startup.

[0048] The output of error amplifier 9 is connected to the COMP terminal. The COMP terminal is connected to ground via an externally connected resistor Rpc and capacitor Cpc. An error signal Verr is generated at the COMP terminal. The error signal Verr is applied to the non-inverting input (+) of PWM comparator 5.

[0049] The protection circuit section 12 includes: a TSD section, a TSDW (thermal warning) section, an OCP section, an OVP section, an LED open circuit detection circuit (OPEN), an LED short circuit detection circuit (SHORT), an output short circuit protection circuit (SCP), and a UVLO section.

[0050] The TSD unit shuts down all circuits except for the internal voltage generation unit 1 when the junction temperature of the LED driver 30 is, for example, 175°C or higher. Furthermore, the TSD unit resumes 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 is, for example, 140°C or higher.

[0051] The OCP unit monitors the CSL terminal voltage (input current detection voltage) derived from the current flowing through the switching element N1 via resistor Rcsl. When the CSL terminal voltage is, for example, 0.3 V or higher, overcurrent protection is activated. Upon activation of overcurrent protection, the OCP unit stops the DC / DC switch operation.

[0052] Additionally, the gate of transistor M1 is connected to the SD terminal. When the current detection unit 2 detects an overcurrent flowing through resistor Rcsh (an overcurrent flowing through inductor L1), it turns off transistor M1, cutting off the path from the input voltage Vin to inductor L1.

[0053] The OVP unit monitors the OVP terminal voltage and applies overvoltage protection when the OVP terminal voltage is, for example, above 1.0 V. When overvoltage protection is activated, the DC / DC switch operation is stopped.

[0054] The LED open circuit detection circuit (OPEN) identifies an LED open circuit when any one of the LED terminal voltages Vled 1 to Vled 6 is, for example, below 0.3 V and the OVP terminal voltage is, for example, above 1.0 V. It then locks off only the LED array that is detected to be open (the constant current circuit 161 of the corresponding channel in the constant current driver 16 is turned off).

[0055] The LED short-circuit detection circuit (SHORT) starts counting when any of the LED terminal voltages Vled 1 to Vled 6 is, for example, above 4.5 V. After about 13 ms, the lockout takes effect, thereby locking off only the LED array that is detected to be short-circuited (the constant current circuit 161 of the corresponding channel in the constant current driver 16 is turned off).

[0056] The output short-circuit protection circuit (SCP) starts counting when the OVP terminal voltage is, for example, below 0.25 V, or when any of the LED terminal voltages Vled 1 to Vled 6 is, for example, below 0.3 V. After approximately 13 ms, it applies a lockout shutdown, turning off all circuits except the internal voltage generation unit 1. The output short-circuit protection circuit can handle both ground short circuits on the anode side (DC / DC output side) of LED arrays 41 to 46 and ground short circuits on the cathode side of LED arrays 41 to 46.

[0057] When the input voltage Vin becomes, for example, 2.8 V or less, or the internal voltage Vreg becomes, for example, 2.7 V or less, the UVLO unit shuts down the circuits other than the internal voltage generation unit 1.

[0058] Based on the abnormal detection state of the TSDW section, the protection circuit section 12 outputs an abnormal detection signal from the FAIL1 terminal to the outside. The VREG terminal is connected to the FAIL1 terminal via a resistor Rf1. When the TSDW section detects an abnormality, the protection circuit section 12 turns on a transistor (not shown) connected to the FAIL1 terminal, thereby setting the output of the FAIL1 terminal to a low level.

[0059] Furthermore, the protection circuit 12 outputs an abnormality detection signal from the FAIL2 terminal based on the abnormality detection states of the LED open-circuit detection circuit, the LED short-circuit detection circuit, and the output short-circuit protection circuit (SCP). The VREG terminal is connected to the FAIL2 terminal via resistor Rf2. When an abnormality is detected in any of the TSD unit, OCP unit, LED open-circuit detection circuit, LED short-circuit detection circuit, and output short-circuit protection circuit (SCP), the protection circuit 12 turns on the transistor (not shown) connected to the FAIL2 terminal, thereby setting the output of the FAIL2 terminal to a low level.

[0060] The Schmitt trigger 15 transmits the PWM dimming signal input from the outside to the PWM terminal to the logic unit 13. The PWM dimming signal is input as a pulse signal. Based on the PWM dimming signal, the logic unit 13 sends a PWM dimming command to the constant current driver 16. Thus, PWM dimming of the LED is implemented.

[0061] The LED current setting unit 14 sets a constant current value to the constant current driver 16, which corresponds to the resistance value of the resistor Riset connected to the ISET terminal (current setting terminal).

[0062] The constant current driver 16 has a constant current circuit 161 with six channels disposed between each of the LED1 to LED6 terminals and the GND terminal connected to the ground terminal. The logic unit 13 controls the constant current circuit 161 to turn it on and off according to the duty cycle of the PWM dimming signal. Specifically, the constant current circuit 161 is turned on during the LED current conduction period according to the conduction duty cycle of the PWM dimming signal, and turned off during the LED current turn-off period according to the conduction duty cycle of the PWM dimming signal. When the constant current circuit 161 is turned on, an LED current ILED flows through the constant current value set by the LED current setting unit 14.

[0063] Furthermore, when the constant current circuit 161 of any channel is in the on state, the logic unit 13 instructs the DC / DC control logic unit 6 to perform DC / DC operation; when the constant current circuit 161 of all channels is in the off state, the logic unit 13 instructs the DC / DC control logic unit 6 to stop the DC / DC operation. This is because if the DC / DC operation is stopped when the constant current circuit 161 of any channel is in the on state, the output capacitor Co will discharge, causing the output voltage Vout to decrease, which may cause malfunctions in the lighting of the LED.

[0064] Additionally, the VDISC terminal is connected to the output discharge unit 8. The VDISC terminal is connected to one end of the output capacitor Co that generates the output voltage Vout. If the LED flickers when started with residual charge in the output capacitor Co, this can cause the LED to blink. To prevent this, the output capacitor Co needs to be discharged during startup. Here, considering that the discharge path, such as the resistors Rovp1 and Rovp2 used for OVP setting, sometimes requires time to discharge the charge, the output discharge unit 8 discharges the residual charge in the output capacitor Co. This discharge occurs when the DC / DC converter is off (when the enable signal Ven applied to the EN terminal decreases or when protection is activated).

[0065] Furthermore, the LED driver 30 has a communication function for communicating with an external microcomputer. This communication function can be achieved, for example, via I2C or SPI communication. 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). Additionally, the communication function can be enabled or disabled by pulling up or down the FAIL1 to FAIL3 terminals.

[0066] When the communication function is enabled, the logic unit 13 controls the on / off state of the constant current circuit 161 channel by channel according to the PWM dimming settings (duty cycle settings) set from the external microcomputer. This enables PWM dimming of the LEDs channel by channel. Furthermore, when the communication function is enabled, the protection circuit unit 12 notifies the external microcomputer of any abnormalities via communication.

[0067] In addition, such as Figure 1 As shown, the MINSELIN, MINSELOUT, PWMIN, and PWMOUT terminals are not used when using a single LED driver 30, but they are used when using multiple LED drivers 30, as will be described later in detail.

[0068] <2. DC / DC Controller>

[0069] Next, the DC / DC controller 301 (including a circuit block comprising an oscillation unit 3, a ramp generation unit 4, a PWM comparator 5, a DC / DC control logic unit 6, a driver 7, and an error amplifier 9) of the LED driver 30 will be described in detail.

[0070] Error amplifier 9 generates an output current based on the difference between the lowest value of the LED terminal voltages Vled 1 to Vled 6 selected by selector 10 and the lower of the OVP terminal voltages, and the reference voltage Vref. The output current is a source current when the lower voltage is lower than the reference voltage Vref, and a sink current when the lower voltage is higher than the reference voltage Vref.

[0071] PWM comparator 5 compares the error voltage Verr with the ramp signal Vslp to generate the internal PWM signal pwm. If the error voltage Verr is higher than the ramp signal Vslp, it becomes high; if the error voltage Verr is lower than the ramp signal Vslp, the internal PWM signal pwm becomes low.

[0072] The DC / DC control logic unit 6 controls the on / off state of the switching element N1 based on the internal PWM signal PWM. Specifically, the DC / DC control logic unit 6 turns on the switching element N1 when the internal PWM signal PWM is high. Conversely, the DC / DC control logic unit 6 turns off the switching element N1 when the internal PWM signal PWM is low.

[0073] Therefore, the feedback control unit, consisting of error amplifier 9, PWM comparator 5, DC / DC control logic unit 6, and driver 7, performs feedback control by outputting switching pulses from the OUTL terminal to the switching element N1. These switching pulses cause the lowest value of the LED terminal voltages Vled1 to Vled6 to match the reference voltage Vref. In other words, the DC / DC controller 301 has the aforementioned feedback control unit.

[0074] When switching element N1 is turned on, current flows from the input voltage Vin through resistor Rcsh, transistor M1, inductor L1, and switching element N1 to ground, accumulating energy in inductor L1. At this time, diode D1 remains reverse-biased, so current does not flow from output capacitor Co towards switching element N1. With charge accumulated in output capacitor Co, LED current ILED flows from output capacitor Co to the anode of LED arrays 41-46.

[0075] When the switching element N1 is turned off, the energy stored in the inductor L1 is released, and the current flows into the LED array 41~46 as the LED current ILED, and also flows into the output capacitor Co to charge the output capacitor Co.

[0076] By repeating the above actions, the anode supply to LED arrays 41-46 is used to boost the input voltage Vin to obtain the output voltage Vout. At this time, the cathode voltage of the LED array in the channel with the maximum forward voltage is controlled to the reference voltage Vref, and the cathode voltage of the LED array in other channels is controlled to a voltage higher than the reference voltage Vref.

[0077] <3. Utilizing multiple LED driver devices>

[0078] Multiple LED driver devices 30 with the above-described structure can be used to drive LEDs in multiple channels. Figure 2 This is a diagram showing an LED light source device 50 consisting of two LED driver devices 30. Figure 2 The LED light source device 50 shown includes an LED driver 30m as a master control device, an LED driver 30s as a slave device, an output stage 35, an LED light source 40m on the master control device side, and an LED light source 40s on the slave device side.

[0079] The LED light source 40m consists of a 6-channel LED array. The number of channels in the LED array of the LED light source 40m is not limited to 6 (the same applies to the LED light source 40s). The cathodes of each LED array in the LED light source 40m are connected to LED1 to LED6 terminals 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 each LED array in the LED light source 40m.

[0080] The LED light source 40s consists of a 6-channel LED array. The cathode of each LED array in the LED light source 40s is connected to LED1 to LED6 terminals of the LED driver device 30s, respectively. One end of the output capacitor Co in the output stage 35 is connected to the anode of each LED array in the LED light source 40s. Thus, the output voltage Vout can be supplied to the anode of the LED light source 40s.

[0081] In the LED driver 30s, which is a slave device, the DC / DC controller 301 is not used. Therefore, the OUTL terminal and CSL terminal in the LED driver 30s are unused.

[0082] Furthermore, the OVP terminal in the LED driver 30s, which is a slave device, is connected to the OVP terminal in the LED driver 30m, which is a master device. This allows for overvoltage protection based on the OVP section and grounding protection based on the output short-circuit protection circuit (SCP) to be implemented in both the master and slave devices.

[0083] In addition, such as Figure 2As shown, the MINSELOUT terminal of LED driver 30s is connected to the MINSELIN terminal of LED driver 30m. The selector 10 in LED driver 30 ( Figure 1 The lowest voltage among the terminal voltages of LED1 to LED6 and the terminal voltage of MINSELIN is output from the MINSELOUT terminal. Additionally, as... Figure 2 Like the LED driver 30s, when the MINSELIN terminal is not used, the lowest voltage among the terminal voltages of LED1 to LED6 is output from the MINSELOUT terminal.

[0084] In addition, in the LED driver 30m, which serves as the main control device, the selector 10 selects the lowest voltage among the terminal voltages of LED1 to LED6 and the terminal voltage of MINSELIN and inputs it to the error amplifier 9 for DC / DC control performed by the DC / DC controller 301.

[0085] Therefore, from Figure 2 The MINSELOUT terminal of the LED driver 30s outputs the lowest voltage among the terminal voltages of LED1 to LED6 in the LED driver 30s (hereinafter referred to as the slave device side minimum voltage). Then, in the LED driver 30m, the selector 10 selects the lowest voltage among the terminal voltages of LED1 to LED6 in the LED driver 30m and the slave device side minimum voltage input to the MINSELIN terminal, and outputs it to the error amplifier 9.

[0086] Therefore, the DC / DC controller 301 and output stage 35 of the LED driver 30m generate the output voltage Vout in such a way that the lowest voltage among the cathode voltages of the 12-channel (6-channel × 2) LED array of the LED light source 40m and 40s is equal to the reference voltage Vref. Thus, the LED terminal voltage (cathode voltage) corresponding to the LED array with the highest forward voltage in the 12-channel LED array is controlled to be equal to the reference voltage Vref, and the voltages of other LED terminals are controlled to be higher than Vref.

[0087] In addition, such as Figure 2 As shown, the PWMOUT terminal of LED driver 30s is connected to the PWMIN terminal of LED driver 30m.

[0088] Here, when any one of the 6-channel 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, the logic section 13 of the LED driver 30 ( Figure 1The logic unit 13 outputs a first logic level (e.g., high level) on / off state signal indicating the on state from the PWMOUT terminal. On the other hand, when all 6 channels of constant current circuit 161 are off and the on / off state signal input to the PWMIN terminal indicates the off state, the logic unit 13 outputs a second logic level (e.g., low level) on / off state signal indicating the off state from the PWMOUT terminal.

[0089] Furthermore, when the PWMIN terminal is not used, the signal input to the PWMIN terminal is disregarded, and the output is performed from the PWMOUT terminal.

[0090] Furthermore, in the LED driver device 30m, which serves as the main control unit, when any one of the six constant current circuits 161 is in a conducting state, or when the on / off state signal input to the PWMIN terminal indicates an on state, the logic unit 13 instructs the DC / DC control logic unit 6 to enable DC / DC control. Conversely, when all six constant current circuits 161 are in a off state and the on / off state signal input to the PWMIN terminal indicates an off state, the logic unit 13 instructs the DC / DC control logic unit 6 to disable DC / DC control. In the DC / DC control enabled state, the DC / DC controller 301 and the output stage 35 generate the output voltage Vout; in the DC / DC control disabled state, the generation of the output voltage Vout stops.

[0091] exist Figure 2 In the structure shown, the PWMIN terminal of the LED driver 30s is not used. Therefore, the on / off state signal corresponding to the on / off state of the 6-channel constant current circuit 161 in the LED driver 30s is output from the PWMOUT terminal.

[0092] Here, Figure 3 An example of the on / off state of the constant current circuit 161 for the six channels (CH1~CH6) of the LED driver 30s (slave device), and an on / off state signal output from the PWMOUT terminal. Furthermore, Figure 3 This is an example of a situation where the communication function is effective when communicating with an external microcomputer as described above, and PWM dimming settings are performed channel by channel via communication (described later). Figure 4 Similarly). Therefore, as Figure 3 As shown, the duty cycle can be different for each channel. Additionally, in Figure 3 In this process, the timing for switching from the off state to the on state is consistent across the six channels, but it doesn't have to be consistent (as discussed later). Figure 4 (The same applies).

[0093] like Figure 3 As shown, when any one of the six constant current circuits 161 is in the on state, the on / off state signal becomes the first logic level (on level), and when all six constant current circuits 161 are in the off state, the on / off state signal becomes the second logic level (off level).

[0094] As described above, the on / off state signal output from the PWMOUT terminal of the LED driver 30s is input to the PWMIN terminal of the LED driver 30m. Here, Figure 4 An example of the on / off state of the constant current circuit 161 of the six channels (CH1~CH6) in the LED driver 30m (main control device), and the on / off state signal input to the PWMIN terminal (i.e., the signal related to the on / off state of the LED driver 30m (main control device)). Figure 3 The same applies to PWMOUT), and the state of DC / DC control in the LED driver 30m.

[0095] like Figure 4 As shown, when any one of the 6-channel constant current circuits 161 is in the on state, or when the on / off state signal is in the on state, the DC / DC control is set to the on state. When all 6 channels of the 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 set to the off state.

[0096] Therefore, if any one of the 12 constant current circuits 161 on the master control device side and the slave device side is in the on state, the DC / DC controller 301 and the output stage 35 in the LED driver device 30m, which serves as the master control device, generate the output voltage Vout. If all 12 constant current circuits 161 are in the off state, the generation of the output voltage Vout stops.

[0097] In this way, the MINSELOUT and MINSELIN terminals can be used to transmit information about the minimum voltage of the LED terminals from the slave device side to the master device side. Additionally, the PWMOUT and PWMIN terminals can be used to transmit information about the on / off state of the constant current circuit 161 from the slave device side to the master device side. Therefore, the output voltage Vout supplied to all channels of the LEDs in both the master and slave devices can be controlled by the DC / DC controller 301 and the output stage 35 on the master device side. This eliminates the need to provide an output stage 35 for each of the multiple LED drivers 30, thus suppressing an increase in the number of components. Consequently, cost and circuit area reduction are achieved.

[0098] In addition, by transmitting the information of the on / off state of the constant current circuit 161 from the slave device side to the master device side, it is possible to perform PWM dimming settings for each channel on the slave device side without relying on the master device side, thereby improving the degree of freedom in dimming.

[0099] Furthermore, in the event of a ground short circuit in the cathode of the LED array in the LED light source 40s on the slave device side, 0V is output from the MINSELOUT terminal of the LED driver 30s. In the LED driver 30m on the master device side, the output short-circuit protection circuit (SCP) can be configured to monitor not only the LED terminal voltages Vled1 to Vled6 but also the MINSELIN terminal. Therefore, when 0V is applied to the MINSELIN terminal, all circuits except the internal voltage generation unit 1 in the LED driver 30m can be shut down. Thus, even if a cathode ground short circuit occurs in the LED light source 40s on the slave device side, the generation of the output voltage Vout can be stopped.

[0100] Furthermore, in the event of a short circuit in the LED array of the LED light source 40s on the slave device side, this situation cannot be transmitted from the MINSELOUT terminal of the LED driver 30s to the LED driver 30m side. However, in this case, the LED short circuit detection circuit (SHORT) in the LED driver 30s only turns off the constant current circuit 161 corresponding to the detected short-circuited LED, so there is no problem in continuing to generate the output voltage Vout. Thus, for example, as a function related to functional safety, the LED can be kept lit.

[0101] In addition, Figure 2 In this case, the number of LED driver devices 30 used is set to two, but it can also be set to three or more. In this case, two or more LED driver devices 30s, which are slave devices, are successively connected to the downstream side of the LED driver device 30m, which is the master control device.

[0102] In this case, the LED driver 30s, which is a slave device except for the last stage, has its MINSELIN terminal connected to the MINSELOUT terminal of its own subsequent stage LED driver 30, and its MINSELOUT terminal connected to the MINSELIN terminal of its own preceding stage LED driver 30. Additionally, the LED driver 30s, which is a slave device except for the last stage, has its PWMIN terminal connected to the PWMOUT terminal of its own subsequent stage LED driver 30, and its PWMOUT terminal connected to the PWMIN terminal of its own preceding stage LED driver 30. In the last stage LED driver 30s, neither the MINSELIN terminal nor the PWMIN terminal is used.

[0103] <4. Variations>

[0104] In structures using multiple LED drivers, the following can be used: Figure 5 The LED driver 30X shown is dedicated to the slave device. Figure 5 The LED driver 30X shown is the same as the LED driver 30 described above. Figure 1 Compared to the LED driver 30, the LED driver 30X does not have a DC / DC controller 301. That is, the LED driver 30X is a dedicated IC device for a constant current driver. Therefore, the size of the LED driver 30X can be smaller than that of the LED driver 30.

[0105] Figure 6 This diagram illustrates the structure of the LED light source device 50X using the LED driver 30X dedicated to the aforementioned slave device. Figure 6 In the LED light source device 50X shown, the LED driver device 30 is used as the master control device. The MINSELOUT terminal of the LED driver device 30X is connected to the MINSELIN terminal of the LED driver device 30, and the PWMOUT terminal of the LED driver device 30X is connected to the PWMIN terminal of the LED driver device 30. Thus, similar to the embodiment described above, information about the minimum voltage of the LED terminal and information about the on / off state of the constant current circuit 161 can be transmitted from the slave device side to the master control device side.

[0106] The aforementioned LED light source device 50X not only requires only one output stage 35, but also further reduces the circuit area by using a small LED driver device 30X. However, it should be noted that the aforementioned LED light source device 50 ( Figure 2 This allows the same product, namely the LED driver 30, to be used as both a master and slave device, thus making the management of the LED driver 30 easier.

[0107] <5. Application of Backlight Devices>

[0108] As an example of an LED driving device that applies the embodiments described above, a backlight device will be described. Figure 7 This illustrates a structural example of a backlight device that can utilize an LED driver. Furthermore, Figure 7 The structure shown is the so-called edge-lit type structure, but it is not limited to this and can also be a direct-lit type structure.

[0109] Figure 7The backlight device 70 shown is an illumination device that illuminates the 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 elements 74. The LED light source device 71 includes LEDs and a circuit board mounting the LEDs. Light emitted from the LED light source device 71 enters the interior from the side of the light guide plate 72. For example, a light guide plate 72 made of acrylic sheet causes total internal reflection of the light entering the interior and guides it inwards, ultimately causing the light to exit as planar light through the side of the light guide plate 72 where the optical elements 74 are disposed. The reflector 73 reflects the light leaking from the light guide plate 72 back into the interior of the light guide plate 72. The optical elements 74 include diffusers and lenses, and are used to uniform and enhance the brightness of the light illuminating the liquid crystal panel 81. The LED light source device 71 can be implemented using the LED light source devices 50 and 50X described above. This helps to achieve a larger size for the liquid crystal panel 81.

[0110] <6. About in-vehicle displays>

[0111] The backlight device of the LED driver using the above-described embodiments is particularly preferably mounted on an in-vehicle display.

[0112] In-vehicle displays, for example Figure 8 The in-vehicle display 85 shown is positioned on the dashboard in front of the driver's seat. The in-vehicle display 85 can display various images, such as navigation information, rear-view images, speedometer, fuel gauge, fuel level, and gear position, and can convey various information to the user. Such an in-vehicle display is called a cluster panel or center information display (CID). Alternatively, the in-vehicle display can also be configured as a rear-seat entertainment system located behind the driver's and passenger's seats.

[0113] <7. Other>

[0114] The exemplary embodiments of the present invention have been described above, but various modifications can be made to the embodiments without departing from the spirit of the present invention.

[0115] <8. Postscript>

[0116] As described above, according to one aspect disclosed herein, an LED driver (30) includes: a plurality of LED terminals (LED1 terminal to LED6 terminal) for respectively connecting the cathodes of a plurality of channels of LEDs (41 to 46); a minimum voltage input terminal (MINSELIN); a minimum voltage output terminal (MINSELOUT); and a selector (10).

[0117] When using the lowest voltage input terminal, the selector selects the lowest voltage among the voltages of the plurality of LED terminals and the voltage of the lowest voltage input terminal, and outputs the lowest voltage from the lowest voltage output terminal.

[0118] Without using the lowest voltage input terminal, the selector selects the lowest voltage among the voltages of the plurality of LED terminals and outputs the lowest voltage from the lowest voltage output terminal (first structure).

[0119] Additionally, the first structure described above may also include a DC / DC controller (301) that controls an output stage (35) for generating an output voltage (Vout) from an input voltage (Vin) and supplying it to the anode of the plurality of LED channels.

[0120] The DC / DC controller can perform an operation that makes the lowest voltage selected by the selector among the voltages of the plurality of LED terminals and the voltage of the lowest voltage input terminal equal to the reference voltage (Vref) (second structure).

[0121] Additionally, the second structure described above may also include a ground short-circuit protection circuit (SCP) that stops the operation of the DC / DC controller if a cathode ground short circuit of any LED is detected based on the voltage of the lowest voltage input terminal (third structure).

[0122] In addition, any of the first to third structures described above may also have:

[0123] A constant current circuit (161) supplies current to the LEDs of the plurality of channels respectively;

[0124] The LED short-circuit detection circuit (SHORT) turns off the corresponding constant current circuit when a short circuit is detected in any of the LEDs based on the voltage at the LED terminals (fourth structure).

[0125] In addition, any of the first to fourth structures described above may further include: a constant current circuit (161) that supplies current to the LEDs of the plurality of channels respectively; an on / off state input terminal (PWMIN terminal); an on / off state output terminal (PWMOUT terminal); and an on / off state signal output section (logic section 13).

[0126] When using the on / off state input terminal.

[0127] When any one of the constant current circuits is in a conducting state, or when the conducting / off state signal input to the conducting / off state input terminal indicates a conducting state, the conducting / off state signal output unit outputs the conducting / off state signal indicating the conducting state from the conducting / off state output terminal.

[0128] When all 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 output unit outputs the on / off state signal indicating the off state from the on / off state output terminal.

[0129] Without using the on / off state input terminal

[0130] When any one of the constant current circuits is in the ON state, the ON / OFF state signal output unit outputs the ON / OFF state signal indicating the ON state from the ON / OFF state output terminal.

[0131] When all the constant current circuits are in the off state, the on / off state signal output unit outputs the on / off state signal indicating the off state from the on / off state output terminal (fifth structure).

[0132] In addition, the fifth structure described above may also include: a DC / DC controller (301) that controls an output stage (35) for generating an output voltage (Vout) based on an input voltage (Vin) and supplying it to the anode of the LEDs in the plurality of channels; and a DC / DC operation on / off control unit (logic unit 13).

[0133] When any one of the constant current circuits is in a conducting state, or when a conducting / turn-off state signal input to the conducting / turn-off state input terminal indicates a conducting state, the DC / DC operation on / off control unit causes the DC / DC controller to perform a DC / DC operation.

[0134] When all 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 operation on / off control unit causes the DC / DC controller to stop the DC / DC operation (sixth structure).

[0135] Alternatively, in the fifth or sixth structure described above, it can also be configured to control the on / off state of the constant current circuit based on the PWM dimming settings of each channel obtained through communication with the outside (seventh structure).

[0136] According to another aspect disclosed herein, an LED light source device (50) includes:

[0137] The output stage (35) generates the output voltage (Vout) based on the input voltage (Vin);

[0138] The LED driver (30m) according to any one of the first to seventh structures, which is the main control device, has a DC / DC controller (301) for controlling the output stage.

[0139] At least one LED driver device (30s) according to any one of the first to seventh structures as a subordinate device;

[0140] A first LED light source (40m) is provided correspondingly to an LED driver device, which serves as the main control device;

[0141] The second LED light source (40s) is provided corresponding to the LED driving device, which is the subordinate device.

[0142] The output voltage is supplied to the anode of the first LED light source and the anode of the second LED light source.

[0143] Each of the at least one LED driver that is a slave device is connected to the stage of another LED driver that is a master device or a slave device.

[0144] The minimum voltage output terminal (MINSELOUT) of each of the at least one LED driver devices that are slave devices is connected to the minimum voltage input terminal (MINSELIN terminal) of another LED driver device that is a slave device or an LED driver device that is a master device (eighth structure) on the front side.

[0145] In addition, in the eighth structure described above, the LED driver (30X) that serves as the slave device may not have a DC / DC controller (ninth structure).

[0146] Furthermore, in the eighth or ninth structure described above, both the LED driver device serving as the master control device and the LED driver device serving as the slave device have: an overvoltage detection terminal (OVP terminal) and an open circuit protection section (OPEN) for LED open circuit protection based on the voltage of the overvoltage detection terminal. The overvoltage detection terminal of at least one LED driver device serving as the slave device is connected to the overvoltage detection terminal of the LED driver device serving as the master control device (tenth structure).

[0147] According to another aspect disclosed herein, a lighting device (70) includes an LED light source device (eleventh structure) of any of the eighth to tenth structures described above.

[0148] According to another aspect disclosed herein, the vehicle display device 85 includes the lighting device of the aforementioned eleventh structure.

[0149] Industrial availability

[0150] This disclosure can be used, for example, as a driver unit for automotive LEDs.

[0151] Explanation of reference numerals in the attached figures

[0152] 1. Internal voltage generation unit

[0153] 2 Current Detection Unit

[0154] 3. Oscillation section

[0155] 4. Slope generation section

[0156] 5 PWM comparators

[0157] 6 DC / DC Control Logic Section

[0158] 7 drives

[0159] 8 Output Discharge Section

[0160] 9. Error Amplifier

[0161] 10 Selectors

[0162] 11. Reference Voltage Generation Unit

[0163] 12 Protection Circuit Section

[0164] 13 Logic Department

[0165] 14 LED Current Setting Section

[0166] 15 Schmitt trigger

[0167] 16 Constant Current Driver

[0168] 30, 30X LED driver device

[0169] 30m, 30s LED driver device

[0170] 35 Output Stage

[0171] 40m, 40s LED light source

[0172] 50, 50X LED light source device

[0173] 70 Backlight device

[0174] 71 LED Light Source Device

[0175] 72 Light guide plate

[0176] 73 Reflector

[0177] 74 Optical Films

[0178] 81 LCD panel

[0179] 85 Car Display

[0180] 161 Constant Current Circuit

[0181] 301 DC / DC Controller

[0182] Co Output capacitor

[0183] D1 diode

[0184] L1 Inductor

[0185] N1 is a switching element.

Claims

1. An LED driver device, comprising: Multiple LED terminals, wherein the multiple LED terminals are respectively connected to the cathodes of multiple channels of LEDs; as well as The input terminals and output terminals are used to transmit information about the lowest voltage among the voltages at the plurality of LED terminals. The output terminal is configured to output information about the lowest voltage among the voltages at the plurality of LED terminals and the voltages input via the input terminal.

2. The LED driving device according to claim 1, further comprising: FAIL terminal; as well as A protection circuit is configured to notify an external fault via the FAIL terminal.

3. The LED driving device according to claim 2, wherein, The protection circuit includes an LED short-circuit detection circuit, which is configured to latch off only the LEDs in the channel where a short circuit is detected.

4. The LED driving device according to claim 2, wherein, The protection circuit includes an LED open-circuit detection circuit, which is configured to latch only the LEDs in the channel where an open circuit is detected.

5. The LED driving device according to claim 2, further comprising: A DC / DC controller is configured to control an output stage for generating an output voltage based on an input voltage and supplying the output voltage to the anodes of LEDs in the plurality of channels. The protection circuit includes a ground short-circuit protection circuit, which is configured to suspend the operation of the DC / DC controller when a ground short circuit is detected at the LED cathode based on the voltage at the input terminal.

6. The LED driving device according to claim 1, further comprising: ISET terminal, The LED current is set according to the resistance value of the external resistor connected to the ISET terminal.

7. The LED driving device according to claim 1, further comprising: Selector, Based on information input via the plurality of LED terminals and via the input terminals, the selector selects the lowest voltage and outputs information about the lowest voltage via the output terminals.

8. The LED driver according to claim 7, wherein, When two LED drivers are used to drive the LEDs in the plurality of channels, the output terminal of the LED driver, which is a slave device, is connected to the input terminal of the LED driver, which is a master device.

9. The LED driving device according to claim 8, wherein, When three or more of the aforementioned LED drivers are used to drive the LEDs in the multiple channels, the input terminals of the LED drivers that are slave devices in each stage except the last stage are supplied with information about the lowest voltage of the LED driver in the stage following the aforementioned LED driver.

10. The LED driving device according to claim 8, wherein, The LED driver, acting as the main control device, uses information about the lowest voltage selected by the selector to control the output voltage of the DC / DC converter supplied to the LED anodes in the plurality of channels.

11. The LED driving device according to claim 10, wherein, When multiple LED drivers are used to drive the LEDs in the multiple channels, a DC / DC converter supplies the output voltage to the LEDs in all channels of the master device and the slave device.

12. The LED driving device according to claim 1, further comprising: A constant current circuit supplies current to the LEDs in the multiple channels respectively; On / off status input terminal; On / off state output terminal; On / off status signal output section in, When using the on / off state input terminal. When any one of the constant current circuits is in a conducting state, or when the conducting / turning-off state signal input to the conducting / turning-off state input terminal indicates a conducting state, the conducting / turning-off state signal output unit outputs the conducting / turning-off state signal indicating the conducting state from the conducting / turning-off state output terminal. When all 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 output unit outputs the on / off state signal indicating the off state from the on / off state output terminal. Without using the on / off state input terminal When any one of the constant current circuits is in the on state, the on / off state signal output unit outputs an on / off state signal indicating the on state from the on / off state output terminal. When all the constant current circuits are in the off state, the on / off state signal output unit outputs an on / off state signal indicating the off state from the on / off state output terminal.

13. The LED driving device according to claim 12, further comprising: A DC / DC controller that controls an output stage for generating an output voltage based on an input voltage and supplying the output voltage to the anode of the plurality of LED channels; DC / DC on / off control unit in, When any one of the constant current circuits is in a conducting state, or when a conducting / turn-off state signal input to the conducting / turn-off state input terminal indicates a conducting state, the DC / DC operation on / off control unit causes the DC / DC controller to perform a DC / DC operation. When all 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 operation on / off control unit causes the DC / DC controller to stop the DC / DC operation.

14. The LED driving device according to claim 12, wherein, The constant current circuit can be controlled to turn on and off based on the PWM dimming settings of each channel obtained through communication with the outside.

15. An LED light source device, comprising: The output stage generates the output voltage based on the input voltage. The LED driver device according to claim 1, which serves as the main control device, includes a DC / DC controller for controlling the output stage; At least one LED driving device according to claim 1 as a subordinate device; A first LED light source is provided correspondingly to an LED driver device, which serves as the main control device; A second LED light source is provided corresponding to at least one LED driver device that serves as the subordinate device. in, The output voltage is supplied to the anodes of the first LED light source and the second LED light source. Each LED driver, which is a slave device, is connected to the downstream side of either the LED driver, which is the master device, or another LED driver, which is a slave device. The output terminal of each LED driver in at least one of the slave devices is connected to the input terminal of another LED driver in at least one of the slave devices on the front-end side, or serves as the input terminal of the LED driver of the master device.

16. The LED light source device according to claim 15, wherein, The at least one LED driver that is a slave device does not include a DC / DC controller.

17. The LED light source device according to claim 15, wherein, The LED driver device as the master control device and the at least one LED driver device as the slave device each include: Overvoltage detection terminals; and Open-circuit protection circuit, which performs LED open-circuit protection based on the voltage at the overvoltage detection terminal. The overvoltage detection terminal of at least one LED driver device, which is a slave device, is connected to the overvoltage detection terminal of the LED driver device, which is a master device.

18. A lighting device comprising an LED light source device according to claim 15.

19. A vehicle-mounted display device, comprising the lighting device according to claim 18.

20. An LED driving method using a master LED driver configured to drive LEDs in a plurality of channels and two or more slave LED drivers configured to drive LEDs in a plurality of channels, the method comprising the following steps: The step of the slave LED driver in the last stage outputting the information of the lowest voltage among the cathode voltages of the LEDs in the plurality of channels driven by the slave LED driver to the slave LED driver in the previous stage. The step of the slave LED driver in each stage except the last stage outputting the cathode voltage of the LED in the multiple channels driven by the slave LED driver and the lowest voltage among the lowest voltages input from the previous stage to the slave LED driver in the previous stage. The step of the master LED driver selecting the cathode voltage of the LED in the plurality of channels driven by the master LED driver and the lowest voltage among the lowest voltages input from the slave LED driver in the previous stage. as well as The master LED driver uses a selected minimum voltage to control a DC / DC converter configured to supply an output voltage to the anodes of LEDs in all channels driven by the master LED driver and the slave LED driver.

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