JP2020198243A - Led driving device and display apparatus, and control apparatus for led driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED drive device capable of avoiding non-lighting of an LED while suppressing a decrease in efficiency of the device. A DC / DC converter 20 is an asynchronous rectifying type step-up chopper circuit. The switching element Q2 is provided in the drive device 50 and is connected in parallel to the SBD 26 of the DC / DC converter 20. The switching element Q2 is off when the open failure of the SBD 26 has not occurred. When an open failure occurs, the current driver 60 adjusts the current so that the current flowing through the LED row 10 becomes smaller than when the open failure does not occur, and the controller 70 synchronizes with the switching element Q1. The switching element Q2 is switched and driven. [Selection diagram] Fig. 1

Description

The present disclosure relates to an LED drive device, a display device including the LED drive device, and a control device for the LED drive device.

The use of LEDs (Light Emitting Diodes) as energy-saving light sources has been expanding in recent years. To drive the LED, an LED driver for supplying a constant current to the LED is used based on the forward voltage-current characteristic and the light emission characteristic of the LED.

For example, Japanese Patent Application Laid-Open No. 2018-19498 (Patent Document 1) discloses an LED driver using a switching power supply circuit. This LED driver includes a DC / DC converter that supplies a current to the LED and a current driver that adjusts the current flowing through the LED. The DC / DC converter is composed of an asynchronous rectifying type chopper circuit including a coil, a switching element, and a diode. With such a configuration, the LED can be driven with high efficiency (low loss) (see Patent Document 1).

JP-A-2018-19498

When the chopper circuit constituting the DC / DC converter is a boost type, if an open failure of the diode constituting the chopper circuit occurs, the current cannot be supplied from the DC / DC converter to the LED, and the LED cannot be lit. .. In preparation for this, it is also conceivable to configure a synchronous rectification type DC / DC converter in which the diode is replaced with a switching element in advance. However, when a synchronous rectification type DC / DC converter is used, the power consumption of the device increases and the efficiency also decreases. Such a problem has not been particularly examined in the above-mentioned Patent Document 1.

The present disclosure has been made in order to solve such a problem, and an object thereof is an LED drive device capable of avoiding the inability to turn on an LED while suppressing a decrease in the efficiency of the device, a display device including the LED drive device, and an LED. It is to provide a control device of a drive device.

The LED drive device of the present disclosure drives a DC / DC converter configured to supply power to the LED, a current driver configured to regulate the current flowing through the LED, and a DC / DC converter. It includes a configured drive device. The DC / DC converter is an asynchronous rectification type boost chopper circuit including a coil, a first switching element, and a diode. The LED drive device further includes a second switching element connected in parallel with the diode. The second switching element is off when no diode open failure has occurred. When an open failure occurs, the current driver adjusts the current so that the current flowing through the LED is smaller than when no open failure has occurred, and the drive unit synchronizes with the first switching element. Drives the second switching element.

In the above LED drive device, since the DC / DC converter is composed of an asynchronous rectification type chopper circuit, a decrease in the efficiency of the device is suppressed as compared with the case where a synchronous rectification type DC / DC converter is adopted. can do. When an open failure of the diode of the DC / DC converter occurs, the second switching element is driven in synchronization with the first switching element, so that it is possible to avoid the LED from turning off. Further, when an open failure of the diode occurs, the current flowing through the LED is reduced as compared with the case where the open failure does not occur, so that the size of the second switching element can be suppressed.

The size of the second switching element may be smaller than the size of the first switching element. Further, the second switching element may be provided in the drive device.

The LED drive may further include a detector configured to detect the voltage at the anode or cathode of the diode, or the current flowing through the diode. Then, the drive device may determine whether or not an open failure of the diode has occurred based on the output of the detector.

The above diode may be a Schottky barrier diode.
Further, the display device of the present disclosure includes any of the above-mentioned LED drive devices and LEDs driven by the LED drive devices.

Further, the control device of the present disclosure is a control device of an LED drive device. The LED drive includes a DC / DC converter configured to power the LED and a current driver configured to regulate the current flowing through the LED. The DC / DC converter is an asynchronous rectification type boost chopper circuit including a coil, a first switching element, and a diode. The control device includes a second switching element connected in parallel to the diode and a controller. The second switching element is off when no diode open failure has occurred. The controller controls the current driver so that when an open failure occurs, the current flowing through the LED becomes smaller than when an open failure does not occur, and the second switching element synchronizes with the first switching element. It is configured to drive a switching element.

According to the LED drive device and the display device of the present disclosure and the control device of the LED drive device, it is possible to avoid the inability to turn on the LED while suppressing the decrease in the efficiency of the device.

It is a figure which shows the whole structure of the display device which used the LED driver according to the embodiment of this disclosure. It is a timing chart which shows operation example of the LED driver shown in FIG. 1 schematically. It is a flowchart which shows an example of the procedure of the process executed by a controller.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

<LED driver configuration>
FIG. 1 is a diagram showing an overall configuration of a display device using an LED driver according to an embodiment of the present disclosure. With reference to FIG. 1, the display device 1 includes an LED row 10, a DC / DC converter 20, and a drive device 50. The DC / DC converter 20 and the drive device 50 form an LED driver that drives the LED row 10.

The LED row 10 includes a plurality of LEDs 12 connected in series. In this example, one row of LED rows 10 including a plurality of LED 12s more than four is shown, but the number of LED rows may be plural, and the number of LEDs 12 included in each LED row is four. It may be less than one.

The DC / DC converter 20 includes a power supply node 22, a coil 24, a switching element Q1, a diode 26, and a capacitor 28. The coil 24 is connected between the power supply node 22 and the switching element Q1. The switching element Q1 is connected between the coil 24 and the ground node. The gate of the switching element Q1 is connected to the external terminal T2 of the drive device 50. In this example, the switching element Q1 is an N-type MOSFET (Metal Oxide Semiconductor Field Effect Transistor), but may be an NPN-type bipolar transistor or the like.

In the diode 26, the anode is connected to the connection point between the coil 24 and the switching element Q1, and the cathode is connected to the anode side of the LED row 10. In this example, the diode 26 is a Schottky barrier diode (hereinafter referred to as "SBD (Schottky Barrier Diode)"). Since the SBD has a small forward voltage, the forward loss is small, the efficiency is high, and the switching speed is high. It is not essential that the diode 26 is an SBD, and a diode other than the SBD can be adopted. The capacitor 28 is connected between the power line to which the cathode of the SBD 26 is connected and the ground node.

A so-called asynchronous rectification type step-up chopper circuit is formed by the power supply node 22, the coil 24, the switching element Q1, the SBD 26, and the capacitor 28. The switching element Q1 is switched and controlled by the drive device 50, and the electric power supplied from the power supply node 22 is boosted and supplied to the LED row 10.

The drive device 50 includes a current driver 60, a controller 70, a switching element Q2, and a detector 80. The drive device 50 is configured as, for example, an IC (Integrated Circuit) in which each of these elements is integrated. The drive device 50 further includes external terminals T1 to T5 for electrically connecting to an external element.

The current driver 60 includes a switching element 62, a resistance element 64, and an error amplifier 66. The switching element 62 is connected between the external terminal T5 to which the cathode side of the LED row 10 is connected and the resistance element 64. In this example, the switching element 62 is an N-type MOSFET, but may be an NPN-type bipolar transistor or the like. The resistance element 64 is connected between the switching element 62 and the ground node.

The connection point between the switching element 62 and the resistance element 64 is connected to the inverting input end (−) of the error amplifier 66. A reference voltage Vref is applied from the controller 70 to the non-inverting input terminal (+) of the error amplifier 66. The output end of the error amplifier 66 is connected to the gate of the switching element 62.

A detection signal (voltage) obtained by converting the current flowing through the switching element 62 (that is, the current flowing through the LED row 10) into a voltage by the resistance element 64 is input to the inverting input terminal (−) of the error amplifier 66. The reference voltage Vref input to the non-inverting input end (+) of the error amplifier 66 is a signal obtained by converting the target value of the current flowing through the LED row 10 into a voltage by the resistance value of the resistance element 64.

The error amplifier 66 drives the switching element 62 by outputting a signal obtained by amplifying the difference between the reference voltage Vref and the detection signal (voltage) to the gate of the switching element 62. As a result, the current flowing through the switching element 62, that is, the current flowing through the LED row 10, is adjusted to the current target value corresponding to the reference voltage Vref. The current driver 60 may be provided outside the IC.

The controller 70 receives the voltage Vfb (voltage on the cathode side of the LED row 10) input from the external terminal T5, and drives the DC / DC converter 20 based on the voltage Vfb. Specifically, the controller 70 includes an error amplifier and a PWM (Pulse Width Modulation) circuit (neither of them is shown). The error amplifier amplifies and outputs the difference between the voltage Vfb and the predetermined value so that the voltage Vfb becomes a predetermined value (for example, 0.5 V). The PWM circuit generates a PWM signal based on the output of the error amplifier, and outputs the generated PWM signal to the external terminal T2 to which the gate of the switching element Q1 is connected.

The controller 70 is not limited to the one executed by hardware (electronic circuit), and may be configured by one executed by software. Specifically, the controller 70 is configured to include a CPU (Central Processing Unit), a memory (ROM (Read Only Memory) and RAM (Random Access Memory)), an input / output buffer for inputting / outputting various signals, and the like. You may. The CPU expands the program stored in the ROM into a RAM or the like and executes it. The program stored in the ROM is a program in which the processing procedure of the controller 70 is described. Then, the controller 70 may be configured to execute various processes according to this program.

Further, the controller 70 outputs the reference voltage Vref obtained by converting the target value of the current flowing through the LED row 10 into a voltage by the resistance value of the resistance element 64 to the non-inverting input terminal (+) of the error amplifier 66.

With the above configuration, in this LED driver, the current driver 60 adjusts the current flowing through the LED row 10 to the current target value corresponding to the reference voltage Vref. Further, the DC / DC converter 20 is driven by the controller 70 based on the voltage Vfb so that the voltage Vfb on the cathode side of the LED row 10 becomes a predetermined value. As a result, the current flowing through the LED row 10 is controlled as a target.

<Open failure of SBD26>
When an open failure of the SBD 26 occurs, the current cannot be supplied from the DC / DC converter 20 to the LED row 10, and the LED row 10 cannot be lit. In preparation for such a failure, it is conceivable to configure a synchronous rectification type DC / DC converter in which the SBD 26 is replaced with a switching element in advance, but if the synchronous rectification type is used, the power consumption of the device increases and the efficiency also decreases. To do.

Therefore, in the LED driver according to the present embodiment, the switching element Q2 connected in parallel to the SBD 26 is provided. The switching element Q2 is provided in the drive device 50 and is driven by the controller 70. In this example, the switching element Q2 is a P-type MOSFET, but may be a PNP-type bipolar transistor or the like.

Then, the controller 70 turns off the switching element Q2 when the open failure of the SBD 26 has not occurred. When an open failure of the SBD 26 occurs, the controller 70 switches and drives the switching element Q2 in synchronization with the switching element Q1. Specifically, the controller 70 drives the switching element Q2 in synchronization with the switching element Q1 so that the switching elements Q1 and Q2 are turned on / off in a complementary manner.

When the open failure of the SBD 26 occurs, the controller 70 further lowers the reference voltage Vref output to the current driver 60 as compared with the case where the open failure does not occur. When the magnitude of the current flowing through the LED row 10 is determined by the reference voltage Vref, the reference voltage Vref is lowered to at least the level at which the LED row 10 is lit. The magnitude of such a reference voltage Vref is appropriately determined based on the characteristics, number, connection configuration, and the like of the LEDs 12 constituting the LED row 10.

The open failure of the SBD 26 is determined based on the detection value of the detector 80. The detector 80 is connected to the external terminal T1 to which the anode of the SBD 26 is connected, and detects the voltage Vd (drain voltage of the switching element Q1) of the anode of the SBD 26. The controller 70 receives the detected value of the voltage Vd from the detector 80, and when an abnormal rise in the voltage Vd is observed, it is determined that an open failure has occurred in the SBD 26.

In this example, it is determined whether or not an open failure of the SBD 26 has occurred based on the voltage Vd of the anode of the SBD 26, but instead of the voltage Vd, the voltage of the cathode of the SBD 26 or the current flowing through the SBD 26 is detected. It may be detected by an instrument and the open failure of the SBD 26 may be determined based on the detected value. Specifically, when an abnormal decrease in the voltage of the cathode of the SBD 26 or an abnormal decrease in the current flowing through the SBD 26 is observed, it can be determined that an open failure of the SBD 26 has occurred.

As described above, in the LED driver according to the present embodiment, the DC / DC converter 20 is not configured with the synchronous rectification type DC / DC converter in advance in preparation for the open failure of the SBD 26, but the DC / DC converter 20 is asynchronous. A rectifier type chopper circuit is used, and the DC / DC converter 20 is operated by asynchronous rectification (switching element Q2 is turned off) as long as the SBD 26 does not fail. As a result, it is possible to suppress a decrease in the efficiency of the apparatus as compared with the case where the DC / DC converter 20 is configured by the synchronous rectification type.

Then, when an open failure of the SBD 26 occurs, the switching element Q2 connected in parallel to the SBD 26 is driven in synchronization with the switching element Q1, so that it is possible to avoid the LED row 10 from being unlit. Here, since the reference voltage Vref is lowered to the extent that the LED row 10 is lit, the current flowing through the LED row 10 and thus the switching element Q2 is suppressed. Therefore, the size of the switching element Q2 driven at the time of the open failure of the SBD 26 can be suppressed. Specifically, if the DC / DC converter 20 is configured as a synchronous rectification type, the size of the switching element replacing the SBD 26 can be designed to be the same as the size of the switching element Q1, but the LED according to the present embodiment. According to the driver, the size of the switching element Q2 can be made smaller than the size of the switching element Q1.

FIG. 2 is a timing chart schematically showing an operation example of the LED driver shown in FIG. With reference to FIG. 2, the voltage Vd of the anode of the SBD 26 fluctuates according to the on / off of the switching element Q1, and the voltage Vd rises when the switching element Q1 is turned off.

It is assumed that an open failure of the SBD 26 has occurred at time t1. Before the occurrence of the open failure, the voltage Vd does not exceed the threshold value Vth even if the switching element Q1 is turned off. Before the time t1 when the open failure does not occur, the reference voltage Vref of the current driver 60 is V1, and the switching element Q2 is turned off.

When an open failure of the SBD 26 occurs at time t1, the voltage Vd rises significantly because the energy output from the coil 24 loses its place at the timing when the switching element Q1 is turned off at time t2. Then, when the voltage Vd exceeds the threshold value Vth, it is determined that the open failure of the SBD 26 has occurred, and the open failure flag is turned on at the time t3. This open failure flag remains on until the open failure is resolved by repair (replacement, etc.) of the SBD26.

When the open failure flag is turned on, the LED driver operates in failure mode. That is, the reference voltage Vref of the current driver 60 is lowered from V1 before the occurrence of the open failure to V2 lower than V1. Then, when the reference voltage Vref is lowered, the switching element Q2 is switched and driven in synchronization with the switching element Q1 after the time t4. As a result, it is possible to prevent the LED row 10 from being turned off due to an open failure of the SBD 26.

Although the voltage Vd falls below the threshold value Vth due to the operation of the switching element Q2, the open failure flag is on until the open failure of the SBD 26 is resolved, so that the failure mode is continued and the reference voltage Vref is lowered. And the driving of the switching element Q2 is continued.

FIG. 3 is a flowchart showing an example of a processing procedure executed by the controller 70. The series of processes shown in this flowchart are repeatedly executed at predetermined intervals.

With reference to FIG. 3, the controller 70 determines whether or not the open failure flag of the SBD 26 is on (step S10). When the open failure flag is on (YES in step S10), the controller 70 shifts the process to step S50 (described later).

When it is determined in step S10 that the open failure flag is off (NO in step S10), the controller 70 determines whether the voltage Vd of the anode of the SBD 26 is higher than the threshold value Vth (step S20). .. The voltage Vd is detected by the detector 80 (FIG. 1).

When it is determined in step S20 that the voltage Vd is equal to or less than the threshold value Vth (NO in step S20), the open failure of the SBD 26 has not occurred, and the controller 70 outputs the reference voltage Vref to the current driver 60. Is V1 (default value) (step S30).

On the other hand, when it is determined in step S20 that the voltage Vd is higher than the threshold value Vth (YES in step S20), the controller 70 determines that an open failure of the SBD 26 has occurred and turns on the open failure flag. (Step S40).

When the open failure flag is turned on, the controller 70 sets the reference voltage Vref output to the current driver 60 to V2 (V2 <V1) (step S50). Then, the controller 70 switches and drives the switching element Q2 in synchronization with the switching element Q1 (step S60). As a result, the LED row 10 can be turned on while limiting the current flowing through the LED row 10 and thus the switching element Q2 as compared with the case where the open failure of the SBD 26 does not occur.

As described above, in this embodiment, since the DC / DC converter 20 is configured by the asynchronous rectification type step-up chopper circuit, it is compared with the case where the DC / DC converter 20 is configured by the synchronous rectification type. , It is possible to suppress a decrease in the efficiency of the device. Then, when an open failure of the SBD 26 of the DC / DC converter 20 occurs, the switching element Q2 connected in parallel to the SBD 26 is driven in synchronization with the switching element Q1 of the DC / DC converter 20, so that the LED row 10 It is possible to avoid lighting failure.

Further, when an open failure of the SBD 26 occurs, the reference voltage Vref of the current driver 60 is lowered from the default V1 to V2, and the current flowing through the LED row 10 and thus the switching element Q2 is limited as compared with the case where the open failure does not occur. Will be done. As a result, the size of the switching element Q2 can be suppressed. For example, the size of the switching element Q2 can be made smaller than the size of the switching element Q1, and the increase in the size of the drive device 50 provided with the switching element Q2 can be suppressed.

The display device 1 can be applied to, for example, a light source of a liquid crystal display (LCD), and is particularly suitable as a light source of an in-vehicle display that displays a vehicle driving situation or the like to a driver. According to the display device 1 described above, even if an open failure of the SBD 26 occurs, it is possible to prevent the in-vehicle display from being completely turned off and to perform limp home driving.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the description of the embodiment described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 Display device, 10 LED trains, 20 DC / DC converter, 22 power supply node, 24 coil, 26 SBD, 28 capacitor, 50 drive device, 60 current driver, 62, Q1, Q2 switching element, 64 resistance element, 66 error amplifier , 70 controller, 80 detector, T1 to T5 external terminals.

Claims (7)

A DC / DC converter configured to supply power to the LEDs,
A current driver configured to adjust the current flowing through the LED,
A drive device configured to drive the DC / DC converter is provided.
The DC / DC converter is an asynchronous rectifying type boost chopper circuit including a coil, a first switching element, and a diode, and further.
A second switching element connected in parallel to the diode is provided.
The second switching element is off when the diode open failure has not occurred.
When the open failure occurs,
The current driver adjusts the current so that the current becomes smaller than that in the case where the open failure does not occur.
The drive device is an LED drive device that drives the second switching element in synchronization with the first switching element. The LED drive device according to claim 1, wherein the size of the second switching element is smaller than the size of the first switching element. The LED drive device according to claim 1 or 2, wherein the second switching element is provided in the drive device. Further comprising a detector configured to detect the anode or cathode voltage of the diode or the current flowing through the diode.
The LED drive device according to any one of claims 1 to 3, wherein the drive device determines whether or not the open failure has occurred based on the output of the detector. The LED drive device according to any one of claims 1 to 4, wherein the diode is a Schottky barrier diode. The LED drive device according to any one of claims 1 to 5.
A display device including an LED driven by the LED drive device. It is a control device for LED drive devices.
The LED drive device is
A DC / DC converter configured to supply power to the LEDs,
Including a current driver configured to regulate the current flowing through the LED.
The DC / DC converter is an asynchronous rectification type boost chopper circuit including a coil, a first switching element, and a diode.
The control device
A second switching element connected in parallel to the diode,
Equipped with a controller
The second switching element is off when the diode open failure has not occurred.
The controller controls the current driver so that when the open failure occurs, the current becomes smaller than when the open failure does not occur, and in synchronization with the first switching element. A control device for an LED drive device configured to drive the second switching element.

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