LED Driver

Abstract

To provide an LED driver that can reduce component damage while ensuring stable operation of the converter. [Solution] The LED driver according to this embodiment comprises a controller, a bypass path, and a voltage detection unit. The controller controls a cutoff switch that cuts off the input of the power supply voltage to a boost circuit that boosts the power supply voltage and outputs it to the LED. The bypass path is connected to the power supply and is connected to the LED, bypassing the cutoff switch. The voltage detection unit detects the bypass voltage, which is the voltage of the bypass path. If the bypass voltage detected by the voltage detection unit during the period when the cutoff switch is off is below a threshold, the controller determines that there is a current abnormality and continues to keep the cutoff switch off.

Description

Technical Field

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[0001] The present invention relates to an LED driver.

Background Art

[0002] Conventionally, an LED (Light-Emitting Diode) configured as a backlight is known to control the switching of a converter to maintain a driving current supplied thereto at a target value (see, for example, Patent Document 1). In Patent Document 1, a technique is disclosed in which, during the operation of a converter, the current flowing through an LED is monitored, and when the current exceeds an overcurrent threshold value, a cutoff switch provided at the input stage of the converter is cut off.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] To solve the above-mentioned problems and achieve the objective, the LED driver according to the present invention comprises a controller, a bypass path, and a voltage detection unit. The controller controls a cutoff switch that cuts off the input of the power supply voltage to a boost circuit that boosts the power supply voltage and outputs it to the LED. The bypass path is connected to the power supply and is connected to the LED, bypassing the cutoff switch. The voltage detection unit detects the bypass voltage, which is the voltage of the bypass path. If the bypass voltage detected by the voltage detection unit during the period when the cutoff switch is off is below a threshold, the controller determines that there is a current abnormality and continues the off state of the cutoff switch. [Effects of the Invention]

[0007] According to the present invention, by detecting the bypass voltage during the period when the cutoff switch is off, a current increase due to a power supply output abnormality can be detected as a current abnormality. Furthermore, by providing a bypass path for voltage detection, it becomes unnecessary to set a low threshold for overcurrent abnormalities used during the operation of the converter (boost circuit), i.e., when the cutoff switch is on. In other words, according to the present invention, it is possible to reduce component damage while ensuring stable operation of the converter. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows an example of the configuration of an LED control system according to the first embodiment. [Figure 2] Figure 2 shows an example configuration of the LED control system according to the second embodiment. [Modes for carrying out the invention]

[0009] The LED driver according to the embodiment will be described in detail below with reference to the attached drawings. However, the present invention is not limited to the embodiments shown below. Furthermore, Figure 1 shows the first embodiment, and Figure 2 shows the second embodiment.

[0010] In the following, an abnormality in which the ground connection is made via resistor 300 (see Figure 1) on the anode side of LED arrays L1 to L4 (see Figure 1) will be referred to as a "current abnormality," and an abnormality in which the ground connection is not made via the component of resistor 300 (i.e., a ground fault) will be referred to as an "overcurrent abnormality."

[0011] First, the configuration and operation of the LED driver according to the first embodiment will be described using Figure 1. Figure 1 is a diagram showing an example of the configuration of the LED control system according to the first embodiment. The LED control system S shown in Figure 1 is mounted on a vehicle, for example, and controls the drive current to the LEDs that are the backlights of the in-vehicle display.

[0012] As shown in Figure 1, the LED control system S comprises an LED driver 1, a boost circuit 10, and multiple LED rows L1 to L4.

[0013] The boost circuit 10 is a switching regulator type boost circuit that boosts the power supply voltage VIN and applies the generated drive voltage to the LED array L1 to L4. Specifically, the boost circuit 10 comprises a coil 11, a diode 12, a first capacitor 13, and a second capacitor 14. One end of the coil 11 is connected to the power supply voltage VIN, and the other end is connected to the anode of the diode 12. The cathode of the diode 12 is connected to the LED array L1 to L4, the first capacitor 13, and the second capacitor 14. The first capacitor 13 is a polarized capacitor, positioned on the diode 12 side relative to the second capacitor 14, with one end connected to the cathode of the diode 12 and the other end connected to ground. The second capacitor 14 is positioned on the LED array L1 to L4 side relative to the first capacitor 13, with one end connected to the cathode of the diode 12 and the other end connected to ground. The boost circuit 10 generates the drive voltage by boosting the power supply voltage VIN through switching control of the LED driver 1.

[0014] Furthermore, a detection resistor 100 and a cutoff switch 200 are provided on the input side of the boost circuit 10. The detection resistor 100 is a shunt resistor. In other words, the LED driver 1 detects the current flowing through the detection resistor 100 from the potential difference across the detection resistor 100.

[0015] The cutoff switch 200 is a switch that cuts off the input of the power supply voltage VIN to the boost circuit 10. The cutoff switch 200 is cut off by the LED driver 1 when the current flowing through the detection resistor 100 exceeds the overcurrent threshold.

[0016] The LED driver 1 comprises a controller 2 and a bypass path 3. The controller 2 comprises a protection unit 21, a boost control unit 22, a voltage detection unit 23, and a constant current control unit 24.

[0017] Controller 2 includes a microcomputer with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM, and various circuits. Controller 2 controls the operation of the entire LED driver 1 by having the CPU execute a program stored in ROM, using RAM as a workspace. Controller 2 may be composed of hardware such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), either partially or entirely.

[0018] Bypass path 3 is a path that bypasses the cutoff switch 200. Specifically, one end of bypass path 3 is connected between the power supply (not shown) and the input side of the detection resistor 100 (the input side of the cutoff switch 200), and the other end is connected to the cathode of the diode 12 (the output side of the boost circuit 10). The other end of bypass path 3 is connected to the input side of the resistor 400. As shown in Figure 1, a constant current source 27 is provided on the bypass path 3. By providing a constant current source 27 on the bypass path 3 in this way, a constant current can be supplied to the bypass path 3, thereby stabilizing the voltage detected by the voltage detection unit 23. This stabilizes the detection accuracy when detecting current abnormalities from the voltage detected by the voltage detection unit 23, which will be described later.

[0019] The LED control system S also includes resistors 400 and 500. Resistors 400 and 500 are connected in series. The input side of resistor 400 is connected to the other end of the bypass path 3, and its output side is connected to the input side of resistor 500. The output side of resistor 500 is connected to ground.

[0020] In addition, the LED driver 1 includes a switch 25, a detection resistor 26, and a switch 28. The switch 25 is an N-type MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Its drain is connected between the coil 11 and the diode 12 (i.e., the switch node), and its source is connected to one end of the detection resistor 26. The switch 25 controls the boosting operation of the boost circuit 10 by being switched by the boost control unit 22. The detection resistor 26 is a shunt resistor whose other end is connected to the ground. The boost control unit 22 detects the current flowing during the period when the switch 25 is conducting based on the potential difference across both ends of the detection resistor 26. The switch 28 is an N-type MOSFET. Its drain is connected to the device to which the FAIL signal is sent, and its source is connected to the ground.

[0021] Next, the operations of each part of the controller 2 will be described.

[0022] The protection unit 21 performs protection to prevent an overcurrent from flowing through the boost circuit 10 or the LED arrays L1 to L4 by controlling the cutoff switch 200. Specifically, when the current detected from the detection resistor 100 is greater than or equal to the overcurrent threshold during the period when the cutoff switch 200 is in the on state, the protection unit 21 switches the cutoff switch 200 to the off state to prevent an overcurrent from flowing through the boost circuit 10. In addition, the protection unit 21 detects the voltage value obtained by dividing the drive voltage generated by the boost circuit 10 by the resistors 400 and 500, detects an abnormality in the boosting of the boost circuit 10 based on the detected voltage value, and turns off the cutoff switch 200 when an abnormality in the boosting is detected.

[0023] Also, the protection unit 21 detects a current abnormality based on the voltage of the bypass path 3 detected by the voltage detection unit 23 during the period when the cutoff switch 200 is in the off state. Specifically, when the voltage detected by the voltage detection unit 23 is less than the threshold value, the protection unit 21 detects a current abnormality and continues the off state of the cutoff switch 200. More specifically, when the input sides of the LED arrays L1 to L4 are connected to the ground via the resistor 300, even when the cutoff switch 200 is in the off state, current leaks and flows through the bypass path 3. That is, the protection unit 21 detects a current abnormality assuming that current leakage has occurred in the LED arrays L1 to L4 by detecting the voltage of the bypass path 3 by the voltage detection unit 23. Thus, in the present disclosure, by detecting the bypass voltage during the period when the cutoff switch 200 is in the off state, it is possible to detect an increase in current due to an abnormal output of the power supply as a current abnormality. Also, by providing the bypass path 3 for detecting the voltage, it is not necessary to set a low threshold value for overcurrent abnormality used during the operation of the boost circuit 10, that is, when the cutoff switch 200 is in the on state. That is, according to the present disclosure, while the converter (boost circuit 10) is operating stably, component damage can be reduced.

[0024] Also, when no current leakage occurs, that is, when the input sides of the LED arrays L1 to L4 are not connected to the ground via the resistor 300, the LED arrays L1 to L4 are not lit, and since the resistance values of the resistors 400 and 500 are large (for example, 500 kΩ or more in total), the current flowing through the bypass path 3 becomes approximately zero. That is, during the period when the cutoff switch 200 is in the off state, if the voltage of the bypass path 3 detected by the voltage detection unit 23 is less than the threshold value, the protection unit 21 determines that it is normal (no current abnormality) and switches the cutoff switch 200 to the on state.

[0025] When the protection unit 21 detects an overcurrent abnormality, a voltage boost abnormality, or a current abnormality, it turns on the switch 28 to notify the outside of a FAIL signal indicating the occurrence of an abnormality. In other words, the protection unit 21 notifies the outside of the determination result of the overcurrent abnormality, voltage boost abnormality, or current abnormality. As a result, the protection unit 21 can notify the outside of not only abnormalities such as overcurrent abnormalities and voltage boost abnormalities, but also current abnormalities, which are current increases that are not determined to be overcurrent abnormalities.

[0026] The boost control unit 22 controls the boost operation of the boost circuit 10 by controlling the switching of the switch 25. The boost control unit 22 also detects the current flowing through the detection resistor 26 and performs switching control based on the detected current.

[0027] The voltage detection unit 23 detects the voltage in the bypass path 3. Specifically, the voltage detection unit 23 is connected to the output side of the constant current source 27. The voltage detection unit 23 outputs the detected voltage to the protection unit 21.

[0028] The constant current control unit 24 is connected to the output side of each of the LED rows L1 to L4 and controls the current so that a constant current flows through each of the LED rows L1 to L4.

[0029] Next, a second embodiment will be described using Figure 2. Figure 2 is a diagram showing an example configuration of the LED control system according to the second embodiment. The second embodiment described below will be explained focusing on the differences from the first embodiment.

[0030] As shown in Figure 2, in the second embodiment, the connection point on the output side of the bypass path 3 differs from that of the first embodiment. Specifically, in the second embodiment, one end of the bypass path 3 is connected between the power supply (not shown) and the input side of the detection resistor 100 (the input side of the cutoff switch 200), and the other end is connected to the anode of the diode 12 (the switch node of the boost circuit 10).

[0031] In other words, in the second embodiment, the bypass path 3 is connected to the drain of the switch 25 inside the LED driver 1. That is, in the second embodiment, the LED driver 1 does not require a terminal to connect the bypass path 3. On the other hand, in the first embodiment, the LED driver 1 requires an output terminal to bring the output side of the bypass path 3 outside the LED driver 1 in order to connect one end to the resistor 400. Thus, in the second embodiment, the LED driver 1 can reduce the number of output terminals by connecting the bypass path 3 to the switch node of the boost circuit 10.

[0032] In the second embodiment, the voltage detected by the voltage detection unit 23 is higher than that of the first embodiment by the amount of the voltage drop across the diode 12. That is, in the second embodiment, the threshold value for detecting current abnormalities, which is compared with the voltage detected by the voltage detection unit 23, is set to a value higher by the amount of the voltage drop across the diode 12.

[0033] Furthermore, as shown in Figure 2, in the second embodiment, a resistor 29 is provided in the bypass path 3 instead of the constant current source 27. In other words, in the second embodiment, by providing a resistor 29 in the bypass path 3, the current flowing through the bypass path 3 can be detected with a simple circuit configuration.

[0034] In the second embodiment, a configuration in which the resistor 29 is provided in the bypass path 3 is shown, but the constant current source 27 may also be provided in the bypass path 3. Also, in the first embodiment, the resistor 29 may be provided in the bypass path 3 instead of the constant current source 27.

[0035] Furthermore, as shown in Figure 2, in the second embodiment, the gate voltage output from the protection unit 21 to the cutoff switch 200 is also input to the voltage detection unit 23. As a result, the voltage detection unit 23 can detect when the cutoff switch 200 is in the off state, and can perform voltage detection processing with high accuracy when the cutoff switch 200 is in the off state.

[0036] In the first embodiment, as in the second embodiment, the gate voltage output from the protection unit 21 to the cutoff switch 200 may also be input to the voltage detection unit 23.

[0037] Furthermore, in the first and second embodiments described above, the timing for detecting a current abnormality using the resistor 300 is preferably the timing of the startup process performed when the LED control system S is started. The startup process is a process that switches the cutoff switch 200 from the off state to the on state, or performs an abnormality detection check process for the LED control system S. Specifically, for example, in the startup process performed when the vehicle ignition is turned on and the LED control system S is started, the controller 2 performs a current abnormality determination process before switching the cutoff switch 200 from the off state to the on state. By doing so, the current abnormality can be detected before the cutoff switch 200 is turned on by the startup process, and the off state of the cutoff switch 200 can be maintained even after the startup process.

[0038] As described above, the LED driver 1 according to this embodiment includes a controller 2, a bypass path 3, and a voltage detection unit 23. The controller 2 controls a cutoff switch 200 that cuts off the input of the power supply voltage VIN to a boost circuit 10 that boosts the power supply voltage VIN and outputs it to LEDs (LED rows L1 to L4). The bypass path 3 is connected to the power supply and bypasses the cutoff switch 200 to connect to the LEDs. The voltage detection unit 23 detects the bypass voltage, which is the voltage of the bypass path 3. If the bypass voltage detected by the voltage detection unit 23 during the period when the cutoff switch 200 is off is below a threshold, the controller 2 determines that there is a current abnormality and continues to keep the cutoff switch 200 off.

[0039] According to this disclosure, by detecting the bypass voltage during the period when the cutoff switch is off, a current increase due to a power supply output abnormality can be detected as a current abnormality. Furthermore, by providing a bypass path 3 for voltage detection, it becomes unnecessary to set a low threshold for overcurrent abnormalities used during the operation of the converter (boost circuit 10), i.e., when the cutoff switch 200 is on. In other words, according to this disclosure, component damage can be reduced while the boost circuit 10 operates stably.

[0040] Further effects and modifications can be readily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents. [Explanation of symbols]

[0041] 1 LED driver 2 Controllers 3 Bypass Route 10 Boost Circuit 11 coils 12 diodes 13. First Capacitor 14. Second Capacitor 21 Protection Department 22 Boost Control Unit 23 Voltage detection unit 24 Constant Current Control Unit 25, 28 switches 26 detection resistors 27 Constant current source 29, 300, 400, 500 resistors 100 detection resistor 200 Cut-off switch L1~L4 LED row S LED control system

Claims

1. A controller that controls a cutoff switch that cuts off the input of the power supply voltage to a boost circuit that increases the power supply voltage and outputs it to an LED, A bypass path connected to the power supply, bypassing the cutoff switch and connecting to the LED, A voltage detection unit that detects the bypass voltage, which is the voltage of the bypass path, Equipped with, The aforementioned controller, If the bypass voltage detected by the voltage detection unit during the period when the cutoff switch is in the off state is below a threshold, it is determined to be a current abnormality and the cutoff switch remains in the off state. LED driver.

2. The aforementioned bypass route is The input side of the cutoff switch and the output side of the boost circuit are connected. The LED driver according to claim 1.

3. The aforementioned boost circuit is a switching regulator type boost circuit. The aforementioned controller, The boost circuit is operated by performing switching control of the boost circuit. The aforementioned bypass route is The input side of the cutoff switch and the switch node of the boost circuit are connected. The LED driver according to claim 1.

4. The aforementioned bypass route is Having a constant current source The LED driver according to claim 1.

5. The aforementioned bypass route is Resistant The LED driver according to claim 1.

6. The aforementioned controller, In the startup process performed at startup, the current abnormality determination process is performed before switching the cutoff switch from the off state to the on state. The LED driver according to claim 1.

7. The aforementioned controller, If the current abnormality is detected, the cutoff switch will remain in the off state and the result of the current abnormality detection will be notified to an external source. The LED driver according to claim 1.

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