LED control device, image recording device, and LED control method

Abstract

To provide an LED control device capable of detecting a short-circuit fault in an LED in a plurality of LED lighting devices without lighting the LEDs when the short-circuit fault of LEDs is detected.SOLUTION: An LED control device includes an LED, a power source for supplying electric power to the LED, a first adjustment unit for outputting a first voltage of less than a predetermined voltage to the LED, a second adjustment unit for outputting a second voltage equal to or greater than the predetermined voltage to the LED, a switching unit for switching a connection destination of the LED to either the first adjustment unit or the second adjustment unit, a control unit for controlling the connection destination of the switching unit, and a detection circuit for detecting that a current greater than a predetermined range of current values has flowed through a circuit to which the LED is connected when the first adjustment unit is connected to the LED and outputs the first voltage.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an LED control device, and more particularly to a technique for detecting overcurrent such as a short circuit in a plurality of LED lighting devices. [Background technology]

[0002] In display devices that use LEDs as light sources, the desired color is expressed by combining LEDs that emit red (hereafter referred to as R), green (hereafter referred to as G), and blue (hereafter referred to as B) colors, and controlling the brightness of each of the R, G, and B LEDs according to a brightness signal. In such display devices, since one color is expressed by the emission of multiple LEDs, if one of the multiple LEDs or the configuration for that emission breaks down, the color emitted will be different from the desired color.

[0003] Patent document 1 describes a fault detection means that detects a fault in any of the R, G, or B LEDs in an LED assembly composed of R, G, and B, and a current detection means that cuts off the current to all the LEDs and turns them off if the fault detection means detects an LED fault. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-108519 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above document, a fault can be detected only when the LED is emitting light, which causes a problem that the LED may emit light of an unintended color during the period from when the fault is detected until the LED is turned off by cutting off the current.

[0006] An object of the present disclosure is to provide an LED control device that is capable of detecting a fault due to an overcurrent in an LED without turning on the LED. [Means for solving the problem]

[0007] To that end, in the present disclosure, an LED control device includes an LED, a power source that supplies power to the LED, a first adjustment unit that outputs a first voltage less than a predetermined voltage to the LED, a second adjustment unit that outputs a second voltage equal to or greater than the predetermined voltage to the LED, a switching control unit that switches the connection of the LED to either the first adjustment unit or the second adjustment unit, and a detection circuit that detects that a current greater than a predetermined range of current values ​​flows in a circuit to which the LED is connected when the first adjustment unit is connected to the LED by the switching control unit and outputs the first voltage. Effect of the Invention

[0008] As described above, according to the present disclosure, when detecting a fault due to an overcurrent in an LED, the fault can be detected without turning on the LED. [Brief description of the drawings]

[0009] [Figure 1] 1 shows a configuration block diagram of an image recording apparatus to which the present disclosure is applied. [Diagram 2] 1 shows a configuration diagram of an LED control circuit according to a first embodiment of the present disclosure. [Diagram 3] 1 shows a flowchart according to a first embodiment of the present disclosure. [Figure 4] FIG. 13 shows a configuration diagram of an LED control circuit according to a second embodiment of the present disclosure. [Diagram 5] 13 shows a flowchart according to a second embodiment of the present disclosure. [Figure 6] FIG. 13 shows a configuration diagram of an LED control circuit according to a third embodiment of the present disclosure. [Figure 7] 13 shows a flowchart according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The following description of the embodiment is merely an example of the present disclosure, specifically described to the extent possible, in order to satisfy the description requirements (description requirements and enablement requirements) of the specification required by law. Therefore, as described below, the present disclosure is not limited in any way to the specific configurations of the embodiment described below.

[0011] Example 1 FIG. 1 is a block diagram showing the configuration of an image recording device 110 according to this embodiment. The image recording device 110 according to this embodiment includes a CPU 101 and a memory 102. The CPU 101 executes processing according to a program stored in the memory 102 and controls a print control unit 108 and a read control unit 109. The memory 102 is, for example, configured with a combination of volatile storage and non-volatile storage, and the volatile storage is used to temporarily store programs and data, while the non-volatile storage is used to store programs and parameters. The display control unit 105 includes an LED control unit 106 and an operation unit 107. The operation unit 107 is configured with keys and a touch panel, and is used to switch functions and operations of the image recording device 110 by accepting user operations. In addition, the operation unit 107 is provided with a plurality of LEDs for notifying the user of the operation mode and error state of the image recording device 110 by optical display, and the display of these LEDs is controlled by the LED control unit 106. In this embodiment, the LED control unit 106 expresses a desired color by controlling the brightness of each of the R, G, and B LEDs, as described later in FIG. 2. An LED driving power supply 104 is supplied to the LED control unit 106 from a power supply control unit 103 that generates and controls the power supply for the entire circuitry related to the image recording device 110 .

[0012] FIG. 2 is a circuit diagram showing the details of the circuit of the LED control unit 106 in FIG. 1. The LED control unit 106 is configured to have an LED202R that emits red light, an LED202G that emits green light, and an LED202B that emits blue light (hereinafter, each of them is simply referred to as LED202) connected thereto. Furthermore, in the LED control unit 106 of this embodiment, current limiting resistors 203R, 203G, and 203B are connected between the cathodes of the LED202R, LED202G, and LED202B and GND, respectively. In addition, feedback control capacitors 204R, 204G, and 204B are connected to GND at nodes between the LED control circuit 201 and the LED202R, LED202G, and LED202B. The LED control circuit 201 is a circuit that performs constant current control using feedback control for the LED202R, LED202G, and LED202B, and its operation will be described below.

[0013] In the LED control circuit 201, switches (SW) 205R, SW205G, and SW205B are connected to the anode sides of LED202R, LED202G, and LED202B, respectively. SW205R, SW205G, and SW205B switch the circuit connection to either low-dropout regulators (LDO: Low Dropout) 206R, LDO206G, and LDO206B corresponding to the LED control circuit 201, or field-effect transistors (FET) 207B, FET207G, and FET207R corresponding to the LED control circuit 201. In addition, power is supplied from an LED drive power supply 104 to the LDO206R, LDO206G, and LDO206B or the FET207B, FET207G, and FET207R.

[0014] When LED 202 is to be illuminated, SW205R is connected to FET 207R, SW205G is connected to FET 207G, and SW205B is connected to FET 207B. Feedback circuit 208R is connected to FET 207R, Feedback circuit 208G is connected to FET 207G, and Feedback circuit 208B is connected to FET 207B. Feedback circuit 208R monitors the voltage at the cathode terminal of LED 202R, Feedback circuit 208G monitors the voltage at the cathode terminal of LED 202G, and Feedback circuit 208B monitors the voltage at the cathode terminal of LED 202B. Then, the Feedback circuit 208R, the Feedback circuit 208G, and the Feedback circuit 208B operate to turn on the FET 207R, the FET 207G, and the FET 207B, respectively, until the voltage values ​​at the cathode terminals of the LED 202R, the LED 202G, and the LED 202B become equal to or greater than a predetermined voltage value. Also, the Feedback circuit 208R, the Feedback circuit 208G, and the Feedback circuit 208B operate to turn off the FET 207R, the FET 207G, and the FET 207B, respectively, until the voltage values ​​at the cathode terminals of the LED 202R, the LED 202G, and the LED 202B become equal to or less than a predetermined voltage value. In this way, the FETs are repeatedly turned on and off with the predetermined voltage value set as a threshold value, so that the voltage on the cathode side of the LED is kept constant at a predetermined voltage value. In this embodiment, the predetermined voltage value refers to a voltage value that determines the light emission brightness of the LED, and specifically, since the light emission brightness of the LED is determined by the current value flowing through the LED, in this embodiment, it is defined as "current value flowing through the LED = the predetermined voltage value / resistance value of limiting resistor 203." In other words, the FET constitutes a second adjustment unit that outputs a second voltage equal to or higher than the predetermined voltage value to the LED, and the LED light emission brightness can be controlled by setting the predetermined voltage value to a desired voltage value.

[0015] On the other hand, when detecting an LED short circuit, SW205R is connected to the LDO206R side, SW205G is connected to the LDO206G side, and SW205B is connected to the LDO206B side. The LDO206R, LDO206G, and LDO206B can vary their output voltages, and thus, when detecting an LED short circuit, the output voltages are output as voltages (first voltages) less than the Vf (forward voltages required to make the LED202 emit light) of the LED202R, LED202G, and LED202B, respectively. In this respect, the LDO206R, LDO206G, and LDO206B are first voltage adjustment units. In this state, the voltages output from the LDO206R, LDO206G, and LDO206B do not cause the LED202R, LED202G, and LED202B to emit light. However, if any of the LEDs 202R, 202G, and 202B, or the capacitors 204R, 204G, and 204B, which are circuit elements for driving the LEDs, is short-circuited, a current (overcurrent) larger than that in the normal case is generated. The short-circuit detection circuit 209 can detect a short circuit by detecting that a current of 0A flows normally and a current of a specific threshold or more flows due to a short-circuit failure. The short-circuit detection circuit here is generally realized by an overcurrent detection circuit or a low-voltage malfunction prevention circuit. In the above-mentioned embodiment, the LDO (first adjustment unit) and the FET (second adjustment unit) are separate control elements, and the respective outputs are switched by a SW, but the application of the present invention is not limited to this form. The LDO and the FET may be configured to output the respective voltages as one control element. That is, this one control element has a function of selectively adjusting the power supply voltage to a voltage Vf for emitting light from the LED and a voltage smaller than the voltage Vf, and outputs the respective voltages according to the emission of the LED and the detection of a short circuit.

[0016] As described above, the LED control circuit of this embodiment is capable of detecting an LED short circuit without emitting light from the LED. During normal light emission, a current of about the threshold value flows through the circuit, so it is preferable to disable the short circuit detection function during normal light emission to prevent erroneous detection. That is, as will be described later with reference to FIG. 3, short circuit detection is performed when the image recording device 110 changes from an OFF state to an ON state.

[0017] The CPU 101 serves as a controller for the LED control circuit 201. The CPU 101 switches SW205R, SW205G, and SW205B, sets predetermined values ​​for the feedback circuits 208R, 208G, and 208B, and sets output voltage values ​​for LDO 206R, LDO 206G, and LDO 206B. Furthermore, the CPU 101 receives a notification of a short circuit detection result from the LED control circuit 201. The memory 102 is connected to the CPU 101, and records the short circuit detection result received by the CPU 101.

[0018] A flow for detecting a short circuit of the LED 202 and lighting the LED in this embodiment will be described below with reference to FIG. 3. The timing for executing the short circuit detection flow in FIG. 3 is preferably the timing when the image recording device 110 shown in FIG. 1 changes from an OFF state to an ON state. Step S1 is a step for checking "whether there is a short circuit detection history by referring to the memory." Specifically, the relevant area of ​​the memory 112 is referenced to check whether there is a history of a previous short circuit detection. If Yes, no further operation is performed and the flow ends. If No, in step S2, SW205R is connected to LDO 206R, SW205G is connected to LDO 206G, and SW205B is connected to LDO 206B. Next, step S3 is a step for outputting voltages set as voltages lower than the Vf of each of LED 202R, LED 202G, and LED 202B from LDO 206R, LDO 206G, and LDO 206B.

[0019] In step S4, it is confirmed whether a short circuit has been detected in any of the LED circuits. If a short circuit is detected by the short circuit detection circuit 209, in step S5, the LED control circuit 201 notifies the CPU 101 that a short circuit has been detected. Next, in step S6, all voltage outputs from LDO 206R, LDO 206G, and LDO 206B are stopped, and in step S7, the CPU 101 stores history information of the short circuit detection occurrence in the relevant area of ​​the memory 112.

[0020] If no short circuit is detected by short circuit detection circuit 209 in step S4, predetermined voltages are set for feedback circuits 208R, 208G, and 208B in step S8. Next, in step S9, SW205R is connected to FET 207R, SW205G is connected to FET 207G, and SW205B is connected to FET 207B. Next, in step S10, a voltage greater than Vf is applied so that FET 207B, FET 207G, and FET 207R are turned ON, and LED 202R, LED 202G, and LED 202B start emitting light.

[0021] In addition, when the short circuit detection history is stored in the memory, such as when the answer is YES in step S1 or after step S7, a notification of an abnormality may be displayed on a display unit provided in the image recording device 110 or on an external terminal (not shown) operated by the user.

[0022] The above short circuit detection is performed sequentially for each RGB LED circuit, making it possible to identify the LED circuit that is short-circuited. On the other hand, by detecting all RGB circuits simultaneously, it is possible to check only the presence or absence of a short circuit and shorten the detection time. When detecting all RGB circuits simultaneously, LDO206R, LDO206G, and LDO206B are output simultaneously, and the short circuit detection circuit is used to detect the current value when a voltage is applied to each LED. In this case, if all LEDs are not short-circuited, the detection value is 0A, and if one or more LEDs are short-circuited, a current above the threshold flows, making it possible to detect a short circuit. Furthermore, if a short circuit detection circuit is provided individually for each LED circuit, it is possible to identify the LED that is short-circuited and simultaneously detect a short circuit in all RGB circuits.

[0023] Example 2 This chapter has many points in common with the first embodiment, so only the differences in configuration and operation from the first embodiment will be described with reference to the drawings.

[0024] 4 is a circuit diagram showing the details of the circuit of the LED control unit 126 in the second embodiment corresponding to the LED control unit 106 in FIG. 1. The difference from the first embodiment is that the LED driving power supplies 306R, 306G, and 306B are connected to SW205R, SW205G, and SW205B in the LED control circuit 201, respectively, and the LDO206R, LDO206G, and LDO206B that existed in the first embodiment are not present. In addition, the LED driving power supplies 306R, 306G, and 306B in the second embodiment are variable voltage sources. When an LED short circuit is detected in the second embodiment, SW205R is directly connected to the LED driving power supply 306R, SW205G is directly connected to the LED driving power supply 306G, and SW205B is directly connected to the LED driving power supply 306B. The LED driving power supplies 306R, 306G, and 306B function as a first adjustment unit and output a voltage lower than the Vf of each LED, making it possible to detect an LED short circuit without causing the LED to emit light by the same means as described in embodiment 1. On the other hand, when causing the LED to emit light, the LED driving power supplies 306R, 306G, and 306B function as a second adjustment unit together with the FET and output a voltage higher than the Vf of each LED.

[0025] The flow for detecting a short circuit of an LED and turning on an LED in the second embodiment will be described below with reference to FIG. 5, focusing only on the difference from the first embodiment. The timing of the short circuit detection flow in FIG. 5 is preferably performed when the image recording device 110 shown in FIG. 1 changes from an OFF state to an ON state, as in the first embodiment. If the result is No in step S1, in step S2, SW205R is directly connected to the LED driving power supply 306R, SW205G is directly connected to the LED driving power supply 306G, and SW205B is directly connected to the LED driving power supply 306B. In step S3b, a voltage lower than the Vf of each LED is output from each of the LED driving power supplies 306R, 306G, and 306B. If a short circuit is detected by the short circuit detection circuit 209 in step S4, the LED control circuit 201 notifies the CPU 101 that a short circuit has been detected in step S5. Next, in step S6b, the voltage output of all of the LED driving power supplies 306R, 306G, and 306B is stopped, and in step S7, the CPU 101 stores history information of the short circuit detection occurrence in the relevant area of ​​the memory 112.

[0026] If no short circuit is detected by the short circuit detection circuit 209 in step S4, a predetermined voltage is set for the feedback circuits 208R, 208G, and 208B in step S8, as in the first embodiment. Next, in step S9, SW205R is connected to FET207R, SW205G is connected to FET207G, and SW205B is connected to FET207B, and in step S11, a voltage higher than the Vf of each LED is output from each of the LED driving power supplies 306R, 306G, and 306B. After that, in step S10, FET207B, FET207G, and FET207R are turned ON, thereby starting the emission of LED202R, LED202G, and LED202B.

[0027] Example 3 This chapter has many points in common with the first embodiment, so only the differences in configuration and operation from the first embodiment will be described with reference to the drawings.

[0028] FIG. 6 is a circuit diagram showing the details of the circuit of the LED control unit 136 in the third embodiment corresponding to FIG. 1. The difference from the first embodiment is that the feedback circuit, the feedback control capacitor, and the FET are used to perform constant current control of the LED in the first embodiment, but the constant current sources 407R, 407G, and 407B are used in the third embodiment. The short circuit detection of the LED 202 is performed in the same manner as the first embodiment, and the LDO constitutes a first adjustment unit that outputs the output voltage value to a first voltage less than Vf of the LED 202R, the LED 202G, and the LED 202B, respectively. When the LED emits light, the constant current sources 407R, 407G, and 407B output a current according to a predetermined light emission brightness as a second adjustment unit so that a voltage of Vf or more is output to each LED.

[0029] The flow for detecting a short circuit of an LED and turning on an LED in the third embodiment will be described below with reference to FIG. 7, focusing only on the difference from the first embodiment. The flow for detecting a short circuit of an LED and turning on an LED in the present embodiment will be described. As for the timing of performing the short circuit detection flow in FIG. 7, it is desirable to perform it at the timing when the image recording device 110 shown in FIG. 1 changes from the OFF state to the ON state, as in the first embodiment. As a difference from the first embodiment, after performing the short circuit detection in steps S1 to S4, the current value of each constant current source is set in step S8b. Next, in step S9b, SW205R is connected to the constant current source 407R, SW205G is connected to the constant current source 407G, and SW205B is connected to the constant current source 407B, and in step S10, current is output from each constant current source to each LED, thereby starting the emission of the LED.

[0030] <<Other embodiments>> The present disclosure includes configurations typified by the following recording apparatus example and recording apparatus control method example.

[0031] <Configuration 1> LEDs and a power source for powering the LED; a first adjustment unit that outputs a first voltage that is less than a predetermined voltage to the LED; a second adjustment unit that outputs a second voltage equal to or higher than the predetermined voltage to the LED; a switching control unit for switching a connection destination of the LED to either the first adjustment unit or the second adjustment unit; a detection circuit that detects that a current having a value larger than a predetermined range of current values ​​flows through a circuit to which the LED is connected when the first adjustment unit is connected to the LED by the switching control unit and outputs the first voltage; An LED control device comprising:

[0032] <Configuration 2> 2. The LED control device according to claim 1, wherein the LED is an LED complex including a plurality of LED elements.

[0033] <Configuration 3> 3. The LED control device according to configuration 1 or 2, wherein the first adjustment unit is a low-loss regulator or a variable voltage source.

[0034] <Configuration 4> 4. The LED control device according to any one of configurations 1 to 3, wherein the predetermined voltage is a forward voltage of the LED.

[0035] <Component 5> 5. The LED control device according to any one of configurations 1 to 4, wherein the second adjustment section is a field effect transistor.

[0036] <Component 6> 6. The LED control device according to any one of configurations 1 to 5, wherein the detection circuit is connected between the switching unit and the LED.

[0037] <Component 7> a storage unit that stores a detection result by the detection circuit, The LED control device according to any one of configurations 1 to 6, wherein the control unit does not apply a voltage to the LED control device when the memory unit has a history of a current having a value larger than the predetermined range of current values ​​flowing through a circuit to which the LED is connected.

[0038] <Component 8> 8. The LED control device according to any one of configurations 1 to 7, wherein the LED is connected to the second adjustment unit and emits light when a second voltage equal to or higher than the predetermined voltage is applied to the LED.

[0039] <Component 9> An LED control device according to any one of claims 1 to 8; An image recording device comprising a recording unit for recording on a recording medium.

[0040] <Component 10> The image recording device according to configuration 8, characterized in that when the first adjustment unit is connected to the LED when the power supply of the image recording device is started up and the first voltage is output, a current having a value greater than a predetermined range of current values ​​flows through a circuit to which the LED is connected.

[0041] <Component 11> providing power to the LED; a first adjustment step in which a first adjustment unit is connected to the LED and outputs a voltage less than a predetermined voltage to the LED; a detection step of detecting whether a current having a value larger than a predetermined range of current values ​​flows through a circuit to which the LED is connected when the first voltage is output; a second adjustment step of switching a connection destination of the LED to a second adjustment unit and outputting a voltage equal to or higher than the predetermined voltage to the LED; An LED control method comprising: [Explanation of symbols]

[0042] 101 CPU 102 Memory 103 Power supply control unit 104 LED drive power supply 105 Display control unit 106 LED control unit 107 Operation section 108 Printing control unit 109 Reading control unit 110 Image recording device 201 LED control circuit 202R, 202G, 202B LEDs 203R, 203G, 203B Limiting Resistor 204R, 204G, 204B Feedback control capacitors 205R, 205G, 205B Switches 206R, 206G, 206B LDOs 207R, 207G, 207B FETs 208R, 208G, 208B Feedback circuit 209 Short circuit detection circuit 306R, 306G, 306B LED drive power supply 407R, 407G, 407B constant current source

Claims

1. LEDs, a power source for supplying power to the LED; a first adjustment unit that outputs a first voltage that is less than a predetermined voltage to the LED; a second adjustment unit that outputs a second voltage equal to or higher than the predetermined voltage to the LED; a switching control unit for switching a connection destination of the LED to either the first adjustment unit or the second adjustment unit; a detection circuit that detects that a current having a value larger than a predetermined range of current values ​​flows through a circuit to which the LED is connected when the first adjustment unit is connected to the LED by the switching control unit and outputs the first voltage; An LED control device comprising:

2. 2. The LED control device according to claim 1, wherein the LED is an LED complex including a plurality of LED elements.

3. 2 . The LED control device according to claim 1 , wherein the first adjustment unit is a low-loss regulator or a variable voltage source.

4. 2. The LED control device according to claim 1, wherein the predetermined voltage is a forward voltage of the LED.

5. The LED control device according to claim 1 , wherein the second adjustment unit is a field effect transistor.

6. The LED control device according to claim 1 , wherein the detection circuit is connected between the switching unit and the LED.

7. a storage unit that stores a detection result by the detection circuit, 2. The LED control device according to claim 1, wherein the control unit does not apply a voltage to the LED control device when the memory unit has a history of a current greater than the predetermined range of current values ​​flowing through a circuit to which the LED is connected.

8. The LED control device according to claim 1 , wherein the LED is connected to the second adjustment unit and emits light when a second voltage equal to or higher than the predetermined voltage is applied to the LED.

9. An LED control device according to claim 1 ; An image recording device comprising a recording unit for recording on a recording medium.

10. The image recording device according to claim 9, characterized in that the first adjustment unit is connected to the LED when the power supply of the image recording device is turned on, and when the first voltage is output, it detects that a current greater than a predetermined range of current values ​​flows in a circuit to which the LED is connected.

11. providing power to the LED; a first adjusting step of connecting a first adjusting unit to the LED and outputting a first voltage that is less than a predetermined voltage to the LED; a detection step of detecting whether a current having a value larger than a predetermined range of current values ​​flows through a circuit to which the LED is connected when the first voltage is output; a second adjustment step of switching a connection destination of the LED to a second adjustment unit and outputting a second voltage equal to or higher than the predetermined voltage to the LED; An LED control method comprising:

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