Lighting control device

Abstract

To realize changeover between a main control circuit and a backup circuit of a lighting control device with a simple circuit configuration.SOLUTION: A lighting control device 10 includes a main control circuit 12 and a backup circuit 13, for controlling a semiconductor switch 11. The backup circuit 13 includes: a first switch element 131 connected to a power supply; a first resistance element 132 connected between the first switch element 131 and an output terminal of the main control circuit 12; and a second resistance element 133 connected between the output terminal of the main control circuit 12 and a reference voltage terminal. Resistance values of the first resistance element 132 and the second resistance element 133 are set so that the main control circuit 12 changes over on / off of the semiconductor switch 11 with a priority higher than the backup circuit 13. If abnormality occurs in the main control circuit 12, an output impedance of the main control circuit 12 becomes higher and the on / off of the semiconductor switch 11 is changed over by the backup circuit 13.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a lighting control device that controls the lighting of a light source. [Background technology]

[0002] For example, there is known a system in which on / off control of a semiconductor switch that supplies power to a load such as a vehicle headlight is performed by a microcomputer as a normal control circuit and a backup circuit as a redundant control circuit (for example, Patent Document 1 listed below).

[0003] In the system of Patent Document 1, the microcomputer has an overcurrent protection function that turns off the semiconductor switch when an overcurrent occurs in the load. In addition, when the overcurrent protection function of the microcomputer is working, the backup circuit prohibits the semiconductor switch from being turned on. This prevents the overcurrent protection function from being disabled by the backup circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2009 / 128525 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to achieve the above operation, the system of Patent Document 1 controls the semiconductor switch by the logical sum (OR) of the output signal of the microcomputer and the output signal of the backup circuit, and inputs to the backup circuit the logical product (AND) of the control signal of the semiconductor switch and the abnormality detection signal of the microcomputer. As such, the system of Patent Document 1 requires logic circuits (OR circuits and AND circuits), which complicates the circuitry and causes problems such as increased manufacturing costs.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to realize switching between a main control circuit and a backup circuit with a simple circuit configuration in a lighting control device in which a semiconductor switch that supplies power to a light source is controlled by a main control circuit and a backup circuit. [Means for solving the problem]

[0007] A lighting control device according to the present disclosure includes a semiconductor switch that supplies power to a light source, a main control circuit that controls the voltage of a control terminal of the semiconductor switch based on a first input signal, and a backup circuit that controls the voltage of the control terminal of the semiconductor switch based on a second input signal. The backup circuit includes a first switch element connected to a power source and controlled based on the second input signal, a first resistive element connected between the first switch element and an output terminal of the main control circuit, and a second resistive element connected between the output terminal of the main control circuit and a reference potential terminal. The resistance values ​​of the first resistive element and the second resistive element are set so that the main control circuit switches the semiconductor switch on and off with priority over the backup circuit. When an abnormality occurs in the main control circuit, the output impedance of the main control circuit increases, and the semiconductor switch is switched on and off by the backup circuit. Effect of the Invention

[0008] In the lighting control device according to the present disclosure, switching between the main control circuit and the backup circuit can be achieved with a simple circuit configuration that does not require a logic circuit. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a configuration of a lighting control system according to a first embodiment. [Diagram 2] 4 is a diagram for explaining the operation of the lighting control device according to the first embodiment. FIG. [Diagram 3] 4 is a diagram for explaining the operation of the lighting control device according to the first embodiment. FIG. [Figure 4]4 is a diagram for explaining the operation of the lighting control device according to the first embodiment. FIG. [Diagram 5] 4 is a diagram for explaining the operation of the lighting control device according to the first embodiment. FIG. [Figure 6] 4 is a diagram for explaining the operation of the lighting control device according to the first embodiment. FIG. [Figure 7] 4 is a diagram for explaining the operation of the lighting control device according to the first embodiment. FIG. [Figure 8] 4 is a diagram for explaining the operation of the lighting control device according to the first embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Embodiment 1> Fig. 1 is a diagram showing a configuration of a lighting control system according to embodiment 1. As shown in Fig. 1, the lighting control system includes a lighting control device 10 and a lamp 20 controlled by the lighting control device 10.

[0011] In the first embodiment, a lighting control system for a vehicle is shown as an example of a lighting control system. Lamps 20 for a vehicle include, for example, headlights, width lamps, and brake lamps of a vehicle, but in this embodiment, the lamps 20 are headlights. The lamps 20 include a light source 21 that is a light-emitting element.

[0012] The lighting control device 10 includes a semiconductor switch 11 that supplies power to a light source 21, a main control circuit 12 that is a control circuit for a normal system, and a backup circuit 13 that is a control circuit for a redundant system.

[0013] Based on a first input signal, main control circuit 12 controls the voltage of the control terminal of semiconductor switch 11. In this embodiment, the first input signal is a turn-on request signal input from a CAN (Controller Area Network).

[0014] The main control circuit 12 includes a micro controller unit (MCU) 121 and a system basis chip (SBC) 122. The MCU 121 and the SBC 122 may be assembled discretely.

[0015] The MCU 121 controls the voltage of the control terminal of the semiconductor switch 11 based on the light-on request signal. The MCU 121 also has an overcurrent detection function that detects an overcurrent in the semiconductor switch 11 (or a circuit including the semiconductor switch 11) and an overcurrent protection function that maintains the semiconductor switch 11 in an off state when an overcurrent is detected. Specifically, the MCU 121 monitors the current flowing through the semiconductor switch 11 and determines whether an overcurrent has occurred in the semiconductor switch 11. When an overcurrent in the semiconductor switch 11 is detected, the MCU 121 controls the voltage of the control terminal of the semiconductor switch 11 so as to maintain the semiconductor switch 11 in an off state, thereby blocking the overcurrent in the semiconductor switch 11.

[0016] The SBC122 includes a watchdog timer (WDT) for monitoring whether the MCU121 is operating normally, a low dropout regulator (LDO) that serves as the power source for the MCU121, and a CAN transceiver that receives a lighting request signal and transmits it to the MCU121. In addition, the SBC122 has a function of resetting the MCU121 to return the MCU121 to a normal state when an abnormality in the MCU121 is detected by the WDT.

[0017] The backup circuit 13 controls the voltage of the control terminal of the semiconductor switch 11 based on the second input signal. Here, the second input signal is an ignition signal that is maintained at a constant voltage value (e.g., 12 V) when the vehicle ignition is turned on. However, the input signal of the backup circuit 13 is not limited to the ignition signal and may be any control signal. For example, the second input signal may be the same signal as the first input signal.

[0018] The backup circuit 13 includes a first switch element 131 , a first resistor element 132 , a second resistor element 133 , a second switch element 134 , and a voltage conversion circuit 135 .

[0019] The first switch element 131 is a transistor connected to a power supply and controlled based on a second input signal. The first resistor element 132 is connected between the first switch element 131 and the output terminal of the main control circuit 12. The second resistor element 133 is connected between the output terminal of the main control circuit 12 and the reference potential terminal. That is, the first switch element 131, the first resistor element 132, and the second resistor element 133 are connected in series between the power supply and the reference potential terminal, and the connection node between the first resistor element 132 and the second resistor element 133 is connected to the output terminal of the main control circuit 12 and the control terminal of the semiconductor switch 11. The output terminal of the backup circuit 13 is the connection node between the first resistor element 132 and the second resistor element 133, and is directly connected to the output terminal of the main control circuit 12.

[0020] The second switch element 134 is a transistor connected between the control electrode of the first resistance element 132 and a reference potential terminal. The voltage conversion circuit 135 converts the voltage (12 V) of the ignition signal into a signal of a predetermined voltage (for example, 5 V) and inputs it to the control terminal of the second switch element 134.

[0021] Here, the resistance values ​​of the first resistor element 132 and the second resistor element 133 are set high enough to allow the main control circuit 12 to switch the semiconductor switch 11 on and off with priority over the backup circuit 13. In other words, the output impedance of the main control circuit 12 is low enough to allow the main control circuit 12 to switch the semiconductor switch 11 on and off with priority over the backup circuit 13.

[0022] However, if the main control circuit 12 detects an abnormality in the MCU 121, the SBC 122 resets the MCU 121, at which point the MCU 121 goes into a high impedance state, increasing the output impedance of the main control circuit 12. When the output impedance of the main control circuit 12 becomes high, the voltage at the output terminal of the main control circuit 12 changes significantly in accordance with the on / off state of the first switch element 131 of the backup circuit 13. Therefore, when an abnormality occurs in the main control circuit 12, the on / off state of the semiconductor switch 11 is switched by the backup circuit 13.

[0023] If the headlights of a vehicle go out due to a malfunction, there is a high possibility that they will cause danger. Therefore, in this embodiment, even if an abnormality occurs in the main control circuit 12 that controls the light source 21, which is the headlight, if the ignition of the vehicle is on (the ignition signal is in a 12V state), the backup circuit 13 turns on the semiconductor switch 11 instead of the main control circuit 12, and turns on the light source 21 (headlight).

[0024] The operation of the lighting control device 10 will now be described in detail.

[0025] First, we will explain the operation of the lighting control device 10 when the main control circuit 12 is operating normally. When the main control circuit 12 is operating normally, the output impedance of the MCU 121 is low, so the main control circuit 12 has priority over the backup circuit 13 in switching the semiconductor switch 11 on and off.

[0026] For example, when the ignition signal is off (0 V), the second switch element 134 and the first switch element 131 of the backup circuit 13 are in the off state. At this time, as shown in Fig. 2, if the output voltage of the MCU 121, which is switched in response to the lighting request signal, is at the H level (lighting instruction), the voltage of the control terminal of the semiconductor switch 11 also becomes the H level, the semiconductor switch 11 turns on, and the light source 21 turns on. Also, as shown in Fig. 3, if the output voltage of the MCU 121 is at the L level (lighting-off instruction), the voltage of the control terminal of the semiconductor switch 11 also becomes the L level, the semiconductor switch 11 turns off, and the light source 21 turns off.

[0027] When the ignition signal is on (12V), the second switch element 134 and the first switch element 131 of the backup circuit 13 are in the on state. At this time, as shown in FIG. 4, if the output voltage of the MCU 121 is at the H level (light-on instruction), the voltage of the control terminal of the semiconductor switch 11 also becomes the H level, the semiconductor switch 11 turns on, and the light source 21 turns on. Also, as shown in FIG. 5, if the output voltage of the MCU 121 is at the L level (light-off instruction), the voltage of the control terminal of the semiconductor switch 11 also becomes the L level, the semiconductor switch 11 turns off, and the light source 21 turns off. In the state shown in FIG. 5, the first switch element 131 is on, but since the output impedance of the MCU 121 is sufficiently low, the current flowing through the first switch element 131 flows into the MCU 121 and no voltage is generated in the second resistor element 133, so that the voltage of the control terminal of the semiconductor switch 11 becomes approximately equal to the output voltage of the MCU 121.

[0028] If the MCU 121 detects an overcurrent in the semiconductor switch 11, the overcurrent protection function is activated, resulting in a state similar to that shown in Fig. 3 or 5. That is, when the output voltage of the MCU 121 becomes L level (light-off command) due to the overcurrent protection function, the voltage of the control terminal of the semiconductor switch 11 becomes L level, regardless of the state of the backup circuit 13, and the semiconductor switch 11 becomes OFF and the overcurrent is cut off. Therefore, the overcurrent protection function of the main control circuit 12 is prevented from being disabled by the backup circuit 13.

[0029] In addition, when it is necessary to prevent the backup circuit 13 from turning on the semiconductor switch 11 before the output voltage of the main control circuit 12 is determined after the main control circuit 12 is started, a delay circuit may be provided in the voltage conversion circuit 135 to delay the timing at which the first switch element 131 is turned on.

[0030] Next, we will explain the operation of the lighting control device 10 when an abnormality is detected in the main control circuit 12. When an abnormality occurs in the main control circuit 12, the SBC 122 resets the MCU 121, causing the main control circuit 12 to enter a high impedance state. As a result, the output impedance of the main control circuit 12 becomes high, and the semiconductor switch 11 is switched on and off by the backup circuit 13.

[0031] For example, when the ignition signal is off (0 V), the second switch element 134 and the first switch element 131 of the backup circuit 13 are in the off state, and the main control circuit 12 is in a high impedance state, so that the voltage of the output terminal of the MCU 121 is pulled down through the second resistance element 133, and the voltage of the control terminal of the semiconductor switch 11 becomes the L level, as shown in FIG. 6, so that the semiconductor switch 11 is turned off and the light source 21 is turned off.

[0032] Furthermore, when the ignition signal is on (12 V), the second switch element 134 and the first switch element 131 of the backup circuit 13 are on and the main control circuit 12 is in a high impedance state, so that the voltage at the output terminal of the MCU 121 becomes H level (the voltage obtained by dividing the power supply voltage by the first resistance element 132 and the second resistance element 133), and as shown in FIG. 7, the voltage at the control terminal of the semiconductor switch 11 also becomes H level, turning on the semiconductor switch 11 and lighting the light source 21.

[0033] Thus, in the lighting control device 10 according to the first embodiment, when the main control circuit 12 is normal, the main control circuit 12 has priority over the backup circuit 13 in switching the semiconductor switch 11 on and off, and when an abnormality occurs in the main control circuit 12, the backup circuit 13 switches the semiconductor switch 11 on and off instead of the main control circuit 12. Also, when the main control circuit 12 detects an overcurrent in the semiconductor switch 11, the main control circuit 12 can turn the semiconductor switch 11 off due to the overcurrent protection function regardless of the operation of the backup circuit 13. In other words, the overcurrent protection function of the main control circuit 12 is prevented from being disabled by the backup circuit 13.

[0034] Furthermore, the output terminal of the backup circuit 13 (the connection node between the first resistance element 132 and the second resistance element 133) is directly wired to the output terminal of the main control circuit 12, and switching between the main control circuit 12 and the backup circuit 13 is achieved without using a logic circuit, which does not complicate the circuit and also contributes to reducing manufacturing costs.

[0035] In the present embodiment, in the backup circuit 13, the voltage conversion circuit 135 is not directly connected to the control terminal of the first switch element 131, but the second switch element 134 is interposed between the control terminal of the first switch element 131 and the voltage conversion circuit 135. This is to prevent the return current (indicated by the dashed arrow in FIG. 8) flowing from the output terminal of the MCU 121 to the first switch element 131 in the state of FIG. 2 (when the first switch element 131 is on and the output voltage of the MCU 121 is at H level) from flowing into the voltage conversion circuit 135 by discharging the return current through the second switch element 134 to the reference potential terminal. This makes it possible to prevent the voltage conversion circuit 135 from breaking down.

[0036] The above-described embodiment can be modified or omitted as appropriate.

[0037] <Additional Notes> Various aspects of the present disclosure are summarized below as appendices.

[0038] (Appendix 1) a semiconductor switch for supplying power to the light source; a main control circuit for controlling a voltage of a control terminal of the semiconductor switch based on a first input signal; a backup circuit that controls a voltage of the control terminal of the semiconductor switch based on a second input signal; Equipped with The backup circuit includes: a first switch element connected to a power supply and controlled based on the second input signal; a first resistor element connected between the first switch element and an output terminal of the main control circuit; a second resistive element connected between the output terminal and a reference potential terminal of the main control circuit; Equipped with resistance values ​​of the first resistive element and the second resistive element are set so that the main control circuit switches the semiconductor switch on and off preferentially over the backup circuit; When an abnormality occurs in the main control circuit, the output impedance of the main control circuit becomes high, and the semiconductor switch is switched on and off by the backup circuit. Lighting control device.

[0039] (Appendix 2) The backup circuit includes: a second switch element connected between a control terminal of the first switch element and the reference potential terminal; a voltage conversion circuit that converts the second input signal into a signal of a predetermined voltage and inputs the signal to a control terminal of the second input signal; Further comprising: 2. The lighting control device according to claim 1.

[0040] (Appendix 3) when an overcurrent is detected in the semiconductor switch or in a circuit including the semiconductor switch, the main control circuit controls a voltage of the control terminal of the semiconductor switch so as to maintain the semiconductor switch in an off state. 3. The lighting control device according to claim 1 or 2. [Explanation of symbols]

[0041] 10 lighting control device, 11 semiconductor switch, 12 main control circuit, 121 MCU, 122 SBC, 13 backup circuit, 131 first switch element, 132 first resistive element, 133 second resistive element, 134 second switch element, 135 voltage conversion circuit, 20 lamp, 21 light source.

Claims

1. a semiconductor switch for supplying power to the light source; a main control circuit for controlling a voltage of a control terminal of the semiconductor switch based on a first input signal; a backup circuit that controls a voltage of the control terminal of the semiconductor switch based on a second input signal; Equipped with The backup circuit includes: a first switch element connected to a power supply and controlled based on the second input signal; a first resistor element connected between the first switch element and an output terminal of the main control circuit; a second resistive element connected between the output terminal and a reference potential terminal of the main control circuit; Equipped with resistance values ​​of the first resistive element and the second resistive element are set so that the main control circuit switches the semiconductor switch on and off preferentially over the backup circuit; When an abnormality occurs in the main control circuit, the output impedance of the main control circuit becomes high, and the semiconductor switch is switched on and off by the backup circuit. Lighting control device.

2. The backup circuit includes: a second switch element connected between a control terminal of the first switch element and the reference potential terminal; a voltage conversion circuit that converts the second input signal into a signal of a predetermined voltage and inputs the signal to a control terminal of the second input signal; Further comprising: The lighting control device according to claim 1 .

3. when an overcurrent is detected in the semiconductor switch or in a circuit including the semiconductor switch, the main control circuit controls a voltage of the control terminal of the semiconductor switch so as to maintain the semiconductor switch in an off state. The lighting control device according to claim 1 or 2.

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