Lighting control device

Abstract

The purpose of the present disclosure is to provide a lighting control device capable of performing correction of individual segments even when the base current of a step-down converter decreases. A lighting control device (8) according to the present disclosure comprises: a step-up converter (2) that steps up a voltage from a battery (1) and outputs the result; a step-down converter (3) that receives the output voltage of the step-up converter (2), steps down the output voltage so as to obtain a desired base current, and outputs the result; a switching element that divides a series circuit of a semiconductor light source connected to the step-down converter (3) into a plurality of segments; a voltage acquisition unit (7) that acquires the sum of forward drop voltages of the semiconductor light source for each segment; and a control unit (4) that indicates the output voltage of the step-up converter (2) and the base current of the step-down converter (3) and controls the driving duty of the switching element for each segment. The control unit (4) performs correction by adding the driving duty of the switching element to each segment in accordance with the sum of the forward drop voltages of the semiconductor light source.

Description

lighting control device

[0001] The present disclosure relates to a lighting control device using a semiconductor light source, and more particularly to a lighting control device that controls the lighting of lamps and the like mounted on a vehicle.

[0002] As exemplified in Patent Document 1, there is a boost converter that boosts the voltage supplied from a battery, and a buck converter that receives the output of the boost converter and adjusts the voltage to supply a desired current to a lamp using a semiconductor light source connected to the buck converter. Currently, the types of lamps used in vehicles are becoming more sophisticated and diverse, and the number of semiconductor light sources, typified by LEDs (Light Emitting Diodes), used in lamps is on the rise. The LED series circuit connected to this buck converter is called a string, and the number of LEDs constituting the string is increasing. Furthermore, due to the increasing variety of functions, strings are often divided into blocks of LED series circuits called segments. These segments are each controlled independently according to their respective functions.

[0003] PCT / JP2023 / 025223

[0004] The step-down converter performs constant current control to ensure a desired current flows through the string. However, as the step-down converter's output voltage (i.e., the sum of the forward voltage drops of the lit LEDs, ΣVf) increases, the current it can output tends to decrease. Each of the segments described above adjusts the current flowing through it according to its function. Specifically, each segment performs duty control to adjust the duty ratio for turning on and off the step-down converter's output current (hereinafter referred to as the base current Ibase). However, as described above, when the base current Ibase decreases, the average current flowing through the LEDs that make up each segment fluctuates, resulting in the problem of not being able to achieve the desired brightness.

[0005] This is particularly problematic for lights with relatively low duty ratios, such as daytime running lights (DRLs), position lights, or room lights. In other words, for lights with high duty ratios, such as headlights, even if the base current Ibase decreases slightly, the average current value may still fall within the allowable error range (e.g., within a few percent). On the other hand, lights with low duty ratios are controlled with a very small current to begin with, and even a slight decrease in the base current Ibase can be significant, resulting in a risk that the average current value may deviate from the allowable error range. In recent years, due to the increasing sophistication of lights and legal regulations, the allowable error range has become increasingly strict, making it particularly difficult to maintain the value within the allowable error range when the duty ratio is low.

[0006] One might think that if the base current Ibase of the buck converter decreases, the target current Iref provided to the buck converter by the control unit should be increased accordingly to compensate for the base current Ibase. However, the base current Ibase decreases according to the sum of the forward voltage drops ΣVf of the semiconductor light sources, and therefore decreases as the number of lit segments increases. In other words, the base current drop ΔIbase varies for each segment, so even if the target current Iref is increased to uniformly increase the base current Ibase, it is not possible to compensate for the average current value of each segment to the desired average current value. Furthermore, the forward voltage drop of a semiconductor light source is easily affected by individual semiconductor light source differences and temperature, making it difficult to achieve current control that requires high precision. Furthermore, the decreasing base current value ΔIbase does not necessarily have a linear relationship.

[0007] The present disclosure has been made to solve the above problem, and its purpose is to provide a lighting control device that can make corrections for each segment even when the base current of the step-down converter decreases.

[0008] The lighting control device of the present disclosure includes a boost converter that boosts and outputs voltage from a battery, a buck converter that receives the output voltage of the boost converter and reduces the output voltage to a desired base current and outputs it, switching elements that divide a series circuit of semiconductor light sources connected to the buck converter into multiple segments, a voltage acquisition unit that acquires the sum of the forward drop voltages of the semiconductor light sources for each segment, and a control unit that indicates the output voltage of the boost converter and the base current of the buck converter and controls the drive duty of the switching elements for each segment, and the control unit additively corrects the drive duty of the switching elements for each segment according to the sum of the forward drop voltages of the semiconductor light sources.

[0009] According to the present disclosure, it is possible to provide a lighting control device that can correct for each segment even when the base current of a step-down converter decreases due to the sum of the forward drop voltages of the semiconductor light sources.

[0010] It is a block diagram showing a configuration of a first embodiment of the present invention.It is a waveform diagram showing the operation of a comparative example.It is a waveform diagram showing the operation of a first embodiment of the present invention.It is a waveform diagram showing the operation of a second embodiment of the present invention.

[0011] First Embodiment Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0012] FIG. 1 is a block diagram illustrating the configuration of a first embodiment of the present invention. In the figure, reference numeral 1 denotes a battery that outputs a voltage of approximately 12 V for standard vehicles and approximately 24 V for large vehicles. A boost converter 2 receives the voltage from battery 1 and boosts it to the desired voltage. A buck converter 3 receives the output of boost converter 2 and performs constant current control. A control unit 4 is composed of a microcomputer and other components that control the output voltage of boost converter 2 and the output current of buck converter 3. Switches 5 are switching elements such as FETs (Field Effect Transistors) and divide a string 6, which is a series circuit of LEDs serving as semiconductor light sources, into multiple segments. FIG. 1 illustrates an example in which string 6 is composed of four segments, with four switches SW1, SW2, SW3, and SW4 acting as switches 5. Although segments 1 through 4 of string 6 are illustrated as each containing a single LED, this is merely a simplified illustration for ease of explanation. In reality, these segments are series circuits of one or more LEDs, and the number of LEDs constituting each segment is not necessarily the same. The number of LEDs constituting each segment is arbitrary. The voltage acquisition unit 7 acquires the forward drop voltage of each segment, and acquires the voltage relative to the circuit power supply common (hereinafter referred to as common). Let us assume that each of the LEDs constituting segments 1 through 4 consists of three LEDs, each with a forward drop voltage Vf of 10 V. For example, when only segment 1 is turned on and segments 2 through 4 are off, the sum of the forward drop voltages ΣVf is the forward drop voltage Vf1 of segment 1. The forward drop voltage Vf1 of segment 1 is the voltage of segment 1 relative to common. Next, when segment 2 is turned on, the sum of the forward drop voltages Vf1 of segment 1 and the forward drop voltages Vf2 of segment 2 is (ΣVf = Vf1 + Vf2). Similarly, when segment 3 and segment 4 are turned on, the sums of the forward voltage drops ΣVf are ΣVf = Vf1 + Vf2 + Vf3 and ΣVf = Vf1 + Vf2 + Vf3 + Vf4, respectively. The voltage acquisition unit 7 acquires the forward voltage drops according to the state of each segment and provides the acquired voltage to the control unit 4.The lighting control device 8 is composed of a step-up converter 2, a step-down converter 3, a control unit 4, a switch 5, and a voltage acquisition unit 7. The string 6 is mounted in a lighting fixture (not shown) that is connected to the lighting control device 8. The voltage acquisition unit 7 has been described as detecting the voltage of the segments. However, the function of detecting the voltage of the segments may be provided in a lighting fixture (not shown), and the voltage acquisition unit 7 may acquire the voltage detection results from the lighting fixture and provide them to the control unit 4.

[0013] Figure 2 is a waveform diagram showing the operation of the comparative example. In Figure 2, the control period of duty control is assumed to be 5 ms. LED1 (which may be single or multiple; the same applies below) as segment 1 is required to have a brightness of 80%, so the drive duty of switch SW1 is assumed to be 80%. In other words, switch SW1 turns on 4 ms before the end of the control period and turns off at the end of the control period. At this time, the forward drop voltage Vf1 when segment 1 is lit is assumed to be 10 V.

[0014] Similarly, LED2 in segment 2 has a drive duty of 60%. That is, switch SW2 turns on 3 ms before the end of the control period. LED3 in segment 3 has a drive duty of 40%. That is, switch SW3 turns on 2 ms before the end of the control period. LED4 in segment 4 has a drive duty of 20%. That is, switch SW4 turns on 1 ms before the end of the control period. At this time, the forward drop voltage Vf2 of segment 2, the forward drop voltage Vf3 of segment 3, and the forward drop voltage Vf4 of segment 4 are each 10 V.

[0015] Furthermore, the step-down converter 3 receives instructions from the control unit 4 and outputs 1000 mA as the base current Ibase. However, when the sum ΣVf of the forward drop voltages of the LEDs exceeds 15 V, the base current Ibase that can be output decreases according to the sum ΣVf of the forward drop voltages of the LEDs.

[0016] The operation of the comparative example will be described below.

[0017] In Figure 2, in the first section, switch SW1 is on and switches SW2 to SW4 are off. At this time, the total forward voltage drop ΣVf is 10 V, which does not exceed 15 V, so the step-down converter outputs 1000 mA as the base current Ibase, as specified. Next, in the second section, switch SW2 is on in addition to switch SW1. At this time, the total forward voltage drop ΣVf is 20 V, which is the sum of the forward voltage drop Vf1 of segment 1 and the forward voltage drop Vf2 of segment 2. At this time, the total forward voltage drop ΣVf exceeds 15 V, so the base current Ibase output by the step-up converter decreases by an amount ΔIbase2 determined by the total forward voltage drop ΣVf. Similarly, in the third section, the total forward voltage drop ΣVf is 30 V, which is the sum of Vf1, Vf2, and Vf3, and the base current Ibase decreases by a further amount ΔIbase3. In the fourth section, the total forward voltage drop ΣVf is 40 V, which is the sum of Vf1, Vf2, Vf3 and Vf4, and the base current Ibase further decreases by ΔIbase4.

[0018] Here, the current product that is insufficient for LED1 in segment 1 is current product (2) x 3 + current product (3) x 2 + current product (4), and LED1 becomes dimmer by this amount. Here, assume that ΔIbase2 = ΔIbase3 = ΔIbase4 = 0.1 A. In this case, the current product that is insufficient for LED1 is current product (2) = current product (3) = current product (4) = 0.1 A x 1 ms = 0.1 A ms, which is current product (2) x 3 + current product (3) x 2 + current product (4), so it is 0.6 A ms.

[0019] Similarly, the current product that is insufficient for LED2 in segment 2 is current product (2)×3+current product (3)×2+current product (4), which is 0.6 A·ms.

[0020] The current product that is insufficient for LED3 of segment 3 is current product (2)×2 + current product (3)×2 + current product (4), which is 0.5 A·ms.

[0021] The current product that is insufficient for LED4 in segment 4 is current product (2) + current product (3) + current product (4), which is 0.3 A·ms. Therefore, the average value of the insufficient base current is calculated as follows:

[0022] LED1: 0.6 A ms / 4 ms = 0.15 A LED2: 0.6 A ms / 3 ms = 0.2 A LED3: 0.5 A ms / 2 ms = 0.25 A LED4: 0.3 A ms / 1 ms = 0.3 A Let's take segment 2 (LED2) as an example. Suppose the current command value given to step-down converter 3 from control unit 4 is uniformly corrected by increasing it by 0.2 A (200 mA). In this case, the base current value Ibase of segment 2 is controlled to the desired value (1000 mA), but segment 1 (LED1) is over-corrected (1050 mA), leaving segments 3 and 4 (LED3 and 4) short of the current.

[0023] In other words, since the average value of the missing base current differs for each segment, even if an attempt is made to make a uniform correction by increasing the current instruction value given to the step-down converter 3 from the control unit 4, the average current value of each segment cannot be correctly corrected.

[0024] Therefore, in this embodiment 1, the drive duty of the switch SW of each segment is corrected by an amount corresponding to the current product deficiency. Figure 3 is a waveform diagram showing the operation of embodiment 1. In the figure, switch SW1 corrects its drive duty by an amount corresponding to the current product deficiency. Similarly, SW2, SW3, and SW4 correct their drive duties by an amount corresponding to the current product deficiency.

[0025] Specifically, the voltage acquisition unit 7 acquires the sum ΣVf of forward voltage drops according to the state of the switch SW and provides the acquired value to the control unit 4. The control unit 4 calculates the base current Ibase that the step-down converter 3 can output according to the sum ΣVf of forward voltage drops, and calculates the current product that is insufficient for each segment. The base current Ibase that the step-down converter 3 can output according to the sum ΣVf of forward voltage drops may be actually measured, or a value obtained experimentally in advance may be stored in the control unit 4 as a table. The control unit 4 calculates the current product that is insufficient for each segment, and then adds and corrects the drive duty for each segment by an amount equivalent to the insufficient current product. Note that the insufficient current product may be calculated based on the sum ΣVf of the forward voltage drops Vf, or based on the forward voltage drop Vf of each segment.

[0026] As a result, even if the base current Ibase of the step-down converter 3 drops due to the sum ΣVf of the forward voltage drops of the semiconductor light sources, such as LEDs, the average current value for each segment can be kept within the error range by performing additive correction for each segment.

[0027] In the first embodiment, the start point of the drive duty signal for each segment is determined based on the end point of the duty control period. In other words, by aligning the ends of the duty control periods, it is not necessary to take into account the direction in which the total forward voltage drop decreases, and control can be simplified.

[0028] The forward voltage drop Vf of semiconductor light sources varies greatly from one source to another. Furthermore, the temperature of the semiconductor light source changes due to factors such as ambient temperature or self-heating caused by lighting, and the forward voltage drop Vf also changes due to the temperature. These variations in the forward voltage drop Vf due to individual differences in semiconductor light sources or temperature changes cannot be ignored when highly accurate control of the average current value is required.

[0029] However, in the first embodiment, the actual measured value of the forward drop voltage Vf is obtained for each segment, so that it is possible to suppress the influence of fluctuations due to individual differences in semiconductor light sources or temperature.

[0030] In the above embodiment, a model is used for explanation to facilitate understanding, and the forward voltage drop Vf or the current drop ΔIbase occurring in each segment is not uniform.

[0031] Embodiment 2 In the above-described embodiment 1, when the sum ΣVf of the forward voltage drop Vf of the semiconductor light sources increases, the step-down converter immediately follows up and boosts the voltage by an amount equivalent to the sum ΣVf of the forward voltage drop Vf of the semiconductor light sources. However, if the forward voltage drop is, for example, 0 V (all LEDs are off), and segment 1 consisting of LED 1 is turned on and the forward voltage drop Vf becomes Vf1, the step-down converter 3 must boost the voltage by an amount equivalent to the increase in the forward voltage drop Vf in order to maintain constant current control. The time required for this boost is not zero; there is always some delay. This delay may cause slight fluctuations in the average current value. However, as the functionality required for lamps becomes increasingly sophisticated, it may be necessary to consider the fluctuations in the allowable error range of the required average current value due to the above-mentioned boost delay.

[0032] Therefore, in the second embodiment, the drive duty of the switch SW is corrected by adding up the delay in boosting the voltage of the step-down converter 3. Specifically, the control unit 4 adds up the delay times for each segment that the step-down converter 3 needs to boost up the semiconductor light source for each segment by the increase in the forward drop voltage Vf, and then adds up the amount equivalent to this sum of delay times to the drive duty of the segment with the largest drive duty.

[0033] FIG. 4 is a waveform diagram showing the operation of the second embodiment. In the first interval, when switch SW1 is turned on, the sum of the forward voltage drop increases from 0 V to Vf1. FIG. 4 illustrates a simulated boost delay in the step-down converter 3, showing that there is a delay in the voltage increase in the first interval. Similarly, in the second interval, switch SW2 is turned on, and the forward voltage drop Vf becomes Vf2. At this time, a boost delay also occurs in the step-down converter 3. The same applies to the third and fourth intervals.

[0034] The control unit 4 acquires information from the voltage acquisition unit 7 and calculates the area of ​​the triangular portion shown in Fig. 4 based on the forward voltage drop Vf and delay time for each segment.The control unit 4 then drives the switch SW1 from the next control cycle with a drive duty obtained by adding an amount equivalent to the total area to the drive duty of the switch SW1, which has the largest drive duty.

[0035] That is, according to the second embodiment, the current drop due to the boost delay of the step-down converter 3 is estimated in advance and added for correction, so that the current drop can be corrected more accurately.

[0036] In this second embodiment, the additive correction is performed starting with the larger drive duty, so that no matter how the indicated drive duty value for each segment changes, additive correction is performed along the steps that occur as the forward voltage drop of the semiconductor light source increases, and correction can be performed taking into account only the amount of current reduction that occurs when the forward voltage drop increases.

[0037] Furthermore, the control unit 4 may perform additive correction so that the total delay time is longer when the command value of the base current Ibase is small than when it is large. The delay time of the voltage step-up of the step-down converter 3 tends to be longer when the command value of the base current Ibase is small than when it is large.

[0038] Therefore, by performing an additive correction so that the total delay time is longer when the command value of the base current Ibase is small than when it is large, the correction also takes into account the fluctuation in the boost delay of the step-down converter 3, which varies depending on the magnitude of the command value of the base current Ibase, and therefore the current drop can be corrected even more accurately.

[0039] In particular, the accuracy of predictive control can be further improved when the area of ​​the triangular portion shown in Fig. 4 is not actually measured but the delay time of the voltage step-up of the step-down converter 3 is estimated based on the forward voltage drop Vf. In the second embodiment, the control unit 4 may perform additive correction to the area of ​​the triangular portion shown in Fig. 4 based on an actual measurement, or may estimate and calculate the delay time of the voltage step-up of the step-down converter 3 based on the forward voltage drop Vf.

[0040] Third Embodiment In the above-described embodiment, the control unit 4 corrects the drive duty of the switch SW for each segment in accordance with the sum ΣVf of the forward drop voltages Vf of the semiconductor light sources in order to correct fluctuations in the average current value resulting from a decrease in the base current Ibase output by the step-down converter 3.

[0041] However, if an additive correction is applied to a segment that has been instructed to be turned off (drive duty is 0%), the switch SW may be driven by the amount of the additive correction, resulting in slight lighting. Therefore, in the third embodiment, the control unit 4 sets the additive correction to 0 or prohibits it for segments that have been instructed to be turned off.

[0042] By performing this process, the drive duty is added to the segments that have been instructed to be turned off, so that even a slight amount of lighting is prevented.

[0043] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0044] 1 Battery, 2 Boost converter, 3 Buck converter, 4 Control unit, 5 Switch, 6 String, 7 Voltage acquisition unit, 8 Lighting control device

Claims

1. A lighting control device comprising: a boost converter that boosts and outputs a voltage from a battery; a buck converter that receives the output voltage of the boost converter and reduces the output voltage to a desired base current and outputs the same; switching elements that divide a series circuit of semiconductor light sources connected to the buck converter into a plurality of segments; a voltage acquisition unit that acquires a sum of the forward drop voltages of the semiconductor light sources for each of the segments; and a control unit that indicates the output voltage of the boost converter and the base current of the buck converter and controls the drive duty of the switching elements for each of the segments, wherein the control unit additively corrects the drive duty of the switching elements for each of the segments in accordance with the sum of the forward drop voltages of the semiconductor light sources.

2. The lighting control device described in claim 1, characterized in that the control unit additively corrects the drive duty of the switching element to compensate for the current product that has decreased for each segment based on the sum of the forward drop voltages of the semiconductor light sources for each segment and the drive duty for each segment.

3. The lighting control device according to claim 1, characterized in that the control unit adds up the delay times for each segment required for the step-down converter to boost the increase in the forward drop voltage of the semiconductor light source for each segment, and adds an amount equivalent to this summed delay time to the drive duty of the segment with the largest drive duty.

4. A lighting control device according to claim 3, wherein the control unit performs additive correction so that the total delay time is longer when the base current instruction value is small than when it is large.

5. The lighting control device according to claim 1, wherein the control unit determines the start point of the drive duty based on the end point of the duty control period of the segment.

6. The lighting control device according to claim 5, wherein the control unit performs the additive correction in order from the segment with the largest drive duty among the segments.

7. The lighting control device according to claim 1, wherein the control unit sets the additive correction to 0 or prohibits it for any of the segments that have been instructed to be turned off.

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