Lighting control device

Abstract

The present disclosure aims to provide a lighting control device capable of performing correction per segment even when the base current of a step-down converter is reduced. The lighting control device (8) according to the present disclosure includes: a step-up converter (2) that steps up a voltage from a battery (1) and outputs the stepped-up voltage; a step-down converter (3) that receives an output voltage of the step-up converter (2), steps down the output voltage to obtain a desired base current, and outputs the stepped-down voltage; 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 a sum of forward voltage drops of the semiconductor light source per 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 a drive duty ratio of the switching element per segment, the control unit (4) performing addition correction of the drive duty ratio of the switching element per segment based on the sum of the forward voltage drops of the semiconductor light source.

Description

Technical Field

[0001] This disclosure relates to a lighting control device using a semiconductor light source, and more particularly to a lighting control device for controlling the lighting of lamps and the like mounted on a vehicle. Background Technology

[0002] As illustrated in Patent Document 1, there is a boost converter that boosts the voltage supplied from the battery; and a buck converter that receives the output of the boost converter, reduces the voltage, and adjusts it to supply the desired current to a luminaire using a semiconductor light source connected to the buck converter. Currently, vehicle lighting fixtures are becoming increasingly functional and diverse, with a growing number of semiconductor light sources, such as LEDs (Light Emitting Diodes), used in these fixtures. The LED series circuit connected to the buck converter is called a light string, and the number of LEDs constituting the light string is increasing. Furthermore, due to functional diversification, light strings are often divided into LED series circuit blocks called segments. These segments are controlled independently according to their functions.

[0003] [Existing Technical Documents]

[0004] [Patent Documents]

[0005] Patent Document 1: PCT / JP2023 / 025223 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] However, while the buck converter uses constant current control to ensure the desired current flows through the LED string, the output current tends to decrease as the output voltage of the buck converter (i.e., the sum of the forward voltage drops ΣVf of the LEDs in operation) increases. Here, each segment adjusts its current flow according to its function. Specifically, duty cycle control is implemented for each segment, where the duty cycle refers to the duty cycle used to switch the output current of the buck converter (hereinafter referred to as the base current Ibase). However, as mentioned above, when the base current Ibase decreases, the average current flowing through the LEDs constituting each segment changes, resulting in a failure to achieve the desired brightness.

[0008] This is particularly problematic for lights with small duty cycles, such as daytime running lights (DRLs), position lights, and interior lights. Specifically, in high-duty-cycle lights, such as headlights, even a slight decrease in the base current Ibase may result in an average current value within the allowable error range (e.g., within a few percent). Conversely, in low-duty-cycle lights, where control is achieved with a small current, even a small decrease in the base current Ibase can have a significant impact, potentially causing the average current value to exceed the allowable error range. In recent years, due to factors such as increased functionality of lighting fixtures and regulatory restrictions, allowable error ranges have become increasingly stringent, making it increasingly difficult to bring the average current value within the allowable range, especially with small duty cycles.

[0009] Here, if the base current Ibase of the buck converter decreases, it might be possible to increase the target current value Iref supplied from the control unit to the buck converter to compensate for the decrease in base current Ibase. However, the base current Ibase decreases based on the sum of the forward voltage drops ΣVf of the semiconductor light source, and therefore decreases each time an additional segment is illuminated. That is, since the decrease in base current ΔIbase varies for each segment, even if the target current value Iref is increased to uniformly increase the base current Ibase, it is impossible to correct the average current value of each segment to the desired average current value. Furthermore, the forward voltage drop of the semiconductor light source is easily affected by individual differences in the semiconductor light source or temperature, making it difficult to handle current control requiring high precision. Moreover, the decrease in base current ΔIbase is not necessarily linear.

[0010] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a lighting control device that can perform correction on a segment-by-segment basis even when the base current of the buck converter decreases.

[0011] Technical means for solving technical problems

[0012] The lighting control device disclosed herein includes: a boost converter that boosts and outputs a voltage from a battery; a buck converter that receives the output voltage from the boost converter and bucks the output voltage to obtain a desired base current and outputs it; a switching element that divides a series circuit of a semiconductor light source connected to the buck converter into multiple segments; a voltage acquisition unit that acquires the sum of the forward voltage drops of the semiconductor light source for each segment; and a control unit that instructs the output voltage of the boost converter and the base current of the buck converter, and controls the drive duty cycle of the switching element for each segment, wherein the control unit performs an additive correction on the drive duty cycle of the switching element for each segment based on the sum of the forward voltage drops of the semiconductor light source.

[0013] Invention Effects

[0014] According to this disclosure, a lighting control device is provided that can perform correction on a segment-by-segment basis even when the base current of the buck converter decreases due to the sum of the forward voltage drops of the semiconductor light source. Attached Figure Description

[0015] Figure 1 This is a block diagram illustrating the structure of Embodiment 1 of the present invention.

[0016] Figure 2 It is a waveform diagram representing the action of the comparative example.

[0017] Figure 3 This is a waveform diagram illustrating the operation of Embodiment 1 of the present invention.

[0018] Figure 4 This is a waveform diagram illustrating the operation of Embodiment 2 of the present invention. Detailed Implementation

[0019] Implementation Method 1

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings, the same or equivalent parts are labeled with the same symbol, and repetition of their descriptions is omitted.

[0021] Figure 1This is a block diagram illustrating the structure of Embodiment 1 of the present invention. In the diagram, 1 is a battery, which outputs approximately 12V in the case of a normal vehicle and approximately 24V in the case of a large vehicle. 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. The control unit 4 consists of a microcontroller or similar component that controls the output voltage of boost converter 2 and the output current of buck converter 3. A switch 5, composed of a FET (Field Effect Transistor) or similar switching element, divides the series circuit of LEDs, i.e., the LED string 6, which serves as a semiconductor light source, into multiple segments. Figure 1 An example of a light string 6 consisting of four segments is shown, with four switches SW1, SW2, SW3, and SW4 serving as switch 5. Furthermore, segments 1 to 4 of the light string 6 are each illustrated with one LED, but this is a simplified illustration only 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 limited to the same number. The number of LEDs constituting each segment is free. The voltage acquisition unit 7 acquires the forward voltage drop of each segment and acquires the voltage referenced to the common terminal of the circuit power supply (hereinafter referred to as the common terminal). Here, it is assumed that the number of LEDs constituting segments 1 to 4 is all 3, and the forward voltage drop Vf of each segment is 10V, and such an example is explained. For example, when only segment 1 is turned on and segments 2 to 4 are turned off, the sum of the forward voltage drops ΣVf becomes the forward voltage drop Vf1 of segment 1. The forward voltage drop Vf1 of segment 1 is the voltage of segment 1 referenced to the common terminal. Next, when segment 2 is turned on, the sum of the forward voltage drops ΣVf becomes the sum of the forward voltage drops Vf1 of segment 1 and Vf2 of segment 2 (ΣVf = Vf1 + Vf2). Similarly, when segments 3 and 4 are turned on, the sum of the forward voltage drops ΣVf becomes 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 them to the control unit 4. The lighting control device 8 consists of a boost converter 2, a buck converter 3, a control unit 4, a switch 5, and the voltage acquisition unit 7. The light string 6 is mounted in a lamp (not shown) connected to the lighting control device 8. The voltage acquisition unit 7 is described as a part that detects the voltage of the segments. However, it is also possible to enable a lamp (not shown) to detect the voltage of segments, and the voltage acquisition unit 7 acquires the voltage detection result of the lamp and provides it to the control unit 4.

[0022] Figure 2 It is a waveform diagram representing the action of the comparative example. Figure 2In this example, the control cycle for duty cycle control is set to 5ms. Furthermore, assuming that LED1 (which may exist as a single LED or multiple LEDs, as will be the case hereinafter) receives a request for 80% brightness, the drive duty cycle of switch SW1 is set to 80%. That is, based on the end of the control cycle, switch SW1 is turned on 4ms before the end of the control cycle and turned off at the end of the control cycle. At this time, the forward voltage drop Vf1 when segment 1 is lit is set to 10V.

[0023] Similarly, let the driving duty cycle of LED2 (segment 2) be 60%. That is, starting from the end of the control cycle, switch SW2 is turned on 3ms in advance. Let the driving duty cycle of LED3 (segment 3) be 40%. That is, starting from the end of the control cycle, switch SW3 is turned on 2ms in advance. Let the driving duty cycle of LED4 (segment 4) be 20%. That is, starting from the end of the control cycle, switch SW4 is turned on 1ms in advance. At this time, let the forward voltage drop Vf2 of segment 2, the forward voltage drop Vf3 of segment 3, and the forward voltage drop Vf4 of segment 4 be 10V each.

[0024] Furthermore, the buck converter 3 receives an instruction from the control unit 4 and outputs a base current Ibase of 1000mA. However, when the sum of the forward voltage drops of the LEDs ΣVf exceeds 15V, the output base current Ibase decreases according to the sum of the forward voltage drops of the LEDs ΣVf.

[0025] The following explains the actions of the comparative example.

[0026] Figure 2 In the first interval, switch SW1 is on, and switches SW2-SW4 are off. The total forward voltage drop ΣVf is 10V, which does not exceed 15V. Therefore, the buck converter outputs a base current Ibase of 1000mA as indicated. Next, in the second interval, switch SW2 is on, except for switch SW1. The total forward voltage drop ΣVf is 20V, which is the sum of the forward voltage drops Vf1 (segment 1) and Vf2 (segment 2). Now, the total forward voltage drop ΣVf exceeds 15V, so the boost converter's base current Ibase decreases by ΔIbase2, which is determined by the total forward voltage drop ΣVf. Similarly, in the third interval, the total forward voltage drop ΣVf is the sum of Vf1, Vf2, and Vf3, i.e., 30V, and the base current Ibase further decreases by ΔIbase3. In the fourth interval, the sum of the forward voltage drops ΣVf is the sum of Vf1, Vf2, Vf3 and Vf4, which is 40V, and the base current Ibase further decreases by ΔIbase4.

[0027] Here, the insufficient current product in LED1 of segment 1 is current product (2) × 3 + current product (3) × 2 + current product (4), and LED1 dims accordingly. Here, let ΔIbase2 = ΔIbase3 = ΔIbase4 = 0.1A. In this case, the insufficient current product in LED1 is current product (2) = current product (3) = current product (4) = 0.1A × 1ms = 0.1A·ms. Since it is current product (2) × 3 + current product (3) × 2 + current product (4), it becomes 0.6A·ms.

[0028] Similarly, the insufficient current product in LED2 of segment 2 is current product (2) × 3 + current product (3) × 2 + current product (4), which becomes 0.6 A·ms.

[0029] The insufficient current product in LED3 of segment 3 is current product (2)×2 + current product (3)×2 + current product (4), which becomes 0.5A·ms.

[0030] The insufficient current product in LED4 of segment 4 is current product (2) + current product (3) + current product (4), which becomes 0.3A·ms. Therefore, the average value of the insufficient base current is calculated as follows.

[0031] LED1: 0.6A·ms / 4ms = 0.15A

[0032] LED2: 0.6A·ms / 3ms = 0.2A

[0033] LED3: 0.5A·ms / 2ms = 0.25A

[0034] LED4: 0.3A·ms / 1ms = 0.3A

[0035] Let's take segment 2 (LED2) as an example. Assume that the current indication value provided from the control unit 4 to the buck converter 3 is increased by 0.2A (200mA) and uniformly corrected. At this time, the base current value Ibase of segment 2 is controlled to the desired value (1000mA), but on the other hand, it becomes an overcorrection (1050mA) in segment 1 (LED1), while segments 3 and 4 (LED3, 4) are still in an insufficient state.

[0036] That is, since the average value of the insufficient base current for each segment is different, even if the current indication value provided from the control unit 4 to the buck converter 3 is increased to uniformly correct the average current value of each segment, it is impossible to accurately correct the average current value of each segment.

[0037] Therefore, in this embodiment 1, the drive duty cycle of the switch SW in each segment is additively corrected according to an amount equivalent to the insufficient current product. Figure 3This is a waveform diagram illustrating the operation of Implementation Method 1. In the diagram, switch SW1 performs additive correction on the drive duty cycle by an amount equivalent to the product of insufficient current. Similarly, SW2, SW3, and SW4 also perform additive correction on the drive duty cycle by an amount equivalent to the product of insufficient current.

[0038] Specifically, the voltage acquisition unit 7 acquires the sum of forward voltage drops ΣVf based on the state of switch SW and provides it to the control unit 4. The control unit 4 calculates the base current Ibase that the buck converter 3 can output based on the sum of forward voltage drops ΣVf, and calculates the insufficient current product for each segment. Here, the base current Ibase that the buck converter 3 can output based on the sum of forward voltage drops ΣVf can be measured, or the value obtained through experiments can be stored in a table in the control unit 4. The control unit 4 calculates the insufficient current product for each segment, and performs an additive correction on the drive duty cycle for each segment according to an amount equivalent to the insufficient current product. In addition, when calculating the insufficient current product, it can be calculated based on the sum of forward voltage drops Vf ΣVf, or it can be calculated based on the forward voltage drops Vf of each segment.

[0039] Therefore, even when the base current Ibase of the buck converter 3 decreases due to the sum of the forward voltage drops ΣVf of semiconductor light sources represented by LEDs, the average current value can be converged to the error range for each segment by performing additive correction for each segment.

[0040] Furthermore, in Implementation 1, the starting point of the drive duty cycle signal for each segment is determined based on the end point of the duty cycle control cycle. That is, by aligning the end points of the duty cycle control cycle, the direction of the sum of forward voltage drops decreases is not considered, thus simplifying control.

[0041] The forward voltage drop Vf of semiconductor light sources exhibits significant individual variations and deviations. Furthermore, the temperature of the semiconductor light source varies due to ambient temperature or self-heating during operation, causing the forward voltage drop Vf to fluctuate with temperature. These individual variations or temperature changes in the semiconductor light source, leading to variations in the forward voltage drop Vf, cannot be ignored when high-precision average current control is required.

[0042] However, by obtaining the measured value of the forward voltage drop Vf for each segment in Implementation 1, the effects of individual differences in the semiconductor light source or variations caused by temperature can be suppressed.

[0043] Furthermore, in the above embodiments, a modeling explanation has been provided for ease of understanding, and the forward voltage drop Vf or the reduced current value ΔIbase generated for each segment is not the same.

[0044] Implementation Method 2

[0045] In Embodiment 1 described above, it was explained that when the sum of the forward voltage drops Vf of the semiconductor light source, ΣVf, increases, the buck converter immediately follows and can boost the voltage by an amount equivalent to the sum of the forward voltage drops Vf of the semiconductor light source, ΣVf. However, if, for example, the forward voltage drop starts from 0V (all LEDs are off), and segment 1 composed of LED1 is turned on, causing the forward voltage drop Vf to become Vf1, then the buck 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 cannot be zero; there is a certain degree of delay. Due to this delay, the average current value may sometimes vary slightly. Here, as the required functions of the lighting fixtures become increasingly sophisticated, the allowable error range of the required average current value sometimes needs to take into account the variation caused by the aforementioned boost delay.

[0046] Therefore, Embodiment 2 also considers the boost delay of the buck converter 3 and performs additive correction on the drive duty cycle of the switch SW. Specifically, the control unit 4 sums up the delay time of each segment required for the increase in the forward voltage drop Vf of the semiconductor light source in each segment of the buck converter 3 boost, and adds an amount equivalent to the summed delay time to the drive duty cycle of the segment with the largest drive duty cycle.

[0047] Figure 4 This is a waveform diagram illustrating the operation of Implementation Method 2. In the first interval, when switch SW1 is turned on, the sum of the forward voltage drops increases from 0V to Vf1. Figure 4 The diagram simulates the boost delay of buck converter 3, showing the case where there is a delay in the voltage rise 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, buck converter 3 also produces a boost delay. The same applies to the third and fourth intervals.

[0048] Control unit 4 acquires information from voltage acquisition unit 7 and calculates the forward voltage drop Vf and delay time for each segment. Figure 4 The area of ​​the triangular portion shown is then calculated. The control unit 4 then drives switch SW1 from the next control cycle using a drive duty cycle obtained by adding and correcting the area to the drive duty cycle of switch SW1, which has the largest drive duty cycle.

[0049] That is, according to Embodiment 2, since the current reduction caused by the boost delay of the buck converter 3 is estimated in advance and additive correction is performed, the current reduction can be corrected more accurately.

[0050] Furthermore, in this embodiment 2, additive correction is performed in descending order of drive duty cycle. Therefore, regardless of how the indicated value of the drive duty cycle of each segment changes, additive correction is performed along the steps generated by the increase in the forward voltage drop of the semiconductor light source, and correction can be performed only by considering the amount of current reduction caused by the increase in the forward voltage drop.

[0051] Furthermore, the control unit 4 can also perform additive correction, so that when the indicated value of the base current Ibase is small, the total delay time is larger compared to when the indicated value is large. The boost delay time of the buck converter 3 exhibits the following trend: when the indicated value of the base current Ibase is small, it is larger compared to when the indicated value is large.

[0052] Therefore, by performing additive correction, the total delay time increases when the indicated value of the base current Ibase is small compared to when the indicated value is large. This also takes into account the variation in the boost delay of the buck converter 3 due to the magnitude of the indicated value of the base current Ibase, thus enabling more accurate correction of the current reduction.

[0053] Especially when it is not determined through actual measurement Figure 4 The area of ​​the triangular portion shown is used to estimate the boost delay time of the buck converter 3 based on the forward voltage drop Vf, which further improves the accuracy of the predictive control. Furthermore, in Embodiment 2, the control unit 4 can adjust the measured values... Figure 4 The area of ​​the triangular portion shown can be added for correction, or the boost delay time of the buck converter 3 can be estimated and added for correction based on the forward voltage drop Vf.

[0054] Implementation Method 3

[0055] In the above embodiment, in order to correct the change in the average current value caused by the decrease in the base current Ibase output by the buck converter 3, the control unit 4 performs additive correction on the drive duty cycle of the switch SW according to the sum ΣVf of the forward voltage drop Vf of the semiconductor light source in each segment.

[0056] However, when additive correction is also performed on the segments indicated by the off state (drive duty cycle of 0%), the switch SW may only be weakly lit by the amount of additive correction. Therefore, in Embodiment 3, the control unit 4 sets the additive correction to 0 or disables additive correction for the segments indicated by the off state in each segment.

[0057] This process prevents the drive duty cycle from being additively corrected and resulting in weak illumination in segments that are indicated to be off.

[0058] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of this disclosure is set forth in the claims, not by the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0059] Label Explanation

[0060] 1 Battery, 2 Boost converter, 3 Buck converter, 4 Control unit, 5 Switch, 6 Lamp string, 7 Voltage acquisition unit, 8 Lighting control device.

Claims

1. A lighting control device, characterized in that, include: A boost converter that boosts the voltage from the battery and outputs it. A buck converter that receives the output voltage of the boost converter, steps down the output voltage to obtain the desired base current, and outputs it. A switching element that divides the series circuit of the semiconductor light source connected to the buck converter into multiple segments; A voltage acquisition unit acquires the sum of the forward voltage drops of the semiconductor light source in each of the segments; as well as The control unit indicates the output voltage of the boost converter and the base current of the buck converter, and controls the drive duty cycle of the switching elements for each segment. The control unit performs additive correction on the drive duty cycle of the switching element according to the sum of the forward voltage drops of the semiconductor light source, for each segment.

2. The lighting control device according to claim 1, characterized in that, The control unit performs additive correction on the drive duty cycle of the switching element based on the sum of the forward voltage drops of the semiconductor light source in each segment and the drive duty cycle of each segment, so as to compensate for the reduced current product for each segment.

3. The lighting control device according to claim 1, characterized in that, The control unit sums the delay time of each segment required for the increase in the forward voltage drop of the semiconductor light source in each segment boosted by the buck converter, and performs an additive correction on an amount equivalent to the summed delay time, starting from the drive duty cycle of the segment with the largest drive duty cycle.

4. The lighting control device according to claim 3, characterized in that, The control unit performs additive correction, so that the total delay time obtained when the indicated value of the base current is smaller is larger than when the indicated value of the base current is larger.

5. The lighting control device according to claim 1, characterized in that, The control unit determines the starting point of the drive duty cycle based on the end point of the duty cycle control cycle of the segment.

6. The lighting control device according to claim 5, characterized in that, The control unit performs additive correction starting from the segment with the larger drive duty cycle in the segment.

7. The lighting control device according to claim 1, characterized in that, For the segments that are indicated to be turned off, the control unit sets the additive correction to 0 or disables the additive correction.

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