Vehicular lighting control device

Abstract

The purpose is to provide the capability to appropriately bring the actual brightness of a semiconductor light source close to an intended brightness level. This vehicular lighting control device includes a ceramic capacitor for smoothing output power from a constant current power source to the semiconductor light source, a drive unit for performing PWM control on a first switching element used for turning on and off a supply of a constant current to the semiconductor light source, a time specification unit for specifying voltage rise delay time on the basis of the voltage of the semiconductor light source after a rise and the constant current, and a correction unit for correcting a duty ratio of the PWM control on the basis of the voltage rise delay time.

Description

Vehicle lighting control device

[0001] The present disclosure relates to a vehicle lighting control device.

[0002] In recent years, various technologies have been proposed for vehicle lighting control devices that control light sources used in vehicle lighting devices such as headlamps. For example, in Patent Document 1, a technology for controlling the brightness (light emission amount) of a light source by performing PWM (Pulse Width Modulation) control has been proposed. In addition, a vehicle lighting control device including a constant current power supply that supplies a constant current to a semiconductor light source, which is a type of light source, and a smoothing capacitor that smooths the output power of the constant current power supply has been proposed.

[0003] Japanese Patent No. 6916668

[0004] As the smoothing capacitor provided in the vehicle lighting control device, a ceramic capacitor is preferably used from the viewpoints of electrical characteristics, miniaturization, durability, and cost. However, a ceramic capacitor has a property that its capacitance changes relatively greatly when the charging voltage changes.

[0005] In the vehicle lighting control device, since the charging voltage of the ceramic capacitor varies in various ways corresponding to the voltage of the semiconductor light source, there is a problem that the capacitance of the ceramic capacitor changes due to the above property, and the time required for the voltage of the semiconductor light source to rise changes. As a result, there is a problem that the actual brightness of the semiconductor light source cannot be appropriately brought close to the target brightness.

[0006] Therefore, the present disclosure has been made in view of the above problems, and an object thereof is to provide a technology capable of appropriately bringing the actual brightness of a semiconductor light source close to the target brightness.

[0007] The vehicle lighting control device according to this disclosure is a vehicle lighting control device for controlling a semiconductor light source, comprising: a constant current power supply that supplies a constant current to the semiconductor light source based on power supplied from a power source; a ceramic capacitor that smooths the output power from the constant current power supply to the semiconductor light source; a first switching element for turning the supply of constant current to the semiconductor light source on and off; a drive unit that performs PWM control on the first switching element; a time determination unit that determines a boost delay time, which is the time required for the voltage of the semiconductor light source to rise, based on the voltage of the semiconductor light source after rise and the constant current; and a correction unit that corrects the duty cycle of the PWM control based on the boost delay time.

[0008] According to this disclosure, the boost delay time is determined based on the voltage and constant current after the semiconductor light source has risen, and the duty cycle of the PWM control is corrected based on the boost delay time. With such a configuration, the actual brightness of the semiconductor light source can be appropriately brought closer to the target brightness.

[0009] The purpose, features, aspects, and advantages of this disclosure will become clearer from the following detailed description and accompanying drawings.

[0010] Figure 1 is a circuit diagram showing the configuration of a vehicle lighting control device according to this embodiment 1. Figure 2(a) is a diagram showing the waveform of the charging voltage of a ceramic capacitor in the related device, and Figure 2(b) is a diagram showing the waveform of the current of an LED connected to the related device. Figure 3 is a diagram for explaining the operation of the second switching element. Figure 4 is a diagram for explaining the operation of the second switching element. Figure 5 is a graph showing the properties of a ceramic capacitor. Figure 6 is a graph showing the simulation results of the control unit according to modification 1 of embodiment 1. Figure 7 is a graph of the regression equation according to modification 1 of embodiment 1. Figure 8 is a circuit diagram showing the configuration of a vehicle lighting control device according to this embodiment 2. Figure 9 is a graph showing the temperature characteristics of a ceramic capacitor.

[0011] <Embodiment 1> Figure 1 is a circuit diagram showing the configuration of a vehicle lighting control device according to this embodiment 1. The vehicle lighting control device in Figure 1 controls a semiconductor light source.

[0012] In Figure 1, the semiconductor light sources are LEDs (light-emitting diodes) 21a, 21b, and 21c, but other semiconductor light-emitting elements, such as LDs (laser diodes), may also be used. In the following explanation, when LEDs 21a, 21b, and 21c are not distinguished, they may be collectively referred to as LED21.

[0013] In the example shown in Figure 1, LEDs 21a, 21b, and 21c are connected in series and are used, for example, in vehicle lighting devices such as high beams, low beams, and signal lights. With this configuration, multiple vehicle lighting devices can be lit using one constant current power supply 1, thus reducing the number of constant current power supplies 1 and enabling miniaturization and reduction of heat generation. Note that the types of vehicle lighting devices to which LEDs 21 are applied are not limited to those described above, and the number of LEDs 21 and vehicle lighting devices are not limited to those described above.

[0014] The vehicle lighting control device shown in Figure 1 comprises a constant current power supply 1, a ceramic capacitor 2, a first switching element 3, a second switching element 4, a drive circuit 5 which is a drive unit, a voltage sensor 6, and a control unit 7.

[0015] The constant current power supply 1 supplies a constant current to the LED 21 based on the power supplied from a power source such as a DC power supply. The constant current power supply 1 may use a converter that, for example, boosts or buckes the voltage included in the power supplied from the power source, and uses the resulting voltage to supply a constant current to the LED 21. The converter is sometimes called a switching power supply. The constant current output from the constant current power supply 1 may fluctuate slightly, as long as it is generally about the same as the constant current output from the converter.

[0016] The ceramic capacitor 2 is connected to the output side of the constant current power supply 1 and smooths the output power from the constant current power supply 1 to the LED 21. As a result, even if the constant current output from the constant current power supply 1 fluctuates, fluctuations in the constant current supplied to the LED 21 are suppressed.

[0017] Furthermore, if there are fluctuations in the constant current output from the constant current power supply 1, the frequency of such fluctuations is expected to be relatively high, ranging from several hundred kHz to several MHz. For this reason, while a certain capacitance is sufficient for the smoothing capacitor that smooths the output power of the constant current power supply 1, it is also required that the parasitic inductance be as small as possible. Considering these electrical characteristics, as well as miniaturization, durability, and cost, the smoothing capacitor in the vehicle lighting control device according to this embodiment 1 is a ceramic capacitor 2.

[0018] The first switching element 3 is, for example, a semiconductor switching element, and is an element for turning on and off the supply of a constant current to the LED 21. The first switching element 3 is connected in parallel with the LED 21, and when the first switching element 3 is turned on, the supply of a constant current to the LED 21 is turned off, and when the first switching element 3 is turned off, the supply of a constant current to the LED 21 is turned on.

[0019] The second switching element 4 is, for example, a semiconductor switching element. One end of the second switching element 4 is connected between the ceramic capacitor 2 and the first switching element 3, and the other end of the second switching element 4 is grounded. When the second switching element 4 is turned on, the charging voltage of the ceramic capacitor 2 is discharged by the ground, and when the second switching element 4 is turned off, the discharge of the ceramic capacitor 2 by the ground is stopped.

[0020] The drive circuit 5 controls the on and off states of the first switching element 3 and the second switching element 4. The drive circuit 5 controls the on and off state of the constant current supply by the first switching element 3 by performing PWM (Pulse Width Modulation) control on the first switching element 3. In addition, the drive circuit 5 turns on the second switching element 4 when the constant current supply is switched off. In other words, the second switching element 4 discharges the ceramic capacitor 2 when the constant current supply to the LED 21 is switched off.

[0021] Before describing the voltage sensor 6 and control unit 7 in Figure 1, we will now describe a related device that does not include the voltage sensor 6 and control unit 7, but does include the constant current power supply 1 to the drive circuit 5 described above.

[0022] Figure 2(a) shows the waveform of the charging voltage of the ceramic capacitor 2 in the related device, and Figure 2(b) shows the waveform of the current of the LED 21 connected to the related device.

[0023] The drive circuit 5 controls the on and off states of the first switching element 3 and the second switching element 4, causing the charging voltage of the ceramic capacitor 2 to decrease and increase, as shown by the solid waveform in Figure 2(a). Since the charging voltage of the ceramic capacitor 2 is substantially the same as the voltage of the LED 21, the two may not be distinguished in the following explanation. When multiple LEDs 21 are lit, the charging voltage of the ceramic capacitor 2 becomes substantially the same as the sum of the voltages of the multiple LEDs 21.

[0024] At time t1, the drive circuit 5 turns off the first switching element 3 and the second switching element 4, causing the charging voltage of the ceramic capacitor 2 (the voltage across LED 21) to rise. Then, at time t2, the charging voltage of the ceramic capacitor 2 (the voltage across LED 21) becomes the voltage at which the constant current smoothed by the ceramic capacitor 2 flows through LED 21, causing LED 21 to light up. Then, at time t3, the drive circuit 5 turns on the first switching element 3 and the second switching element 4, causing the charging voltage of the ceramic capacitor 2 (the voltage across LED 21) to fall, and LED 21 to turn off. After that, the drive circuit 5 repeats the operation from time t1 to t3.

[0025] The drive circuit 5 performs PWM control, which controls the duty cycle defined by the time the first switching element 3 is turned on (the time the LED 21 is turned off) at time points t3 to t1, and the time the first switching element 3 is turned off (the time the LED 21 is turned on) at time points t1 to t3. Therefore, the drive circuit 5 can control the brightness (amount of light emitted) of the LED 21 by controlling the duty cycle of the PWM control in the first switching element 3.

[0026] In the following explanation, the time required for the voltage of LED 21 to rise from time t1 to time t2 is referred to as the "boost delay time t ＢＯＯＳＴ It is sometimes written as follows: As shown in Figure 2(a), the rise in the charging voltage of the ceramic capacitor 2, that is, the rise in the voltage of the LED 21, is gradual due to the capacitance of the ceramic capacitor 2. On the other hand, the decrease in the charging voltage of the ceramic capacitor 2 is steep due to the discharge caused by the grounding of the second switching element 4.

[0027] In the following explanation, the voltage of LED 21 at time t2, that is, the voltage of LED 21 at which a constant current begins to flow through LED 21, may also be referred to as the "voltage of LED 21 after rising." Typically, the voltage required for the vehicle lighting device (LED 21) to light up, that is, the voltage of LED 21 after rising, differs depending on the type of vehicle lighting device (LED 21).

[0028] Next, we will explain the significance of the second switching element 4 discharging the ceramic capacitor 2.

[0029] First, let's consider the case where the high beams of the headlights, the low beams of the headlights, and the signal lights are all illuminated. In this case, as shown in Figure 3, all LEDs 21a, 21b, and 21c are illuminated, and the charging voltage of the ceramic capacitor 2 is the same as the sum of the voltages Va, Vb, and Vc of LEDs 21a, 21b, and 21c (= Va + Vb + Vc).

[0030] Let's consider a scenario where, after the state shown in Figure 3, the high beam and low beam headlights are turned off, and only the signal lights are illuminated. In this case, as shown in Figure 4, only LED 21c is illuminated.

[0031] As a result, the voltage of LED 21c becomes effectively approximately Va + Vb + Vc, which can damage LED 21c, whose rated voltage is approximately Vc. This is also true when multiple LEDs 21a, 21b, and 21c are lit, and then either LED 21b or 21c is lit.

[0032] Therefore, the second switching element 4 of the related device discharges the ceramic capacitor 2 when the constant current supply to the LED 21 is switched off. With this configuration, the charging voltage of the ceramic capacitor 2 can be sufficiently reduced during the period when the LEDs 21a, 21b, and 21c are off after all of them have been lit up, until one of the LEDs 21a, 21b, or 21c is lit up. As a result, it is possible to suppress the destruction of the LED 21 by the charging voltage of the ceramic capacitor 2.

[0033] Next, the problems with the related device will be explained. In the related device, the charging voltage of the ceramic capacitor 2 before the voltage rises becomes 0V due to discharge using the second switching element 4. Therefore, the voltage boost delay time t in Figure 2(a) ＢＯＯＳＴ The rise time tends to be longer, and the rise time of the actual charging voltage (solid line waveform) of ceramic capacitor 2 tends to be longer than the rise time of the ideal charging voltage (dotted line waveform) of ceramic capacitor 2.

[0034] Due to this tendency, as shown in Figure 2(b), the period during which current actually flows through LED 21 (solid waveform) tends to be shorter than the period during which current ideally flows through LED 21 (dotted waveform). As a result, the actual average current shown by the dashed line becomes smaller than the target average current shown by the dashed line, which leads to the problem that the actual brightness of LED 21 is dimmer than the target brightness.

[0035] As a solution to this problem, the boost delay time t is set to the charging time of the ceramic capacitor 2. ＢＯＯＳＴ In addition, it is conceivable to make the duty cycle of the charging voltage of the ceramic capacitor 2 larger than the design value (making the duty cycle of the first switching element 3 smaller than the set value).

[0036] However, generally speaking, the boost delay time t ＢＯＯＳＴ This changes depending on the capacitance of the ceramic capacitor 2. As shown in Figure 5, the ceramic capacitor 2 has the property that its capacitance changes relatively large when the charging voltage changes. For this reason, in a vehicle lighting control device using the ceramic capacitor 2, the boost delay time t ＢＯＯＳＴThis changes depending on the charging voltage of the ceramic capacitor 2, that is, the voltage after the LED 21 has risen.

[0037] Here, the voltage of LED 21 after it has risen varies depending on the current and temperature of LED 21, and also varies depending on the combination of LEDs 21a, 21b, and 21c that are lit. Furthermore, the voltage of LED 21 after it has risen also differs depending on the type of vehicle lighting system, and even if the type of vehicle lighting system is the same, it will differ depending on the individual performance of LED 21.

[0038] Therefore, a constant time longer than the design value is set as the boost delay time t. ＢＯＯＳＴ Simply using it in this way presented a problem: it was not possible to appropriately bring the actual brightness of LED 21 closer to the target brightness.

[0039] In contrast, the vehicle lighting control device according to this embodiment 1, which includes the voltage sensor 6 and control unit 7 shown in Figure 1, makes it possible to appropriately bring the actual brightness of the LED 21 closer to the target brightness. This will be explained below.

[0040] The voltage sensor 6 measures the voltage of the LEDs 21. For example, when LEDs 21a, 21b, and 21c are lit, the voltage sensor 6 measures the voltage of LEDs 21a, 21b, and 21c. The voltage measurement of the LEDs 21 by the voltage sensor 6 may be performed periodically (every second), or when the vehicle lighting device being lit is changed.

[0041] The control unit 7 includes a time-specification unit 7a and a correction unit 7b. The time-specification unit 7a and the correction unit 7b will be hereinafter referred to as "time-specification unit 7a, etc." The time-specification unit 7a, etc. is implemented by the processing circuit 81 shown in Figure 1. The processing circuit 81 may be made of dedicated hardware or a processor that executes a program stored in memory. Examples of processors include central processing units, processing units, arithmetic units, microprocessors, microcomputers, and DSPs (Digital Signal Processors).

[0042] If the processing circuit 81 is dedicated hardware, it may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. Each function of the time-specific unit 7a, etc., may be implemented by a circuit with distributed processing circuits, or the functions of each part may be implemented together by a single processing circuit.

[0043] When the processing circuit 81 is a processor, the functions of the time-specification unit 7a, etc., are realized in combination with software, etc. The software, etc., may include, for example, software, firmware, or both. The software, etc., is written as a program and stored in memory. The processor applied to the processing circuit 81 realizes the functions of each part by reading and executing the program stored in memory. That is, the control unit 7 has memory for storing a program that, when executed by the processing circuit 81, will result in the execution of steps performed by the time-specification unit 7a and the correction unit 7b. In other words, this program can be said to cause the computer to execute the procedures and methods of the time-specification unit 7a, etc. Here, memory may be non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), HDD (Hard Disk Drive), magnetic disk, flexible disk, optical disk, compact disk, minidisc, DVD (Digital Versatile Disc), their drive devices, or any storage medium used in the future.

[0044] The time specifying unit 7a acquires the voltage after the rise of the LED 21 and the constant current of the constant current power supply 1. For example, the time specifying unit 7a acquires the voltage after the rise of the LED 21 from the waveform of the voltage measured by the voltage sensor 6.

[0045] For example, a higher-level device of the vehicle lighting control device determines a current value based on the combination of the LEDs 21a, 21b, and 21c to be lit, and the time specifying unit 7a acquires the current value determined by the higher-level device as the constant current of the constant current power supply 1. Also, for example, a higher-level device of the vehicle lighting control device determines the combination of the LEDs 21a, 21b, and 21c to be lit, and the time specifying unit 7a acquires the current value corresponding to the combination determined by the higher-level device from the correspondence table as the constant current of the constant current power supply 1. The higher-level device is, for example, an ECU (Electronic Control Unit). Since the constant current of the constant current power supply 1 is controlled to an accurate value by various circuits, the time specifying unit 7a can acquire the value of the constant current of the constant current power supply 1 as described above without providing a current sensor.

[0046] The time specifying unit 7a is the voltage V after the rise of the LED 21 ＬＥＤ and the constant current I of the constant current power supply 1 ＯＵＴ Based on, the boost delay time t ＢＯＯＳＴ To identify. Here, the boost delay time t ＢＯＯＳＴ Is the constant current I ＯＵＴ Tends to be inversely proportional to, and when the constant current I ＯＵＴ Becomes half, the boost delay time t ＢＯＯＳＴ Tends to double. The boost delay time t ＢＯＯＳＴ Is the capacitance C of the ceramic capacitor 2 ＳＭＯＯＴＨ Tends to be proportional to, and when the capacitance C ＳＭＯＯＴＨ Doubles, the boost delay time t ＢＯＯＳＴ Tends to double. The boost delay time t ＢＯＯＳＴ Is the voltage V ＬＥＤ Tends to be proportional to, and when the voltage V ＬＥＤ Doubles, the boost delay time t ＢＯＯＳＴ Tends to double. From the above, the boost delay time t ＢＯＯＳＴ The constant current I ＯＵＴ The capacitance C ＳＭＯＯＴＨ And the voltage VＬＥＤ The following relationship (1) holds between them.

[0047]

[0048] In this embodiment 1, the time-specific unit 7a corresponds to the capacity C shown in the graph in Figure 5. ＳＭＯＯＴＨ and voltage V ＬＥＤ A correspondence table is pre-stored in the above memory. The time-specific unit 7a determines the acquired voltage V after the rise of the LED 21. ＬＥＤ Capacity C corresponding to ＳＭＯＯＴＨ The corresponding table is read, and the read capacity C ＳＭＯＯＴＨ And constant current I ＯＵＴ and voltage V ＬＥＤ Applying and to equation (1), the boost delay time t ＢＯＯＳＴ Identify.

[0049] As a result, the voltage V after the rise of LED 21 ＬＥＤ Boost delay time t when high ＢＯＯＳＴ The voltage V after the rise of LED21 is ＬＥＤ Boost delay time t when low ＢＯＯＳＴ It becomes larger than that. Also, constant current I ＯＵＴ Boost delay time t when low ＢＯＯＳＴ is a constant current I ＯＵＴ Boost delay time t when high ＢＯＯＳＴ It will become larger than that.

[0050] The correction unit 7b adjusts the boost delay time t specified by the time specification unit 7a. ＢＯＯＳＴ Based on this, the duty cycle of the PWM control in the first switching element 3 is corrected. As described above, when the first switching element 3 is turned on, the constant current supply to the LED 21 is turned off, and when the first switching element 3 is turned off, the constant current supply to the LED 21 is turned on. For this reason, the correction unit 7b adjusts the boost delay time t ＢＯＯＳＴ As the length increases, the duty cycle of the PWM control of the first switching element 3 is reduced, thereby increasing the duty cycle of the PWM control of the LED 21.

[0051] <Summary of Embodiment 1> According to the vehicle lighting control device of Embodiment 1 described above, the time-specific unit 7a determines the voltage V after the LED 21 has risen.ＬＥＤ And the constant current I of constant current power supply 1 ＯＵＴ Based on this, the boost delay time t ＢＯＯＳＴ The correction unit 7b identifies the boost delay time t ＢＯＯＳＴ Based on this, the duty cycle of the PWM control in the first switching element 3 is corrected. For example, the voltage V after the LED 21 rises. ＬＥＤ Boost delay time t when high ＢＯＯＳＴ The voltage V after the rise of LED21 is ＬＥＤ Boost delay time t when low ＢＯＯＳＴ It becomes larger than the constant current I ＯＵＴ Boost delay time t when low ＢＯＯＳＴ is a constant current I ＯＵＴ Boost delay time t when high ＢＯＯＳＴ This becomes larger than the specified value. With this configuration, the period during which current actually flows through the LED 21 in Figure 2(b) (solid waveform) can be appropriately brought closer to the period during which current ideally flows through the LED 21 (dotted waveform), thereby allowing the actual brightness of the LED 21 to be appropriately brought closer to the target brightness.

[0052] Furthermore, in this embodiment 1, the second switching element 4 discharges the ceramic capacitor 2 when the constant current supply to the LED 21 is switched off. With this configuration, it is possible to suppress the destruction of the LED 21 by the charging voltage of the ceramic capacitor 2. However, the discharge of the ceramic capacitor 2 by the second switching element 4 is not essential for appropriately bringing the actual brightness of the LED 21 closer to the target brightness.

[0053] <Modification 1> As shown in Figure 5, the capacitance of the ceramic capacitor 2 decreases as the charging voltage of the ceramic capacitor 2 increases. Here, the capacitance C of the ceramic capacitor 2 ＳＭＯＯＴＨ Voltage V ＬＥＤ Function (C ＳＭＯＯＴＨ (V ＬＥＤ )) If so, the small boost delay time dt ＢＯＯＳＴ and a very small voltage dV ＬＥＤ The following equation (2) holds between them.

[0054]

[0055] The time-specific unit 7a of the control unit 7 uses this equation (2) to determine the minute voltage dV ＬＥＤ From 0V to voltage V ＬＥＤ By performing a simulation that adds up to this point, a graph in Figure 6 is created, and the boost delay time t is used with this graph in Figure 6. ＢＯＯＳＴ The constant current I of the constant current power supply 1 may be calculated (specified). ＯＵＴ Even if it is constant, as shown in Figure 6, the boost delay time t ＢＯＯＳＴ As it increases, the charging voltage of ceramic capacitor 2 (voltage after the LED 21 rises V) ＬＥＤ The degree to which ) increases increases. This trend in the graph of Figure 6 is consistent with the trend in the graph of Figure 5.

[0056] When the time-specific unit 7a of the control unit 7 performs the above simulation, the boost delay time t ＢＯＯＳＴ This can be calculated accurately. However, since this calculation requires numerous numerical calculations, if the control unit 7 is a microcontroller with relatively low computational performance, for example, the boost delay time t ＢＯＯＳＴ This makes the calculation difficult.

[0057] Therefore, the time-specific unit 7a pre-stores the following equation (3), which approximates the graph in Figure 6, and adds a constant current I to the following equation (3). ＯＵＴ and voltage V ＬＥＤ By applying this, the boost delay time t ＢＯＯＳＴ The coefficients A, B, and C in the following equation (3) can be determined regressively by, for example, the least squares method for the external components of a vehicle lighting control device, in which case the following equation (3) is equal to the boost delay time t. ＢＯＯＳＴ , constant current I ＯＵＴ and voltage V ＬＥＤ This becomes the regression equation.

[0058]

[0059] Figure 7 is a graph represented by equation (3). The graph in Figure 7 is roughly identical to the graph in Figure 6, except that the horizontal and vertical axes are reversed. With this configuration, the control unit 7 corresponds to the capacitance C in the graph of Figure 5. ＳＭＯＯＴＨ and voltage V ＬＥＤWithout having to pre-store a correspondence table or perform numerous numerical calculations, the boost delay time t can be calculated. ＢＯＯＳＴ This can be easily calculated.

[0060] <Modification 2> The ceramic capacitor 2 may be changed in accordance with the change of the LED 21. Therefore, the time specification unit 7a may pre-store the coefficients A, B, and C of equation (3) for each of the multiple ceramic capacitors 2. Then, when the ceramic capacitor 2 being used is changed, the time specification unit 7a uses equation (3) to which the coefficients A, B, and C corresponding to the ceramic capacitor 2 being used are applied to determine the boost delay time t ＢＯＯＳＴ You may calculate this.

[0061] Alternatively, if the ceramic capacitor 2 used is changed, the time-specification unit 7a performs a simulation using equation (2) to determine the boost delay time t ＢＯＯＳＴ You may calculate this.

[0062] Alternatively, the time-specification unit 7a may pre-store a correspondence table corresponding to the graph in Figure 5 for each of the multiple ceramic capacitors 2. Then, when the ceramic capacitor 2 being used is changed, the time-specification unit 7a uses the correspondence table corresponding to the ceramic capacitor 2 being used to determine the boost delay time t ＢＯＯＳＴ You may calculate this.

[0063] <Embodiment 2> Figure 8 is a circuit diagram showing the configuration of a vehicle lighting control device according to Embodiment 2. Hereinafter, among the components of Embodiment 2, components that are the same as or similar to the components described above will be denoted by the same or similar reference numerals, and the different components will be mainly described.

[0064] The configuration in Figure 8 is similar to the configuration in Figure 1, but with the addition of a temperature sensor 11. The temperature sensor 11 is, for example, a thermistor, which measures the temperature of the ceramic capacitor 2.

[0065] Fig. 9 is a graph showing the temperature characteristics of the ceramic capacitor 2. As shown in Fig. 9, since the capacitance of the ceramic capacitor 2 changes depending on the temperature of the ceramic capacitor 2, from the equation (5), the boost delay time t ＢＯＯＳＴ also changes depending on the temperature of the ceramic capacitor 2.

[0066] Therefore, in the second embodiment, the time specifying unit 7a is based on the voltage V ＬＥＤ after the rise of the LED 21, the constant current I ＯＵＴ of the constant current power supply 1, and the temperature of the ceramic capacitor 2 measured by the temperature sensor 11, and specifies the boost delay time t ＢＯＯＳＴ . For example, the time specifying unit 7a may previously store a correspondence table between the rate of change of the capacitance corresponding to the graph of Fig. 9 and the temperature (per 1 °C). Then, the time specifying unit 7a reads out the rate of change of the capacitance corresponding to the measured temperature from the correspondence table, and multiplies the rate of change by the boost delay time t ＢＯＯＳＴ specified in the first embodiment and each modification example, so as to change the boost delay time t ＢＯＯＳＴ used by the correction unit 7b. For example, when the temperature of the ceramic capacitor 2 changes from room temperature to 100 °C, the time specifying unit 7a may reduce the boost delay time t ＢＯＯＳＴ by 10% in accordance with the graph of Fig. 9.

[0067] According to the vehicle lighting control device according to the second embodiment as described above, based on the voltage V ＬＥＤ after the rise of the LED 21, the constant current I ＯＵＴ of the constant current power supply 1, and the temperature of the ceramic capacitor 2, the boost delay time t [[ID=2Y]] ＢＯＯＳＴ is specified. According to such a configuration, the boost delay time t ＢＯＯＳＴ can be appropriately changed according to the temperature of the ceramic capacitor 2, so that the actual brightness of the LED 21 can be made closer to the target brightness more appropriately.

[0068] In the above description, the time specifying unit 7a uses a correspondence table regarding the temperature of the ceramic capacitor 2 to determine the boost delay time t ＢＯＯＳＴThe above was changed, but it is not limited to this. For example, the time specification unit 7a performs a simulation on the temperature of the ceramic capacitor 2, similar to the simulation using equation (2), to determine the boost delay time t ＢＯＯＳＴ The following can be changed. Also, for example, the time-specification unit 7a can use a regression equation relating to the temperature of the ceramic capacitor 2, similar to the regression equation in equation (3), to determine the boost delay time t ＢＯＯＳＴ You may change it.

[0069] In this disclosure in English, 'a' and 'an' mean one or more. Therefore, 'a', 'an', 'one or more', and 'at least one' can be used interchangeably.

[0070] Furthermore, it is possible to freely combine each embodiment and each variation, and to modify or omit each embodiment and each variation as appropriate.

[0071] The above explanation is illustrative and not limiting in all respects. It should be understood that countless variations not illustrated are conceivable.

[0072] 1 Constant current power supply, 2 Ceramic capacitor, 3 First switching element, 4 Second switching element, 5 Drive circuit, 7a Time specification unit, 7b Correction unit, 21, 21a, 21b, 21c LEDs.

Claims

1. A vehicle lighting control device for controlling a semiconductor light source, comprising: a constant current power supply that supplies a constant current to the semiconductor light source based on power supplied from a power source; a ceramic capacitor that smooths the output power from the constant current power supply to the semiconductor light source; a first switching element for turning on and off the supply of the constant current to the semiconductor light source; a drive unit that performs PWM control on the first switching element; a time determination unit that determines a boost delay time, which is the time required for the voltage of the semiconductor light source to rise, based on the voltage of the semiconductor light source after it has risen and the constant current; and a correction unit that corrects the duty cycle of the PWM control based on the boost delay time.

2. A vehicle lighting control device according to claim 1, wherein the voltage boost delay time when the voltage after the rise of the semiconductor light source is high is greater than the voltage boost delay time when the voltage after the rise of the semiconductor light source is low.

3. A vehicle lighting control device according to claim 1, wherein the voltage boost delay time when the constant current is low is greater than the voltage boost delay time when the constant current is high.

4. A vehicle lighting control device according to claim 1, wherein the time-determining unit determines the voltage boost delay time based on the voltage after the semiconductor light source has risen, the constant current, and the temperature of the ceramic capacitor.

5. A vehicle lighting control device according to claim 1, further comprising a second switching element that discharges the ceramic capacitor when the supply of the constant current to the semiconductor light source is switched off.

6. A vehicle lighting control device according to claim 1, wherein the time-determining unit determines the voltage boost delay time from the voltage after the semiconductor light source has risen and the constant current using a regression equation of the voltage boost delay time, the voltage after the semiconductor light source has risen, and the constant current.

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