EP2675246A2

EP2675246A2 - Semiconductor-light-source control device

Info

Publication number: EP2675246A2
Application number: EP20130171423
Authority: EP
Inventors: Kentarou Murakami; Masaru Sasaki
Original assignee: Koito Manufacturing Co Ltd
Current assignee: Koito Manufacturing Co Ltd
Priority date: 2012-06-12
Filing date: 2013-06-11
Publication date: 2013-12-18
Also published as: EP2675246A3; CN103491670A; JP2013258003A; CN103491670B

Abstract

A semiconductor-light-source control device includes a regulator and a driving control section. The regulator generates a driving current flowing through a semiconductor light source. The driving control section controls the regulator so that a magnitude of the driving current approaches a target value. A luminance of the semiconductor light source is adjusted by repeating a first state in which the magnitude of the driving current is controlled to approach the target value and a second state in which the driving current is smaller than that in the first state. Both the duty ratio of the first and second states and the target value change according to a setting value of the luminance of the semiconductor light source. One of the target value and the duty ratio is set so as to have a one-to-one correspondence relationship with the setting value.

Description

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to a semiconductor-light-source control device that controls a semiconductor light source such as an LED (light emitting diode).

2. Description of the Related Art

Recently, an LED with low power consumption and long life has been used in a vehicle lamp, such as a headlight, instead of a halogen lamp having a filament. The degree of light emission of the LED, that is, the brightness of the LED depends on the magnitude of a current flowing through the LED. Therefore, when the LED is used as a light source, a lighting circuit for adjusting the current flowing through the LED is required. Such a lighting circuit generally has an error amplifier that performs feedback control so that the current flowing through the LED is constant.
For example, states of the headlight include a high-beam state and a low-beam state. In order to make it easier to fit standards, it is desirable to be capable of adjusting the brightness of the LED. As one of methods for changing the brightness of the LED, a pulse width modulation (PWM) dimming that switches on and off a current so as to change the duty ratio has been known.
US 2010/0181914 A (corresponding to JP 2010-170704 A ) describes a lighting control device that adopts the PWM dimming.
In general PWM dimming, the lower limit of the dimming ratio that can be realized is limited depending on the response speed of the switching element for switching on/off the current. JP 2005-332586 A describes a countermeasure thereto, that is, a method for performing dimmer control by changing a target value of a current to the LED based on a control signal that is different from a control signal for PWM driving a switching element.

SUMMARY OF THE INVENTION

The method described in JP 2005-332586 A uses two different values are used as the current supplied to the light source. When a relative luminance is high, the larger current value is used, while when the relative luminance is low, the smaller current value is used. In this case, the number of the setting values of the current is two, change in current at the time of current switching is relatively large. When the relative luminance is changed gradually and passes through a s current witching point, the peak value of the current changes greatly at the switching point, which may cause relatively large change in emission characteristics of the LED.
The invention has been made in view of the above circumstances and provides a semiconductor-light-source control device that can change the luminance of a semiconductor light source more smoothly while realizing PWM dimming with a wide setting range of the luminance of the semiconductor light source.
One embodiment of the invention relates to a semiconductor-light-source control device. The semiconductor-light-source control device includes a regulator and a driving control section. The regulator generates a driving current flowing through a semiconductor light source. The driving control section controls the regulator so that a magnitude of the driving current approaches a target value. A luminance of the semiconductor light source is adjusted by repeating (i) a first state in which the magnitude of the driving current flowing through the semiconductor light source is controlled so as to approach the target value and (ii) a second state in which the driving current is smaller than that in the first state. Both of a duty ratio of the first and second states during the repeating and the target value in the driving control section change in accordance with a setting value of the luminance of the semiconductor light source. One of the target value and the duty ratio is set so as to have a one-to-one correspondence relationship with the setting value of the luminance of the semiconductor light source.
With this embodiment, the target value or the duty ratio have the one-to-one correspondence relationship with the setting value of the luminance of the semiconductor light source.
It should be noted that embodiments of the invention include a modification in which components of the above embodiment are arbitrarily combined.
With the above configuration, the luminance of a semiconductor light source can be changed more smoothly while the PWM dimming with the wide setting range of the luminance of the semiconductor light source is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a circuit diagram showing the configuration of an in-vehicle circuit including a semiconductor-light-source control device according to an embodiment;
Fig. 2 is a timing chart showing an operation state of the semiconductor-light-source control device shown in Fig. 1 under gradual change control; and
Fig. 3 is an explanatory view showing interrupt control of a microcomputer.

DETAILED DESCRIPTION

Detailed description will be given on embodiments of the invention with reference to the accompanying drawings. The same or equivalent elements, components, and signals shown in the drawings will be denoted by the same reference numerals, and redundant description thereon will be omitted. Also, some members that are not important in explanation will be omitted in each drawings. Furthermore, reference numerals and reference signs given to voltages, currents, and resistances may be used to indicate voltage values, current values, and resistance values as necessary.
In this specification, "a state in which a member A is connected to a member B" includes not only a case where the members A and B are connected to each other physically and directly but also a case where the members A and B are indirectly connected via another member that does not affect an electrical connection state therebetween. Similarly, "a state in which a member C is provided between members A and B" includes not only a case where the members A and C or the members B and C are directly connected to each other but also a case where the members A and C or the members B and C are indirectly connected via another member that does not affect an electrical connection state therebetween.
A semiconductor-light-source control device according to one embodiment includes a switching regulator and a driving control section. The switching regulator generates a driving current flowing through an LED using a switching element. The driving control section feedback-controls ON/OFF of the switching element so that a magnitude of the driving current approaches a target value. In the semiconductor-light-source control device, PWM dimming is also performed. In other words, a degree of light emission of the LED, that is, a luminance of the LED is adjusted by repeating (i) a current control state in which the magnitude of the driving current is controlled so as to approach the target value and (ii) a current suppression state in which the driving current is smaller than that in the current control state. More specifically, the semiconductor-light-source control device adjusts the luminance of the LED by turning on and off a dimmer switch element that is disposed on a path, between the LED and the switching regulator, through which the driving current flows path at a predetermined dimming frequency f1. In this case, the current control state corresponds to an ON state of the dimmer switch element. Also, the current suppression state corresponds to the OFF state of the dimmer switch element. In the OFF statement of the dimmer switch element, the driving current flowing through the LED is substantially zero.
The semiconductor-light-source control device changes a duty ratio between the current control state and the current suppression state during the repeating of the current control state and the current suppression state, that is, a duty ratio of ON/OFF of the dimmer switch element in accordance with the setting value of the luminance of the LED (hereinafter, the luminance of the LED is expressed in dimming ratio that is a percentage of the maximum luminance). The semiconductor-light-source control device changes the target value of the driving current according to the setting value of the dimming ratio. In particular, each of the duty ratio and the target value changes monotonically with respect to the setting value of the dimming ratio that is in a range of values which the dimming ratio can take, that is, in a range of 1 % to 100 %. In this manner, it is possible to suppress sudden changes in driving current or in duty ratio during the dimming control while to realize a relatively wide range of dimming control. As a result, it is possible to suppress sudden changes in emission characteristics of the LED.
Fig. 1 is a circuit diagram showing the configuration of an in-vehicle circuit 10. The in-vehicle circuit 10 includes a semiconductor-light-source control device 100 according to this embodiment, an electronic control unit (ECU) 20, an in-vehicle battery 30, an LED 40 that is configured such that three in-vehicle LEDs are connected in series, and a switch SW. It is suitable that the LED 40 and the semiconductor-light-source control device 100 are mounted on a vehicle lamp.
The electronic control unit 20 is a microcomputer that performs overall electrical control of a vehicle such as an automobile. The electronic control unit 20 is connected to the in-vehicle battery 30 through the switch SW. When the switch SW is turned on, the electronic control unit 30 receives a battery voltage Vbat from the in-vehicle battery 30. The electronic control unit 20 supplies the DC battery voltage Vbat to the semiconductor-light-source control device 100 as an input voltage Vin. The electronic control unit 20 also supplies a fixed voltage, that is, a ground potential V_GND (= 0 V) to the semiconductor-light-source control device 100. The electronic control unit 20 generates a PWM dimming signal S1 and supplies it to the semiconductor-light-source control device 100.
The PWM dimming signal S1 is a signal for blinking the LED 40 at high speed, for example, at a dimming frequency f1 in a range of several hundred Hz to several kHz. More specifically, the PWM dimming signal S1 is a signal having a voltage that changes in a rectangular waveform manner at the dimming frequency f1. The electronic control unit 20 sets a duty ratio of the PWM dimming signal S1 based on a setting value of the dimming ratio to be realized in the LED 40. For example, the duty ratio of the PWM dimming signal S1 corresponds to the setting value of the dimming ratio.
The semiconductor-light-source control device 100 includes a driving control section 102, a switching regulator 104, a low pass filter (LPF) 106, a light ON/OFF dimming control section 108, a dimmer switch element 110, and a current detection section 112.
The switching regulator 104 converts the input voltage Vin, which is input from the electronic control unit 20, into an output voltage Vout corresponding to a forward voltage drop Vf of the LED 40 using a switching element 122 which may be a transistor such as MOSTFET (metal oxide semiconductor field effect transistor). The switching regulator 104 applies the output voltage Vout to the anode of the LED 40 through the dimmer switch element 110. In terms of the current, the switching regulator 104 generates a driving current I_LED and supplies the driving current I_LED to the LED 40 through the dimmer switch element 110. The ground potential of the switching regulator 104 is supplied from the electronic control unit 20.
The current detection section 112 detects the magnitude of the driving current I_LED. For example, the current detection section 112 is a current detection resistance through which the driving current I_LED flows, and generates a detection voltage Vd corresponding to the magnitude of the driving current I_LED and supplies the detection voltage Vd to the driving control section 102.
The driving control section 102 controls ON/OFF of the switching element 122 so that the magnitude of the driving current I_LED approaches a target value. The driving control section 102 generates an element control signal S4 based on the detection voltage Vd and a target value setting signal S3 and outputs the element control signal S4 to a control terminal of the switching element 122, that is, the gate of the switching element 122. The driving control section 102 adjusts the duty ratio of the element control signal S4 so that the magnitude of the driving current I_LED corresponding to the detection voltage Vd approaches the target value corresponding to the voltage level of the target value setting signal S3.
The dimmer switch element 110 is provided on a path through which the driving current I_LED flows. In particular, the dimmer switch element 110 is provided between an output terminal of the switching regulator 104 and the anode of the LED 40. ON/OFF of the dimmer switch element 110 is controlled in accordance with a PWM control signal S2. When the PWM control signal S2 is asserted, that is, when the PWM control signal S2 is at a high level, the dimmer switch element 110 is in an ON state. In this case, since the magnitude of the driving current I_LED flowing through the LED 40 is controlled so as to approach the target value by the driving control section 102, the ON state of the dimmer switch element 110 corresponds to a current control state. When the PWM control signal S2 is negated, that is, when the PWM control signal S2 is at a low level, the dimmer switch element 110 is in an OFF state. In this case, since the driving current I_LED does not flow substantially through the LED 40, the OFF state of the dimmer switch element 110 corresponds to a current suppression state.
The light ON/OFF dimming control section 108 generates the pulse-width-modulated PWM control signal S2 based on the PWM dimming signal S1. The light ON/OFF dimming control section 108 is a microcomputer. The PWM control signal S2 is output from the same terminal of the microcomputer to each of the dimmer switch element 110 and the low pass filter 106.
The light ON/OFF dimming control section 108 has a first look-up table in which the setting values of the dimming ratio indicated by the PWM dimming signals S1 are associated with the duty ratios of the dimmer switch element 110. The light ON/OFF dimming control section 108 extracts the setting value of the dimming ratio from the PWM dimming signal S1. The light ON/OFF dimming control section 108 converts the extracted setting value of the dimming ratio into the duty ratio with reference to the first look-up table. The light ON/OFF dimming control section 108 generates the PWM control signal S2 that realize the duty ratio of the dimmer switch element 110 obtained through the conversion. In particular, the light ON/OFF dimming control section 108 sets the duty ratio of the PWM control signal S2 to the duty ratio of the dimmer switch element 110 obtained through the conversion.
The duty ratio of the PWM control signal S2 is a ratio of a high period, during which the PWM control signal S2 is at a high level, to one cycle of the PWM control signal S2. Since the dimmer switch element 110 is in the ON state during the high period, the length of the high period is substantially the same as the length of the duration during which the current suppression state continues. Similarly, the length of a low period, during which the PWM control signal S2 is at a low level, is substantially the same as the length of the duration during which the current suppression state continues. Accordingly, a ratio of the duration of the current suppression state to the duration of the current control state decreases as the duty ratio of the PWM control signal S2 increases, and the ratio of the duration of the current suppression state to the duration of the current control state increases as the duty ratio of the PWM control signal S2 decreases.
The PWM control signal S2 is input to the low pass filter 106. The low pass filter 106 performs low pass filtering for the PWM control signal S2 to generate the target value setting signal S3 having a substantially DC voltage when viewed on the time scale of the dimming frequency f1 for output to the driving control section 102. The voltage level of the target value setting signal S3 corresponds to the duty ratio of the PWM control signal S2. The voltage level of the target value setting signal S3 increases as the duty ratio of the PWM control signal S2 increases. Also, the voltage level of the target value setting signal S3 decreases as the duty ratio decreases. The low pass filter 106 is configured such that the cutoff frequency of the low pass filter 106 is lower than the dimming frequency f1.
The driving control section 102 has a second look-up table in which the voltage levels of the target value setting signal S3 are associated with target values. The driving control section 102 converts the voltage level of the target value setting signal S3 into the target value with reference to the second look-up table. Alternatively, the driving control section 102 may scale the voltage of the target value setting signal S3 appropriately and then apply the scaled voltage of the target value setting signal S3 to a reference input side of an error amplifier.

The relationship among the duty ratio of the PWM control signal S2, the target value of the driving current I_LED, and the setting value of the dimming ratio is shown in the following Table 1.

[Table 1]

Duty ratio of S2 (%)	Target value of I_LED (mA)	Average value of I_LED (mA)	Setting value of dimming ratio (%)
100	1,500	1,500	100
80	1,200	960	64
50	750	375	25
30	450	135	9
10	150	15	1

In Table 1, the correspondence relationship between the duty ratio of the PWM control signal S2 and the setting value of the dimming ratio is stored in the first look-up table of the light ON/OFF dimming control section 108. The correspondence relationship between the duty ratio of the PWM control signal S2 and the target value of the driving current I_LED is stored in the second look-up table of the driving control section 102 in the form of the correspondence relationship between the voltage level of the target value setting signal S3 corresponding to the duty ratio of the PWM control signal S2 and the target value.
Referring to Table 1, when the dimming ratio is to be reduced, the semiconductor-light-source control device 100 reduces the duty ratio of the PWM control signal S2 and also reduces the target value of the driving current I_LED. When the dimming ratio is to be increased, the semiconductor-light-source control device 100 increases the duty ratio of the PWM control signal S2 and also increases the target value of the driving current I_LED.
Also, the setting value of the dimming ratio is substantially proportional to the square of the duty ratio of the PWM control signal S2.
The operation of the semiconductor-light-source control device 100 having the above configuration will be described below.
Fig. 2 is a timing chart showing an operation state of the semiconductor-light-source control device 100 under gradual change control. Fig. 2 shows a voltage of the PWM control signal S2, the target value of the driving current I_LED used in the driving control section 102, and the setting value of the dimming ratio indicated by the PWM dimming signal S1 in order from the top. The gradual change control is control to change the dimming ratio slowly over several seconds. In particular, Fig. 2 shows a case where the dimming ratio is reduced.
In a first period TP1 in which the dimming ratio is set to 100%, the duty ratio of the PWM control signal S2 is set to 100%. That is, the PWM control signal S2 is fixed to a high level, and the dimmer switch element 110 is kept to be in the ON state. The target value of the driving current I_LED is set to the maximum value of 1,500 mA.
In a second period TP2 in which the dimming ratio is set to 64%, the duty ratio of the PWM control signal S2 is set to 80%. The target value of the driving current I_LED is set to 1,200 mA.
In a third period TP3 in which the dimming ratio is set to 25%, the duty ratio of the PWM control signal S2 is set to 50%. The target value of the driving current I_LED is set to 750 mA.
In a fourth period TP4 in which the dimming ratio is set to 9%, the duty ratio of the PWM control signal S2 is set to 30%. The target value of the driving current I_LED is set to 450 mA.
In a fifth period TP5 in which the dimming ratio is set to 1%, the duty ratio of the PWM control signal S2 is set to 10%. The target value of the driving current I_LED is set to 150 mA.
The following relationship is satisfied between the duty ratio of each period and the setting value of the dimming ratio of each period. $\frac{\sqrt{(setting value of dimming ratio)}}{(duty ratio)} = (constant)$
The semiconductor-light-source control device 100 according to this embodiment changes the dimming ratio of the LED by changing both the target value of the driving current I_LED and the duty ratio of ON/OFF of the dimmer switch element 110. Therefore, it becomes possible to perform the dimming control in a wider range. In particular, when the setting value of the dimming ratio is relatively low, it is not necessary to reduce the duty ratio largely. Therefore, influence of rising/falling at a time of ON/OFF of the dimmer switch element 110 on the dimming ratio can be reduced, and it is possible to enhance the accuracy of the dimming ratio.
Also, in the semiconductor-light-source control device 100 according to this embodiment, while it becomes possible to perform the dimming control in such a wide range as described above, variation in target value with respect to variation in setting value of the dimming ratio is suppressed and variation in duty ratio with respect to variation in setting value of the dimming ratio is also suppressed. Therefore, for example, the luminance of the LED changes more smoothly even under the gradual change control. As a result, it is possible to realize a vehicle lamp that is more reliable and has high commercial value.
The inventions has also intensively studied the minimum value of the duty ratio of the PWM control signal S2 generated by the microcomputer.
The minimum value of the duty ratio of the PWM control signal S2 depends on a processing time of an interrupt process used in software control. $\begin{matrix} (\begin{matrix} Sum of maximum values of \\ all interrupt processing times \end{matrix}) < (\begin{matrix} Duty ratio of PWM control signal S 2 \\ (compoare match register) \end{matrix}) \end{matrix}$
Therefore, the following relationship can be obtained. $\begin{matrix} (Minimum value of the duty ratio) = (\begin{matrix} Sum of maximum values of \\ all interrupt processing times \end{matrix}) \end{matrix}$
When a design is made with the above relationship ignored, the following events may occur. Fig. 3 is an explanatory view showing interrupt control of the microcomputer.
In a timer period interruption process for the PWM dimming (period of 2 ms), a duty value (compare match register) is set (written). When the interrupt process occurs during another interrupt process, the interrupt process in interest is suspended until another interrupt process is completed. Even in this suspended period, the count of the timer for the PWM dimming is increased. After the suspended period, if (compare match register) < (timer count) at a time when the duty value (compare match register) is written, compare match of "timer output = OFF" is skipped one time. As a result, a high level (ON) occurs for one period or more. The ON period may also be continuous depending on the occurrence timing of another interrupt process. Such skip of the compare match is likely to occur more easily as the duty ratio of the PWM control signal S2 becomes smaller, that is, as the value of the compare match register becomes smaller. Therefore, usually, in order to avoid such skip of the compare match, the minimum value of the duty ratio of the PWM control signal S2 is set as described above.
On the other hand, in the semiconductor-light-source control device 100 according to this embodiment, the lower dimming ratio is realized by changing the target value of the driving current I_LED in parallel with changing the duty ratio of the PWM control signal S2. Therefore, in a situation where the lower limit of the duty ratio of the PWM control signal S2 is limited by the affect of software multiple interrupt processes as above described, the low dimming ratio can be realized.
Also, in the semiconductor-light-source control device 100 according to this embodiment, the PWM control signal S2 is output from the same terminal of a microcomputer, which may be the light ON/OFF dimming control section 108, to each of the dimmer switch element 110 and the low pass filter 106. Accordingly, the number of terminals of the microcomputer for controlling the ON/OFF of the dimmer switch element 110 and the target value of the driving current I_LED may be 1. Therefore, the number of terminals of the microcomputer can be reduced as compared with a case where these controls are performed through separate terminals using separate signals. As a result, since it is not necessary to adopt a large and expensive microcomputer with a large number of terminals, it is possible to select an inexpensive microcomputer with a small number of terminals. This also contributes to reducing the size of the device.
Also, when a plurality of LEDs 40 are provided and ON/OFF and dimming control is performed for these LEDs 40 separately, terminals are required whose number is at least equal to the number of LEDs 40 are required. Accordingly, the effect of reducing the number of terminals becomes more noticeable.
Up to now, the configuration and operation of the semiconductor-light-source control device according to the embodiments have been described. This embodiment is only illustrative, those skilled in the art would appreciate that various modifications of the combination of the constituent elements and the processing can be made and such modifications still fall within the scope of the invention.
In the embodiments, description has been given on the case in which the electronic control unit 20 generates the PWM dimming signal S1 and supplies the generated PWM dimming signal S1 to the semiconductor-light-source control device 100 and also supplies the input voltage Vin, which is almost constant, to the semiconductor-light-source control device 100 regardless of the PWM dimming signal S1. The invention is not limited thereto. For example, in place of the PWM dimming signal S1, a signal corresponding to the PWM dimming signal S1 may be set as one of pieces of communication information using serial communication based on the in-vehicle network such as LIN (Local Interconnect Network) or CAN (Control Area Network), and the set signal may be input to the light ON/OFF dimming control section 108. Alternatively, the PWM dimming signal S1 may be eliminated, and PWM dimming may be realized by turning ON/OFF the input voltage Vin at the dimming frequency f1 instead.
In the above embodiments, description has been given on the case in which when the dimming ratio is to be reduced, the semiconductor-light-source control device 100 reduces the duty ratio of the PWM control signal S2 while reducing the target value of the driving current I_LED, and when the dimming ratio is to be increased, the semiconductor-light-source control device 100 increases the duty ratio of the PWM control signal S2 while increasing the target value of the driving current I_LED. However, the invention is not limited thereto. One of the target value of the driving current I_LED and the duty ratio of the PWM control signal S2 may be set so that a one-to-one relationship is established between the other one and the setting value of the dimming ratio. Even in this case, it is possible to change the luminance of the LED more smoothly.
Description has been given on the case in which the dimmer switch element 110 is provided on the path through which the driving current I_LED flows. However, the invention is not limited thereto. For example, instead of or in addition to the dimmer switch element 110, a bypass switch element may be provided in parallel with the LED 40. The light ON/OFF dimming control section may realize the PWM dimming by controlling ON/OFF of the bypass switch element.

Description of Reference Numerals and Signs

10:: in-vehicle circuit
20:: electronic control unit
30:: in-vehicle battery
40:: LED
100:: semiconductor-light-source control device
102:: driving control section
104:: switching regulator
106:: low pass filter (LPF)
108:: light ON/OFF dimming control section
110:: dimmer switch element
112:: current detection section

Claims

A semiconductor-light-source control device (100) comprising:
a regulator (104) that generates a driving current (I_LED) flowing through a semiconductor light source (40); and

a driving control section (102) that controls the regulator (104) so that a magnitude of the driving current (I_LED) approaches a target value, wherein

a luminance of the semiconductor light source (40) is adjusted by repeating (i) a first state (H) in which the magnitude of the driving current (I_LED) flowing through the semiconductor light source (40) is controlled so as to approach the target value and (ii) a second state (L) in which the driving current (I_LED) is smaller than that in the first state (H),

both of a duty ratio of the first and second states (H, L) during the repeating and the target value in the driving control section (102) change in accordance with a setting value of the luminance of the semiconductor light source (40), and

one of the target value and the duty ratio is set so as to have a one-to-one correspondence relationship with the setting value of the luminance of the semiconductor light source (40).
The device (100) according to claim 1, wherein
when the luminance of the semiconductor light source (40) is to be reduced, a ratio of a duration of the second state (L) to a duration of the first state (H) is increased and the target value is reduced, and
when the luminance of the semiconductor light source (40) is to be increased, the ratio of the duration of the second state (L) to the duration of the first state (H) is reduced and the target value is increased.
The device (100) according to any one of claims 1 to 2, wherein the setting value of the luminance of the semiconductor light source (40) is substantially proportional to a square of the duty ratio.
The device (100) according to any one of claims 1 to 3, further comprising:
a light ON/OFF control section (108) that generates a pulse-width-modulated control signal (S2);

a switching element (110) that realizes the first and second states (H, L) alternately based on the pulse-width-modulated control signal (S2) generated by the light ON/OFF control section (108); and

a low pass filter (106) to which the pulse-width-modulated control signal (S2) generated by the light ON/OFF control section (108) is input, wherein

the driving control section (102) controls the regulator (102) so that the magnitude of the driving current (I_LED) approaches the target value corresponding to an output of the low pass filter (106).
The device (100) according to claim 4, wherein
the light ON/OFF control section (108) is a microcomputer, and
the control signal (S2) is output from the same terminal of the microcomputer (108) to each of the switching element (110) and the low pass filter (106).
The device (100) according to any one of claims 1 to 3, further comprising:
a switching element (110) that is disposed on a path between the regulator (104) and the semiconductor light source (40), the path through which the driving current (I_LED) flows, wherein

the switching element (110) is controlled to turn on and off at a predetermined dimming frequency so that the first state and the second state are repeated.
The device (100) according to claim 6, wherein
a state in which the switching element (110) is turned on corresponds to the first state,
and
a state in which the switching element (110) is turned off corresponds to the second state in which the driving current (I_LED) flowing through the semiconductor light source (40) is substantially equal to zero.
The device (100) according to any one of claims 6 to 7, further comprising:
a light ON/OFF control section (108) that generates a pulse-width-modulated control signal (S2); and

a low pass filter (106) to which the pulse-width-modulated control signal (S2) generated by the light ON/OFF control section (108) is input, wherein

the driving control section (102) controls the regulator (102) so that the magnitude of the driving current (I_LED) approaches the target value corresponding to an output of the low pass filter (106).
The device (100) according to claim 8, wherein
the light ON/OFF control section (108) includes a microcomputer that generates pulse-width-modulated control signal (S2), and
the control (S2) signal is output from the same terminal of the microcomputer (108) to each of the switching element (110) and the low pass filter (106).
The device (100) according to any one of claims 1 to 9, wherein the duty ratio changes monotonically with respect to the setting value of the luminance of the semiconductor light source (40) that is in a range of values which the luminance of the semiconductor light source (40) can take.
The device (100) according to claim 10, wherein where the setting value of the luminance of the semiconductor light source (40) is expressed in percentage of a maximum luminance of the semiconductor light source (40), the duty ratio changes monotonically with respect to the setting value of the luminance of the semiconductor light source (40) that is in a range of 1% to 100%.
The device (100) according to any one of claims 1 to 11, wherein the target value changes monotonically with respect to the setting value of the luminance of the semiconductor light source (40) that is in a range of values which the luminance of the semiconductor light source (40) can take.
The device (100) according to claim 12, wherein where the setting value of the luminance of the semiconductor light source (40) is expressed in percentage of a maximum luminance of the semiconductor light source (40), the target value changes monotonically with respect to the setting value of the luminance of the semiconductor light source (40) that is in a range of 1 % to 100%.
A vehicle lamp comprising:
the semiconductor-light-source control device (100) according to any one of claims 1 to 13; and

a semiconductor light source (40).