JP2013258003A - Semiconductor light source control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change the luminance of a semiconductor light source further smoothly while achieving PWM extinction with a wide settable range of the luminance of the semiconductor light source.SOLUTION: A semiconductor light source control device 100 comprises: a switching regulator 104 generating a drive current Iflowing in an LED 40; and a drive controller 102 controlling the switching regulator 104 so that a magnitude of the drive current Iapproaches a target value. A first state where the control is performed so that the magnitude of the drive current Iapproaches the target value, and a second state where the drive current Iis reduced compared with the first state, are repeated to adjust the luminance of the LED 40. Both a duty ratio in the repetition of the first state and the second state and the target value in the drive controller 102 are changed depending on a setting value of the luminance of the LED 40. Any one of the target value and the duty ratio is set so that the other and the setting value of the luminance of the LED 40 have one-to-one relation with each other.

Description

  The present invention relates to a semiconductor light source control device for controlling a semiconductor light source such as an LED (Light Emitting Diode).

  In recent years, longer life and lower power consumption LEDs have been used in vehicle lamps such as headlamps in place of conventional halogen lamps having filaments. Since the degree of light emission, that is, the brightness of the LED depends on the magnitude of the current flowing through the LED, a lighting circuit for adjusting the current flowing through the LED is required when the LED is used as a light source. Such a lighting circuit usually has an error amplifier and performs feedback control so that the current flowing through the LED becomes constant.

  For example, the headlamp has a high beam state and a low beam state, and it is desirable that the brightness of the LED can be adjusted in order to easily meet the standard. As one of the methods for changing the brightness of the LED, PWM (Pulse Width Modulation) dimming is known in which the current is turned on and off to change its duty ratio.

  The present applicant has proposed a lighting control device adopting PWM dimming in Patent Document 1.

  In general PWM dimming, the lower limit of the dimming rate that can be realized is limited by the response speed of the switch element for turning on and off the current. As a countermeasure against this, there has been proposed a method of dimming by changing the target value of the current to the LED based on a control signal different from the control signal for PWM driving the switch element (see, for example, Patent Document 2). .

JP 2010-170704 A JP 2005-332586 A

  In the technique described in Patent Document 2, two different values are used as the current supplied to the light source. When the relative luminance is high, the larger current value is used, and when the relative luminance is low, the smaller current value is used. In this case, since the set value of the current is binary, the change in current when switching the current is relatively large. When the relative luminance is gradually changed and the current switching point is passed, the peak value of the current greatly fluctuates there, and a relatively large fluctuation may occur in the light emission characteristics of the LED.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a semiconductor light source capable of smoothly changing the brightness of the semiconductor light source while realizing PWM dimming with a wide setting range of the brightness of the semiconductor light source. The provision of control devices.

  One embodiment of the present invention relates to a semiconductor light source control device. The semiconductor light source control device includes a regulator that generates a drive current that flows through the semiconductor light source, and a drive control unit that controls the regulator so that the magnitude of the drive current approaches a target value. The brightness of the semiconductor light source is adjusted by repeating the first state in which the magnitude of the drive current flowing through the semiconductor light source is controlled to approach the target value and the second state in which the drive current is smaller than the first state. Is done. Both the duty ratio in the repetition of the first state and the second state and the target value in the drive control unit change according to the set value of the luminance of the semiconductor light source. Either the target value or the duty ratio is set so that the other and the set value of the luminance of the semiconductor light source have a one-to-one relationship.

  According to this aspect, the target value or duty ratio and the set value of the luminance of the semiconductor light source have a one-to-one relationship.

  It should be noted that any combination of the above-described constituent elements and those obtained by replacing the constituent elements and expressions of the present invention with each other among apparatuses, methods, systems, etc. are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the brightness | luminance of a semiconductor light source can be changed more smoothly, implement | achieving PWM dimming with the wide setting range of the brightness | luminance of a semiconductor light source.

It is a circuit diagram which shows the structure of a vehicle-mounted circuit provided with the semiconductor light source control apparatus which concerns on embodiment. It is a time chart which shows the operation state of the semiconductor light source control apparatus of FIG. 1 during gradual change control. It is explanatory drawing which shows the interruption control of a microcomputer.

  Hereinafter, the same or equivalent components, members, and signals shown in the respective drawings are denoted by the same reference numerals, and repeated description thereof will be omitted as appropriate. In addition, in the drawings, some of the members that are not important for explanation are omitted. Moreover, the code | symbol attached | subjected to the voltage, electric current, or resistance may be used as what represents each voltage value, electric current value, or resistance value as needed.

  In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected in addition to the case where the member A and the member B are physically directly connected. It includes the case of being indirectly connected through another member that does not affect the connection state. Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. This includes the case of being indirectly connected through another member that does not affect the state of connection.

  The semiconductor light source control device according to the embodiment feedback-controls the switching regulator that generates the drive current flowing through the LED using the switching element and the on / off of the switching element so that the magnitude of the drive current approaches the target value. A drive control unit. Further, the semiconductor light source control device performs PWM dimming. That is, by repeating the current control state in which the magnitude of the drive current is controlled to approach the target value and the current suppression state in which the drive current is smaller than the current control state, the degree of light emission of the LED, that is, the luminance Is adjusted. More specifically, the semiconductor light source control device controls the brightness of the LED by turning on and off the dimming switch element provided on the drive current path between the LED and the switching regulator at a predetermined dimming frequency f1. Adjust. In this case, the current control state corresponds to the ON state of the dimming switch element. The current suppression state corresponds to the off state of the dimming switch element, and the drive current flowing through the LED is substantially zero.

  In the semiconductor light source control device, the duty ratio in the repetition of the current control state and the current suppression state, that is, the duty ratio of ON / OFF of the dimming switch element is set as the LED brightness setting value (hereinafter, the LED brightness is a percentage of the maximum brightness). It is changed according to the light control rate. The semiconductor light source control device changes the target value of the drive current according to the set value of the dimming rate. In particular, each of the duty ratio and the target value changes monotonously with respect to the set value of the dimming rate in a range where the dimming rate can be taken, that is, 1% to 100%. As a result, it is possible to suppress a sudden change in drive current and duty ratio during dimming while realizing a relatively wide range of dimming control. As a result, a sudden change in the light emission characteristics of the LED can be suppressed.

  FIG. 1 is a circuit diagram showing the configuration of the in-vehicle circuit 10. The in-vehicle circuit 10 includes a semiconductor light source control device 100 according to the embodiment, an electronic control unit 20, an in-vehicle battery 30, and an LED 40 configured by connecting three in-vehicle LEDs in series. And a switch SW.

The electronic control unit 20 is a microcomputer for comprehensively performing electrical control of a vehicle such as an automobile. The electronic control unit 20 is connected to the in-vehicle battery 30 via the switch SW, and receives the battery voltage Vbat from the in-vehicle battery 30 by turning on the switch SW. The electronic control unit 20 supplies a DC battery voltage Vbat as the input voltage Vin to the semiconductor light source control device 100. The electronic control unit 20 supplies a fixed voltage, that is, a ground potential V _GND (= 0V) to the semiconductor light source control device 100. The electronic control unit 20 generates a PWM dimming signal S <b> 1 and supplies it to the semiconductor light source control device 100.

  The PWM dimming signal S1 is a signal for causing the LED 40 to blink at a high speed, for example, at a dimming frequency f1 of several hundred Hz to several kHz. More specifically, the PWM dimming signal S1 is a signal whose voltage changes in a rectangular wave shape at the dimming frequency f1. The electronic control unit 20 sets the duty ratio of the PWM dimming signal S1 based on the set value of the dimming rate to be realized by the LED 40. In one example, the duty ratio of the PWM dimming signal S1 corresponds to the set value of the dimming rate.

  The semiconductor light source control device 100 includes a drive control unit 102, a switching regulator 104, a low-pass filter 106, a lighting on / off dimming control unit 108, a dimming switch element 110, and a current detection unit 112.

The switching regulator 104 uses the switching element 122, which may be a transistor such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), to convert the input voltage Vin input from the electronic control unit 20 into a forward voltage drop Vf of the LED 40. Is converted into an output voltage Vout corresponding to. The switching regulator 104 applies the output voltage Vout to the anode of the LED 40 via the dimming switch element 110. From the viewpoint of current, the switching regulator 104 generates a drive current I _LED and supplies it to the LED 40 via the dimming switch element 110. The ground potential of the switching regulator 104 is supplied from the electronic control unit 20.

The current detection unit 112 detects the magnitude of the drive current I _LED . The current detection unit 112 is, for example, a current detection resistor through which the drive current I _LED flows, and generates a detection voltage Vd corresponding to the magnitude of the drive current I _LED and supplies the detection voltage Vd to the drive control unit 102.

The drive control unit 102 controls on / off of the switching element 122 so that the magnitude of the drive current I _LED approaches the target value. The drive control unit 102 generates an element control signal S4 based on the detection voltage Vd and the target value setting signal S3, and outputs it to the control terminal of the switching element 122, that is, the gate. The drive control unit 102 adjusts the duty ratio of the element control signal S4 so that the magnitude of the drive 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 dimming switch element 110 is provided on the path of the drive current I _LED . In particular, the dimming switch element 110 is provided between the output terminal of the switching regulator 104 and the anode of the LED 40. On / off of the dimming switch element 110 is controlled by the 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 dimming switch element 110 is turned on. In this case, since the magnitude of the drive current I _LED flowing through the LED 40 is controlled by the drive control unit 102 so as to approach the target value, the ON state of the dimming switch element 110 corresponds to the current control state. When the PWM control signal S2 is negated, that is, at a low level, the dimming switch element 110 is turned off. In this case, since the drive current I _LED does not substantially flow through the _LED 40, the OFF state of the dimming switch element 110 corresponds to the current suppression state.

  The lighting / light-out dimming control unit 108 generates a pulse width-modulated PWM control signal S2 based on the PWM dimming signal S1. The lighting / light-out dimming control unit 108 is a microcomputer. The PWM control signal S2 is output to the dimming switch element 110 and the low-pass filter 106 from the same terminal of the microcomputer.

  The lighting / light-out dimming control unit 108 has a first lookup table in which the setting value of the dimming rate indicated by the PWM dimming signal S1 and the duty ratio of the dimming switch element 110 are associated with each other. The lighting / light-out dimming control unit 108 extracts the set value of the dimming rate from the PWM dimming signal S1. The lighting / light-out dimming control unit 108 converts the extracted setting value of the dimming rate into a duty ratio with reference to the first lookup table. The lighting / light-out dimming control unit 108 generates a PWM control signal S2 that realizes the duty ratio of the dimming switch element 110 obtained as a result of the conversion. In particular, the lighting / light-out dimming control unit 108 sets the duty ratio of the PWM control signal S2 as the duty ratio of the dimming switch element 110 obtained as a result of 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 occupies one cycle of the PWM control signal S2. Since the dimming switch element 110 is in the on state during the high period, the length of the high period is substantially equal to the duration of the current control state. Similarly, the length of the low period during which the PWM control signal S2 is at the low level is substantially equal to the length of the duration of the current suppression state. Therefore, when the duty ratio of the PWM control signal S2 increases, the ratio of the duration of the current suppression state to the duration of the current control state decreases, and when the duty ratio of the PWM control signal S2 decreases, the ratio increases.

The low-pass filter 106 receives the PWM control signal S2. The low-pass filter 106 performs a low-pass filter on the PWM control signal S2, generates a target value setting signal S3 having a substantially DC voltage when viewed on the time scale of the dimming frequency f1, and outputs the target value setting signal S3 to the drive control unit 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 is higher as the duty ratio of the PWM control signal S2 is larger, and the voltage level of the target value setting signal S3 is lower as the duty ratio is smaller.
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 drive control unit 102 has a second lookup table in which the voltage level of the target value setting signal S3 is associated with the target value. The drive control unit 102 converts the voltage level of the target value setting signal S3 into a target value with reference to the second lookup table. Alternatively, the drive control unit 102 may appropriately apply the voltage of the target value setting signal S3 to the reference input side of the error amplifier after scaling.

The relationship between the duty ratio of the PWM control signal S2, the target value of the drive current I _LED , and the set value of the dimming rate is shown in Table 1 below.

In Table 1, the correspondence relationship between the duty ratio of the PWM control signal S2 and the set value of the dimming rate is held in the first look-up table of the lighting / light-out dimming control unit 108. The correspondence between the duty ratio of the PWM control signal S2 and the target value of the drive current I _LED is driven in the form of the correspondence 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. It is held in the second lookup table of the control unit 102.

Referring to Table 1, when the dimming rate is decreased, the semiconductor light source control device 100 decreases the duty ratio of the PWM control signal S2 and decreases the target value of the drive current I _LED . When increasing the dimming rate, the semiconductor light source control device 100 increases the duty ratio of the PWM control signal S2 and increases the target value of the drive current I _LED .
The set value of the dimming rate 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.
FIG. 2 is a time chart showing an operation state of the semiconductor light source control device 100 during the gradual change control. FIG. 2 shows, in order from the top, the voltage of the PWM control signal S2, the target value of the drive current I _LED used in the drive control unit 102, and the set value of the dimming rate indicated by the PWM dimming signal S1. The gradual change control is a control in which the dimming rate is slowly changed over several seconds, and FIG. 2 shows a case where the dimming rate is particularly lowered.

In the first period TP1 in which the dimming rate 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 at a high level, and the dimming switch element 110 is kept on. The target value of the drive current I _LED is set to a maximum of 1500 mA.

In the second period TP2 in which the dimming rate is set to 64%, the duty ratio of the PWM control signal S2 is set to 80%. The target value of the drive current I _LED is set to 1200 mA.
In the third period TP3 in which the dimming rate is set to 25%, the duty ratio of the PWM control signal S2 is set to 50%. The target value of the drive current I _LED is set to 750 mA.
In the fourth period TP4 in which the dimming rate is set to 9%, the duty ratio of the PWM control signal S2 is set to 30%. The target value of the drive current I _LED is set to 450 mA.
In the fifth period TP5 in which the dimming rate is set to 1%, the duty ratio of the PWM control signal S2 is set to 10%. The target value of the drive current I _LED is set to 150 mA.
The following relationship is established between the duty ratio of each period and the set value of the dimming rate.

The semiconductor light source control device 100 according to the present embodiment changes the dimming rate of the LED by changing both the target value of the drive current I _LED and the on / off duty ratio of the dimming switch element 110. Therefore, a wider range of light control can be performed. In particular, when the setting value of the dimming rate is relatively low, the duty ratio does not have to be so small. Therefore, the influence on the dimming rate due to the rising / falling of the on / off of the dimming switch element 110 can be reduced. The accuracy of the light rate can be increased.

  Further, in the semiconductor light source control device 100 according to the present embodiment, while it is possible to perform dimming control over a wide range, the variation of the target value with respect to the variation of the setting value of the dimming rate is suppressed, and the dimming is performed. Variations in the duty ratio with respect to variations in the rate setting value can also be suppressed. Therefore, for example, even during gradual change control, the brightness of the LED changes more smoothly. As a result, a vehicle lamp with higher reliability and higher commercial value can be realized.

The inventor independently conducted the following study on 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 the processing time of interrupt processing used in software control.

Therefore,
Minimum duty ratio = total sum of all interrupt processing time maximum values.

When designing with the above ignored, the following events can occur. FIG. 3 is an explanatory diagram showing interrupt control of the microcomputer.
The duty value (compare match register) is set (written) in the process of the timer cycle interrupt (2 ms cycle) for PWM dimming. If the interrupt occurs during other interrupt processing, the interrupt processing is put on hold until the other interrupt processing is completed. Even during this hold, the count of the PWM dimming timer is up. When the duty value (compare match register) is written after the hold, if the compare match register <timer count, the timer output = OFF compare match is skipped once and a high level (ON) is generated for one cycle or more. . Depending on the generation timing of other interrupt processing, the ON period may continue. Such a skip of the compare match is more likely to occur as the duty ratio of the PWM control signal S2 is decreased, that is, as the value of the compare match register is decreased. Therefore, in order to avoid such a compare match skip, the minimum value of the duty ratio of the PWM control signal S2 is normally set as described above.

On the other hand, in the semiconductor light source control device 100 according to the present embodiment, a lower dimming rate is realized by changing the target value of the drive current I _{LED in} parallel with the duty ratio of the PWM control signal S2. Therefore, even in a situation where the lower limit of the duty ratio of the PWM control signal S2 is limited due to the influence of the multiple interrupt processing of software as described above, a low dimming rate can be realized.

In the semiconductor light source control device 100 according to the present embodiment, the PWM control signal S2 is output to the dimming switch element 110 and the low-pass filter 106 from the same terminal of the microcomputer that is the lighting / light-out dimming control unit 108. The Therefore, only one microcomputer terminal is required for on / off control of the dimming switch element 110 and target value control of the drive current I _LED . Therefore, the number of terminals of the microcomputer can be reduced as compared with the case where these controls are performed with different signals via different terminals. As a result, it is not necessary to use a large and expensive microcomputer with a large number of terminals, and an inexpensive microcomputer with a small number of terminals can be selected, which contributes to downsizing of the apparatus.

  In addition, when a plurality of LEDs 40 are provided and are individually controlled to be turned on / off and dimmed, as many terminals as the number of LEDs 40 are required, so the effect of reducing the number of terminals is more remarkable.

  The configuration and operation of the semiconductor light source control device according to the embodiment have been described above. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to each component and combination of processes, and such modifications are within the scope of the present invention.

  In the embodiment, the electronic control unit 20 generates the PWM dimming signal S1 and supplies it to the semiconductor light source control device 100. On the other hand, the semiconductor light source control device 100 supplies a substantially constant input voltage Vin regardless of the PWM dimming signal S1. However, the present invention is not limited to this. For example, instead of the PWM dimming signal S1, serial communication by an in-vehicle network such as LIN or CAN is used to set a signal corresponding to the PWM dimming signal S1 as one of the communication information, and the signal is turned on / off The dimming control unit 108 may be input. Alternatively, PWM dimming may be realized by eliminating the PWM dimming signal S1 and turning on / off the input voltage Vin at the dimming frequency f1 instead.

In the embodiment, when reducing the dimming rate, the semiconductor light source control device 100 decreases the duty ratio of the PWM control signal S2 and decreases the target value of the drive current I _LED to increase the dimming rate. Although the semiconductor light source control device 100 has been described with respect to increasing the duty ratio of the PWM control signal S2 and increasing the target value of the drive current I _LED , the present invention is not limited to this, and either the target value or the duty ratio is: What is necessary is just to set so that the other side and the setting value of a light control rate may have a one-to-one relationship. Even in this case, the luminance of the LED can be changed more smoothly.

In the embodiment, the case where the dimming switch element 110 is provided on the path of the drive current I _LED has been described. However, the present invention is not limited to this. For example, instead of or in addition to the dimming switch element 110, a bypass switch element may be provided in parallel with the LED 40. The on / off dimming control unit may realize PWM dimming by controlling on / off of the bypass switch element.

  DESCRIPTION OF SYMBOLS 10 In-vehicle circuit, 20 Electronic control unit, 30 In-vehicle battery, 40 LED, 100 Semiconductor light source control device, 102 Drive control part, 104 Switching regulator, 106 Low pass filter, 108 Light-off dimming control part, 110 Dimming switch element, 112 Current detector.

Claims (5)

A regulator that generates a drive current flowing through the semiconductor light source;
A drive control unit that controls the regulator so that the magnitude of the drive current approaches a target value,
The luminance of the semiconductor light source is repeated by repeating a first state in which the magnitude of the drive current flowing through the semiconductor light source is controlled so as to approach a target value and a second state in which the drive current is smaller than the first state. Is adjusted,
Both the duty ratio in the repetition of the first state and the second state and the target value in the drive control unit change according to the set value of the luminance of the semiconductor light source,
One of the target value and the duty ratio is set so that the other and the set value of the brightness of the semiconductor light source have a one-to-one relationship.   When reducing the luminance of the semiconductor light source, increasing the ratio of the duration of the second state to the duration of the first state and decreasing the target value to increase the luminance of the semiconductor light source, the continuation of the first state 2. The semiconductor light source control device according to claim 1, wherein the semiconductor light source control device is configured to decrease a ratio of a duration of the second state to a period and increase a target value.   3. The semiconductor light source control device according to claim 1, wherein a set value of luminance of the semiconductor light source is substantially proportional to a square of a duty ratio. A lighting on / off control unit for generating a pulse width modulated control signal;
A switching element that alternately realizes the first state and the second state based on a control signal generated by the lighting on / off control unit;
A low pass filter to which a control signal generated by the lighting on / off control unit is input,
4. The semiconductor light source control according to claim 1, wherein the drive control unit controls the regulator so that a magnitude of a drive current approaches a target value corresponding to an output of the low-pass filter. 5. apparatus. The lighting on / off control unit is a microcomputer,
5. The semiconductor light source control device according to claim 4, wherein the control signal is output from the same terminal of the microcomputer to each of the switch element and the low-pass filter.

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