JP5958851B2 - LED driving device and lighting device using the same - Google Patents

Description

  The present invention relates to an LED driving device using a light emitting diode as a light source and an illumination device using the same.

  In recent years, light-emitting diodes (hereinafter referred to as “LEDs”) are actively used in the lighting field, and their uses are diversified. For example, in the field of vehicles, white LEDs are used for interior lighting, and white LEDs are also used for high-intensity headlights and daytime running lamps.

  The LED has a longer life than the incandescent bulb, has a quick response, can be mounted compactly in structure, can easily realize various colors without a filter according to the application, and can be easily controlled by dimming. And since lighting fixtures, such as a lamp, are thin and can be mounted three-dimensionally, there is an advantage that a free design that does not restrict the shape such as a car design is possible.

  For example, Patent Document 1 discloses a power supply device that maintains a constant output voltage applied to a load using an LED as a light source. A power supply device described in Patent Document 1 includes a step-down chopper transistor and a step-up chopper transistor connected to the same choke coil, and an input voltage determination circuit that compares and determines the magnitude of an input voltage and a desired output voltage. Prepare. In addition, the power supply device includes a switching circuit that selectively operates the step-down and step-up chopper transistors in accordance with the output from the input voltage determination circuit, and automatically includes a step-down power supply in accordance with the input voltage, Switching operation is performed as a boost type power supply.

  Further, for example, Patent Document 2 discloses a DC-DC converter that controls the output voltage to be kept constant with respect to fluctuations in the input voltage. A DC-DC converter described in Patent Document 2 includes a step-down unit that outputs an output voltage lower than an input voltage, a step-up unit that outputs an output voltage higher than the input voltage, and a control unit that controls the step-down unit and the step-up unit. Is provided. In this DC-DC converter, since the step-down and the step-up are simultaneously performed by simultaneously switching the step-down switch of the step-down unit and the step-up switch of the step-up unit, the output voltage is changed without performing the operation of step-down and step-up switching. It can output continuously.

Japanese Patent Laid-Open No. 62-018970 JP 2010-268590 A

  By the way, for example, a power supply voltage used for an in-vehicle light source using an LED is usually about 12 V, and becomes 9 to 16 V in consideration of fluctuations in the power supply voltage. Furthermore, if transient fluctuations in the power supply voltage are included, the light source may be turned on assuming a power supply voltage in the range of 6 to 20V. In recent years, improvements have been made so that necessary light fluxes can be obtained even when the number of LEDs used as a light source is small, for example, by improving the luminous efficiency of LEDs. Since the luminous flux changes in proportion to the forward current flowing through the LEDs, when using a plurality of LEDs, it is common to connect the LEDs in series and cause the LEDs to emit light uniformly by flowing the same current. It is.

  In an in-vehicle light source (for example, a low beam) using LEDs, the number of LEDs to be used is about 4 to 12. The forward voltage of one LED varies depending on the element configuration, material, operating temperature, operating current, etc., but is about 3 to 3.5 V when the forward current is several hundred mA. Therefore, when the number of LEDs is 4, the load voltage applied to both ends of the LEDs is 12 to 14V, and when the number is 5, the load voltage is 15 to 17.5V.

  Here, the correlation between the range of the power supply voltage V1 and the fluctuation range of the load voltage V2 is shown in FIG. In the figure, with the line V1 = V2 as a boundary line, the upper region is a region where V1 <V2, and the lower region is a region where V1> V2. Also, in the figure, the two regions surrounded by solid lines indicate the range of variation between the power supply voltage V1 and the load voltage V2 that are actually used, and the LED is driven assuming that range. The LED driving device is operated.

  As a circuit system of the LED driving device used in the above range, there is a step-up / step-down chopper circuit system in which a step-down circuit and a step-up circuit are combined as described in the conventional example. FIG. 10B shows a conventional basic configuration of an LED driving device that employs this step-up / step-down chopper circuit. This LED driving device includes a DC power source DC1, a step-down circuit 100, a step-up circuit 101, and a light source unit 102 composed of a plurality of LEDs. The load voltage (output voltage) V2 is output to the light source unit 102 by stepping down and boosting the power supply voltage (input voltage) V1 of the DC power supply DC1.

  However, the configuration in which the step-down circuit 100 is connected to the power supply side and the step-up circuit 101 is connected to the load side as in the basic configuration and the conventional example has the following problems. That is, when the input voltage V1 is smaller than the output voltage V2, the load side is constituted by the booster circuit 101. Therefore, the control when dimming the light source unit 102 controls the amplitude of the output voltage of the booster circuit 101. It will be. For this reason, if the forward current is significantly reduced by controlling the amplitude of the output voltage of the booster circuit 101, the color change of the LED may increase. In particular, a white LED configured by combining a blue LED and a yellow phosphor has a strong tendency.

  The light source unit 102 can also be dimmed by turning on and off the switching element of the voltage-lowering circuit 100 on the power supply side at a low frequency. However, in this case, since the booster circuit 101 operates at a low frequency, the fluctuation of the load voltage V2 becomes large, and an overcurrent flows through the LED, which may increase the stress.

  In order to avoid dimming of the light source unit 102 by amplitude control as described above, a switching element 103 is added between the booster circuit 101 and the light source unit 102 as shown in FIG. Dimming is also conceivable. However, in this case, it is necessary to newly add the switching element 103, and there is a problem that the circuit becomes complicated because the switching element 103 needs to be controlled.

  The present invention has been made in view of the above points, and provides an LED driving device capable of dimming while suppressing a change in the color of the LED without complicating the circuit, and an illumination device using the LED driving device. For the purpose.

The LED driving device of the present invention is connected to a direct current power source to boost the power supply voltage of the direct current power source and output an intermediate voltage, and connected to a light source unit composed of a plurality of light emitting diodes, and connected to the boost circuit. Based on a step-down circuit that steps down an intermediate voltage and outputs a load voltage to the light source unit, a main control circuit that controls the step-up circuit and the step-down circuit, and a dimming rate of the light source unit set from the outside A dimming control circuit for dimming the light source unit in the main control circuit, the step-down circuit includes at least a switching element, and the main control circuit performs the step-up until the dimming rate falls below a predetermined value. The light source unit is dimmed by amplitude control of the intermediate voltage of the circuit, and when the dimming rate falls below the predetermined value, the switching element of the step-down circuit is PWM controlled at a predetermined frequency, and It characterized by dimming the light source unit by PWM control at a higher frequency than the predetermined frequency in the period.
In this LED driving device, the main control circuit performs PWM control of the switching element of the step-down circuit at a frequency higher than the predetermined frequency until the dimming rate falls below the predetermined value, thereby controlling the light source unit. It is preferable to perform dimming and control so that the intermediate voltage of the booster circuit becomes constant at a target value when the dimming rate falls below the predetermined value.

  In this LED drive device, it is preferable that the main control circuit performs PWM control of the switching element of the step-down circuit so that a load current flowing through the light source unit maintains a rated current value of the light source unit.

  In this LED driving device, the main control circuit stops the operation of the booster circuit when the power supply voltage exceeds the load voltage, and starts the operation of the booster circuit when the power supply voltage falls below the load voltage. Is preferred.

  The illuminating device of this invention is equipped with one of said LED drive devices, the said light source part, and the instrument main body holding the said light source part and the said LED drive device, It is characterized by the above-mentioned.

  The present invention has an effect that dimming can be performed while suppressing a change in the color of the LED without complicating the circuit.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the basic form of the LED drive device which concerns on this invention, (a) is a circuit schematic, (b) is a wave form diagram of an input voltage, an intermediate voltage, and an output current. It is a figure which shows the operation example of the step-up circuit and step-down circuit in the LED drive device same as the above. It is a figure which shows the operation | movement in each lighting mode in a LED drive device same as the above. It is the circuit schematic which shows Embodiment 1 of the LED drive device which concerns on this invention. It is a circuit schematic diagram showing each control circuit in the LED drive device same as the above, (a) is a diagram of a step-up control circuit, (b) is a diagram of a step-down control circuit, (c) is a diagram of a dimming control circuit. . FIG. 5 is a circuit schematic diagram showing each control circuit in Embodiment 2 of the LED drive device according to the present invention, where (a) is a diagram of a step-up control circuit and (b) is a diagram of a step-down control circuit. It is explanatory drawing of the mode switching operation | movement of the pressure | voltage fall control circuit in an LED drive device same as the above. FIG. 5 is a diagram illustrating an LED driving device according to a third embodiment of the present invention, where (a) is a schematic circuit diagram, (b) is a diagram illustrating an example of arrangement of detection resistors, and (c) is a waveform diagram of current flowing through the detection resistors. It is. 1 is an overall schematic diagram showing an embodiment of a lighting device according to the present invention. (A) is a correlation diagram of the range of the power supply voltage used for vehicle-mounted LED, and the fluctuation range of a load voltage, (b) is a circuit schematic diagram which shows the basic composition of the conventional LED drive device. It is the circuit schematic which shows the other structure of the conventional LED drive device same as the above.

(Basic form)
Hereinafter, the basic form of the LED driving device according to the present invention will be described with reference to the drawings. As shown in FIG. 1 (a), the basic form includes a step-up circuit 1 connected to a DC power source DC1, a step-down circuit 2 connected to a light source unit 3 formed by connecting a plurality of LEDs 30 in series, A control circuit 4 and a dimming control circuit 5 are included.

  The booster circuit 1 includes a choke coil L1, a diode D1, a switching element Q1, and a capacitor C1. The booster circuit 1 boosts the power supply voltage (input voltage) V1 of the DC power supply DC1 by switching on / off of the switching element Q1 at a high frequency (several tens of kHz to several hundreds of kHz) by a main control circuit 4 described later. Then, the intermediate voltage VC1 is output as the voltage across the capacitor C1.

  The step-down circuit 2 includes a choke coil L2, a diode D2, and a switching element Q2. The step-down circuit 2 steps down the intermediate voltage VC1 and outputs a load voltage (output voltage) V2 by switching on / off of the switching element Q2 at a low frequency (100 to 500 Hz) by a main control circuit 4 described later. And applied to the light source unit 3.

  The main control circuit 4 controls the intermediate voltage VC1 and the output voltage V2 by controlling on / off of the switching elements Q1, Q2 of the booster circuit 1 and the step-down circuit 2. The dimming control circuit 5 controls the main control circuit 4 based on a dimming signal from the outside to thereby obtain an output voltage V2 applied to the light source unit 3 and a load current (output current) I1 flowing through the light source unit 3. The light source unit 3 is dimmed by changing. The specific configurations of the main control circuit 4 and the dimming control circuit 5 will be described later in the following embodiments.

  Here, in this basic mode, as shown in FIG. 1B, the switching element Q2 of the step-down circuit 2 is turned on / off at a low frequency of the period T1, and the on-duty ratio is changed, that is, the low-frequency PWM The light source unit 3 is dimmed by performing (pulse width modulation) control. In addition, in this basic mode, as shown in FIG. 1B, in the on period T10 of the switching element Q2, the switching element Q2 is turned on / off at a high frequency (several tens of kHz to several hundreds of kHz). The duty ratio is changed. That is, the step-down circuit 2 performs high-frequency PWM control during the ON period T10 of the switching element Q2.

  Hereinafter, an operation example of the booster circuit 1 and the step-down circuit 2 in this basic mode will be described. A specific circuit for realizing each operation will be described in each embodiment described later. First, an operation example of the booster circuit 1 will be described. When the input voltage V1 is smaller than the output voltage V2, the booster circuit 1 controls the intermediate voltage VC1 to be constant at a predetermined voltage value or receives a dimming signal from the dimming control circuit 5. By changing the intermediate voltage VC1, the light source unit 3 is dimmed by changing the output current I1. Further, when the input voltage V1 is larger than the output voltage V2, the booster circuit 1 stops the operation so as not to boost the input voltage V1.

  Next, an operation example of the step-down circuit 2 will be described. When the step-up circuit 2 does not perform dimming in the step-up circuit 1, regardless of the magnitude of the input voltage V <b> 1, the switching element Q <b> 2 is PWM-controlled at a low frequency of the period T <b> 1 to dimm the light source unit 3. To do. As already described, the step-down circuit 2 performs PWM control at a high frequency during the on period T10 of the switching element Q2. That is, in the full lighting mode in which the luminous flux is 100%, the switching element Q2 is always in the on state, so that the step-down circuit 2 operates by high-frequency PWM control. Further, in the dimming lighting mode in which the luminous flux is less than 100%, the step-down circuit 2 operates in the low frequency PWM control described above and the high frequency PWM control in the on period T10.

  Combinations of the operations of the booster circuit 1 and the step-down circuit 2 are shown in (1) to (6) of FIG. FIG. 3 shows operations of the booster circuit 1 and the step-down circuit 2 in each mode of the full lighting mode and the dimming lighting mode. In this basic mode, the dimming lighting mode is further divided into two modes with a luminous flux of 70% as a boundary.

  For example, when the input voltage V1 is smaller than the output voltage V2, the operation of (1) in FIG. 2 is performed in the full lighting mode, and the operation of (2) in FIG. 2 is performed in the dimming lighting mode. Similarly, when the input voltage V1 is smaller than the output voltage V2, the operation of FIG. 2 (1) is performed in the full lighting mode, and in the dimming lighting mode, if the luminous flux is 70% or more ( If the operation of 3) is less than 70%, the operation of (4) in FIG. 2 may be performed. When the input voltage V1 is higher than the output voltage V2, the operation of (5) in FIG. 2 is performed in the full lighting mode, and the operation of (6) in FIG. 2 is performed in the dimming lighting mode.

  As described above, in this basic mode, the booster circuit 1 is connected to the DC power source DC1 and the step-down circuit 2 is connected to the light source unit 3. In this basic mode, the switching element Q2 of the step-down circuit 2 is PWM-controlled at a low frequency, and the light source unit 3 is dimmed by PWM-controlling the switching element Q2 at a high frequency during the ON period T10 of the switching element Q2. doing. Thereby, in this basic form, it can light-control by suppressing the change of the color of LED30, especially the white LED comprised combining blue LED and yellow fluorescent substance. If the output current I1 maintains 70 to 80% or more of the rated current value of the light source unit 3 in the on period T10 of the switching element Q2 of the step-down circuit 2, the color change of the LED 30 can be suppressed. Further, in this basic mode, since there is no need to provide a new switching element 103 in the booster circuit 101 unlike the conventional example, the circuit is not complicated.

(Embodiment 1)
Hereinafter, Embodiment 1 of the LED drive device according to the present invention will be described with reference to the drawings. However, since the basic configuration of this embodiment is the same as that of the basic mode, the same parts are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 4, the present embodiment includes a booster circuit 1 connected to a DC power source DC1, a step-down circuit 2 connected to a light source unit 3, a main control circuit 4, and a dimming control circuit 5. Is done.

  A series circuit of resistors R1 and R2 is connected to the booster circuit 1 in parallel with both ends of the capacitor C1 at the output end. The voltage across the resistor R2 in this series circuit is input to a boost control circuit 40 described later as a detection voltage VD1 for detecting the intermediate voltage VC1 of the boost circuit 1. In the step-down circuit 2, a resistor R3 is connected in series between the switching element Q2 and the ground. The voltage across the resistor R3 is input to a step-down control circuit 41, which will be described later, as a detection voltage VD2 for detecting the output voltage V2 of the step-down circuit 2.

  The main control circuit 4 includes a step-up control circuit 40 that controls the switching element Q1 of the step-up circuit 1 and a step-down control circuit 41 that controls the switching element Q2 of the step-down circuit 2. As shown in FIG. 5A, the boost control circuit 40 includes an error amplifier 400, a PWM control circuit 401 including a sawtooth wave generation circuit 402 and a comparator 403, and a drive circuit 404 that drives the switching element Q1. The

  The detection voltage VD1 and the reference voltage VR1 based on the target value of the intermediate voltage VC1 of the booster circuit 1 are input to each input terminal of the error amplifier 400, and an output voltage obtained by amplifying the error is input to the comparator 403. . The sawtooth wave generation circuit 402 generates a high-frequency sawtooth wave and inputs it to the comparator 403. The comparator 403 outputs a high-frequency pulse voltage by comparing the output voltage of the error amplifier 400 with a high-frequency sawtooth wave.

  The pulse width of this pulse voltage becomes narrower when the detection voltage VD1 becomes larger and becomes wider when the detection voltage VD1 becomes smaller. That is, the pulse width of the pulse voltage changes based on the magnitude of the detection voltage VD1, and the drive circuit 404 controls on / off of the switching element Q1 based on this pulse voltage.

  Therefore, the boost control circuit 40 controls the switching element Q1 at high frequency so that the detection voltage VD1 becomes equal to the reference voltage VR1, thereby controlling the intermediate voltage VC1 of the boost circuit 1 to be constant at the target value. .

  As shown in FIG. 5B, the step-down control circuit 41 includes an error amplifier 410, a PWM control circuit 411 including a sawtooth wave generation circuit 412, and a comparator 413, an AND element 414, and a drive circuit that drives the switching element Q2. 415. The detection voltage VD2 and the reference voltage VR2 based on the target value of the output current I1 of the step-down circuit 2 are input to each input terminal of the error amplifier 410, and an output voltage obtained by amplifying the error is input to the comparator 413. . The sawtooth wave generation circuit 412 generates a high-frequency sawtooth wave and inputs it to the comparator 413. The comparator 413 compares the output voltage of the error amplifier 410 with the high frequency sawtooth wave, thereby outputting a high frequency pulse voltage and inputting it to the AND element 414.

  The AND element 414 receives an output voltage of the comparator 413 and a low-frequency pulse voltage having a period T1 from the light control circuit 5 described later, and inputs the product to the drive circuit 415. The drive circuit 415 controls on / off of the switching element Q2 based on the output voltage of the AND element 414. Therefore, the switching element Q2 is PWM controlled at a low frequency by the low frequency pulse voltage from the dimming control circuit 5, and is PWM controlled at a high frequency by the high frequency pulse voltage from the PWM control circuit 411. The

  Here, the pulse width of the high-frequency pulse voltage from the PWM control circuit 411 decreases as the detection voltage VD2 increases, and increases as the detection voltage VD2 decreases. Accordingly, the step-down control circuit 41 performs PWM control of the switching element Q2 at a high frequency so that the detection voltage VD2 becomes equal to the reference voltage VR2 during the ON period T10 of the switching element Q2, thereby making the output current I1 constant at the target value. Control to be. In the present embodiment, the target value of the output current I1 is set to the rated current value of the light source unit 3.

  Further, the pulse width of the low frequency pulse voltage from the dimming control circuit 5 changes based on the dimming signal from the outside. For example, as the dimming rate increases, the pulse width increases, and as the dimming rate decreases, the pulse width decreases. Therefore, the step-down control circuit 41 performs the PWM control of the switching element Q2 at a low frequency by the low frequency pulse voltage from the dimming control circuit 5, thereby dimming the light source unit 3 at a target dimming rate.

  As shown in FIGS. 5B and 5C, the dimming control circuit 5 generates a dimming voltage generation circuit 50 that generates a dimming voltage VD3 based on the dimming rate, and a pulse voltage based on the dimming voltage VD3. And a generated pulse voltage generation circuit 51. The dimming voltage generation circuit 50 includes a series circuit of a variable resistor R4 and a resistor R5 that divides the power supply voltage of the DC power source DC1, and inputs the voltage across the resistor R5 to the pulse voltage generation circuit 51 as the dimming voltage VD3. .

  The resistance value of the variable resistor R4 changes when the user turns a dimming knob (not shown), for example. As a result, the dimming voltage VD3 based on the dimming rate is input to the pulse voltage generation circuit 51. Of course, the means for changing the resistance value of the variable resistor R4 is not limited to the dimming knob. For example, an infrared signal including the dimming rate is received from an external remote controller (not shown), and the dimming rate is adjusted. Based on this, the resistance value of the variable resistor R4 may be changed.

  The pulse voltage generation circuit 51 changes the pulse width of the pulse voltage based on the voltage level of the dimming voltage. For example, the pulse width of the pulse voltage is increased when the dimming rate is increased, that is, the dimming voltage is increased, and the pulse width of the pulse voltage is decreased when the dimming rate is decreased, that is, the dimming voltage is decreased.

  Hereinafter, the operation of this embodiment will be described. First, the case where the input voltage V1 is smaller than the output voltage V2 will be described. In this case, in the full lighting mode, since the switching element Q2 is always in the ON period T10, the step-down control circuit 41 performs PWM control of the switching element Q2 at a high frequency. On the other hand, in the dimming lighting mode, the step-down control circuit 41 performs PWM control of the switching element Q2 at a low frequency based on the dimming rate, and performs PWM control of the switching element Q2 at a high frequency in the on period T10. That is, in the present embodiment, when the input voltage V1 is smaller than the output voltage V2, the operation shown in the upper part of FIG. 3 is performed.

  Next, a case where the input voltage V1 is higher than the output voltage V2 will be described. In this case, since the detection voltage VD1 exceeds the reference voltage VR1 in the boost control circuit 40, the PWM control circuit 401 does not output a high-frequency pulse voltage, and the boost control circuit 40 stops the operation of the boost circuit 1. In the step-down control circuit 41, the switching element Q2 is PWM-controlled as in the case where the input voltage V1 is smaller than the output voltage V2. That is, this embodiment performs the operation shown in the lower part of FIG. 3 when the input voltage V1 is higher than the output voltage V2.

  As described above, in this embodiment, the booster circuit 1 is connected to the DC power source DC1 and the step-down circuit 2 is connected to the light source unit 3. In the present embodiment, in the dimming lighting mode, the switching element Q2 of the step-down circuit 2 is PWM-controlled at a low frequency, and the switching element Q2 is PWM-controlled at a high frequency during the ON period T10 of the switching element Q2. The light source unit 3 is dimmed. Thereby, in this embodiment, since the light source part 3 can be dimmed, maintaining the output current I1 at the rated current value of the light source part 3, it is white LED comprised combining LED30, especially blue LED and yellow fluorescent substance. The light can be dimmed while suppressing changes in color. Further, in the present embodiment, it is not necessary to provide a new switching element 103 in the booster circuit 101 unlike the conventional example, so that the circuit is not complicated.

(Embodiment 2)
Hereinafter, Embodiment 2 of the LED driving device according to the present invention will be described with reference to the drawings. However, since the basic configuration of the present embodiment is common to that of the first embodiment, common portions are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, the light source unit 3 is dimmed by controlling the amplitude of the intermediate voltage VC1 of the booster circuit 1 until the dimming rate of the light source unit 3 falls below a predetermined value (70% here). In the present embodiment, when the dimming rate falls below a predetermined value, the light source unit 3 is dimmed by PWM-controlling the switching element Q2 of the step-down circuit 2 at a low frequency, as in the first embodiment.

  Hereinafter, the step-up control circuit 40, the step-down control circuit 41, and the dimming voltage generation circuit 50 that are different from the first embodiment in the present embodiment will be described with reference to the drawings. In the step-up control circuit 40, as shown in FIG. 6A, the reference voltage VR1 is input to one input terminal of the error amplifier 400 via the resistor R6 and the diode D3, and via the diode D4 and the resistor R7. The dimming voltage VD3 is input. The reference voltage VR1 is set to a value based on the intermediate voltage VC1 of the booster circuit 1 at a predetermined dimming rate.

  Therefore, until the dimming voltage VD3 falls below the reference voltage VR1, that is, until the dimming rate reaches a predetermined value, the error amplifier 400 compares the detection voltage VD1 with the dimming voltage VD3 and amplifies the error. The output voltage is input to the comparator 403. That is, the boosting control circuit 40 performs PWM control of the switching element Q1 at a high frequency so that the detection voltage VD1 becomes equal to the dimming voltage VD3 until the dimming rate reaches a predetermined value, whereby an intermediate voltage of the boosting circuit 1 is obtained. VC1 is changed in conjunction with the dimming rate. Thereby, the amplitude of the intermediate voltage VC1 of the booster circuit 1 is controlled in conjunction with the dimming rate.

  When the dimming rate falls below a predetermined value, the reference voltage VR1 exceeds the dimming voltage VD3, so that the reference voltage VR1 is input to the error amplifier 400. Therefore, when the dimming rate falls below a predetermined value, the boost control circuit 40 performs PWM control of the switching element Q1 at a high frequency so that the detection voltage VD1 becomes equal to the reference voltage VR1, thereby reducing the intermediate voltage VC1 of the boost circuit 1. Control so as to be constant at the target value. As a result, the intermediate voltage VC1 of the booster circuit 1 is kept constant regardless of the dimming rate.

  The step-down control circuit 41 is newly provided with a comparator 416 and a NAND element 417 as shown in FIG. The dimming voltage generation circuit 50 according to the present embodiment includes a series circuit of a variable resistor R9, a resistor R8, and a resistor R5 that divides the power source voltage of the DC power source DC1, and uses a voltage across the resistor R5 as the dimming voltage VD3. This is input to the pulse voltage generation circuit 51 and the comparator 416.

  The dimming voltage VD3 from the dimming voltage generation circuit 50 and the reference voltage VR3 are input to the input terminals of the comparator 416 via the resistors R10 and R11. The reference voltage VR3 is set based on the level of the dimming voltage VD3 at a predetermined dimming rate. The output voltage of the comparator 416 is input to the pulse voltage generation circuit 51. The pulse voltage generation circuit 51 always outputs a high level signal while the output voltage of the comparator 416 is low, and when the output voltage of the comparator 416 is inverted to high level, a low frequency pulse voltage based on the dimming rate. Is output. The NAND element 417 receives the low frequency pulse voltage from the pulse voltage generation circuit 51 and the output voltage of the comparator 416, and inputs the product to the AND element 414.

  Here, operations of the comparator 416 and the NAND element 417 will be described with reference to the drawings. As shown in FIG. 6C, since the output voltage of the comparator 416 is low until the dimming voltage VD3 matches the reference voltage VR3, that is, until the dimming rate reaches a predetermined value, the NAND element 417 Output voltage becomes high level, and the AND element 414 outputs a high-frequency pulse voltage. Therefore, the drive circuit 415 performs PWM control of the switching element Q2 at a high frequency until the dimming rate reaches a predetermined value.

  Next, when the dimming voltage VD3 is lower than the reference voltage VR3, that is, when the dimming rate is lower than a predetermined value, the output voltage of the comparator 416 is switched to a high level, so that a low frequency pulse voltage is output from the NAND element 417. Is done. Therefore, the switching element Q2 is PWM-controlled at a low frequency by the low-frequency pulse voltage from the pulse voltage generation circuit 51, and is PWM-controlled at a high frequency by the high-frequency pulse voltage from the PWM control circuit 411 in the on period T10. Is done. That is, the step-down control circuit 41 is configured to switch its operation at a predetermined dimming rate.

  Hereinafter, the operation of this embodiment will be described. First, the case where the input voltage V1 is smaller than the output voltage V2 will be described. In this case, in the full lighting mode, the boost control circuit 40 performs control so that the intermediate voltage VC1 becomes a value based on the dimming rate of 100%.

  Next, in the dimming lighting mode, the boost control circuit 40 performs amplitude control so as to change the intermediate voltage VC1 in conjunction with the dimming rate until the dimming rate reaches a predetermined value. Thereby, since the output current I1 changes in conjunction with the dimming rate, the light source unit 3 is dimmed.

  When the dimming rate falls below a predetermined value, the boost control circuit 40 controls the intermediate voltage VC1 to be constant at a value based on the predetermined dimming rate. On the other hand, the step-down control circuit 41 performs PWM control of the switching element Q2 at a low frequency based on the dimming rate, and performs PWM control of the switching element Q2 at a high frequency during the ON period T10. That is, in the present embodiment, when the input voltage V1 is smaller than the output voltage V2, the operation shown in the middle stage of FIG. 3 is performed.

  Next, a case where the input voltage V1 is higher than the output voltage V2 will be described. In this case, since the detection voltage VD1 exceeds the reference voltage VR1 in the boost control circuit 40, the PWM control circuit 401 does not output a high-frequency pulse voltage, and the boost control circuit 40 stops the operation of the boost circuit 1. In the step-down control circuit 41, the switching element Q2 is PWM-controlled as in the case where the input voltage V1 is smaller than the output voltage V2. That is, this embodiment performs the operation shown in the lower part of FIG. 3 when the input voltage V1 is higher than the output voltage V2.

  As described above, in the present embodiment, in the dimming lighting mode, the light source unit 3 is dimmed by controlling the amplitude of the intermediate voltage VC1 of the booster circuit 1 until the dimming rate reaches a predetermined value. When the dimming rate falls below a predetermined value, the switching element Q2 of the step-down circuit 2 is PWM-controlled at a low frequency, and the switching element Q2 is PWM-controlled at a high frequency during the ON period T10 of the switching element Q2. Dimming part 3. Thereby, in this embodiment, since the light source part 3 can be dimmed, maintaining the output current I1 to 70-80% or more of the rated current value of the light source part 3, it combines LED30, especially blue LED and yellow fluorescent substance. The light can be dimmed while suppressing the change in the color of the white LED. Further, in the present embodiment, it is not necessary to provide a new switching element 103 in the booster circuit 101 unlike the conventional example, so that the circuit is not complicated.

(Embodiment 3)
Hereinafter, Embodiment 3 of the LED driving device according to the present invention will be described with reference to the drawings. Since the basic configuration of the present embodiment is common to either of the first and second embodiments, the same parts are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, as shown in FIG. 8A, the switching element Q2 of the step-down circuit 2 is not connected to the ground but connected to the high voltage side. In FIG. 8A, the main control circuit 4 and the dimming control circuit 5 are not shown.

  Thereby, since one end of the light source unit 3 is connected to the ground, as shown in FIG. 8B, a resistor R3 for detecting the output current I1 can be arranged according to the purpose. For example, when the resistor R3 is disposed at the position shown in FIG. 8B (1), the current waveform flowing through the resistor R3 is the waveform shown in FIG. 8C (1). When the resistor R3 is disposed at the position shown in (2) of FIG. 8B, the current waveform flowing through the resistor R3 is the waveform shown in (2) of FIG. 8C. When the resistor R3 is disposed at the position shown in (3) of FIG. 8B, the current waveform flowing through the resistor R3 is the waveform shown in (3) of FIG. 8C.

  In each of the above embodiments, the PWM control in the booster circuit 1 and the step-down circuit 2 is realized using a sawtooth wave. However, the duty control may be performed by changing the frequency. Further, the main control unit 4 may be configured by a microcomputer, and the same control as in each of the above embodiments may be performed by the microcomputer.

  In each of the above embodiments, the light source unit 3 is dimmed by changing the luminous flux from 100% to several percent. For example, the light source unit 3 is dimmed so as to increase the luminous flux to 110 to 120%. May be.

  Furthermore, in each said embodiment, there is no restriction | limiting in particular in the number of LED30 which comprises the light source part 3. FIG. For example, assuming that the above-described embodiments are used for the light source unit 3 composed of five LEDs 30, the same circuit configuration can be used even when the number of LEDs 30 is changed from five to two. That is, since each said embodiment can be shared irrespective of the fluctuation | variation of the element number of LED30 of the light source part 3, there exists an advantage that it is not necessary to prepare several types of LED drive device according to the element number of LED30. is there.

  Hereinafter, an embodiment of a lighting device according to the present invention will be described with reference to the drawings. The present embodiment is a headlamp (headlight), and as shown in FIG. 9, an instrument main body A1, a light source unit A2 having a light source unit 3, and an optical that distributes light emitted from the light source unit 3. Unit A3. In the present embodiment, the light source unit 3 is attached and fixed to dissipate the heat generated by the light source unit 3, and the fixing plate A4 for fixing the light source unit A2 and the heat dissipating plate A4 to the instrument body A1. With. The light source unit 3 is connected to the LED driving device B1 according to any one of the above embodiments via an output line B2. Further, the LED driving device B1 is connected to a DC power source DC1 through an input line B3. In this embodiment, a vehicle-mounted battery is used as the DC power source DC1.

  Since this embodiment includes the LED driving device B1 of any one of the above embodiments, the same effects as any of the above embodiments can be achieved.

  Note that the lighting device is not limited to the head lamp of the above embodiment, and is widely used in, for example, a vehicle interior lighting device such as a room lamp, and an exterior light lighting device such as a tail lamp, a width lamp, and a brake lamp. Can do. Of course, you may use for the lighting fixture of general lighting uses other than the object for vehicles.

  For example, when the LED driving device B1 according to any one of the above embodiments is used for a vehicle interior lighting device such as a room lamp, the light distribution characteristic of the optical unit A3 disposed on the front surface of the light source unit 3 is far away. It should be changed from the characteristic suitable for the lighting of the vehicle to the characteristic suitable for the lighting in the vehicle interior. In this case, it is needless to say that the shape of the instrument main body A1 should be changed to a shape suitable for arrangement in the passenger compartment. In addition, when used for lighting fixtures for general lighting purposes other than those for vehicles, it is desirable to use a DC power supply circuit that rectifies and smoothes a commercial AC power supply as the DC power supply DC1 instead of a vehicle-mounted battery.

DESCRIPTION OF SYMBOLS 1 Booster circuit 2 Buck converter 3 Light source part 30 LED (light emitting diode)
4 Main control circuit 5 Dimming control circuit DC1 DC power supply Q1, Q2 Switching element V1 Power supply voltage (input voltage)
V2 Load voltage (output voltage)
VC1 intermediate voltage

Claims (5)

A booster circuit that is connected to a DC power supply and boosts the power supply voltage of the DC power supply to output an intermediate voltage; and a load voltage that is connected to a light source unit composed of a plurality of light emitting diodes and steps down the intermediate voltage of the booster circuit. A step-down circuit for outputting the light source unit to the light source unit, a main control circuit for controlling the step-up circuit and the step-down circuit, and the light source unit to the main control circuit based on a dimming rate of the light source unit set from the outside. A dimming control circuit for dimming, wherein the step-down circuit has at least a switching element,
The main control circuit dimmes the light source unit by controlling the amplitude of the intermediate voltage of the booster circuit until the dimming rate falls below a predetermined value, and when the dimming rate falls below the predetermined value, An LED driving device characterized in that the light source unit is dimmed by performing PWM control of the switching element of the step-down circuit at a predetermined frequency and performing PWM control at a frequency higher than the predetermined frequency during the ON period . The main control circuit dimmes the light source unit by PWM controlling the switching element of the step-down circuit at a frequency higher than the predetermined frequency until the dimming rate falls below the predetermined value. 2. The LED driving device according to claim 1 , wherein when the light rate falls below the predetermined value, the intermediate voltage of the booster circuit is controlled to be constant at a target value . 3. The LED according to claim 1 , wherein the main control circuit performs PWM control of the switching element of the step-down circuit so that a load current flowing through the light source unit maintains a rated current value of the light source unit. Drive device.   The main control circuit stops operation of the booster circuit when the power supply voltage exceeds the load voltage, and starts operation of the booster circuit when the power supply voltage falls below the load voltage. The LED driving device according to any one of 1 to 3.   5. An illumination device comprising: the LED driving device according to claim 1, the light source unit, and a fixture main body that holds the light source unit and the LED driving device.

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