JP2010015887A - Led lighting control circuit and vehicle lamp fixture equipped with this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED lighting control circuit capable of controlling an output current for driving an LED so that the output power of the LED falls within a predetermined range corresponding to the Vf variation of the LED, and a vehicular lamp provided with the LED lighting control circuit. Can do.
An LED lighting control circuit 10 includes, for example, a DC power source that inputs a battery, a transformer 16 connected to the DC power source, a voltage detection unit 18 that detects output voltages of a plurality of LED light sources 14, and an LED. A current detection unit 20 that detects an output current of the light source 14, a calculation unit 22 that sets a current value for driving the LED light source 14 based on an output voltage value detected by the voltage detection unit 18, and an output of the current detection unit 20 A PWM control unit 24 that controls the output current that drives the LED light source 14 from the current value and the set current value of the calculation unit 22, and an FET driver 26 that turns on and off the switching element Q <b> 1 by a signal from the PWM control unit 24 are provided. .
[Selection] Figure 1

Description

  The present invention relates to an LED lighting control circuit that drives a plurality of LEDs connected in series, and a vehicular lamp including the LED lighting control circuit.

  Conventionally, light-emitting diodes (LEDs) have been used for illumination in the interior of a vehicle or illumination of instruments at night. In recent years, in addition to the practical use of red LED stop lamps, white LEDs have been actively developed as light sources for automobile lighting such as daytime running lamps and headlamps by improving the performance of white LEDs with higher brightness. It has come to be.

  In in-vehicle lighting using these LEDs as a light source, a battery, which is a vehicle power source, is used as an input power source, and the LEDs are turned on based on the battery voltage.

  In general, when an LED is lit, a current limiting element such as a resistor that limits a current with respect to an applied voltage is required. Particularly in a headlamp, a large current is required in order to maximize the performance of the LED. If it is attempted to limit the current with a resistor, the power loss due to the resistor becomes considerably large. In order to solve the problem of increased resistance and heat generation, a switching power supply circuit using constant current control for controlling the current for driving the LED to be constant is used instead of the resistance.

  For example, Patent Document 1 discloses that as a lighting circuit, a converter circuit is connected to a light emitting unit composed of a plurality of LEDs connected in series, and the output voltage of the converter circuit is constant so that the voltage between terminals of the constant current circuit is constant. It is disclosed that the current flowing through the light emitting unit and the constant current circuit is made constant while controlling the current.

Further, in Patent Document 2, a constant current circuit for keeping a current flowing through the LED unit constant is connected to an LED unit formed by connecting a plurality of LEDs in series, and applied to the LED unit by a voltage detection circuit. A rear combination lamp device is disclosed for detecting a voltage being applied.
JP 2001-215913 A JP 2003-187614 A

  By the way, in the conventional LED lighting control circuit, a constant current is always supplied to the LED regardless of the value of the forward voltage (Vf) of the LED to light the LED. Generally, in a high-intensity LED, the variation in Vf occurs in the range of 3 to 4V. Therefore, when a constant current is passed through a light source including an LED having a large Vf value as shown at point C in FIG. 7, Vf indicated by point B is compared with a standard value LED. The output power is increased, and the junction temperature of the LED chip is extremely increased. As the output power increases, the heat generation increases, so it is necessary to increase the size of the heat dissipating fins attached to the vehicle lamps such as headlights, or to select the LED itself having a Vf value close to reduce the current. .

  In addition to the variation in the initial value of LED Vf, in addition to the increase due to aging of Vf, constant current control may cause a heat generation failure of the circuit itself due to an increase in output power or an accelerated deterioration due to an abnormal temperature of the LED. It was.

  On the other hand, as shown at point A in FIG. 7, when a constant current is passed through a light source including an LED having a small Vf value, Vf indicated by point B is compared with a standard value LED. Since the output power is small, there is a thermal margin, but there is a problem that the brightness cannot be increased unless Vf is selected and the current is adjusted. Further, even when some LEDs are short-circuited and Vf is greatly reduced, the brightness of the headlamp is inevitably reduced due to the failure of the LED because control is always performed at a constant current.

  In addition, since the LED was always lit at a constant current value, as a general characteristic of a high-brightness LED, a phenomenon in which light emission efficiency decreases due to an increase in the temperature of the LED chip occurs. There was a problem that the brightness gradually decreased for about 30 minutes until stabilization.

  The present invention has been made in view of such circumstances, and an LED lighting control circuit capable of controlling an output current for driving an LED so that the output power of the LED falls within a predetermined range corresponding to the Vf variation of the LED. And it aims at providing the vehicular lamp provided with this.

  In order to achieve the above object, an LED lighting control circuit of the present invention is an LED lighting control circuit that drives a plurality of LEDs connected in series, and a current detection unit that detects an output current flowing through the LED; A voltage detection unit that detects the output voltage of the LED, and a current value for driving the LED so that the output power value of the LED is within a predetermined range based on the output voltage value detected by the voltage detection unit. A control unit for controlling the output current value for driving the LED within a predetermined range based on the calculation unit to be set and the output current value detected by the current detection unit and the current value set by the calculation unit And.

  In the invention, the LED lighting control circuit according to the present invention preferably includes a current limiting unit that limits the output current value detected by the current detection unit within a predetermined output current value.

  The LED lighting control circuit according to the present invention is the LED lighting control circuit according to the present invention, wherein the predetermined output current limit value is a predetermined value in an output voltage range obtained by adding a forward voltage of the LED, and in a range from the lowest value to the maximum value. It is preferable to set the current value to be an output power.

  The LED lighting control circuit of the present invention drives the LED in the invention so that the output power value is within a range of ± 15% with respect to the output power value calculated from the rated output current and the rated output voltage of the LED. Preferably, the current value to be set is set.

  In the LED lighting control circuit of the present invention, in the invention, the control unit preferably includes a PWM control unit.

  In order to achieve the above object, a vehicle lamp according to the present invention includes any one of the LED lighting control circuits and a plurality of LEDs connected in series driven by the LED lighting control circuit. And

  The vehicular lamp according to the present invention preferably includes a radiation fin that radiates heat generated by the LED.

  According to the present invention, the sum of Vf of LEDs connected in series is detected as an output voltage, the output current of the LED is increased or decreased according to the sum of each VF, and the maximum output power of the LED is suppressed. Can be reduced in size, and Vf variation selection and current adjustment are not required.

  According to the present invention, the control is performed to increase the output current with respect to the decrease in Vf. When Vf is low and the LED has a thermal margin with respect to the temperature, the output current is increased and the LED is lit brighter. Can do. Further, even when a part of the LED has a short circuit failure, the decrease in Vf is detected and the output current is increased, so that the decrease in brightness can be compensated for by a normal LED.

  According to the present invention, the control is to increase the output current with respect to the decrease in Vf. Further, since the decrease in Vf can be detected when the LED temperature rises, Can be compensated for by reducing the output current.

  According to the present invention, since the output current is decreased with respect to the increase in Vf, the LED output power is not increased, and the LED deterioration is suppressed. Similarly, the output power of the circuit does not increase, so that a circuit failure due to heat generation can be prevented.

  According to the present invention, the temperature of the LED junction is directly detected by controlling the output power of the LED based on the output voltage value of the LED without directly detecting the temperature of the LED junction by a sensor or the like. Without this, the LED temperature rise can be reduced at low cost.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described with reference to the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments than the present embodiment can be used. Can do. Accordingly, all modifications within the scope of the present invention are included in the claims.

  FIG. 1 is a circuit diagram showing an outline of an LED lighting control circuit according to the present embodiment. In this embodiment, an example in which an LED is used as a light source of a headlamp will be described.

  When an LED is used as a light source for a headlamp, a plurality of LEDs are required to obtain a predetermined brightness. Therefore, all LEDs are connected in series in order to efficiently light at a constant current. Thereby, all LEDs can be simultaneously controlled with a single power supply circuit. As shown in FIG. 1, a plurality of LED light sources 14 composed of a plurality of LEDs 12 connected in series are connected in series.

  The LED lighting control circuit 10 includes, for example, a DC power source (not shown) that receives a battery, a transformer 16 connected to the DC power source, a voltage detection unit 18 that detects output voltages of the plurality of LED light sources 14, and an LED. A current detection unit 20 that detects an output current of the light source 14, a calculation unit 22 that sets a current value for driving the LED light source 14 based on an output voltage value detected by the voltage detection unit 18, and an output of the current detection unit 20 A PWM control unit 24 that controls the output current that drives the LED light source 14 from the current value and the set current value of the calculation unit 22, and an FET driver 26 that turns on and off the switching element Q <b> 1 by a signal from the PWM control unit 24 are provided. . A current limiting unit 28 is provided for limiting the output current value detected by the current detection unit 20 within a predetermined output current value. Here, the maximum rated current value of the LED can be used as the predetermined current value.

  The LED lighting control circuit 10 is in series with the input capacitor C1 connected between the input power supply side of the DC power supply and the ground, the diode D1 connected to the secondary winding of the transformer 16, and the diode D1. A smoothing capacitor C2 connected in parallel to the LED light source 14 is provided.

  Next, the circuit operation of the LED lighting control circuit 10 according to the present embodiment will be described with reference to FIG. 1 using a headlight as an example.

  The forward voltage (Vf) of the high-brightness type LED 12 used for the LED light source 14 is, for example, about 3 to 4 V when InGaN is the main material. Considering the current LED light emission efficiency, about 20 chips are required for the passing Lo beam, and a total output voltage of 80 V or more is required in total.

  On the other hand, since the battery voltage of the vehicle is about 12V, when the headlight described above is turned on, the lighting circuit serves as a boost power source. Therefore, as shown in FIG. 1, the battery input voltage and the current charged in the input capacitor C1 are powered with a switching frequency of about several tens kHz to several hundreds kHz of a pulse width that takes a battery as an input and becomes a predetermined output voltage. The switching element Q1, such as a MOS • FET, turns on / off the conduction of the primary winding of the transformer 16 to generate pulse power. This is converted to the secondary side of the transformer 16 as magnetic energy.

  As a result, the pulse power generated in the secondary winding of the transformer 16 is rectified by the diode D1, smoothed by the smoothing capacitor C2, and converted into a predetermined output voltage.

  In order to control this output with a constant set current, a current detection unit 20 is provided in an output path through which the drive current of the LED light source 14 passes. In the current detection unit 20, a resistor is provided as a current detection circuit. By using the voltage signal detected by the current detection resistor as a reference and comparing with a reference voltage signal provided as a set current value and performing feedback control, it becomes possible to control the output with a constant set current. .

  A PWM control unit 24 is provided for feedback control. The PWM control unit 24 increases the switching pulse width on the primary side and increases the output when the output is lower than the set value with reference to the output current value of the current detection unit 20, and the output becomes higher. In this case, the output is reduced by narrowing the pulse width, so that an appropriate pulse width is feedback-controlled for each switching frequency so that the output current always has a constant value.

  In the present embodiment, in addition to the feedback control described above, the output current of the LED 12 is arbitrarily set so that the output power of the plurality of LED light sources 14 falls within a predetermined range in accordance with the variation in the forward voltage of the LED 12. Can be set.

  Therefore, a voltage detection unit 18 that detects the output voltage of the LED light source 14 and a calculation unit 22 that sets the drive current of the LED light source 14 based on the signal of the output voltage value detected by the voltage detection unit 18 are provided.

  In the calculating part 22, the output power value of the some LED light source 14 used as a reference | standard is set. When the signal of the output voltage value detected by the voltage detection unit 18 is supplied to the calculation unit 22, the LED light source 14 is controlled so as to obtain a predetermined output power value from the set output power value and the detected output voltage value. An output current value to be driven is set. Based on the set output current value, the PWM control unit 24 controls the FET driver 26 to control on / off of the switching element Q1. By this control, the output current value for driving the LED light source 14 is changed to the current value set by the calculation unit 22.

As the output voltage value set in the calculation unit 22, it is preferable to use a value obtained by multiplying the output power value calculated from the rated output current and the rated output voltage of the LED by the number of LEDs used as the light source. The number of LEDs used as the light source is determined from the brightness of the light source necessary for constituting the headlamp and the brightness performance of the single LED. Therefore, the set output voltage value can be obtained by the following equation.
Set output voltage value = number of LEDs used x rated output voltage x rated output current Also, set the current value to drive the LED so that the output power value is within ± 15% of the set rated output voltage value. It is preferable to do. Here, when the drive current of the LED 12 is set so that the output power of the plurality of LEDs 12 increases by 15% or more with respect to the rated output voltage value, the heat generated in the LED 12 increases.

  In addition, when the drive current of the LED 12 is set so that the output power of the plurality of LEDs 12 is reduced by 15% or more with respect to the rated output voltage value, the heat generated in the LED 12 is reduced, but the output current is reduced. There is a risk of lack of brightness.

  Here, the output power value set in advance in the calculation unit 22 is set based on the rated power curve based on the rated output voltage and the rated output current of the LED, as indicated by a one-dot chain line in FIG. Actually, a rated power curve obtained by multiplying the number of LEDs used as the LED light source is used as a reference for the set value. In FIG. 2, a dotted line W 'indicates a conventional maximum power line.

  Next, the control method of the present embodiment will be described with reference to FIGS.

  In the present embodiment, the forward voltage (Vf) of the series connection of the LEDs 12 is added, and the output voltage is detected by the voltage detector 18. When the output voltage obtained by serially adding each Vf detected by the voltage detection unit 18 becomes larger as shown by the point C in FIG. 2 than the addition value of the rated output voltage value of the LED 12, it is indicated by W in FIG. The PWM control unit 24 performs control to reduce the output current so as to approximate the rated power curve.

  Therefore, even when Vf is maximum, the total output power of each LED 12 is equal to or less than the value of the rated power curve passing through point B. Thereby, at the point C, the output power of the LED can be reduced as compared with the output power generated at the maximum value of the Vf variation, which is generated by the conventional constant current driving.

  Further, since the variation in Vf occurs for each LED 12, the heat generation of each LED 12 actually differs individually. However, when used in a headlamp, the LED 12 is attached to a heat-dissipating fin disposed on the housing cover of the sealed headlamp. The temperature drops. Since the temperature inside the housing cover is lowered, it is effective in reducing the temperature rise of all the LEDs 12.

  In addition, when some LEDs 12 deteriorate and Vf increases, the present invention detects the increase in Vf and decreases the current. Therefore, it is possible to suppress acceleration deterioration due to an increase in output power of the LED 12 whose Vf has increased. Here, as the light emission characteristics of the LED 12, the brightness changes linearly with the current value, but the increase in the output power of the LED due to the increase in Vf does not contribute to the light emission and becomes the main factor of the temperature increase of the LED 12 as a loss. .

  As a result, it is possible to prevent the power from being increased due to the control with a constant current, and the failure to turn on due to the final LED open failure due to further accelerated deterioration.

  On the other hand, when the output voltage obtained by serially adding each Vf detected by the voltage detector 18 is small as indicated by point A in FIG. The PWM control unit 24 performs control to increase the output current so as to approximate the power curve. Therefore, even when Vf is minimized, the total output power of the LED 12 is approximately the same as the rated output power, and does not significantly decrease. Since the control for increasing the output current is performed, the LED 12 can be lit brighter than in the prior art.

  Further, even when the output voltage obtained by adding each Vf in series is equal to or less than the point A which is the minimum value of Vf variation, the current limiter 28 always outputs a predetermined current value so that the current does not exceed the maximum rated current value of the LED 12. Therefore, an inrush current due to a control delay or an abnormal current exceeding the maximum rating flows at the time of a Vf drop or short circuit of a part of the LED 12, and an LED failure is not induced.

  In addition, the current limiting unit 28 sets the current limiting value to an arbitrary current value that provides a constant output power with respect to an arbitrary output voltage in the range from the lowest to the highest output voltage, thereby limiting the maximum luminous intensity of the LED 12. You can also In this case, the maximum luminance can be reduced by limiting the current by setting the current value shown in FIG. 2 to an arbitrary value between the maximum rated current value and the rated current value.

  Therefore, when a part of the LED 12 is short-circuited, the present invention can detect the voltage of the plurality of LEDs 12 connected in series and set an appropriate current value. Therefore, if there is a thermal margin even if Vf decreases, the output current is controlled to increase to the maximum rated current, and the brightness of the LED 12 that is not short-circuited can be increased within a range that is not too bright. Can be safely compensated for. The LEDs 12 used in the headlamp are all normal and are designed so as not to be dazzled by the oncoming vehicle even when a maximum rated current is passed. Therefore, as long as the plurality of partially short-circuited LEDs 12 are turned on with the maximum rated current as an upper limit, there is no problem of being too dazzling with respect to the oncoming vehicle.

  FIG. 3 is a schematic configuration diagram of a headlamp incorporating the LED lighting control circuit according to the present invention. The headlamp 50 includes a housing cover 52 and a lens cover 54 provided at the tip of the housing cover 52. In the housing cover 52, an LED substrate 56 in which a plurality of LEDs are connected in series, a reflector 58 that reflects light from the LED substrate 56 forward, a radiation fin 60 disposed on the back surface of the LED substrate 56, an LED An LED lighting control circuit 62 connected to the substrate 56 via an output line 64 is provided.

  In the headlamp 50, the above-described LED lighting control is performed. As a result, the radiating fin 60 can be made smaller than the conventional one.

  FIG. 4 shows experimental data comparing output changes when the forward voltage of the LED is similarly changed in the current control according to the present invention and the conventional constant current control. Vf of each LED is (1) 2.6V, (2) 3.5V, (3) 4.4V, and an LED light source having 17 LEDs connected in series was used.

  (2) When the output current of each LED is set to a rated current of 0.7 A at a value of 3.5 V, the output power of the LED of the current control according to the present invention and the conventional constant current control is as follows. Is the same as 42.7W.

  When Vf is increased to the maximum value (3) 4.4V, the LED current by the current control of the present invention is reduced from 0.7A to 0.6A, so the output power of the LED is about 44.4W, It is about an increase of about 4% with respect to the output power at the time. On the other hand, in the conventional constant current control, even if Vf increases, the set output current of the LED is constant at 0.7A. Therefore, the output power of the LED is 53.9 W, which is a large increase of about 26% with respect to the rated output power.

  Therefore, in the conventional current control, if the rise of Vf or the initial variation of Vf is taken into consideration, the radiating fin for the LED is inevitably enlarged. Also, since the output power greatly increases in the lighting circuit, it is necessary to increase the size of the lighting circuit in consideration of the accompanying increase in circuit heat generation.

  When Vf drops to the minimum value (1) 2.6 V, the current control of the present invention controls the LED output current to increase to 0.8 A. Even when some of the LEDs connected in series are short-circuited, the brightness of the LEDs can be increased by increasing the output current. Therefore, a decrease in brightness can be compensated for with a normal LED. The output power at this time is about 37.7 W, which is about 12% lower than the rated output power, and it can be understood that there is no thermal problem.

On the other hand, in the conventional current control, the output current value of the LED is constant at a setting of 0.7 A, the output power is greatly reduced to 31.5 W, and is about 26% with respect to the rated output power. It is drastically reduced and it is not possible to compensate for the lack of brightness when some LEDs are short-circuited.

Based on the experimental data, the range of the output power change by the control with respect to the rated output power is verified. When 17 LEDs are used at a rated voltage of 3.5 V and a rated current of 0.7 A, the output power is 42.7 W. In general, naturally radiated aluminum radiating fins have a heat radiating performance of about 1 ° C./W (1 K / W). When the output power of the LED is 42.7 W, a temperature increase of 42.7 ° C. is involved.

  In the case of an automobile, the ambient temperature near the engine room is assumed to be 100 ° C. at the maximum. Therefore, when the output power of the LED is 42.7 W, the temperature of the LED chip is 100 ° C. (environmental temperature) + 42.7 ° C. (temperature increase due to the output power of the LED) = 142.7 ° C.

  Generally, the limit temperature is 150 ° C. with respect to the junction temperature of the LED chip. Since the output power is 142.7 ° C. in the case of 42.7 W, there is a temperature margin of about 7 ° C. with respect to 150 ° C.

  When Vf is increased to (3) 4.4V which is the maximum value, the LED current by the current control of the present invention is reduced from 0.7 A to 0.6 A, so the output power of the LED is about 44.4 W. This is an increase of about 4% with respect to the rated output power. In this case, the temperature of the LED chip is 144.4 ° C. There is a thermal margin of about 5 ° C. with respect to 150 ° C.

  Next, a case where the output power is increased by about 10% with respect to the rated output power as a result of controlling the output current will be examined. An increase of about 10% with respect to the rated output power results in an output power of about 47W. In this case, the temperature of the LED chip is 147 ° C. There is a thermal margin of about 3 ° C for 150 ° C.

  Next, a case where the output power is increased by about 15% with respect to the rated output power as a result of controlling the output current will be examined. An increase of about 15% with respect to the rated output power results in an output power of about 49.1 W. In this case, the temperature of the LED chip is 149.1 ° C. There is a thermal margin of about 1 ° C with respect to 150 ° C.

  In the conventional constant current control, even if Vf increases, the set output current of the LED is constant at 0.7A. Therefore, the output power of the LED is 53.9 W, which is a large increase of about 26% with respect to the rated output power. In this case, the temperature of the LED chip is 153.9 ° C. Since it exceeds 150 degreeC, it will cause quality degradation, such as destruction of an LED chip.

  When Vf decreases to (1) 2.6 V which is the minimum value, the current control of the present invention is controlled so that the output current of the LED increases to 0.8 A which is the maximum rated current. The output power at this time is about 37.7 W, which is about 12% lower than the rated output power. In this case, the temperature of the LED chip is 137.7 ° C., and it can be understood that there is no thermal problem.

  Therefore, in order to reduce the size of the radiating fin to the limit and not to exceed the junction temperature of the LED chip, it is preferable to perform current control so that the output power is ± 15% with respect to the rated output power. From the viewpoint of thermal margin with respect to the junction temperature, it is more preferable to control the current so that the output power becomes ± 10% with respect to the rated output power.

  FIG. 5 is a graph showing the relationship between LED brightness and time in the current control of the present invention and the conventional current control when the high-brightness LED is turned on. Generally, since the luminous efficiency of an LED decreases as the temperature rises, when the LED is lit by conventional constant current control, the period from when it is lit until the temperature stabilizes gradually becomes brighter as shown in FIG. It was the characteristic which falls.

  On the other hand, in the present invention, as shown in FIG. 6, since the voltage detector can detect the output voltage value as the forward voltage gradually decreases as the LED temperature increases, the luminous efficiency due to the LED temperature increase. In accordance with the decrease in temperature, the output current of the LED can be controlled to increase, and temperature compensation for brightness can be performed.

  That is, when the temperature of the LED rises and the light emission efficiency gradually decreases, the forward voltage gradually decreases. Accordingly, in the present invention, the output current of the LED is gradually increased to compensate for the light emission decrease. Can do. Thus, by controlling the maximum output power of the LED from the output voltage value detected by the voltage detection unit without directly detecting the temperature of the LED junction by a sensor or the like, the temperature of the LED junction can be reduced at a low cost. The rise can be reduced.

  According to the current control of the present invention, as shown in FIG. 5b, it is possible to prevent a decrease in light emission efficiency even if time elapses.

The schematic block diagram of the LED lighting control circuit which shows embodiment of this invention The graph which shows the relationship between the output current and output voltage in LED which concerns on this invention Headlamp schematic configuration diagram Table showing experimental results of the present invention and conventional current control The graph which shows the relationship between the brightness and time of LED in this invention and the conventional current control Graph showing relationship between forward voltage and LED junction temperature Graph showing the relationship between output current and output voltage in a conventional LED

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... LED lighting control circuit, 12 ... LED (light emitting diode), 14 ... LED light source, 16 ... Transformer, 18 ... Voltage detection part, 20 ... Current detection part, 22 ... Calculation part, 24 ... PWM control part, 26 ... FET Driver, 28 ... Current limiting unit, 50 ... Head lamp, 52 ... Housing cover, 54 ... Lens cover, 56 ... LED substrate, 58 ... Reflector, 60 ... Radiation fin, 62 ... LED lighting control circuit, 64 ... Output line

Claims (7)

An LED lighting control circuit for driving a plurality of LEDs connected in series,
A current detector for detecting an output current flowing through the LED;
A voltage detector for detecting an output voltage of the LED;
Based on the output voltage value detected by the voltage detection unit, a calculation unit that sets a current value for driving the LED so that the output power value of the LED is within a predetermined range;
A control unit for controlling the output current value for driving the LED within a predetermined range based on the output current value detected by the current detection unit and the current value set by the calculation unit;
An LED lighting control circuit comprising:   The LED lighting control circuit according to claim 1, further comprising a current limiting unit that limits an output current value detected by the current detection unit within a predetermined output current value.   The predetermined output current limit value is set to an arbitrary current value that provides a predetermined output power in a range from the minimum value to the maximum value in an output voltage range obtained by adding forward voltages of the LEDs. The LED lighting control circuit according to claim 2, wherein:   The current value for driving the LED is set so that the output power value is within a range of ± 15% with respect to the output power value calculated from the rated output current and the rated output voltage of the LED. LED lighting control circuit.   The LED lighting control circuit according to claim 1, wherein the control unit includes a PWM control unit.   6. A vehicular lamp comprising: the LED lighting control circuit according to claim 1; and a plurality of LEDs connected in series driven by the LED lighting control circuit.   The vehicular lamp according to claim 6, further comprising a radiation fin that radiates heat generated by the LED.

Images