JP2013033644A - Led drive device and lighting device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED drive device and a lighting device therewith which can prevent a flow of overcurrent to a light source section when a dropped supply voltage is recovered.SOLUTION: The LED drive device comprises: a DC/DC converter section 1 for converting a supply voltage of a DC power supply DC1 to output a desired DC voltage; an input voltage detection section 2 for detecting the supply voltage; a current detection section 4 for detecting a load current flowing through a light source section 6 comprising a plurality of LEDs 60; and a control section 5 for controlling the load current on the basis of the voltage detected by the input voltage detection section 2. The control section 5 controls the load current to a lower level than during a normal operation, where the supply voltage does not drop, when the supply voltage drops below a first threshold voltage V1, and controls the load current to a level lower than a value based on the voltage detected by the input voltage detection section 2 for a fixed period when the supply voltage is recovered above a second threshold voltage V2.

Description

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

  Since light-emitting diodes (hereinafter referred to as “LEDs”) have a longer lifetime and better responsiveness than incandescent bulbs, many lighting devices using LEDs as light sources have been provided. For example, a vehicle rear combination lamp using an LED as a light source is often used for a stop lamp of an automobile, and a driving device thereof is disclosed in Patent Document 1.

  The vehicle rear combination lamp device described in Patent Literature 1 includes an LED unit in which a plurality of LEDs are connected in series, and a control unit that applies a voltage boosted by a booster circuit to the LEDs. The control unit has a constant current circuit and a voltage detection circuit that detects a voltage applied to the constant current circuit, and the voltage detected by the voltage detection circuit is as low as possible to cause the plurality of LEDs to emit light. Thus, the boost voltage is controlled.

  On the other hand, when the power supply voltage becomes lower than a predetermined voltage value, the amount of current supplied to the LED is reduced, so that the amount of current supplied to the device performing the function more important than the LED is secured. An LED driving device is disclosed in Patent Document 2.

  In this vehicle LED drive device, the duty ratio of the drive signal input to the switching element provided in the power supply wiring is controlled based on the measurement means for measuring the voltage value of the power supply and the measured voltage value of the power supply. Control means. The control means controls the duty ratio of the drive signal so that the LED emits light with a constant luminance when the voltage value of the power supply is larger than the predetermined voltage value. The control means is driven so that the brightness of the LED decreases with respect to a constant brightness when the voltage value of the power supply is equal to or lower than a predetermined voltage value, that is, the amount of current supplied to the LED is reduced. Controls the duty ratio of the signal. Thereby, the electric current amount supplied to apparatus more important than LED, such as a meter, is ensured.

JP 2003-187614 A JP 2010-163105 A

  However, in the above-described vehicle LED driving device, when the voltage value of the power supply returns to a predetermined voltage value or higher, the current is controlled so that the LED has a predetermined luminance. For this reason, for example, when the voltage value of the power supply instantaneously returns to a predetermined voltage value or more, there is a problem that an overcurrent flows through the LED, causing the LED to deteriorate.

  The present invention has been made in view of the above points, and an LED driving device capable of preventing an overcurrent from flowing in a light source section when a power supply voltage is reduced and returned, and an illumination device using the same The purpose is to provide.

  The LED driving device of the present invention detects a power supply unit that converts a power supply voltage of an external power supply into a predetermined DC voltage and supplies lighting power to a light source unit composed of a light emitting diode, and the power supply voltage input to the power supply unit An input voltage detection unit, a current detection unit that detects a load current flowing through the light source unit, and a control unit that controls the load current based on a detection voltage of the input voltage detection unit, When the power supply voltage is lower than a predetermined threshold voltage, the load current is controlled to be smaller than a normal time when the power supply voltage is not reduced, and the power supply voltage is restored to be lower than the predetermined threshold voltage. When the voltage rises, the load current is controlled to be smaller than a value based on a detection voltage of the input voltage detection unit for a certain period.

  In this LED driving device, it is preferable that the control unit performs control so as to increase the load current stepwise in the certain period.

  In this LED driving apparatus, it is preferable that the control unit performs control so as to increase the load current exponentially during the certain period.

  In this LED driving apparatus, the power supply unit includes a DC / DC converter unit that has at least one switching element and controls output by switching on / off of the switching element, and the control unit includes the switching unit. It is preferable to control the load current by changing the width of the on-time of the element.

  In this LED driving device, it is preferable that the control unit is constituted by a microcomputer.

  In this LED drive device, it is preferable that the control unit controls the load current to decrease with a decrease in the power supply voltage when the power supply voltage decreases.

  In this LED drive device, the control unit sets the predetermined threshold voltage to the first threshold voltage during the normal time, and sets the predetermined threshold voltage to be lower than the first threshold voltage when the power supply voltage decreases. It is preferable to set a large second threshold voltage.

  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 it is possible to prevent an overcurrent from flowing through the light source unit when the power supply voltage is reduced and recovered.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows Embodiment 1 of the LED drive device based on this invention, (a) is a circuit schematic, (b) is an operation | movement waveform diagram. It is a correlation diagram of the power supply voltage and target current value in a LED drive device same as the above. It is a figure which shows Embodiment 2 of the LED drive device based on this invention, (a) is a circuit schematic, (b) is an operation | movement waveform diagram. It is a flowchart figure for demonstrating operation | movement in a LED drive device same as the above. It is a correlation diagram of the power supply voltage and target current value in a LED drive device same as the above. It is the schematic which shows embodiment of the illuminating device which concerns on this invention.

(Embodiment 1)
Hereinafter, Embodiment 1 of the LED drive device according to the present invention will be described with reference to the drawings. In the present embodiment, as shown in FIG. 1A, a DC / DC converter unit (power supply unit) 1, an input voltage detection unit 2, an output voltage detection unit 3, a current detection unit 4, and a control unit 5. It consists of. A DC power source DC1, which is an external power source, is connected between the input ends of the DC / DC converter unit 1, and a light source unit 6 formed by connecting one or more LEDs 60 in series is connected between the output ends. In the present embodiment, the light source unit 6 is configured by connecting a plurality of LEDs 60 in series, but may be configured by connecting in parallel. As the DC power source DC1, for example, a battery, a DC power source device, a DC power source circuit that rectifies and smoothes a commercial AC power source, or the like is employed.

  The DC / DC converter unit 1 is a flyback converter including a step-up transformer T1, and a capacitor C1 and a switching element Q0 composed of a MOSFET are connected to a primary winding T10 of the step-up transformer T1. A smoothing capacitor C2 is connected to the secondary winding T11 of the step-up transformer T1 through a diode D1. The switching element Q0 is on / off controlled by being given a drive signal from an output control unit 50 described later. The DC / DC converter unit 1 boosts the input voltage to a desired DC voltage by changing the ON time width of the switching element, that is, the ON duty ratio, by the output control unit 50, and outputs the boosted voltage. Accordingly, the DC / DC converter unit 1 supplies lighting power to the light source unit 6.

  The input voltage detection unit 2 detects the input voltage of the DC / DC converter unit 1, that is, the power supply voltage of the DC power source DC1, and is a series of resistors R1 to R3 connected between the input terminals of the DC / DC converter unit 1. Consists of a circuit. The input voltage detection unit 2 divides the input voltage of the DC / DC converter unit 1 by resistors R1 to R3. Then, the divided input voltage is input to a non-inverting input terminal of a comparator CP2 of the control unit 5 described later.

  The output voltage detection unit 3 detects a load voltage applied to the light source unit 6 and includes a series circuit of resistors R4 to R6 connected in parallel to the light source unit 6. The output voltage detection unit 3 divides the load voltage of the light source unit 6 by the resistors R4 to R6. The divided output voltage is input to the output control unit 50 of the control unit 5 described later.

  The current detection unit 4 detects a load current flowing through the light source unit 6, and includes a detection resistor R7 connected in series with the light source unit 6, and a non-inverting amplifier circuit including resistors R8 and R9 and an operational amplifier OP1. Composed. A voltage across the detection resistor R7 generated by the flow of the load current is amplified by a non-inverting amplifier circuit and input to a non-inverting input terminal of a comparator CP1 of the output control unit 50 described later.

  The control unit 5 includes an output control unit 50 that controls the output voltage of the DC / DC converter unit 1. The output control unit 50 includes a drive circuit 50A that supplies a drive signal to the switching element Q0 of the DC / DC converter unit 1 and a comparator CP1. The output voltage of the operational amplifier OP1 is input to the non-inverting input terminal of the comparator CP1, and the voltage obtained by dividing the control voltage VC1 of the control power supply 7 described later is input to the inverting input terminal. Here, the input voltage of the non-inverting input terminal is a voltage corresponding to the load current flowing through the detection resistor R7 of the current detection unit 4, and the input voltage of the inverting input terminal is a voltage corresponding to the target current value of the load current. is there. That is, the comparator CP1 compares the load current with the target current value.

  Therefore, the comparator CP1 compares the load current value with the target current value, and outputs an output signal based on the error to the drive circuit 50A. The drive circuit 50A controls the width of the ON time of the drive signal based on the output signal of the comparator CP1. Thereby, the output voltage of the DC / DC converter unit 1 is controlled so that the load current flowing through the light source unit 6 matches the target current value.

  Further, the load voltage detected by the output voltage detection unit 3 is input to the output control unit 50, and an abnormality of the light source unit 6 due to disconnection or the like is determined based on the load voltage. When the output control unit 50 determines that an abnormality has occurred in the light source unit 6, the drive circuit 50A stops the on / off control of the switching element Q0 or shortens the width of the on time of the drive signal. As a result, the output of the DC / DC converter unit 1 is limited.

  The control unit 5 operates by being supplied with the control voltage VC1 from the control power supply 7. The control power supply 7 generates the control voltage VC1 based on the power supply voltage input from the DC power supply DC1. The control voltage VC1 is divided by a voltage dividing circuit including resistors R10, R11, and R12, and a voltage obtained by dividing the control voltage VC1 is input to the inverting input terminal of the comparator CP2.

Here, a switching element Q1 made of an NPN transistor is connected in parallel to the resistor R11, and its base terminal is connected to the output terminal of the comparator CP2. Therefore, on / off of the switching element Q1 is switched by the output signal of the comparator CP2, and the connection of the resistor R11 to the voltage dividing circuit is switched. When the connection of the resistor R11 to the voltage dividing circuit is switched, the divided value of the control voltage VC1 changes, and the voltage value input to the inverting input terminal of the comparator CP2 also changes.

  That is, the control unit 5 compares the input voltage of the non-inverting input terminal of the comparator CP2 with the input voltage of the inverting input terminal when the switching element Q1 is turned on, so that the power supply voltage of the DC power supply DC1 and the first threshold value are compared. The voltage V1 is compared. Further, the control unit 5 compares the input voltage of the non-inverting input terminal of the comparator CP2 with the input voltage of the inverting input terminal when the switching element Q1 is turned off, so that the power supply voltage of the DC power supply DC1 and the second threshold value are compared. The voltage V2 (> V1) is compared.

  The output terminal of the comparator CP2 is connected to the base terminal of the switching element Q2 made of an NPN transistor. The control voltage VC1 is input to the collector terminal of the switching element Q2 via the resistor R17. The collector terminal of the switching element Q2 is connected to the base terminal of the switching element Q3 made of an NPN transistor. The emitter terminal of the switching element Q3 is connected to the ground via a resistor R16. A resistor R15 and a capacitor C3 are connected in parallel to the series circuit of the switching element Q3 and the resistor R16.

  The control voltage VC1 is input to the collector terminal of the switching element Q3 via the resistors R13 and R14. The connection point between the resistor R13 and the resistor 14 is connected to the inverting input terminal of the comparator CP1 of the output control unit 50. Therefore, a voltage obtained by dividing the control voltage VC1 is input to the inverting input terminal of the comparator CP1.

  Hereinafter, the operation of this embodiment will be described. First, at a normal time when the power supply voltage is not lowered, the input voltage at the non-inverting input terminal of the comparator CP2 is larger than the input voltage at the inverting input terminal, so the comparator CP2 outputs a high level output signal. Therefore, the switching element Q2 is kept on and the switching element Q3 is kept off, and a voltage obtained by dividing the control voltage VC1 by the voltage dividing circuit constituted by the resistors R13 to R15 is applied to the inverting input terminal of the comparator CP1. Entered. The input voltage at the inverting input terminal of the comparator CP1 corresponds to the target current value at the normal time. Therefore, during normal times, the output control unit 50 controls the width of the on-time of the switching element Q0 so that the load current matches the normal target current value (see FIG. 1B).

  On the other hand, when the power supply voltage decreases and the input voltage of the non-inverting input terminal of the comparator CP2 becomes smaller than the input voltage of the inverting input terminal, that is, when the power supply voltage falls below the first threshold voltage V1, the comparator CP2 becomes low level. The output signal is output. For this reason, when the switching element Q2 is turned off and the switching element Q3 is turned on, the resistor R16 is connected to a voltage dividing circuit constituted by the resistors R13 to R15. As a result, the divided value of the control voltage VC1 is lower than normal, and the divided value is input to the inverting input terminal of the comparator CP1. The input voltage at the inverting input terminal of the comparator CP1 corresponds to the target current value when the power supply voltage is lowered. Therefore, when the power supply voltage decreases, the output control unit 50 controls the width of the on-time of the switching element Q0 so that the load current matches the target current value when the power supply voltage decreases. Thereby, when the power supply voltage is lowered, a load current smaller than that in the normal state flows in the light source unit 6 (see FIG. 1B).

  Here, when the power supply voltage decreases, the low-level output signal of the comparator CP2 is input to the base terminal of the switching element Q1, so that the switching element Q1 is turned off. Thereby, the threshold voltage compared with the power supply voltage in the comparator CP1 is switched from the first threshold voltage V1 to the second threshold voltage V2.

  Thereafter, the power supply voltage recovers and rises, and when the input voltage of the non-inverting input terminal of the comparator CP2 becomes larger than the input voltage of the inverting input terminal, that is, when the power supply voltage exceeds the second threshold voltage V2, the comparator CP2 Outputs a high level output signal. For this reason, the switching element Q2 is turned on and the switching element Q3 is turned off, so that the resistor R16 is disconnected from the voltage dividing circuit constituted by the resistors R13 to R15.

  Here, when the capacitor C3 connected in parallel to the resistor R15 starts charging, the divided value of the control voltage VC1 increases exponentially. That is, as shown in FIG. 1B, the target current value gradually increases from the target current value when the power supply voltage is reduced to the target current value at the normal time. Therefore, when the power supply voltage is restored, the output control unit 50 controls the width of the on-time of the switching element Q0 so that the load current matches the target current value. Increase gradually.

  As described above, in the present embodiment, when the power supply voltage of the DC power supply DC1 drops and recovers, the load current flowing through the light source unit 6 is longer than the value based on the detection voltage of the input voltage detection unit 2 for a certain period. The control unit 5 controls the DC / DC converter unit 1 so that the current becomes small. Therefore, in the present embodiment, when the power supply voltage of the DC power supply DC1 drops and returns, it is possible to prevent an excessive current from flowing through the light source unit 6 and to prevent the LED 60 from deteriorating due to the overcurrent. can do. In the present embodiment, the load current gradually increases exponentially when the power supply voltage is restored, so that the light output of the light source unit 6 does not change suddenly, and the uncomfortable feeling can be reduced.

  In the present embodiment, the target current value does not decrease unless the power supply voltage falls below the first threshold voltage V1 during normal operation, and must be restored until the power supply voltage exceeds the second threshold voltage V2 when the power supply voltage decreases. Thus, the target current value at the normal time is not restored. That is, in the present embodiment, as shown in FIG. 2, the control unit 5 sets the first threshold voltage V1 and the second threshold voltage V2, thereby giving the threshold voltage hysteresis characteristics. For this reason, it is possible to prevent the target current value from fluctuating due to minute fluctuations in the power supply voltage due to noise or the like.

(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. The present embodiment is characterized in that the control unit 5 is composed of a microcomputer 51 as shown in FIG.

  The microcomputer 51 is a general-purpose microcomputer that incorporates, for example, an A / D conversion function and a flash memory that stores various programs, and operates by a control voltage VC1 supplied from the control power supply 7. The microcomputer 51 of the present embodiment uses an oscillation signal oscillated from a resonance circuit composed of a crystal resonator 52 and capacitors C4 and C5 as a reference clock, but uses an internal clock of the microcomputer 51 as a reference clock. Also good.

  The microcomputer 51 performs A / D conversion on the voltage detected by the input voltage detection unit 2 and reads it as a digital power supply voltage value. Further, the microcomputer 51 performs A / D conversion on the voltage across the detection resistor R7 of the current detection unit 4 and reads it as a digital load current detection value. Further, the microcomputer 51 sets the width of the ON time of the switching element Q0 so that the load current matches the target current value, performs D / A conversion based on the set value, and sends the analog signal drive signal to the switching element Q0. input.

  In the present embodiment, a switching element Q4 made of a MOSFET is connected between the current detection unit 4 and the light source unit 6. Then, a PWM signal is input from the microcomputer 51 to the gate terminal of the switching element Q4 to control on / off of the switching element Q4, thereby changing the lighting period of the light source unit 6 and dimming the light source unit 6. Can do. Since dimming of the light source unit 6 by PWM control is well known in the art, detailed description thereof is omitted here.

  Hereinafter, the operation of the present embodiment will be described mainly with reference to FIG. First, the normal operation when the power supply voltage is not lowered will be described. The microcomputer 51 reads the power supply voltage value from the input voltage detection unit 2 and compares the power supply voltage value with the normal threshold voltage V0 stored in the built-in memory. When the power supply voltage value is larger than the normal threshold voltage V0, that is, when the power supply voltage is not lowered, the normal target current value I0 is read from the built-in memory. On the other hand, the microcomputer 51 reads the load current detection value from the current detection unit 4, calculates the error between the normal target current value I0 and the load current detection value, and sets the ON time of the switching element Q0 to eliminate the error. Set the width. And the output of the DC / DC converter part 1 is controlled by giving a drive signal from the microcomputer 51 to the switching element Q0. The above operation is repeated until the power supply voltage value becomes lower than the normal threshold voltage V0.

  On the other hand, when the power supply voltage value is smaller than the normal threshold voltage V0, that is, when the power supply voltage decreases, the microcomputer 51 reads the target current value corresponding to the power supply voltage value from the built-in memory. Similarly to the above, the microcomputer 51 reads the load current detection value from the current detection unit 4, calculates the error between the target current value and the load current detection value, and sets the ON time of the switching element Q0 so as to eliminate the error. Set the width. And the output of the DC / DC converter part 1 is controlled by giving a drive signal from the microcomputer 51 to the switching element Q0. The above operation is repeated until the power supply voltage value becomes larger than the normal threshold voltage V0, that is, until the power supply voltage is restored.

  Therefore, as shown in FIG. 5, when the power supply voltage decreases, the microcomputer 51 sets a target current value corresponding to the power supply voltage, and the DC / DC converter unit so that the load current matches the target current value. The output of 1 is controlled. Thereby, since the microcomputer 51 performs control so as to decrease the load current flowing through the light source unit 6 as the power supply voltage decreases, it is possible to suppress an increase in the load current accompanying the decrease in the power supply voltage. In addition, since the load current changes finely based on the power supply voltage, the light output of the light source unit 6 does not change suddenly, and the uncomfortable feeling can be reduced.

  After that, when the power supply voltage value becomes larger than the normal threshold voltage V0, that is, when the power supply voltage is restored, the microcomputer 51 starts counting by the built-in timer and keeps the current target current value constant. The increased value is read as a new target current value. Similarly to the above, the microcomputer 51 reads the load current detection value from the current detection unit 4, calculates the error between the target current value and the load current detection value, and sets the ON time of the switching element Q0 so as to eliminate the error. Set the width. And the output of the DC / DC converter part 1 is controlled by giving a drive signal from the microcomputer 51 to the switching element Q0. The above operation is repeated until a predetermined time P1 elapses after the timer starts counting.

  When the predetermined time P1 elapses, the microcomputer 51 reads the load current detection value from the current detection unit 4 and compares the detection value with the target current value I0 at the normal time. If the load current detection value is larger than the normal target current value I0, the microcomputer 51 returns to the normal operation. When the load current detection value does not reach the normal target current value I0, the microcomputer 51 reads again a value obtained by increasing the current target current value by a constant value as a new target current value, and performs the above operation. repeat.

  Therefore, when the power supply voltage is restored, the target current value is increased stepwise, and the microcomputer 51 controls the width of the on-time of the switching element Q0 so that the load current matches the target current value. The current gradually increases stepwise (see FIG. 3B).

  As described above, in the present embodiment, when the power supply voltage of the DC power supply DC1 drops and recovers, the load current flowing through the light source unit 6 is longer than the value based on the detection voltage of the input voltage detection unit 2 for a certain period. The control unit 5 controls the DC / DC converter unit 1 so that the current becomes small. Therefore, in the present embodiment, as in the first embodiment, when the power supply voltage of the flow power supply DC1 drops and returns, it is possible to prevent an excessive current from flowing through the light source unit 6 and to prevent the overcurrent. Deterioration of the LED 60 can be avoided. Further, in this embodiment, since the load current gradually increases stepwise when the power supply voltage is restored, the light output of the light source unit 6 does not change abruptly, and the uncomfortable feeling can be reduced. Furthermore, in this embodiment, since the control part 5 is comprised by the microcomputer 51, various settings can be performed by changing a program and detailed lighting control can be performed.

  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 (headlamp), and as shown in FIG. 6, an instrument main body A1, a light source unit A2 having a light source unit 6, and an optical for distributing light emitted from the light source unit 6. Unit A3. In the present embodiment, the light source 6 is attached and fixed, and the heat radiating plate A4 that radiates heat generated by the light source 6 and the fixing jig A5 for fixing the light source unit A2 and the heat radiating plate A4 to the instrument main body A1. With. The light source unit 6 is connected to the LED driving device B1 of any of the above embodiments via the 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 the present embodiment includes the LED driving device B1 of any one of the above embodiments, it is possible to prevent an overcurrent from flowing through the light source unit 6 when the power supply voltage drops and returns.

  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 in 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 6 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.

1 DC / DC converter (power supply)
2 Input voltage detection unit 4 Current detection unit 5 Control unit 6 Light source unit 60 LED
DC1 DC power supply (external power supply)

Claims (8)

  A power supply unit that converts a power supply voltage of an external power supply into a predetermined DC voltage and supplies lighting power to a light source unit composed of a light emitting diode; an input voltage detection unit that detects the power supply voltage input to the power supply unit; A current detection unit that detects a load current flowing through the light source unit; and a control unit that controls the load current based on a detection voltage of the input voltage detection unit, wherein the control unit is configured such that the power supply voltage is a predetermined threshold voltage. The load current is controlled to be smaller than the normal time when the power supply voltage is not lowered, and when the power supply voltage recovers and rises above the predetermined threshold voltage, the input is continued for a certain period of time. An LED driving device, wherein the load current is controlled to be smaller than a value based on a detection voltage of a voltage detection unit.   The LED driving device according to claim 1, wherein the control unit performs control so as to increase the load current in a stepwise manner during the certain period.   The LED driving device according to claim 1, wherein the control unit controls the load current to increase exponentially in the certain period.   The power supply unit includes a DC / DC converter unit that includes at least one switching element and controls output by switching on / off of the switching element. The control unit includes a width of an on time of the switching element. The LED drive device according to claim 1, wherein the load current is controlled by changing the voltage.   The LED drive device according to claim 1, wherein the control unit is configured by a microcomputer.   6. The LED driving device according to claim 1, wherein the control unit controls the load current to decrease with a decrease in the power supply voltage when the power supply voltage decreases. .   The control unit sets the predetermined threshold voltage to the first threshold voltage at the normal time, and sets the predetermined threshold voltage to a second threshold voltage larger than the first threshold voltage when the power supply voltage decreases. The LED driving device according to claim 1, wherein the LED driving device is set as follows.   An illumination device comprising: the LED driving device according to claim 1; the light source unit; and an instrument main body that holds the light source unit and the LED driving device.

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