JP2017117606A - Led lighting device and led illumination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED lighting device capable of suppressing influence on flux due to variations in LED forward voltage and performing initial flux correction control without influencing output control responsiveness.SOLUTION: An LED lighting device (1) comprises: a DC power supply circuit (20, 40) which supplies output current according to a target current value to an LED (2); a detection circuit (30) which detects forward voltage of the LED; a correction function determination unit (51) which determines a correction function defining change of a target current value to cumulative lighting time of the LED on the basis of an initial value of the forward voltage detected by the detection circuit at initial lighting of the LED; lighting time acquisition unit (52) which acquires cumulative lighting time; and a target current determination unit (53) which determines a target current value by applying the cumulative lighting time to the correction function.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an LED lighting device and an LED lighting device using the LED lighting device.

  In general, as a property of an LED, it is known that the luminous flux decreases as the cumulative lighting time increases. This is because as the lighting time of the LED increases, the lattice defects that contribute to light emission change, and the YAG phosphor that converts blue light into white light deteriorates, resulting in a decrease in light emission efficiency. . The LED lighting device may be provided with a so-called initial light beam correction function in order to compensate for such a change in light beam (see Patent Document 1). The initial luminous flux correction function is a function of reducing the LED current from the rated current at the beginning of lighting of the LED, and increasing the LED current as the cumulative lighting time proceeds to approach the rated current. As a result, a constant luminous flux can be obtained regardless of the elapsed time of use from the beginning of LED lighting. In addition, the initial luminous flux correction function prevents the lighting from being performed with an unnecessarily high luminous flux at the beginning of lighting, thereby realizing energy saving and extending the life of the LED.

  By the way, the luminous flux of the LED substantially correlates with the product of the LED current and the LED forward voltage, that is, the LED power. Therefore, if the variation in the LED forward voltage is not taken into account in the initial light flux correction control, the initial light flux correction control is executed while the light flux (brightness) of the LED varies among the plurality of LED illumination devices. In addition, the variation in the luminous flux causes variation in the effect of the initial luminous flux correction function for the same cumulative lighting time. In other words, LEDs whose forward voltage is higher than the standard value are lit relatively brightly and the luminous flux decreases quickly, whereas LEDs whose forward voltage is lower than the standard value are lit relatively dark and the luminous flux decreases slowly. Therefore, the initial luminous flux correction control with the same specifications for these LEDs (for example, the initial luminous flux correction control with the specifications for the LEDs having a forward voltage of the standard value) is not optimal.

  On the other hand, in the LED lighting device, this problem can be solved if the power feedback control is executed so that the LED power matches the target power value. For example, a lighting device disclosed in Patent Document 2 includes a lighting circuit that supplies current to an LED, a Vf detection circuit that detects a forward voltage of the LED when current is supplied to the LED, and a Vf detection circuit. And a control circuit that controls the lighting circuit so that a smaller current flows as the detected forward voltage increases. According to this document, the control circuit has a smaller current flowing through the LED as the forward voltage of the LED increases, and the product of the forward voltage and the LED current (that is, the output) without depending on the forward voltage. The constant power control is executed so that the power is constant. More specifically, the control circuit controls the control target value (that is, the output current) so that the product of the forward voltage indicated by the detection signal sent from the Vf detection circuit and the output current from the lighting circuit is constant. ) And a control signal indicating the control target value is output to the output control unit.

JP 2012-22880 A JP 2014-130768 A

  However, when sequential constant power control as disclosed in Patent Document 2 is applied in order to suppress the influence of variations in LED forward voltage, a problem of delay in response occurs. In order to perform sequential constant power control, the output current detection value of the lighting circuit and the output voltage detection value are multiplied to calculate the output power detection value, and this output power detection value is calculated as the target power value. Thus, it is necessary to sequentially execute a process of calculating a target current value and outputting the target current value to a circuit for output current feedback. However, the operation speed (program processing speed) of a general microcomputer is slower than the response speed required for the output current feedback loop. Furthermore, the microcomputer performs processing other than constant power control (processing for determining whether or not to perform protection functions, etc.) ) Also needs to be performed, which reduces the output current feedback response. Therefore, in the initial light flux correction control, it is required to simultaneously suppress the influence on the light flux due to the variation in the forward voltage of the LED and ensure the responsiveness of the output control.

  Accordingly, the present invention provides an LED lighting device that performs initial luminous flux correction control by suppressing the influence on the luminous flux due to variations in the forward voltage of the LED without affecting the responsiveness of the output control, and the LED illumination using the same It is an object to provide an apparatus.

  The LED lighting device of the present invention includes a DC power supply circuit that supplies an output current corresponding to a target current value to the LED, a detection circuit that detects a forward voltage of the LED, and a change in the target current value with respect to the cumulative lighting time of the LED. A correction function determining unit that determines a correction function to be defined based on an initial value of a forward voltage detected by a detection circuit at the time of initial lighting of the LED, a lighting time acquiring unit that acquires a cumulative lighting time, and a cumulative lighting time And a target current determining unit that determines a target current value by applying the correction function.

  According to the LED lighting device, the correction function that defines the change in the target current value with respect to the cumulative lighting time of the LED is determined based on the initial value of the forward voltage, and the target current is obtained by applying the cumulative lighting time to the correction function. The value is determined. In this way, after the correction function is determined based on the initial value at the time of initial lighting, the target current value is determined using only the cumulative lighting time as a variable, so the target current value determination process is included in the output control loop. I can't. Therefore, it is possible to execute the initial light flux correction control while suppressing the influence on the light flux due to the variation in the forward voltage without affecting the responsiveness of the output control in the LED lighting device.

  The detection circuit is further configured to detect an output current, the DC power supply circuit supplies a DC / DC converter that supplies the output current to the LED, and the output current detected by the detection circuit matches the target current value. A control circuit for controlling the DC / DC converter. Even in such a configuration in which the output current is controlled at constant current, the target current value determination processing is not included in the constant current control loop after the correction function is determined based on the initial value. Therefore, it is possible to execute the initial light flux correction control while suppressing the influence on the light flux due to the variation in the forward voltage without reducing the responsiveness of the constant current control of the LED current.

  The LED lighting device according to the first aspect further includes a storage unit that stores a plurality of correction functions that define, for each initial value, a change in the target current value with respect to the cumulative lighting time, and the correction function determination unit is configured to respond to the initial value. A correction function is selected from a plurality of correction functions. As described above, since the correction function is selected from the storage unit according to the initial value, the process for determining the correction function by the correction function determination unit is realized with a simple configuration.

  Here, the plurality of correction functions include at least a first correction function for the first initial value and a second correction function for the second initial value, and a given cumulative lighting time is defined as the first correction function. The second target current value and the second initial value obtained by applying the same cumulative lighting time to the second correction function as the product of the first target current value obtained by applying and the first initial value. It is preferable that the first and second correction functions are set so as to be equal to the product of. Thereby, the coincidence of the light flux between the LEDs fed from the plurality of LED lighting devices is increased.

  The LED lighting device according to the second aspect further includes a storage unit that stores a reference function that defines a change in the target current value with respect to the cumulative lighting time with respect to a reference value of the forward voltage of the LED, and the correction function determination unit includes the reference value And a correction function is derived from the reference function based on the ratio of the initial value. As a result, the correction function can be determined continuously with respect to variations in the initial value, and the initial light flux correction accuracy is improved.

  Here, the product of the target current value obtained by applying a given cumulative lighting time to the correction function and the initial value is the difference between the target current value obtained by applying the same cumulative lighting time to the reference function and the reference value. Preferably, the correction function determination unit is configured to derive a correction function so as to be equal to the product. Thereby, the coincidence of the light flux between the LEDs fed from the plurality of LED lighting devices is increased.

  As a third mode, in any one of the above LED lighting devices, the correction function determination unit redetermines the correction function based on the forward voltage of the LED detected by the detection circuit at a predetermined timing after the initial lighting. It may be configured to. In the first embodiment, the correction function determination unit replaces the forward voltage of the LED detected by the detection circuit with an initial value at a predetermined timing after the initial lighting, and uses one correction function from a plurality of correction functions. Configured to reselect. Further, in the second embodiment, the correction function determination unit calculates the reference function based on the ratio between the forward voltage of the LED detected by the detection circuit and the reference value at a predetermined timing after the initial lighting. A correction function is configured to be derived again. Thus, by re-determining the correction function in consideration of the temporal change of the forward voltage, the accuracy of the initial light flux correction control can be improved over the lifetime of the LED.

  The LED lighting device of the present invention includes the LED lighting device according to any one of the first to third embodiments and an LED. As described above, in the LED lighting device, the initial luminous flux correction control is executed while suppressing the influence on the luminous flux due to the variation in the forward voltage of the LED without reducing the response speed of the output control. Illumination with appropriate brightness can be obtained over the lifetime of the LED, and in particular, illumination with uniform brightness can be obtained for a plurality of LEDs.

It is a block diagram of the LED lighting device and LED lighting device by 1st thru | or 3rd embodiment. It is a figure explaining operation | movement of the LED lighting device by 1st Embodiment. It is a figure explaining operation | movement of the LED lighting device by 2nd Embodiment. It is a figure explaining operation | movement of the LED lighting device by 3rd Embodiment. It is a block diagram of the LED lighting device and LED lighting device by a modification.

<First Embodiment>
FIG. 1 shows a block diagram of LED lighting devices 1-1 to 1-n and LED lighting devices 3-1 to 3-n according to the first embodiment of the present invention. Each of the LED lighting devices 3-1 to 1-n and each of the LEDs 2-1 to 2-n constitute each of the LED lighting devices 3-1 to 3-n. The LED lighting devices 1-1 to 1-n are supplied with power from an AC power source AC such as a commercial power source and light the respective LEDs 2-1 to 2-n. The LED lighting devices 1-1 to 1-n may be connected to one AC power source, or may be grouped and connected to a plurality of AC power sources. Each of the LED lighting devices 1-1 to 1-n has the same configuration. In the following description, any one of the LED lighting devices 1-1 to 1-n is represented or collectively referred to as an LED lighting device 1. Similarly, any one of the LED lighting devices 3-1 to 3-n is represented or collectively referred to as an LED lighting device 3.

  Each of the LEDs 2-1 to 2-n is an LED module including a plurality of LED elements connected in series or in series and parallel. Each of the LEDs 2-1 to 2-n is composed of LED modules having the same specifications, but the total forward voltage Vf of the LED elements in each LED module may vary. In the following description, any one of the LEDs 2-1 to 2-n is represented or collectively referred to as LED2.

  The LED lighting device 1 includes an input circuit 10, a DC / DC converter 20, a detection circuit 30, a control circuit 40, and a light flux correction circuit 50, which converts an AC input supplied from an AC power source AC into a predetermined DC output. Is supplied to LED2. The DC / DC converter 20 and the control circuit 40 are also collectively referred to as a DC power supply circuit.

  The input circuit 10 includes a diode bridge 11 and an input capacitor 12. The AC input voltage is full-wave rectified by the diode bridge 11, and a pulsating voltage appears at the input capacitor 12. Note that the input circuit 10 is not required when a DC voltage from a DC power source is input to the LED lighting device 1.

  The DC / DC converter 20 includes a switching element 21 (MOSFET), a transformer 22, a diode 23, and an output capacitor 24, and supplies DC power to the LED 2 by PWM driving of the switching element 21. In the present embodiment, the DC / DC converter 20 is an insulating flyback converter, and constitutes a so-called one-converter flyback circuit having a power factor improving function. The DC / DC converter 20 may be other types of converters such as a buck converter and a buck boost converter.

  Energy is accumulated by the primary winding of the transformer 22 during the ON period of the switching element 21, and the energy is charged to the output capacitor 24 from the secondary winding side of the transformer 22 via the diode 23 during the OFF period of the switching element 21. . The output power of the DC / DC converter 20 is determined by the on-duty (duty ratio) in the PWM control of the switching element 21, the turn ratio of the secondary winding to the primary winding, and the like. The switching element 21 is driven by a control IC 45 for switching control described later. In the following description, the low potential electrode side node of the input capacitor 12 is referred to as a primary side ground G1, and the low potential electrode side node of the output capacitor 24 is referred to as a secondary side ground G2. The output current of the DC / DC converter 20 is simply referred to as “output current”, and the output voltage of the DC / DC converter 20 is simply referred to as “output voltage”. In each embodiment, the output current is equal to the LED current, and the output voltage is equal to the forward voltage Vf of LED2.

  The detection circuit 30 includes a voltage detection circuit including resistors 31 and 32 and a current detection circuit including a current detection resistor 33, and uses the secondary side ground G2 as a reference potential. The voltage detection circuit (resistors 31 and 32) is a voltage dividing resistor circuit connected in parallel to the output capacitor 24, and a voltage proportional to the output voltage is generated in the resistor 32. The current detection resistor 33 is a low resistance element inserted between the secondary side ground G2 and the cathode end of the LED 2, and a voltage proportional to the output current is generated in the current detection resistor 33.

  The control circuit 40 includes an operational amplifier 41, a constant voltage source 42 (for example, a control power source), a resistor 43, a photocoupler 44, and a control IC 45, and performs constant current control on the output of the DC / DC converter 20. The photocoupler 44 includes a photodiode 44d and a phototransistor 44t, and the photodiode 44d and the preceding circuit (the operational amplifier 41, the constant voltage source 42, etc.) use the secondary side ground G2 as a reference potential, and the phototransistor 44t and the subsequent stage The circuit (control IC 45) operates using the primary side ground G1 as a reference potential. Note that a control power source is appropriately supplied to the control circuit 40.

  The detection current value from the detection circuit 30 is input to the negative input terminal (−) of the operational amplifier 41, and the target current value from the light flux correction circuit 50 is input to the positive input terminal (+) of the operational amplifier 41. A feedback element (not shown) (resistor, capacitor, or a series circuit or a parallel circuit thereof) is connected between the negative input terminal and the output terminal of the operational amplifier 41, and an error between the negative input terminal voltage and the positive input terminal voltage is detected at the output terminal. Is output. The output of the operational amplifier 41 is connected to the cathode of the photodiode 44 d, and the anode of the photodiode 44 d is connected to the constant voltage source 42 via the resistor 43. In the photocoupler 44, the output state of the phototransistor 44t is determined according to the current flowing through the photodiode 44d, and the output of the phototransistor 44t is input to the control IC 45 as an input signal. During normal lighting, the operational amplifier 41 determines the ON width in the PWM control of the switching element 21 so that the output current (detected current value) matches the target current value.

  The control IC 45 includes a general LED driver IC, and peripheral circuit elements (not shown) are appropriately connected to the control IC 45. The control IC 45 generates a PWM drive signal having a pulse width corresponding to the output state of the phototransistor 44 t and outputs it as the gate voltage of the switching element 21. For example, the control IC 45 decreases / increases the on width of the PWM control and decreases the output current with respect to the increase / decrease of the current of the photodiode 44d and the phototransistor 44t. That is, the control circuit 40 performs constant current control on the DC / DC converter 20 so that the output current matches the target current value.

  The light beam correction circuit 50 is composed of, for example, a microcomputer and executes an initial light beam correction function. The luminous flux correction circuit 50 includes a correction function determination unit 51, a lighting time acquisition unit 52, a target current determination unit 53, an A / D conversion unit 54, a storage unit 55, and a time measuring unit 56. These units are mutually connected by a bus B. They are connected in such a manner that signals or data can be exchanged. The correction function determination unit 51, the lighting time acquisition unit 52, and the target current determination unit 53 constitute a part of the CPU, and the CPU can appropriately execute general processing functions not included in the above-described units. The A / D conversion unit 54 performs A / D conversion on the output voltage detected by the voltage detection circuit (resistors 31 and 32) of the detection circuit 30 and takes it into the microcomputer. The A / D converter 54 may be outside the microcomputer.

The storage unit 55 is a nonvolatile memory for storing data and programs. In the present embodiment, the storage unit 55 stores a plurality of correction functions that define a change in the target current value with respect to the cumulative lighting time of the LED ₂ for each initial value Vf ₀ of the forward voltage Vf. The initial value Vf ₀ is a forward voltage Vf (output voltage) detected by the detection circuit 30 (resistors 31 and 32) during initial lighting. The initial lighting means lighting within a few times after the LED 2 is mounted on the LED lighting device 1, preferably the first lighting. Therefore, the initial lighting does not include lighting or operation in a state where the test LED, the pseudo load, or the like is mounted before the LED lighting device 1 is shipped.

  With reference to FIG. 2, the operation of the LED lighting device 1 will be described together with examples of the plurality of correction functions. FIG. 2 shows the lighting state (dimming rate:%), the target current value It (mA), and the luminous flux (lm) from the top, and the horizontal axis is the cumulative lighting time T (hour). It is assumed that the output current matches the target current value.

The lighting state starts from 80% dimming at the start of lighting (T = 0) regardless of the initial value Vf ₀ , and becomes all light (100%) when T = 60000 is reached. Is set. And after T = 60000, a lighting state is maintained by all the lights. By the transition of the lighting state and the application of the correction function described below, the luminous flux becomes constant at a specified value (for example, 10000 lm) over the lifetime in all the LEDs 2.

As shown in FIG. 2, the target current value It is defined for each of the initial values Vf ₀ , the correction curve A (correction function A) is a correction function for the initial value Vf ₀ = 140 (V), and the correction curve B (Correction function B) indicates a correction function for the initial value Vf ₀ = 160 (V). Each correction function is set so that the product of the forward voltage Vf and the target current value It during a given cumulative lighting time is the same between the correction functions. Thereby, the coincidence of the luminous flux between the LEDs 2-1 to 2-n fed from the LED lighting devices 1-1 to 1-n is increased.

For example, in the correction function A (Vf ₀ = 140), the target current value It increases at 480 ≦ It ≦ 600 when 0 ≦ T ≦ 60000, and is maintained at It = 600 when 60000 <T. On the other hand, in the correction function B (Vf ₀ = 160), the target current value It increases with 420 ≦ It ≦ 525 when 0 ≦ T ≦ 60000, and is maintained at It = 525 when 60000 <T. For example, regarding target value It × initial value Vf ₀ in correction functions A and B,
At T = 0, 140V × 480 mA = 160V × 420 mA,
At 60000 ≦ T, 140 V × 600 mA = 160 V × 525 mA
It turns out that it is. The above relationship also holds in the range of 0 <T <60000. In FIG. 2, two correction functions for two initial values are shown, but three or more correction functions for three or more initial values may be defined.

Returning to FIG. 1, the correction function determination unit 51 determines a correction function that defines a change in the target current value with respect to the cumulative lighting time based on the initial value Vf ₀ . In the present embodiment, the correction function determining unit 51 selects one of the correction function according to the initial value Vf ₀ from a plurality of correction functions stored in the storage unit 55. More specifically, the correction function determination unit 51 first performs initial lighting in a default correction function or lighting state (for example, dimming rate 80%), and forward voltage Vf (initial value) detected at the time of initial lighting. A correction function for the initial value closest to Vf ₀ ) is then adopted. For example, in the example illustrated in FIG. 2, when the forward voltage Vf detected at the time of initial lighting with the default setting is 155 V, the correction function determination unit 51 selects and employs the correction function B for Vf ₀ = 160. .

  The lighting time acquisition unit 52 acquires the cumulative lighting time of the LED 2. The accumulated lighting time is acquired from the time measurement output by the time measuring unit 56 including a timer or a counter, and is stored in the storage unit 55. In the period after the dimming rate becomes constant at 100% (the period after the cumulative lighting time exceeds 60000 hours in the example of FIG. 2), it is not necessary to acquire the cumulative lighting time.

  The target current determination unit 53 determines the target current value by applying (substituting) the cumulative lighting time acquired by the cumulative time acquisition unit 52 to the correction function selected by the correction function determination unit 51. Is output to the operational amplifier 41 of the control circuit 40. In the period after the dimming rate becomes constant at 100% (the period after the cumulative lighting time exceeds 60000 hours in the example of FIG. 2), it is not necessary to newly perform the target value determination process.

  The cumulative lighting time acquisition by the lighting time acquisition unit 52 and the target current value determination by the target current determination unit 53 are performed at a relatively low frequency in consideration of the gradient of the correction function and the bit resolution of the target current value. The target current value may be fixed to a single value for a predetermined period (for example, 100 hours, 1000 hours, etc.) or for a predetermined lighting time (one lighting, 100 lightings). Good.

  Further, a mask function or a reset function may be added to the light flux correction circuit 50. The mask function is a function that invalidates the determination of the correction function, the counting of the cumulative lighting time, the counting of the number of blinks, etc., when the LED lighting device 1 is in the test lighting before shipment (the load is not necessarily LED2). is there. Such a mask function can be implemented, for example, by operating a predetermined terminal of the microcomputer of the light beam correction circuit 50. The reset function is a cumulative lighting time count, lighting count count, or a determined correction function when the test lighting is performed or when the LED 2 is replaced due to a failure while the LED lighting device 1 is in use. This is a function that resets etc. to the initial state (default state). Such a reset function can also be implemented by operating a predetermined terminal of the microcomputer of the light beam correction circuit 50, for example.

As described above, the LED lighting device 1 according to the present embodiment is detected by the DC / DC converter 20 that supplies the output current to the LED 2, the detection circuit 30 that detects the output current and the forward voltage of the LED 2, and the detection circuit 30. In the light beam correction circuit 50, which includes a control circuit 40 that controls the DC / DC converter 20 so that the output current that is output becomes constant at the target current value, and a light beam correction circuit 50, the correction function determination unit 51 accumulates the LEDs 2 A correction function that defines a change in the target current value with respect to the lighting time is determined based on the initial value Vf ₀ , the lighting time acquisition unit 52 acquires the cumulative lighting time, and the target current determination unit 53 uses the cumulative lighting time as a correction function. Apply to determine the target current value.

As described above, a correction function that defines a change in the target current value with respect to the cumulative lighting time of the LED 2 is determined based on the initial value Vf ₀ , and the target current value is determined by applying the cumulative lighting time to this correction function. . That is, after the correction function is determined based on the initial value Vf ₀ at the time of initial lighting, the target current value is determined using only the cumulative lighting time as a variable, so that the target current value determination process is a constant current control of the output current. Not included in the loop. Therefore, the initial luminous flux correction is performed by suppressing the influence on the luminous flux due to the variation in the forward voltage without affecting the responsiveness of the output control in the LED lighting device 1 (that is, without reducing the responsiveness of the constant current control). Control can be executed. Thereby, the user of LED lighting apparatus 3-1 to 3-n can obtain the illumination of uniform and appropriate brightness over the lifetime of LED2-1 to 2-n.

In particular, in the present embodiment, a plurality of correction function defining the change in the target current value for the cumulative lighting time for each initial value stored in the storage unit 55, the correction function determining unit 51, in response to the initial value Vf ₀ more A correction function is selected from the correction functions. As described above, since the correction function is selected from the storage unit 55 according to the initial value Vf ₀ , the process for determining the correction function by the correction function determination unit 51 is realized with a simple configuration.

<Second Embodiment>
In the first embodiment, a configuration in which a plurality of correction functions for a plurality of initial values Vf ₀ is stored in the storage unit 55 is shown. However, in the present embodiment, a reference correction function is stored in the storage unit 55. The configuration in which the function is corrected in accordance with the reference value of the forward voltage Vf is shown. Since the block diagram of the LED lighting device 1 of the present embodiment is substantially the same as that of the first embodiment (FIG. 1), the overlapping description is omitted. This embodiment differs from the first embodiment in the operations related to the correction function determination unit 51 and the storage unit 55.

The storage unit 55 stores a reference value Vf _ref of the forward voltage Vf of the LED 2 and a reference function serving as a correction function for the reference value Vf _ref . Note that the reference value Vf _ref is not necessarily the standard value of the forward voltage Vf. First, the correction function determining unit 51 performs initial lighting in a default correction function (for example, a reference function) or a lighting state (for example, dimming rate 80%), and sets the ratio between the reference value Vf _ref and the initial value Vf _0. Based on the reference function, a correction function is derived and adopted.

  With reference to FIG. 3, the operation of the LED lighting device 1 will be described together with an example of the correction function. FIG. 3 shows the lighting state (dimming rate:%), the target current value It (mA), and the luminous flux (lm) from the top, and the horizontal axis is the cumulative lighting time T (hour). In addition, the lighting state and light flux in FIG. 3 are the same as those shown in the first embodiment (FIG. 2). The output current is assumed to match the target current value.

As shown in FIG. 3, the reference function R is a correction function for Vf _ref = 140 (V) (same as the correction function A in FIG. 2), It = 480 at T = 0 and It = 480 at 60000 ≦ T. 600. That is, the reference function R is
It = 0.002T + 480, 0 ≦ T ≦ 60000
It = 600, 60000 <T
It becomes.

Here, the correction function determining unit 51 applies the same cumulative lighting time T to the reference function R as the product of the target current value It and the initial value Vf ₀ obtained by applying the cumulative lighting time T to the correction function R. The correction function C is derived so as to be equal to the product of the target current value It obtained in this way and the reference value Vf _ref . Specifically, in the example of FIG.
It = (0.002T + 480) × Vf _ref / Vf ₀ , 0 ≦ T ≦ 60000
It = 600 × Vf _ref / Vf ₀ , 60000 <T
It becomes. Thereby, the coincidence of the luminous flux between the LEDs 2-1 to 2-n fed from the LED lighting devices 1-1 to 1-n is increased.

  After the correction function C is determined by the correction function determination unit 51, as in the first embodiment, the lighting time acquisition unit 52 acquires the cumulative lighting time of the LED 2, and the target current determination unit 53 calculates the cumulative lighting time. The target current value is determined by applying it to the correction function C and output to the operational amplifier 41.

As described above, also in the LED lighting device 1 according to the present embodiment, the target current value is cumulatively lit after the correction function is determined based on the initial value Vf ₀ at the time of initial lighting, as in the first embodiment. Since only the time is determined as a variable, the target current value determination process is not included in the constant current control loop of the output current. Therefore, it is possible to execute the initial light flux correction control while suppressing the influence on the light flux due to the variation in the forward voltage without affecting the responsiveness of the output control in the LED lighting device 1.

In particular, in the present embodiment, a reference function that defines the change in the target current value with respect to the cumulative lighting time with respect to the reference value Vf _ref of the forward voltage of the LED 2 is stored in the storage unit 55, and the correction function determination unit 51 stores the reference value Vf. configured to derive the correction function from the reference function based on the ratio of _ref and the initial value Vf _0. Thus, it is possible to determine continuously correcting function for the variation of the initial value Vf _0, it is improved initial luminous flux correction accuracy.

<Third Embodiment>
In the first and second embodiments, the configuration in which the correction function is determined based on the initial value Vf ₀ is shown. However, in the present embodiment, after the initial lighting, in consideration of the time course of the forward voltage Vf. The structure by which a correction function is changed is shown. Since the block diagram of the LED lighting device 1 of the present embodiment is the same as that of the first embodiment (FIG. 1), the overlapping description is omitted. This embodiment differs from the first and second embodiments in the operation relating to the correction function determination unit 51.

In the present embodiment, the correction function determination unit 51 is configured to redetermine the correction function based on the forward voltage Vf detected by the detection circuit 30 at a predetermined timing after the initial lighting. The predetermined timing may be a point in time when the forward voltage Vf exceeds or falls below a predetermined value, and the forward voltage Vf is the forward voltage Vf (for example, the initial voltage Vf when the previous correction function is determined). It may be the time when the value fluctuates from the value Vf ₀ ) by a predetermined value or more.

  Alternatively, the predetermined timing may be periodic with respect to the cumulative lighting time (for example, every 1000 hours, every 10000 hours, every 30000 hours, etc.), or may be periodic with respect to the number of times of lighting (for example, 30 Every lighting, every 100 times lighting, every 365 times lighting, every 1000 times lighting, etc.). The number of times of lighting can be measured by a counter (not shown) in the light beam correction circuit 50. Alternatively, the predetermined timing may be not periodic (for example, when the cumulative lighting time reaches 60000 hours).

  In any case, in order to prevent the output current and the luminous flux from switching sharply (although a slight difference) during lighting, the change at the time of switching of the target current value may be made gentle. . Alternatively, the redetermined correction function may be applied at the first lighting after the predetermined timing occurs.

When the correction function is selected from a plurality of correction functions as shown in the first embodiment, the correction function determination unit 51 replaces the forward voltage Vf at the predetermined timing with the initial value Vf ₀ , and One correction function is reselected from the plurality of correction functions stored in the storage unit 55.

  With reference to FIG. 4, the operation of the LED lighting device 1 will be described together with an example of the correction function in this case. FIG. 4 shows the lighting state (dimming rate:%), the target current value It (mA), the forward voltage Vf (V), and the luminous flux (lm) from the top, and the horizontal axis is the cumulative lighting time T (hour). is there. Note that the lighting state and light flux in FIG. 4 are the same as those shown in the first embodiment (FIG. 2). The output current is assumed to match the target current value.

In the example of FIG. 4, the storage unit 55 stores correction functions D, E, and F corresponding to Vf ₀ = 140, 150, and 160 (V), respectively. The correction functions D and F are the same as the correction functions A and B of the first embodiment, respectively. More specifically, the correction function determination unit 51 selects the correction function D when Vf ₀ ≦ 145, selects the correction function E when 145 <Vf ₀ ≦ 155, and selects the correction function F when 155 <Vf ₀ . select. FIG. 4 shows by way of example that the correction function E is selected for Vf ₀ = 152 at T = 0, the function F is selected when the forward voltage Vf exceeds 155 V at time t1 near T = 40000, and T = The forward voltage Vf becomes 145 V or less at time t2 near 80000, indicating that the function D is selected. Note that, as shown at time t2 in FIG. 4, as a factor that the forward voltage Vf rapidly decreases, there may be a partial short-circuit failure of the LED elements that constitute the module of LED2. In other words, the configuration of this example ensures the accuracy of the initial light flux correction control even when a partial short circuit of the LED elements in the LED module occurs.

When the correction function is derived from the reference function as shown in the second embodiment, the correction function determination unit 51 calculates the forward voltage Vf and the reference value Vf _ref at the predetermined timing. Based on the ratio, the correction function is re-derived from the reference function. In the example described above with respect to the second embodiment, the reference value _Vf ref = 140, a Vf = Vf ₀ during initial lighting, indicating an Vf = Vf ₁ at a predetermined timing, the correction function,
It = (0.002T + 480) × 140 / Vf _{0 is changed} to It = (0.002T + 480) × 140 / Vf ₁

  As described above, according to the present embodiment, the correction function determination unit 51 re-determines the correction function based on the forward voltage Vf detected by the detection circuit 30 at a predetermined timing after the initial lighting. Composed. Thus, the accuracy of the initial light flux correction control can be improved over the lifetime of the LED 2 by re-determining the correction function in consideration of the temporal change of the forward voltage Vf.

<Modification>
Although preferred embodiments of the present invention have been described above, the present invention can be modified into various modes as shown below, for example.

(1) Modification of Correction Function In each of the above embodiments, the increase in the target current value in the correction function (and the reference function) is a linear function, but the correction function (and the reference function) is not limited to this. . For example, other types of correction functions such as a correction function in which the current target value increases in a curve with respect to the cumulative lighting time, a correction function in which the current target value increases in steps, and the like may be employed.

(2) Modification of output current control In each of the above embodiments, the configuration in which current feedback is employed for output current control in the DC power supply circuit (DC / DC converter 20 and control circuit 40) has been described. A configuration in which feedforward is adopted for output current control is also possible. FIG. 5 shows a block diagram of the LED lighting device 1 and the LED lighting device 3 in this case. The LED lighting device 1 of the present modification and the LED lighting device 1 (FIG. 1) of the first embodiment are different in the detection circuit 30 and the control circuit 40, and the other components are the same. As shown in FIG. 5, the detection circuit 30 includes only a voltage detection circuit (resistors 31 and 32). In the control circuit 40, the output of the target current determination unit 53 of the light flux correction circuit 50 is input to the photodiode 44 d via the amplifier circuit 46. As described above, the control circuit 40 performs feedforward control on the output current of the DC / DC converter 20 in accordance with the target current value determined by the target current determination unit 53.

1, 1-1 to 1-n LED lighting device 2, 2-1 to 2-n LED
3, 3-1 to 3-n LED lighting device 20 DC / DC converter (DC power supply circuit)
30 detection circuit 40 control circuit (DC power supply circuit)
50 Light flux correction circuit 51 Correction function determination unit 52 Lighting time acquisition unit 53 Target current determination unit 55 Storage unit

Claims (10)

An LED lighting device,
A DC power supply circuit for supplying an output current corresponding to the target current value to the LED;
A detection circuit for detecting a forward voltage of the LED;
A correction function determining unit that determines a correction function defining a change in the target current value with respect to the cumulative lighting time of the LED based on an initial value of a forward voltage detected by the detection circuit at the time of initial lighting of the LED;
A lighting time acquisition unit for acquiring the cumulative lighting time;
An LED lighting device comprising: a target current determining unit that determines the target current value by applying the cumulative lighting time to the correction function. The LED lighting device according to claim 1,
The detection circuit is further configured to detect the output current;
The DC power supply circuit supplies a DC / DC converter that supplies the output current to the LED, and a control circuit that controls the DC / DC converter so that the output current detected by the detection circuit matches the target current value. LED lighting device. The LED lighting device according to claim 1 or 2,
A storage unit that stores a plurality of correction functions that define, for each initial value, a change in the target current value with respect to the cumulative lighting time;
The LED lighting device, wherein the correction function determination unit is configured to select one correction function from the plurality of correction functions according to the initial value. In the LED lighting device according to claim 3,
The plurality of correction functions include at least a first correction function for a first initial value and a second correction function for a second initial value;
The product of the first target current value obtained by applying a given cumulative lighting time to the first correction function and the first initial value is the second correction of the given cumulative lighting time. The LED lighting device in which the first and second correction functions are set to be equal to a product of a second target current value obtained by applying the function to the second initial value. The LED lighting device according to claim 1 or 2,
A storage unit that stores a reference function that defines a change in the target current value with respect to the cumulative lighting time with respect to a reference value of a forward voltage of the LED;
The LED lighting device, wherein the correction function determination unit is configured to derive the correction function from the reference function based on a ratio between the reference value and the initial value. In the LED lighting device according to claim 5,
The product of the target current value obtained by applying a given cumulative lighting time to the correction function and the initial value is the target current value obtained by applying the given cumulative lighting time to the reference function and the The LED lighting device configured such that the correction function determination unit derives the correction function so as to be equal to a product with a reference value.   The LED lighting device according to any one of claims 1 to 6, wherein the correction function determination unit sets the forward voltage of the LED detected by the detection circuit at a predetermined timing after the initial lighting. An LED lighting device configured to re-determine the correction function based thereon.   5. The LED lighting device according to claim 3, wherein the correction function determination unit replaces the forward voltage of the LED detected by the detection circuit with the initial value at a predetermined timing after the initial lighting. An LED lighting device configured to reselect one correction function from the plurality of correction functions.   7. The LED lighting device according to claim 5, wherein the correction function determination unit calculates the forward voltage of the LED detected by the detection circuit and the reference value at a predetermined timing after the initial lighting. An LED lighting device configured to re-derived the correction function from the reference function based on a ratio. The lighting device provided with the LED lighting device as described in any one of Claim 1 to 9, and the said LED.

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