JP6153112B2 - Lighting device and lighting apparatus - Google Patents

Description

  The present invention relates to a lighting device that lights a solid light emitting element such as an LED, and a lighting fixture including the lighting device.

  In a lighting device that stably lights an LED (Light Emitting Diode) that is a load, it is desirable to perform constant current control that outputs a constant output current regardless of the load. Because, the voltage-current characteristic of the LED element has a non-linear characteristic that the forward voltage hardly changes in a state where the current suddenly flows above a certain applied voltage and the current near the rated current value flows, and This is because the light output is basically determined according to the value of the current that flows. In the constant current control, by controlling so that a constant current flows through the LED elements regardless of the output voltage, it is possible to reduce the variation in light output when there is a variation in the lighting voltage due to individual differences of the LED elements. In addition, constant current control supports a variety of connection modes by allowing a constant current to flow even when a load with a different rated lighting voltage is connected or when the number of the same load is changed in series. Is possible.

  Conventionally, various lighting devices that suppress variations in light output of LED elements have been proposed on the basis of constant current control as described above (see, for example, Patent Documents 1 and 2).

  In Patent Document 1, a measure for reducing variation in output current due to pulsation of the voltage of a DC power supply is devised.

  In general, by operating a buck converter in a current critical mode (BCM) & peak current control, a constant current is controlled to flow to a connected LED regardless of its forward voltage. Can do. Here, the BCM & peak current control means that in the buck converter, when the current value detected by the current detection circuit reaches a predetermined value, the switching element is turned off, and when it is detected that the inductor has released predetermined energy, the switching element is turned off. This is the control to turn on. In such BCM control, the average output current is half of the current peak value. In peak current control, when the current flowing through the inductor reaches the peak current target value Iref, the switching element is turned off. Thus, the peak value of the current flowing through the inductor is matched with the target value Iref, so that the output current can be set to a constant value (1/2 of the current target value Iref) regardless of the output voltage. However, there are delay times (for example, the delay time of the detection arithmetic circuit, the signal output delay time of the driver IC, the drive delay time of the switching element, etc.) possessed by the components constituting the buck converter. As a result, a delay occurs between the timing when the current flowing through the inductor reaches the peak current target value Iref and the timing when the switching element is turned off. When the input voltage of the buck converter pulsates, due to the presence of this delay time, the current peak value Ipeak flowing in the actual inductor becomes a value larger than the target value Iref, and the optical output also varies. To solve this problem, Patent Document 1 detects a voltage corresponding to the input voltage of the buck converter by the secondary winding of the inductor and corrects the peak current target value Iref.

  Patent Document 2 devises a circuit that uses the same current for each output in a lighting device having a plurality of outputs (output terminals). For each common current target value REF, each buck converter calculates an average current flowing through the switching element, and feedback control is performed so as to match the target value. That is, the current flowing through the switching element of each buck converter is monitored, and the difference between the monitoring current Isen and the target current REF is calculated by the error amplifier. Then, by calculating the logical sum of the error amplifier output and the sawtooth waveform (RAMP waveform), the duty of the driving signal of the switching element is made equal to the average value of the monitoring current Isen during the period when the switching element is on. Adjust the ratio. In such control, normally, constant current control is performed in a continuous current mode (CCM).

JP 2012-109141 A JP 2010-40509 A

  However, the techniques of Patent Documents 1 and 2 have the following problems.

  In the technique of Patent Document 1, the existence of a delay time of components constituting the buck converter is considered, but it solves the fluctuation of the output current due to the pulsation of the input voltage of the buck converter. Therefore, the technique of Patent Document 1 cannot improve current fluctuation when the output voltage fluctuates due to the presence of the delay time, and the output voltage-current characteristic does not become a complete constant current characteristic, and is output as the output voltage decreases. The current becomes large. In a lighting device having such characteristics, the light output varies depending on the load due to individual differences in voltage / current characteristics or temperature characteristics of the connected load (that is, LED), or the light output changes over time. It is possible to end up. Also, when connecting different types of loads (that is, LEDs) with the same current rating but different voltage ratings, or when changing the number of loads connected in series, the output current may deviate from the rated value due to the difference in output voltage. As a result, a desired light output may not be obtained.

  Further, in the technique of Patent Document 2, each buck converter calculates an average current flowing through the switching element with respect to a common current target value REF, and performs feedback control for performing control so as to match the current target value. The output current can be the same. However, since an error amplifier and a peripheral circuit are required to configure the feedback circuit, the cost of circuit components is increased. Since the switching element drive signal is created by calculating the logical sum of the error amplifier output and the sawtooth waveform (RAMP waveform), the switching frequency always matches the frequency of the sawtooth wave (RAMP wave). That is, the operation is basically performed in a current continuous mode (CCM) with a constant frequency. In the continuous current mode, the current flowing through the inductor of the buck converter is continuous and does not return to 0. In order to turn on and off the continuous current, a through current flows through components such as a switching element of the buck converter. Stress and loss occur. Therefore, it leads to a reduction in circuit efficiency, an increase in cost of circuit components, and an increase in circuit size. It is not particularly suitable for high output lighting applications.

  The present invention has been made in view of the above points, and is a lighting device that operates by BCM & peak current control, in which variation in light output is suppressed with a simple configuration with respect to solid-state light emitting devices having different characteristics. An object of the present invention is to provide a lighting device or the like that can perform stable lighting.

In order to achieve the above object, one embodiment of a lighting device according to the present invention is a lighting device for lighting a solid light emitting element, and receives a current from the DC power supply and the DC power supply to the solid light emitting element. And a control circuit for controlling the buck converter, the buck converter being connected in series with the switching element, and when the switching element is turned on, the current from the DC power supply An inductor through which the current flows, and a diode that supplies the current emitted from the inductor to the solid state light emitting device, and the control circuit detects a current flowing through the switching device, and a current detecting circuit of the solid state light emitting device. A voltage detection circuit for detecting a voltage at both ends or a voltage at both ends of the inductor, and detection by the current detection circuit When the detected current value reaches a predetermined current command value, the switching element is turned off, and when it is detected that the inductor releases predetermined energy, a control signal is generated to turn on the switching element. a drive circuit for outputting to the switching element and, depending on the voltage detected by the voltage detection circuit, have a correction circuit for adding the correction to the current command value, wherein the correction circuit, by the voltage detecting circuit In each of the cases where the detected voltage is smaller and larger than the predetermined threshold, the peak value of the current flowing through the inductor decreases as the voltage increases, and the voltage detected by the voltage detection circuit and the inductor Two in each of the small case and the large case in relation to the peak value of the flowing current As the peak value of the current at said different voltages are substantially equal, adding the correction to the current command value.

  The correction circuit corrects the current command value to a first correction value smaller than the current command value when the output voltage detected by the voltage detection circuit is equal to or lower than a first threshold value. Also good.

  In addition, the correction circuit further converts the current command value to the first correction when the output voltage detected by the voltage detection circuit is equal to or less than a second threshold value that is smaller than the first threshold value. You may correct | amend to the 2nd correction value smaller than a value.

  The first threshold value and the second threshold value are values between forward voltages of two types of solid-state light emitting elements having different forward voltages among the solid-state light emitting elements connected to the lighting device. Also good.

  Further, the correction circuit may correct the current command value so that a peak value of a current flowing through the inductor becomes constant without depending on a voltage detected by the voltage detection circuit.

  The lighting device is a device for lighting a plurality of solid state light emitting elements, and the lighting device includes a plurality of the back converters corresponding to the plurality of solid state light emitting elements, and the plurality of back converters, respectively. You may provide the said several control circuit to control.

  The lighting device may further include a dimming control circuit that outputs the current command value corresponding to a desired light output to the plurality of control circuits.

  Moreover, in order to achieve the said objective, one form of the lighting fixture which concerns on this invention comprises the said lighting device and the solid light emitting element supplied with an electric current from the said lighting device.

  According to the present invention, a lighting device that operates with BCM & peak current control, and capable of stably lighting a solid state light emitting device having different characteristics with a simple configuration and suppressing variations in light output. And the lighting fixture using the lighting device is realized.

  Therefore, the practical value of the present invention is extremely high in the present day when lighting devices for solid-state light emitting elements such as LEDs have become widespread.

Circuit diagram of lighting device according to Embodiment 1 of the present invention Detailed circuit diagram of a control circuit provided in the lighting device in Embodiment 1 of the present invention The figure which shows the dispersion | variation in the peak value of the electric current which flows into the inductor in the conventional lighting device The figure which shows the output voltage-current characteristic in the conventional lighting device The figure which shows the relationship between the output voltage and current command value of the lighting device in Embodiment 1 of this invention. The figure which shows the output voltage-current characteristic of the lighting device in Embodiment 1 of this invention. Detailed circuit diagram of correction circuit in embodiment 2 of the present invention The figure which shows the relationship between the output voltage and current command value of the lighting device in Embodiment 2 of this invention. The figure which shows the output voltage-current characteristic of the lighting device in Embodiment 2 of this invention. Detailed circuit diagram of voltage detection circuit and correction circuit in Embodiment 3 of the present invention The figure which shows the relationship between the output voltage and current command value of the lighting device in Embodiment 3 of this invention. The figure which shows the output voltage-current characteristic of the lighting device in Embodiment 3 of this invention. Circuit diagram of lighting device according to Embodiment 4 of the present invention The figure which shows the example of a waveform of the electric current which flows through the inductor of each buck converter of the lighting device in Embodiment 4 of this invention. The external view which shows an example of the lighting fixture in embodiment of this invention The external view which shows another example of the lighting fixture in embodiment of this invention The external view which shows another example of the lighting fixture in embodiment of this invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Each of the embodiments described below shows a preferred specific example of the present invention. The numerical values, shapes, materials, constituent elements, arrangement positions and connecting forms of the constituent elements, steps, order of steps, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept of the present invention are described as optional constituent elements that constitute a more preferable embodiment.

(Embodiment 1)
FIG. 1 is a circuit diagram of a lighting device 1a according to Embodiment 1 of the present invention, and FIG. 2 is a detailed circuit diagram of a control circuit 5 provided in the lighting device 1a. The difference from the conventional technique is that a correction circuit 9 is added in the control circuit 5.

  The lighting device 1a is a device that lights an LED 4 that is an example of a solid-state light emitting element serving as a load. The lighting device 1a includes a smoothing capacitor C1 that serves as a DC power source, a buck converter 3, a control circuit 5 that controls the buck converter 3, and a control circuit. A light control circuit 11. The buck converter 3 is a constant current output converter that receives a current from a smoothing capacitor C1 serving as a DC power supply and provides a predetermined current to the LED 4. That is, the lighting device 1a includes a smoothing capacitor C1 serving as a DC power supply, and a back converter 3 that steps down a DC voltage of the smoothing capacitor C1 and supplies a DC current to a solid-state light emitting element (LED 4) serving as a load. The control circuit 5 and the dimming control circuit 11 are provided.

  The smoothing capacitor C1 serving as a DC power supply is charged with a DC voltage obtained by full-wave rectifying a commercial AC power supply using a full-wave rectifier (not shown), for example. Generally, a filter circuit for removing high frequency components is provided on the AC input side of the full-wave rectifier. Further, a power factor correction circuit using a step-up chopper circuit or the like may be interposed between the DC output side of the full-wave rectifier and the smoothing capacitor C1.

  The dimming control circuit 11 is a circuit that transmits the current command value Iref_i to the control circuit 5 (strictly, the current detection circuit 6 of the control circuit 5). For this purpose, the dimming control circuit 11 receives, for example, an external dimming signal (not shown), sets a target for the output current Iout of the lighting device 1a that can obtain a desired light output, and outputs the target. A current command value Iref_i for obtaining the current Iout is calculated. Note that the current command value Iref_i is, for example, a voltage corresponding to the magnitude of the commanded output current.

  The buck converter 3 includes a switching element Q1, an inductor L1, and a diode D1 as main components. The inductor L1 is connected in series with the switching element Q1 and the LED 4 that is lit by a direct current, and a current from the smoothing capacitor C1 flows through the inductor L1 when the switching element Q1 is turned on. The switching element Q1 is an element for connecting a series circuit of the inductor L1 and the LED 4 between both ends of the smoothing capacitor C1 serving as a DC power source, and is, for example, a transistor. The diode D1 is a regenerative diode that supplies the current emitted from the inductor L1 to the LED 4. That is, the diode D1 is connected in parallel with the series circuit of the inductor L1 and the LED 4, and releases the stored energy of the inductor L1 to the LED 4 when the switching element Q1 is turned off. An output capacitor C2 is connected in parallel with the LED 4. The output capacitor C2 is set to have a capacity so that a direct current smoothed by the LED 4 flows by smoothing a pulsating component caused by the on / off of the switching element Q1. The LED 4 may be a single LED chip or an LED module in which a plurality of LEDs are connected in series, in parallel, or in series-parallel.

  The resistors R12 and R13 shown in FIG. 1 are voltage dividing resistors for detecting the voltage Vout_K at the connection point between the LED 4 and the inductor L1, and belong to the voltage detection circuit 8 as described later. Since the voltage Vout_K is also a voltage at the cathode of the LED 4, hereinafter, the voltage Vout_K is also referred to as a cathode voltage Vout_K. Similarly, the resistors R10 and R11 are voltage dividing resistors for detecting the voltage Vc1 at both ends of the smoothing capacitor C1, and belong to the voltage detection circuit 8 as described later. The resistor R1 is a resistor for detecting the current flowing through the switching element Q1, and belongs to the current detection circuit 6 as will be described later.

  The control circuit 5 generates a signal for turning on and off the switching element Q1 at a high frequency, and controls the current IL1 flowing through the inductor L1 so that an appropriate current flows through the load (LED 4). The control circuit 5 includes a current detection circuit 6, a ZCD detection circuit 7, a voltage detection circuit 8, a correction circuit 9, and a drive circuit 10.

  FIG. 2 shows a simplified internal configuration of the control circuit 5 used in the present embodiment.

  The current detection circuit 6 detects the current flowing through the switching element Q1 as the detection value Isen by monitoring the voltage at the connection point between the current detection resistor R1 and the switching element Q1. Specifically, as illustrated in FIG. 2, the current detection circuit 6 includes a comparator 60, a resistor 61, and a capacitor 62. In the current detection circuit 6, a signal indicating the detection value Isen is smoothed by a low-pass filter including a resistor 61 and a capacitor 62 and input to the comparator 60. Then, the comparator 60 compares the detection value Isen with the current command value Iref_o from the correction circuit 9 and outputs a signal indicating that the detection value Isen is greater than the current command value Iref_o from the drive circuit 10.

  The ZCD detection circuit 7 is an example of a circuit that detects when the inductor L1 releases predetermined energy. In the present embodiment, the ZCD detection circuit 7 detects that the voltage of the secondary winding n2 coupled to the inductor L1 is equal to or lower than the threshold voltage Vref, and thereby the current IL1 becomes substantially zero. To detect. Specifically, as shown in FIG. 2, the ZCD detection circuit 7 includes a comparator 70, a reference voltage generator 71 that generates a threshold voltage Vref, and the like. The ZCD detection circuit 7 compares the voltage of the secondary winding n2 coupled to the inductor L1 with the threshold voltage Vref generated by the reference voltage generator 71 by the comparator 70, and the voltage of the secondary winding n2 is A signal indicating when the voltage is smaller than the threshold voltage Vref is output to the drive circuit 10.

  The voltage detection circuit 8 is an example of a circuit that detects the voltage across the LED 4 (forward voltage) or the voltage across the inductor L1. In the present embodiment, the voltage detection circuit 8 is a circuit that detects the voltage Vout across the LED 4 that is a load, and detects the difference between the voltage Vc1 and the cathode output voltage Vout_K, as shown in FIG. A differential amplifier 80 is included. In the voltage detection circuit 8, the differential amplifier 80 divides the voltage VC1 on the anode side of the LED 4 (which is divided by the resistors R10 and R11 from the voltage Vout_K on the cathode side 1 by the resistors R12 and R13). The differential amplifier 80 calculates the output voltage Vout (Vout = Vc1−Vout_K) to the LED 4 and outputs the calculated output voltage Vout to the correction circuit 9.

  The correction circuit 9 corrects the current command value Iref_i from the dimming control circuit 11 in accordance with the voltage (here, the output voltage Vout) detected by the voltage detection circuit 8 to obtain a corrected current command value Iref_o. And output to the current detection circuit 6. More specifically, the correction circuit 9 has at least two different voltages (output voltage Vout) in the relationship between the voltage detected by the voltage detection circuit 8 (here, the output voltage Vout) and the peak value of the current flowing through the inductor L1. The current command value Iref_i is corrected so that the current peak values at are substantially equal. For this purpose, as shown in FIG. 2, the correction circuit 9 includes a comparator 90, a reference voltage generator 91 that generates a reference voltage (first threshold) Vth1, a transistor 92, and the like. The comparator 90 compares the output voltage Vout from the voltage detection circuit 8 with the first threshold value Vth1 from the reference voltage generator 91, and the transistor 92 is turned on or off according to the comparison result. In accordance with the comparison result, the current command value Iref_i from the dimming control circuit 11 is divided by a resistor or output as a current command value Iref_o without being divided. Specifically, when the output voltage Vout from the voltage detection circuit 8 is equal to or lower than the first threshold value Vth1, the transistor 92 is turned on, and the current command value Iref_i from the dimming control circuit 11 becomes a smaller value. And output as a current command value Iref_o.

  The drive circuit 10 generates a control signal for turning on / off the switching element Q1, and outputs the generated control signal to the gate of the switching element Q1. The control signal is a signal for turning off the switching element Q1 when it is detected that the current value (detection value Isen) detected by the current detection circuit 6 has reached a predetermined current command value (current command value Iref_o). . Further, when the control signal detects that the inductor L1 has released predetermined energy (in this embodiment, when the ZCD detection circuit 7 detects that the current IL1 has become substantially zero), This signal turns on the switching element Q1. That is, the drive circuit 10 is a circuit that receives the detection results of the current detection circuit 6 and the ZCD detection circuit 7, generates a gate signal of the switching element Q1, and drives the switching element Q1. Since the resistor R1 is a small resistor for detecting current, it hardly affects the gate signal.

  Specifically, as shown in FIG. 2, the drive circuit 10 includes a flip-flop 100, a buffer amplifier 101, and the like. The flip-flop 100 is reset when the current (detection value Isen) detected by the current detection circuit 6 reaches a predetermined current command value Iref_o. Then, it is set when the inductor L1 releases predetermined energy (when the ZCD detection circuit 7 detects that the current IL1 becomes substantially zero). The buffer amplifier 101 outputs the output signal from the flip-flop 100 to the gate of the switching element Q1 as a control signal.

  Next, the operation of the lighting device 1a in the present embodiment configured as described above will be described.

  First, peak current control and current critical mode (BCM) control, which are basic operations of the buck converter 3 in the present embodiment, will be described. These are the same as the operations shown in Patent Document 1. The peak current control is control for turning off the switching element Q1 when the current IL1 of the inductor L1 reaches a predetermined value. BCM control is control for turning on the switching element Q1 when the current IL1 becomes substantially zero.

  When the switching element Q1 is on, a current flows from the positive electrode of the smoothing capacitor C1 to the negative electrode of the smoothing capacitor C1 via the output capacitor C2, the inductor L1, the switching element Q1, and the resistor R1. At this time, the chopper current i flowing through the inductor L1 is a current that rises substantially linearly unless the inductor L1 is magnetically saturated. Since the voltage across the inductor L1 is the difference between the voltage Vc1 across the smoothing capacitor C1 and the voltage Vc2 across the output capacitor C2, the current i in the inductor L1 has a substantially constant slope di / dt (≈ (Vc1−Vc2). ) / L1). Therefore, when the voltage Vc2 across the output capacitor C2, that is, the output voltage is large, the current i of the inductor L1 increases slowly, and when it is small, it increases rapidly.

  The value of the current flowing through the inductor L1 when the switching element Q1 is on is detected by the current detection circuit 6 based on the voltage generated in the resistor R1 connected in series with the switching element Q1. The current detection circuit 6 includes a comparator 60 that compares the detection value Isen and the current command value Iref_o. The current command value Iref_o is a value obtained by correcting the current command value Iref_i from the dimming control circuit 11 by the correction circuit 9. The current command value Iref_i is obtained by the dimming control circuit 11 according to the detection ratio of the current detection Isen by the detection resistor R1 (the ratio between the actual current value and the detection voltage). It is set to a value that is twice the value of Iout_T. For example, when R1 = 0.1Ω and Iout_T = 1A, Ipeak_T = 2A and Iref = 0.2V are set.

  Therefore, when the inductor current reaches the current peak target value ipeak_T determined by the current command value Iref, the detection value Isen of the current detection circuit 6 exceeds the current command value Iref_o, and the output of the comparator 60 becomes High level. As a result, a reset signal is input to the reset input terminal R of the flip-flop (FF) 100 of the drive circuit 10. As a result, the Q output of the flip-flop 100 becomes a low level. Therefore, the gate-source charge of the switching element Q1 is extracted, and the switching element Q1 is quickly turned off.

  When the switching element Q1 is off, the electromagnetic energy stored in the inductor L1 is released to the output capacitor C2 via the diode D1. At this time, the voltage across the inductor L1 is clamped to the voltage Vc2 of the output capacitor C2, so the current i of the inductor L1 decreases with a substantially constant slope di / dt (≈−Vc2 / L1).

  During the period when the current i flows through the inductor L1, a voltage corresponding to the slope of the current i of the inductor L1 is generated in the secondary winding n2 of the inductor L1. This voltage disappears when the current i of the inductor L1 finishes flowing. The timing is detected by the ZCD detection circuit 7.

  The ZCD detection circuit 7 includes a comparator 70 for zero cross detection. The voltage generated in the secondary winding n2 of the inductor L1 is connected to the negative input terminal of the comparator 70, and the reference voltage Vref for zero cross detection generated by the reference voltage generator 71 is connected to the positive input terminal of the comparator 70. Applied. When the voltage of the secondary winding n2 disappears, the output of the comparator 70 becomes a high level, and the set pulse is supplied to the set input terminal S of the flip-flop 100 of the drive circuit 10. As a result, the Q output of the flip-flop 100 becomes High level, the gate signal of the switching element Q1 is applied, and the switching element Q1 is turned on.

  By repeating such an operation, the inductor current has a current waveform that turns back at a point where the peak value is constant and substantially zero. At this time, the voltage Vout is equal to the voltage Vc2 of the output capacitor C2, and the output current Iout has an average value of the inductor current, that is, a current value that is approximately half of the peak current value.

  When the output voltage Vout increases, the on time of the switching element Q1 is automatically extended and shortened, and when the output voltage Vout decreases, the on time of the switching element Q1 is automatically shortened and the off time is increased. . Therefore, the constant current characteristic can be maintained regardless of the voltage characteristic of the load (LED 4).

  By the way, as described in the background art, the delay time td0 is generated from the current peak detection timing at the switching-off timing due to the existence of the delay time of the components constituting the buck converter 3.

  As shown in FIG. 3, due to the presence of such a delay time tdo, the peak value Ipeak_R of the current IL1 flowing through the actual inductor L1 becomes a value larger than the current peak target value Ipeak_T (current command value). FIG. 3 is a diagram showing variations in the current peak value Ipeak_R of the current (inductor current IL1) flowing in the actual inductor L1 in the conventional lighting device. The left diagram of FIG. 3 shows examples of various current peak values Ipeak_R, and the right diagram of FIG. 3 shows the waveform of the inductor current IL1 in the vicinity of the current peak value Ipeak_R. Further, as can be seen from the equation below, as the output voltage Vout of the buck converter 3 is smaller, the difference Δipeek = Ipeak_R−Ipeak_T between the actual peak current value Ipeak_R and the current peak target value Ipeak_T increases.

  Δpeak = Ipeak_R−Ipeak_T = di / dt × td0 = (Vc1−Vout) / L × td0

  This is because even when the delay time td0 is constant, the slope of the current of the inductor L1 during the period when the switching element Q1 is on is di / dt≈ (Vc1−Vout) / L1, and the slope di depends on the output voltage Vout. This is because / dt is different. As a result, when the buck converter 3 is simply operated in the current critical mode (BCM) & peak current control, the output voltage-current characteristic does not become a completely constant current characteristic as shown in FIG. The output current increases as the voltage Vout decreases. FIG. 4 is a diagram showing output voltage-current characteristics in a conventional lighting device. The output voltage-current characteristic shown here is as shown in the following equation.

  Iout = Ipeak_R / 2 = (Δipeek + Ipeak_T) / 2 = (Vc1−Vout) / L × td0 / 2 + Ipeak_T / 2

  In an actual lighting device having such characteristics, when there is an individual difference in the forward voltage (that is, the output voltage Vout) in the connected load (LED 4), the output current varies depending on the connected individual. The output will vary. When different types of loads with the same current rating and different voltage ratings are connected, or when multiple identical loads are connected in series, the output current will be out of the rated range due to the difference in output voltage. It is conceivable that a desired light output cannot be obtained.

  For example, when a plurality of LED modules whose forward voltage (ie, voltage Vout) is rated at 100V are connected in series to the lighting device having the output characteristics of FIG. 4, the output current is 1.10A in one series (Vout = 100V). With a load of 2 series (Vout = 200V), it becomes 1.07 A, and the variation of 30 mA occurs in the output current. In this case, in spite of the same LED module, the light output output per unit varies depending on the number of serial connections. The calculation conditions of the output current are Vc1 = 420V, inductor L = 800uH, Td0 = 500nS, and Ipeak_T = 2A.

  Therefore, in the present embodiment, when the output voltage Vout detected by the voltage detection circuit 8 is equal to or lower than the first threshold value, the correction circuit 9 that corrects the current command value Iref_i given from the dimming control circuit 11 is provided. It is provided in the control circuit 5. As a result, the difference Δipeek between the actual peak current value Ipeak_R and the current peak target value Ipeak_T of the inductor current IL1 is set to a constant value regardless of the output voltage Vout. In the present embodiment, in the relationship between the output voltage Vout detected by the voltage detection circuit 8 and the peak value of the current flowing through the inductor L1, the peak value of the current is substantially equal at least at two different output voltages Vout. Be controlled.

  The correction circuit 9 is supplied with the current command value Iref_i from the dimming control circuit 11 as an input, and outputs the current command value Iref_o as an output. More specifically, when the output voltage Vout detected by the voltage detection circuit 8 is larger than the first threshold value Vth1, the correction circuit 9 uses the current command value Iref_i from the dimming control circuit 11 as the current command value Iref_o. Output as is. On the other hand, when the output voltage Vout is equal to or lower than the first threshold value Vth1, the current command value Iref_i from the dimming control circuit 11 is attenuated (divided), and a current command value Iref_o that satisfies Iref_o <Iref_i is output.

  By this operation, the difference due to the output voltage Vout of the actual peak current value Ipeak_R is reduced.

  FIG. 5 shows an example of the relationship between the output voltage Vout and the current command value Iref (Iref_i, Iref_o) when Vc1 = 420 V, Td0 = 500 nS, the inductor L = 800 uH, and Ipeak_T = 2A. With respect to the current command value Iref_i = 2, the current command value Iref_i output from the correction circuit 9 is corrected in a stepwise manner so that Iref_o = 0.194 at Vout <150V.

  By correcting the current command value as described above, it is possible to reduce the difference between the actual peak current value Ipeak_R and the output voltage Vout, as shown in FIG. FIG. 6 is a diagram showing an output voltage-current characteristic of the lighting device 1a in the present embodiment. As can be seen by comparing FIG. 6 with FIG. 4 of the conventional lighting device, the lighting device 1a according to the present embodiment can make the output voltage-current characteristic a characteristic with a small fluctuation range due to the voltage Vout. .

  In the lighting device having the output voltage-current characteristic shown in FIG. 6, when an LED module having a forward voltage Vout of 100V is connected, the module 1 series (Vout = 100V) has a module 2 series (Vout = 100V). Even with a load of (Vout = 200V), it becomes 1.070A, and an output current difference does not occur. The calculation conditions at this time are Vc1 = 420V, inductor L = 800uH, Td0 = 500nS, and Ipeak_T = 2A.

  As described above, in the present embodiment, by correcting the current command value Iref_i from the dimming control circuit 11, even when the number of LEDs connected in series as the LEDs 4 is changed, the output current is made substantially the same. (The output voltage dependency of the output current can be suppressed).

  In order to make the correction circuit 9 in this embodiment function effectively, the forward voltage of two types of LEDs 4 having different forward voltages among the LEDs 4 connected to the lighting device 1a is used for the first threshold value Vth1. It is set to be between Vr1 and Vr2. For example, Vth1 is set so that Vr1 <Vth1 <Vr2. More preferably, since the output current is suddenly changed in the vicinity of the output voltage at which the comparator 90 of the correction circuit 9 is switched, the first threshold value Vth1 is preferably set to an output voltage that is not normally taken. For example, it is good to set to the intermediate value of the output voltage of the load (LED4) assumed to be connected. In the case of the above calculation example, since the output voltage is assumed to be 100 V or 200 V, the intermediate value of 150 V is selected as the first threshold value Vth1. The first threshold value Vth1 may have a predetermined hysteresis value.

  The buck converter 3 capable of realizing the present embodiment is not only a circuit as shown in FIG. 1, but also a converter in which the slope of the current flowing through the inductor changes according to the output voltage when the switching element Q1 is on. If it is. That is, the buck converter in the present invention may be a converter of a type in which current flows from the positive electrode of the smoothing capacitor C1 to the negative electrode of the smoothing capacitor C1 via the output capacitor C2 and the inductor L1. However, it may be necessary to change the details such as the logic of some detection circuits according to the circuit configuration to be adopted.

  As described above, in the first embodiment, when the output voltage detected by the voltage detection circuit 8 is equal to or lower than the first threshold value, the current command value Iref_i from the dimming control circuit 11 is corrected by the correction circuit 9. Thereby, it is possible to realize the lighting device 1a in which the output current Iout is constant regardless of the output voltage Vout (the dependency of the output current Iout on the output voltage Vout is suppressed). Therefore, a desired light output can be obtained even when a load (LED 4) having a different voltage rating is connected or when the number of LEDs connected in series as a load is changed.

(Embodiment 2)
Next, a lighting device according to Embodiment 2 of the present invention will be described.

  The lighting device of the second embodiment is different from the first embodiment in that the correction circuit has a plurality of switching points (that is, threshold values) for switching the relationship between the output voltage Vout and the current command value Iref_o. Only the configuration (correction circuit) different from the first embodiment will be described below.

  FIG. 7 is a detailed circuit diagram of the correction circuit 19 in the present embodiment. As shown in the figure, the correction circuit 19 includes two comparators 190 and 192, two reference voltage generators 191 and 193, two transistors 194 and 195, resistors 196 to 198, and the like. The correction circuit 19 corresponds to two sets of the correction circuit 9 in the first embodiment (however, the reference voltages are different). The reference voltages (first threshold Vth1 and second threshold Vth2) generated by the two reference voltage generators 191 and 193 are set so as to satisfy Vth2 <Vth1.

  In the correction circuit 19 having such a configuration, the output voltage Vout from the voltage detection circuit 8 is compared with the second threshold value Vth2 and the first threshold value Vth1 by the comparators 190 and 192. Depending on the comparison result, the transistors 194 and 195 are turned on or off, and the current command value Iref_i is divided by the first voltage dividing ratio, or divided by the second voltage dividing ratio, or divided by voltage. The current command value Iref_o is output without being processed.

  Specifically, when the output voltage Vout from the voltage detection circuit 8 is larger than the first threshold value Vth1 (Vth1 <Vout), a low level signal is output from the comparators 192 and 190, and the two transistors 194 and 195 are turned on. Turn off. As a result, the current command value Iref_i from the dimming control circuit 11 is output as the current command value Iref_o without being divided.

  When the output voltage Vout from the voltage detection circuit 8 is larger than the second threshold value Vth2 and equal to or lower than the first threshold value Vth1 (Vth2 <Vout ≦ Vth1), the comparator 192 outputs a high level signal, and the comparator 190 outputs A low level signal is output. As a result, only the transistor 194 of the two transistors 194 and 195 is turned on, and the current command value Iref_i from the dimming control circuit 11 is divided by the first voltage division ratio determined by the resistor 196 and the resistor 197, and the current It is output as the command value Iref_o.

  In addition, when the output voltage Vout from the voltage detection circuit 8 is equal to or lower than the second threshold value Vth2 (Vout ≦ Vth2), a high level signal is output from the comparators 192 and 190, and the two transistors 194 and 195 are turned on. . As a result, the current command value Iref_i from the dimming control circuit 11 is divided by a second voltage division ratio (<first voltage division ratio) determined by the resistor 196 and the parallel combined resistance of the resistor 197 and the resistor 198, It is output as a current command value Iref_o.

  By such an operation, the correction circuit 19 can switch the current command value Iref_o at two points Vout (first threshold value Vth1, second threshold value Vth2) as shown in FIG. The current characteristics are as shown in FIG. FIG. 8 is a diagram illustrating an example of the relationship between the output voltage Vout of the lighting device and the current command value Iref (Iref_i, Iref_o) in the present embodiment. FIG. 9 is a diagram showing an output voltage-current characteristic of the lighting device in the present embodiment.

  As can be seen by comparing FIG. 9 with FIG. 4 in the conventional lighting device, the lighting device in the present embodiment can further reduce the difference in the actual peak current value Ipeak_R due to the output voltage Vout. In this way, by providing the correction circuit 19 with a plurality of voltage switching points, it is possible to cope with more loads (LED4) having different rated voltages (that is, substantially equal output currents can be supplied).

  For example, in the characteristics as shown in FIG. 9, almost the same current can be output to the LED 4 at Vout = 100V, 200V, and 300V.

  In order to make the correction circuit 19 in this embodiment function effectively, the first threshold value Vth1 and the second threshold value Vth2 are two types of LEDs 4 that are connected to the lighting device and have different forward voltages. It is preferable to set between the forward voltages Vr1 and Vr2 of the LED 4. For example, it is preferable to set Vr1 <Vth2 <Vth1 <Vr2.

(Embodiment 3)
Next, a lighting device according to Embodiment 3 of the present invention will be described.

  The lighting device of the third embodiment is different from the first embodiment in that the correction circuit detects the cathode voltage Vout_k that changes in accordance with the output voltage Vout and continuously corrects the current command value Iref in accordance with the cathode voltage Vout_k. Different. As a result, a lighting device is realized in which the output current Iout is reliably constant regardless of the output voltage Vout. For this reason, in the lighting device of the present embodiment, some changes are made to the voltage detection circuit 8 and the correction circuit 9 in the lighting device 1a of the first embodiment. Only the configuration (voltage detection circuit and correction circuit) different from the first embodiment will be described below.

  FIG. 10 is a detailed circuit diagram of the voltage detection circuit 28 and the correction circuit 29 in the present embodiment.

  The voltage detection circuit 28 divides the cathode voltage Vout_K by the resistor R12 and the resistor R13, and outputs the obtained divided voltage to the correction circuit 29. Note that the cathode voltage Vout_K is substantially equal to the voltage VL across the inductor L1 during the period when the switching element Q1 is on. This is because the on-resistance and the resistance R1 of the switching element Q1 are small enough to be ignored. In the present embodiment, the voltage detection circuit 28 detects the cathode voltage Vout_K, thereby detecting the voltage VL across the inductor L1 during the period when the switching element Q1 is on.

  The correction circuit 29 is a circuit that corrects the current command value iref_i so that the peak value of the current flowing through the inductor L1 is constant without depending on the voltage detected by the voltage detection circuit 28. That is, the correction circuit 29 continuously corrects the current command value Iref by the correction circuit 29 according to the voltage detected by the voltage detection circuit 28 (here, the cathode voltage Vout_K). For this purpose, the correction circuit 29 includes a transconductance amplifier 290, a reference voltage generator 291 that generates a reference voltage (threshold voltage Vth), a transistor 292, and the like.

  The operations of the voltage detection circuit 28 and the correction circuit 29 configured as described above are as follows.

  The voltage detection circuit 28 outputs a voltage obtained by dividing the cathode voltage Vout_k to the correction circuit 29.

  In the correction circuit 29, the transconductance amplifier 290 outputs a current corresponding to the voltage difference between the voltage from the voltage detection circuit 28 and the threshold voltage Vth generated by the reference voltage generator 291 to the base of the transistor 292. The corrected current command value Iref_o is a value divided from the input current command value Iref_i according to the illustrated resistance and the collector current of the transistor 292 (in other words, the on-resistance of the transistor 292).

  With such a voltage detection circuit 28 and correction circuit 29, the collector current of the transistor 292 increases as the cathode voltage Vout_k increases, and the corrected current command value Iref_o decreases continuously. In other words, a smaller current command value Iref_o is generated as the output voltage Vout is smaller than the relationship between the output voltage Vout and the cathode voltage Vout_K (Vout = Vc1−Vout_K) described above.

  The threshold voltage Vth generated by the reference voltage generator 291 is set as an offset value that appropriately correlates the cathode voltage Vout_K (or the output voltage Vout) and the corrected current command value Iref_o.

  FIG. 11 (current command value correction) and FIG. 12 (voltage-current characteristics) show the results of implementation by the voltage detection circuit 28 and the correction circuit 29. That is, FIG. 11 is a diagram illustrating an example of the relationship between the output voltage Vout of the lighting device and the corrected current command value Iref_o in the present embodiment. FIG. 12 is a diagram showing an output voltage-current characteristic of the lighting device in the present embodiment.

  As shown in FIG. 11, in the present embodiment, the corrected current command value Iref_o continuously changes so that the corrected current command value Iref_o increases as the output voltage Vout of the lighting device increases. Yes. Further, as can be seen by comparing FIG. 12 with FIG. 4 of the conventional lighting device, the output current Iout is constant regardless of the output voltage Vout.

  Thus, according to the lighting device in the present embodiment, the dimming control circuit 11 provides a constant peak value of the current flowing through the inductor L1 without depending on the voltage detected by the voltage detection circuit 28. Correction is applied to the current command value Iref_i. As a result, the same output current Iout is ensured without depending on the output voltage Vout.

(Embodiment 4)
Next, a lighting device according to Embodiment 4 of the present invention will be described.

  The fourth embodiment is different from the first to third embodiments in that a plurality of buck converters, control circuits, and solid state light emitting elements (here, LEDs) are provided.

  FIG. 13 is a circuit diagram of the lighting device 1b of the present embodiment.

  Here, for example, a description will be given using a circuit in which the lighting device 1b is configured by three buck converters 3a to 3c. This lighting device 1b includes a plurality of buck converters 3a to 3c and control circuits 5a to 5c that step down a DC voltage of a smoothing capacitor C1 serving as a common DC power source and supply a DC current to the LEDs 4a to 4c serving as loads. .

  Each of the buck converters 3a to 3c has a circuit configuration similar to that of the buck converter 3 of the first embodiment. For example, the buck converter 3a includes an inductor L1a, a switching element Q1a, a diode D1a, and an output capacitor C2a.

  Each of the control circuits 5a to 5c has a circuit configuration similar to that of the control circuit 5 of the first embodiment. For example, the control circuit 5a includes a current detection circuit 6a, a ZCD detection circuit 7a, a voltage detection circuit 8a, a correction circuit 9a, and a drive circuit 10a. A common current command value Iref_i is input from the dimming control circuit 11 to the three control circuits 5a to 5c.

  Each of the buck converters 3a to 3c and its control circuits 5a to 5c independently operate in the same manner as in the first embodiment. For example, in the buck converter 3a and the control circuit 5a, the current command value Iref_i is corrected by the correction circuit 9 when the output voltage detected by the voltage detection circuit 8 is equal to or lower than the first threshold value. As a result, the peak value of the current flowing through the inductor L1 regardless of the output voltage becomes a constant value (or the fluctuation range is suppressed), and the output current is constant regardless of the output voltage (or the fluctuation of the output current). A lighting device in which the width is suppressed can be realized.

  FIG. 14 shows a waveform example of currents IL_a to IL_c flowing through the inductors of the buck converters 3a to 3c. As the correction circuit provided in each control circuit 5a to 5c, the same one as the correction circuit 19 shown in the second embodiment is used. The following loads (LEDs 4a to 4c) having different rated voltages were connected to the three buck converters 3a to 3c. That is, the rated voltage Vout_a = 100V of the LED 4a connected to the back converter 3a, the rated voltage Vout_b = 200V of the LED 4b connected to the back converter 3b, and the rated voltage Vout_c = 300V of the LED 4c connected to the back converter 3c.

  As can be seen from the waveform example of FIG. 14, in each of the buck converters 3a to 3c, the on-time Ton and the current gradient Δi of the switching element are different, but the target value Iref_i is corrected according to the output voltage Vout. Thereby, the current peak value Ipeak_R becomes substantially the same, and the output current can also be made substantially constant.

  As described above, according to the present embodiment, a lighting device is realized in which the output current is constant regardless of the output voltage by ensuring the constant current characteristics of the output voltage-current characteristics at each output. In addition, when an LED with a different voltage rating is connected to each output, or when a load (LED) with a different number of LEDs connected in series is connected, a desired current can flow, so that a desired light output Can be obtained.

  As described above, in the present embodiment, it is possible to realize a lighting device that can secure a desired light output at each output of a plurality of outputs and reduce the light output unevenness of the entire output by a simple circuit.

  The lighting device 1b according to the present embodiment includes three sets of the back converter and the control circuit according to the first embodiment. However, the lighting device 1b may include the number of the back converter and the control circuit other than three sets. The buck converter and the control circuit of form 2 or 3 may be provided.

  It goes without saying that the lighting devices 1a and 1b described in the first to fourth embodiments can be applied to a lighting fixture. 15-17 is an external view of a lighting fixture provided with the lighting devices 1a and 1b of the said Embodiment 1-4. Here, a downlight 200a (FIG. 15), spotlights 200b (FIG. 16), and 200c (FIG. 17) are illustrated as examples of lighting fixtures. In the figure, 201 is a circuit box containing the circuit of the lighting device (back converter and control circuit), 202 is a lamp mounted with an LED, 203 is a circuit box 201 and the LED of the lamp 202. This is an electrical connection wiring. In the circuit box 201, for example, any one of the lighting devices according to the first to third embodiments or one or more sets of circuits (back converter and control circuit) in the lighting device 1b according to the fourth embodiment are housed. The

  In such a lighting fixture, since the lighting device according to the above-described embodiment is used, stable illumination in which variation in light output is suppressed with a simple configuration is realized. Furthermore, when the lighting device of the fourth embodiment is applied, the same light output is ensured in a plurality of lighting fixtures.

  As described above, the lighting device in the above-described embodiment is a lighting device that lights a solid light emitting element (LED 4 or the like), and receives a current from the DC power source (smoothing capacitor C1) and the DC power source. Are provided with a buck converter 3 and the like for providing a predetermined current, and a control circuit 5 for controlling the buck converter 3 and the like. The buck converter 3 and the like are connected in series with the switching element Q1 and the switching element Q1, and supply the current emitted from the DC power source when the switching element Q1 is turned on and the current emitted from the inductor L1 to the solid state light emitting element. And a diode D1. The control circuit 5 or the like includes a current detection circuit 6 or the like that detects a current flowing through the switching element Q1, a voltage detection circuit 8 or the like that detects a voltage at both ends of the solid light emitting element or a voltage at both ends of the inductor L1, and a current detection circuit 6 The switching element Q1 is turned off when it is detected that the detected current value has reached a predetermined current command value, and the switching element Q1 is turned on when it is detected that the inductor L1 has released predetermined energy. A drive circuit 10 that generates a control signal and outputs the control signal to the switching element Q1, and a correction circuit 9 that corrects the current command value according to the voltage detected by the voltage detection circuit 8 or the like.

  More specifically, the correction circuit 9 or the like is configured so that the peak values of the current at at least two different voltages are substantially equal in the relationship between the voltage detected by the voltage detection circuit 8 and the like and the peak value of the current flowing through the inductor L1. The current command value is corrected.

  As a result, variations in output current depending on the magnitude of the output voltage are suppressed, so that even if there are variations in the forward voltage or rated voltage of the solid state light emitting device, the current within a certain range determined by the current command value is solid. Output to the light emitting element. Further, such constant current control is realized by a simple correction circuit. Therefore, it is a lighting device using a switching power supply circuit that operates by BCM & peak current control, and can be stably lit with a simple configuration and suppressed variation in light output for solid-state light emitting devices having different characteristics. A lighting device is realized.

  In the first embodiment, the correction circuit 9 changes the current command value to a first correction value smaller than the current command value when the output voltage detected by the voltage detection circuit 8 is equal to or lower than the first threshold value. To correct. As a result, when the output voltage detected by the voltage detection circuit is equal to or lower than the first threshold value, the current command value is corrected to a smaller first correction value, and variations in the peak value of the current flowing through the inductor are suppressed. The

  In the second embodiment, the correction circuit 19 further sets the current command value when the output voltage detected by the voltage detection circuit 8 is equal to or lower than the second threshold value that is smaller than the first threshold value. Correction is made to a second correction value smaller than the correction value of 1. Thereby, since a plurality of switching points (that is, threshold values) for switching the relationship between the output voltage and the current command value are provided, variations in the peak value of the current flowing through the inductor are further suppressed.

  In addition, about a threshold value, a 1st threshold value and a 2nd threshold value are the values between the forward voltage of two types of solid light emitting elements from which the forward voltage differs among the solid light emitting elements connected to the said lighting device. is there. Thereby, since the threshold value is set within the range of the forward voltage of the solid state light emitting element connected to the lighting device, the variation in the peak value of the current flowing through the inductor is reliably suppressed.

  In the third embodiment, the correction circuit 29 corrects the current command value so that the peak value of the current flowing through the inductor L1 is constant without depending on the voltage detected by the voltage detection circuit 28. As a result, the peak value of the current flowing through the inductor becomes constant without depending on the voltage detected by the voltage detection circuit 28, so that the output current becomes constant without depending on the output voltage.

  Moreover, in Embodiment 4, the lighting device 1b is a device that lights a plurality of solid state light emitting elements, and a plurality of back converters 3a to 3c and a plurality of back converters 3a to 3c corresponding to the respective solid state light emitting elements. And a plurality of control circuits 5a to 5c for controlling each of 3c. At this time, the lighting device 1b further includes a dimming control circuit 11 that outputs a current command value corresponding to a desired light output to the plurality of control circuits 5a to 5c. As a result, the same output current determined by a common current command value is applied to a plurality of solid state light emitting elements, so that the light output size is unified among the plurality of solid state light emitting elements, and the light output varies as a whole. The illumination is suppressed.

  Moreover, the lighting fixture (downlight 200a, spotlight 200b, and 200c) in the said embodiment is equipped with lighting device 1a and 1b and the solid light emitting element to which an electric current is supplied from a lighting device. As a result, stable illumination in which variations in light output are suppressed with a simple configuration is realized. Furthermore, in the some lighting fixture to which the lighting device of the said Embodiment 3 is applied, the illumination by which the dispersion | variation in the light output was suppressed between several lighting fixtures is implement | achieved.

  As mentioned above, although the lighting device and lighting fixture which concern on this invention were demonstrated based on embodiment, this invention is not limited to these embodiment. Unless it deviates from the gist of the present invention, one or more of the present invention may be applied to various modifications that can be conceived by those skilled in the art, or forms constructed by combining components in different embodiments. It may be included within the scope of the embodiments.

  For example, in the lighting device of the above embodiment, the LED is used as the solid light emitting element, but the solid light emitting element according to the present invention may be another solid light emitting element such as an organic EL element.

  Moreover, when applying the lighting device in the said embodiment to a some lighting fixture, the lighting device of the type in any one of the said Embodiment 1-4 may be applied to all the lighting fixtures, and several This type of lighting device may be applied to a plurality of lighting fixtures. Furthermore, when the lighting device according to the fourth embodiment is applied to a plurality of lighting fixtures, each of a plurality of sets of back converters and control circuits may be distributed and housed in each lighting fixture, The buck converter and the control circuit may be housed together in one lighting fixture.

C1, C1a Smoothing capacitor D1, D1a Diode Q1, Q1a Switching element L1, L1a Inductor C2, C2a Output capacitor R1, R1a, R10-R13, R12a, R13a, 61, 196-198 Resistance 1a, 1b Lighting device 3, 3a- 3c, 13 Buck converter 4, 4a-4c LED
5, 5a to 5c, 15 Control circuit 6, 6a Current detection circuit 7, 7a ZCD detection circuit 8, 8a, 28 Voltage detection circuit 9, 9a, 19, 29 Correction circuit 10, 10a Drive circuit 11 Dimming control circuit 60, 70 Comparator 62 Capacitor 71, 91, 191, 193, 291 Reference voltage generator 90, 190, 192 Comparator 92, 194, 195, 292 Transistor 100 Flip-flop 101 Buffer amplifier 200a Downlight 200b, 200c Spotlight 201 Circuit box 202 Light Body 290 transconductance amplifier

Claims (8)

A lighting device for lighting a solid state light emitting device,
DC power supply,
A buck converter that receives a current from the DC power supply and provides a predetermined current to the solid state light emitting device;
A control circuit for controlling the buck converter,
The buck converter is
A switching element;
An inductor that is connected in series with the switching element and through which a current flows from the DC power source when the switching element is turned on;
A diode for supplying a current emitted from the inductor to the solid state light emitting device,
The control circuit includes:
A current detection circuit for detecting a current flowing through the switching element;
A voltage detection circuit for detecting a voltage across the solid-state light emitting element or a voltage across the inductor;
When it is detected that the current value detected by the current detection circuit has reached a predetermined current command value, the switching element is turned off, and when it is detected that the inductor has released predetermined energy, the switching element A drive circuit that generates a control signal for turning on and outputs the control signal to the switching element;
Depending on the voltage detected by the voltage detection circuit, have a correction circuit for adding the correction to the current command value,
In each of the case where the voltage detected by the voltage detection circuit is smaller than or larger than a predetermined threshold, the correction circuit reduces the peak value of the current flowing through the inductor as the voltage increases, and the voltage detection The relationship between the voltage detected by the circuit and the peak value of the current flowing through the inductor is such that the peak values of the current at two different voltages in the small case and the large case are approximately equal. A lighting device that corrects the command value . The correction circuit, when the output voltage detected by said voltage detection circuit is equal to or less than the first threshold value, according to claim 1, the current command value is corrected in the first correction value smaller than the current command value serial mounting of the lighting device. The correction circuit further sets the current command value from the first correction value when the output voltage detected by the voltage detection circuit is equal to or lower than a second threshold value that is smaller than the first threshold value. lighting device according to claim 2, wherein the correction to the even smaller second correction value. Said first threshold and said second threshold value, of the solid state light element connected to the lighting device, according to claim 3 forward voltage is a value between the forward voltages of the two different types of solid-state light-emitting element The lighting device described. The lighting device according to claim 1, wherein the correction circuit corrects the current command value so that a peak value of a current flowing through the inductor is constant without depending on a voltage detected by the voltage detection circuit. The lighting device is a device for lighting a plurality of solid state light emitting elements,
The lighting device includes a plurality of said buck converter corresponding to each of the plurality of solid state light emitting devices, claim 1-5 comprising a plurality of said control circuit for controlling each of the plurality of buck converter 1 The lighting device according to item. The lighting device according to claim 6 , further comprising a dimming control circuit that outputs the current command value corresponding to a desired light output to the plurality of control circuits. The lighting device according to any one of claims 1 to 7 ,
A lighting fixture comprising: a solid-state light emitting element supplied with current from the lighting device.

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