Luminaire

Abstract

To provide a luminaire capable of determining whether a current flowing to a booster circuit is an overcurrent without reference to the level of an input voltage.SOLUTION: A luminaire comprises a light source, a booster circuit which boosts an input voltage from an external power supply, a step-down circuit which steps the voltage boosted by the booster circuit down to a voltage suitable for illumination of the light source, and a controller. The controller is configured to perform processing to detect a current flowing to a switching element of the booster circuit and processing to determine whether the current is an overcurrent based upon a threshold of the current set according to the input voltage. The threshold of the current is set to a less value as the input voltage is larger.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a lighting device.

Background Art

[0002] In recent years, LEDs are generally used as the light source of lighting devices. It is known that the brightness of LEDs is more likely to follow changes in the input voltage compared to incandescent bulbs and fluorescent lamps. Therefore, unless the ripple of the voltage supplied to the light source is reduced, there is a problem that the light source appears to flicker. To address this problem, a two-converter method has become increasingly common, in which the input voltage from an external power source is first boosted to reduce the ripple and then stepped down to a voltage suitable for the light source in the subsequent stage. Furthermore, a technique for improving the power factor by operating the front-stage boost circuit in a PFC (Power Factor Correction) mode is also known.

[0003] Patent Document 1 discloses a lighting device that operates to stop the switching control of a switching element when it detects that an overcurrent exceeding the upper limit is flowing through the switching element of a converter circuit. This can protect the circuit from overcurrent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a converter circuit, the current flowing through the upstream boost circuit has the characteristic that it becomes larger as the input voltage becomes lower. However, in the above-described method, since the threshold value for determining whether or not it is an overcurrent is a single value, the threshold value set based on a certain input voltage does not serve as a threshold value at an input voltage higher than that, and it is impossible to determine whether or not it is an overcurrent. Therefore, there has been a problem that the circuit cannot be protected in a region where the input voltage is large.

[0006] An object of the present disclosure is to provide a lighting device that can determine whether or not the current flowing through the boost circuit is an overcurrent regardless of the magnitude of the input voltage in order to solve the above-described problems.

Means for Solving the Problems

[0007] Aspects of the present disclosure include a light source, a boost circuit that boosts an input voltage from an external power source, a buck circuit that steps down the voltage boosted by the boost circuit to a voltage suitable for lighting the light source, and a control device, The control device performs a process of detecting the current flowing through the switching element of the boost circuit, a process of determining whether or not the current is an overcurrent based on a threshold value of the current set according to the input voltage, is configured to execute, The lighting device is preferably configured such that the threshold value of the current is set to a lower value as the input voltage becomes larger.

Advantages of the Invention

[0008] According to the present disclosure, since the threshold value of the current is set to a lower value as the input voltage increases, it is possible to determine whether or not it is an overcurrent even when the input voltage is large. Thereby, it is possible to provide a lighting device that can determine whether or not the current flowing through the boost circuit is an overcurrent regardless of the magnitude of the input voltage.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0010] Embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding components may be denoted by the same reference numerals, and repeated descriptions may be omitted.

[0011] Embodiment 1 FIG. 1 is a circuit diagram of a lighting device 100 according to Embodiment 1 of the present disclosure. The lighting device 100 includes an LED module 11 including one or more LEDs, a lighting device 12, a dimmer 61, and a dimming interface circuit 62.

[0012] The lighting device 12 includes an input filter circuit 1, an input voltage detection circuit 2, a boost circuit 3, a buck circuit 4 to which the LED module 11 is connected, and a control device 50 (microcomputer).

[0013] An external power supply is connected to the input filter circuit 1, and the input filter circuit 1 receives an input voltage from the external power supply. The input filter circuit 1 includes a fuse 25 for protecting against overcurrent, a capacitor 26, and a diode bridge 27 that full-wave rectifies an AC voltage from the external power supply and converts it into a DC voltage. The output of the diode bridge 27 has its high potential side connected to the input voltage detection circuit 2 and its low potential side connected to a ground terminal (not shown).

[0014] The input voltage detection circuit 2 includes resistors 21 and 22 connected in series, which divide the input voltage. As a result, the divided voltage (referred to as the first voltage) can be detected by the control device 50, enabling the detection of the input voltage of the external power supply.

[0015] The boost circuit 3 boosts the DC voltage received from the input filter circuit 1. The capacitor 31 is connected in parallel with the diode bridge 27. One end of the inductor 33 is connected to the positive electrode of the capacitor 31, and the negative electrode of the capacitor 31 is connected to the grounding terminal. The other end of the inductor 33 is connected to the first terminal of the switching element 32 and the anode of the diode 34.

[0016] The switching element 32 is, for example, a MOSFET (Metal - Oxide - Semiconductor Field - Effect Transistor). In the switching element 32, the first terminal is connected to the inductor 33, the second terminal is connected to the resistor 38, and the control terminal is connected to the control device 50. In the case of a MOSFET, the first terminal is the drain terminal, the second terminal is the source terminal, and the control terminal is the gate terminal. By the switching element 32 responding to the switch control by the control device 50, the on - off of the voltage in the boost circuit 3 can be achieved.

[0017] Also, the positive electrode of the electrolytic capacitor 35 is connected to the cathode of the diode 34, and the negative electrode of the electrolytic capacitor 35 is connected to the grounding terminal.

[0018] The resistors 36 and 37 are provided at the output end of the boost circuit 3 to divide the output voltage of the boost circuit 3. The divided voltage (referred to as the second voltage) is detected by the control device 50. The control device 50 controls the switching element 32 so that the output voltage of the boost circuit 3 becomes constant based on the second voltage.

[0019] The resistor 38 is connected to the source terminal of the switching element 32 and to the grounding terminal, and inputs the voltage (referred to as the third voltage) applied to the switching element 32 to the control device 50. Based on the third voltage, the control device 50 can detect the current flowing through the switching element 32. Since the current flowing through the switching element 32 exhibits the same behavior as the current flowing through the entire boost circuit 3, it serves as an indicator of the current flowing through the boost circuit 3.

[0020] The buck circuit 4 steps down the voltage received from the boost circuit 3 to a voltage suitable for lighting the LED module 11. The buck circuit 4 is, for example, a buck - converter circuit, a fly - back circuit, etc., but other buck - down methods may also be used. The switching element 41 of the buck circuit 4 is, like the above - mentioned switching element 32, a MOSFET or the like. The first terminal of the switching element 41 is connected to the positive electrode of the electrolytic capacitor 35, the second terminal is connected to the cathode of the diode 42, and the control terminal is connected to the control circuit 40. By the switching element 41 responding to the switch control by the control circuit 40, the voltage in the circuit can be turned on and off.

[0021] One end of the sense resistor 44 is connected to the negative electrode of the capacitor 43, and the other end of the sense resistor 44 and the anode of the diode 42 are connected to the grounding terminal.

[0022] The sense resistor 44 is provided in the buck circuit 4 and is used for detecting the LED current flowing through the LED module 11. The voltage corresponding to the LED current applied to the sense resistor 44 is detected by the control circuit 40. Based on this voltage, the control circuit 40 controls the switching element 41 so that the current flowing through the LED module 11 becomes a constant current.

[0023] The resistors 45 and 46 are provided at the output terminal of the buck circuit 4 and are used for detecting the voltage of the LED module 11. When the voltage (referred to as the fourth voltage) divided by the resistors 45 and 46 is input to the control device 50, the control device 50 detects the connection status of the LED module 11, voltage abnormality, etc. based on this detected voltage.

[0024] The control device 50 can be composed of a known microcomputer provided as a control device for a digital power supply, or can also be composed of an arithmetic device such as a DSP (Digital Signal Processor). The control device 50 includes a storage unit, a processing device, and an A / D conversion unit.

[0025] The first voltage, the second voltage, the third voltage, and the fourth voltage described above are input to the control device 50.

[0026] The storage unit has a non-volatile memory and stores an arithmetic program to be executed by the processing device and various data used for the arithmetic operation. Data can be written to and read from the storage unit from the outside. The A / D conversion unit converts the voltage value input to the control device 50 into a digital value. The processing device performs arithmetic processing necessary for lighting control based on the digitally converted voltage value. The arithmetic processing performed by the processing device includes a threshold determination process for the first voltage described later and an overcurrent determination process for the current flowing through the switching element 32.

[0027] The control device 50 adjusts the on-time of the switching element 32 based on the second voltage and performs constant voltage control of the boost circuit 3 so as to match the target voltage set in the storage unit in advance.

[0028] The control device 50 receives a dimming command value from the dimming device 61 via a dimming interface (I / F) circuit 62. The control device 50 notifies the received dimming command value to the control circuit 40.

[0029] The control circuit 40 outputs a PWM signal for lighting the LED module 11 at the dimming rate commanded by the dimming command value. In the output of the PWM signal, the control circuit 40 adjusts the on-time of the switching element 41 so that the current flowing through the LED module 11 matches the target current determined based on the dimming command value based on the current detected by the sense resistor 44.

[0030] FIG. 2 is a diagram showing a method for monitoring an input voltage from an external power supply according to Embodiment 1 of the present disclosure. The control device 50 detects a first voltage input from the input voltage detection circuit 2, and determines whether the first voltage exceeds a voltage threshold V th . The voltage threshold V th is stored in the storage unit.

[0031] In the threshold determination, it is determined whether the first voltage constantly exceeds the threshold V th over a certain determination period. Thereby, it is possible to distinguish between a steady voltage change and a temporary voltage change due to noise or the like, and it is possible to improve the accuracy of the determination.

[0032] FIG. 3 is a diagram showing a method for monitoring an input voltage from an external power supply according to Embodiment 1 of the present disclosure. In the case of Japan, the frequency of the commercial power supply is 50 Hz or 60 Hz. Therefore, in the threshold determination, the maximum value of the first voltage is detected for each period or half period of the external power supply, and after calculating the cumulative average of the obtained maximum values, it may be determined whether the average value exceeds the voltage threshold V th . By using the cumulative average value, a statistical effect can be obtained, and the accuracy of the threshold determination can be improved.

[0033] For example, in the example of FIG. 3, the maximum value of the first voltage is detected for each half period of the external power supply. Reflecting the fact that the input voltage has risen immediately after the external power supply is connected to the input voltage detection circuit 2, a large maximum value is detected in the first voltage. That is, the maximum value of 141 V is detected in the first voltage in the first half period, and the maximum value of 113 V is detected in the next half period. However, as the input voltage from the external power supply stabilizes, the maximum value of the first voltage stabilizes at 85 V. Here, assuming that the voltage threshold V th is 85 V or more and less than 113 V, it is desirable that the detected first voltage is determined not to exceed the voltage threshold V th .

[0034] The average value obtained by accumulating and averaging the maximum value of the first voltage exceeds 85V at the beginning of the connection of the external power supply, so it exceeds the voltage threshold V th However, since the average value approaches 85V over time, at a certain point in time, it will no longer exceed the voltage threshold V th . In this way, the desired judgment result can be obtained.

[0035] Note that in FIGS. 2 and 3, the case where the voltage threshold V th for the first voltage has only one value was described, but the voltage threshold V th may be plural. By providing a plurality of voltage thresholds, a plurality of current thresholds I th can be provided, and it becomes possible to finely correspond the current threshold I th with the input voltage from the external power supply.

[0036] FIG. 4 is a diagram showing a method for setting the current threshold I th flowing through the switching element 32 according to Embodiment 1 of the present disclosure. As already described, the larger the input voltage from the external power supply, the smaller the current flowing through the boost circuit 3. However, the current flowing through the switching element 32 also exhibits the same behavior as the current flowing through the boost circuit 3.

[0037] The control device 50 monitors the current flowing through the switching element 32 and determines whether the current is an overcurrent based on the threshold I th . The current threshold I th is set to either I th or I th1 to I th3 according to the determination result of the voltage threshold V

[0038] For example, when the voltage thresholds are two values of V th1 and V th2 , the control device 50 sets the current threshold I th as follows. However, here I th1 > I th2 > I th3 . · When the first voltage is V th1The following: The threshold value of the current is I th1 · When the first voltage exceeds V th1 and is less than or equal to V th2 The following: The threshold value of the current is I th2 · When the first voltage exceeds V th2 : The threshold value of the current is I th3

[0039] In this way, since the current threshold value I th is set to be lower as the input voltage increases, it becomes possible to determine whether there is an overcurrent even when the input voltage is large. Thereby, the safety of the boost circuit 3 and the buck circuit 4 can be ensured even when the input voltage is large.

[0040] In the prior art, since the current threshold value I th is a single value, it was not possible to determine whether there is an overcurrent in the region where the input voltage is equal to or higher than the threshold value. In a state where it is not possible to determine whether there is an overcurrent, for example, even if the switching element 41 of the buck circuit 4 causes a half-dead failure and an excessive current flows through the LED module 11, this could not be detected. Therefore, it was not possible to stop the switching and protect the buck circuit 4.

[0041] Here, if the voltage of the sense resistor 44 is input to the control device 50 and the current flowing through the LED module 11 is monitored, it is possible to protect the buck circuit 4 when an excessive current flows through the LED module 11. However, additional wiring for input etc. is required, leading to an increase in cost. Also, in recent years, many lighting devices equipped with a plurality of LED modules 11 with different color temperatures have been sold, but in such lighting devices, individually detecting the current flowing through the plurality of LED modules 11 not only increases the cost but also raises concerns about an increase in size. On the other hand, the present disclosure has the advantage of being able to protect the buck circuit 4 without requiring additional wiring and without increasing the cost or size.

[0042] As described above, in the present disclosure, it is possible to provide a lighting device capable of determining whether or not the current flowing through the booster circuit is an overcurrent regardless of the magnitude of the input voltage.

[0043] In addition, in the above description, the case where the light source is the LED module 11 has been described, but the light source is not limited to an LED, and may be an incandescent lamp or the like. This point is common to all embodiments.

[0044] Embodiment 2 In this embodiment, the threshold value I of the current flowing through the switching element 32 th is set to a value corresponding not only to the first voltage described in Embodiment 1 but also to the dimming rate. Hereinafter, the points of change from Embodiment 1 will be described. FIG. 5 is a diagram showing a method of setting the threshold value I of the current flowing through the switching element 32 according to Embodiment 2 of the present disclosure. The current flowing through the switching element 32 of the booster circuit 3 changes depending on the dimming rate, and has a characteristic that the current increases as the dimming rate increases. th

[0045] In this embodiment, the threshold value I of the current set based on the first voltage th is changed as follows based on the dimming rate commanded from the dimmer 61. However, here, I th1 > I th2 > I th3 is satisfied. · When the dimming rate is DIM th1 or less: The threshold value of the current is I th3 · When the dimming rate exceeds DIM th1 and is DIM th2 or less: The threshold value of the current is I th2 · When the dimming rate exceeds DIM th2 : The threshold value of the current is I th1

[0046] Thus, the threshold value I of the current th is set to a lower value as the dimming rate is lower. Thereby, an appropriate threshold value I according to the dimming rate thIt becomes possible to set. As in this embodiment, the current threshold I set according to the first voltage and the dimming rate th By determining whether the current flowing through the switching element 32 is an overcurrent based on th , the determination of overcurrent can be performed more precisely. Therefore, the accuracy of determining the necessity of circuit protection can be improved compared to Embodiment 1.

[0047] Here, the case where the threshold of the dimming rate is the two values of DIM th1 and DIM th2 has been described, but the number of thresholds is not limited.

[0048] Note that the numerical values of the first voltage and the dimming rate shown in this disclosure are merely examples and are not limited.

[0049] Hereinafter, various aspects of the present disclosure will be collectively described as appendices. (Appendix 1) A lighting device comprising a light source, a boost circuit for boosting an input voltage from an external power source, a buck circuit for bucking the voltage boosted by the boost circuit to a voltage suitable for lighting the light source, and a control circuit, The control circuit is configured to execute a process of detecting a current flowing through a switching element of the boost circuit, and a process of determining whether the current is an overcurrent based on the current threshold set according to the input voltage, wherein the current threshold is set to a lower value as the input voltage is higher. (Appendix 2) The lighting device according to Appendix 1, wherein the current threshold set according to the input voltage is set to a lower value as the dimming rate of the light source is lower. (Appendix 3) The control circuit further executes a process of determining whether the input voltage exceeds a voltage threshold, and the current threshold is changed when the input voltage exceeds the voltage threshold. The lighting device according to Appendix 1 or 2. (Appendix 4) The lighting device further includes a resistor connected in series with the switching element. The lighting device according to any one of appended claims 1 to 3, wherein the control circuit detects the current flowing through the switching element by detecting the voltage applied to the resistor.

Explanation of Signs

[0050] 1 Input filter circuit 2 Input voltage detection circuit 3 Boost circuit 4 Buck circuit 11 LED module 12 Lighting device 21 Resistor 22 Resistor 25 Fuse 26 Capacitor 27 Diode bridge 31 Capacitor 32 Switching element 33 Inductor 34 Diode 35 Electrolytic capacitor 36 Resistor 37 Resistor 38 Resistor 40 Control circuit 41 Switching element 42 Diode 43 Capacitor 44 Sense resistor 45 Resistor 46 Resistor 50 Control device 61 Dimmer 62 Dimming interface circuit

Claims

Claim 1 A lighting device comprising: a light source; a boost circuit that boosts an input voltage from an external power source; a buck circuit that steps down the voltage boosted by the boost circuit to a voltage suitable for lighting the light source; and a control device. The control device: performs a process of detecting a current flowing through a switching element of the boost circuit; performs a process of determining whether the current is an overcurrent based on a threshold value of the current set according to the input voltage; is configured to execute the above; wherein the threshold value of the current is set to a lower value as the input voltage is higher. Claim 2 The lighting device according to claim 1, wherein the threshold value of the current set according to the input voltage is set to a lower value as the dimming rate of the light source is lower. Claim 3 The control device further performs a process of determining whether the input voltage exceeds a voltage threshold value, and the threshold value of the current is changed when the input voltage exceeds the voltage threshold value. The lighting device according to claim 1 or 2. Claim 4 The lighting device according to claim 1 or 2, further comprising a resistor connected in series with the switching element, wherein the control device detects the current flowing through the switching element by detecting a voltage across the resistor.

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