Lighting device and luminaire

Abstract

To obtain a lighting device and a luminaire that can suppress flashes from point light sources.SOLUTION: A lighting device according to the present disclosure includes a constant current circuit connected in series with a light source, a voltage conversion circuit that receives power from the outside and supplies power to both ends of the series circuit formed by the light source and the constant current circuit by turning a first switching element on and off, and a control device, and the constant current circuit includes a resistor connected in series with the light source and a second switching element connected in series with the resistor, and when power starts to be supplied to the voltage conversion circuit from the outside, the control device starts operation of the voltage conversion circuit and then starts operation of the constant current circuit, and during the period from when power starts to be supplied to the voltage conversion circuit to when the constant current circuit starts operating, the control device controls the on / off of the first switching element such that the output voltage of the voltage conversion circuit becomes a predetermined target voltage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a lighting device and an illumination device. [Background technology]

[0002] Patent Document 1 discloses a lighting circuit in which a constant current circuit is connected in series to a light-emitting unit made of a light-emitting diode. A converter circuit supplies DC power to the series circuit of the light-emitting unit and constant current circuit while controlling the output voltage so that the voltage between the terminals of the constant current circuit is constant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-215913 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, LEDs have become the norm for lighting equipment light sources. Compared to incandescent or fluorescent lamps, LEDs are known to have brightness that follows voltage changes more easily. In other words, if the ripple in a lighting device is not reduced, there is a high possibility that the light will appear to flicker. For this reason, many power supplies use a two-converter system in which the commercial power supply is boosted once to reduce the ripple, and then stepped down to a voltage suitable for LED light sources.

[0005] However, installing two converters increases the size of the lighting device. In response to this, there is a method, as described in Patent Document 1, in which a constant current circuit is added to one step-up or step-down converter to reduce ripple. This method controls the voltage between the terminals of the constant current circuit to be constant, thereby supplying a stable current to the LED and allowing the current value to be set accurately and easily.

[0006] On the other hand, in lighting equipment, due to the regulations for harmonics or the benefits of a high power factor, converters are often operated using power factor correction (PFC) to improve the power factor. In order for a converter to operate in PFC mode, its response must be sufficiently slow. In particular, when the response is slowed down in this way, there is a risk that the LED may appear to flash if the converter's output voltage is not stable at the start-up timing of the constant current circuit.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a lighting device and an illumination device that can suppress flashing of a light source. [Means for solving the problem]

[0008] The lighting device according to the present disclosure comprises a constant current circuit connected in series with a light source, a voltage conversion circuit that receives power from an external source and supplies power to both ends of a series circuit formed by the light source and the constant current circuit by turning a first switching element on and off, and a control device that controls the voltage conversion circuit, wherein the constant current circuit has a resistor connected in series with the light source and a second switching element connected in series with the resistor, and when the constant current circuit is operating, the control device controls the on and off of the first switching element so that the voltage generated across the constant current circuit becomes a predetermined first target voltage, and controls the voltage applied to the second switching element based on the voltage generated across the resistor so that the current flowing through the constant current circuit becomes a predetermined value, and when power supply to the voltage conversion circuit starts from the outside, the control device starts the operation of the voltage conversion circuit and then starts the operation of the constant current circuit, and during the period from when the power supply to the voltage conversion circuit starts to when the constant current circuit starts to operate, controls the on and off of the first switching element so that the output voltage of the voltage conversion circuit becomes a predetermined second target voltage. [Effects of the Invention]

[0009] In the lighting device according to the present disclosure, during the period from when the supply of power to the voltage conversion circuit starts until the constant current circuit starts operating, the on / off of the first switching element is controlled so that the output voltage of the voltage conversion circuit becomes a predetermined second target voltage, thereby suppressing flashing of the light source. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a circuit block diagram of a lighting device according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing operational waveforms at the time of startup according to a comparative example. [Figure 3] FIG. 4 is a diagram showing operational waveforms at the time of startup according to the first embodiment. [Figure 4] 5 is a diagram illustrating the responsiveness of the phase compensation circuit according to the first embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] A lighting device and an illumination device according to the present embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0012] Embodiment 1 1 is a circuit block diagram of a lighting device 100 according to embodiment 1. The lighting device 100 includes an LED module 11 having a plurality of LEDs, a lighting device 12, an external device 61, and a dimming interface (I / F) circuit 62. The LED module 11 corresponds to a light source. The lighting device 12 includes an input filter circuit 1, a voltage conversion circuit 3, a constant current circuit 4, and a control device 50.

[0013] The input filter circuit 1 includes a fuse 25 for overcurrent protection, an AC capacitor 26, and a diode bridge 27 for converting AC to DC. The output of the diode bridge 27 is connected to the voltage conversion circuit 3. The low potential side of the output of the diode bridge 27 is connected to a ground terminal.

[0014] The voltage conversion circuit 3 receives power from an external source and supplies power to both ends of a series circuit formed by the LED module 11 and the constant current circuit 4 by turning on and off the switching element 15. In the voltage conversion circuit 3, a capacitor 10 is connected in parallel with the output of the diode bridge 27 to perform full-wave rectification of the external AC power source and reduce ripple caused by switching. The positive electrode of the capacitor 10 is connected to a control power generation circuit 19 and one end of the primary side of the transformer 14. The other end of the primary side of the transformer 14 is connected in series to a first terminal of the switching element 15. The second terminal of the switching element 15 is connected to the negative electrode of the capacitor 10. The control terminal of the switching element 15 is connected to a control device 50. The control terminal is a terminal for switching between the first terminal and the second terminal. The control device 50 controls the voltage conversion circuit 3.

[0015] The switching element 15 is, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). When the switching element 15 is a MOSFET, the first terminal is a drain terminal, the second terminal is a source terminal, and the control terminal is a gate terminal. In the switching element 15, the first terminal is connected to the transformer 14, the second terminal is connected to a ground terminal, and the control terminal is connected to the control device 50.

[0016] The control device 50 is composed of components including, for example, a microcomputer. The control device 50 includes, for example, an arithmetic circuit such as a CPU (central processing unit) 51 that performs various calculations, a memory 52, and a timer 53. The control device 50 may have multiple arithmetic circuits and multiple memories. The arithmetic circuit performs various calculations to realize the functions of the lighting device 100. The memory 52 is composed of, for example, a non-volatile memory. A program to be executed by the arithmetic circuit is stored in the memory 52. ​​For example, a program to realize the PFC operation of the voltage conversion circuit 3 is written in the memory 52. ​​The control device 50 also drives the switching element 15.

[0017] Various microcomputers are already known as digital power supply control devices, and any of these known microcomputers can be used appropriately for the control device 50. It can also be configured with an arithmetic device such as a DSP (Digital Signal Processor).

[0018] An anode of a diode 20 is connected to one end of the flyback winding on the secondary side of the transformer 14. The diode 20 is connected in series with the secondary side of the transformer 14 and is provided to transmit a stable voltage to the output side. The cathode of the diode 20 is connected to the positive electrode of an electrolytic capacitor 21. The negative electrode of the electrolytic capacitor 21 is connected to a ground terminal.

[0019] The voltage conversion circuit 3 includes an input voltage detection unit. The input voltage detection unit is composed of resistors 16 and 17 connected in series. The input voltage detection unit is connected in parallel with the capacitor 10. The voltage division value of resistors 16 and 17 is input to the control device 50. As a result, the control device 50 detects the input voltage of the voltage conversion circuit 3.

[0020] The voltage conversion circuit 3 includes an output voltage detection unit. The output voltage detection unit is composed of resistors 22 and 23 connected in series. The output voltage detection unit is connected in parallel with the electrolytic capacitor 21. The voltage division value of resistors 22 and 23 is input to the control device 50. As a result, the control device 50 detects the output voltage of the voltage conversion circuit 3.

[0021] The voltage conversion circuit 3 includes a terminal voltage detection unit that detects the voltage across the constant current circuit 4. The terminal voltage detection unit is composed of resistors 31 and 32 connected in series. The terminal voltage detection unit is connected in parallel with the constant current circuit 4. The voltage division value of resistors 31 and 32 is input to the control device 50. This enables the control device 50 to detect the terminal voltage, which is the voltage across the constant current circuit 4.

[0022] The control device 50 compares the inter-terminal voltage generated across the constant current circuit 4 with a predetermined first target voltage, and controls the on / off of the switching element 15 so that the inter-terminal voltage becomes the first target voltage. As described above, constant voltage feedback control is realized by the voltage conversion circuit 3, which is a flyback circuit.

[0023] The constant current circuit 4 is connected in series with the LED module 11. The constant current circuit 4 has a resistor 43 connected in series with the LED module 11, a switching element 41 connected in series with the resistor 43, and a comparator 42. The switching element 41 is, for example, a MOSFET. When the switching element 41 is a MOSFET, the first terminal is a drain terminal, the second terminal is a source terminal, and the control terminal is a gate terminal. In the switching element 41, the first terminal is connected to the LED module 11, the second terminal is connected to the resistor 43, and the control terminal is connected to the comparator 42.

[0024] Comparator 42 changes the voltage applied to switching element 41 so that the voltage generated across resistor 43 matches the specified voltage preset and output by control device 50. In other words, comparator 42 controls the voltage applied to switching element 41 based on the voltage generated across resistor 43 so that the current flowing through constant current circuit 4 becomes a predetermined value. This changes the impedance of switching element 41, and the current flowing through resistor 43 becomes constant. Constant current circuit 4 achieves a constant current by utilizing the active region of switching element 41. As described above, constant current feedback control is achieved by constant current circuit 4, which is a regulator circuit.

[0025] In this way, while the constant current circuit 4 is operating, the control device 50 performs constant voltage feedback control, which controls the on / off of the switching element 15 so that the inter-terminal voltage generated across the constant current circuit 4 becomes the first target voltage. In addition to this constant voltage feedback control, the control device 50 also performs constant current feedback control, which controls the voltage applied to the switching element 41 based on the voltage generated across the resistor 43 so that the current flowing through the constant current circuit 4 becomes a predetermined value. The first target voltage and program for the constant voltage feedback control, and the specified voltage and program for the constant current feedback control are stored in the memory 52.

[0026] Next, the operation at startup will be described. Fig. 2 shows the operating waveforms at startup according to the comparative example. In Figs. 2 and 3, the output voltage corresponds to the voltage across voltage conversion circuit 3, that is, the voltage detected across resistors 22 and 23. The voltage between terminals corresponds to the voltage across constant current circuit 4.

[0027] In the lighting device according to the comparative example, when the application of commercial power supply voltage begins at startup, the voltage conversion circuit 3 starts operating, followed by the constant current circuit 4. When the constant current circuit 4 is stopped, the switching element 41 is in an open state. Furthermore, since resistors 31 and 32 are connected to the constant current circuit 4, the voltage between the terminals is in a pulled-down state.

[0028] Immediately after the commercial power supply voltage is applied, the constant current circuit 4 is stopped. Furthermore, the voltage conversion circuit 3 starts switching operation so that the voltage between the terminals of the constant current circuit 4 becomes the first target value set in advance, as in the constant voltage feedback control described above. This causes the output voltage of the voltage conversion circuit 3 to increase. When the output voltage of the voltage conversion circuit 3 increases, a voltage is applied to the constant current circuit 4. The voltage between the terminals of the constant current circuit 4 increases depending on the characteristics of the LED module 11 and resistors 31 and 32.

[0029] When the voltage across the terminals of the constant current circuit 4 exceeds the first target voltage, the voltage conversion circuit 3 attempts to reduce the output voltage. However, while the constant current circuit 4 is stopped, the voltage across the terminals is rising depending on the characteristics of the LED module 11 and resistors 31 and 32, making it difficult to reduce the output voltage. For this reason, the voltage conversion circuit 3 attempts to further reduce the output voltage.

[0030] Next, the constant current circuit 4 starts operating. The timer 53 may count the timing at which the constant current circuit 4 starts operating. The responsiveness of the constant current circuit 4 is set to be sufficiently faster than the responsiveness of the voltage conversion circuit 3. As a result, the load on the voltage conversion circuit 3 increases suddenly. This causes the switching element 15 of the voltage conversion circuit 3 to suddenly increase its on-time. At this time, the constant current circuit 4 has low impedance, and the output voltage of the voltage conversion circuit 3 increases, so the current flowing through the LED module 11 temporarily increases. This may cause the LED module 11 to appear to be flashing to the user.

[0031] 3 is a diagram showing operational waveforms at startup according to the first embodiment. In this embodiment, when power supply to the voltage conversion circuit 3 starts from the outside, the control device 50 starts the operation of the voltage conversion circuit 3 and then starts the operation of the constant current circuit 4, similar to the comparative example. In this embodiment, during the period from when the supply of power to the voltage conversion circuit 3 starts to when the constant current circuit 4 starts to operate, the control device 50 controls the on / off of the switching element 15 so that the output voltage, which is the voltage across the voltage conversion circuit 3, becomes a predetermined second target voltage.

[0032] That is, immediately after the commercial power supply voltage is applied, the voltage conversion circuit 3 starts a switching operation so that the output voltage of the voltage conversion circuit 3 becomes the preset second target voltage, thereby increasing the output voltage of the voltage conversion circuit 3.

[0033] To light the LED module 11 smoothly, it is necessary to minimize the voltage change immediately after lighting. For this reason, it is preferable to set the second target voltage to a large value. However, if the second target voltage is too large, the LED module 11 may start lighting or dim lighting at an unintended timing. For this reason, it is preferable to set the second target voltage so as to maintain the LED module 11 in an off state. The second target voltage is set, for example, to the maximum voltage value that allows the LED module 11 to remain off. The second target voltage and a program for control at startup are stored in memory 52.

[0034] When the output voltage of the voltage conversion circuit 3 increases, a voltage is applied to the constant current circuit 4. The voltage across the terminals of the constant current circuit 4 increases depending on the characteristics of the LED module 11 and the resistors 31 and 32. At this time, the second target voltage is set to the maximum voltage value at which the LED module 11 can remain off, so the voltage conversion circuit 3 further increases the output voltage.

[0035] Next, the constant current circuit 4 starts operating. The response speed of the feedback control of the constant current circuit 4 is faster than the response speed of the feedback control of the voltage conversion circuit 3. In other words, the response of the constant current circuit 4 is set to be sufficiently faster than the response of the voltage conversion circuit 3. As a result, the load on the voltage conversion circuit 3 increases suddenly. However, because the output voltage of the voltage conversion circuit 3 is controlled to be the second target voltage, flashing of the LED module 11 can be suppressed.

[0036] In particular, by setting the output voltage of the voltage conversion circuit 3 to the maximum voltage value at which the LED module 11 can remain off, fluctuations in the output voltage at the time of startup of the constant current circuit 4 can be further suppressed, thereby making it possible to suppress flashing. This embodiment can also be realized by modifying the program of the control device 50, and a high-quality lighting device 100 can be obtained at low cost.

[0037] When the constant current circuit 4 starts operating, the control device 50 switches from control based on the second target voltage to control based on the first target voltage. That is, the control device 50 performs constant voltage feedback control so that the voltage between the terminals of the constant current circuit 4 becomes the first target voltage, and also performs constant current feedback control based on the voltage generated across the resistor 43. After the supply of power to the voltage conversion circuit 3 has started, the control device 50 may switch from control based on the second target voltage to control based on the first target voltage when starting the operation of the constant current circuit 4.

[0038] FIG. 4 is a diagram showing the responsiveness of the phase compensation circuit according to the first embodiment. FIG. 4 is also called a Bode diagram. A Bode diagram is a graph showing the frequency characteristics of a transfer function, with the vertical axis on the left representing gain and the vertical axis on the right representing phase. By increasing the gain starting from low frequencies, the response can be made faster. However, if the response is made too fast, there is a problem that the phase margin disappears and the circuit oscillates. For this reason, it is necessary to ensure the phase even at low frequencies.

[0039] In lighting devices, power factor correction is often performed by operating the voltage conversion circuit 3 in PFC mode. To perform PFC operation, the response of the voltage conversion circuit 3 must be sufficiently slow. On the other hand, if the response is not fast enough at startup, it will take a long time to reach the target value, which could lead to startup delays.

[0040] Therefore, when the voltage conversion circuit 3 starts operating and is operating using the second target voltage, it is advisable to set the constants of the phase compensation circuit so that the first gain and first phase are as shown by the dashed lines. Also, when the constant current circuit 4 starts operating and is operating using the first target voltage, it is advisable to set the constants of the phase compensation circuit so that the second gain and second phase are as shown by the solid lines. This makes it possible to perform PFC operation to improve the power factor while preventing delays in startup time.

[0041] The technical features described in this embodiment may be used in appropriate combination.

[0042] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) a constant current circuit connected in series with the light source; a voltage conversion circuit that receives power from an external source and supplies power to both ends of a series circuit formed by the light source and the constant current circuit by turning on and off a first switching element; a control device that controls the voltage conversion circuit; Equipped with The constant current circuit is a resistor connected in series with the light source; a second switching element connected in series with the resistor; and When the constant current circuit is operating, the control device controlling the on / off of the first switching element so that a voltage generated across the constant current circuit becomes a predetermined first target voltage; controlling a voltage applied to the second switching element based on a voltage generated across the resistor so that a current flowing through the constant current circuit becomes a predetermined value; When power supply from an external source to the voltage conversion circuit is started, the control device starting the operation of the voltage conversion circuit and then starting the operation of the constant current circuit; A lighting device characterized by controlling the on / off of the first switching element so that the output voltage of the voltage conversion circuit becomes a predetermined second target voltage during the period from when the supply of power to the voltage conversion circuit begins to when the constant current circuit begins to operate. (Appendix 2) 2. The lighting device according to claim 1, wherein a response speed of the feedback control of the constant current circuit is faster than a response speed of the feedback control of the voltage conversion circuit. (Appendix 3) 3. The lighting device according to claim 1, wherein the second target voltage is set to maintain the light source in an off state. (Appendix 4) The lighting device described in any one of Supplementary Note 1 to Supplementary Note 3, characterized in that the control device switches from control based on the second target voltage to control based on the first target voltage when starting operation of the constant current circuit after the supply of power to the voltage conversion circuit has started. (Appendix 5) A lighting device according to any one of Supplementary Note 1 to Supplementary Note 4; the light source; A lighting device comprising: [Explanation of symbols]

[0043] 1 input filter circuit, 3 voltage conversion circuit, 4 constant current circuit, 10 capacitor, 11 LED module, 12 lighting device, 14 transformer, 15 switching element, 16 resistor, 17 resistor, 19 control power generation circuit, 20 diode, 21 electrolytic capacitor, 22 resistor, 23 resistor, 25 fuse, 26 capacitor, 27 diode bridge, 31 resistor, 32 resistor, 41 switching element, 42 comparator, 43 resistor, 50 control device, 52 memory, 53 timer, 61 external device, 62 dimming interface circuit, 100 lighting device, AC external power supply

Claims

1. a constant current circuit connected in series with the light source; a voltage conversion circuit that receives power from an external source and supplies power to both ends of a series circuit formed by the light source and the constant current circuit by turning on and off a first switching element; a control device that controls the voltage conversion circuit; Equipped with The constant current circuit is a resistor connected in series with the light source; a second switching element connected in series with the resistor; and When the constant current circuit is operating, the control device controlling the on / off of the first switching element so that a voltage generated across the constant current circuit becomes a predetermined first target voltage; a voltage applied to the second switching element is controlled based on the voltage generated across the resistor so that the current flowing through the constant current circuit is at a predetermined value; When power supply from an external source to the voltage conversion circuit is started, the control device starting the operation of the voltage conversion circuit and then starting the operation of the constant current circuit; A lighting device characterized by controlling the on / off of the first switching element so that the output voltage of the voltage conversion circuit becomes a predetermined second target voltage during the period from when the supply of power to the voltage conversion circuit begins to when the constant current circuit begins to operate.

2. 2. The lighting device according to claim 1, wherein a response speed of the feedback control of the constant current circuit is faster than a response speed of the feedback control of the voltage conversion circuit.

3. 3. The lighting device according to claim 1, wherein the second target voltage is set so as to maintain the light source in an off state.

4. The lighting device described in claim 1 or claim 2, characterized in that the control device switches from control based on the second target voltage to control based on the first target voltage when starting operation of the constant current circuit after the supply of power to the voltage conversion circuit has started.

5. The lighting device according to claim 1 or 2; the light source; A lighting device comprising:

Images