JP6954201B2 - Lighting device - Google Patents

Description

An embodiment of the present invention relates to a lighting device.

There is a lighting device that supplies a direct current to a lamp having a light source such as an LED (Light Emitting Diode) to light the lamp. It is known that such a lighting device is provided with a constant current circuit and a dimming circuit (for example, Patent Document 1).

The constant current circuit has an inductor and a switching element, and the direct current supplied to the lamp is made constant by switching the switching element. The dimming circuit has a switching element, and dims the light emitted from the lamp by periodically switching the supply and stop of the supply of the direct current to the lamp by switching the switching element. As a result, the lamp can be turned on so as to be substantially constant at a desired brightness.

However, the direct current output from the constant current circuit fluctuates slightly with the switching of the switching element. Therefore, for example, when continuous shooting is performed by a shooting device such as a high-speed camera, the brightness may be different for each of a plurality of consecutive shot images. For example, there is a possibility that the moving image will be observed as flickering. In particular, if the magnitude of the direct current changes depending on the timing of supply on the lower limit of dimming, the ratio of the change in the amount of received light (integrated value of the amount of light) to the exposure time becomes large, and a plurality of continuous shots are taken. There is a possibility that the change in brightness for each image will be large. For example, flicker in a moving image may become noticeable.

Therefore, even when the lighting device has a constant current circuit and a dimming circuit, it is desired to be able to suppress a change in the brightness of a plurality of captured images continuously captured by the photographing device.

JP-A-2017-59500

An embodiment of the present invention provides a lighting device capable of suppressing a change in brightness of a plurality of captured images continuously captured by a photographing device even when having a constant current circuit and a dimming circuit.

According to the embodiment of the present invention, in a lighting device for lighting the lamp by supplying a direct current to the lamp, a third is controlled of an output unit connected to the lamp, an inductor, and a current flowing through the inductor. A second switching connected in parallel to the lamp and a constant current circuit having one switching element and controlling so that the current value of the direct current becomes constant by switching of the first switching element. A dimming circuit having an element and switching the second switching element according to a dimming signal input from the outside to control dimming of the light emitted from the lamp, and the first switching element. By controlling the timing at which the second switching element is brought into the conductive state according to the timing at which the second switching element is brought into the conductive state, the control timing between the first switching element and the second switching element is controlled to be synchronized. A lighting device comprising a control circuit is provided.

According to the embodiment of the present invention, even when a constant current circuit and a dimming circuit are provided, a lighting device capable of suppressing a change in brightness of a plurality of captured images continuously captured by the photographing device is provided. Can be done.

It is a block diagram which shows typically the lighting device which concerns on embodiment. 2 (a) to 2 (d) are graphs schematically showing an example of the operation of the lighting device according to the embodiment. 3 (a) to 3 (d) are graphs schematically showing a reference operation of the lighting device. 4 (a) to 4 (d) are graphs schematically showing a reference operation of the lighting device. It is a block diagram which shows typically the modification of the lighting apparatus which concerns on embodiment.

Hereinafter, each embodiment will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between the parts, and the like are not necessarily the same as the actual ones. Further, even when the same parts are represented, the dimensions and ratios may be different from each other depending on the drawings.
In addition, in the present specification and each figure, the same elements as those described above with respect to the above-mentioned figures are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a block diagram schematically showing a lighting device according to an embodiment.
As shown in FIG. 1, the lighting device 10 includes an output unit 12, a constant current circuit 14, a dimming circuit 16, and a control unit 18.

The lighting device 10 is electrically connected to, for example, the AC power supply 2. AC power is supplied to the lighting device 10 from the AC power supply 2. The AC power supply 2 is, for example, a commercial power supply. The AC power source 2 may be, for example, a private power generator. The electric power supplied to the lighting device 10 is not limited to AC electric power, but may be DC electric power or the like. Further, in the specification of the present application, "electrically connected" includes not only the case where the connection is made by direct contact but also the case where the connection is made via another conductive member or the like.

The lighting device 10 is electrically connected to the lamp 4. The lighting device 10 converts the AC power supplied from the AC power supply 2 into DC power corresponding to the lamp 4 and supplies the DC current to the lamp 4. As a result, the lighting device 10 lights the lamp 4. The control unit 18 comprehensively controls each unit of the lighting device 10. In other words, the control unit 18 controls the lighting and extinguishing of the lamp 4.

The lamp 4 includes a light source 5. The lamp 4 includes, for example, a plurality of light sources 5. Each light source 5 is connected in series, for example. Each light source 5 may be a combination of, for example, a series connection and a parallel connection. The number of light sources 5 may be arbitrary. The number of light sources 5 may be, for example, one.

For the light source 5, for example, a light emitting diode (LED) is used. The light source 5 may be, for example, an organic light emitting diode (OLED), an inorganic electroluminescent light emitting element, an organic electroluminescent light emitting element, or another electroluminescent light emitting element. good. The light source 5 may be, for example, a light bulb. Hereinafter, the light source 5 will be described as an LED.

The output unit 12 is used for electrical connection with the lamp 4. The output unit 12 has a first terminal 12a connected to the high-voltage side terminal 4a of the lamp 4 and a second terminal 12b connected to the low-voltage side terminal 4b of the lamp 4. In other words, the terminal 4a on the high voltage side of the lamp 4 is the anode of the light source 5 which is an LED. In other words, the terminal 4b on the low voltage side of the lamp 4 is the cathode of the light source 5 which is an LED. The lamp 4 is detachably connected to the lighting device 10 via the output unit 12. The lighting device 10 is not limited to this, and may be directly connected to the lamp 4 by wiring or the like.

The lighting device 10 further includes, for example, a filter circuit 20, a rectifier circuit 22, a power factor improving circuit 24, a detection unit 26, and the like.

The filter circuit 20 is electrically connected to the AC power supply 2. The filter circuit 20 suppresses noise included in the AC power supplied from the AC power supply 2, for example.

The rectifier circuit 22 is electrically connected to the filter circuit 20. The rectifier circuit 22 rectifies the AC voltage input via the filter circuit 20 and converts it into a rectified voltage. For the rectifier circuit 22, for example, a diode bridge in which four rectifier elements are combined is used. That is, the rectifier circuit 22 is a full-wave rectifier. The rectified voltage is, for example, a pulsating voltage.

The rectifier circuit 22 has a pair of input terminals 22a and 22b, a high potential output terminal 22c, and a low potential output terminal 22d. The input terminals 22a and 22b are electrically connected to the filter circuit 20. The rectifier circuit 22 converts the AC voltage input via the input terminals 22a and 22b into a rectifier voltage, and outputs the AC voltage from the high potential output terminal 22c and the low potential output terminal 22d. The potential of the low potential output terminal 22d is set to a reference potential (for example, a ground potential). The potential of the high potential output terminal 22c is set to a higher potential than the potential of the low potential output terminal 22d.

The rectifier circuit 22 may be a half-wave rectifier or the like. The rectified voltage may be a full-wave rectified pulsating current or a half-wave rectified pulsating current. For the rectifier circuit 22, for example, a Schottky barrier diode is used. Thereby, for example, good responsiveness can be obtained.

The power factor improving circuit 24 is electrically connected to the output side of the rectifier circuit 22. The power factor improving circuit 24 suppresses the generation of harmonics that are integral multiples of the power supply frequency in the rectified voltage. As a result, the power factor improving circuit 24 improves the power factor of the rectified voltage.

The power factor improving circuit 24 includes, for example, a switching element 30, an inductor 31, a diode 32, and a smoothing capacitor 33. The switching element 30 has electrodes 30a to 30c. One end of the inductor 31 is electrically connected to the high potential output terminal 22c. The other end of the inductor 31 is electrically connected to the electrode 30a. The electrode 30b is electrically connected to the low potential output terminal 22d. The anode of the diode 32 is electrically connected to the electrode 30a. The cathode of the diode 32 is electrically connected to one end of the smoothing capacitor 33. The other end of the smoothing capacitor 33 is electrically connected to the low potential output terminal 22d. That is, in this example, the power factor improving circuit 24 is a boost chopper circuit. The power factor improving circuit 24 is not limited to this, and may be any circuit capable of improving the power factor of the rectified voltage.

The electrode 30c is electrically connected to the control unit 18. The electrode 30c is a so-called control electrode. The switching element 30 switches according to a signal from the control unit 18. The power factor improving circuit 24 improves the power factor by switching the switching element 30 and bringing the input current closer to a sine wave, for example.

The switching element 30 is, for example, an n-channel type FET. For example, the electrode 30a is a drain, the electrode 30b is a source, and the electrode 30c is a gate. The switching element 30 may be, for example, a p-channel type FET, a bipolar transistor, or the like.

The smoothing capacitor 33 converts the pulsating voltage into a DC voltage by smoothing the pulsating voltage after the power factor is improved.

For example, when the electric power supplied to the lighting device 10 is DC electric power, the filter circuit 20, the rectifier circuit 22, and the power factor improving circuit 24 may be omitted. As described above, the filter circuit 20, the rectifier circuit 22, and the power factor improving circuit 24 are provided as necessary and can be omitted.

The constant current circuit 14 controls the output current so that the direct current supplied to the lamp 4 connected to the output unit 12 becomes constant. The constant current circuit 14 has a pair of input terminals 14a and 14b and a pair of output terminals 14c and 14d. The input terminal 14a on the high potential side is electrically connected to one end on the high potential side of the smoothing capacitor 33. The input terminal 14b on the low potential side is electrically connected to the low potential output terminal 22d. That is, in the constant current circuit 14, DC power is supplied to the pair of input terminals 14a and 14b. The output terminal 14c is electrically connected to the first terminal 12a of the output unit 12. The output terminal 14d is electrically connected to the second terminal 12b of the output unit 12. As a result, the current output from the constant current circuit 14 is supplied to the lamp 4.

The constant current circuit 14 includes, for example, a switching element 40 (first switching element), an inductor 41, and a diode 42. The switching element 40 has electrodes 40a to 40c. The electrode 40a is electrically connected to the input terminal 14a. The electrode 40b is connected to one end of the inductor 41. The other end of the inductor 41 is electrically connected to the output terminal 14c on the high potential side. The cathode of the diode 42 is electrically connected to the electrode 40b of the switching element 40. The anode of the diode 42 is electrically connected to the input terminal 14b and the output terminal 14d on the low potential side.

The electrode 40c is electrically connected to the control unit 18. The switching element 40 switches according to a signal from the control unit 18. The switching element 40 controls the current flowing through the inductor 41. The constant current circuit 14 controls so that the direct current supplied to the lamp 4 becomes constant by switching the switching element 40.

Further, in this example, the constant current circuit 14 is a so-called step-down chopper circuit. The constant current circuit 14 steps down the voltage value of the DC voltage boosted by the power factor improving circuit 24 to a voltage value corresponding to the lamp 4. The configuration of the constant current circuit 14 is not limited to the above, and may be any configuration capable of supplying a substantially constant current to the lamp 4. The constant current circuit 14 may be a current type converter having at least a switching element 40 and an inductor 41.

The dimming circuit 16 has a switching element 44 (second switching element) connected in parallel with the lamp 4. The switching element 44 has electrodes 44a to 44c. As the switching element 40 of the constant current circuit 14 and the switching element 44 of the dimming circuit 16, for example, a semiconductor element (semiconductor switching element) containing at least one of silicon, gallium nitride, and gallium oxide is used. More specifically, transistors, MOSFETs, IGBTs using silicon, GaN-HEMT using gallium nitride, and the like are used.

The electrode 44a is electrically connected to the output terminal 14c of the constant current circuit 14. The electrode 44b is electrically connected to the output terminal 14d of the constant current circuit 14. As a result, the switching element 44 is connected in parallel with the lamp 4. The electrode 44c is electrically connected to the control unit 18. The switching element 44 switches in response to a signal from the control unit 18.

The dimming circuit 16 and the control unit 18 switch between a conductive state and a non-conducting state of the switching element 44 according to a dimming signal input from the outside, and periodically stop supplying and stopping the supply of direct current to the lamp 4. By switching, the dimming control of the light emitted from the lamp 4 is performed. Therefore, in the lighting device 10, a charge storage element (for example, a capacitor) having a relatively large capacity for smoothing the voltage is not provided on the lamp 4 side (output side) of the dimming circuit 16. As a result, for example, it is possible to prevent the rising and falling edges of the DC voltage (DC current) that changes in a pulse shape from being delayed, resulting in an undesired dimming degree.

In the dimming circuit 16, a direct current can be supplied to the lamp 4 by making the switching element 44 connected in parallel with the lamp 4 in a non-conducting state. On the other hand, when the switching element 44 is brought into a conductive state, the current flows through the switching element 44, so that the supply of the direct current to the lamp 4 side is stopped.

The detection unit 26 is provided on the downstream side of the lamp 4 and the switching element 44, and detects the current value of the direct current flowing through the lamp 4 when the switching element 44 is in a non-conducting state and a direct current flows through the lamp 4. When the switching element 44 becomes conductive and the supply of the direct current to the lamp 4 is stopped, the current value of the direct current flowing through the switching element 44 is detected. The detection unit 26 is electrically connected to the control unit 18 and inputs the detection result to the control unit 18.

The detection unit 26 is provided, for example, between the connection point of the low-voltage side terminal 4b of the lamp 4 and the electrode 44b of the switching element 44 and the low-potential output terminal 22d. The detection unit 26 is, for example, a detection resistor for detecting the current value of a direct current. The detection unit 26 may be, for example, a clamp-type ammeter that measures changes in magnetic flux or the like. The detection unit 26 may be configured to detect the voltage of the lamp 4 and the voltage of the switching element 44. The detection unit 26 may be configured to detect both current and voltage.

The control unit 18 includes a control circuit 50, a comparator 52, a resistance element 54, a rectifying element 56, a comparator 58, and a driver 60. The control circuit 50 includes, for example, at least one of a microcomputer, a dedicated control IC (Integrated Circuit), and an FPGA (Field-Programmable Gate Array). The control circuit 50 may be configured by one element or may be configured by combining a plurality of elements.

The driver 60 controls the operation of the power factor improving circuit 24. The driver 60 is electrically connected to the electrode 30c of the switching element 30 and switches the switching element 30 to control the operation of the power factor improving circuit 24.

The non-inverting input terminal of the comparator 52 is electrically connected to the detection unit 26. The detection result of the detection unit 26 is input to the non-inverting input terminal of the comparator 52. On the other hand, a first reference voltage REF1 is set at the inverting input terminal of the comparator 52. As a result, the output of the comparator 52 becomes low when the current flowing through the lamp 4 or the switching element 44 is less than a predetermined value, and the output of the comparator 52 when the current flowing through the lamp 4 or the switching element 44 is equal to or more than a predetermined value. Becomes high.

The output terminal of the comparator 52 is electrically connected to the inverting input terminal of the comparator 58 via a resistance element 54 and a rectifying element 56. A second reference voltage REF2 is set at the non-inverting input terminal of the comparator 52. As a result, when the output of the comparator 52 is low, the output of the comparator 58 becomes high, and when the output of the comparator 52 is high, the output of the comparator 58 becomes low.

The output terminal of the comparator 58 is electrically connected to the electrode 40c of the switching element 40. Therefore, when the output of the comparator 58 is low, the switching element 40 is in a non-conducting state, and when the output of the comparator 58 is high, the switching element 40 is in a conductive state. That is, when the current flowing through the lamp 4 or the switching element 44 is less than a predetermined value, the control unit 18 sets the output of the comparator 52 to low and the output of the comparator 58 to high, puts the switching element 40 in a conductive state, and sets the lamp 4 or When the current flowing through the switching element 44 is equal to or greater than a predetermined value, the output of the comparator 52 is set to high, the output of the comparator 58 is set to low, and the switching element 40 is put into a non-conducting state.

Further, the inverting input terminal of the comparator 58 is electrically connected to the control circuit 50. The control circuit 50 inputs a pulse signal that periodically repeats high and low to the inverting input terminal of the comparator 58.

During the low period of the pulse signal, the output of the comparator 58 becomes high, the switching element 40 becomes conductive, current is supplied to the inductor 41, and during the high period of the pulse signal, the output of the comparator 58 becomes low. As a result, the switching element 40 becomes non-conducting, and the supply of current to the inductor 41 is stopped. Further, when the current flowing through the lamp 4 or the switching element 44 becomes a predetermined value or more during the low period of the pulse signal, the switching element 40 becomes non-conducting as described above, and the supply of the current to the inductor 41 is stopped. NS. As a result, the current flowing through the lamp 4 or the switching element 44 is controlled to be constant.

In this way, the control circuit 50 controls only the switching of the switching element 40 regardless of the switching of the switching element 44 and the detection result of the detection unit 26. The control circuit 50 only performs control for periodically switching between the conductive state and the non-conducting state of the switching element 40.

Further, the control circuit 50 is electrically connected to the electrode 44c of the switching element 44. The control circuit 50 controls the operation of the dimming circuit 16 by switching the switching element 44.

The control unit 18 is electrically connected to the communication control device 6. The communication control device 6 is communicably connected to the external device 8 via a network or the like. The communication control device 6 is capable of mutual communication with, for example, an external device 8. The communication control device 6 receives a dimming signal from the external device 8. The communication control device 6 may be configured to enable only reception of a dimming signal from, for example, an external device 8.

The control unit 18 can communicate with the communication control device 6, for example. The control unit 18 receives a dimming signal from the communication control device 6. The control unit 18 may be configured to only receive a dimming signal from the communication control device 6. Further, the dimming signal may be input to the control unit 18 from an operation unit such as a dial or a slide switch provided in the lighting device 10, for example.

The control unit 18 inputs the received dimming signal to the control circuit 50. The control circuit 50 controls the dimming of the dimming circuit 16 by switching the switching element 44 based on the dimming signal. As a result, the lamp 4 can be turned on with a desired brightness according to the dimming degree of the dimming signal.

The dimming control performed by the control circuit 50 and the dimming circuit 16 includes, for example, one of a pulse width modulation method, a pulse density modulation method, and an amplitude modulation method. In the pulse width modulation method, for example, the larger the luminous intensity, the longer the period of the conduction state of the switching element 44, so that the brightness of the light emitted from the lamp 4 is dimmed. In the pulse density modulation method, for example, the greater the luminous intensity, the higher the density of the switching element 44 during the conduction state, thereby dimming the brightness of the light emitted from the lamp 4. In the amplitude modulation method, for example, the greater the dimming degree, the higher the DC voltage boosted by the power factor improving circuit 24, thereby dimming the brightness of the light emitted from the lamp 4. Hereinafter, the control circuit 50 and the dimming circuit 16 will be described as assuming that the dimming control of the pulse width modulation method is performed.

2 (a) to 2 (d) are graphs schematically showing an example of the operation of the lighting device according to the embodiment.
3 (a) to 3 (d) are graphs schematically showing a reference operation of the lighting device.
2 (a) and 3 (a) schematically show an example of the control voltage Vg1 of the electrode 40c of the switching element 40 of the constant current circuit 14.
FIG. 2 (b), the FIG. 3 (b) shows an example of a current _{I L} flowing through the inductor 41 schematically. 2 (c) and 3 (c) schematically show an example of the control voltage Vg2 of the electrode 44c of the switching element 44 of the dimming circuit 16.
2 (d) and 3 (d) schematically show an example of the _{current IV flowing through the lamp 4.}
Further, in FIGS. 2 (a) to 2 (d) and 3 (a) to 3 (d), the horizontal axis is time t.

As shown in FIGS. 2A to 2D, when dimming is performed by switching the switching element 44, the current _IV flowing through the lamp 4 becomes intermittent. For this reason, when continuous shooting is performed with a shooting device such as a high-speed camera, if the number of times the lamp 4 is lit changes after one shooting, the brightness will be increased for each of a plurality of consecutive shot images. It will be different. For example, if the lamp 4 lights up four times during the shooting of the first shot image and the lamp 4 lights up three times during the shooting of the second shot image in succession, the second shot image is one. It will be darker than the captured image of the eyes.

Therefore, the control circuit 50 sets, for example, the switching frequency of the switching element 44 of the dimming circuit 16 to an integral multiple of the photographing interval of the photographing apparatus. 2 (a) to 2 (d) illustrate a state in which the switching frequency of the switching element 44 of the dimming circuit 16 is set to four times the shooting interval of the shooting device. As a result, the number of times the lamp 4 is turned on during one shooting can be kept constant even when the shooting device continuously shoots. It is possible to prevent the brightness from being different for each of a plurality of consecutive captured images.

Alternatively, the switching frequency of the switching element 44 may be made sufficiently higher than the photographing interval of the photographing apparatus. The switching frequency of the switching element 44 may be set to, for example, an integral multiple of 10 times or more or more than 1 of the photographing interval of the photographing apparatus. As a result, the influence on the exposure of the photographing apparatus can be suppressed by shortening the lighting time of the lamp 4 once or by matching the timing of photographing and lighting. That is, when the switching frequency of the switching element 44 is set to 10 times or more the shooting interval of the shooting device, even if the number of times the lamp 4 is turned on differs in one shooting, the brightness of the shot image is increased. When the switching frequency of the switching element 44 is set to a multiple of an integer exceeding 1 with respect to the shooting interval of the shooting device, the number of lightings in one shooting can be adjusted. Therefore, the influence on the brightness of the captured image can be suppressed.

However, the shooting interval of the shooting device differs depending on the model and setting of the shooting device. Therefore, the control circuit 50 sets, for example, the switching frequency of the switching element 44 to about 15 kHz (10 kHz or more and 20 kHz or less). Thereby, for example, in shooting up to about 1000 FPS (Frames Per Second), it is possible to prevent the brightness from being different for each of a plurality of consecutive shot images.

As shown in FIG. 2 (a) ~ FIG 2 (d) and FIG. 3 (a) ~ FIG 3 (d), the current _{I L} flowing through the inductor 41 increases by the switching elements 40 in a conductive state , It is reduced by making the switching element 40 in a non-conducting state.

Therefore, as shown in the reference examples of FIGS. 3A to 3D, when dimming is performed by switching the switching element 44, the switching timing of the switching element 40 of the constant current circuit 14 and the switching timing of the switching element 40 are determined. If the switching timing (frequency) of the switching element 44 of the dimming circuit 16 does not match, the magnitude of the current flowing through the lamp 4 changes depending on the timing when the switching element 44 is made non-conducting, and the brightness of the captured image is increased. May affect. In particular, this tendency becomes stronger on the lower limit side of dimming.

Therefore, as shown in FIGS. 2A to 2D, the control circuit 50 controls the timing at which the switching element 44 is brought into the conductive state according to the timing at which the switching element 40 is brought into the conductive state. Therefore, the control timings of the switching element 40 and the switching element 44 are controlled to be synchronized. The control circuit 50, for example, sets the switching element 44 in the conductive state after an arbitrary timing from the timing in which the switching element 40 is brought into the conductive state.

As a result, it is possible to prevent variations in the magnitude of the current flowing through the lamp 4 when the switching element 44 is brought into a non-conducting state. It is possible to prevent the magnitude of the current flowing through the lamp 4 from changing depending on the timing at which the switching element 44 is brought into the non-conducting state, which affects the brightness of the captured image.

The control circuit 50 sets, for example, the switching frequency of the switching element 40 to an integral multiple of the switching frequency of the switching element 44. As a result, the switching element 40 and the switching element 44 can be synchronized as described above.

The control circuit 50 controls the switching frequencies of the switching element 40 and the switching element 44 to be constant regardless of, for example, the dimming degree set by the dimming signal. The control circuit 50 controls, for example, the switching frequency of the switching elements 40 and 44 to be constant at about 15 kHz. As a result, it is possible to support high-speed shooting while synchronizing the switching elements 40 and 44, and it is possible to appropriately suppress changes in the brightness of a plurality of continuously shot images.

As described above, even when the lighting device 10 according to the present embodiment has the constant current circuit 14 and the dimming circuit 16, it suppresses the change in the brightness of a plurality of captured images continuously captured by the photographing device. can do.

The control circuit 50 may set the switching frequency of the switching element 40 to be sufficiently higher than the switching frequency of the switching element 44. For example, the switching frequency of the switching element 40 may be an integral multiple of 10 times or more or more than 1 of the switching frequency of the switching element 44.

In this case, when the switching element 44 is set to the non-conducting state and a current is passed through the lamp 4, the switching element 40 repeats the conducting state and the non-conducting state a plurality of times. Therefore, it is possible to more reliably suppress that the magnitude of the current flowing through the lamp 4 changes depending on the timing when the switching element 44 is brought into the non-conducting state on the dimming lower limit side or the like. Further, in this case, the switching element 40 and the switching element 44 do not necessarily have to be synchronized with each other.

4 (a) to 4 (d) are graphs schematically showing a reference operation of the lighting device.
In the above embodiment, the switching frequency of the switching element 44 is set to about 15 kHz (10 kHz or more and 20 kHz or less). However, since the frequency of 20 kHz or less is in the human audible region, for example, when the switching element 44 is switched, the inductor 41 may vibrate and an abnormal noise may be generated. Therefore, from the viewpoint of suppressing the generation of abnormal noise, it is preferable that the switching frequency of the switching element 44 is higher than 20 kHz.

The control circuit 50 sets, for example, the switching frequency of the switching element 44 to about 24 kHz. As a result, it is possible to suppress the occurrence of abnormal noise while suppressing the brightness from being different for each of a plurality of consecutive captured images. For example, in shooting up to about 3000 FPS, it is possible to prevent the brightness from being different for each of a plurality of consecutive shot images.

On the other hand, the path through which the current flows through the switching element 44 consumes less energy stored in the inductor 41 than the path through which the current flows through the lamp 4. Therefore, when the switching frequency of the switching element 44 is set higher than 20 kHz, as shown in FIGS. 4A to 4D, the period of the non-conducting state of the switching element 40 is on the dimming lower limit side. In, there is a possibility that the energy stored in the inductor 41 will not be properly consumed.

In this way, when the energy stored in the inductor 41 is not properly consumed, the current flowing through the lamp 4 or the switching element 44 (inductor 41) immediately reaches during the period of the conduction state of the next switching element 40. Will reach the specified value. Therefore, even if the switching element 40 and the switching element 44 are synchronized, the magnitude of the current flowing through the lamp 4 varies, which affects the brightness of a plurality of continuously captured images. Possibility arises.

Therefore, for example, when the switching frequency of the switching element 44 is made higher than 20 kHz, the control circuit 50 is at least the switching element 40 and the switching when the dimming degree set by the dimming signal is equal to or less than a predetermined value. The switching frequency of the element 44 is lowered. The control circuit 50 sets the switching frequency of the switching element 40 and the switching element 44 to 20 kHz or less (for example, about 15 kHz) when the dimming degree set by the dimming signal is, for example, a predetermined value or less.

As a result, when the dimming degree is higher than the predetermined value, the switching frequency of the switching elements 40 and 44 is increased, and the brightness is appropriately suppressed from being different for each of a plurality of consecutive captured images. The generation of abnormal noise can also be suppressed. When the dimming degree is equal to or less than a predetermined value, the energy stored in the inductor 41 can be appropriately consumed by lowering the switching frequency of the switching elements 40 and 44. It is possible to prevent variations in the magnitude of the current flowing through the lamp 4 from affecting the brightness of a plurality of continuously captured images.

Further, when high-speed shooting is performed with a high-speed camera or the like, there is a high possibility that the dimming degree is set high in order to obtain an appropriate exposure even at a short shutter speed. Therefore, even if the switching frequency of the switching elements 40 and 44 is lowered on the dimming lower limit side, it is considered that the influence on actual use is small. The switching frequency of the switching elements 40 and 44 may be lowered stepwise as the dimming degree decreases, or may be continuously lowered as the dimming degree decreases. good.

FIG. 5 is a block diagram schematically showing a modified example of the lighting device according to the embodiment.
Those having substantially the same functions and configurations as those of the above-described embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.
As shown in FIG. 5, in the lighting device 10a, the detection result of the detection unit 26 is input to the control circuit 50. In the lighting device 10a, the control circuit 50 is electrically connected to the detection unit 26. The control circuit 50 is directly connected to the detection unit 26 via wiring or the like, or indirectly via a switching element or the like. The detection result of the detection unit 26 may be input to the control circuit 50 from another control circuit such as a microcomputer, for example.

The control circuit 50 controls the switching of the switching element 40 of the constant current circuit 14 so that the current value of the direct current flowing through the lamp 4 or the switching element 44 becomes constant based on the detection result of the detection unit 26.

The control circuit 50 switches the switching element 40 from the non-conducting state to the conducting state when, for example, the detection value of the detection unit 26 becomes equal to or less than the lower limit value from the non-conducting state of the switching element 40. Then, for example, when the detection value of the detection unit 26 becomes equal to or higher than the upper limit value from the state in which the switching element 40 is in the conductive state, the control circuit 50 switches the switching element 40 from the conductive state to the non-conducting state. Further, the control circuit 50 controls the switching of the switching element 44 in synchronization with the switching element 40.

As a result, even when the consumption of energy stored in the inductor 41 changes according to the switching and dimming of the switching element 44, the brightness of a plurality of continuously captured images is affected. It is possible to more reliably suppress the storage. That is, the switching frequencies of the switching element 40 and the switching element 44 can be arbitrarily changed in accordance with the change in the energy consumption stored in the inductor 41. Further, it is possible to eliminate the need to provide the comparators 52, 58 and the like, reduce the number of parts in the control unit 18, and simplify the circuit configuration.

Although some embodiments and examples of the present invention have been described, these embodiments or examples are presented as examples and are not intended to limit the scope of the invention. These novel embodiments or examples can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments or examples and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

2 ... AC power supply, 4 ... Lamp, 5 ... Light source, 6 ... Communication control device, 8 ... External device, 10, 10a ... Lighting device, 12 ... Output unit, 14 ... Constant current circuit, 16 ... Dimming circuit, 18 ... Control unit, 20 ... filter circuit, 22 ... rectifier circuit, 24 ... power factor improvement circuit, 26 ... detection unit, 30 ... switching element, 31 ... inductor, 32 ... diode, 33 ... smoothing capacitor, 40 ... switching element, 41 ... Inductor, 42 ... diode, 44 ... switching element, 50 ... control circuit, 52 ... comparator, 54 ... resistance element, 56 ... rectifying element, 58 ... comparator, 60 ... driver

Claims (11)

In a lighting device that lights a lamp by supplying a direct current to the lamp.
The output unit connected to the lamp and
A constant current circuit having an inductor and a first switching element for controlling the current flowing through the inductor, and controlling the current value of the direct current to be constant by switching of the first switching element.
It has a second switching element connected in parallel to the lamp, and by switching the second switching element in response to a dimming signal input from the outside, dimming of the light emitted from the lamp. A dimming circuit for control and
By controlling the timing at which the second switching element is brought into the conductive state according to the timing at which the first switching element is brought into the conductive state, the control timing between the first switching element and the second switching element is synchronized. A control circuit that controls to make it
Lighting device equipped with. The lighting device according to claim 1, wherein the dimming control performed by the dimming circuit includes a pulse width modulation method. The lighting device according to claim 1 or 2, wherein the switching frequency of the second switching element is higher than 20 kHz. The lighting device according to claim 1 or 2, wherein the switching frequency of the second switching element is 10 kHz or more and 20 kHz or less. The lighting device according to claim 1 or 2, wherein the switching frequency of the second switching element is an integral multiple or 10 times or more of the shooting interval of the shooting device. The lighting device according to any one of claims 1 to 5, wherein the switching frequency of the first switching element is an integral multiple or 10 times or more of the switching frequency of the second switching element. The lighting device according to any one of claims 1 to 6, wherein the control circuit controls switching of the first switching element regardless of the switching of the second switching element. The control circuit according to any one of claims 1 to 7 for lowering at least the switching frequency of the first switching element and the second switching element when the dimming degree set by the dimming signal is equal to or less than a predetermined value. The lighting device according to one. The control circuit according to claim 8 sets the switching frequency of the first switching element and the second switching element to 20 kHz or less when the dimming degree set by the dimming signal is equal to or less than the predetermined value. Lighting device. The lighting device according to any one of claims 1 to 7, wherein the control circuit controls the switching frequency of the second switching element to be constant regardless of the dimming intensity set by the dimming signal. Further, a detector for detecting at least one of the direct current flowing through the lamp and the voltage of the lamp is provided.
The control circuit according to any one of claims 1 to 10, which controls switching of the first switching element so that the current value of the direct current becomes constant based on the detection result of the detection unit. Lighting device.

Images