JP4542787B2 - Lighting device - Google Patents

Description

  The present invention relates to a lighting device using LEDs.

Conventionally, a xenon tube has been mainly used for a strobe device of a photographing device such as a camera. However, since a capacitor is required to drive the xenon tube, there are problems such as occupying a predetermined space in the photographing apparatus and high voltage flows, which adversely affects other control circuits. In order to solve these problems, LEDs have begun to be used instead of xenon tubes (for example, Patent Document 1).
JP 2003-101836 A

  However, in general, the higher the ambient temperature of the LED, the lower the amount of emitted light. That is, the LED has a negative characteristic with respect to the temperature rise. Therefore, when an LED is used in a lighting device, if the ambient temperature increases as the LED is energized, the illuminance of the lighting device decreases, and a sufficient amount of light that is originally required cannot be obtained. As a result, there has been a problem that photographing cannot be performed in a good state.

  An object of the present invention is to solve the above-described problems, and an object of the present invention is to suppress accumulation of heat due to light emission of an LED and to secure a necessary light amount in an illumination device using the LED.

  An illumination device according to the present invention includes a plurality of semiconductor light emitting elements, a temperature detecting means for detecting the ambient temperature of the plurality of semiconductor light emitting elements, and driving of the plurality of semiconductor light emitting elements based on the detection result of the temperature detecting means. Drive control means for controlling the motor.

  Preferably, the plurality of semiconductor light emitting elements are divided into a first group and a second group, the temperature detection unit detects the ambient temperature of the first group, and the control unit detects the detection result of the temperature detection unit. When it is higher than the predetermined reference value, the driving of the first group is suppressed, and when the detection result is lower than the reference value, the driving of the first group is promoted, and the amount of light supplied by the first group and the second The driving of the second group is controlled so that the total amount of light supplied by the group is always maintained above a certain level.

  For example, the control unit determines the duty ratio of the first drive pulse signal that drives the first group based on the detection result of the temperature detection unit, and the phase of the second drive pulse signal that drives the second group. The duty ratio of the second drive pulse signal is determined so that is opposite in phase to the first drive pulse signal.

  Preferably, when the detection result of the temperature detection unit is higher than the reference value, the control unit reduces the duty ratio of the first drive pulse signal so that the ambient temperature of the first group is lowered, and the detection result is the above-described detection result. When the reference value is lower, the duty ratio of the first drive pulse signal is increased so that the amount of illumination light supplied by the first group is increased.

  According to this embodiment, the ambient temperature of the semiconductor light emitting element is detected, and the driving of the semiconductor light emitting element is controlled according to the result. Therefore, it is possible to maintain the light amount at a certain level or more while suppressing the temperature rise accompanying the continued driving of the semiconductor light emitting element.

  FIG. 1 is a perspective view showing a camera to which an embodiment according to the present invention is applied from the back, and FIG. 2 is a front view of the camera. An operation button 11 is provided on the back of the camera body 10. By appropriately operating the operation button 11, a shooting mode (still image mode, continuous shooting mode, moving image mode) is selected. An LCD monitor 12 is provided in the approximate center of the back surface. The state of the subject obtained by the CCD in the camera body 10 and the already taken image can be confirmed on the LCD monitor 12. A finder window 13 is formed in the vicinity of the LCD monitor 12. By looking through the finder window 13, the state of the subject can be confirmed through the optical finder in the camera body 10. A shutter button 14 is provided on the upper surface of the camera body 10. In the still image mode and the continuous shooting mode, photometry is performed by half-pressing the shutter button 14, and shooting is performed by fully pressing the shutter button 14.

  An illumination unit 15 is provided substantially at the center of the upper surface of the camera body 10. A first illumination LED 16, a second illumination LED 17, and a temperature sensor 18 are disposed in the illumination unit 15. The first and second illumination LEDs 16 and 17 are light sources for supplying illumination light to the subject. The temperature sensor 18 is disposed in the vicinity of the first illumination LED 16 and detects the ambient temperature of the first illumination LED 16. An illumination button 19 is provided on the back surface of the illumination unit 15. By operating the illumination button 19, the driving of the first and second illumination LEDs 16, 17 is started and stopped. In the present embodiment, the first illumination LED 16 and the second illumination LED 17 use the same type of LED.

  FIG. 3 is a block diagram of the camera body 10. The CPU 100 is, for example, a microprocessor that controls the entire camera body 10. The power switch SWP is controlled to be turned on / off by operating a power button (not shown) provided on the camera body 10. When the power switch SWP is turned on, power is supplied to the CPU 100.

  The metering switch SWS is turned on when the shutter button 14 (see FIGS. 1 and 2) is half-pressed. When the photometry switch SWS is turned on, the CPU 100 executes photometry processing and distance measurement processing. That is, the exposure value is calculated based on the input from the photometric device 102, and the aperture value, shutter speed, and charge accumulation time of the CCD 105 necessary for photographing are calculated based on the exposure value. Further, the driving amount of the focusing lens (not shown) is calculated based on the input from the distance measuring device 103, and a control signal is output to the focus driving circuit 106, and the driving signal from the focus driving circuit 106 to the focusing lens accordingly. Is output.

  The release switch SWR is turned on when the shutter button 14 is fully pressed. When the release switch SWR is turned on, a shutter (not shown) is driven according to the aperture value calculated by the photometric process. Further, a control signal is output to the CCD drive circuit 104 based on the charge accumulation time, and a drive signal is output from the CCD drive circuit 104 to the CCD 105. The CCD 105 photoelectrically converts the optical image of the subject formed in the light receiving area and outputs an analog image signal. The analog signal is subjected to predetermined image processing by the image processing unit 107.

  The continuous shooting switch SWC is turned on when the continuous shooting mode is selected by operating the operation button 11 (see FIG. 1). When the continuous shooting switch SWC is turned on, continuous shooting of still images is performed based on the control of the CPU 100.

  The illumination switch SWL is controlled to be turned on / off by operating the illumination button 19. When the illumination switch SWL is turned on, drive signals are appropriately output from the port P1 and the port P2 based on the control of the CPU 100. The first illumination LED 16 is connected to the port P1 of the CPU 100 via the transistor TR1. When a drive signal is output from the port P1, the transistor TR1 becomes active, the first illumination LED 16 is driven, and illumination light is emitted. Similarly, the second illumination LED 17 is connected to the port P2 of the CPU 100 via the transistor TR2. When a drive signal is output from the port P2, the transistor TR2 becomes active, the second illumination LED 17 is driven, and illumination light is emitted.

  As described above, the ambient temperature of the first illumination LED 16 is detected by the temperature sensor 18. The output result of the temperature sensor 18 is input to the CPU 100 via the A / D conversion port P3. The CPU 100 controls drive signals output from the port P1 and the port P2 based on the output result of the temperature sensor 18.

  FIG. 4 is a flowchart showing a first half of the still image shooting process in the camera body 10, and FIG. 5 is a flowchart showing a second half of the shooting process. When the power supply SWP is turned on, in step S100, the frequency of the driving pulse of the first and second illumination LEDs 16 and 17 is set to a predetermined value. When the emitted light from the first and second illumination LEDs 16 and 17 is irradiated on the subject as illumination light, a frequency that is generally regarded as a limit that does not flicker is 50 Hz (hertz). Therefore, in step S100, the frequency of the drive pulses for the first and second illumination LEDs 16 and 17 is set to 50 Hz or higher.

  In step S102, the state of the photometric switch SWS is checked. If it is confirmed that the photometric switch SWS is on, the process proceeds to step S104. In step S104, photometric processing is performed, and the aperture value, shutter speed, and charge accumulation time of the CCD 105 are calculated. Next, in step S106, a distance measurement process is performed, and a focusing operation is performed by driving the focusing lens.

  Next, in step S108, the state of the release SWR is checked. If it is confirmed that the release SWR is not turned on, the process proceeds to step S110, and the state of the photometric switch SWS is confirmed. If it is confirmed in step S110 that the photometric switch SWS is kept on, the process returns to step S108, and the release SWR check is repeated. If it is confirmed that the half-pressed state of the shutter button 14 is released and the photometric switch SWS is turned off, the process returns to step S102 and the above-described processing is repeated. On the other hand, if it is confirmed in step S108 that the release SWR is on, the process proceeds to step S112 in FIG.

  In step S112 of FIG. 5, the state of the lighting switch SWL is checked. If it is confirmed that the illumination button 19 is pressed and the illumination switch SWL is turned on, the process proceeds to step S114. In step S114, LED control timer interrupt processing is permitted. Also, the duty ratio S1 used in the PWM (Pulse Width Modulation) timer function of the CPU 100 for controlling the pulse width of the pulse signal is set to 50% (percent). The duty ratio S1 indicates the length of the lighting drive time of the first illumination LED 16 per unit time, and the larger the value, the longer the lighting drive time per unit time.

  FIG. 6 is a flowchart showing the LED control timer interrupt processing procedure. In S200, the result of A / D conversion of the output of the temperature sensor 18 is stored in the variable temp. Next, in S202, the value of the variable temp is compared with a predetermined reference value. In the present embodiment, this reference value is set based on the temperature at which the light emission amount of the first illumination LED 16 to be used decreases to about 80% of the maximum light emission amount. If it is confirmed in step S202 that the value of the variable temp is larger than the reference value, that is, the ambient temperature of the first illumination LED 16 has increased due to the continuation of driving of the first illumination LED 16, and the first illumination LED 16 If it is confirmed that a sufficient amount of light cannot be obtained as a single illumination light, the process proceeds to step S204.

  In step S204, the duty ratio S1 is decremented by “1”. That is, in order to suppress the temperature rise of the first illumination LED 16, the energization time to the first illumination LED 16 is shortened. Next, in step S206, it is checked whether the duty ratio S1 after decrement is smaller than the minimum limit value min.

  If it is confirmed in step S206 that the duty ratio S1 after decrement is lower than the minimum limit value min, the process proceeds to step S208, and the duty ratio S1 is set to the minimum limit value min. Next, the process proceeds to step S216. If it is confirmed in step S206 that the duty ratio S1 after decrement is equal to or greater than the minimum limit value min, step S208 is skipped and the process proceeds to step S216.

  On the other hand, if it is confirmed in step S202 that the value of the variable temp is equal to or less than the reference value, the process proceeds to step S210. In step S210, the duty ratio S1 is incremented by “1”. That is, in order to make effective use of the light emission capability of the LED 16, the energization time to the LED 16 is extended. Next, the process proceeds to step S212, and it is checked whether the incremented S1 exceeds “100”. If it is confirmed that the duty ratio S1 after the increment exceeds “100”, the process proceeds to step S214, where the duty ratio S1 is set to “100” and DC driving is performed. Next, the process proceeds to step S210. If it is confirmed in step S218 that the duty ratio S1 after the increment is “100” or less, step S214 is skipped and the process proceeds to step S216.

  In step S216, the PWM timer function of the CPU 100 is set to operate at the duty ratio S1. Next, in step S218, the CPU 100 generates and outputs a drive signal for the first illumination LED 16. That is, the CPU 100 generates a pulse signal having a duty ratio S1 based on the PWM timer function, converts the voltage value and current value of the pulse signal into predetermined values suitable for LED driving, and drives the first illumination LED 16. A signal is output from the port P1.

  Next, in step S <b> 220, the CPU 100 generates and outputs a drive signal for the second illumination LED 17. First, a pulse signal having a duty ratio obtained by inverting the duty ratio S1 is generated. For example, when the duty ratio S1 is 60%, a pulse signal with a duty ratio of 40% is generated, and when the duty ratio S1 is 45%, a pulse signal with a duty ratio of 55% is generated. Next, the voltage value and current value of the pulse signal are converted into predetermined values suitable for LED driving, and are output from the port P2 as driving signals for the second illumination LED 17. As a result, a drive signal having a phase opposite to that of the drive signal output from the port P1 is output from the port P2.

  The above interrupt processing is executed every 1 ms (millisecond). That is, detection of the ambient temperature of the first illumination LED 16 and pulse control of the drive signals of the first and second illumination LEDs 16 and 17 according to the detection result are performed every 1 ms.

  When the above-described timer interrupt process is permitted in step S114 of FIG. 5, the process proceeds to step S116. In step S116, the CCD 105 is driven and charge accumulation is performed. That is, photoelectric conversion processing is performed on the optical image of the subject imaged on the imaging area of the CCD 105. When the charge accumulation time calculated in step S104 has elapsed, the charge accumulation process is terminated, that is, the driving of the CCD 105 is stopped, and the process proceeds to step S118.

  When the charge accumulation of the CCD 105 is completed, it is not necessary to supply illumination light to the subject. Therefore, in step S118, the above-described LED control timer interrupt is prohibited, and in step S120, the driving of the first and second illumination LEDs 16, 17 is stopped.

  When the driving of the first and second illumination LEDs 16, 17 is stopped, the process proceeds to step S122. In step S122, predetermined image processing is performed on the image signal output from the CCD 105 in the image processing unit 107. Next, in step S124, the image signal subjected to the image processing is processed as image data for one frame. It is stored in the video memory in the unit 107. In step S126, image data is read from the video memory and displayed on the LCD 12.

  In step S128, it is checked whether the continuous shooting switch SWC is on. If it is confirmed that the continuous shooting switch SWC is on, the process returns to step S108 in FIG. 4 and the subsequent processing is repeated. That is, the process from step S108 to step S126 is performed while the continuous shooting switch SWC is turned on by the operation of the operation button 11 and the shutter button 14 is fully pressed and the release SWR is kept on. Is repeatedly executed.

  In the present embodiment, the execution of the LED control timer interruption is determined based on the state of the illumination switch SWL by the operation of the illumination button 19, but may be determined based on the photometric result in step S104. That is, if it is determined that the luminance of the subject is insufficient for photographing based on the photometric result, the LED control timer interruption may be performed.

  FIG. 7 is a graph showing drive pulses of the first and second illumination LEDs 16 and 17 and changes in ambient temperature of both LEDs accompanying the drive. At the start of driving the first and second illumination LEDs 16 and 17 (T1), the duty ratio S1 of the first illumination LED 16 is set to “50”. The ambient temperature of the first and second illumination LEDs 16 and 17 at the start of driving is lower than the reference value. Accordingly, since the first illumination LED 16 has sufficient capacity, the duty ratio S1 gradually increases due to the above-described LED control timer interruption processing. Accordingly, the ambient temperature of the first illumination LED 16 increases. On the other hand, the second illumination LED 17 is driven by a pulse signal generated based on a duty ratio obtained by inverting the duty ratio S1. That is, the second illumination LED 17 is driven by a drive signal having a phase opposite to that of the first illumination LED 16. Therefore, while the duty ratio S1 increases, the duty ratio of the drive pulse of the second illumination LED 17 decreases. For this reason, the temperature of 2nd illumination LED17 maintains a low temperature compared with 1st illumination LED16.

  When the ambient temperature of the first illumination LED 16 exceeds the reference value (T2), the duty ratio S1 gradually decreases due to the LED control timer interruption process. Along with this, the ambient temperature of the first illumination LED 16 decreases. The decrease in the duty ratio S1 is continued until the ambient temperature of the first illumination LED 16 becomes equal to or lower than the reference value (T3). Thereafter, the ambient temperature of the first illumination LED 16 increases or decreases in the vicinity of the reference value by repeating the LED control timer interruption process.

  According to the present embodiment, the first and second illumination LEDs 16 and 17 are always driven by pulse signals having opposite phases. That is, one of the first and second illumination LEDs 16 and 17 is always lit. Therefore, even if the duty ratio S1 of the drive signal of the first illumination LED 16 decreases as the ambient temperature of the first illumination LED 16 increases, the amount of light emitted by the second illumination LED 17 is increased by that amount. In order to supplement the light amount, the light amount of the illumination light supplied as the entire illumination unit 15 is maintained at a certain level or more. As a result, it is possible to supply illumination light having a sufficient amount of light while suppressing heat generation due to continued driving of the LED.

  In the present embodiment, the illumination unit 15 has two illumination LEDs, but is not limited thereto. A plurality of illumination LEDs that are driven by the drive pulse signal having the duty ratio S1 may be provided, and the same number of illumination LEDs may be driven by the drive pulse signals having opposite phases.

  In the present embodiment, the first and second illumination LEDs 16 and 17 are driven by pulse signals and the duty ratio is controlled, but the present invention is not limited to this. It is good also as a structure which controls the electric current value supplied to each illumination LED according to the detection result of the temperature sensor 18. FIG.

  In the present embodiment, the case where a still image is captured has been described as an example. However, when a moving image is captured, similar control is performed during the exposure period.

It is a perspective view shown from the back of a camera to which an embodiment according to the present invention is applied. It is a front view of the camera of FIG. It is a block diagram of a camera. It is a flowchart which shows the process sequence of the first half of the imaging process of a still image. 6 is a flowchart illustrating a second half of a still image shooting process. It is a flowchart which shows the process sequence of interruption operation | movement of LED drive. It is a graph which shows the change of the drive pulse of LED, and ambient temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Camera body 11 Operation | movement button 12 LCD monitor 13 Finder window 14 Shutter button 15 Illumination unit 16 1st illumination LED
17 Second illumination LED
18 Temperature sensor 19 Illumination button

Claims (3)

A plurality of semiconductor light emitting elements;
Temperature detecting means for detecting the ambient temperature of the plurality of semiconductor light emitting elements;
On the basis of the detection result the temperature detecting means, and a plurality of semiconductor light emitting that controls control means to drive the element,
The plurality of semiconductor light emitting devices are divided into a first group and a second group,
The temperature detecting means detects an ambient temperature of the first group;
The control unit suppresses driving of the first group when a detection result of the temperature detection unit is higher than a predetermined reference value, and drives the first group when the detection result is lower than the reference value. And controlling the driving of the second group so that the total amount of light supplied by the first group and the total amount of light supplied by the second group is always maintained above a certain level. A lighting device. The control means determines a duty ratio of a first drive pulse signal that drives the first group based on the detection result, and a phase of the second drive pulse signal that drives the second group is The lighting device according to claim 1 , wherein the duty ratio of the second drive pulse signal is determined so as to be in an opposite phase to the first drive pulse signal. The control means reduces the duty ratio of the first drive pulse signal so that the ambient temperature decreases when the detection result is higher than the reference value, and when the detection result is lower than the reference value, 3. The lighting device according to claim 2 , wherein the duty ratio of the first drive pulse signal is increased so that the amount of illumination light supplied by one group is increased.

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