JP2020003521A - LED strobe device - Google Patents

Abstract

To provide a relatively easily operable and inexpensive LED strobe device with which a photographer himself or herself can adjust a light emission amount and a color temperature.SOLUTION: When each of variable first and second threshold voltages V1, V2 is set to an appropriate voltage value and a light emission signal 1 generated in conjunction with a shutter operation is sent to a strobe circuit, charging of a capacitor C of the strobe circuit is started and only a first LED 7 is simultaneously turned on to emit light. When the terminal voltage of the capacitor C rises to reach the first threshold voltage V1, the first LED 7 is turned off and only a second LED 8 is turned on to emit light, and when the terminal voltage of the capacitor C further rises to reach the second threshold voltage V2, the second LED 8 is turned off.SELECTED DRAWING: Figure 7

Description

  The present invention mainly relates to an LED strobe device for photographing.

  With the diversification of shooting purposes, there is a demand for an inexpensive strobe device that is relatively easy to operate and that allows the photographer to adjust the amount of emitted strobe light and the color temperature. Therefore, there is a need for an LED strobe device capable of changing the color temperature while keeping the light amount constant, and changing the light amount without changing the color temperature.

  A strobe device capable of adjusting the color temperature of strobe light according to the environment at the time of strobe shooting is disclosed in Patent Document 1.

  The disclosed strobe device controls light emission balance by using four or more types of LEDs having different emission colors as strobe light sources, and controlling the light emission amount of each LED by a system controller according to the color temperature of an object scene and the like. Things.

JP 2007-86178 A

  By the way, the above-mentioned strobe device is not configured so that the photographer himself can adjust the light emission amount and the color temperature. Further, the circuit configuration is a complicated configuration including a CPU, a memory, and the like, and is not an inexpensive configuration.

  Accordingly, the present invention has been made in view of the above-described problems, and an object thereof is to provide a relatively easy-to-operate and inexpensive LED strobe device capable of adjusting a light emission amount and a color temperature by a photographer himself. It is in.

  In order to solve the above-mentioned problem, the invention described in claim 1 of the present invention provides a first LED and a second LED having different emission colors from each other, the first LED having a first current value, and the second LED having a second current value. A control unit for sequentially driving the constant current pulse width, a light amount per unit time when the first LED is driven with the first current value, and a unit time when the second LED is driven with the second current value. A current value setting unit that sets the light amount of the first LED to be equal to the first LED without changing a total width of the driving pulse width of the first LED and the driving pulse width of the second LED. A color temperature variable control unit that changes the ratio of the drive pulse width of the second LED to the drive pulse width of the second LED; and the first L without changing the ratio of the drive pulse width of the first LED to the drive pulse width of the second LED. Light quantity variable control unit for changing the total width of the drive pulse width of the drive pulse width and said second 2LED and D, is characterized in that comprises a city.

  Also, in the invention described in claim 2 of the present invention, in claim 1, the first LED and the second LED include a common driver, and the first LED has a first threshold voltage by a first variable resistor. The second LED is connected to a first comparator to be set, the second LED is connected to a second comparator to set a second threshold voltage by a second variable resistor, and the first LED emits light until the timing when the first threshold voltage is reached. The second LED emits light from the timing at which the first threshold voltage is reached to the timing at which the second threshold voltage is reached.

  According to the present invention, the first LED and the second LED having different emission colors are used as light sources, and the first LED driving pulse width and the second LED driving pulse width are changed without changing the total width of the first LED driving pulse width and the second LED driving pulse width. By changing the ratio of the drive pulse widths of the first and second LEDs, the color temperature of the mixed light can be varied, and the drive pulse width of the first LED and the drive of the second LED can be changed without changing the ratio of the drive pulse width of the first LED to the drive pulse width of the second LED. By changing the total width of the pulse widths, the amount of mixed color light can be varied.

  This makes it possible to provide an inexpensive LED strobe device that is relatively easy to operate and allows the photographer to adjust the light emission amount and color temperature.

4 is a graph showing current versus light amount characteristics of an LED. 4 is a graph showing current versus color temperature characteristics of an LED. 5 is a graph showing current-light quantity / color temperature characteristics of mixed color light by two types of LEDs having different emission colors. 4 is a graph showing a light emission time versus color temperature characteristic of an LED. 4 is a graph showing light emission time versus light amount characteristics of an LED. (A) is a graph showing the light emission time vs. light quantity / color temperature characteristics of mixed color light when the drive time ratio of two types of LEDs having different emission colors is fixed at 1: 1. (B) A graph showing the light quantity / color temperature characteristics of mixed color light when the total of the light emission times of two types of LEDs having different light emission colors is 10 msec and the light emission time ratio of each light emission color is changed. FIG. 3 is a circuit diagram illustrating an LED strobe device. 6 is a light emission timing chart of each LED when the amount of mixed color light by two kinds of LEDs having different light emission colors is varied. 5 is a light emission timing chart of each LED when the color temperature of mixed color light by two types of LEDs having different light emission colors is varied.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 9 (the same portions are denoted by the same reference numerals). The embodiment described below is a preferred specific example of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise described.

  The LED strobe device of the present invention uses a plurality of types of LEDs having different emission colors (color temperatures) as light sources, and emits light (hereinafter, referred to as “mixed light”) obtained by additive color mixing of light emitted from each LED. The light is emitted toward the subject as strobe light.

  In a specific embodiment of the LED strobe device, an LED that emits white light with a relatively low color temperature (hereinafter, referred to as a “first LED”) and an LED that emits white light with a relatively high color temperature A light source is composed of two types of LEDs (hereinafter, referred to as a “second LED”), and the mixed light of the emitted light from the first LED and the emitted light from the second LED is used as strobe light, and the amount of strobe light ( The brightness and the color temperature (color tone) can be easily adjusted by the photographer himself.

  When changing the light amount and color temperature of the mixed color light due to the light emitted from each of a plurality of types of LEDs having different color temperatures, a method of mainly controlling the drive (light emission) current of each LED and the corresponding LED There are two methods for controlling the driving (light emission) time of the device.

  Among them, the method of controlling the driving current to adjust the light amount and the color temperature needs to take into account the electro-optical characteristics of the LED. That is, in the LED, the light amount of the emitted light does not change linearly with respect to the drive current (see the graph of FIG. 1).

The graph of FIG. 1 shows the light quantity (lux · s) with respect to the current ratio when the maximum drive current value that can be applied to each of the first LED having a lower color temperature and the second LED having a higher color temperature than the first LED is 100%. FIG.
In the following embodiments, the first LED and the second LED are both white LEDs, the first LED has a light bulb color, and the second LED has a light emission color called daylight color.

  From the graph of FIG. 1, the light amount of the first LED and the second LED does not change linearly with respect to the current ratio. At the same time, the rate of change of the light amount with respect to the current ratio differs between the first LED and the second LED. It can be seen that the change rate of the second LED is larger than that of the second LED.

  In the LED, the color temperature of the emitted light changes depending on the drive current (see the graph in FIG. 2).

  The graph of FIG. 2 shows the relationship between the color temperature (K) and the current ratio when the maximum drive current value that can be applied to each of the first LED having a lower color temperature and the second LED having a higher color temperature than the first LED is 100%. It is a figure showing a change. The color temperature of the first LED corresponds to the scale on the right vertical axis, and the color temperature of the second LED corresponds to the scale on the left vertical axis.

  According to the graph of FIG. 2, the color temperature of both the first LED and the second LED greatly changes with respect to the current ratio, and at the same time, the rate of change of the color temperature with respect to the current ratio differs between the first LED and the second LED. It can be seen that the change rate of the second LED is larger than that of the second LED.

  Therefore, the amount of light of the mixed light due to the light emitted from the first LED and the light emitted from the second LED does not change linearly with respect to the drive current, and the color temperature also changes at the same time (see the graph of FIG. 3).

  The graph of FIG. 3 shows that the first LED having a lower color temperature and the second LED having a higher color temperature than the first LED change the current value at the same rate when the maximum applicable drive current value is 100%. FIG. 7 is a diagram illustrating a change in light amount (lux · s) and a change in color temperature (K) with respect to a current ratio value of mixed color light when the light is mixed. The change in light amount corresponds to the scale on the right vertical axis, and the change in color temperature corresponds to the scale on the left vertical axis.

  According to the graph of FIG. 3, when trying to change the amount of mixed color light by changing the drive current of each of the first LED and the second LED, the color temperature also changes because the rate of change of the color temperature with respect to the current ratio of the first LED and the second LED is different. You can see that it changes. Further, it can be seen that if the color temperature of the mixed color light is changed by changing the drive current of each of the first LED and the second LED, the light amount also changes.

  As described above, in order to change the amount of light and the color temperature of the mixed color light by the first LED and the second LED so as not to affect each other by controlling the respective drive currents, the electro-optic of each LED is required. Characteristic grasp and complicated current control based on it are necessary, and it is hard to say that the method is efficient in both hardware and software.

  Therefore, the strobe device of the present invention keeps the drive current of each of the first LED and the second LED constant, and sets the first current value for driving the first LED and the second current value for driving the second LED per unit time. The light amount of the first LED and the light amount of the second LED are set to be equal. By controlling only the total length of the driving time (light emission time) of each of the first LED and the second LED or only the ratio of the drive time (light emission time) of both LEDs, only the light amount of the mixed color light (color temperature , Or only the color temperature (without changing the amount of light).

  That is, in each of the first LED and the second LED, at a constant current value, the color temperature of the emitted light hardly changes depending on the driving time (see the graph of FIG. 4).

  FIG. 4 is a graph showing a change in color temperature with respect to the drive time (msec) when the drive current is constant in each of the first LED having a lower color temperature and the second LED having a higher color temperature than the first LED. The color temperature of the first LED corresponds to the scale on the right vertical axis, and the color temperature of the second LED corresponds to the scale on the left vertical axis.

  It can be seen from the graph of FIG. 4 that the color temperature of the first LED and the second LED hardly change even when the drive time is changed while the respective drive currents are kept constant.

  In the LED, the amount of emitted light changes almost linearly with the driving time (see the graph in FIG. 5).

  The graph of FIG. 5 is a diagram illustrating a change in the amount of light with respect to the drive time of each of the first LED having a lower color temperature and the second LED having a higher color temperature than the first LED.

  It can be seen from the graph of FIG. 5 that the light amount of each of the first LED and the second LED changes linearly with respect to the drive time.

  Accordingly, the amount of light emitted from the first LED and the light emitted from the second LED also changes linearly with respect to the total drive time, and at the same time, there is almost no change in color temperature (see the graph in FIG. 6).

The graph of FIG. 6 shows the change in the light amount of the mixed color light and the change in the color temperature when the first LED having a lower color temperature and the second LED having a higher color temperature than the first LED are driven for each driving time by the constant current pulse width drive. It is a figure showing a change. The first current value for driving the first LED and the second current value for driving the second LED were set such that the amount of light per unit time was equal. The change in light amount corresponds to the scale on the right vertical axis, and the change in color temperature corresponds to the scale on the left vertical axis.
FIG. 6A shows a change in the amount of light of the mixed color light and a change in the color temperature when the ratio of the driving time of the first LED to the driving time of the second LED is fixed to 1: 1. In the graph of FIG. 6A, the horizontal axis indicates the driving time of the first LED and the second LED. That is, 10 msec on the horizontal axis in the graph of FIG. 6A indicates a case where the driving time of the first LED and the driving time of the second LED are each 10 msec, and the total driving time is 20 msec.
In FIG. 6B, the change in the amount of light and the change in the color temperature measured with the total drive time of the first LED and the second LED being 10 msec are shown with the drive time (light emission time) of the second LED as the horizontal axis.

From the graph of FIG. 6A, it can be seen that the color temperature hardly changes even when the light amount of the mixed color light is changed by changing the drive time while keeping the ratio of the drive time of the first LED and the second LED constant.
Further, from the graph of FIG. 6B, even if the color temperature of the mixed color light is changed by changing the ratio of the respective driving times of the first LED and the second LED, the sum of the driving time of the first LED and the driving time of the second LED is obtained. By keeping the drive time constant, the amount of mixed color light does not change.

  From the above, by controlling only the ratio of the respective driving times (the total driving time is constant) or only the driving time (the ratio of the driving times is constant) for the mixed color light of the first LED and the second LED. The light quantity and the color temperature can be varied so as not to affect each other. As a result, a relatively easy-to-operate and inexpensive strobe device that allows the photographer to adjust the light emission amount and color temperature is realized.

  As a specific color mixing method, first, respective drive currents of the first LED and the second LED having a higher color temperature than the first LED are set. When the first LED having a lower color temperature and the second LED having a higher color temperature are driven with the same current value, the second LED having a higher color temperature tends to emit more light than the first LED having a lower color temperature. Therefore, the drive current of the first LED is set, and the drive current of the second LED is set such that the amount of emitted light per unit time at that time is equal to the amount of emitted light per unit time of the second LED.

  At this time, the driving current of the first LED can be set to a current value close to the maximum rated value in pulse driving.

  Variation (adjustment) of the color temperature of the mixed color light by the emitted light of the first LED and the emitted light of the second LED is made possible by changing the ratio of the drive time of the first LED to the drive time of the second LED. At this time, the light amount can be kept constant by keeping the sum of the driving time of the first LED and the driving time of the second LED constant.

  In other words, by changing the ratio between the driving time of the first LED and the driving time of the second LED while keeping the total time of the driving time of the first LED and the driving time of the second LED constant, only the color temperature is changed without changing the light amount be able to.

  On the other hand, the amount (adjustment) of the amount of mixed color light by the emitted light of the first LED and the emitted light of the second LED can be changed by changing the total drive time of the drive time of the first LED and the drive time of the second LED. At this time, the color temperature can be kept constant by keeping the ratio of the drive time of the first LED to the drive time of the second LED constant.

  In other words, by changing the total driving time of the driving time of the first LED and the driving time of the second LED while keeping the ratio of the driving time of the first LED to the driving time of the second LED constant, only the light amount without changing the color temperature Can be changed.

  FIG. 7 is an example of a circuit diagram for varying the color temperature and light amount of mixed color light by the emitted light of the first LED and the emitted light of the second LED.

  As shown in FIG. 7, when the light emission signal 1 is input to the LED driver 2, the LED driver 2 starts operating, and at the same time, the transistors Q5 and Q6 connected to the light emission signal line are sequentially turned on and the current mirror from the power supply 3 through the transistor Q6. A current is supplied to the circuit 4 and a current flows through the variable resistor VR1 forming the current mirror circuit 4 through the transistor Q7, and at the same time, a constant current flows through the capacitor C forming the current mirror circuit 4 through the transistor Q8. The charging current flows, and the terminal voltage V0 of the capacitor C, which rises linearly, is input to the respective non-inverting input terminals of the first comparator 5 and the second comparator 6 connected to the terminal of the capacitor C opposite to the ground side. .

  The divided voltage V1 (first threshold voltage) of the variable resistor VR2 in the series circuit composed of the transistor Q6, the resistor R, and the variable resistor VR2 is input to the inverting input terminal of the first comparator 5, and the second comparator 6 Similarly, the terminal voltage V2 (second threshold voltage) of the variable resistor VR2 in the series circuit including the transistor Q6, the resistor R, and the variable resistor VR2 is input to the inverting input terminal.

When the light-emitting signal 1 is input to the LED driver 2, both outputs of the first comparator 5 and the second comparator 6 are L, and when the transistor Q 1 connected to the output of the first comparator 5 is in the ON state, the first LED 7 There emits light at a current value set by VR _A. At this time, the transistor Q2 connected to the output of the second comparator 6 also tries to be turned on similarly. As a result, the second LED 8 does not emit light.

Thereafter, when the terminal voltage V0 rises to V1 of the first threshold voltage divided by the variable resistor VR2 by charging the capacitor C, the output of the first comparator 5 becomes H, the transistor Q1 is turned off, and the first LED 7 Will not emit light. At this time, similarly the transistor Q3 is also the transistor Q2 becomes OFF is turned ON, a current value set by the synthesis of the 2LED8 to become ON in conjunction also transistor Q4 connected to the transistor Q2 is VR _A and VR _B Emits light.

  Further, when the terminal voltage V0 of the capacitor C rises and reaches the second threshold voltage V2 set by the resistor R and the variable resistor VR2, the output of the second comparator 6 becomes H and the transistor Q2 is turned off. And the second LED 8 does not emit light.

  FIG. 8 and FIG. 9 are timing charts showing respective drive (light emission) timings of the first LED 7 and the second LED 8 controlled by the LED light emission control circuit. 9 is a timing chart in the case where the color temperature of the mixed light by the light emitted from the first LED 7 and the light emitted from the second LED 8 is changed, and FIG. 8 is a timing chart in the case where the light amount of the mixed light is changed. .

  FIG. 8A is a graph V0 showing the time change of the terminal voltage V0 of the capacitor C when the variable resistor VR1 is adjusted (the time change of the terminal voltage V0 of the capacitor C is adjusted) to change the amount of mixed color light. (A) and V0 (b). V0 (a) and V0 (b) show a time change when the variable resistor VR1 is set to a different resistance value. V0 (a) is a case where the resistance value of the variable resistor VR1 is larger than V0 (b). Is shown.

  FIG. 8B is a timing chart of the light emission of the first LED and the second LED when the time change of the terminal voltage V0 of the capacitor C has the characteristic of V0 (a), and FIG. 5 is a timing chart of light emission of a first LED and a second LED when a temporal change of a terminal voltage V0 has a characteristic of V0 (b).

  8B, the light emission time of the first LED 7 is such that the terminal voltage V0 (a) of the capacitor C becomes equal to the first threshold voltage V1 set by the divided voltage of the variable resistor VR2 from the time when the light emission signal 1 is input. The light emission time of the second LED 8 is determined when the terminal voltage V0 (a) of the capacitor C reaches the first threshold voltage V1 set by the divided voltage of the variable resistor VR2 (in other words, the first LED 7). Is the time from when the light emission stops to the second threshold voltage V2 set by the resistor R and the variable resistor VR2.

  In FIG. 8C, the light emission time of the first LED 7 is such that the terminal voltage V0 (b) of the capacitor C becomes equal to the first threshold voltage V1 set by the divided voltage of the variable resistor VR2 from the time when the light emission signal 1 is input. The light emission time of the second LED 8 is the time when the terminal voltage V0 (b) of the capacitor C reaches the first threshold voltage V1 set by the divided voltage of the variable resistor VR2 (in other words, the first LED 7). Is the time from when the light emission stops to the second threshold voltage V2 set by the resistor R and the variable resistor VR2.

  Accordingly, each of the first LED 7 and the second LED 8 sequentially emits light by one-shot pulse driving in a time-division manner, and the ratio of the light emission time is determined by V1 / V2. By adjusting V1 / V2 to be constant, the resistance value of the variable resistor VR1 is adjusted. By varying the time gradient of the terminal voltage V0 of the capacitor C, only the light amount can be changed without changing the color temperature of the mixed light.

  FIG. 9A shows a graph V0 showing a time change of the terminal voltage V0 of the capacitor C when the variable resistor VR2 is adjusted (the first threshold voltage is adjusted) to change the color temperature of the mixed light, and the variable resistor. The relationship between the voltages V1 (a) and V1 (b) set by the divided voltage VR2 is shown. The voltages V1 (a) and V1 (b) indicate a first threshold voltage set by adjusting the variable resistor VR2, and V1 (b) indicates a case where the voltage value is higher than V1 (a). .

  FIG. 9B is a timing chart of light emission of the first LED 7 and the second LED 8 when the first threshold voltage by the variable resistor VR2 is V1 (a), and FIG. 9C is the first threshold by the variable resistor VR2. It is a timing chart of light emission of the first LED7 and the second LED8 when the voltage is V1 (b).

  9B, the light emission time of the first LED 7 is such that the terminal voltage V0 of the capacitor C is equal to the first threshold voltage V1 (a) set by the divided voltage of the variable resistor VR2 from the time when the light emission signal 1 is input. The light emission time of the second LED 8 is determined when the terminal voltage V0 of the capacitor C reaches the first threshold voltage V1 (a) set by the divided voltage of the variable resistor VR2 (in other words, This is the time from when the first LED 7 stops emitting light) to when it reaches the second threshold voltage V2 set by the resistor R and the variable resistor VR2.

  In FIG. 9C, the light emission time of the first LED 7 is set such that the terminal voltage V0 of the capacitor C is set to the divided voltage of the variable resistor VR2 from the time when the light emission signal 1 is input, and the first threshold voltage is V1 ( The light emission time of the second LED 8 is the time when the terminal voltage V0 of the capacitor C reaches the first threshold voltage V1 (b) set by the divided voltage of the variable resistor VR2 (in other words, the light emission time of the second LED 8). Then, it is the time from when the first LED 7 stops emitting light) to when it reaches the second threshold voltage V2 set by the resistor R and the variable resistor VR2.

  Therefore, each of the first LED 7 and the second LED 8 emits light sequentially by time-division one-shot pulse driving, and the total light emission time is determined by the second threshold voltage V2. By varying the voltage V1, only the color temperature can be changed without changing the light quantity.

  In the variable light quantity and color temperature of the mixed color light by the first LED and the second LED, the total of the light emission times of the respective LEDs needs to be shorter than the shutter open time of the camera, and is set to about 10 msec or less. preferable. Therefore, since the first LED and the second LED are both used for short-time pulse emission, the current value of the drive current is the maximum rated value in the pulse drive that can be driven at a current value larger than the maximum rated value in the DC drive. The value can be adopted. Therefore, the first LED and the second LED can emit light by pulse driving of a large current, and a sufficient amount of light can be secured.

  As described above, the LED strobe device of the present invention uses the first LED and the second LED having different light emission colors (color temperatures) as light sources, and when a light emission signal emitted in conjunction with a shutter operation is sent to the strobe circuit, In the strobe circuit, the first LED and the second LED are sequentially driven by one-shot pulses in a time-sharing manner for a short time of about 10 msec, and the object is illuminated by additive mixed-color strobe light due to the light emission of each LED with a time difference.

  As described above, since each LED emits light by pulse driving, the LED can be driven with a current value larger than the maximum rated value in DC driving, and a subject brightly illuminated by strobe light is clearly photographed by the camera. be able to.

  In addition, in order to cope with diversification of shooting purposes, the strobe circuit has a light emission time control means for controlling the light emission time of the first LED and a light emission time control means for controlling the light emission time of the second LED. By appropriately controlling the emission time control means, it is possible to emit strobe light of different color temperatures while keeping the light amount constant, and to emit different amounts of strobe light while keeping the color temperature constant. Can be.

  Each of these light emission time control means of the strobe circuit is provided so as to be able to be controlled from the outside, and the photographer himself or herself can perform the light quantity and the color temperature of the strobe light by a relatively simple operation according to the subject or the photographing purpose. Can be adjusted freely and easily.

  In the above-mentioned strobe device, each of the first LED and the second LED emits a one-shot pulse according to a one-shot emission signal. However, the first LED and the second LED can be repeatedly emitted by repeatedly inputting the emission signal. Thus, it can be used for other lighting devices.

DESCRIPTION OF SYMBOLS 1 ... Light emission signal 2 ... LED driver 3 ... Power supply 4 ... Current mirror circuit 5 ... 1st comparator 6 ... 2nd comparator 7 ... 1st LED
8 ... Second LED

Claims (2)

A first LED and a second LED having different emission colors,
A control unit that sequentially drives the first LED with a first current value and the second LED with a second current value at a constant current pulse width;
A current value set so that the amount of light per unit time when the first LED is driven with the first current value is equal to the amount of light per unit time when the second LED is driven with the second current value. And a setting unit,
The control unit may change a ratio of a driving pulse width of the first LED to a driving pulse width of the second LED without changing a total width of the driving pulse width of the first LED and the driving pulse width of the second LED. A variable control unit,
A light amount variable control unit that changes the total width of the drive pulse width of the first LED and the drive pulse width of the second LED without changing the ratio of the drive pulse width of the first LED to the drive pulse width of the second LED; An LED strobe device, comprising: The first LED and the second LED include a common driver,
The first LED is connected to a first comparator in which a first threshold voltage is set by a first variable resistor,
The second LED is connected to a second comparator in which a second threshold voltage is set by a second variable resistor,
The first LED emits light until the first threshold voltage is reached,
The LED strobe device according to claim 1, wherein the second LED emits light from a timing at which the first threshold voltage is reached to a timing at which the second threshold voltage is reached.

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