JP2019160756A - Illumination light communication device - Google Patents

Abstract

To provide an illumination light communication device reducing the loss of reliability of a light source, which may occur when performing an operation for interrupting the LED current with small ON duty ratio.SOLUTION: An illumination light communication device includes a switch 22 connected in series with a light source 20, and interrupting a current flowing through the light source 20 according to a communication signal, a current detection circuit 60 connected in series with the switch 22, and detecting the magnitude of the current flowing through the light source 20 as a voltage drop, a feedback circuit 5 generating a feedback signal indicating the error of the voltage drop of the current detection circuit 60 and a first reference voltage, a DC-DC converter 3 outputting a current to the light source 20, and keeping the average value of the output current constant based on the feedback signal, and a shunt circuit 70 for limiting the voltage applied to the light source 20, so that the peak value of the current flowing through the light source 20 does not exceed the maximum rating of the light source 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an illumination light communication apparatus that performs visible light communication by modulating illumination light.

  Patent Document 1 discloses an illumination light communication device that modulates illumination light by intermittently passing a current flowing through a light source in a lighting fixture including a light emitting diode (LED) as a light source. This illumination light communication apparatus includes a power supply circuit that performs constant current feedback control for controlling the average value of the current flowing through the light source to be constant in order to stabilize the brightness of the illumination light.

JP 2017-139211 A

  However, according to the above prior art, there is a problem that the peak value of the LED current increases as the on-duty ratio for intermittently passing the current flowing through the light source (hereinafter referred to as the LED current) decreases, and the reliability of the light source is impaired.

  More specifically, the conventional illumination light communication device operates to keep the average value of the LED current substantially constant by constant current feedback control. For example, when the intermittent on-duty ratio is 50%, the peak value of the LED current is twice the LED current when not intermittent. Further, when the intermittent on-duty ratio is 10%, the peak value of the LED current is 10 times the LED current when the intermittent current is not intermittent.

  Therefore, when the on-duty ratio is small, the peak value of the LED current may exceed the rating. If the peak value of the LED current exceeds the rating, there arises a problem that reliability of the LED is deteriorated, such as aging deterioration, shortening the lifetime, and inducing a failure.

  The present invention provides an illuminating light communication apparatus that reduces the loss of reliability of a light source when an operation for intermittently switching LED current is performed with a small on-duty ratio.

  In order to achieve the above object, an embodiment of an illumination light communication apparatus according to the present invention includes a light source that emits illumination light, a signal generation circuit that generates a binary communication signal, and the light source connected in series, and the communication A switch that interrupts the current flowing through the light source according to a signal, a current detection circuit that is connected in series with the switch and detects the magnitude of the current flowing through the light source as a voltage drop, and a voltage drop of the current detection circuit A feedback circuit that generates a feedback signal indicating an error from one reference voltage, a DC-DC converter that outputs a current to the light source and maintains an average value of the output current based on the feedback signal, and flows through the light source A shunt circuit that limits a voltage applied to the light source so that a peak value of the current does not exceed a maximum rating of the light source.

  The illumination light communication apparatus according to the present invention can reduce the loss of the reliability of the light source when the operation of intermittently switching the LED current is performed with a small on-duty ratio.

FIG. 1 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the first embodiment. FIG. 2 is a circuit diagram illustrating a configuration example of the shunt circuit according to the first embodiment. FIG. 3A is a diagram showing a characteristic of an LED current with respect to a duty ratio in the illumination light communication apparatus according to Embodiment 1. FIG. 3B is a diagram showing the characteristics of the output voltage with respect to the duty ratio in the illumination light communication apparatus according to Embodiment 1. FIG. 4 is a block diagram showing a modification of the illumination light communication apparatus according to the first embodiment. FIG. 5A is a diagram illustrating a characteristic of an LED peak current with respect to a duty ratio in an illumination light communication apparatus according to a modified example. FIG. 5B is a diagram illustrating a characteristic of an output voltage with respect to a duty ratio in an illumination light communication apparatus according to a modified example. FIG. 6A is a diagram illustrating a loss characteristic with respect to a duty ratio in an illumination light communication apparatus according to a modification. FIG. 6B is a diagram illustrating a loss characteristic with respect to a duty ratio in an illumination light communication apparatus according to a modification. FIG. 7 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the second embodiment. FIG. 8 is a circuit diagram illustrating a configuration example of the shunt circuit, the adjustment circuit, and the reference voltage source according to the second embodiment. FIG. 9 is a diagram illustrating a characteristic of loss with respect to the duty ratio in the illumination light communication apparatus according to Embodiment 2. In FIG. FIG. 10 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the third embodiment. FIG. 11 is a circuit diagram showing a configuration example of a shunt circuit and a pulse control circuit according to the third embodiment. FIG. 12 is a diagram illustrating various signal waveforms in the pulse control circuit according to the third embodiment. FIG. 13 is a diagram illustrating a characteristic of loss with respect to the duty ratio in the illumination light communication apparatus according to Embodiment 3. FIG. 14 is a diagram showing LED current versus duty ratio when the loss in the illumination light communication apparatus according to Embodiment 3 is kept constant. FIG. 15 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the fourth embodiment. FIG. 16 is a circuit diagram illustrating a configuration example of the shunt circuit and the peak value detection circuit according to the fourth embodiment. FIG. 17 is a block diagram illustrating a configuration example of the illumination light communication apparatus in the comparative example. FIG. 18A is a diagram illustrating a peak value characteristic and an average value characteristic of the LED current with respect to the duty ratio in the illumination light communication apparatus of the comparative example. FIG. 18B is a diagram illustrating an output voltage with respect to a duty ratio in the illumination light communication apparatus of the comparative example. FIG. 19 is a diagram illustrating the waveform of the output voltage and the waveform of the LED current in the illumination light communication device of the comparative example.

(Knowledge that became the basis of the present invention)
The inventor has found that the following problems occur with respect to the illumination light communication apparatus described in the “Background Art” section.

  FIG. 17 is a block diagram illustrating a configuration example of the illumination light communication apparatus in the comparative example according to the knowledge of the present inventor. The illumination light communication apparatus of FIG. 1 includes a rectifier bridge 2, a DC-DC converter 3, a smoothing capacitor 4, a feedback circuit 5, a current detection circuit 6, a light source 20, and a modulator 21.

  In this illumination light communication apparatus, an AC voltage from a commercial power source is full-wave rectified by a rectifier bridge 2 and input to a DC-DC converter 3. A smoothing capacitor 4 is connected between both ends of the output of the DC-DC converter 3. In parallel with the smoothing capacitor 4, a series circuit of a light source 20 including a light emitting diode that emits illumination light and a current detection resistor 61 is formed. The voltage drop of the current detection resistor 61 is fed back to the DC-DC converter 3 via the input resistor 62 and the feedback circuit 5. The DC-DC converter 3 performs feedback control to keep the average of the output current constant, and functions as a constant current power source.

  When optical communication is performed using such a DC-DC converter 3, a modulator 21 is provided in series with the light source 20, and a binary communication signal (also referred to as an intermittent signal) generated by the signal generation circuit 23 is used for the switch 22. Drive intermittent. The modulator 21 performs modulation to superimpose a communication signal on the illumination light by intermittently switching the LED current.

  Next, how the current flowing through the light source 20 (hereinafter referred to as LED current) changes with respect to the duty ratio of the intermittent signal in the comparative example will be described. The term “duty ratio” means the on-duty ratio, that is, the proportion of the period during which the LED current flows during one cycle, unless otherwise specified.

  FIG. 18A is a diagram illustrating a peak value characteristic and an average value characteristic of the LED current with respect to the duty ratio in the illumination light communication apparatus of the comparative example. The horizontal axis of the figure shows the duty ratio of the intermittent signal, that is, the ratio at which the switch 22 is turned on. The vertical axis represents the LED current, and the relative magnification when the LED current is 1 when the duty ratio is 100% (that is, the switch 22 is always on).

  As shown in FIG. 18A, the average value of the LED current is constant regardless of the duty ratio. This is due to feedback control in the DC-DC converter 3. In the illumination light communication apparatus of the comparative example, the apparent brightness of the illumination light is the same even if the duty ratio is too high.

  In contrast, the LED peak value increases as the duty ratio decreases. For example, if the duty ratio is 10%, the peak value of the LED current is 10 times that of the LED current when not intermittent. Such a large peak value of the LED current may exceed the rating of the light source 20.

  FIG. 18B is a diagram illustrating an output voltage with respect to a duty ratio in the illumination light communication apparatus of the comparative example. The horizontal axis of the figure shows the duty ratio as in FIG. 18A. The vertical axis represents the output voltage of the DC-DC converter 3. The output voltage also increases as the duty ratio decreases. Such a large output voltage causes an overshoot in the LED current during the period when the switch 22 is turned on, and may exceed the rating of the light source 20.

  FIG. 19 is a diagram illustrating the waveform of the output voltage and the waveform of the LED current in the illumination light communication device of the comparative example. The horizontal axis of the figure shows time. The vertical axis in the upper part of the figure shows the output voltage of the DC-DC converter 3. The vertical axis in the lower part of the figure shows the LED current. In the figure, respective waveforms when the duty ratio of the intermittent signal is 20%, 40%, 60%, and 80% are shown.

  In FIG. 19, as in FIGS. 18A and 18B, both the output voltage and the LED current increase as the duty ratio decreases.

  As in the illumination light communication device of the comparative example, in the illumination light communication device including the DC-DC converter 3 that operates to keep the average value of the LED current almost constant by feedback control, the peak of the LED current is obtained when the duty ratio is small. The value may exceed the rating. If the peak value of the LED current exceeds the rating, there arises a problem that reliability of the LED is deteriorated, such as aging deterioration, shortening the lifetime, and inducing a failure.

  In order to solve such a problem, an illumination light communication device according to an aspect of the present invention includes a light source that emits illumination light, a signal generation circuit that generates a binary communication signal, and the light source connected in series, A switch that interrupts the current flowing through the light source according to a communication signal, a current detection circuit that is connected in series with the switch and detects the magnitude of the current flowing through the light source as a voltage drop, and a voltage drop of the current detection circuit; A feedback circuit that generates a feedback signal indicating an error from the first reference voltage; a DC-DC converter that outputs a current to the light source and maintains an average value of an output current based on the feedback signal; and the light source A shunt circuit that limits a voltage applied to the light source so that a peak value of a flowing current does not exceed a maximum rating of the light source.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that each of the embodiments described below shows a preferred specific example of the present invention. The numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of the constituent elements, steps, the order of steps, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims showing the highest concept of the present invention will be described as optional constituent elements that constitute a more preferable embodiment. Moreover, each figure is a schematic diagram and does not necessarily represent a strict dimension.

[1.1 Illumination light communication device configuration]
FIG. 1 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the first embodiment. The illuminating light communication apparatus shown in FIG. 1 includes a rectifier bridge 2, a DC-DC converter 3, a smoothing capacitor 4, a feedback circuit 5, a light source 20, a modulator 21, a current detection circuit 60, and a shunt circuit 70.

  The DC-DC converter 3 converts the voltage that has been full-wave rectified by the rectifier bridge 2 into a desired voltage. The DC-DC converter 3 outputs a current to the light source 20, and performs feedback control that keeps the average value of the output current constant based on the feedback signal.

  The smoothing capacitor 4 smoothes the output voltage of the DC-DC converter 3.

  The feedback circuit 5 includes an operational amplifier 51, a reference voltage source 52, a capacitor 53, and a resistor 54. As a result, the feedback circuit 5 generates a feedback signal indicating an error between the voltage drop of the current detection resistor 7 and the reference value (also referred to as a first reference voltage) generated by the reference voltage source 52, and supplies the feedback signal to the DC-DC converter 3. Output. For example, the feedback circuit 5 performs control so that the error indicated by the feedback signal becomes zero.

  The light source 20 includes one or more light emitting diodes that emit illumination light. The light source 20 may include an organic EL light emitting element or a laser light emitting element instead of the light emitting diode.

  The modulator 21 includes a switch 22 and a signal generation circuit 23. The signal generation circuit 23 generates a binary communication signal (also called an intermittent signal). The binary communication signal may be an ID signal indicating an ID unique to the illumination light communication device, or may be a communication signal based on a signal input from an external device. The modulator 21 is connected in series with the light source 20, and modulates the illumination light by intermittently switching the switch 22 according to the binary communication signal generated by the signal generating circuit 23 and intermittently switching the LED current.

  The current detection circuit 60 includes a current detection resistor 61 and an input resistor 62. The current detection resistor 61 is a resistance element for detecting the magnitude of the current flowing through the light source 20 as a voltage drop. The input resistor 62 inputs the voltage drop of the current detection resistor 61 to the feedback circuit 5.

  The shunt circuit 70 is a circuit that limits the voltage applied to the light source 20 so that the peak value of the current flowing through the light source 20 (hereinafter referred to as LED current) does not exceed the maximum rating of the light source 20. Specifically, the shunt circuit 70 is connected in parallel to a series circuit including the light source 20 and the switch 22, and is connected in series to the current detection circuit 60. The shunt circuit 70 detects the voltage applied to the light source 20 and limits the voltage applied to the light source 20 by sucking a part of the output current of the DC-DC converter 3 according to the detected voltage. The voltage to be limited is set to a value larger than the maximum output voltage of the DC-DC converter 3 in the lighting operation in which the switch 22 is not interrupted.

  Next, a specific example of the shunt circuit 70 will be described.

  FIG. 2 is a circuit diagram illustrating a configuration example of the shunt circuit according to the first embodiment. In the figure, the shunt circuit 70 includes a transistor 71, a resistor 72, an operational amplifier 73, a resistor 74, a resistor 75, a resistor 76, a resistor 77, and a reference voltage source 78. The terminal T1 in the figure is connected to the anode of the light source 20, and the terminal T2 is connected to one end of the switch 22.

  The series circuit of the transistor 71 and the resistor 72 is a circuit that sucks a part of the output current of the DC-DC converter 3. The amount of current that can be absorbed by the series circuit of the transistor 71 and the resistor 72 is determined according to the voltage of the gate signal of the transistor 71 and is adjusted by the resistor 72.

  The operational amplifier 73 amplifies an error between the reference voltage from the reference voltage source 78 and a signal indicating the magnitude of the voltage applied to the light source 20, and supplies the amplified signal to the transistor 71 as a gate signal. The greater the error, the greater the amount of current that can be drawn.

  The series circuit including the resistor 76 and the resistor 77 outputs a signal indicating the magnitude of the voltage applied to the light source 20 to the plus input terminal of the operational amplifier 73. Specifically, a series circuit including the resistor 76 and the resistor 77 detects a voltage applied to the light source 20 (more precisely, a voltage applied to the light source 20 and the switch 22), and connects the resistor 76 and the resistor 77. The divided voltage value generated at the point is output to the plus input terminal of the operational amplifier 73 as a signal indicating the magnitude of the voltage applied to the light source 20.

  The reference voltage source 78 generates a reference voltage. The reference voltage is determined so that the peak value of the current flowing through the light source 20 does not exceed the maximum rating of the light source 20.

  With such a configuration, the shunt circuit 70 detects the voltage applied to the light source 20 and sucks a part of the output current of the DC-DC converter 3 in accordance with the detected voltage to be applied to the light source 20. Limit the voltage.

[1.2 Operation of illumination light communication device]
Next, operation | movement of an illumination light communication apparatus is demonstrated using the simulation result of an illumination light communication apparatus.

  FIG. 3A is a diagram showing a characteristic of an LED current with respect to a duty ratio in the illumination light communication apparatus according to Embodiment 1. FIG. 3B is a diagram showing the characteristics of the output voltage with respect to the duty ratio in the illumination light communication apparatus according to Embodiment 1. The horizontal axis of FIG. 3A and FIG. 3B shows the duty ratio with which the switch 22 is intermittent. The vertical axis of FIG. 3A indicates the peak value of the LED current, and indicates a relative magnification with the current being 1 when the duty ratio is 100%. The vertical axis in FIG. 3B indicates the output voltage of the DC-DC converter 3 (that is, the voltage of the smoothing capacitor 4).

  The shunt levels L1 to L4 in FIGS. 3A and 3B correspond to the four reference voltages generated by the reference voltage source 78. The shunt levels L1, L2, L3, and L4 increase in the amount of current drawn in this order.

  The peak current of the shunt level L1 is about 9 times that when the duty ratio is 10% and when the duty ratio is 100%. When the duty ratio is 10%, the output voltage of the shunt level L1 increases from 45V when the duty ratio is 100% to about 78V. The peak current and output voltage of the shunt level L1 are almost the same as the comparative examples shown in FIGS. 18A and 18B, and the effect of suppressing the peak value of the LED current by the shunt circuit 70 is hardly obtained. That is, the reference voltage is inappropriate for the shunt circuit 70.

  The shunt level L2 peak current is suppressed to about 6 times when the duty ratio is 10% and when the duty ratio is 100%. When the duty ratio is 10%, the output voltage of the shunt level L2 increases from about 45V when the duty ratio is 100% to about 65V. The peak current of the shunt level L2 is suppressed as compared with the comparative example shown in FIG. 18A, and the effect of suppressing the peak value of the LED current by the shunt circuit 70 is achieved. Further, the output voltage of the shunt level L2 is suppressed more than the comparative example shown in FIG. 18B, and the effect of limiting the output voltage by the shunt circuit 70 is achieved. That is, the reference voltage is an appropriate example for the shunt circuit 70.

  The shunt level L3 has a stronger effect of suppressing the peak value of the LED current than the shunt level L2, and also has a strong effect of limiting the output voltage. The example of the shunt level L3 is also an example in which the reference voltage as the shunt circuit 70 is appropriate.

  In shunt level L4, the effect of suppressing the peak value of the LED current is stronger than in shunt level L3, and the effect of limiting the output voltage is also stronger. The example of the shunt level L4 is also an example in which the reference voltage as the shunt circuit 70 is appropriate.

  Which of the shunt levels L2 to L4 corresponds to the reference voltage may be selected according to the rating of the light source 20.

  According to the illumination light communication apparatus according to the first embodiment configured as described above, the voltage applied to the light source 20 is limited so that the peak value of the current flowing through the light source 20 does not exceed the maximum rating of the light source 20. Therefore, there is an effect that it is possible to reduce the loss of the reliability of the light source even when the intermittent on-duty ratio becomes small.

  Next, a modified example of the illumination light communication apparatus according to Embodiment 1 will be described.

  FIG. 4 is a block diagram showing a modification of the illumination light communication apparatus according to the first embodiment. FIG. 4 is different from FIG. 1 in the circuit configuration in the current detection circuit 60. Hereinafter, different points will be mainly described.

  The current detection circuit 60 in FIG. 4 has a function of limiting the LED current as compared with FIG. The function of limiting the LED current is to realize a dimming function that indicates the brightness of the illumination light. That is, the current detection circuit 60 has a function of detecting the magnitude of the LED current and a function of limiting the LED current. Therefore, the current detection circuit 60 includes a transistor 611, a current detection resistor 612, an operational amplifier 613, a resistor 614, and a reference voltage source 615.

  The transistor 611 and the current detection resistor 612 are connected in series with the switch 22. A series circuit including the transistor 611 and the current detection resistor 612 is a circuit for detecting the magnitude of the LED current as a voltage drop across the both ends. That is, the potential at the connection point between the switch 22 and the transistor 611 indicates the magnitude of the LED current.

  The operational amplifier 613 generates a gate signal corresponding to an error between the voltage drop of the current detection resistor 612 of the current detection circuit 60 and the reference potential of the reference voltage source 615 and supplies the gate signal to the transistor 611. The transistor 611 has a resistance value corresponding to the voltage of the gate signal, thereby limiting the LED current. Note that the voltage drop of the current detection circuit 60 (that is, the potential at the connection point between the switch 22 and the transistor 611) is input to the feedback circuit 5 via the input resistor 62, and DC-DC so that the voltage drop maintains a constant value. The output of the converter 3 is controlled.

  The reference voltage source 615 generates a reference voltage corresponding to the dimming rate that indicates the brightness of the illumination light.

  Next, the operation of the modified example of the illumination light communication apparatus according to Embodiment 1 will be described using the simulation result of the illumination light communication apparatus.

  FIG. 5A is a diagram illustrating a characteristic of an LED peak current with respect to a duty ratio in an illumination light communication apparatus according to a modified example. Moreover, FIG. 5B is a figure which shows the characteristic of the output voltage with respect to the duty ratio in the illumination light communication apparatus which concerns on a modification. 5A and 5B are almost the same as FIGS. 3A and 3B.

  As described above, also in the modified example of FIG. 4 having the dimming function, the same effect as that of FIG. Therefore, even when the intermittent on-duty ratio is reduced, it is possible to reduce the loss of the reliability of the light source.

  As described above, the illumination light communication apparatus according to Embodiment 1 is connected in series with the light source 20 that emits illumination light, the signal generation circuit 23 that generates a binary communication signal, and the light source 20, and the light source 20 is connected according to the communication signal. A switch 22 that interrupts the flowing current, a current detection circuit 60 that is connected in series with the switch 22 and detects the magnitude of the current flowing through the light source 20 as a voltage drop, the voltage drop of the current detection circuit 60 and the first reference voltage A feedback circuit 5 that generates a feedback signal indicating an error between the output current, a current output to the light source 20, a DC-DC converter 3 that keeps an average output current constant based on the feedback signal, and a current flowing through the light source 20. A shunt circuit for limiting the voltage applied to the light source so that the peak value does not exceed the maximum rating of the light source.

  According to this, even in the illumination light communication device having the dimming function, it is possible to reduce the loss of the reliability of the light source when the operation for intermittently switching the LED current is performed with a small on-duty ratio.

  Here, the shunt circuit 70 detects the voltage applied to the light source 20, and limits the voltage applied to the light source 20 by sucking a part of the output current of the DC-DC converter 3 according to the detected voltage. May be.

  According to this, the voltage applied to the light source 20 is limited by sucking a part of the output current of the DC-DC converter 3 so that the peak value of the LED current does not exceed the maximum rating of the light source 20. Can do.

  Here, the shunt circuit 70 may be connected in parallel to a series circuit including the light source 20 and the switch 22, and may be connected in series to the current detection circuit 60.

  Here, the current detection circuit 60 includes a current detection resistor 61 connected in series to the switch 22, and the voltage drop may be a voltage across the current detection resistor 61.

  Here, the current detection circuit 60 includes a transistor 611 connected in series to the switch 22, a current detection resistor 612 connected in series to the transistor 611, the potential of the current detection resistor 612, and the first dimming rate corresponding to the dimming rate. 2 is provided with an operational amplifier 613 for supplying a gate signal corresponding to an error from the reference voltage, and the voltage drop of the current detection circuit 60 is a voltage across the series circuit composed of the transistor 611 and the current detection resistor 612. May be.

  According to this, the illumination light communication apparatus having the light control function has the same effect as described above.

  Next, the loss caused by the shunt circuit 70 sinking a part of the output current of the DC-DC converter 3 will be described.

  FIG. 6A is a diagram illustrating a loss characteristic with respect to a duty ratio in an illumination light communication apparatus according to a modification. The horizontal axis of the figure shows the intermittent duty ratio. The vertical axis of the figure shows the loss that occurs in the shunt circuit 70. FIG. 6A shows the result of simulating the loss generated in the shunt circuit 70 for three cases in which the output voltage of the DC-DC converter 3 is 67.6V, 62.4V, and 57.2V. As shown in FIG. 6A, when the duty ratio is small, it can be seen that the lower the output voltage (that is, the greater the amount of current drawn and the greater the voltage), the greater the loss.

  Moreover, FIG. 6B is a figure which shows the characteristic of the loss with respect to the duty ratio in the illumination light communication apparatus which concerns on a modification. FIG. 6B shows the result of simulating the loss occurring in the shunt circuit 70 for five cases where the dimming rate is 100%, 75%, 50%, 25%, and 10%. As shown in FIG. 6B, it can be seen that when the duty ratio is small, the loss increases as the dimming rate increases (that is, the illumination light becomes brighter).

  The amount of current drawn in the shunt circuit 70 should be set so that the loss in FIGS. 6A and 6B is reduced. In the following embodiment, an example of suppressing loss generated in the shunt circuit 70 will be described.

(Embodiment 2)
Next, the illumination light communication apparatus according to Embodiment 2 will be described. In the present embodiment, a configuration example will be described in which the dimming function is linked to reduce the loss of the shunt circuit 70 with respect to the modification shown in FIG.

[2.1 Illumination light communication device configuration]
FIG. 7 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the second embodiment. This figure is different from FIG. 4 in that an adjustment circuit 520 is added. Hereinafter, different points will be mainly described.

  The adjustment circuit 520 is a circuit that adjusts the reference voltage of the reference voltage source 615 so that the amount of current sucked by the shunt circuit 70 is constant. This adjustment suppresses the loss generated in the shunt circuit 70 so as not to exceed a certain level.

  Next, a specific circuit example of the adjustment circuit 520 will be described.

  FIG. 8 is a circuit diagram illustrating a configuration example of the shunt circuit 70, the adjustment circuit 520, and the reference voltage source 615 according to the second embodiment.

  The shunt circuit 70 of FIG. 8 has a resistor 79 added to the shunt circuit of FIG. The resistor 79 is a current detection resistor that is connected in series with the resistor 72 and the transistor 71 and detects the magnitude of the sink current (also referred to as shunt current).

  The adjustment circuit 520 includes an operational amplifier 521, a reference voltage source 522, an output resistor 523, and a light emitting element 524.

  A resistor 79 is connected to the positive input terminal of the operational amplifier 521, and a signal SH indicating the magnitude of the shunt current is input. The reference voltage of the reference voltage source 522 is input to the negative input terminal of the operational amplifier 521. The operational amplifier 521 outputs an error between the signal SH indicating the magnitude of the shunt current and the reference voltage of the reference voltage source 522 to the light emitting element 524 via the output resistor 523.

  The light emitting element 524 emits light with a light amount corresponding to an error between the signal SH and the reference voltage of the reference voltage source 522.

  The reference voltage source 615 includes a resistor 616 and a light receiving element 617. The light receiving element 617 forms a photocoupler together with the light emitting element 524, and allows a current corresponding to the amount of light received from the light emitting element 524 to flow. The resistor 616 and the light receiving element 617 are connected in series, and the potential at the connection point is output as the reference voltage Vref. The reference voltage Vref of the reference voltage source 615 is adjusted to a voltage corresponding to the magnitude of the shunt current.

  With such a configuration, the illumination light communication apparatus operates when the shunt circuit 70 operates when the intermittent duty ratio of the switch 22 is small and sucks a part of the output current of the DC-DC converter 3. When the shunt current is increased, the adjustment circuit 520 adjusts the reference voltage of the reference voltage source 615 to be smaller. Thereby, the current of the current detection circuit 60 is limited, and the output current of the DC-DC converter 3 is reduced by the feedback control by the feedback circuit 5 and the DC-DC converter 3. As a result, the shunt current also decreases, and an increase in loss that occurs in the shunt circuit 70 can be suppressed.

[2.2 Operation of illumination light communication device]
Next, operation | movement of an illumination light communication apparatus is demonstrated using the simulation result of an illumination light communication apparatus.

  FIG. 9 is a diagram illustrating a characteristic of loss with respect to the duty ratio in the illumination light communication apparatus according to Embodiment 2. In FIG. The horizontal axis of the figure shows the intermittent duty ratio of the switch 22 and shows a portion with a small duty ratio from 5% to 20%. The vertical axis indicates the loss that occurs in the shunt circuit 70. The characteristic curve (A) “with adjustment” in FIG. 8 shows the loss characteristic in the illumination light communication apparatus of FIG. The characteristic curve (B) “No adjustment” in the figure shows the loss characteristic in the illumination light communication apparatus of FIG.

  As indicated by the characteristic curve (A) in the figure, the illumination light communication apparatus in the present embodiment is suppressed without increasing the loss generated in the shunt circuit 70 even when the duty ratio is reduced.

  As described above, the illumination light communication apparatus according to Embodiment 2 includes the adjustment circuit 520 that adjusts the second reference voltage so that the amount of current that the shunt circuit 70 absorbs from the output current is constant.

  According to this, the adjustment circuit 520 adjusts the reference voltage of the reference voltage source 615 so that the amount of current that the shunt circuit 70 sinks from the output current is constant, so that the loss generated in the shunt circuit 70 is suppressed to a certain level or less. be able to.

(Embodiment 3)
Next, the illumination light communication apparatus according to Embodiment 3 will be described. In the present embodiment, a configuration example in which the pulse width of the communication signal is controlled to reduce the loss of the shunt circuit 70 will be described with respect to the configuration example shown in FIG.

[3.1 Configuration of Illumination Optical Communication Device]
FIG. 10 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the third embodiment. This figure is different from FIG. 1 in that a pulse control circuit 200 is added. Hereinafter, different points will be mainly described.

  The pulse control circuit 200 is a circuit that adjusts the pulse width of the communication signal in accordance with the amount of current that the shunt circuit 70 sucks from the output current of the DC-DC converter 3.

  FIG. 11 is a circuit diagram showing a configuration example of the shunt circuit 70 and the pulse control circuit 200 according to the third embodiment.

  The shunt circuit 70 has already been described with reference to FIG.

  The pulse control circuit 200 of FIG. 11 includes an operational amplifier 223, a reference voltage source 224, a one-shot IC 225, a resistor 226, a capacitor 227, a capacitor 228, a diode 229, a resistor 230, an inverting circuit 231, and an output resistor 232.

  The operational amplifier 223 amplifies an error between the signal SH indicating the magnitude of the shunt current and the reference voltage of the reference voltage source 224 and supplies the amplified error to the one-shot IC 225.

  The one-shot IC 225 is a so-called “555” timer IC, and constitutes a monostable multivibrator that generates a one-shot pulse in response to a trigger signal. As shown in FIG. 12, the communication signal ID generated by the signal generation circuit 23 is extracted from the rising edge (point A potential) by a differentiating circuit including a capacitor 228, a diode 229, and a resistor 230. This rising edge change is input to the trigger input terminal of the one-shot IC 225 via the inverting circuit 231 as a trigger signal. The one-shot IC 225 outputs a one-shot pulse from the output terminal Out in accordance with the trigger signal (point B potential). The width of this one-shot pulse is determined by the voltage of the resistor 226, the capacitor 227, and the control terminal Cont. For example, when the error signal output from the operational amplifier 223 is 0, the one-shot pulse width has the same width as the pulse of the original communication signal ID, and depends on the voltage of the error signal (that is, the voltage of the control terminal Cont). Become wider. The pulse output from the output terminal Out of the one-shot IC 225 is input to the gate of the switch 22 via the output resistor 232.

[3.2 Operation of illumination optical communication device]
Next, operation | movement of an illumination light communication apparatus is demonstrated using the simulation result of an illumination light communication apparatus.

  FIG. 13 is a diagram illustrating a characteristic of loss with respect to the duty ratio in the illumination light communication apparatus according to Embodiment 3. The horizontal axis of the figure shows the duty ratio of the pulse output from the pulse control circuit 200. The vertical axis indicates the loss that occurs in the shunt circuit 70. The figure shows the loss characteristics when the width of the pulse output from the pulse control circuit 200 is changed for three cases where the average LED current is 20 mA, 50 mA, and 100 mA.

  In the case of 20 mA of LED current, loss is shown when the duty ratio of the pulse output from the pulse control circuit 200 is about 4%, about 5%, about 6%, about 7%, or about 8%. .

  In the case of 50 mA of LED current, loss is shown when the duty ratio of the pulse output from the pulse control circuit 200 is about 12%, about 13%, about 14%, about 16%, and about 17%. .

  In the case of 100 mA of LED current, the loss is shown when the duty ratio of the pulse output from the pulse control circuit 200 is about 23%, about 24%, about 25%, about 27%, about 30%. .

  From FIG. 13, it can be seen that the loss of the shunt circuit 70 is greatly reduced by a slight increase in the pulse width of the intermittent signal. For example, an increase of about 2% in pulse width reduces the loss by half.

  FIG. 14 is a diagram showing LED current versus duty ratio when the loss in the illumination light communication apparatus according to Embodiment 3 is kept constant. The horizontal axis of FIG. 14 shows the average LED current. The vertical axis represents the intermittent duty ratio of the switch 22. FIG. 14 is a graph obtained by extracting the LED current (average) and the duty ratio when the loss is 100 mW in FIG. If the pulse control circuit 200 controls the pulse width so as to satisfy FIG. 14, the loss generated in the shunt circuit 70 can be suppressed so as not to exceed 100 mW.

  As described above, the illumination light communication apparatus according to the third embodiment includes the pulse control circuit 200 that increases the pulse width of the communication signal according to the amount of current that the shunt circuit 70 sucks from the output current of the DC-DC converter 3. The switch 22 interrupts the current flowing through the light source 20 in accordance with the communication signal from the pulse control circuit 200.

  According to this, in addition to the above effect, the loss generated in the shunt circuit 70 can be reduced by slightly widening the pulse width of the communication signal that intermittently switches the switch 22, and the loss can be reduced to a certain level or less. Can be suppressed.

(Embodiment 4)
Subsequently, an illumination light communication apparatus according to Embodiment 4 will be described. In the present embodiment, a configuration example will be described in which the amount of sink current is changed in order to reduce the loss of the shunt circuit 70 below a certain level with respect to the configuration example shown in FIG.

[4.1 Configuration of Illumination Optical Communication Device]
FIG. 15 is a block diagram illustrating a configuration example of the illumination light communication apparatus according to the fourth embodiment. Compared with FIG. 1, this figure mainly differs in that a current detection resistor 24 is added and a peak value detection circuit is added. Hereinafter, different points will be mainly described.

  The current detection resistor 24 is connected to the light source 20 and the switch 22 in series, and is a resistance element for detecting the magnitude of the LED current.

  The peak value detection circuit 780 is a peak hold circuit that receives the potential of the current detection resistor 24 and detects and holds the peak value (peak value) of the current flowing through the light source 20.

  The shunt circuit 70 changes the amount of current that can be absorbed from the output current of the DC-DC converter 3 in accordance with the peak value held in the peak value detection circuit 780. Thereby, the height of the LED current pulse necessary for optical communication can be maintained. For example, when the LED current pulse height is insufficient, the amount of current drawn by the shunt circuit 70 is reduced, and when the pulse is too high, the amount of current drawn is increased.

  FIG. 16 is a circuit diagram showing a configuration example of the shunt circuit 70 and the peak value detection circuit 780 according to the fourth embodiment.

  The peak value detection circuit 780 includes a diode 781, a capacitor 782, a resistor 783, a resistor 784, an operational amplifier 785, a reference voltage source 786, a resistor 787, a resistor 788, a resistor 789, and a resistor 7810. With this configuration, the peak value detection circuit 780 detects the peak value (peak value) of the potential (that is, the magnitude of the LED current) of the current detection resistor 24 in the modulator 21 and holds it in the capacitor 782. The potential of the capacitor 782 is amplified by an operational amplifier 785 and output to the shunt circuit 70 through a resistor circuit including a resistor 788, a resistor 789 and a resistor 7810.

  In the shunt circuit 70, the output of the peak value detection circuit 780 is input to the negative input terminal of the operational amplifier 73 instead of the reference voltage of the reference voltage source 78 in FIG. 2 being input to the negative input terminal of the operational amplifier 73. . As a result, the amount of current that can be absorbed by the shunt circuit 70 becomes variable according to the peak value of the LED current.

  Further, the shunt circuit 70 changes the magnitude of the reference voltage of the reference voltage source 52 in the feedback circuit 5 according to the signal SH indicating the amount of current drawn from the output current of the DC-DC converter 3. In this case, the reference voltage of the reference voltage source 52 is variable according to the dimming rate, and is further adjusted according to the signal SH from the shunt circuit 70.

  As described above, the illumination light communication apparatus according to Embodiment 4 includes the peak value detection circuit 780 that detects the peak value of the current flowing through the light source 20, and the shunt circuit 70 is configured to perform DC according to the peak value. -The amount of current that can be drawn from the output current of the DC converter 3 is changed.

  According to this, since the amount of current that can be drawn from the output current of the DC-DC converter 3 is changed according to the peak value of the LED current, for example, even when the dimming rate is low (even when dark), it is visible It becomes easy to ensure the high LED current required for optical communication.

  Here, the illumination light communication apparatus includes a peak value detection circuit 780 that detects a peak value of the current flowing through the light source 20, and the shunt circuit 70 outputs the output of the DC-DC converter 3 according to the peak value. The amount of current drawn from the current may be changed, and the magnitude of the first reference voltage may be changed according to the amount of current drawn from the output current.

  As described above, the illumination light communication apparatus according to the present invention has been described based on the embodiment, but the present invention is not limited to the embodiment. Without departing from the gist of the present invention, various modifications conceived by those skilled in the art have been made in this embodiment, and other forms constructed by arbitrarily combining some components in the embodiments and modifications are also possible. Are included within the scope of the present invention.

3 DC-DC converter 5 feedback circuit 20 light source 22 switch 23 signal generation circuit 60 current detection circuit 61 current detection resistor 70 shunt circuit 200 pulse control circuit 520 adjustment circuit 611 transistor 612 current detection resistor 613 operational amplifier 780 peak value detection circuit

Claims (9)

A light source that emits illumination light;
A signal generation circuit for generating a binary communication signal;
A switch that is connected in series with the light source and interrupts the current flowing through the light source according to the communication signal;
A current detection circuit connected in series with the switch and detecting the magnitude of the current flowing through the light source as a voltage drop;
A feedback circuit for generating a feedback signal indicating an error between a voltage drop of the current detection circuit and a first reference voltage;
A DC-DC converter that outputs a current to the light source and keeps an average value of the output current constant based on the feedback signal;
An illumination optical communication apparatus comprising: a shunt circuit that limits a voltage applied to the light source so that a peak value of a current flowing through the light source does not exceed a maximum rating of the light source. The shunt circuit limits a voltage applied to the light source by detecting a voltage applied to the light source and sucking a part of an output current of the DC-DC converter according to the detected voltage. The illumination light communication apparatus according to 1. The illumination optical communication apparatus according to claim 1, wherein the shunt circuit is connected in parallel to a series circuit including the light source and the switch, and is connected in series to the current detection circuit. The current detection circuit has a current detection resistor connected in series to the switch,
The illumination light communication device according to claim 1, wherein the voltage drop is a voltage across the current detection resistor. The current detection circuit includes:
A transistor connected in series to the switch;
A current detection resistor connected in series with the transistor;
An operational amplifier that supplies the transistor with a gate signal corresponding to an error between the potential of the current detection resistor and a second reference voltage corresponding to a dimming rate;
The illumination light communication apparatus according to any one of claims 1 to 3, wherein the voltage drop of the current detection circuit is a voltage across a series circuit including the transistor and the current detection resistor. The illumination light communication device further includes:
The illumination light communication apparatus according to claim 5, further comprising an adjustment circuit that adjusts the second reference voltage so that the amount of current that the shunt circuit sinks from the output current is constant. The illumination light communication device further includes a pulse control circuit that increases a pulse width of the communication signal according to an amount of current sucked from an output current of the DC-DC converter by the shunt circuit.
The illumination light communication apparatus according to any one of claims 1 to 6, wherein the switch interrupts a current flowing through the light source in accordance with a communication signal from the pulse control circuit. The illumination light communication device further includes a peak value detection circuit that detects a peak value of a current flowing through the light source,
The illumination light communication apparatus according to claim 1, wherein the shunt circuit changes an amount of current that can be absorbed from an output current of the DC-DC converter according to the peak value. The illumination light communication device further includes a peak value detection circuit that detects a peak value of a current flowing through the light source,
The shunt circuit changes the amount of current drawn from the output current of the DC-DC converter according to the peak value, and the magnitude of the first reference voltage according to the amount of current drawn from the output current. The illumination light communication apparatus according to any one of claims 1 to 5 and 7, wherein: