Light-emitting unit and optical sensor

Abstract

A light-emitting unit (1) comprises: a light-emitting diode (22) that is provided in a light-emitting branch route section (Rl) branching from between an inductor (241) and a capacitor (242) in a resonance circuit unit (240) and that generates irradiation light by light emission; a discharge switching element (246) that is provided in the light-emitting branch route section (Rl) and that turns on and off the discharge from the capacitor (242) by switching; a charge switching element (247) that is provided on a side closer to the inductor (241) in the resonance circuit unit (240) as compared with the branch point of the light-emitting branch route section (Rl) and that turns on and off the charge for the capacitor (242) by switching; and a drive circuit unit (248) that controls the discharge switching element (246) and the charge switching element (247) by individual on and off drive operations. The drive circuit unit (248) performs control on the on-period of the charge switching element (247) prior to the on-timing of the discharge switching element (246).

Description

Light-emitting unit, optical sensor CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2023-150338 filed in Japan on September 15, 2023, and the contents of the original application are incorporated by reference in their entirety.

[0002] The present disclosure relates to a light emitting technology in an optical sensor that senses a target by receiving light reflected from the target in response to light irradiated onto a sensing area.

[0003] In an optical sensor that receives reflected light from irradiated light, a light-emitting technology that emits light to emit the irradiated light is disclosed in Patent Document 1. In the technology disclosed in Patent Document 1, in a resonant circuit having an inductor and a capacitor, charging and discharging of the capacitor are switched by a switching element, and a light-emitting diode emits light in response to the discharge of the capacitor.

[0004] U.S. Pat. No. 9,368,936

[0005] However, in the technology disclosed in Patent Document 1, the peak intensity of the emitted light remains constant. Therefore, when the reflected intensity of the emitted light is high, such as in the case of a nearby target or a highly reflective target, the intensity of the received light relative to the reflected light may become saturated, which may result in a decrease in sensing accuracy.

[0006] Therefore, an object of the present disclosure is to provide a light-emitting unit and an optical sensor that ensure target sensing accuracy.

[0007] The technical means of the present disclosure for solving the problems will be described below.

[0008] a light-emitting diode (LED) provided in the light-emitting branch path section, the light-emitting diode generating the illumination light by emitting light; a discharge switching element provided in the light-emitting branch path section, the light-emitting diode switching on and off the discharge from the capacitor; a charge switching element provided in the resonant circuit section, closer to the inductor than the branch point of the light-emitting branch path section, the charge switching element switching on and off the charge to the capacitor; and a drive circuit section controlling the discharge switching element and the charge switching element by individual on / off driving, wherein the drive circuit section controls the on period of the charge switching element prior to the on timing of the discharge switching element.

[0009] A second aspect of the present disclosure includes the light-emitting unit of the first aspect and a light-receiving unit that receives reflected light of the irradiated light emitted by the light-emitting unit.

[0010] According to the first and second aspects, the light-emitting branch path section branching off between the inductor and the capacitor in the resonant circuit section includes a light-emitting diode that generates irradiated light by emitting light and a discharge switching element that switches on and off the discharge from the capacitor. In particular, a charge switching element that switches on and off the charge to the capacitor is provided in the resonant circuit section closer to the inductor than the branch point of the light-emitting branch path section. This arrangement allows the light-receiving sensitivity to be relatively reduced by shortening the on-period of the charge switching element prior to the on-timing of the discharge switching element, even if the received light intensity of the reflected light relative to the irradiated light becomes saturated. Therefore, this shortening control suppresses the peak intensity of the irradiated light to a low intensity that matches the received light intensity of the reflected light, ensuring target sensing accuracy.

[0011] FIG. 1 is a cross-sectional view showing the configuration of an optical sensor according to an embodiment; FIG. 2 is a schematic diagram showing the mechanical configuration of a light-emitting unit according to an embodiment; FIG. 3 is a schematic diagram showing the mechanical configuration of a light-receiving unit according to an embodiment; FIG. 4 is a circuit diagram showing the electrical configuration of a light-emitting unit according to an embodiment; FIG. 5 is a graph showing the light-emitting characteristics of a light-emitting unit according to an embodiment; FIG. 6 is a graph showing the light-emitting characteristics of a light-emitting unit according to an embodiment;

[0012] 1 , one embodiment of the present disclosure relates to an optical sensor 2 including a light-emitting unit 1. The optical sensor 2 is mounted on a vehicle 5. The vehicle 5 is a mobile body such as an automobile that can travel on a road with an occupant on board.

[0013] The vehicle 5 is capable of steady or temporary autonomous driving in an autonomous driving control mode. Here, the autonomous driving control mode may be realized by autonomous driving control, such as conditional driving automation, highly automated driving, or fully automated driving, in which a system performs all driving tasks when activated. The autonomous driving control mode may also be realized by advanced driving assistance control, such as driving assistance or partial driving automation, in which a passenger performs some or all driving tasks. The autonomous driving control mode may be realized by either autonomous driving control or advanced driving assistance control, or by a combination of these, or by switching between them.

[0014] In the following description, unless otherwise specified, the directions of front, rear, up, down, left, and right are defined with respect to the vehicle 5 on a horizontal plane. The horizontal direction refers to a direction parallel to the horizontal plane that serves as the directional reference for the vehicle 5. The vertical direction refers to a vertical direction that is also the up-down direction with respect to the horizontal plane that serves as the directional reference for the vehicle 5.

[0015] The optical sensor 2 is a so-called LiDAR (Light Detection and Ranging / Laser Imaging Detection and Ranging) for acquiring image data that can be used for driving control, including automatic driving mode, of the vehicle 5. The optical sensor 2 is disposed in at least one location on the vehicle 5, such as the front, left and right side portions, rear portion, or upper roof.

[0016] In the optical sensor 2, a three-dimensional Cartesian coordinate system is defined by three mutually orthogonal axes: an X axis, a Y axis, and a Z axis. In particular, in this embodiment, the X axis and the Z axis are set along different horizontal directions of the vehicle 5, and the Y axis is set along the vertical direction of the vehicle 5. Note that in Fig. 1, the left side of the dashed dotted line along the Y axis (the side of a translucent panel 12 described below) actually illustrates a cross section perpendicular to the right side of the dashed dotted line (the side of modules 21 and 41 described below) where the three-dimensional Cartesian coordinate system is defined.

[0017] The optical sensor 2 emits light toward a sensing area As corresponding to the installation location and field of view angle in the external space of the vehicle 5. The optical sensor 2 receives reflected light that enters the sensing area As when the emitted light is reflected from the sensing area As. In response to receiving the reflected light of the emitted light, the optical sensor 2 senses a target that reflects light within the sensing area As. Here, sensing means measuring at least the reflection point distance from the optical sensor 2 to the target and the reflection intensity from the target.

[0018] A typical sensing target in the optical sensor 2 applied to the vehicle 5 may be at least one of moving objects such as a pedestrian, a cyclist, a non-human animal, and another vehicle. A typical sensing target in the optical sensor 2 applied to the vehicle 5 may be at least one of stationary objects such as a guardrail, a road sign, a roadside structure, and an object fallen on the road.

[0019] The optical sensor 2 includes a casing module 10, a light-projecting module 21, a scanning module 31, a light-receiving module 41, and a control module 51. The casing module 10 includes a housing 11 and a light-transmitting panel 12. The housing 11 is formed in a hollow box shape and is mainly made of a light-blocking material such as metal or synthetic resin. The housing 11 houses the light-projecting module 21, the scanning module 31, and the light-receiving module 41 inside. The housing 11 holds the light-transmitting panel 12, which is formed in a plate shape from a light-transmitting material such as glass or synthetic resin.

[0020] The light-projecting module 21 includes a light-emitting unit 1 and a light-projecting lens system 28. As shown in FIG. 2 , the light-emitting unit 1 is constructed by mounting a plurality of light-emitting diodes 22 in an array on a substrate 21. Each light-emitting diode 22 generates pulsed infrared laser light that is used to irradiate the sensing area As under the control of the control module 51. Each of these light-emitting diodes 22 is provided as a laser diode, such as an edge-emitter laser or a vertical cavity surface-emitting laser (VCSEL).

[0021] As shown in FIG. 1 , the light projection lens system 28 projects the illumination light emitted by the light-emitting unit 1 toward the scanning mirror 32 of the scanning module 31. The light projection lens system 28 performs at least one optical function, such as focusing, collimating, and shaping. The light projection lens system 28 forms a projection optical axis along the Z axis. The light projection lens system 28 has at least one projection lens 29 on the projection optical axis, the lens shape of which corresponds to the optical function to be performed. The light-emitting unit 1 is positioned on the projection optical axis of the light projection lens system 28. The illumination light emitted by each light-emitting diode 22 in the light-emitting unit 1 is guided along the projection optical axis of the light projection lens system 28.

[0022] The scanning module 31 includes a scanning mirror 32 and a scanning motor 35. The scanning mirror 32 is formed into a plate shape by depositing a reflective film on a reflective surface 33, which is one side of a base material. The scanning mirror 32 is supported by the housing 11 so as to be rotatable around a rotation center line along the Y axis. The scanning mirror 32 oscillates within a driving range that is finite due to the function of a mechanical or electrical stopper.

[0023] The scanning mirror 32 is provided in common to the light-projecting module 21 and the light-receiving module 41. The scanning mirror 32 irradiates the sensing area As with the irradiated light incident from the light-projecting lens system 28 of the light-projecting module 21 by reflection from a reflecting surface 33 oriented in accordance with the rotation angle through the light-transmitting panel 12, thereby scanning the area As both temporally and spatially. In particular, in the optical sensor 2, the mechanical scanning of the sensing area As with the irradiated light is substantially limited to scanning in the horizontal direction.

[0024] Simultaneously with this scanning, the scanning mirror 32 further reflects the reflected light incident from the sensing area As through the light-transmitting panel 12 toward the light-receiving module 41 by the reflecting surface 33 oriented according to the rotation angle. Here, the speeds of the irradiated light and reflected light are sufficiently high compared to the rotational speed of the scanning mirror 32. As a result, the reflected light relative to the irradiated light is guided toward the light-receiving module 41 by the scanning mirror 32, which has approximately the same rotation angle as the irradiated light, so as to travel in the opposite direction to the irradiated light.

[0025] The scanning motor 35 is, for example, a voice coil motor, a brushed DC motor, or a stepping motor. The scanning motor 35 drives the scanning mirror 32 to rotate (i.e., swing) within the finite driving range under the control of the control module 51. At this time, the rotation angle of the scanning mirror 32 is sequentially changed in synchronization with the light emission period Pl (see FIG. 5 described later) of the light-emitting unit 1 of the light-projecting module 21.

[0026] The light-receiving module 41 is disposed offset in the Y-axis direction relative to the light-projecting module 21. The light-receiving module 41 includes a light-receiving lens system 42 and a light-receiving unit 45. The light-receiving lens system 42 exerts an optical function to image the light reflected from the sensing area As onto the light-receiving unit 45. The light-receiving lens system 42 forms a light-receiving optical axis along the Z-axis. The light-receiving lens system 42 has at least one light-receiving lens 43 on the light-receiving optical axis, the lens shape of which corresponds to the optical function to be exerted. The reflected light incident from the reflecting surface 33 of the scanning mirror 32 is guided along the light-receiving optical axis of the light-receiving lens system 42, regardless of the rotation angle of the scanning mirror 32 within the driving section.

[0027] The light receiving unit 45 is positioned on the light receiving optical axis of the light receiving lens system 42. As shown in FIG. 3 , the light receiving unit 45 is constructed by arranging a plurality of light receiving pixels 46 in an array on a substrate. Each light receiving pixel 46 is further constructed from a plurality of light receiving elements 460. The light receiving elements 460 of each light receiving pixel 46 are mainly composed of photodiodes such as single photon avalanche diodes (SPADs). With this configuration, each light receiving pixel 46 receives reflected light incident from the light receiving lens system 42 with each light receiving element 460.

[0028] 1 , the light receiving unit 45 is integrally provided with an output circuit 48. The output circuit 48 performs sampling processing under control of the control module 51 for each scanning line associated with the rotation angle of the scanning mirror 32 according to the light emission period Pl. Thus, through the sampling processing, the output circuit 48 generates light reception data for each scanning line based on the output signal from each light receiving pixel 46 of the light receiving unit 45. The light reception data generated in this manner is output from the output circuit 48 to the control module 51.

[0029] The control module 51 is mainly composed of at least one computer having a processor 52 and a memory 53. The control module 51 may be entirely housed inside the housing 11 (example of FIG. 1 ). The control module 51 may be entirely disposed in the vehicle 5 outside the housing 11. The control module 51 may be distributed across the inside of the housing 11 and the external vehicle 5.

[0030] The control module 51 is connected to the light-emitting unit 1, the scanning motor 35, and the output circuit 48. The control module 51 controls these connected components by executing a control program stored in the memory 53 using the processor 52. Specifically, the control module 51 synchronously controls the light emission of each light-emitting diode 22 in the light-emitting unit 1 and the rotation of the scanning mirror 32 by the scanning motor 35 for each light-emitting period Pl. In parallel with this, the control module 51 acquires light-receiving data from the output circuit 48 for each scanning line, which corresponds to each light-receiving period Pl, thereby sensing at least the reflection point distance from the optical sensor 2 to the target and generating sensing information based on the light-receiving data.

[0031] Next, the detailed configuration of the light-emitting unit 1 shown in Fig. 4 will be described. In the light-emitting unit 1, a plurality of light-emitting circuits 24 corresponding to the number of light-emitting diodes 22 are constructed. In addition to the light-emitting diodes 22, the light-emitting circuits 24 include a resonant circuit section 240, switching elements 246 and 247, and a drive circuit section 248. Note that Fig. 4 representatively shows a light-emitting circuit 24 corresponding to one light-emitting diode 22.

[0032] The resonant circuit section 240 is provided with a power supply terminal Ev to which a power supply voltage Vin is applied and a ground terminal E0 to which a ground voltage is applied. The resonant circuit section 240 is a so-called LC series circuit having an inductor 241 and a capacitor 242 connected in series between the power supply terminal Ev and the ground terminal E0. The inductor 241 is mainly composed of an induction coil. The capacitor 242 is mainly composed of a heat-resistant capacitor, such as an electrolytic type.

[0033] In the light-emitting circuit 24, the section from the midpoint E1 between the inductor 241 and the capacitor 242 in the resonant circuit section 240 to the ground terminal E0 is connected in parallel with the capacitor 242 by the light-emitting branch path section RI. The light-emitting branch path section RI is provided with a discharge switching element 246. The discharge switching element 246 is mainly composed of a field-effect transistor such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Due to this arrangement and configuration in the light-emitting branch path section RI, the discharge switching element 246 can turn on and off the discharge from the capacitor 242 by switching.

[0034] In the light-emitting circuit 24, the light-emitting branch path Rl extending from the midpoint E1 to the ground terminal E0 is provided with a light-emitting diode 22 on the ground terminal E0 side relative to the discharge switching element 246. The forward direction in which the light-emitting diode 22 rectifies the current Io is set to the direction from the discharge switching element 246 side toward the ground terminal E0 side. The light-emitting diode 22 generates illumination light by emitting light due to discharge from the capacitor 242 in response to the discharge switching element 246 being turned on.

[0035] In the light-emitting circuit 24, a charge switching element 247 is provided at another midpoint E2, which is closer to the inductor 241 than the midpoint E1, which is the branch point where the light-emitting branch path RI branches off from between the inductor 241 and the capacitor 242 in the resonant circuit section 240. The charge switching element 247 is mainly composed of a field-effect transistor such as a MOSFET. Due to its placement and configuration at the midpoint E2, the charge switching element 247 can turn the charging of the capacitor 242 on and off by switching.

[0036] In the light-emitting circuit 24, a drive circuit unit 248 is connected to each of the switching elements 246, 247. The drive circuit unit 248 is also connected to the control module 51. The drive circuit unit 248 drives each of the switching elements 246, 247 to turn on and off individually, as shown in FIGS. 5 to 7, in accordance with control from the control module 51. That is, the switching of each of the switching elements 246, 247 is controlled by the on / off drive function of the drive circuit unit 248.

[0037] 5 to 7 , in the drive circuit unit 248, the reference ON timing Tn0 for switching the charge switching element 247 from an OFF drive state to an ON drive state is set to coincide with the start timing of each light emission cycle P1. At the same time, in the drive circuit unit 248, the reference OFF timing Tf0 for switching the charge switching element 247 from an ON drive state to an OFF drive state is set to a timing that is a certain period ΔTm after the reference ON timing Tn0 for each light emission cycle P1. By setting the periods of the reference ON timing Tn0 and the reference OFF timing Tf0 in this way, the maximum ON period ΔTm of the charge switching element 247 is controlled to a time that is substantially equal to the time constant of the resonant circuit unit 240.

[0038] In the drive circuit unit 248, the on-period ΔT of the charge switching element 247 is controlled for each light emission period Pl to a time equal to or shorter than the maximum on-period ΔTm. In this case, the on-timing Tn of the charge switching element 247 may be adjusted to match the reference on-timing Tn0, while the off-timing Tf may be adjusted to a variable timing before the reference off-timing Tf0, as shown by the two-dot-dash line graph in FIG. 5A. The off-timing Tf of the charge switching element 247 may be adjusted to match the reference off-timing Tf0, while the on-timing Tn may be adjusted to a variable timing after the reference on-timing Tn0, as shown by the two-dot-dash line graph in FIG. 7A. The on-timing Tn of the charge switching element 247 may be adjusted to a variable timing after the reference on-timing Tn0, while the off-timing Tf may be adjusted to a variable timing before the reference off-timing Tf0 that is later than the on-timing Tn, as shown by the two-dot-dash line graph in FIG. 7A.

[0039] In this way, the more the drive circuit unit 248 controls to shorten the on-period ΔT of the charge switching element 247, the less time the current Ii (see also FIG. 4) flows through the inductor 241 in the resonant circuit unit 240, as shown by the solid line graphs and two-dot chain line graphs corresponding to the other subdivisions in each of the subdivisions (B) in Figures 5 to 7. Correspondingly, in the resonant circuit unit 240, the voltage Vc (see also FIG. 4) charged to the capacitor 242 decreases, as shown by the solid line graphs and two-dot chain line graphs corresponding to the other subdivisions in each of the subdivisions (C) in Figures 5 to 7. In other words, the more the drive circuit unit 248 controls to shorten the on-period ΔT of the charge switching element 247, the less the charging voltage Vc of the capacitor 242 decreases.

[0040] 5 to 7 , in the drive circuit unit 248, the discharge switching element 246 in the OFF drive state is turned on at a timing that is later than the reference OFF timing Tf0 of the charge switching element 247 for each light emission period Pl. In other words, the control of the ON period ΔT for turning on the charge switching element 247 occurs prior to the ON timing Td for switching the discharge switching element 246 in the OFF drive state to ON for each light emission period Pl.

[0041] In response to the ON driving of the discharge switching element 246, a discharge current discharged from the capacitor 242, which is in a state of a charging voltage Vc, flows into the light-emitting branch path section RI through the resonant circuit section 240. As a result, a current Io (see also FIG. 4) that rises and falls following the charging voltage Vc flows through the light-emitting diode 22, and the light-emitting diode 22 emits light with a peak intensity that follows the rise and fall of the current Io, as shown by the solid line graphs and two-dot chain line graphs corresponding to the other subdivisions in each of FIGS.

[0042] Therefore, when the control module 51 recognizes an intensity saturation state, for example, where the received light intensity of reflected light from a nearby target or a highly reflective target exceeds the upper limit intensity at the light receiving unit 45, based on the light reception data from the output circuit 48, the control module 51 issues a shortening control command to the drive circuit unit 248. As a result, the drive circuit unit 248 controls the on / off driving of the charge switching element 247 so as to shorten the on period ΔT to be shorter than the maximum on period ΔTm, in accordance with the degree to which the received light intensity exceeds the upper limit intensity.

[0043] On the other hand, when the control module 51 recognizes an insufficient intensity state, for example, where the received light intensity of reflected light from a distant target falls below the lower limit intensity that ensures sensing accuracy in the light-receiving unit 45, based on the light-receiving data from the output circuit 48, the control module 51 issues an extension control command to the drive circuit unit 248. As a result, the drive circuit unit 248 controls the on / off driving of the charge switching element 247 so as to increase the on-period ΔT up to the maximum on-period ΔTm in accordance with the degree of insufficiency of the received light intensity from the lower limit intensity.

[0044] (Operations and Effects) The operations and effects of the present embodiment described above will be described below.

[0045] According to this embodiment, the light-emitting branch path RI, which branches off between the inductor 241 and the capacitor 242 in the resonant circuit 240, is provided with a light-emitting diode 22 that generates irradiated light by emitting light and a discharge switching element 246 that switches on and off the discharge from the capacitor 242. Therefore, in particular, a charge switching element 247 that switches on and off the charge to the capacitor 242 is provided in the resonant circuit 240 closer to the inductor 241 than the branch point of the light-emitting branch path RI. This allows the light-receiving sensitivity to be relatively reduced by shortening the on-period ΔT of the charge switching element 247 prior to the on-timing Td of the discharge switching element 246, even if saturation occurs in the received light intensity of reflected light relative to the irradiated light. Therefore, this shortening control suppresses the peak intensity of the irradiated light to a low intensity that matches the received light intensity of reflected light, ensuring target sensing accuracy.

[0046] According to this embodiment, the on-period ΔT of the charge switching element 247 may be controlled by adjusting the off-timing Tf of the charge switching element 247, which is turned on prior to the on-timing Td of the discharge switching element 246, to a value before the periodically set reference off-timing Tf0. In this case, the on-period ΔT of the charge switching element 247 can be stably shortened by adjusting the off-timing Tf of the charge switching element 247 to be earlier than the reference off-timing Tf0 when the intensity of the reflected light is saturated. This is because the off-timing Tf of the charge switching element 247 is also earlier than the on-timing Td of the discharge switching element 246, reducing the effect of noise components generated when the charge switching element 247 is turned off on the current Io (see FIGS. 4, 5, and 7) flowing through the light-emitting diode 22 when the discharge switching element 246 is turned on. Therefore, this shortening control accurately stabilizes the peak intensity of the irradiated light at a low intensity that matches the received reflected light, ensuring sensing accuracy.

[0047] According to this embodiment, the on-timing Tn of the charge switching element 247, which is turned on prior to the on-timing Td of the discharge switching element 246, may be adjusted to a timing after the periodically set reference on-timing Tn0, thereby controlling the on-period ΔT of the charge switching element 247. In this case, when the intensity of the received reflected light is saturated, the on-period ΔT of the charge switching element 247 can be shortened by adjusting the on-timing Tn of the charge switching element 247 to be later than the reference on-timing Tn0. Therefore, such shortening control accurately suppresses the peak intensity of the irradiated light to a low intensity that matches the received reflected light, thereby improving sensing accuracy.

[0048] According to this embodiment, the maximum on-period ΔTm of the charge switching element 247 is controlled by the time constant of the resonant circuit section 240. This allows the peak intensity of the irradiated light to be increased up to the maximum intensity according to the time constant of the resonant circuit section 240 so as to match the received reflected light, even if the received light intensity of the reflected light becomes insufficient rather than saturated, thereby making it possible to improve sensing accuracy.

[0049] (Other Embodiments) Although one embodiment has been described above, the present disclosure should not be construed as being limited to the embodiment described above, and can be applied to various embodiments within the scope that does not deviate from the gist of the present disclosure.

[0050] In a modified example, the vehicle 5 to which the optical sensor 2 including the light-emitting unit 1 is applied may be, for example, an autonomous robot that is capable of autonomously or remotely traveling to transport luggage or collect information, etc. In a modified example, the object to which the optical sensor 2 including the light-emitting unit 1 is applied may be, for example, a moving object other than the vehicle 5, or a stationary object such as a structure.

[0051] (Additional Remarks) This specification discloses the following technical ideas and combinations thereof.

[0052] (Technical Idea 1) In an optical sensor (2) that senses a target by receiving light reflected from the target in response to illumination light illuminated onto a sensing area (As), a light emitting unit that provides the illumination light by emitting light includes: a resonance circuit section (240) having an inductor (241) and a capacitor (242); an illumination branch path section (Rl) that branches off between the inductor and the capacitor in the resonance circuit section; a light emitting diode (22) that is provided in the illumination branch path section and generates the illumination light by emitting light; a discharge switching element (246) that is provided in the illumination branch path section and switches on and off discharge from the capacitor; a charge switching element (247) that is provided in the resonance circuit section on the inductor side of the branch point of the illumination branch path section and switches on and off charge to the capacitor; and a drive circuit section (248) that controls the discharge switching element and the charge switching element by individual on and off drive, and the drive circuit section a light-emitting unit that controls an on-period of the charge switching element prior to the on-timing of the discharge switching element;

[0053] (Technical Idea 2) The driving circuit section controls the on period of the charge switching element by adjusting the off timing of the charge switching element, which is turned on prior to the on timing of the discharge switching element, to a value before a periodically set reference off timing, in the light-emitting unit described in Technical Idea 1.

[0054] (Technical Idea 3) The driving circuit section controls the on period of the charge switching element by adjusting the on timing of the charge switching element, which is turned on prior to the on timing of the discharge switching element, to a time after a periodically set reference on timing. This is the light-emitting unit described in Technical Idea 1 or 2.

[0055] (Technical Concept 4) The light-emitting unit according to any one of Technical Concepts 1 to 3, wherein the drive circuit section controls the maximum on-period of the charge switching element to the time constant of the resonant circuit section.

[0056] (Technical Idea 5) An optical sensor comprising: a light-emitting unit (1) according to any one of Technical Ideas 1 to 4; and a light-receiving unit (45) that receives the reflected light of the irradiated light emitted by the light-emitting unit.

Claims

1. In an optical sensor (2) for sensing a target by receiving reflected light from the target in response to irradiation light irradiated onto a sensing area (As), a light-emitting unit for providing the irradiation light by emitting light, comprising: a resonance circuit section (240) having an inductor (241) and a capacitor (242); a light-emitting branch path section (Rl) branching off between the inductor and the capacitor in the resonance circuit section; a light-emitting diode (22) provided in the light-emitting branch path section and generating the irradiation light by emitting light; a discharge switching element (246) provided in the light-emitting branch path section and switching on and off discharge from the capacitor by switching; a charge switching element (247) provided in the resonance circuit section on the inductor side relative to the branch point of the light-emitting branch path section and switching on and off charge to the capacitor by switching; and a drive circuit section (248) for controlling the discharge switching element and the charge switching element by individual on / off drive, A light emitting unit that controls an on-period of the charge switching element prior to the on-timing of the discharge switching element.

2. The light-emitting unit according to claim 1, wherein the drive circuit section controls the on-period of the charge switching element by adjusting the off-timing of the charge switching element, which is turned on prior to the on-timing of the discharge switching element, to be before a periodically set reference off-timing.

3. The light-emitting unit according to claim 1 or 2, wherein the drive circuit section controls the on-period of the charge switching element by adjusting the on-timing of the charge switching element, which is turned on prior to the on-timing of the discharge switching element, to a timing after a reference on-timing that is periodically set.

4. The light-emitting unit according to claim 1, wherein the drive circuit section controls the maximum on-period of the charge switching element to the time constant of the resonant circuit section.

5. An optical sensor comprising: a light-emitting unit (1) according to claim 1; and a light-receiving unit (45) for receiving the reflected light in response to the irradiated light emitted by the light-emitting unit.

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