Laser emitting device and optical distance measuring device

Abstract

To provide technology that prevents the abnormal light emission of laser diodes.SOLUTION: A laser emission device 10 comprises: a laser diode 110; a DC power supply 120; a booster circuit 130 that boosts the DC voltage supplied from the DC power supply via a main wiring 136 connected to the positive pole of the DC power supply and supplies it to the laser diode; a drive wiring 144 that connects the main wiring and the negative pole of the DC power supply; a drive circuit 140 that has a switch 141 for switching between the electrical continuity state and the non-electrical continuity state of the laser diode, and in which the series connection of the laser diode and the switch is located in the drive wiring; a current detection unit 150 that detects the current value of a DC current flowing in the main wiring in a direction heading from the DC power supply toward the laser diode; a determination unit 160 that determines whether or not the current value is normal; and a relay unit 170 that cuts off the supply of the DC current in accordance with the determination result of the determination unit.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a laser emitting device and an optical distance measuring device. [Background technology]

[0002] Distance measuring devices are known that measure the distance to an object by irradiating the object with a laser beam, receiving the reflected light from the object, and measuring the time between irradiation and reception. To improve distance measurement performance, it is necessary to irradiate a high-power laser beam. To irradiate a high-power laser beam, a high voltage must be applied to a laser diode that emits the laser beam. A known method for applying a high voltage to a laser diode is to use a boost circuit. Patent Document 1 describes a boost circuit that uses an inductor, a transistor, a diode, and a resistor to boost voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 9,368,936 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the above-mentioned conventional technology, if a transistor in the boost circuit shorts out, an unintended large current flows from the DC power supply to the laser diode, resulting in the generation of excessively intense light. [Means for solving the problem]

[0005] According to a first aspect of the present disclosure, there is provided a laser light emitting device (10) comprising: a laser diode (110), a DC power supply (120), a boost circuit (130) that boosts a DC voltage supplied from the DC power supply via a main wiring (136) connected to the positive electrode of the DC power supply and supplies the boosted DC voltage to the laser diode, a drive wiring (144) that connects the main wiring to the negative electrode of the DC power supply, a drive circuit (140) that has a first switch (141) that switches the laser diode between a powered state and a powered-off state, the drive circuit (140) having a series connection of the laser diode and the first switch arranged on the drive wiring, a current detection unit (150) that detects a current value of a DC current flowing on the main wiring in a direction from the DC power supply to the laser diode, a determination unit (160) that determines whether the current value is normal or abnormal, and a relay unit (170) that cuts off the supply of the DC current depending on the determination result of the determination unit. The drive circuit includes a second switch (142) connected in parallel with the series connection of the laser diode and the first switch. a capacitor (133) connected in parallel with the series connection of the laser diode and the first switch; The first switch is configured to switch from an off state to an on state during a period in which the second switch is in an off state, and to switch from an on state to an off state during a period in which the second switch is in an on state.

[0006] According to this laser light emitting device, when the value of the DC current flowing from the DC power supply toward the laser diode is abnormal, the relay section cuts off the DC current, thereby preventing abnormal light emission from the laser diode.

[0007] According to a second aspect of the present disclosure, there is provided an optical distance measuring device (100). The optical distance measuring device includes a laser emitting device (10) including a laser diode (110), a light receiving unit (30) that receives light reflected from an object when the laser light emitted from the laser diode is reflected, and a calculation unit (62) that calculates the distance to the object using the time from when the laser light is emitted until the reflected light is received. The laser light emitting device includes a DC power supply (120), a boost circuit (130) that boosts the DC voltage supplied from the DC power supply via a main wiring (136) connected to the positive terminal of the DC power supply and supplies the boosted DC voltage to the laser diode, a drive wiring (144) that connects the main wiring to the negative terminal of the DC power supply, a drive circuit (140) that has a first switch (141) that switches the laser diode between a powered state and a powered-off state, the drive circuit (140) having a series connection of the laser diode and the first switch arranged on the drive wiring, a current detection unit (150) that detects the current value of a DC current flowing on the main wiring in a direction from the DC power supply to the laser diode, a determination unit (160) that determines whether the current value is normal or abnormal, and a relay unit (170) that cuts off the supply of the DC current depending on the determination result of the determination unit. a capacitor (133) connected in parallel with the series connection of the laser diode and the first switch; The first switch is configured to switch from an off state to an on state during a period in which the second switch is in an off state, and to switch from an on state to an off state during a period in which the second switch is in an on state.

[0008] According to this optical distance measuring device, when the value of the DC current flowing from the DC power supply toward the laser diode is abnormal, the relay section cuts off the DC current, thereby preventing abnormal light emission from the laser diode. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of an optical distance measuring device. [Figure 2] FIG. 1 is a circuit diagram showing the configuration of a laser light emitting device according to a first embodiment. [Figure 3] FIG. 3 is a circuit diagram showing a specific example of a current detection unit, a determination unit, and a relay unit. [Figure 4] 4 is a timing chart of a light emission process in the first embodiment. [Figure 5] 10 is a timing chart of a recovery process. [Figure 6] FIG. 10 is a circuit diagram showing the configuration of a laser light emitting device according to a second embodiment. [Figure 7] 10 is a timing chart of a light emission process in the second embodiment. [Figure 8] FIG. 10 is a circuit diagram showing the configuration of a laser light emitting device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A. First embodiment: The optical distance measuring device 100 shown in FIG. 1 detects the distance to an object OB by emitting laser light IL and receiving reflected light RL reflected by the object OB. The optical distance measuring device 100 is mounted on, for example, a vehicle and used to measure the distance to objects present around the vehicle. In this embodiment, the optical distance measuring device 100 is a LiDAR (Light Detection and Ranging). The optical distance measuring device 100 includes a laser emitting device 10, a scanning unit 20, a light receiving unit 30, and a control unit 60. The laser emitting device 10 emits laser light IL for distance measurement.

[0011] The control unit 60 is configured as a computer including a CPU and a memory. The control unit 60 controls the operations of the laser emitting device 10, the scanning unit 20, and the light receiving unit 30. The control unit 60 further includes a calculation unit 62. The calculation unit 62 calculates the distance to the object OB. The calculation unit 62 may be realized by the CPU executing a program stored in the memory, or may be realized by an electronic circuit.

[0012] The laser emitting device 10 includes a laser diode that emits pulsed laser light IL. The laser light IL emitted from the laser diode is collimated by a collimating lens (not shown) and enters the scanning unit 20.

[0013] The scanning unit 20 scans the laser light IL within an angular range that includes a predetermined measurement range MR. The scanning unit 20 includes a mirror 21 that reflects the laser light IL and a rotary solenoid (not shown) that drives the mirror 21. The rotary solenoid repeatedly rotates forward and backward within the predetermined angular range, causing the laser light IL to scan within the measurement range MR.

[0014] The light receiving unit 30 receives reflected light RL, which is laser light IL emitted from the laser diode LD and reflected by the object OB. The light receiving unit 30 outputs a detection signal corresponding to the intensity of the received light to the calculation unit 62.

[0015] The calculation unit 62 calculates the distance to the object OB using the detection signal input from the light receiving unit 30. Specifically, the calculation unit 62 calculates the distance to the object OB using the time of flight (TOF), which is the time from when the laser light IL is emitted until the reflected light RL is received.

[0016] As shown in FIG. 2, the laser light emitting device 10 includes a laser diode 110, a DC power supply 120, a boost circuit 130, a drive circuit 140, a current detection section 150, a determination section 160, and a relay section 170.

[0017] The boost circuit 130 boosts the DC voltage supplied from the DC power supply 120 via a main wiring 136 connected to the positive electrode 120p of the DC power supply 120 and supplies the boosted voltage to the laser diode 110. The main wiring 136 is also referred to as the "positive electrode side wiring," and the wiring 137 connected to the negative electrode 120n of the DC power supply 120 is also referred to as the "negative electrode side wiring." The main wiring 136 is provided with a boost coil 131 and a forward-connected diode 132, and the diode 132 is installed downstream of the boost coil 131. In this disclosure, of any two positions on the main wiring 136, the position closer to the positive electrode 120p of the DC power supply 120 is referred to as the "upstream" position, and the position farther from the positive electrode 120p is referred to as the "downstream" position. A capacitor 133 is connected downstream of the diode 132 between the main wiring 136 and the negative electrode 120n of the DC power supply 120. This capacitor 133 is charged to a high voltage and has the function of increasing the voltage across the laser diode 110. Since the boost circuit 130 has the function of charging the capacitor 133, it can also be called a "charging circuit." The boost circuit 130 further has a capacitor 134 connected in parallel with the DC power supply 120. This capacitor 134 has the function of stabilizing the output voltage of the DC power supply 120. The capacitor 134 may be omitted. The configuration of the boost circuit 130 is an example, and boost circuits with other configurations may also be used.

[0018] The drive circuit 140 has a drive wiring 144 connecting the main wiring 136 and the negative electrode 120n of the DC power supply 120, and a switch 141 that switches the laser diode 110 between a powered state and a non-powered state. The switch 141 is connected in series with the laser diode 110 on the drive wiring 144. For example, an N-channel IGFET (Insulated Gate Field Effect Transistor) or other transistors may be used as the switch 141. The same applies to the other switches described below. A control signal S1 output from the control unit 60 is input to a control terminal of the switch 141.

[0019] The current detection unit 150 detects the current value of the DC current Ia flowing in the direction from the DC power supply 120 toward the laser diode 110. This DC current Ia is also called a "coil current" because it flows through the boost coil 131. The determination unit 160 determines whether the value of the DC current Ia is normal or abnormal. The relay unit 170 cuts off the supply of the DC current Ia in accordance with the determination result of the determination unit 160. That is, if the current value of the DC current Ia is within a normal range, the DC current Ia is not cut off, but if the current value of the DC current Ia is abnormally high, the DC current Ia is cut off.

[0020] 3, the current detection unit 150 can be configured to include a shunt resistor 151 and a current sense amplifier 152. The shunt resistor 151 is installed on the main wiring 136. The current sense amplifier 152 outputs a voltage Va proportional to a DC current Ia flowing through the shunt resistor 151. Hereinafter, the output voltage Va of the current sense amplifier 152 will also be referred to as the "current value of the DC current Ia."

[0021] The determination unit 160 can be configured to include a comparator 161 and a holding unit 162. The comparator 161 compares the voltage value Va of the DC current Ia with a preset reference value Vref and outputs a determination result. Specifically, the comparator 161 outputs a high-level voltage when the voltage value Va of the DC current Ia is less than the reference value Vref, and outputs a low-level voltage when the voltage value Va of the DC current Ia is greater than the reference value Vref. The reference value Vref is preferably set to a value that is smaller than the oscillation current threshold of the laser diode 110 and greater than the peak current value of the DC current Ia when the switch 141 of the drive circuit 140 is operating normally. This point will be described further below. During normal operation, the voltage value Va of the DC current Ia is less than the reference value Vref, so the output of the comparator 161 is high. On the other hand, if a short circuit occurs in switch 141, the DC current value Ia becomes larger than the reference value Vref, and the output of comparator 161 drops from H level to L level. Holding unit 162 is a circuit that holds the output of comparator 161 at L level after the output of comparator 161 drops from H level to L level.

[0022] The relay unit 170 can be configured to include a switch control unit 171, a relay switch 172, and a Zener diode 173. The relay switch 172 is installed in the main wiring 136 and turns the connection state of the main wiring 136 on and off. The switch control unit 171 supplies a control signal S3 for the relay switch 172 to a control terminal of the relay switch 172 in accordance with the determination result provided by the determination unit 160. That is, if the current value of the DC current Ia is within a normal range, the control signal S3 is set to an ON level, and if the current value of the DC current Ia becomes abnormally high, the control signal S3 is set to an OFF level. When the relay switch 172 is turned off, the supply of the DC current Ia flowing through the boost coil 131 is cut off.

[0023] The Zener diode 173 is connected in reverse between a node P3 on the main wiring 136 and the negative electrode 120n of the DC power supply 120. By providing the Zener diode 173, it is possible to absorb a surge voltage that occurs in the main wiring 136 when the supply of DC current Ia is cut off by the relay switch 172. The node P3 of the Zener diode 173 is preferably located between the boost coil 131 and the relay switch 172. Furthermore, it is preferable that the breakdown voltage of the Zener diode 173 is higher than the peak voltage of the node P3 when the switch 141 of the drive circuit 140 is operating normally. Note that the Zener diode 173 may be omitted.

[0024] 2 and 3 are merely examples, and the boost coil 131 and diode 132 may be provided at other positions on the main wiring 136. Specifically, the boost coil 131 may be provided upstream of the current detection unit 150. The diode 132 may be provided upstream of the current detection unit 150 or downstream of the relay unit 170.

[0025] 4, the laser light emitting device 10 executes a light emitting process in accordance with a distance measurement process for measuring the distance to the object OB performed by the control unit 60. In Fig. 4, a control signal S1 of the switch 141 of the drive circuit 140, a voltage Vc1 across the boost capacitor 133, a DC current Ia flowing through the boost coil 131, a control signal S3 of the relay switch 172, and a current Id flowing through the laser diode 110 are depicted.

[0026] During normal light emission, when the switch 141 changes from on to off at time t11, the capacitor 133 is charged, causing the voltage Vc1 across the capacitor 133 to rise and reach a voltage higher than the voltage across the DC power supply 120. When the switch 141 turns on at time t12, the charge stored in the capacitor 133 flows to the laser diode 110, and when the current Id flowing through the laser diode 110 reaches or exceeds the oscillation current threshold Ith, the laser diode 110 emits light. When the switch 141 turns off at time t13, the voltage Vc1 across the capacitor 133 rises again. As the switch 141 repeatedly turns on and off at regular intervals, the laser diode 110 emits light at regular intervals. During normal light emission without a malfunction, the DC current Ia flowing through the boost coil 131 is equal to or lower than the peak current Ipeak. This peak current Ipeak is lower than the oscillation current threshold Ith of the laser diode 110. In normal light emission processing, the relay switch 172 is maintained in the on state.

[0027] On the other hand, if a short circuit occurs in the switch 141 driving the laser diode 110 at time t31, the DC current Ia flowing through the boost coil 131 increases and exceeds the normal peak current Ipeak. Then, if the DC current Ia exceeds the reference value Iref at time t32, the relay switch 172 switches from ON to OFF, cutting off the supply of the DC current Ia. This reference value Iref is a current value represented by the reference value Vref input to the comparator 161 in the circuit of FIG. 3. The reference value Iref is set to a value smaller than the oscillation current threshold Ith of the laser diode 110 and larger than the peak current Ipeak of the DC current Ia when the switch 141 is operating normally. Therefore, even if a short circuit occurs in the switch 141, the DC current Ia will not reach the oscillation current threshold Ith of the laser diode 110, preventing the laser diode 110 from emitting abnormal light. As a result, safety standards for laser light (eye-safe standards) can be complied with.

[0028] Once the relay unit 170 has been brought into the cut-off state, it is preferable that the cut-off state of the relay unit 170 be maintained even when the current value of the DC current Ia becomes equal to or less than the determination value Ith. In this embodiment, after the output of the comparator 161 falls to the L level, the holding unit 162 holds the output of the comparator 161 at the L level, and accordingly the control signal S3 of the relay switch 172 is maintained at the OFF level. Note that the function of maintaining the relay unit 170 in the cut-off state may be realized by the relay unit 170 instead of by the determination unit 160.

[0029] 3, the voltage of the capacitor 133 is supplied to the control unit 60 as a relay state signal SS. The control unit 60 can determine whether the relay unit 170 is in the interrupted state using the relay state signal SS. For example, the control unit 60 can determine whether the relay unit 170 is in the interrupted state by checking whether the voltage level of the relay state signal SS exceeds a preset reference value after the switch 141 is switched to the off state. This reference value is set to a value smaller than the peak current value of the DC current Ia when the switch 141 is operating normally.

[0030] When the relay unit 170 is in a cutoff state, it is preferable that the control unit 60 notify the user of the optical distance measuring device 100 that an abnormality or failure has occurred in the laser emitting device 10 or the optical distance measuring device 100. This notification may be displayed, for example, on the meter panel of the vehicle in which the optical distance measuring device 100 is installed.

[0031] The control unit 60 further outputs a recovery signal Srec at a predetermined timing after the relay unit 170 has entered the cut-off state to cancel the cut-off state of the relay unit 170. When the recovery signal Srec is input to the holding unit 162 of the determination unit 160, the output of the comparator 161 is forced to rise to an H level, and the cut-off state of the relay unit 170 is canceled.

[0032] 5, it is preferable that the control unit 60 generates the return signal Srec multiple times during a non-distance measurement period when the optical distance measuring device 100 is not measuring distances. The reason for generating the return signal Srec multiple times is to ensure that if the relay unit 170 goes into a cut-off state due to some kind of noise, the cut-off state can be reliably resolved. However, the control unit 60 may also generate the return signal Srec only once.

[0033] The reason why the control unit 60 generates the return signal Srec during the non-distance measurement period is to prevent the laser light generated when the relay unit 170 is released from its cut-off state from irradiating a person. That is, during the non-distance measurement period, even if the laser diode 110 emits light, the scanning range of the scanning unit 20 is within an angular range in which the laser light does not exit the optical distance measuring device 100. Therefore, even if the relay unit 170 is connected in response to the return signal Srec and the laser diode 110 emits light, there is no risk of the laser light irradiating a person. However, the control unit 60 may be configured to generate the return signal Srec during the distance measurement period.

[0034] As described above, in the first embodiment, when the current value of the DC current Ia flowing from the DC power supply 120 toward the laser diode 110 is abnormal, the relay unit 170 cuts off the DC current Ia, thereby preventing abnormal light emission from the laser diode 110.

[0035] B. Second embodiment: As shown in Figure 6, the laser emitting device 10 of the second embodiment has a configuration in which a second switch 142 is added to the laser emitting device of the first embodiment shown in Figure 3, and the other configurations are the same as those of the first embodiment.

[0036] The second switch 142 and the first switch 141 constitute a drive circuit 140. The second switch 142 is connected in parallel with the series connection of the laser diode 110 and the switch 141. In the example of FIG. 6, a second drive wiring 146 provided with the second switch 142 is provided so as to connect a node P2 downstream of the relay unit 170 in the main wiring 136 and the negative electrode 120n of the DC power supply 120. A control signal S2 is supplied from the control unit 60 to a control terminal of the second switch 142.

[0037] As shown in Fig. 7, the operation of the light emission process in the second embodiment is similar to the operation of the light emission process in the first embodiment shown in Fig. 4, except for the addition of an on / off operation of the second switch 142. The second switch 142 switches from the off state to the on state at time t21, turns off at time t22, and turns on again at time t24. Meanwhile, the first switch 141 switches from the off state to the on state at time t23 and turns off at time t25. That is, the first switch 141 switches from the off state to the on state while the second switch 142 is in the off state, and switches from the on state to the off state while the second switch 142 is in the on state.

[0038] In the second embodiment, even if the first switch 141 does not turn on for some reason, the second switch 142 turns on, and the charge accumulated in the capacitor 133 is discharged via the second switch 142. As a result, it is possible to prevent an overvoltage from being applied to the laser diode 110.

[0039] Furthermore, if we assume that the second switch 142 is switched to the ON state after the first switch 141 is switched to the OFF state, the capacitor 133 is charged as the first switch 141 is switched to the OFF state, and then, when the second switch 142 is switched to the ON state, the capacitor 133 is discharged via the second switch 142. On the other hand, according to the light-emitting process of the second embodiment, the first switch 141 is switched to the OFF state after the second switch 142 is switched to the ON state, so that the charging of the capacitor 133, which does not contribute to boosting the voltage of the capacitor 133, can be reduced. In this way, by adjusting the ON / OFF switching timing of the two switches 141 and 142, the charging of the capacitor 133 can be controlled with higher precision. In other words, the DC current Ia flowing through the boost circuit 130 can be controlled with higher precision using the second switch 142.

[0040] 7, the processing after time t31 when a short circuit failure occurs in the first switch 141 is the same as the processing in the first embodiment shown in Fig. 4, and therefore description thereof will be omitted. In addition, in the second embodiment, the recovery processing using the recovery signal Srec can also be performed in the same way as in the first embodiment.

[0041] The second embodiment also has the same effects as the first embodiment. Furthermore, in the second embodiment, by using the second switch 142, the DC current Ia flowing through the boost circuit 130 can be controlled with higher precision.

[0042] C. Third embodiment: As shown in FIG. 8, the laser light emitting device 10 of the third embodiment differs from the laser light emitting device of the second embodiment shown in FIG. 6 in the following differences (a) to (d), and other configurations are the same as those of the second embodiment. (a) The second drive wiring 146 including the second switch 142 is connected to the upstream side of the relay section 170, not the downstream side of the relay section 170. (b) The holding unit 162 of the determination unit 160 is omitted, and a holding unit 174 is added to the switch control unit 171 of the relay unit 170. The holding unit 174 maintains the control signal S3 of the relay switch 172 at the off level after the control signal S3 temporarily drops to the off level. In other words, the holding unit 174 has the function of maintaining the relay unit 170 in the cut-off state. (c) The recovery signal Srec is supplied to the relay unit 170, not to the determination unit 160. When the recovery signal Srec is supplied to the switch control unit 171, the level of the control signal S3 held in the holding unit 174 switches from the OFF level to the ON level. (d) A signal indicating the level of the control signal S3 of the relay switch 172 is supplied from the switch control section 171 to the control section 60 as a relay state signal SS.

[0043] As can be understood from the circuit configurations of the second and third embodiments, the laser emitting device 10 can be configured so that a recovery signal Srec for canceling the cut-off state of the relay unit 170 is supplied to the judgment unit 160 or the relay unit 170.

[0044] The laser emitting device 10 of the third embodiment operates in almost the same way as the laser emitting device of the second embodiment, and therefore a description thereof will be omitted. Furthermore, the laser emitting device 10 of the third embodiment also achieves almost the same effects as the laser emitting device of the second embodiment.

[0045] D. Other Embodiments: The present disclosure is not limited to the above-described embodiments and modifications, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and modifications corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0046] 10...laser emitting device, 20...scanning unit, 21...mirror, 30...light receiving unit, 60...control unit, 62...calculating unit, 100...optical distance measuring device, 110...laser diode, 120...DC power supply, 120n...negative electrode, 120p...positive electrode, 130...booster circuit, 131...booster coil, 132...diode, 133...capacitor, 134...capacitor, 136...main wiring (positive electrode side wiring), 137...negative electrode side wiring, 140...drive circuit, 141...first switch, 142...second switch, 144...drive wiring, 146...second drive wiring, 150...current detection unit, 151...shunt resistor, 152...current sense amplifier, 160...determination unit, 161...comparator, 162...holding unit, 170...relay unit, 171...switch control unit, 172...relay switch, 173...zener diode, 174...holding unit

Claims

1. A laser emitting device (10), a laser diode (110); a DC power source (120); a boost circuit (130) that boosts the DC voltage supplied from the DC power supply via a main wiring (136) connected to the positive electrode of the DC power supply and supplies the boosted voltage to the laser diode; a drive circuit (140) including a drive wiring (144) connecting the main wiring and the negative electrode of the DC power supply, and a first switch (141) for switching the laser diode between a conducting state and a non-conducting state, the laser diode and the first switch being connected in series to the drive wiring; a current detection unit (150) that detects the current value of a DC current flowing on the main wiring in a direction from the DC power supply toward the laser diode; a determination unit (160) for determining whether the current value is normal or abnormal; a relay unit (170) that cuts off the supply of the direct current in accordance with the determination result of the determination unit; Equipped with the drive circuit includes a second switch (142) connected in parallel with the series connection of the laser diode and the first switch, and a capacitor (133) connected in parallel with the series connection of the laser diode and the first switch; The first switch is configured to switch from an off state to an on state during a period in which the second switch is in an off state, and to switch from an on state to an off state during a period in which the second switch is in an on state.

2. 2. The laser light emitting device according to claim 1, the determination unit is configured to compare a preset determination value (Iref) with the current value (Ia), and determine that the current value is abnormal when the current value is greater than the determination value; A laser light emitting device, wherein the judgment value is set to a value smaller than the oscillation current threshold (Ith) of the laser diode and larger than the peak current value (Ipeak) of the DC current when the first switch is operating normally.

3. 2. The laser light emitting device according to claim 1, further comprising: A laser light emitting device comprising a control unit (60) that transmits a recovery signal (Srec) to the determination unit or the relay unit to cancel the interrupted state of the relay unit after the relay unit has interrupted the supply of DC current.

4. 2. The laser light emitting device according to claim 1, The boost circuit includes a boost coil (131) provided in the main wiring and a forward-connected diode (132) provided downstream of the boost coil, The relay unit includes a relay switch (172) connected downstream of the boost coil in the main wiring, and a reverse-connected Zener diode (173) installed between the node between the boost coil and the relay switch and the negative electrode.

5. An optical distance measuring device (100), comprising: a laser emitting device (10) including a laser diode (110); a light receiving unit (30) that receives reflected light of the laser light emitted from the laser diode and reflected by an object; a calculation unit (62) that calculates the distance to the object using the time from when the laser light is emitted until when the reflected light is received; Equipped with The laser light emitting device a DC power source (120); a boost circuit (130) that boosts the DC voltage supplied from the DC power supply via a main wiring (136) connected to the positive electrode of the DC power supply and supplies the boosted voltage to the laser diode; a drive circuit (140) including a drive wiring (144) connecting the main wiring and the negative electrode of the DC power supply, and a first switch (141) for switching the laser diode between a conducting state and a non-conducting state, the laser diode and the first switch being connected in series to the drive wiring; a current detection unit (150) that detects the current value of a DC current flowing on the main wiring in a direction from the DC power supply toward the laser diode; a determination unit (160) for determining whether the current value is normal or abnormal; a relay unit (170) that cuts off the supply of the direct current in accordance with the determination result of the determination unit; Equipped with the drive circuit includes a second switch (142) connected in parallel with the series connection of the laser diode and the first switch, and a capacitor (133) connected in parallel with the series connection of the laser diode and the first switch; an optical distance measuring device, wherein the first switch is configured to switch from an off state to an on state during a period in which the second switch is in an off state, and to switch from an on state to an off state during a period in which the second switch is in an on state.

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