Light emitting element driving circuit and laser processing machine

Abstract

A light emitting element drive circuit (100) comprises: a boost voltage source (7) that applies a first voltage to an LD (10); a main voltage source (4) that applies a second voltage that is lower than the first voltage to the LD (10); a MOSFET (2A) that switches on / off of application of the first voltage to the LD (10); and a linear regulator (6) that controls current flowing to the LD (10). The linear regulator (6) includes: a current detector (62); a MOSFET (61) through which current that flows to the LD (10) flows; and a drive unit (63A) that drives the MOSFET (61). The drive unit (63A) includes: a gate drive circuit (68) that drives the MOSFET (61); two or more constant circuits to each of which a different control constant is set; and a switching mechanism (SW1) that selects one of the two or more constant circuits and performs connecting thereof to the gate drive circuit (68), in accordance with whether voltage applied to the LD (10) is the first voltage or the second voltage.

Description

Light-emitting element drive circuit

[0001] The present disclosure relates to a light-emitting element drive circuit that drives a light-emitting element such as a laser diode (LD) or a light-emitting diode (LED).

[0002] LDs or LEDs are light-emitting elements that emit light at a brightness corresponding to the current flowing through them, and are driven by direct current. A typical driving circuit for these light-emitting elements includes a light-emitting element, a constant-voltage source, and a linear regulator connected in series, with the linear regulator controlling the current of the light-emitting element. To minimize losses in the driving circuit, the voltage of the constant-voltage source is set to a value slightly higher than the forward voltage of the light-emitting element. In a driving circuit configured in this way, no particular problems arise while the light-emitting element is steadily lit. On the other hand, when controlling the light-emitting element from an OFF state to an ON state, a slight potential difference between the constant-voltage source and the forward voltage of the light-emitting element must be used as a potential gradient to pass current through the wiring inductance. This poses a problem of extremely slow current rise.

[0003] To solve the above problem, Patent Document 1 below discloses a drive circuit having two power supplies: a high-voltage source with a relatively high voltage and a low-voltage source with a relatively low voltage. In Patent Document 1, when the current rises immediately after turning on the LD, the high-voltage source is controlled to be on and a high voltage is applied to the drive circuit, thereby speeding up the current rise. After the LD current rises, the high-voltage source is controlled to be off, and a constant current flows through the LD using only the low-voltage source.

[0004] Special Publication No. 2011-513988

[0005] However, in the control of Patent Document 1, when switching from a high voltage source to a low voltage source, the speed of the current flowing through the LD changes significantly, which causes the control to become unstable and the current flowing through the LD to oscillate. Although oscillation can be suppressed by slowing down the rate at which the current rises immediately after the LD is turned on, the rise rate cannot be increased.

[0006] The present disclosure has been made in view of the above, and aims to provide a light-emitting element drive circuit that can achieve both faster current rise immediately after turning on an LD and stable control.

[0007] In order to solve the above-mentioned problems and achieve the object, a light-emitting element drive circuit according to the present disclosure is a light-emitting element drive circuit for driving a light-emitting element, and includes first and second DC power supplies, a first switch element, a backflow prevention element, and a linear regulator for controlling a current flowing through the light-emitting element. The first DC power supply holds a first voltage and is connected to be able to apply the first voltage to an anode of the light-emitting element. The second DC power supply is connected to be able to apply a second voltage lower than the first voltage to the anode of the light-emitting element. The first switch element switches on and off application of the first voltage to the anode of the light-emitting element. The backflow prevention element is connected in a direction that prevents the first voltage from being applied to the second DC power supply. The linear regulator also includes a current detector that detects the current flowing through the light-emitting element, a second switch element through which the current flowing through the light-emitting element flows, and a drive unit that drives the second switch element. The drive unit includes a gate drive circuit that drives the gate of the second switch element, two or more constant circuits in which different control constants are set, and a switch mechanism that selects one of the two or more constant circuits and connects it to the gate drive circuit depending on whether the voltage applied to the light-emitting element is the first voltage or the second voltage.

[0008] The light-emitting element drive circuit according to the present disclosure has the effect of achieving both a faster current rise immediately after turning on the LD and stable control.

[0009] 6 is a diagram showing a circuit configuration of the second drive unit 64, which is a general example of the second drive unit 64A shown in FIG. 1; 18. A circuit diagram showing a configuration of a light-emitting element drive circuit 100E according to a second modified example of the embodiment 3. A time chart serving to explain the operation of the light-emitting element drive circuit 100E according to the embodiment 3. A circuit diagram showing a configuration of a light-emitting element drive circuit 100F according to the embodiment 4. A circuit diagram showing a configuration example of the drive unit 63B shown in FIG. 18. A circuit diagram showing a configuration example of the drive unit 63C shown in FIG. 18. A first time chart serving to explain the operation when control is performed using the drive units 63B, 63C, and 63D of FIG.18 is used to cause a current to flow through the LD10 using only the MOSFET 61C of FIG. 18. A time chart used to explain the operation when a current is flowed through the LD10 using only the MOSFET 61D of FIG. 18. A circuit diagram showing another example of the configuration of the drive unit 63B shown in FIG. 18. A circuit diagram showing another example of the configuration of the drive unit 63C shown in FIG. 18. A circuit diagram showing another example of the configuration of the drive unit 63D shown in FIG. 18. A circuit diagram showing the configuration of the light-emitting element drive circuit 100G according to the fifth embodiment. A circuit diagram showing the connection relationship between the control unit 81 and the drive unit 63A according to the fifth embodiment.

[0010] A light-emitting element drive circuit according to an embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that, in the following embodiments, an LD drive circuit for driving an LD will be described as an example, but this does not mean that light-emitting elements other than LDs will be excluded. Furthermore, in the following description, physical connection and electrical connection will not be distinguished from each other, and will be simply referred to as "connection." In other words, the term "connection" includes both a case where components are directly connected to each other and a case where components are indirectly connected to each other via other components.

[0011] Embodiment 1. FIG. 1 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100 according to embodiment 1. The light-emitting element drive circuit 100 includes an LD 10, a metal-oxide-semiconductor field-effect transistor (MOSFET) 2A, a drive unit 64A for driving the MOSFET 2A, a diode 3 serving as a backflow prevention element, a boost voltage source 7 serving as a first DC power source, a main voltage source 4 serving as a second DC power source, and a linear regulator 6. The linear regulator 6 includes, as components for controlling the current flowing through the LD 10, a MOSFET 61, a current detector 62 serving as a first current detector, and a drive unit 63A for driving the MOSFET 61. The boost voltage source 7 includes a capacitor 71 serving as a charge storage element and a voltage source 72. The capacitor 71 is connected across the voltage source 72. In this document, MOSFET 2A may be referred to as a "first switch element" and MOSFET 61 may be referred to as a "second switch element."

[0012] The LD 10 is an example of a light-emitting element. The anode of the LD 10 is connected to the connection point between the source of the MOSFET 2A and the cathode of the diode 3. The cathode of the LD 10 is connected to the drain of the MOSFET 61. Although the LD 10 is illustrated as a single element in FIG. 1, it is not limited to a single element. The LD 10 may be a plurality of elements connected in series or series-parallel.

[0013] The anode of diode 3 is connected to the positive terminal of main voltage source 4. The drain of MOSFET 2A is connected to the positive terminal of boost voltage source 7. The source of MOSFET 61 is connected to the negative terminal of main voltage source 4 via current detector 62, and the connection point is connected to the negative terminal of boost voltage source 7.

[0014] 1 shows two voltage sources, the main voltage source 4 and the boost voltage source 7, but the number of each is not limited to one. That is, there may be two or more main voltage sources 4, and there may also be two or more boost voltage sources 7. Increasing the number of at least one of the main voltage sources 4 and the boost voltage source 7 makes it possible to output in accordance with the load situation, enabling more stable control.

[0015] Wiring inductances L1 and L2 are shown on both sides of LD 10. Wiring inductance L1 is the inductance of the electrical wiring between the anode of LD 10 and the connection point between the cathode of diode 3 and the source of MOSFET 2A, and wiring inductance L2 is the inductance of the electrical wiring between the negative pole of main voltage source 4 and the cathode of LD 10. In addition, wiring inductances L3-1, L3-2, and L3-3 are shown on both ends of diode 3 and main voltage source 4.

[0016] Wiring inductance L3-1 is the inductance of the electrical wiring between the connection point between the source of MOSFET 2A and the anode of LD10 and the cathode of diode 3. Wiring inductance L3-2 is the inductance of the electrical wiring between the anode of diode 3 and the positive electrode of main voltage source 4. Wiring inductance L3-3 is the inductance of the electrical wiring between the connection point between the negative electrode of main voltage source 4, the negative electrode of boost voltage source 7, and the linear regulator 6.

[0017] Next, the features of the circuit configuration of the light-emitting element drive circuit 100 according to the first embodiment, which is connected as described above, will be described. The boost voltage source 7 holds a first voltage and is connected to the anode of the LD 10 via the MOSFET 2A so as to be able to apply the first voltage. The main voltage source 4 holds a second voltage lower than the first voltage and is connected so as to be able to apply the second voltage to the anode of the LD 10. The diode 3 is connected in a direction that prevents the first voltage from being applied to the main voltage source 4. The MOSFET 2A switches on and off the application of the first voltage to the anode of the LD 10. The linear regulator 6 controls the current flowing through the LD 10. The current flowing through the LD 10 flows through the MOSFET 61. The current detector 62 detects the current flowing through the LD 10 by detecting the current flowing through the MOSFET 61. The drive unit 63A drives the MOSFET 61 based on the value detected by the current detector 62.

[0018] Fig. 2 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100A according to a modified example of embodiment 1. In Fig. 2, the diode 3 shown in Fig. 1 is replaced with a MOSFET 3A. The other configuration is the same as or equivalent to the configuration in Fig. 1, and the same or equivalent components are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0019] MOSFET 3A is an example of a switching element equipped with an anti-parallel connected diode. "Anti-parallel" means that the anode of the diode is connected to the source of MOSFET 3A, and the cathode of the diode is connected to the drain of MOSFET 3A. The orientation of the anti-parallel connected diode is the same as that of diode 3, and it functions as a reverse current prevention element. The anti-parallel connected diode may be an externally connected diode or a parasitic diode contained inside MOSFET 3A. The parasitic diode is also called a body diode. Using a parasitic diode eliminates the need for a separate diode, reducing the number of components and leading to cost savings.

[0020] The MOSFET 3A may be subjected to synchronous rectification control, which turns on the MOSFET 3A at the timing when a current flows through the anti-parallel connected diode. By performing synchronous rectification control on the MOSFET 3A, it is possible to further reduce circuit loss and improve power supply efficiency.

[0021] Fig. 3 is a circuit diagram showing a typical configuration example of the driving unit 63A shown in Fig. 1. In Fig. 3, a MOSFET 61 and a current detector 62 are shown together with the driving unit 63A.

[0022] The notation "constant circuit 1 or 2" means that either "constant circuit 1" or "constant circuit 2" is provided. The configuration of the conventionally used drive unit 63A generally has only one constant circuit, as shown in FIG. 3.

[0023] One constant circuit is connected to a gate drive circuit 68. The gate drive circuit 68 drives the gate of the MOSFET 61 and is connected to the MOSFET 61 via a gate resistor Rg. The constant circuit is, for example, an error amplifier, which compares a reference voltage with a feedback voltage derived from the current flowing through the MOSFET 61 and controls the gate voltage of the MOSFET 61 to a desired voltage. In this paper, the control constant set by constant circuit 1 will be referred to as "control constant 1," and the control constant set by constant circuit 2 will be referred to as "control constant 2."

[0024] As explained in the section [Problem to be Solved by the Invention], when switching from a high voltage source to a low voltage source, the speed change of the LD current (the current flowing through the LD) is large, which can lead to unstable control and oscillation of the LD current. For example, if the control constant is set at a first voltage (high voltage) to speed up the rise of the LD current, control becomes unstable and oscillation is likely to occur when switching to a second voltage (low voltage) to reduce loss after rise. Conversely, if the control constant is set at the second voltage, control becomes unstable during rise, making overshoot and oscillation more likely to occur. This phenomenon is due to the control characteristics that require a response of 100 μs or less for control at the first voltage, while a response of 100 ms or less is sufficient for control at the second voltage. In other words, the cause is the large difference in control response before and after switching the applied voltage.

[0025] Fig. 4 is a first time chart illustrating the operation when control is performed using the driving unit 63A in Fig. 3. Fig. 5 is a second time chart illustrating the operation when control is performed using the driving unit 63A in Fig. 3.

[0026] Specifically, FIG. 4 is a time chart showing the operation of constant circuit 1, which has control constant 1 set to match the first voltage, when the second voltage is also applied. Meanwhile, FIG. 5 is a time chart showing the operation of constant circuit 2, which has control constant 2 set to match the second voltage, when the first voltage is also applied. In both FIGS. 4 and 5 , the waveforms, from top to bottom, represent the LD current, applied voltage, operating state of MOSFET 61, operating state of MOSFET 2A, and the set control constant. The LD current is the current flowing through LD 10, and the applied voltage is the voltage between the anode of LD 10 and the negative electrode of main voltage source 4. The MOSFET operating state represents the operating state of each MOSFET, as visualized by the gate-source voltage applied to each MOSFET. The horizontal axis in both figures represents time. Differences in the control constants are represented by numerical values ​​and hatching patterns. Specifically, "1" represents control constant 1, and "2" represents control constant 2. The on / off of MOSFET 2A is controlled by drive unit 64A, not drive unit 63A. To enable drive units 63A and 64A to be distinguished without reference numerals, drive unit 64A may be referred to as a "second drive unit 64A" or as a "second drive unit" without the reference numeral.

[0027] In the case of Fig. 4, the LD current oscillates when the second voltage is applied. This is because the control constant 1 set to match the first voltage is also used when the second voltage is applied. In addition, in the case of Fig. 5, the LD current oscillates when the first voltage is applied. This is because the control constant 2 set to match the second voltage is also used when the first voltage is applied.

[0028] Oscillation of the LD current causes unevenness in the light emission intensity of the LD 10, affecting the lifespan of the LD 10. If the LD is used in a product such as a laser processing machine, this can affect processing quality. To solve these problems, for example, two linear regulators 6 are provided, one for each of the first and second voltages. However, this approach requires two MOSFETs 61, two current detectors 62, and two drive units 63A, which increases the circuit area and number of components, inevitably resulting in an increase in product size and cost. Furthermore, there is the issue of mutual resonance between the two linear regulators 6, which increases the design man-hours required to address the resonance.

[0029] Therefore, in the first embodiment, the configuration shown in Fig. 6 is proposed. Fig. 6 is a circuit diagram showing the configuration of a drive unit 63A according to the first embodiment. Components that are the same as or equivalent to those in Fig. 3 are indicated by the same reference numerals. As shown in Fig. 6, the drive unit 63A includes a constant circuit 1 corresponding to a first voltage and a constant circuit 2 corresponding to a second voltage, as well as a switch mechanism SW1 that selects one of the constant circuits 1 and 2 and connects it to the gate drive circuit 68. The switch mechanism SW1 is switched to either the constant circuit 1 side or the constant circuit 2 side depending on whether the voltage applied to the LD 10 is the first voltage or the second voltage.

[0030] Fig. 7 is a time chart illustrating the operation when control is performed using the driving unit 63A of Fig. 6. The types of waveforms and notation are the same as those of Figs. 4 and 5. Fig. 7 shows that although the LD current drops immediately after the application of the second voltage, a stable LD current flows when both the first voltage and the second voltage are applied.

[0031] As described above, the light-emitting element drive circuit according to the first embodiment includes first and second DC power supplies, a first switch element, a backflow prevention element, and a linear regulator that controls a current flowing through the light-emitting element. The first DC power supply holds a first voltage and is connected to be able to apply the first voltage to the anode of the light-emitting element. The second DC power supply is connected to be able to apply a second voltage lower than the first voltage to the anode of the light-emitting element. The first switch element switches on and off application of the first voltage to the anode of the light-emitting element. The backflow prevention element is connected in a direction that prevents the first voltage from being applied to the second DC power supply. The linear regulator also includes a current detector that detects the current flowing through the light-emitting element, a second switch element through which the current flowing through the light-emitting element flows, and a drive unit that drives the second switch element. The drive unit includes a gate drive circuit that drives the gate of the second switch element, two constant circuits having different control constants, and a switch mechanism that selects and connects one of the two constant circuits to the gate drive circuit depending on whether the voltage applied to the light-emitting element is a first voltage or a second voltage. In the light-emitting element drive circuit configured in this manner, for example, when the voltage applied to the light-emitting element is the first voltage, the switch mechanism operates to select one of the two constant circuits, and when the voltage applied to the light-emitting element is the second voltage, the switch mechanism operates to switch the selection of the constant circuit and select the other of the two constant circuits. As a result, the light-emitting element drive circuit selects the constant circuit appropriate for the applied voltage, allowing a stable LD current to flow at both the first and second voltages, thereby achieving both a fast rise in the LD current immediately after turning on the LD and stable control.

[0032] Furthermore, according to the light-emitting element drive circuit of embodiment 1, a single linear regulator is sufficient without the need for additional linear regulators, thereby suppressing increases in circuit area and component count, and making it possible to avoid increases in product size and manufacturing costs. Furthermore, since only one linear regulator is required, measures to address the mutual resonance that can occur between two linear regulators are not required, which is expected to reduce development man-hours. As a result, it is possible to improve product performance while suppressing increases in design costs, manufacturing costs, and product size.

[0033] In the first embodiment, the number of constant circuits is set to two, but it may be set to three or more. When at least one of the first and second DC power supplies has two or more voltage sources, the number of constant circuits may be set to three or more in accordance with this power supply configuration.

[0034] Second Embodiment As previously mentioned, in the operating waveforms shown in FIG. 7, a phenomenon in which the LD current drops immediately after the application of the second voltage is observed. This drop in LD current is believed to be caused by the presence of the wiring inductances L3-1, L3-2, and L3-3 shown in FIG. 1. Inductances, including those inductances L3-1, L3-2, and L3-3, have the characteristic of suppressing a sudden current increase. Even when the first voltage is applied and current begins to flow through the LD 10, no LD current flows through the wiring inductances L3-1, L3-2, and L3-3. Therefore, immediately after switching from the first voltage to the second voltage, the LD current cannot immediately follow due to the back electromotive force generated in the wiring inductances L3-1, L3-2, and L3-3, resulting in the drop shown in the figure. In the second embodiment, a solution to this problem is presented.

[0035] Fig. 8 is a diagram showing the circuit configuration of the second drive unit 64, which is a general example of the second drive unit 64A shown in Fig. 1. Fig. 8 shows the MOSFET 2A together with the second drive unit 64. The second drive unit 64 includes a gate drive circuit 69 and a gate resistor Rg1. The gate drive circuit 69 is a circuit that drives the gate of the MOSFET 2A and is connected to the MOSFET 2A via the gate resistor Rg1.

[0036] 9 is a circuit diagram showing the configuration of a second drive unit 64A according to the second embodiment. Components that are the same as or equivalent to those in FIG. 8 are denoted by the same reference numerals. As shown in FIG. 9, the second drive unit 64A includes a gate drive circuit 69, gate resistors Rgon and Rgoff, and diodes D1 and D2. Diodes D1 and D2 have the same or equivalent characteristics.

[0037] The gate drive circuit 69 turns on MOSFET 2A by injecting charge into the gate capacitance of MOSFET 2A via gate resistor Rgon and diode D1. The gate drive circuit 69 also turns off MOSFET 2A by extracting charge accumulated in the gate capacitance of MOSFET 2A via gate resistor Rgoff and diode D2. The gate resistors Rgon and Rgoff have a relationship of (resistance value of Rgon)<(resistance value of Rgoff). When such a second drive unit 64A is used, the drive speed when gate-on MOSFET 2A is faster than the drive speed when gate-off MOSFET 2A. In other words, the drive speed when gate-off MOSFET 2A is slower than the drive speed when gate-on MOSFET 2A.

[0038] FIG. 10 is a time chart illustrating operation when the second driver 64A of FIG. 9 is used for control. The waveform types and notation are the same as those of the other time charts. Comparing the applied voltage waveform of FIG. 10 with that of FIG. 7, the applied voltage in FIG. 10 falls more slowly. This is because, as can be seen by comparing the rising and falling portions of the operating waveform of MOSFET 2A in FIG. 10, the drive speed when gate-off MOSFET 2A is slower than the drive speed when gate-on MOSFET 2A. As a result, the current supply from the boost voltage source 7 is slowly cut off, allowing the main voltage source 4 to supply current to the LD 10 in time. This eliminates or reduces the drop in LD current, as can be seen by comparing the LD current waveform of FIG. 10 with that of FIG. 7.

[0039] The function of the second drive unit 64A described above is referred to herein as a "voltage change mitigation means." The voltage change mitigation means is a means for realizing a function of mitigating a change in the voltage applied to the LD 10 when the voltage applied to the LD 10 switches from a first voltage (high voltage) to a second voltage (low voltage). In FIG. 10, an example in which the voltage change mitigation means is provided inside the second drive unit 64A has been described as a first embodiment.

[0040] When the second driving section 64A is used, it is preferable to use a MOSFET having a planar structure as the MOSFET 2A, for the reasons described below.

[0041] The on-speed and off-speed of a MOSFET depend on the voltage gain, gate capacitance, and gate resistance of the MOSFET. The voltage gain and gate capacitance depend on the structure of the MOSFET. Specifically, the voltage gain generally has the relationship (voltage gain of a trench structure) > (voltage gain of a planar structure). The gate capacitance generally has the relationship (gate capacitance of a trench structure) < (gate capacitance of a planar structure).

[0042] That is, when comparing a trench MOSFET with a planar MOSFET, the trench MOSFET has a relatively large voltage amplification factor due to its structure and a small gate capacitance. Therefore, the trench MOSFET is less susceptible to the effect of the charge / discharge time on the gate capacitance due to the gate resistance and has a large voltage amplification factor, so the change range of the gate voltage applied when turning on the MOSFET can be small. Note that a small change range means that the sensitivity of adjusting the on-speed and off-speed is low.

[0043] In contrast, a planar-structure MOSFET has a relatively small voltage amplification factor due to its structure and a large gate capacitance. Therefore, in a planar-structure MOSFET, the gate capacitance is significantly affected by the charge / discharge time due to the gate resistance, and the voltage amplification factor is small, so the range of change in the gate voltage applied when turning on the MOSFET must be large. This means that the sensitivity of the on-speed and off-speed adjustment is high, and speed adjustment is easier than with a trench-structure MOSFET. Therefore, by using a planar-structure MOSFET as MOSFET 2A, the effect of the voltage change mitigation means can be easily obtained.

[0044] Next, another example of the voltage change mitigation means will be described with reference to Figures 11 and 12. First, Figure 11 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100B according to a second embodiment.

[0045] Comparing the light-emitting element drive circuit 100B according to the second embodiment shown in FIG. 11 with the light-emitting element drive circuit 100 according to the first embodiment shown in FIG. 1, a parallel circuit of a MOSFET 2B and a resistor 2C is added in FIG. 11. In the light-emitting element drive circuit 100B, the parallel circuit functions as a voltage change mitigation means. Also, in FIG. 11, the drive unit 64A is changed to the drive unit 64. Note that the drive unit 64 may also be the drive unit 64A. The other configurations are the same as or equivalent to those in FIG. 1, and the same or equivalent components are denoted by the same reference numerals, and redundant explanations will be omitted. Note that in this document, the MOSFET 2B may be referred to as the "third switch element."

[0046] 11 shows an example in which the parallel circuit is arranged between the connection point of the LD 10 and the diode 3 and the source of the MOSFET 2A, but the present invention is not limited to this. The parallel circuit may also be arranged between the positive electrode of the boost voltage source 7 and the MOSFET 2A.

[0047] 12 is a time chart illustrating the operation of the light-emitting element drive circuit 100B according to embodiment 2. In Fig. 12, the waveforms represent, from the top, the LD current, the applied voltage, the operating state of MOSFET 2A, and the operating state of MOSFET 2B, and the horizontal axis represents time.

[0048] As shown in FIG. 12 , MOSFETs 2A and 2B are simultaneously turned on. This causes the first voltage to be applied to the anode of LD 10 via MOSFETs 2A and 2B. Then, only MOSFET 2B is turned off. Since MOSFET 2A remains on, the first voltage also continues to be applied. However, since the first voltage is applied via resistor 2C, the LD current is supplied slowly. Then, as shown in FIG. 12 , the applied voltage gradually decreases toward the second voltage. This operation eliminates or minimizes the drop in LD current. When MOSFET 2B is turned off, it is expected that the applied voltage will decrease due to the voltage drop across resistor 2C. However, since resistor 2C is intended to mitigate voltage changes and its resistance is set small, no sudden voltage change will occur. In this case, gradually turning off MOSFET 2B can further suppress the voltage change. It is also possible to use an element with an inductance component instead of resistor 2C.

[0049] The period during which MOSFET 2A is on and MOSFET 2B is off is short, and the first voltage applied during the period during which both MOSFETs 2A and 2B are on does not pass through resistor 2C, so heat generation by resistor 2C does not become a problem. Also, if the required LD current is small and the time for which current is supplied from boost voltage source 7 is short, heat generation by resistor 2C does not become a problem, so it is possible to omit MOSFET 2B.

[0050] As described above, the light-emitting element drive circuit according to the second embodiment further includes a voltage change mitigation unit that mitigates a change in the applied voltage to the light-emitting element when the voltage applied to the light-emitting element switches from the first voltage to the second voltage. The voltage change mitigation unit can be provided in the second drive unit that drives the first switch element. The voltage change mitigation unit operates to mitigate a change in the applied voltage to the light-emitting element when the voltage applied to the light-emitting element switches from the first voltage to the second voltage. This allows the current supply from the first DC power supply to be slowly cut off, allowing the second DC power supply to supply current to the light-emitting element in time. As a result, it is possible to eliminate or reduce a drop in the light-emitting element current that may occur immediately after application of the second voltage. Therefore, the light-emitting element drive circuit according to the second embodiment can achieve both the effects of the first embodiment, namely, faster LD current rise and stable control, while also ensuring current stability during constant current drive.

[0051] In the light-emitting element drive circuit according to the second embodiment, the first switch element may be a metal oxide semiconductor field effect transistor having a planar structure. If a metal oxide semiconductor field effect transistor having a planar structure is used, it is possible to easily obtain the effect of the voltage change mitigation means described above.

[0052] Furthermore, in the light-emitting element drive circuit according to the second embodiment, the voltage change mitigating means may be configured as a parallel circuit of a third switch element and a resistor. This parallel circuit may be disposed between the connection point of the light-emitting element and the backflow prevention element and the second switch element, or between the positive electrode of the first DC power supply and the second switch element. In this configuration, the third switch element is controlled to be on when the first voltage is applied and is controlled to be off when switching from the first voltage to the second voltage. By controlling in this manner, it is possible to obtain the effects of the voltage change mitigating means described above.

[0053] Third Embodiment As explained in the second embodiment, in the operating waveforms shown in FIG. 7, a drop in LD current is observed immediately after the application of the second voltage. This drop in LD current is believed to be caused by the presence of the wiring inductances L3-1, L3-2, and L3-3 shown in FIG. 1. Inductances, including those inductances L3-1, L3-2, and L3-3, have the characteristic of suppressing a sudden current increase. Even when the first voltage is applied and current begins to flow through the LD 10, no LD current flows through the wiring inductances L3-1, L3-2, and L3-3. Therefore, immediately after switching from the first voltage to the second voltage, the LD current cannot immediately follow the back electromotive force generated in the wiring inductances L3-1, L3-2, and L3-3, resulting in the drop shown in the figure. In the third embodiment, a solution to this problem different from that of the second embodiment is presented.

[0054] FIG. 13 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100C according to a third embodiment. Comparing the light-emitting element drive circuit 100C according to the third embodiment shown in FIG. 1 with the light-emitting element drive circuit 100 according to the first embodiment shown in FIG. 1, a series circuit including a power supply 8A (auxiliary power supply), a MOSFET 8B, and a diode 8C is added in FIG. 13, and the entire series circuit is connected in parallel to the diode 3. In the light-emitting element drive circuit 100C, the series circuit functions as a voltage adder. Similarly to the diode 3, the diode 8C functions as a backflow prevention element. Also, in FIG. 13, the driver 64A is replaced with the driver 64. The driver 64 may be replaced with the driver 64A. The remaining configuration is the same or equivalent to that shown in FIG. 1. The same reference numerals are used to denote the same or equivalent components, and redundant description will be omitted. In this document, the MOSFET 8B may be referred to as the "fourth switch element."

[0055] 13, the negative electrode of power supply 8A is connected to the junction between the positive electrode of main voltage source 4 and the anode of diode 3, and the positive electrode of power supply 8A is connected to the source of MOSFET 8B. The drain of MOSFET 8B is connected to the anode of diode 8C, and the junction between the cathode of diode 3 and the cathode of diode 8C is connected to the anode of LD 10. While FIG. 13 illustrates a configuration in which power supply 8A, MOSFET 8B, and diode 8C are arranged in this order from the low potential side to the high potential side between the anode and cathode of diode 3, this configuration is not limiting. Any two of the components constituting the series circuit may be interchanged, or all three may be interchanged.

[0056] 14 is a time chart illustrating the operation of the light-emitting element drive circuit 100C according to embodiment 3. In FIG. 14, the waveforms, from the top to bottom, represent the LD current, applied voltage, operating state of MOSFET 2A, operating state of MOSFET 8B, and voltage of power supply 8A, with the horizontal axis representing time. The voltage of power supply 8A is the output voltage of power supply 8A.

[0057] First, when MOSFET 2A is turned on, a first voltage is applied to the anode of LD 10. Next, MOSFET 2A is turned off, while MOSFET 8B is turned on. The time chart shown in FIG. 14 illustrates an operation in which the voltage at the anode of LD 10 immediately after MOSFET 8B is turned on is set so as not to change from the first voltage. Specifically, the first voltage, the second voltage, and the open-circuit voltage of power supply 8A have the relationship shown in Equation (1) below.

[0058] (Power supply 8A open circuit voltage)=(first voltage)−(second voltage) (1)

[0059] The open-circuit voltage of power supply 8A is the output voltage when no load is connected to power supply 8A. Note that in Fig. 14, the scale of the vertical axis of applied voltage and the scale of the vertical axis of power supply 8A voltage are different, and the power supply 8A voltage is shown expanded vertically.

[0060] When the LD current flows through the power supply 8A, the voltage of the power supply 8A drops by the sum of the voltage drop due to the internal resistance (not shown) of the power supply 8A, the voltage drop due to the on-resistance of the MOSFET 8B, and the forward voltage drop of the diode 8C. This allows the LD current to be supplied slowly. Thereafter, the applied voltage gradually decreases toward the second voltage, as shown in FIG. 14. This operation can eliminate or reduce the drop in the LD current.

[0061] The output from power supply 8A only needs to compensate for the current drop as shown in Figure 7. Therefore, power supply 8A may be a low-capacity power supply. However, in order to reduce the change in applied voltage immediately after MOSFET 2A is turned off and MOSFET 8B is turned on, it is preferable that the voltage of power supply 8A be set as shown in equation (1) above. Setting the voltage as shown in equation (1) above makes it possible to suppress a voltage jump immediately after switching from the first voltage to the second voltage.

[0062] Furthermore, in order to reduce the change in the applied voltage immediately after MOSFET 8B is turned off, it is preferable that the voltage of power supply 8A be set as shown in the following formula (2): If the voltage is set as shown in the following formula (2), it is possible to suppress a voltage jump when switching from the first voltage to the second voltage is completed.

[0063] (Power supply 8A switching completion voltage) = (power supply 8A open circuit voltage) - (power supply 8A internal resistance voltage drop) - (MOSFET 8B on resistance voltage drop) - (diode 8C forward voltage drop) = (second voltage) ... (2)

[0064] Fig. 15 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100D according to a first modification of embodiment 3. In the configuration of Fig. 13, if the power supply 8A itself has a power-on or power-off function, it is also possible to omit the MOSFET 8B arranged between the power supply 8A and the diode 8C as shown in Fig. 15.

[0065] FIG. 16 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100E according to a second modification of the third embodiment. Comparing the light-emitting element drive circuit 100E shown in FIG. 1 with the light-emitting element drive circuit 100 according to the first embodiment shown in FIG. 1 , a parallel-series circuit is added in FIG. 16 , in which a parallel circuit including a resistor 8E and a diode 8F is connected in series with a capacitor 8D, and the entire parallel-series circuit is connected in parallel with a diode 3. In the light-emitting element drive circuit 100E, the parallel-series circuit operates as a voltage adder. Furthermore, the capacitor 8D operates as an auxiliary power supply. Also, in FIG. 16 , the driver 64A is replaced with the driver 64. The driver 64 may be the driver 64A. The remaining configuration is the same or equivalent to that of FIG. 1 . The same or equivalent components are designated by the same reference numerals, and redundant description will be omitted.

[0066] 17 is a time chart illustrating the operation of the light-emitting element drive circuit 100E according to embodiment 3. In FIG. 17, the waveforms, from the top to bottom, represent the LD current, the applied voltage, the operating state of the MOSFET 2A, and the voltage of the capacitor 8D, and the horizontal axis represents time. The voltage of the capacitor 8D is the voltage across the capacitor 8D.

[0067] When MOSFET 2A is controlled to be turned on, a first voltage is applied from boost voltage source 7 to LD 10. When the first voltage is applied, capacitor 8D is charged to a voltage that is the difference between this first voltage and the output voltage of main voltage source 4. The charging current of capacitor 8D is limited by resistor 8E, which is a current limiting resistor. This prevents an excessive inrush current from flowing through capacitor 8D due to the high first voltage.

[0068] Furthermore, when MOSFET 2A is controlled to be turned off, the voltage of capacitor 8D is added to the voltage output by main voltage source 4 and applied to the anode of LD 10. Since diode 8F is connected across resistor 8E, the discharge path of the charge stored in capacitor 8D is the path passing through diode 8F. This allows power to be supplied to LD 10 efficiently.

[0069] Although the circuit operation is different, the voltage jump immediately after switching from the first voltage to the second voltage and the voltage jump when switching from the first voltage to the second voltage is completed can be suppressed by a method similar to the method explained using the time chart of Fig. 14. Specifically, the capacitance value of capacitor 8D, the resistance value of resistor 8E, the forward voltage characteristics of diode 8F, etc. are parameters, and by appropriately setting these parameters, the drop in LD current can be eliminated or reduced.

[0070] As described above, the light-emitting element drive circuit according to the third embodiment includes a series circuit including an auxiliary power supply, a fourth switch element, and a diode, and further includes a voltage adder connected in parallel across the reverse current prevention element. The voltage adder operates to add the voltage of the auxiliary power supply to the output voltage of the second DC power supply when the voltage applied to the light-emitting element switches from the first voltage to the second voltage. This slowly cuts off the current supply from the first DC power supply, allowing the second DC power supply to supply current to the light-emitting element in time. As a result, it is possible to eliminate or reduce the drop in light-emitting element current that may occur immediately after application of the second voltage. Therefore, the light-emitting element drive circuit according to the third embodiment can achieve both the effects of the first embodiment, namely, faster LD current rise and stable control, while also ensuring current stability during constant current drive.

[0071] In the light-emitting element drive circuit according to the third embodiment, if the auxiliary power supply itself is a power supply that can be turned on or off, the fourth switch element can be omitted.

[0072] In the light-emitting element drive circuit according to the third embodiment, the voltage adder may be configured as a parallel-series circuit in which a parallel circuit including a resistor and a diode is connected in series with a capacitor. In this configuration, when the first voltage is applied, the capacitor is charged by a differential voltage between the first voltage and the output voltage of the second DC power supply, and when switching from the first voltage to the second voltage, the capacitor operates as an auxiliary power supply for the voltage adder. This operation makes it possible to obtain the effects of the voltage adder described above.

[0073] Fourth Embodiment. FIG. 18 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100F according to a fourth embodiment. In the light-emitting element drive circuit 100F, components corresponding to the linear regulator 6 in FIG. 1 are configured in parallel in order to be used in applications requiring a large current. Comparing the light-emitting element drive circuit 100F according to the fourth embodiment shown in FIG. 18 with the light-emitting element drive circuit 100 according to the first embodiment shown in FIG. 1, the one MOSFET 61 in FIG. 18 is replaced with three MOSFETs 61B, 61C, and 61D, the one current detector 62 is replaced with three current detectors 62B, 62C, and 62D, and the one drive unit 63 is replaced with three drive units 63B, 63C, and 63D. Also, in FIG. 18, the drive unit 64A is replaced with the drive unit 64. The drive unit 64 may be replaced with the drive unit 64A. The remaining configuration is the same as or equivalent to the configuration in FIG. 1. The same or equivalent components are designated by the same reference numerals, and redundant description will be omitted.

[0074] The magnitude of the forward voltage drop of a diode load such as an LD or LED changes depending on the current flowing through the diode load. Therefore, in the configuration of Figure 18, to optimize the operation of MOSFETs 61B, 61C, and 61D connected in series with LD 10, it is necessary to adjust the second voltage applied to MOSFETs 61B, 61C, and 61D. Accordingly, constant circuit 1 or 2 shown in Figure 3 must also be a constant circuit adapted to the adjusted second voltage.

[0075] 19 is a circuit diagram showing an example of the configuration of the drive unit 63B shown in FIG. 18, FIG. 20 is a circuit diagram showing an example of the configuration of the drive unit 63C shown in FIG. 18, and FIG. 21 is a circuit diagram showing an example of the configuration of the drive unit 63D shown in FIG. 18.

[0076] In the first embodiment, we have described switching between two constant circuits to achieve both faster rise times for the LD current and stable control. If the LD current varies significantly, it is preferable to have a constant circuit that matches the current. Figures 19 to 21 show examples in which the LD current is divided into two cases, a large current and a small current, and one driver switches between four constant circuits accordingly.

[0077] Specifically, in the drive unit 63B shown in FIG. 19, four constant circuits 1-1, 2-1, 3-1, and 4-1 are configured to be switched by a switch mechanism SW1-1, in the drive unit 63C shown in FIG. 20, four constant circuits 1-2, 2-2, 3-2, and 4-2 are configured to be switched by a switch mechanism SW1-2, and in the drive unit 63D shown in FIG. 21, four constant circuits 1-3, 2-3, 3-3, and 4-3 are configured to be switched by a switch mechanism SW1-3.

[0078] Fig. 22 is a first time chart illustrating the operation when control is performed using the drivers 63B, 63C, and 63D of Fig. 18. In Fig. 22, the upper part shows the waveforms of the drain currents flowing through the MOSFETs 61B, 61C, and 61D, and the lower part shows the control constants set in the drivers 63B, 63C, and 63D. The horizontal axis represents time.

[0079] 22 shows an example in which 90 A flows through the LD 10, and this 90 A current is equally shared by the three MOSFETs 61B, 61C, and 61D. 90 A is an example of a large current. The maximum current that can flow through the MOSFETs 61B, 61C, and 61D is 30 A.

[0080] 22, when the drain current reaches the set value of 30 A, the driver 63B switches the constant circuit from constant circuit 1-1 to constant circuit 2-1. Similarly, when the drain current reaches 30 A, the driver 63C switches the constant circuit from constant circuit 1-2 to constant circuit 2-2, and when the drain current reaches 30 A, the driver 63D switches the constant circuit from constant circuit 1-3 to constant circuit 2-3. These operations enable stable driving of the LD 10 without causing oscillation of the LD current.

[0081] Fig. 23 is a second time chart illustrating the operation when controlled using the driving units 63B, 63C, and 63D of Fig. 18. The types of waveforms and the notation are the same as those in Fig. 22.

[0082] 23, a current of 30 [A] flows through the LD 10, and this current of 30 [A] is equally shared by three MOSFETs 61B, 61C, and 61D. 30 [A] is another example of a large current.

[0083] 23, when the drain current reaches the set value of 10 A, the driver 63B switches the constant circuit from constant circuit 3-1 to constant circuit 4-1. Similarly, when the drain current reaches 10 A, the driver 63C switches the constant circuit from constant circuit 3-2 to constant circuit 4-2, and when the drain current reaches 10 A, the driver 63D switches the constant circuit from constant circuit 3-3 to constant circuit 4-3. These operations enable stable driving of the LD 10 without causing oscillation of the LD current.

[0084] When passing 30 [A] through the LD 10, it is also possible to operate only one MOSFET without operating all of the MOSFETs. FIG. 24 is a time chart used to explain operation when current is passed through the LD 10 using only MOSFET 61B in FIG. 18. The types of waveforms and notation are the same as those in FIG. 22. When current is passed through only MOSFET 61B as in FIG. 24, the drivers 63C and 63D are inactive, and when the drain current reaches 30 [A], the driver 63B switches the constant circuit from constant circuit 1-1 to constant circuit 2-1. This prevents the LD current from oscillating, and the LD 10 is driven stably.

[0085] 25 is a time chart used to explain operation when current is passed through LD 10 using only MOSFET 61C in FIG. 18. The types of waveforms and notation are the same as those in FIG. 22. When current is passed through only MOSFET 61C as in FIG. 25, drivers 63B and 63D stop operating, and driver 63C switches the constant circuit from constant circuit 1-2 to constant circuit 2-2 when the drain current reaches 30 A. This prevents the LD current from oscillating, and LD 10 is driven stably.

[0086] Figure 26 is a time chart used to explain operation when current is passed through LD 10 using only MOSFET 61D in Figure 18. The types of waveforms and notation are the same as those in Figure 22. When current is passed through only MOSFET 61D as in Figure 26, drivers 63B and 63C stop operating, and driver 63D switches the constant circuit from constant circuit 1-3 to constant circuit 2-3 when the drain current reaches 30 A. This prevents the LD current from oscillating, and LD 10 is driven stably.

[0087] Note that, when comparing the operation of the light-emitting element drive circuit 100F according to embodiment 4 as shown in FIGS. 22 and 23 with the operation as shown in FIGS. 24 to 26, the latter has more advantages. When operating as the former, each drive unit requires four constant circuits, as shown in FIGS. 19 to 21. In contrast, when operating as the latter, each drive unit may be configured to have two constant circuits. Specific configuration examples are shown in FIGS. 27 to 29. FIG. 27 is a circuit diagram showing another configuration example of the drive unit 63B shown in FIG. 18. FIG. 28 is a circuit diagram showing another configuration example of the drive unit 63C shown in FIG. 18. FIG. 29 is a circuit diagram showing another configuration example of the drive unit 63D shown in FIG. 18. In FIG. 27, the constant circuits 3-1 and 4-1 shown in FIG. 19 can be omitted. In FIG. 28, the constant circuits 3-2 and 4-2 shown in FIG. 20 can be omitted. In FIG. 29, the constant circuits 3-3 and 4-3 shown in FIG. 21 can be omitted. Therefore, in the latter case, effects such as a reduction in circuit area can be obtained.

[0088] When only one MOSFET is operated, it is necessary to consider equalizing the load. To achieve this, it is necessary to level the frequency of use of the MOSFETs by, for example, periodically or irregularly switching the MOSFETs that are energized. Examples of ways to level the frequency of use of the MOSFETs include providing a timer function that counts the operating time of the MOSFET, or providing a function that counts the cumulative amount of current flowing through the MOSFET.

[0089] Furthermore, in the above example, equal currents are assumed to flow through the three MOSFETs 61B, 61C, and 61D, but this is not a limitation. For example, consider a case where the maximum current that can flow through MOSFET 61B is 10 A, the maximum current that can flow through MOSFET 61C is 20 A, and the maximum current that can flow through MOSFET 61D is 40 A. In this case, it is possible to pass currents of 10 to 70 A in increments of 10 A through the LD 10. Depending on the load characteristics of the LD 10, if the current differs by 10 A, it may be necessary to provide a constant circuit corresponding to that current and switch the constant circuit when switching the applied voltage. In this case, to accommodate seven currents ranging from 10 to 70 A, 7 × 2 = 14 constant circuits are required. In contrast, by using a parallel drive configuration such as that shown in FIG. 18, it is possible to achieve this with 2 × the number of MOSFETs, i.e., 3 × 2 = 6 constant circuits.

[0090] As described above, the light-emitting element drive circuit according to the fourth embodiment has the same configuration as the light-emitting element drive circuits according to the first to third embodiments, except that the number of linear regulators is two or more, and the second switch elements of the two or more linear regulators are connected in parallel with each other. Only one of the two or more second switch elements is driven at a time, and the driven second switch elements are alternated periodically or irregularly. In this way, it is possible to equalize the frequency of use of the two or more second switch elements.

[0091] In the above configuration, the two or more second switch elements may be configured to be driven simultaneously. When two or more second switch elements are driven simultaneously, the second switch elements are driven so that different currents flow through them. By driving in this manner, even when the drive current value is set in small increments, it is possible to avoid a proportional increase in the number of constant circuits. This makes it possible to suppress an increase in the circuit area even when the number of drive current setting values ​​increases.

[0092] Fifth Embodiment In the fifth embodiment, a more specific circuit configuration for realizing the control of the first to fourth embodiments described above in driving a light-emitting element will be described. FIG. 30 is a circuit diagram showing the configuration of a light-emitting element drive circuit 100G according to the fifth embodiment. In FIG. 30, a control unit 81 is added to the configuration of the light-emitting element drive circuit 100 shown in FIG. 1. The other configuration is the same as or equivalent to that of the light-emitting element drive circuit 100 shown in FIG. 1, and the same or equivalent components are designated by the same reference numerals, and redundant description will be omitted.

[0093] The control unit 81 generates a control signal for controlling the drive unit 63A based on an external current command value and a detection value of the current detector 62, and outputs the control signal to the drive unit 63A. The drive unit 63A controls the conduction of the MOSFET 61 based on the control signal output from the control unit 81.

[0094] Specific signals will be described. Fig. 31 is a circuit diagram showing the connection relationship between a control unit 81 and a drive unit 63A according to embodiment 5. In Fig. 31, a MOSFET 61 and a current detector 62 are shown together with the control unit 81 and the drive unit 63A shown in Fig. 6.

[0095] The control unit 81 generates a control signal for controlling the drive unit 63A based on an external current command value and the detection value of the current detector 62. Specifically, the control unit 81 generates a control signal for the switch mechanism SW1 that switches between constant circuit 1 and constant circuit 2, and a control signal for the gate drive circuit 68 that controls the MOSFET 61. The control unit 81 also outputs the current detection value detected by the current detector 62 to the constant circuits 1 and 2. The current detection value may be transmitted directly from the current detector 62 to the constant circuits 1 and 2 without passing through the control unit 81. When the current detection value is transmitted to the constant circuits 1 and 2 via the control unit 81, the control unit 81 can perform noise removal, signal level shifting, amplification, and the like. Therefore, this configuration can prevent overvoltage to the constant circuits 1 and 2 and the subsequent gate drive circuit 68, and can also improve the control accuracy of the drive unit 63A. Furthermore, in this configuration, when the detected current value is an overcurrent, a signal to that effect is sent to the gate drive circuit 68, which can turn off the MOSFET 61, thereby making it possible to prevent an overcurrent from flowing through the LD 10.

[0096] The operation of the control unit 81 will be described with reference to FIG. 7 . The control unit 81 controls the switch mechanism SW1 to turn on the MOSFET 61 so that the constant circuit 1 can be used during the second voltage period. When the current flowing through the LD 10 reaches a target value, the control unit 81 controls the switch mechanism SW1 to switch to the first voltage so that the constant circuit 2 can be used. This makes it possible to minimize the drop in the LD current. Note that the switch to the constant circuit 2 does not have to be immediately after the current flowing through the LD 10 reaches the target value, but may be after a certain period has elapsed since the current flowing through the LD 10 reaches the target value. Note that the target current value is input from the outside as a current command value.

[0097] In the fifth embodiment, an example has been described in which a configuration including the control unit 81 is applied to the light-emitting element drive circuit 100 shown in Fig. 1, but the present invention is not limited to this example. The control unit 81 can be applied to each of the light-emitting element drive circuits 100A, 100B, 100C, 100D, 100E, and 100F.

[0098] The hardware configuration of the control unit 81 can include a processing circuit and an interface for inputting and outputting signals. The processing circuit can be a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof, including a noise filter circuit and a signal amplifier circuit. Information input to and output from the processing circuit can be obtained via an interface. Furthermore, when performing more advanced arithmetic processing to realize the functions of the control unit 81 according to the present disclosure, the control unit 81 may be configured to include a processor for performing arithmetic operations and a memory for storing programs read by the processor instead of a processing circuit.

[0099] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0100] 1, 1-1, 1-2, 1-3, 2, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 4-1, 4-2, 4-3 Constant circuit, 2A, 2B, 3A, 8B, 61, 61B, 61C, 61D MOSFET, 2C, 8E Resistor, 3, 8C, 8F, D1, D2 Diode, 4 Main voltage source, 6 Linear regulator, 7 Boost voltage source, 8A Power supply, 8D, 71 Capacitor, 10 LD, 62, 62B, 62C, 62D Current detector, 63A, 63B, 63C, 63D Driver, 64, 64A Second driver, 68, 69 Gate driver circuit, 72 Voltage source, 81 Control unit, 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G: Light emitting element drive circuit, L1, L2, L3-1, L3-2, L3-3: Wiring inductance, Rg, Rg1, Rgoff, Rgon: Gate resistance, SW1, SW1-1, SW1-2, SW1-3: Switch mechanism.

Claims

1. A light emitting element drive circuit for driving a light emitting element, a first DC power supply that holds a first voltage and is connected to the anode of the light-emitting element so as to be able to apply the first voltage; a second DC power source connected to the anode of the light emitting element so as to be capable of applying a second voltage lower than the first voltage; a first switch element that switches on and off the application of the first voltage to the anode of the light-emitting element; a linear regulator for controlling a current flowing through the light emitting element; Equipped with The linear regulator comprises: a second switch element through which a current flows to the light emitting element; a drive unit that drives the second switch element; Equipped with The drive unit is a gate drive circuit that drives a gate of the second switch element; Two or more constant circuits in which different control constants are set; Equipped with Selecting one of the two or more constant circuits depending on whether a voltage applied to the light emitting element is the first voltage or the second voltage. A light-emitting element drive circuit comprising:

2. A current detector for detecting a current flowing through the light-emitting element is provided.

2. The light emitting element drive circuit according to claim 1.

3. 2. The light-emitting element drive circuit according to claim 1, further comprising a voltage change mitigation means for mitigating a change in the applied voltage when the applied voltage to the light-emitting element is switched from the first voltage to the second voltage.

4. a second drive unit that drives the first switch element, The voltage change mitigation means is provided in the second drive unit.

4. The light emitting element drive circuit according to claim 3.

5. The first switch element is a metal oxide semiconductor field effect transistor having a planar structure.

5. The light emitting element drive circuit according to claim 4.

6. A reverse current prevention element is connected in a direction to prevent the first voltage from being applied to the second DC power source; the voltage change mitigation means is configured with a parallel circuit of a third switch element and a resistor, The parallel circuit is disposed between a connection point of the light emitting element and the backflow prevention element and the second switch element, or between a positive electrode of the first DC power supply and the second switch element.

6. The light emitting element drive circuit according to claim 5.

7. The third switch element is controlled to be on when the first voltage is applied, and is controlled to be off when switching from the first voltage to the second voltage.

7. The light emitting element drive circuit according to claim 6.

8. 2. The light-emitting element driving circuit according to claim 1, further comprising a voltage adding means for adding a voltage of the auxiliary power supply to the output voltage of the second DC power supply when the voltage applied to the light-emitting element is switched from the first voltage to the second voltage.

9. A reverse current prevention element is provided, the reverse current prevention element being connected in a direction to prevent the first voltage from being applied to the second DC power source; the voltage adder means is configured with a series circuit of the auxiliary power supply, a fourth switch element, and a diode, The series circuit is connected in parallel to both ends of the backflow prevention element.

9. The light emitting element drive circuit according to claim 8.

10. A reverse current prevention element is connected in a direction to prevent the first voltage from being applied to the second DC power source, the voltage adder means is configured with a series circuit of the auxiliary power supply and a diode, The auxiliary power supply is a power supply that can be turned on or off, The series circuit is connected in parallel to both ends of the backflow prevention element.

9. The light emitting element drive circuit according to claim 8.

11. A reverse current prevention element is provided, the reverse current prevention element being connected in a direction to prevent the first voltage from being applied to the second DC power source; the voltage adding means is configured with a parallel-series circuit in which a parallel circuit made of a resistor and a diode is connected in series with a capacitor, The parallel-series circuit is connected in parallel to both ends of the backflow prevention element.

9. The light emitting element drive circuit according to claim 8.

12. The capacitor is When the first voltage is applied, the capacitor is charged by a differential voltage between the first voltage and an output voltage of the second DC power supply, When switching from the first voltage to the second voltage, the power supply operates as the auxiliary power supply for the voltage adder.

12. The light emitting element driving circuit according to claim 11.

13. the number of the linear regulators is two or more; The second switch elements in the two or more linear regulators are connected in parallel with each other.

2. The light emitting element drive circuit according to claim 1.

14. Only one of the two or more second switch elements is driven at a time, and the driven second switch elements are switched periodically or irregularly.

14. The light emitting element drive circuit according to claim 13.

15. One or more of the two or more second switch elements are driven simultaneously, and when two or more are driven simultaneously, different currents flow through the driven second switch elements.

14. The light emitting element drive circuit according to claim 13.

16. 3. The light-emitting element drive circuit according to claim 2, further comprising a control unit that generates a control signal for controlling the drive unit based on a current command value from an external source and a detection value of the current detector.

17. The light emitting device; A light emitting element drive circuit according to claim 1 for driving the light emitting element; A laser processing machine comprising: