Light-emitting element drive circuit and laser oscillator

Abstract

The light-emitting element drive circuit (100) includes a main voltage source (4), a boost voltage source (7), a MOSFET (3), a MOSFET (2), a diode (5), a MOSFET (61) connected in series to an LD (1), and a drive unit (63) that drives the MOSFET (61). A linear regulator (6) that controls the current flowing through the LD (1) is configured with a series circuit including the main voltage source (4), the MOSFET (3), the LD (1), the MOSFET (61), and wiring inductances (L1, L2). A voltage monitor unit (8) detects a third voltage and a fourth voltage for detecting voltage fluctuations between the drain and source of the MOSFET (61), and a constant current circuit unit (9) controls injection of a first current to the gate of the MOSFET (61) based on the third voltage and the fourth voltage.

Description

Technical Field

[0001] The present disclosure relates to a light-emitting element drive circuit and a laser oscillator that drive light-emitting elements including a laser diode (LD), a light-emitting diode (LED), and the like.

Background Art

[0002] An LD or an LED is a light-emitting element that emits light with a luminance corresponding to the flowing current and is driven by a direct current. In a drive circuit that drives these light-emitting elements, a configuration in which a light-emitting element, a constant voltage source, and a linear regulator are arranged in series and the current of the light-emitting element is controlled by the linear regulator is generally adopted. Further, in order to reduce the loss in the drive 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 drive circuit having such a configuration, no particular problem occurs while the light-emitting element is constantly lit. On the other hand, when controlling the light-emitting element from the off state to the on state, a current must be passed through the inductance of the wiring using the slight potential difference between the constant voltage source and the forward voltage of the light-emitting element as a potential gradient. For this reason, there is a problem that the rise of the current becomes extremely slow.

[0003] In order to solve the above problems, Patent Document 1 discloses that by rapidly switching between a high-voltage source with a relatively high voltage and a low-voltage source with a relatively low voltage by a switch, the current is rapidly raised when the current of the light-emitting element rises, and after the current rise, the high-voltage source is controlled to be off, and a constant current is caused to flow through the light-emitting element only by the low-voltage source. Further, Patent Document 1 includes a diode connected in a direction in which energy accumulated in the wiring inductance on the anode side and the cathode side of the light-emitting element is regenerated to the high-voltage source when a current flows through the light-emitting element, so that even when used in applications where the on / off of the current frequently occurs, an increase in circuit loss can be suppressed.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2022-161687 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] However, in Patent Document 1, as will be described later, there is a problem that large current overshoot and undershoot that may affect actual applications occur due to circuit response delay during the transition from a current ramp-up period for rapidly ramping up the current to a constant current control period for controlling a constant current to flow through the light-emitting element.

[0006] The present disclosure has been made in view of the above, and an object thereof is to obtain a light-emitting element drive circuit that can suppress an increase in circuit loss and suppress overshoot and undershoot of the current flowing through the light-emitting element even in applications where current on / off frequently occurs. [Means for Solving the Problems]

[0007] To solve the above problems and achieve the object, a light-emitting element driving circuit according to the present disclosure drives a light-emitting element. The light-emitting element driving circuit includes a first DC power source that holds a first voltage and is connected to be able to apply the first voltage to the anode of the light-emitting element, a second DC power source that is connected to be able to apply a second voltage higher than the first voltage to the anode of the light-emitting element, a first switch element that is connected in a direction to prevent the second voltage from being applied to the first DC power source and switches on and off the application of the first voltage to the anode of the light-emitting element, a second switch element that switches on and off the application of the second voltage to the anode of the light-emitting element, a diode that is connected in a direction such that energy accumulated in the wiring inductances on the anode side and the cathode side of the light-emitting element is regenerated to the second DC power source when a current flows through the light-emitting element, a third switch element connected in series with the light-emitting element, and a driving unit that drives the third switch element. A series circuit including the first DC power source, the first switch element, the light-emitting element, and the third switch element and the wiring inductances on the anode side and the cathode side of the light-emitting element is configured to form a linear regulator that controls the current flowing through the light-emitting element, a voltage monitor unit that detects a third voltage and a fourth voltage for detecting voltage fluctuations between the drain and source of the third switch element, and a constant current circuit unit that controls the injection of a first current to the gate of the third switch element based on the third voltage and the fourth voltage.

Effects of the Invention

[0008] According to the light-emitting element driving circuit of the present disclosure, even in applications where the on / off of the current frequently occurs, an increase in circuit loss can be suppressed, and overshoot and undershoot of the current flowing through the light-emitting element can be suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the light-emitting element driving circuit and the laser oscillator according to the embodiments will be described in detail with reference to the drawings.

[0011] Before describing the embodiments, the problems of Patent Document 1 will be described with reference to FIG. 4. FIG. 4 is a circuit diagram for explaining Patent Document 1. The light-emitting element driving circuit of Patent Document 1 includes an LD1, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) 2, a MOSFET 3, a low voltage source 4, a diode 5, a linear regulator 6, and a high voltage source 7. The linear regulator 6 includes a MOSFET 61, a current detector 62, and a driving unit 63 for driving the MOSFET 61.

[0012] In the light-emitting element driving circuit of FIG. 4, while switching between the high voltage of the high voltage source 7 and the low voltage of the low voltage source 4 to drive the LD1, the linear regulator 6 controls the current flowing through the LD1. Specifically, when the LD1 emits light, the voltage is switched from the low voltage of the low voltage source 4 to the high voltage of the high voltage source 7, and the current flowing through the LD1 is raised to the target current. The period during which the high voltage of the high voltage source 7 is supplied to the LD1 and the current flowing through the LD1 is raised to the target current is called the current rise period. When the current flowing through the LD1 rises to the target current, the voltage is switched from the high voltage of the high voltage source 7 to the low voltage of the low voltage source 4, and the MOSFET 61 and the driving unit 63 maintain the current flowing through the LD1 constant. The period during which the low voltage of the low voltage source 4 is supplied to the LD1 and the current flowing through the LD1 is controlled to be constant is called the current constant control period. When a current flows through the LD1, energy is stored in the wiring inductances L1 and L2 on the anode side and the cathode side of the LD1. Thereafter, during the current fall period, the energy stored in the wiring inductances L1 and L2 is regenerated to the high voltage source 7 through the diode 5.

[0013] In the light-emitting element drive circuit of FIG. 4, ideally, even at the moment when the voltage of the anode of LD1 switches from a low voltage to a high voltage or from a high voltage to a low voltage, the linear regulator 6 operates to control the current so that the current flowing through LD1 remains constant. However, in reality, when transitioning from the current rise period to the constant current control period, that is, when the voltage of the anode of LD1 switches from a low voltage to a high voltage or from a high voltage to a low voltage, due to the response delay of the control of the linear regulator 6, current distortion including overshoot and undershoot occurs in the current flowing through LD1.

[0014] This current distortion is affected by the characteristics of the MOSFET61, which is the current output element of the linear regulator 6 that controls the current of LD1, and the drive unit 63 that controls the gate voltage of the MOSFET61. Generally, in a MOSFET, when trying to control the current to be constant, if the gate voltage of the MOSFET and the drain-source voltage of the MOSFET are constant, a constant current can flow. However, when trying to maintain the original current when the drain-source voltage increases, the current can be kept constant by relatively lowering the gate voltage. Also, when the drain-source voltage decreases, the current can be kept constant by relatively increasing the gate voltage.

[0015] During the current rise period when the voltage of the anode of LD1 switches from the low voltage of the low voltage source 4 to the high voltage of the high voltage source 7, the drain-source voltage of the MOSFET61, which is controlling the current to flow constantly, rapidly increases. To keep the current constant, it is necessary to lower the gate voltage of the MOSFET61. However, due to the response delay of the drive unit 63 that controls the gate voltage of the MOSFET61, the operation of lowering the gate voltage cannot keep up, and an overshoot operation of the current flowing through LD1 occurs.

[0016] Also, during the constant current control period when the voltage of the anode of LD1 switches from the high voltage of the high voltage source 7 to the low voltage of the low voltage source 4, the voltage between the drain and source of the MOSFET 61 that controls the current to flow constantly drops steeply. To keep the current constant, it is necessary to increase the gate voltage of the MOSFET 61. However, due to the response delay of the drive unit 63 that controls the gate voltage of the MOSFET 61, the operation of increasing the gate voltage cannot keep up, and an operation occurs in which the current flowing through the LD1 undershoots.

[0017] Here, it is possible to improve the responsiveness of the drive unit 63. However, the drive unit 63 is generally composed of an operational amplifier. When improving the responsiveness of the operational amplifier, it may cause unstable operations such as output oscillation in the operation of the linear regulator 6, leading to possible operations such as current oscillation.

[0018] Therefore, in the embodiment, without changing the response characteristics of the drive unit 63, overshoot and undershoot of the current flowing through the LD1 can be suppressed.

[0019] Embodiment 1. FIG. 1 is a circuit diagram showing the configuration of a light emitting element drive circuit 100 according to Embodiment 1. In FIG. 1, components that achieve the same functions as those of the light emitting element drive circuit shown in FIG. 4 are denoted by the same reference numerals. The light emitting element drive circuit 100 includes an LD1, a metal oxide semiconductor field effect transistor (MOSFET) 2, a MOSFET 3, a main voltage source (low voltage source) 4 which is a first DC power source, a diode 5, a linear regulator 6, a boost voltage source (high voltage source) 7 which is a second DC power source, a voltage monitor unit 8, and a constant current circuit unit 9. The linear regulator 6 includes a MOSFET 61, a current detector 62, a drive unit 63, and a resistance element 64. The MOSFET 2 corresponds to the second switch element, the MOSFET 3 corresponds to the first switch element, and the MOSFET 61 corresponds to the third switch element.

[0020] LD1 is an example of a light-emitting element. The anode of LD1 is connected to the connection point between the source of MOSFET2 and the drain of MOSFET3. The cathode of LD1 is connected to the connection point between the anode of diode 5 and the drain of MOSFET61. Note that in FIG. 1, LD1 is illustrated as a single element, but it is not limited to a single element. LD1 may be a plurality of elements connected in series or in series-parallel.

[0021] The source of MOSFET3 is connected to the positive electrode of the main voltage source 4. The drain of MOSFET2 and the cathode of diode 5 are connected, and the connection point is connected to the positive electrode of the boost voltage source 7. The source of MOSFET61 is connected to the negative electrode of the main voltage source 4 via the current detector 62, and the connection point is connected to the negative electrode of the boost voltage source 7.

[0022] Wiring inductances L1 and L2 are shown on both sides of LD1. The wiring inductance L1 is the inductance of the electrical wiring between the positive electrode of the main voltage source 4 and the anode of LD1, and the wiring inductance L2 is the inductance of the electrical wiring between the negative electrode of the main voltage source 4 and the cathode of LD1. When a current flows through LD1, energy is stored in the wiring inductances L1 and L2 on the anode side and the cathode side of LD1.

[0023] The linear regulator 6 is a component that controls the current flowing through LD1, and includes MOSFET61, a current detector 62, a drive unit 63 for driving MOSFET61, and a resistance element 64. The resistance element 64 is connected in series between the gate of MOSFET61 and the drive unit 63. The resistance element 64 serves both as a resistance for suppressing the current of MOSFET61 and as a resistance for converting the current from the constant current circuit unit 9 into a correction voltage for the gate voltage of MOSFET61.

[0024] The linear regulator 6 forms a series circuit together with the main voltage source 4, the MOSFET 3, the LD1, and the wiring inductances L1 and L2. Therefore, when driving the LD1, the current flowing through the LD1 also flows through the MOSFET 61. The current detector 62 can detect the current flowing through the MOSFET 61, and thus the current flowing through the LD1. The drive unit 63 compares the current command value for the LD1 with the current value detected by the current detector 62, and drives the MOSFET 61 so that the difference between the current command value and the detected current value becomes zero.

[0025] The voltage monitor unit 8 detects a third voltage and a fourth voltage for detecting voltage fluctuations between the drain and source of the MOSFET 61. In Embodiment 1, the voltage monitor unit 8 monitors the second voltage of the boost voltage source 7 as the third voltage, and monitors the voltage at the anode of the LD1 as the fourth voltage.

[0026] The input of the voltage monitor unit 8 is connected to the connection point of the drain of the MOSFET 2, the cathode of the diode 5, and the positive electrode of the boost voltage source 7, the connection point of the anode of the LD1, the source of the MOSFET 2, and the drain of the MOSFET 3, and the connection point of the negative electrode of the boost voltage source 7 and the negative electrode of the main voltage source 4. The two outputs of the voltage monitor unit 8 are connected to the constant current circuit unit 9. The voltage monitor unit 8 detects the voltage of the boost voltage source 7 with reference to the potential of the connection point of the negative electrode of the boost voltage source 7 and the negative electrode of the main voltage source 4. Also, the voltage monitor unit 8 detects the voltage of the connection point of the anode of the LD1, the source of the MOSFET 2, and the drain of the MOSFET 3 with reference to the potential of the connection point of the negative electrode of the boost voltage source 7 and the negative electrode of the main voltage source 4, thereby detecting the voltage at the anode of the LD1. The voltage of the boost voltage source 7 and the voltage at the anode of the LD1 monitored by the voltage monitor unit 8 are input to the constant current circuit unit 9.

[0027] In the voltage monitor unit 8, the voltage of the boost voltage source 7 may be divided by a resistance element and output, or may be directly output to the constant current circuit unit 9 without division. Also, in the voltage monitor unit 8, the voltage of the anode of LD1 may be divided by a resistance element and output, or may be directly output to the constant current circuit unit 9 as it is. Further, in the voltage monitor unit 8, there may be a filter function or level conversion by other methods.

[0028] The constant current circuit unit 9 takes as inputs two voltages including the voltage of the boost voltage source 7 and the voltage of the anode of LD1 from the voltage monitor unit 8. The output of the constant current circuit unit 9 is connected to the connection point between the gate of the MOSFET 61 of the linear regulator 6 and the resistance element 64. In the constant current circuit unit 9, when connecting to the connection point between the gate of the MOSFET 61 of the linear regulator 6 and the resistance element 64, it may be directly connected as it is, or a switch element such as a MOSFET may be interposed, and the current flowing from the constant current circuit unit 9 may be conducted at an arbitrary timing by the switch element.

[0029] The constant current circuit unit 9 controls the injection of current to the gate of the MOSFET 61 based on the two monitored voltages input from the voltage monitor unit 8, namely the voltage of the boost voltage source 7 and the voltage of the anode of LD1, thereby controlling the rise and fall of the gate voltage of the MOSFET 61. The current injected from the constant current circuit unit 9 to the gate of the MOSFET 61 corresponds to the first current.

[0030] Next, the light emission operation of LD1 in the light emitting element drive circuit 100 according to Embodiment 1 will be described. In this light emitting element drive circuit 100, the pulse drive period in which LD1 repeats at a duty ratio with on / off set includes an off period in which LD1 is turned off, and the current rise period, current constant control period, and current fall period described above. In the off period, the first voltage from the main voltage source 4 is supplied, and a simmer current is flowing through LD1. In the current rise period, the second voltage from the boost voltage source 7 is supplied to LD1. In the current constant control period and the current fall period, the first voltage from the main voltage source 4 is supplied to LD1.

[0031] Therefore, when transitioning from the off period to the current rise period, MOSFET3 is turned off and MOSFETs 2 and 61 are turned on. As a result, the second voltage from the boost voltage source 7 is applied to the anode of LD1 via MOSFET2, and current flows through LD1, MOSFET61, and the current detector 62. By applying the second voltage from the boost voltage source 7 to LD1 at the time of current rise in this way, the current rise is accelerated.

[0032] When the current flowing through LD1 rises to the target current, MOSFET2 is controlled to turn off, but the on state of MOSFET61 is continued and MOSFET3 is controlled to turn on. As a result, the first voltage from the main voltage source 4 is applied to the anode of LD1 via MOSFET3, and current flows through LD1, MOSFET61, and the current detector 62. When current flows through LD1, energy is stored in the wiring inductances L1 and L2 on the anode side and cathode side of LD1. The current flowing through LD1 is maintained constant by MOSFET61 and the drive unit 63. This period corresponds to the constant current control period.

[0033] After that, in the current fall period, MOSFET61 is controlled to turn off. At this time, MOSFET3 maintains the on state. As a result, in the current fall period, the energy stored in the wiring inductances L1 and L2 can be regenerated to the boost voltage source 7 via the diode 5.

[0034] Next, the functions and circuit configuration features of the light-emitting element drive circuit 100 according to Embodiment 1 connected as described above will be described. The main voltage source 4 holds the first voltage and is connected to be able to apply the first voltage to the anode of LD1. The boost voltage source 7 holds a second voltage higher than the first voltage and is connected to be able to apply the second voltage to the anode of LD1. MOSFET3 is connected in a direction to prevent the second voltage from being applied to the first DC power source. That is, MOSFET3 operates as a reverse current prevention element.

[0035] When MOSFET2 is turned on, the second voltage from the boost voltage source 7 is applied to the anode of LD1 via MOSFET2. Also, when MOSFET2 is turned off, the application of the second voltage to LD1 is stopped. That is, MOSFET2 performs an operation of switching on and off the application of the second voltage to the anode of LD1.

[0036] When MOSFET3 is turned on, the first voltage from the main voltage source 4 is applied to the anode of LD1 via MOSFET3. Also, when MOSFET3 is turned off, the application of the first voltage to LD1 is stopped. That is, MOSFET3 performs an operation of switching on and off the application of the first voltage to the anode of LD1.

[0037] MOSFET3 is an example of a switching element having an antiparallel diode. Antiparallel means that the anode of the diode is connected to the source of MOSFET3 and the cathode of the diode is connected to the drain of MOSFET3. The antiparallel diode may be an externally connected diode or a parasitic diode that MOSFET3 has internally. The parasitic diode is also called a body diode. By using the parasitic diode, an individual diode becomes unnecessary, so the number of parts can be reduced, leading to cost reduction.

[0038] The diode 5 is connected in such a direction that the energy accumulated when current flows through LD1 is regenerated to the boost voltage source 7. With this configuration, the energy accumulated in the wiring inductances L1, L2 is regenerated to the boost voltage source 7 via the diode 5. Also, the diode 5 prevents the current due to the voltage of the boost voltage source 7 from flowing through MOSFET61.

[0039] The linear regulator 6 forms a series circuit together with the main voltage source 4, MOSFET3, LD1, and the wiring inductances L1, L2. As described above, the resistance element 64 serves both as a resistance for suppressing the current of MOSFET61 and as a resistance for converting the current from the constant current circuit section 9 into a correction voltage for the gate voltage of MOSFET61.

[0040] The voltage monitor unit 8 monitors the second voltage of the boost voltage source 7 and the voltage of the anode of LD1.

[0041] The constant current circuit unit 9 performs current injection control on the gate of the MOSFET 61 based on the second voltage of the boost voltage source 7 and the voltage of the anode of LD1 input from the voltage monitor unit 8. The constant current circuit unit 9 obtains the voltage difference between the voltage of the anode of LD1 and the second voltage of the boost voltage source 7, with the second voltage of the boost voltage source 7 as a reference, among the two monitored voltages input from the voltage monitor unit 8. When this voltage difference is relatively small and the voltage of the anode of LD1 is at the same voltage level as the second voltage of the boost voltage source 7, the constant current circuit unit 9 relatively reduces the amount of current flowing to the connection point between the gate of the MOSFET 61 and the resistance element 64.

[0042] Also, when the voltage at the anode of LD1 approaches a voltage equal to the second voltage of the boost voltage source 7, the current injection circuit 9 operates such that the smaller the voltage difference between the two, the smaller the amount of current injected into the connection point between the gate of MOSFET 61 and the resistor element 64. This current injection lowers the gate voltage of MOSFET 61. That is, when the voltage at the anode of LD1 sharply transitions from a low voltage level to a high voltage, the level of the gate voltage of MOSFET 61 sharply decreases. Specifically, during the current rise period when the voltage at the anode of LD1 switches from the first voltage to the second voltage, which is relatively higher than the first voltage, if the voltage between the drain and source of MOSFET 61 sharply increases, it is necessary to lower the gate voltage of MOSFET 61 in order to keep the current between the drain and source of MOSFET 61 constant. In this case, by relatively reducing the current flowing from the constant current circuit section 9 to the connection point between the gate of MOSFET 61 and the resistor element 64, the operation of lowering the gate voltage of MOSFET 61 is accelerated. In this case, the driving section 63 performs an operation of lowering the gate voltage of MOSFET 61 in order to keep the current between the drain and source of MOSFET 61 constant, but the operation of lowering the gate voltage by the current injection by the constant current circuit section 9 can be accelerated. In this way, the constant current circuit section 9 assists in the operation of lowering the gate voltage of MOSFET 61 that is being executed by the driving section 63. In this manner, it is possible to suppress the overshoot of the current flowing through LD1 caused by the response delay of the driving section 63.

[0043] On the other hand, when the voltage at the anode of LD1 moves away from the second voltage of the boost voltage source 7, the constant current circuit section 9 operates so that the greater the voltage difference between the two, the greater the amount of current injected into the connection point between the gate of MOSFET61 and the resistance element 64. This current injection increases the gate voltage of MOSFET61. That is, when the voltage at the anode of LD1 sharply transitions from a high voltage level to a low voltage level, the constant current circuit section 9 operates so that the gate voltage of MOSFET61 sharply increases. Specifically, in a constant current control period in which the voltage at the anode of LD1 switches from the second voltage to the first voltage, which is relatively lower than the second voltage, when the voltage between the drain and source of MOSFET61 sharply decreases, in order to keep the current between the drain and source of MOSFET61 constant, it is necessary to increase the gate voltage of MOSFET61. In this case, the constant current circuit section 9 relatively increases the current flowing from the constant current circuit section 9 to the connection point between the gate of MOSFET61 and the resistance element 64, thereby accelerating the operation of increasing the gate voltage of MOSFET61. In this case, the drive section 63 is performing an operation of increasing the gate voltage of MOSFET61 in order to keep the current between the drain and source of MOSFET61 constant, but the operation of increasing the gate voltage by the current injection by the constant current circuit section 9 can be accelerated. In this way, the constant current circuit section 9 assists the operation of increasing the gate voltage of MOSFET61 executed by the drive section 63. In this manner, it is possible to suppress the undershoot of the current flowing through LD1 generated due to the response delay of the drive section 63.

[0044] In this way, when the voltage at the anode of LD1 moves away from the second voltage of the boost voltage source 7, the constant current circuit section 9 increases the injection current to the gate of MOSFET61 as the voltage difference between the two increases, controls the increase of the gate voltage of MOSFET61, and when the voltage at the anode of LD1 approaches the voltage equivalent to the second voltage of the boost voltage source 7, the constant current circuit section 9 decreases the injection current to the gate of MOSFET61 as the voltage difference between the two decreases, and controls the decrease of the gate voltage of MOSFET61.

[0045] FIG. 2 is a time chart showing the operation of the light-emitting element driving circuit according to Embodiment 2. The upper diagram in FIG. 2 shows the voltage VLD at the anode of LD1, the middle diagram in FIG. 2 shows the LD current ILD flowing through LD1, and the lower diagram in FIG. 2 shows the gate voltage VGS of MOSFET61. The horizontal axis in each diagram of FIG. 2 indicates time. In the upper diagram of FIG. 2, Vmain indicates the main power supply voltage corresponding to the first voltage of the main voltage source 4, and VBoost indicates the boost voltage corresponding to the second voltage of the boost voltage source 7. In the middle and lower diagrams of FIG. 2, the solid line corresponds to the ideal operation, the dashed-dotted line corresponds to the operation of Patent Document 1, and the thick solid line corresponds to the operation of Embodiment 1.

[0046] When switching from the main power supply voltage Vmain to the boost voltage VBoost, in Patent Document 1, a large overshoot occurs in the LD current ILD, and a large delay occurs in the operation of lowering the gate voltage VGS of MOSFET61. In contrast, in Embodiment 1, when switching from the main power supply voltage Vmain to the boost voltage VBoost, the overshoot of the LD current ILD can be reduced, and the responsiveness of the operation of lowering the gate voltage VGS of MOSFET61 can be increased.

[0047] Also, when switching from the boost voltage VBoost to the main power supply voltage Vmain, in Patent Document 1, a large undershoot occurs in the LD current ILD, and a large delay occurs in the operation of raising the gate voltage VGS of MOSFET61. In contrast, in Embodiment 1, when switching from the boost voltage VBoost to the main power supply voltage Vmain, the undershoot of the LD current ILD can be reduced, and the responsiveness of the operation of raising the gate voltage VGS of MOSFET61 can be increased.

[0048] As described above, according to Embodiment 1, a voltage monitor unit 8 that monitors the second voltage of the boost voltage source 7 and the voltage at the anode of LD1, and a constant current circuit unit 9 that controls the injection of a first current to the gate of MOSFET61 based on the second voltage of the boost voltage source 7 and the voltage at the anode of LD1 are provided. Since a current is injected from the constant current circuit unit 9 to MOSFET61 to correct the gate voltage of MOSFET61, overshoot and undershoot of the current flowing through LD1 can be suppressed without changing the response characteristics of the drive unit 63. Further, even in applications where current on / off frequently occurs, an increase in circuit loss can be suppressed.

[0049] Embodiment 2. FIG. 3 is a circuit diagram showing the configuration of the light-emitting element drive circuit 100A according to Embodiment 2. In Embodiment 2, the connection destination of one of the three inputs of the voltage monitor unit 8 is changed from the anode of LD1 to the drain of MOSFET61. Other configurations in FIG. 3 are the same as or equivalent to the configurations in FIG. 1. The same or equivalent components are denoted by the same reference numerals, and redundant descriptions are omitted.

[0050] In Embodiment 2, the voltage monitor unit 8 monitors the second voltage of the boost voltage source 7 as the third voltage and the drain voltage of MOSFET61 as the fourth voltage in order to detect voltage fluctuations between the drain and source of MOSFET61.

[0051] The constant current circuit section 9 controls the injection of current to the gate of the MOSFET 61 based on the second voltage of the boost voltage source 7 and the drain voltage of the MOSFET 61 input from the voltage monitor section 8. The operation of the constant current circuit section 9 in the second embodiment is the same as that of the constant current circuit section 9 in the first embodiment. That is, in the constant current circuit section 9, when the drain voltage of the MOSFET 61 moves away from the second voltage of the boost voltage source 7, the greater the voltage difference between the two, the larger the injection current to the gate of the MOSFET 61, and the gate voltage of the MOSFET 61 is controlled to rise. When the drain voltage of the MOSFET 61 approaches the voltage of the second voltage of the boost voltage source 7, the smaller the voltage difference between the two, the smaller the injection current to the gate of the MOSFET 61, and the gate voltage of the MOSFET 61 is controlled to fall.

[0052] Thus, according to the second embodiment, a voltage monitor section 8 that monitors the second voltage of the boost voltage source 7 and the drain voltage of the MOSFET 61, and a constant current circuit section 9 that controls the injection of the first current to the gate of the MOSFET 61 based on the second voltage of the boost voltage source 7 and the drain voltage of the MOSFET 61 are provided. By injecting current from the constant current circuit section 9 to the MOSFET 61 and correcting the gate voltage of the MOSFET 61, it is possible to suppress the overshoot and undershoot of the current flowing through the LD1 without changing the response characteristics of the drive section 63. Also, even in applications where the current is frequently turned on and off, an increase in circuit loss can be suppressed.

[0053] The light emitting element drive circuits 100 and 100A described in the first and second embodiments are applicable to a laser oscillator that performs pulse oscillation.

[0054] The configurations shown in the above embodiments are examples of the content of the present disclosure, and it is possible to combine them with other known technologies, combine the embodiments with each other, and omit or change a part of the configuration without departing from the gist of the present disclosure.

Description of Reference Numerals

[0055] 1 LD, 2, 3, 61 MOSFET, 4 main voltage source (low voltage source), 5 diode, 6 linear regulator, 7 boost voltage source (high voltage source), 8 voltage monitor section, 9 constant current circuit section, 62 current detector, 63 drive section, 64 resistance element, 100, 100A light emitting element drive circuit, L1, L2 wiring inductance.

Claims

1. A light emitting element drive circuit for driving a light emitting element, a first DC power source 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 higher than the first voltage; a first switch element that is connected in a direction that prevents the second voltage from being applied to the first DC power supply and that switches on and off the application of the first voltage to the anode of the light-emitting element; a second switch element that switches on and off the application of the second voltage to the anode of the light-emitting element; a diode connected in such a direction that energy stored in wiring inductances on the anode side and the cathode side of the light emitting element is regenerated to the second DC power source when a current flows through the light emitting element; a linear regulator including a third switch element connected in series to the light emitting element and a drive unit that drives the third switch element, the linear regulator constituting a series circuit including the first DC power source, the first switch element, the light emitting element, the third switch element, and the wiring inductances on the anode side and the cathode side of the light emitting element, and controlling a current flowing through the light emitting element; a voltage monitor unit that detects a third voltage and a fourth voltage for detecting a voltage fluctuation between the drain and source of the third switch element; a constant current circuit section that performs injection control of a first current to a gate of the third switch element based on the third voltage and the fourth voltage; A light-emitting element driving circuit comprising:

2. The third voltage is the second voltage of the second DC power source, and the fourth voltage is a voltage of the anode of the light-emitting element.

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

3. The third voltage is the second voltage of the second DC power supply and is a drain voltage of the third switch element.

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

4. The constant current circuit unit is When the fourth voltage is moving away from the third voltage, the first current is increased as the voltage difference between the fourth voltage and the third voltage is increased, thereby performing an increase control of the gate voltage of the third switch element; When the fourth voltage approaches the third voltage, the smaller the voltage difference between the fourth voltage and the third voltage, the smaller the first current is made to be, thereby performing a decrease control of the gate voltage of the third switch element.

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

5. the linear regulator further includes a resistive element connected between the gate of the third switch element and the drive unit; The constant current circuit unit injects the first current into a connection point between the gate of the third switch element and the resistive element.

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

6. the linear regulator further includes a current detector that detects a current flowing through the third switch element, The drive unit drives and controls the third switch element based on a difference between a current command value of the third switch element and a detected current value of the current detector.

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

7. The light-emitting element; A light emitting element drive circuit according to any one of claims 1 to 6, which drives the light emitting element; A laser oscillator comprising:

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