Light source device

Abstract

Provided is a light source device that can simultaneously light up a plurality of light-emitting elements to increase light output while suppressing damage to any light-emitting element from inducing damage to other light-emitting elements. The light source device is a light source device that allows a fixed current to flow through a diode load (10) in which a plurality of light-emitting elements (1) are connected in series, and comprises: a power supply circuit (20) connected to the diode load (10), and a peak current limiting circuit (30) connected in series with the diode load (10). In addition, the peak current limiting circuit (30) comprises: a current detector (31) connected in series with the diode load (10), and a current adjustment circuit (32) that controls the current of the diode load (10) by the detection voltage of the current detector (31). Furthermore, the current detector (31) is composed of a series circuit of a resistor (4) and a coil (5).

Description

Technical Field

[0001] The present disclosure relates to a light source device in which a plurality of light-emitting elements are connected in series. Background Art

[0002] The resistance of a light-emitting diode changes with voltage or current, and the voltage-current characteristic does not change linearly. Therefore, a light source device using a light-emitting diode as a light source may be connected to a constant current circuit and lit. Furthermore, in order to increase the light output, the light source device connects a plurality of light-emitting diodes in series and lights them up at the same time. In order to flow a fixed current through each light-emitting diode connected in series and light them up, the light source device has a constant current circuit. (Refer to Patent Document 1)

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-129129 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The constant current circuit works so that the current is controlled to be constant when the current increase is detected, but there is a concern that a time delay will occur before the current increase is detected and controlled to be constant. The time delay may cause an instantaneous excessive peak current to flow, and there is a concern that the peak current may cause damage to normal light-emitting elements due to overcurrent.

[0008] The present disclosure provides a light source device capable of suppressing damage to any light-emitting element from being induced by other light-emitting elements.

[0009] Means for solving problems

[0010] The light source device disclosed in the present invention is a light source device in which a constant current flows through a diode load formed by connecting a plurality of light-emitting elements in series, and the light source device comprises: a power supply circuit connected to the diode load; and a peak current limiting circuit connected in series with the diode load. In addition, the peak current limiting circuit comprises: a current detector connected in series with the diode load and a current regulating circuit for controlling the current of the diode load according to the detection voltage of the current detector. In addition, the current detector is composed of a series circuit of a resistor and a coil.

[0011] Effects of the Invention

[0012] According to the present disclosure, it is possible to suppress damage to any light-emitting element from being induced by other light-emitting elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a block diagram of the light source device according to Embodiment 1.

[0014] Figure 2 This is a block diagram of a light source device according to Embodiment 2.

[0015] Figure 3 This is a block diagram of a light source device according to Embodiment 3.

[0016] Figure 4 This is a block diagram of a light source device according to Embodiment 4.

[0017] Figure 5 This is a schematic diagram showing a current waveform of a light source device that is not provided with a peak current limiting circuit.

[0018] Figure 6 Schematic diagram showing a current waveform of a light source device provided with a peak current limiting circuit according to an embodiment. DETAILED DESCRIPTION

[0019] According to a light source device involved in one embodiment, the light source device allows a constant current to flow through a diode load in which a plurality of light-emitting elements are connected in series. The light source device comprises: a power supply circuit connected to the diode load, and a peak current limiting circuit connected in series with the diode load. The peak current limiting circuit comprises: a current detector connected in series with the diode load, and a current adjustment circuit that controls the current of the diode load according to a detection voltage of the current detector, wherein the current detector is composed of a series circuit of a resistor and a coil.

[0020] The above-mentioned light source device is provided with a peak current limiting circuit connected in series with a diode load, wherein the diode load is formed by connecting a plurality of light-emitting elements in series, and the peak current limiting circuit is provided with a current detector connected in series with the diode load and a current regulating circuit for controlling the current of the diode load according to the detection voltage of the current detector. Furthermore, in the current detector, a coil is connected in series with a resistor, so that when the resistance of the diode load suddenly decreases due to a fault such as an internal short circuit in any light-emitting element, thereby causing the current to increase instantaneously, a peak voltage is instantaneously induced in the coil of the current detector in proportion to the sudden current change of the diode load and the inductance of the coil. The instantaneously induced peak voltage controls the current regulating circuit, causing the current of the diode load, which is the output current, to decrease instantaneously. Thus, even in a state where any light-emitting element fails and the resistance of the diode load decreases instantaneously, the current of the diode load can be controlled at an extremely fast response speed, thereby suppressing the increase of the current.

[0021] In particular, the above-mentioned light source device connects a coil in series with the resistor of the current detector, and controls the current adjustment circuit through the peak voltage induced by the coil, that is, the peak voltage is fed back to the input side of the current adjustment circuit to limit the current of the diode load, so that the instantaneous increase of the diode load current can be suppressed by the coil with extremely small inductance. For example, in the light source device of the following embodiment, the inductance of the coil connected in series with the resistor is extremely small, such as 0.9μH. In particular, the above light source device connects a coil with extremely small inductance to the current detector of the peak current limiting circuit provided to stabilize the current of the diode load to a constant current. Despite such a simple circuit configuration, it is possible to suppress the instantaneous increase of the current of the diode load.

[0022] In addition, after the instantaneous peak current is suppressed by the inductance of the coil, the diode load can be stabilized to a constant current value through the resistor of the current detector. Therefore, in a light source device in which a plurality of light-emitting elements are connected in parallel, even if the resistance of any one of the light-emitting elements decreases due to a fault such as an internal short circuit, the other light-emitting elements can be protected from damage by overcurrent, and thereafter, a predetermined constant current can be made to flow through the diode load as before the light-emitting element fails. Thus, in the above light source device, even if any one of the light-emitting elements fails, the other light-emitting elements can be protected from being affected by the peak current that flows instantaneously, and further, even if the number of light-emitting elements connected in series decreases, the light-emitting elements of the diode load can be stabilized to a predetermined constant current value and lit.

[0023] In addition, according to the light source device involved in other embodiments, the current adjustment circuit includes a transistor connected in series with a diode load and a current detector, a comparator connected to the input side of the transistor, and a reference voltage circuit that inputs a reference voltage to a first input terminal of the comparator. The detection voltage induced by the current detector is input to a second input terminal of the comparator, and the output of the comparator is input to the transistor, and the transistor can control the current of the diode load.

[0024] Furthermore, according to the light source device according to another embodiment, the transistor can be a FET. Also, according to the light source device according to another embodiment, a plurality of FETs can be connected in parallel.

[0025] Furthermore, according to the light source device according to another embodiment, the reference voltage circuit can be a circuit capable of changing the reference voltage.

[0026] Furthermore, according to a light source device according to another embodiment, a sub-amplifier for amplifying a voltage sensed by the current detector is provided, and an output voltage of the sub-amplifier can be input to an input terminal of the comparator.

[0027] Furthermore, according to the light source device according to another embodiment, a buffer amplifier that reduces the output impedance of the comparator and outputs the comparator can be connected between the output side of the comparator and the input side of the transistor.

[0028] Furthermore, according to the light source device according to another embodiment, the power supply circuit can be a constant current power supply.

[0029] Furthermore, according to the light source device according to another embodiment, the resistor can be a winding resistor.

[0030] Furthermore, according to a light source device according to another embodiment, the light emitting element can be a laser diode.

[0031] The present disclosure is described in detail below based on the accompanying drawings. In addition, in the following description, terms indicating specific directions or positions (such as "upper", "lower" and other terms including these terms) may be used as needed, but these terms are used to make the understanding of the invention with reference to the accompanying drawings easier, and the technical scope of the present invention is not limited by the meaning of these terms. In addition, parts with the same symbols appearing in multiple drawings represent the same or equivalent parts or components.

[0032] Furthermore, the embodiments shown below are used to represent specific examples of the technical ideas of the present invention and are not used to limit the present disclosure to the following. In addition, the dimensions, materials, shapes and corresponding configurations of the structural components described below, unless otherwise specified, are not intended to limit the scope of the present invention, but are for illustration. In addition, the contents described in one embodiment can be applied in other embodiments. In addition, the size or positional relationship of the components shown in the drawings may be exaggerated in order to make the description clear.

[0033] Figures 1 to 4This is a block diagram of the light source device 100, 200, 300, 400 involved in this embodiment. A plurality of light emitting elements 1 are connected in series as a diode load 10, and the diode load 10 is connected to a constant current power supply 2 so that a predetermined rated current flows through it and it is illuminated. The light emitting element 1 is, for example, a light emitting diode (Light Emitting Diode (LED)) or a laser diode (Laser Diode (LE)). The diode load 10 uses a diode array in which a plurality of light emitting elements 1 are connected in series and mounted on a circuit substrate (not shown), or an object in which a plurality of light emitting elements 1 are electrically connected in a detachable manner. The light source device 100, 200, 300, 400 can increase the number of light emitting elements 1 connected in series, and illuminate a plurality of light emitting elements 1 to increase the light output. When all the light emitting elements 1 are in a normal working state, all the light emitting elements 1 are driven by a fixed set current supplied by the constant current power supply 2. However, when a plurality of light-emitting elements 1 are connected in series and lit, if an internal short circuit occurs in any light-emitting element 1, or the operating voltage of any light-emitting element 1 drops sharply, the resistance of the diode load 10 drops, and thus the current of the diode load 10 increases. The constant current power supply 2 detects the increase in current and controls it to a set value, but there is a time delay before the increased current is controlled to the set value. The delay in response time may cause excessive current to flow through the non-faulty light-emitting element 1, resulting in damage caused by the current. For example, the failure of any light-emitting element is induced by other light-emitting elements. In particular, in a light source device in which the light-emitting element is a laser diode, damage caused by overcurrent or over-output based on the laser is prone to occur due to the good response characteristics of the laser diode.

[0034] The constant current power supply 2 is connected in series with a semiconductor switching element on the output side, and has an analog mode of adjusting the internal resistance of the semiconductor switching element to control the voltage drop value of the semiconductor switching element to control the output current, and a switching mode of controlling the output current by a DC / DC converter. The switching mode can achieve constant current characteristics by switching the duty cycle of the semiconductor switching element on and off to achieve high power efficiency. In order to reduce the fluctuation of the output voltage and form a neat direct current, the switching mode is connected to an electrolytic capacitor with a large electrostatic capacitance on the output side, but the electrolytic capacitor becomes the reason for slowing down the response speed of controlling the output current to a fixed value. This is because the time delay of the discharge and charging of the electrolytic capacitor slows down the response time of the output current. The constant current power supply of the high power efficiency switching mode can reduce the power loss of the semiconductor switching element, but the delay in the response time caused by the large-capacitance electrolytic capacitor connected to the output side will cause damage caused by excessive current or over-output of the laser to the non-faulty light-emitting element.

[0035] 1. Implementation Method 1

[0036] (Light source device)

[0037] Figure 1 This is a block diagram of the light source device 100 according to the first embodiment.

[0038] The light source device 100 includes a power supply circuit 20 for causing a current to flow through a diode load 10 in which a plurality of light emitting elements 1 are connected in series, and a peak current limiting circuit 30 connected in series with the diode load 10. In addition, the peak current limiting circuit 30 includes a current detector 31 connected in series with the diode load 10, and a current regulating circuit 32 for controlling the current of the diode load 10 by outputting a detection voltage to both ends of the current detector 31. The current detector 31 is a series circuit of a resistor 4 and a coil 5.

[0039] (Power supply circuit)

[0040] The power supply circuit 20 includes a constant current power supply 2 that allows a pre-controlled current to flow through the diode load 1. The power supply circuit 20 preferably uses a constant voltage constant current power supply. The constant voltage constant current power supply provides an output voltage below a set value and controls the current of the diode load 10 to a set value. Preferably, the constant current power supply 2 includes a circuit that changes the current value flowing through the diode load 10. The constant current power supply 2 that can change the current value changes the current value flowing through the diode load 10, that is, the output current, within a range of, for example, 1A to 10A, so that the light-emitting element 1 flows through the optimal current and lights up. The constant current power supply 2 is a switching mode or an analog mode controlled by the output voltage of the DC / DC converter. The switching mode constant current power supply 2 has the characteristics of being lightweight while improving power efficiency. Lightweighting can be achieved by omitting a heavy power transformer. The constant current power supply 2 controls the output current to a set value by switching the duty cycle of the semiconductor switch element that is turned on and off, so that the set current can be greatly changed and the heat generation can be reduced.

[0041] (Peak current limiting circuit)

[0042] The current regulating circuit 32 of the peak current limiting circuit 30 limits the instantaneous increase of the current of the diode load 10 when any light emitting element 1 is short-circuited internally or the operating voltage of any light emitting element 1 drops sharply, thereby preventing the damage caused by overcurrent of the light emitting element 1 or over-output of the laser. The light source device 100 in which the power supply circuit 20 is a constant current power supply 2 makes the set current of the peak current limiting circuit 30 the same or substantially the same as the set current of the constant current power supply 2 of the power supply circuit 20. The light source device 100 supplies a set fixed current from the constant current power supply 2 to the diode load 10. If any light emitting element 1 is short-circuited internally or the operating voltage of any light emitting element 1 drops sharply, thereby causing a peak current to flow through the diode load 10 due to the delay in the response time of the constant current power supply 2, the peak current limiting circuit 30 will suppress the peak current.

[0043] Figure 5 The current characteristics of the diagram show the current waveform of a light source device without a peak current limiting circuit. The diagram shows the current change state of a diode load 10 when multiple (for example, 20) light emitting elements 1 are connected in series and the two ends of a specific light emitting element 1 are short-circuited. If a specific light emitting element 1 is short-circuited, the resistance of the diode load 10 decreases, causing a peak current to flow. Figure 5 In the current characteristics, the time length of the peak current, that is, the time length until the peak current decays, is close to 20msec. The time when the peak current flows varies according to the delay of the response time of the constant current power supply 2, but the light emitting element 1 may be damaged by overcurrent or over-output of the laser.

[0044] The peak current limiting circuit 30 suppresses the peak current, thereby suppressing damage to the light emitting element 1 caused by overcurrent or over-output due to laser. The current regulating circuit 32 of the peak current limiting circuit 30 includes a transistor 3 and a comparator 33. The transistor 3 increases its internal resistance at the timing when the current detector 31 detects the peak current, thereby suppressing the peak current. The comparator 33 increases the internal resistance of the transistor 3 at the timing when the current detector 31 detects the peak current. The comparator 33 compares the detection voltage input from the current detector 31 with the reference voltage, and outputs a signal to increase the internal resistance of the transistor 3 to the transistor 3 at the timing when the current detector 31 detects the peak current and the detection voltage increases.

[0045] (Current Detector)

[0046] The current detector 31 connects the resistor 4 and the coil 5 in series. Figure 1 The current detector 31 has a coil 5 connected in series to a resistor 4. The current detector 31 can adjust the resistance of the resistor 4 and the inductance of the coil 5 to an optimal value. The resistor 4 can use a winding resistor in which a resistance wire is wound in a coil shape on the surface of an insulating material such as an insulator. The winding resistor has inductance, and the resistance is adjusted by the resistivity and length of the resistance wire, and the inductance is adjusted by the number of turns of the resistance wire. In the winding resistor, the resistor and the coil are integrally formed, but in the equivalent circuit, the resistor and the coil are connected in series.

[0047] The resistor 4 increases the voltage across both ends in proportion to the current flowing therethrough. When the peak current flows through the coil 5 and the current changes sharply, the detection voltage of the current detector 31 is increased, and the peak current of the diode load 10 is suppressed. The coil 5 increases the induced voltage across both ends when the peak current is generated. In particular, the detection voltage is increased at the rising edge of the peak current. This is because, as shown in the following formula (1), the peak current increases the voltage (E) induced across both ends of the coil 5 in proportion to the inductance (L) of the coil 5.

[0048] E=L×di / dt Formula (1)

[0049] However, in formula (1), di represents the amount of change in current, dt represents the time of current change, and di / dt represents the ratio of the increase of the peak current per unit time. Since the peak current suddenly increases at the rising edge, di / dt becomes extremely large at this timing, and the induced voltage becomes quite high. Therefore, at the moment when the peak current flows through the current detector 31 in which the coil 5 is connected in series with the resistor 4, especially at the rising edge timing of the peak current, the induced voltage across the coil 5 becomes high, and the detection voltage becomes high. The instantaneously high detection voltage is input to the input terminal of the comparator 33. The inductance of the coil 5 is set to an optimal value in consideration of the resistance of the resistor 4 connected in series, the current flowing through the diode load 10, the transistor 3, the required response speed, etc. For example, in a circuit structure in which the current of the diode load 10 is set to 1A to 10A and the resistance of the resistor 4 is set to 0.2Ω to 0.5Ω, it is set to 0.5μH to 5μH.

[0050] (Current Regulation Circuit)

[0051] The current regulating circuit 32 controls the current flowing through the diode load 10 by the detection voltage input from the current detector 31. When the peak current flows through the diode load 10 and the detection voltage input from the current detector 31 increases instantaneously, the current regulating circuit 32 limits the current to suppress the peak current. The current detector 31 increases the detection voltage at the rising edge of the peak current, so the current regulating circuit 32 effectively suppresses the current at the timing when the detection voltage increases, that is, the timing when the peak current flows through the diode load 10. The current regulating circuit 32 increases the internal resistance of the transistor 3 to suppress the peak current of the diode load 10. Thus, the transistor 3 connected in series with the diode load 10 is provided, and the comparator 33 that controls the internal resistance of the transistor 3 by the detection voltage input from the current detector 31 is provided.

[0052] (transistor)

[0053] Transistor 3 preferably uses FET (Field Effect Transistor). MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with excellent large current characteristics is particularly suitable. This is because FET has a large input resistance and a small connection resistance, and can efficiently control the current. However, it is not limited to FET. Transistor 3 can use all transistors that can control the internal resistance through the input signal, such as bipolar transistors or IGBT (Insulated Gate Bipolar Transistor). FET can control the internal resistance through the input voltage. FET can increase the input voltage to reduce the internal resistance, and reduce the input voltage to increase the internal resistance. Furthermore, Figure 4 The current regulating circuit 32C of the light source device 400 shown includes a plurality of FETs, and by connecting the plurality of FETs in parallel, the maximum allowable current can be increased in proportion to the number of FETs connected in parallel.

[0054] (Comparator)

[0055] The comparator 33 compares the detection voltage input from the current detector 31 with a reference voltage, and controls the internal resistance of the transistor 3 . Figure 1 The comparator 33 includes a differential amplifier 6. The output side of the differential amplifier 6 is connected to the input side of the transistor 3, and the internal resistance of the transistor 3 is controlled by the output voltage. A reference voltage circuit 34 for inputting a reference voltage is connected to the first input terminal 6A of the differential amplifier 6, and the detection voltage of the current detector 31 is input to the second input terminal 6B. The differential amplifier 6 amplifies the voltage difference between the first input terminal 6A and the second input terminal 6B, or inputs it to the transistor 3 without amplification. The first input terminal of the differential amplifier 6 is set as a + side input terminal, and the second input terminal is set as a - side input terminal. The reference voltage circuit 34 is a circuit that can change the reference voltage, and can change the set current of the peak current limiting circuit 30.

[0056] The peak current limiting circuit 30 described above performs the following operation to suppress the peak current of the diode load 10 .

[0057] 1. When a peak current flows through the diode load 10 , the detection voltage of the current detector 31 rises in accordance with the peak current.

[0058] In particular, the change value of the current becomes larger at the rising edge of the peak current, so the voltage induced in the coil 5 becomes higher at this timing, and the detection voltage becomes higher instantaneously.

[0059] 2. The instantaneously rising detection voltage is input to the second input terminal 6B of the differential amplifier 6 provided as the comparator 33 .

[0060] 3. The differential amplifier 6 compares the voltage of the second input terminal 6B with the reference voltage of the first input terminal 6A, and changes the output voltage to the negative side when the voltage of the second input terminal 6B increases.

[0061] 4. The output voltage changed to the negative side is input to the input side of transistor 3.

[0062] 5. The input voltage changes to the negative side of transistor 3, which increases the internal resistance.

[0063] 6. The transistor 3 with increased internal resistance reduces the current of the diode load 10 and suppresses the peak current.

[0064] The peak current limiting circuit 30 performs the above operation to suppress the peak current of the diode load 10, and the detection voltage rises instantaneously at the rising edge of the peak current. At this moment, the coil 5 connected in series with the resistor 4 instantly increases the internal resistance of the transistor 3. The transistor 3 whose internal resistance increases instantaneously quickly suppresses the peak current flowing through the diode load 10.

[0065] Figure 6 The current characteristics flowing through the diode load 10 in the light source device 100 in which the coil 5 is connected in series to the resistor 4 in the current detector 31 are shown. Figure 5 The following figure shows the current waveform flowing through the diode load in a light source device using a current detector with no coil connected but only a resistor. Figure 5 As shown in the figure, in a light source device consisting of a resistor and no coil connected to the current detector, the peak current flows for a period of about 20 msec, which is quite long, and the light-emitting element may be damaged by overcurrent or over-output of the laser. Figure 6 As shown, in the light source device 100 in which the coil 5 is connected to the current detector 31, the time length for which the peak current flows is reduced to about 100 μsec, which is shortened to about 1 / 200, and the maximum current of the peak current is also reduced, thereby preventing the light emitting element 1 from being damaged by overcurrent or over-output of laser light. Figure 6 The current characteristics are measured when the current of the diode load is set to 2A, the resistance of the resistor is set to 0.5Ω, and the inductance of the coil is set to 0.9μH.

[0066] 2. Implementation Method 2

[0067] Figure 2: is a block diagram of a light source device 200 according to Embodiment 2. The current regulating circuit 32A of the light source device 200 of the figure includes a sub-amplifier 7 for amplifying the voltage induced by the current detector 31. The light source device 200 is characterized in that the heat generated by the Joule heat of the current detector 31 is reduced, and the detection error caused by the temperature change of the current detector 31 can be reduced. The sub-amplifier 7 amplifies the voltage of the current detector 31 and inputs it to the comparator 33, thereby reducing the resistance and inductance of the current detector 31, thereby reducing the detection voltage of the current detector 31, and a predetermined voltage can be input to the comparator 33. For example, if the amplification factor of the sub-amplifier 7 is set to 10 times, the resistance and inductance of the current detector 31 can be reduced to 1 / 10, and the heat generated by the Joule heat of the current detector 31 can be reduced to 1 / 10. If the reference voltage and the detection voltage input to the comparator 33 are too small, it is difficult to control the current with high accuracy. For example, if the resistance of the resistor 4 is 0.2Ω, the current value of the diode load 10 is 2A, the output voltage is 0.4V, and this voltage is input to the comparator 33. Although the amount of heat generated by Joule heat can be reduced by reducing the resistance of the resistor 4 to 1 / 10, that is, 0.02Ω, the input voltage of the comparator 33 is reduced to 0.04V, and it is difficult to accurately control the internal resistance of the transistor 3. If the detection voltage of the current detector 31 is amplified 10 times and input to the comparator 33, the input voltage of the comparator 33 becomes 0.4V, and the current can be controlled with high accuracy.

[0068] 3. Implementation Method 3

[0069] Figure 3 : is a block diagram of a light source device 300 according to Embodiment 3. A current regulating circuit 32B of the light source device 300 in the figure connects a buffer amplifier 8 between the output side of the comparator 33 and the input side of the transistor. The buffer amplifier 8 can reduce the output impedance by using a 100% negative feedback amplifier circuit. The buffer amplifier 8 converts the output impedance of the comparator 33 and inputs it to the transistor 3. The light source device 300 reduces the output impedance of the comparator 33 through the buffer amplifier 8 and inputs it to the transistor 3, so that the input capacitance of the transistor 3 can be quickly charged. Thus, the internal resistance of the transistor 3 is quickly controlled by the output signal of the comparator 33, and the increase of the peak current is suppressed more efficiently in a short time.

[0070] Transistors with large current capacitance, such as MOSFET or IGBT, have large input capacitance. Therefore, setting transistor 3 as a peak current limiting circuit of MOSFET or IGBT can increase the current of the diode load and increase the light output, but the large input capacitance of transistor 3 becomes the reason for slowing down the response time. Figure 3In the peak current limiting circuit 30, the output impedance of the buffer amplifier 8 with 100% negative feedback is small, which can shorten the response time delay of the transistor 3 with large input capacitance. Therefore, the peak current limiting circuit 30 can quickly suppress the peak current of the diode load 10 while increasing the current of the diode load 10 to increase the light output.

[0071] Although several embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments, and can be implemented in any form without departing from the spirit and scope of the present invention.

[0072] Industrial Applicability

[0073] The light source device according to the present disclosure can be effectively used as a light source device in which a plurality of light emitting elements are connected in series to increase light emission output.

[0074] Description of symbols

[0075] 100, 200, 300, 400 light source devices

[0076] 1 Light-emitting element

[0077] 2 Constant current power supply

[0078] 3 Transistors

[0079] 4 Resistors

[0080] 5 Coil

[0081] 6 Differential Amplifier

[0082] 6A First input terminal

[0083] 6B Second input terminal

[0084] 7 sub amplifier

[0085] 8 Buffer Amplifier

[0086] 10 Diode load

[0087] 20 Power circuit

[0088] 30 Peak current limiting circuit

[0089] 31 Current detector

[0090] 32, 32A, 32B, 32C current regulation circuit

[0091] 33 Comparator

[0092] 34 Reference voltage circuit.

Claims

1. A light source device that allows a fixed current to flow through a diode load in which a plurality of light-emitting elements are connected in series, characterized in that: have: a power supply circuit connected to the diode load; and A peak current limiting circuit is connected in series with the diode load, The peak current limiting circuit comprises: a current detector connected in series with the diode load; and A current regulating circuit controls the current of the diode load through the detection voltage of the current detector, The current detector is a series circuit of a resistor and a coil, The light source device does not include an inductor for a smoothing circuit connected in series with the power supply circuit.

2. The light source device according to claim 1, wherein: The current regulating circuit comprises: a transistor connected in series with the diode load and the current detector; a comparator connected to the input side of the transistor; and a reference voltage circuit for inputting a reference voltage to a first input terminal of the comparator, The detection voltage sensed by the current detector is input to the second input terminal of the comparator. The output of the comparator is input to the transistor, The transistor is configured to control a current in the diode load.

3. The light source device according to claim 2, characterized in that: The transistor is a field effect transistor, namely, a FET.

4. The light source device according to claim 3, characterized in that: A plurality of the FETs are provided, and the plurality of FETs are connected in parallel.

5. The light source device according to any one of claims 2 to 4, characterized in that: The reference voltage circuit is a circuit capable of changing a reference voltage.

6. The light source device according to any one of claims 2 to 4, characterized in that: have: A sub-amplifier is used to amplify the voltage sensed by the current detector. An output voltage of the sub-amplifier is input to an input terminal of the comparator.

7. The light source device according to any one of claims 2 to 4, characterized in that: A buffer amplifier is connected between the output side of the comparator and the input side of the transistor, and the buffer amplifier reduces the output impedance of the comparator and outputs it.

8. The light source device according to any one of claims 1 to 4, characterized in that: The power supply circuit is a constant current power supply.

9. The light source device according to any one of claims 1 to 4, characterized in that: The resistor is a winding resistor.

10. The light source device according to any one of claims 1 to 4, characterized in that: The light emitting element is a laser diode.

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