JP2023132938A - Light source device and concentration measurement device - Google Patents

Abstract

To stabilize a forward voltage of a semiconductor light emitting element to accurately measure the concentration of solutes dissolved in various solutions such as aqueous solutions and of each gas in a mixed gas.SOLUTION: A light source device 2 has an LED 21 and the following parts. A constant current drive circuit 101 supplies a constant current toward the LED 21. A current correction circuit 102 sends a part of the constant current supplied from the constant current drive circuit 101 to a bypass circuit 124 as a bypass current, supplies the remaining current to the LED 21 as an LED current, reduces the bypass current when the LED current is smaller than a predetermined target current value, and corrects the bypass current to be increased when the LED current is larger than the predetermined target current value.SELECTED DRAWING: Figure 2

Description

The present invention relates to a light source device used to measure the concentration of a measurement target such as a solution, and a concentration measuring device that performs the measurement.

2. Description of the Related Art Conventionally, there has been known a technique for measuring the concentration of an aqueous solution such as a semiconductor etching solution or cleaning solution using light. One example of such technology is a technology that irradiates an aqueous solution with light from an LED (Light Emitting Diode), which is a semiconductor light emitting device, and measures the concentration of the aqueous solution from the intensity of the emitted light and the intensity of the light received through the aqueous solution. Are known.

For example, the forward voltage (forward voltage) when a constant current is passed through the LED is obtained in advance, and the corresponding information indicating the relationship with the emission intensity of light of a specific wavelength emitted by the LED and the information measured by the measurement unit are obtained. A technique has been proposed for measuring the concentration of a measurement target based on a forward voltage and the intensity of light of a specific wavelength separated by a spectroscopic section. More specifically, there is a method in which the emission intensity is estimated from the forward voltage Vf of an LED, which is a light source, and the concentration of the measurement target is calculated from the estimated emission intensity and the received light intensity of a specific wavelength detected by a spectrometer.

Further, as constant current drive circuits for LEDs, there are known a linear type that allows high-speed response and highly accurate current control, and a switching type that generates little heat in the circuit, that is, has low power consumption.

When measuring concentration using the forward voltage of an LED, it is desirable to stabilize the forward voltage of the LED as much as possible in order to accurately measure the concentration of a liquid. For example, if the amount of change in the forward voltage is large or the reproducibility is poor, it becomes difficult to estimate the emission intensity. However, since the forward voltage changes depending on the drive current of the LED, in order to stabilize the forward voltage of the LED, it is desirable to make the drive current as highly accurate and highly stable as possible.

Further, since the forward voltage changes depending on the heat generation temperature of the LED itself, in order to stabilize the forward voltage of the LED, it is desirable to set the lighting time to the minimum necessary. The minimum necessary lighting time is the minimum time necessary for measuring the received light intensity with a spectrometer. For this purpose, it is desirable to turn on the LED dynamically (intermittent lighting) and to make the rising response of the drive current from the off state to the on state as fast as possible.

For example, if the startup response is slow, it is necessary to lengthen the lighting time accordingly, which increases the amount of heat generated and affects the forward voltage. As a countermeasure for this, in order to suppress the overall amount of heat generated, it is conceivable to lengthen the turn-off time by the length of the lighting time to lengthen the blinking cycle (=PWM (Pulse Width Modulation) cycle). However, when the blinking period is lengthened, the detection period on the light receiving side also becomes longer, which slows down the response speed of concentration measurement, which ultimately affects the performance of the concentration measuring device. For example, bubble detection may become difficult. Therefore, the concentration can be measured more accurately by increasing the rising response and suppressing the forward voltage variation, rather than suppressing the variation in the forward voltage while keeping the rising response slow. Incidentally, since the luminous intensity of LEDs gradually decreases over the lifespan, a dynamic lighting method is generally used to extend the lifespan.

Furthermore, the forward voltage also changes due to the influence of ambient temperature, so in order to stabilize the forward voltage of the LED, it is generally necessary to minimize the heat generation of the components of the LED drive circuit, which are placed near the LED or in the same case. is desirable.

Japanese Patent Application Publication No. 2021-124385 Japanese Patent Application Publication No. 2012-164746 Japanese Patent Application Publication No. 2012-049179 JP2020-202689A

High precision and high stability of the drive current, as well as faster rise response of the drive current from the off state to the on state, can be achieved by using a linear constant current drive circuit. However, in the case of a linear type, the current control transistor generates heat, so it is difficult to minimize the heat generated by components of the LED drive circuit.

Further, if a switching type constant current drive circuit is used, the heat generated by the current control transistor is significantly reduced compared to a linear type, so it is possible to minimize the heat generated by components of the LED drive circuit. However, in the switching type constant current drive circuit, it is difficult to achieve high precision and high stability of the drive current, and to increase the speed of the rise response of the drive current from the off state to the on state. That is, in the case of a switching type, a ripple current is generated in principle, but the rise of the LED current is delayed due to the capacitance of a smoothing capacitor for removing this ripple current. Furthermore, if the capacitance of the smoothing capacitor is made small in order to speed up the rise of the LED current, it becomes difficult to completely remove the ripple current, and a large ripple occurs in the LED current, deteriorating the stability of the light emission intensity. Furthermore, since the ripple of the current detection signal due to the current detection resistor of the constant current control circuit also increases, it becomes difficult to perform constant current control with high precision. In addition, if the peak of the LED current due to this ripple exceeds the maximum rated current of the LED element, the LED element may deteriorate and its life may be significantly shortened.

As described above, conventional LED drive circuits have the following objectives: high precision and high stability of drive current, faster rise response of drive current from off state to on state, and minimization of component heat generation in the LED drive circuit. It was difficult to solve all three problems. That is, with the conventional LED drive circuit, it is difficult to stabilize the forward voltage of the LED and measure the concentration with high accuracy.

This application is intended to solve such problems, and aims to stabilize the forward voltage of a semiconductor light emitting device and accurately measure the concentration of solutes dissolved in various solutions such as aqueous solutions and each gas in a mixed gas. shall be.

The light source device according to the present application includes a semiconductor light emitting element, a constant current drive circuit that supplies a constant current to the semiconductor light emitting element, and a part of the constant current supplied from the constant current drive circuit that is sent to the bypass circuit as a bypass current. , the remaining current is supplied to the semiconductor light emitting device as a semiconductor light emitting device current, and if the semiconductor light emitting device current is smaller than the predetermined target current value, the bypass current is reduced and the semiconductor light emitting device current reaches the predetermined target current value. On the other hand, if the bypass current is larger, a current correction circuit is provided that corrects the bypass current to increase it.

In the light source device, the constant current drive circuit may include a switching element and a switching control circuit that controls on/off of the switching element, and may completely supply the constant current according to the on/off operation of the switching element.

Furthermore, in the light source device, the current correction circuit may perform the bypass current correction operation faster than the on/off operation of the switching element of the constant current drive circuit.

Further, in the above light source device, the constant current drive circuit may control the switching element based on a timing signal given from the outside.

Further, in the above light source device, the switching control circuit may control the on/off interval of the switching element based on the detected value of the constant current output from the constant current drive circuit.

Further, in the above light source device, the current correction circuit adjusts the bypass current based on the forward voltage of the semiconductor light emitting element and the reference voltage detected by the semiconductor light emitting element current detection resistor arranged on the output side of the semiconductor light emitting element. The size may be controlled.

Further, in the above light source device, the current correction circuit includes a differential amplifier circuit, and compares the voltage value of the voltage output from the differential amplifier circuit with a reference voltage using the forward voltage as input, and determines the magnitude of the bypass current. You can also control the

Further, in the above light source device, the constant current drive circuit has a high side current detection circuit that detects the current value of the constant current between the input terminal of the input voltage and the semiconductor light emitting element, and the high side current detection circuit detects the current value of the constant current. The constant current may be controlled based on the current value determined, and the current correction circuit may control the magnitude of the bypass current based on the difference between the voltage value of the forward voltage and the voltage value of the reference voltage.

Further, in the light source device, the current correction circuit may set the bypass current to 25% or less of the constant current.

According to the light source device described above, of the output current output from the constant current drive circuit and smoothed by the smoothing capacitor, the current exceeding the control target value of the semiconductor light emitting element current is passed through the bypass path as a bypass current. . Thereby, the capacitance of the smoothing capacitor can be reduced to the minimum necessary capacitance. It also solves all three problems: increasing the precision and stability of the drive current, increasing the speed of the rise response of the drive current from the off state to the on state, and minimizing the heat generation of components in the semiconductor light emitting device drive circuit. be able to. Therefore, it is possible to stabilize the forward voltage of the semiconductor light emitting device and to accurately measure the concentration of solutes dissolved in various solutions such as aqueous solutions and of each gas in a mixed gas.

FIG. 1 is a diagram for explaining a measurement method in an embodiment. FIG. 2 is a configuration diagram of the LED drive circuit according to the first embodiment. FIG. 3 is a diagram showing operating waveforms of each part of the LED drive circuit. FIG. 4 is a diagram showing an enlarged waveform of a portion corresponding to a period when the LED current starts up. FIG. 5 is a configuration diagram of an LED drive circuit according to the second embodiment.

Next, embodiments will be described with reference to the drawings. In addition, in the following description, the same reference numerals are given to the same component in each embodiment, and repeated description is omitted.

[About the principle of measurement method]
Aqueous solutions such as hydrochloric acid, nitric acid, phosphoric acid, ammonium hydroxide, and hydrogen peroxide are used as cleaning and etching solutions for semiconductors, and a technique for measuring the concentration of an aqueous solution based on its absorbance is known. . Simply, the concentration is calculated by irradiating an aqueous solution with light, spectroscopy of the transmitted light at two or more wavelengths, and measuring the light intensity. More specifically, the absorbance of the aqueous solution is calculated from the intensity of the light emitted by the light source and the intensity of the light that is transmitted through the solution, and the concentration is calculated based on the calculated absorbance. Here, an LED is used as a light source used for such density measurement.

FIG. 1 is a diagram for explaining a measurement method in an embodiment. A measurement method in the embodiment will be described using FIG. 1.

For example, the concentration measuring device 1 includes a light source device 2, a flow cell 3, a spectroscopic device 4, and a measuring device 5.

The light source device 2 is a light source device capable of projecting light, and is realized using an LED 21, which is a semiconductor light emitting element, as a light source. For example, the LED 21 emits light containing a predetermined specific wavelength under the control of the measuring device 5. The light emitted by the LED 2 in this manner is transmitted to the spectrometer 4 via the flow cell 3 along the optical path OP.

Here, the LED 21 is a light source capable of emitting light in a wavelength band including a specific wavelength corresponding to each of the solutes whose concentrations are measured one or at the same time. That is, the LED 21 is a light source that can emit light of a specific wavelength corresponding to the measurement target with sufficient intensity (for example, illuminance) necessary for measuring the measurement target. For example, the LED 21 is a light source that has a center wavelength of about 1550 nanometers and a half width of about 100 nanometers. In this case, when the solute is ammonia and hydrogen peroxide, the LED 21 is optimally a light source that can output light with sufficient intensity in the wavelength band of at least 1,500 nanometers to 1,600 nanometers. However, other wavelength bands may be used. In this case, select a light source whose center wavelength matches the wavelength band used.

Note that the LED 21 only needs to be able to emit light with a wavelength width that includes the specific wavelength, which is a specific wavelength that can be separated and captured by the spectroscope 4 . In other words, the LED 21 defines a specific wavelength as a wavelength at which the absorbance (and thus concentration) of the measurement target can be measured with a preset target accuracy, and emits light of a wavelength matched to the specific wavelength.

The flow cell 3 is made of a material (eg, quartz glass, etc.) that is transparent to the light emitted by the light source device 2, and allows a sample such as an aqueous solution to flow therein. Note that the flow cell 3 may be realized by a test tube, a cell, or the like, or may be a pipe itself through which a chemical solution flows. Furthermore, the flow cell 3 does not need to be made of a transparent material as a whole, and the input portion into which the light emitted from the light source device 2 enters and the output portion through which the input light is emitted through the sample have a specific wavelength. It suffices if it is transparent.

The spectrometer 4 is a device that separates light of a specific wavelength from the light received through the flow cell 3 and measures the intensity of the separated light. This is realized by a light-receiving element that measures the intensity of the light separated by the meter. However, the spectroscope 4 may use a spectrometer using other spectroscopy methods, such as a grating type spectrometer.

For example, the spectroscopic device 4 includes a Fabry-Perot spectroscopy tunable filter 41 and a light receiving element 42 . The Fabry-Perot spectroscopy tunable filter 41 is a Fabry-Perot interferometer that can change the wavelength of light that can be transmitted, and has two semi-transparent mirrors arranged in parallel. For example, the Fabry-Perot spectroscopy tunable filter 41 includes an upper mirror UM that is a semi-transparent mirror placed on the light source device 2 side, and a lower mirror DM that is a semi-transparent mirror placed on the light receiving element 42 side. The Fabry-Perot spectroscopic tunable filter 41 controls the distance between the upper mirror UM and the lower mirror DM, so that the light received through the flow cell 3 can be adjusted according to the distance between the upper mirror UM and the lower mirror DM. Transmits light of a certain wavelength. For example, the Fabry-Perot spectroscopy tunable filter 41 transmits light of a specific wavelength corresponding to the solute from the light received through the sample under control from the measurement device 5 .

The light receiving element 42 is an element that measures the intensity of the received light upon receiving the light transmitted by the Fabry-Perot spectroscopy tunable filter 41, and is realized by, for example, a photoelectric element such as a photodiode. For example, upon receiving the transmitted light, the light receiving element 42 generates an electric signal indicating the intensity of the received light, and transmits the generated electric signal to the measuring device 5.

The measuring device 5 measures the concentration of solute contained in the sample based on the intensity of the light received by the spectroscopic device 4. The measuring device 5 includes a timing generating circuit 51, a generating section 52, and a concentration measuring section 53. The timing generation circuit 51 inputs a PWM signal to the LED drive circuit 100 to intermittently generate a constant current and drive the LED 21 intermittently.

The generation unit 52 generates correspondence information of the LED 21. For example, the generation unit 52 acquires, from the forward voltage measurement circuit 22, the value of the forward voltage when the LED current is applied to the LED 21 from the LED drive circuit 100. Furthermore, the generation unit 52 measures the intensity of light of a specific wavelength received by the light receiving element 42 when the LED current is applied to the LED 21 from the LED drive circuit 100 . Note that when generating the correspondence information, it is assumed that no sample is flowing through the flow cell 3.

Then, the generation unit 52 generates correspondence information indicating the relationship between the value of the forward voltage of the LED 21 when the current is applied and the intensity of light of a specific wavelength received by the light receiving element 42. For example, the generation unit 52 generates correspondence information that associates the value of the forward voltage with the intensity of light of a specific wavelength.

Note that if there are a plurality of specific wavelengths used for measurement, the generation unit 52 generates correspondence information for each specific wavelength. In such a case, for example, the LED drive circuit 100 may change the value of the current applied to the LED 21 each time the spectrometer 4 separates light of each specific wavelength and measures the intensity of the separated light. . Further, for example, the LED drive circuit 100 may cause a current that changes from a first current value to a second current value to flow through the LED 21 multiple times. In such a case, the spectroscopic device 4 separates light of a different specific wavelength each time a current is applied, and measures changes in the intensity of the separated light.

The concentration measurement unit 53 determines the sample size based on the correspondence information generated by the generation unit 52, the intensity of light of a specific wavelength measured by the light receiving element 42, and the forward voltage measured by the forward voltage measurement circuit 22. Measure the absorbance of the solute and estimate the concentration of the solute from the measured absorbance. For example, for each specific wavelength, the concentration measurement unit 53 specifies the light intensity associated with the forward voltage measured by the forward voltage measurement circuit 22 in the correspondence information as the intensity of the emitted light. Subsequently, the concentration measurement unit 53 calculates the absorbance of the sample from the intensity of the light of each specific wavelength received by the LED 42 and the intensity of the specified emitted light.

Then, the measuring device 5 calculates the absorbance at a specific wavelength, and measures the concentration of the solute from the calculated absorbance. In this way, the measuring device 5 generates in advance correspondence information indicating the relationship between the forward voltage of the LED 21 and the intensity of the light emitted from the LED 21 when current is applied. Furthermore, the measuring device 5 measures the concentration of the object to be measured based on the correspondence information measured in advance, the forward voltage of the LED 21, and the intensity of light of a specific wavelength received through the object to be measured.

[First embodiment]
[LED drive circuit]
Here, the concentration measuring device 1 estimates the emission intensity of the LED 21 from the value of the forward voltage Vf of the LED 21, and calculates the concentration from the estimated emission intensity and the received light intensity detected by the spectrometer 4. Therefore, in order to stabilize the forward voltage, the LED drive circuit 100 supplies the drive current of the LED 21 to the LED 21 with high accuracy and stability. FIG. 2 is a configuration diagram of the LED drive circuit according to the first embodiment. In FIG. 2, a path connected to the forward voltage measurement circuit 22 is omitted. Below, with reference to FIG. 2, details of the LED drive circuit 100 according to the first embodiment will be described. As shown in FIG. 2, the LED drive circuit 100 includes two circuit blocks, a constant current drive circuit 101 and a current correction circuit 102.

[Constant current drive circuit]
The constant current drive circuit 101 is a circuit that outputs a constant current Iout to the LED 21 by applying an input voltage Vin. The constant current drive circuit 101 includes a constant current control IC (Integrated Circuit) 111, a switching element Q1, an inductor L1, a free wheel diode D1, a smoothing capacitor C1, and an output current detection element R1. A general switching type LED driver IC can be used as the constant current control IC 111.

The constant current control IC 111 compares the output current feedback signal detected by the output current detection element R1 with its own reference voltage. Then, the constant current control IC 111 outputs the comparison result as a switching signal to the switching element Q1. The constant current control IC 111 controls the on/off time ratio of the switching element Q1 using a switching signal output to the switching element Q1.

Moreover, the constant current control IC 111 can also intermittently drive the LED 21 with a constant current according to the PWM signal by inputting the PWM signal from the timing generation circuit 51.

Switching element Q1 receives input of a switching signal. The switching element Q1 is turned on or off according to the switching signal, and supplies the input voltage Vin to the inductor L1 in the on state.

Freewheeling diode D1 is a diode for circulating output current when switching element Q1 is off.

Vin is applied to the inductor L1 when the switching element Q1 is on, and energy is accumulated in the inductor L1. Inductor L1 releases energy when switching element Q1 is off.

The smoothing capacitor C1 is a capacitor for smoothing the ripple component of the output current Iout.

The output current detection element R1 is a resistor for output current detection. The detection signal from the output current detection element R1 is compared with the internal reference voltage of the constant current control IC 111, and the time ratio between on and off of the switching element Q1 is controlled. Therefore, the output current detection element R1 is set to have an appropriate constant depending on the control target current value of the output current Iout.

Here, the ripple component of the output current can be reduced by increasing the capacitance of the smoothing capacitor C1. However, if the capacitance of the smoothing capacitor C1 is increased, the current rise time during intermittent driving becomes longer. Conversely, if the capacitance of the smoothing capacitor C1 is too small, there is a risk that the current value exceeds the allowable current value of the LED 21 and deteriorates the LED 21, and there is also a risk that uneven light emission intensity of the LED 21 will affect measurement on the light receiving side. For this reason, the smoothing capacitor C1 is set to the minimum necessary capacity that does not exceed the allowable current value of the LED 21, so that the rise time is as fast as possible. Thereby, it is possible to realize a faster rise response of the drive current from the light-off state to the light-on state. Note that suppression of light emission intensity unevenness due to ripple current is realized by a current correction circuit 102, which will be described later.

Here, the accuracy of the output current Iout of the constant current drive circuit 101 does not need to be very accurate, and output current drift due to temperature does not pose much of a problem. This is due to the operation of the current correction circuit 102, which will be described later. Therefore, as the constant current control IC 111, it is possible to use an inexpensive IC that is commonly used for lighting LEDs.

[Current correction circuit]
The current correction circuit 102 is a circuit for correcting a part of the output current Iout from the constant current drive circuit 101 to the LED 21 to an appropriate LED current Iled by bypassing the bypass current Ibyp. The current correction circuit 102 includes an LED current detection element R10, a differential amplifier circuit 121, a reference voltage Vref, an operational amplifier 123, a bypass current control FET (Field Effect Transistor) Q10, and a current limiting resistor R15. The differential amplifier circuit 121 includes resistors R11 to R14 and an operational amplifier 122. Further, the bypass current control FET Q10 and the current limiting resistor R15 form a bypass circuit 124.

The LED current detection element R10 is a resistance for detecting the LED current Iled, and is set to have an appropriate constant depending on the target LED current value.

The differential amplifier circuit 121 is a differential amplifier circuit that amplifies the voltage across the LED current detection element R10. In the differential amplifier circuit 121, if the resistors R11 to R14 are all set to the same constant, the amplification factor is 1 times. At this time, a part of the LED current Iout flows into the differential amplifier circuit 121, but by setting the resistors R11 to R14 to sufficiently large constants, the current flowing into the differential amplifier circuit 121 can be ignored.

The operational amplifier 123, the bypass current control FET Q10, and the current limiting resistor R15 are a circuit that controls the bypass current Ibyp according to the voltage difference between the output voltage from the operational amplifier 122, which is the LED current detection signal, and the reference voltage Vref. The current limiting resistor R15 is a resistor for preventing overcurrent when the bypass current control FET Q10 is short-circuited. The current limiting resistor R15 may not be provided if overcurrent is not taken into consideration.

When the LED current Iled is smaller than the target current value, the operational amplifier 123 controls the bypass current Ibyp to be reduced by throttling the current flowing through the bypass current control FET Q10. Conversely, when the LED current Iled is larger than the target current value, the operational amplifier 123 controls the bypass current Ibyp to increase by increasing the current flowing through the bypass current control FET Q10.

Further, a relational expression among the output current Iout of the constant current drive circuit, the bypass current Ibyp, and the LED current Iled can be expressed by the following equation (1).
Iled=Iout-Ibyp...(1)

That is, the LED drive circuit 100 sets the control target current value of the constant current drive circuit Iout to a value slightly higher than the target current value of the LED current Iled, and calculates this difference using the bypass current Ibyp of the current correction circuit 102. Let it be consumed. As a result, even if the output current Iout of the constant current drive circuit 101 contains a ripple component, it can be suppressed and it can be made more direct current.

Furthermore, the current accuracy of the LED current Iled is determined by the reference voltage Vref in the current correction circuit 102 and component accuracy. Therefore, the current accuracy of the output current Iout of the constant current drive circuit 101 does not need to be very accurate, and the temperature drift of the output current Iout does not pose much of a problem. From the above, it is possible to use an inexpensive IC that is commonly used for lighting LEDs as the constant current control IC 111.

Note that it is desirable that the frequency characteristics of the operational amplifiers 122 and 123 be sufficiently good with respect to the switching frequency of the constant current control IC 111, which is the switching IC of the constant current drive circuit 101. Specifically, for example, when the switching frequency of the constant current control IC 111 is 500 kHz, it is desirable that the unity gain frequency of the operational amplifiers 122 and 123 is 5 MHz or more.

Thereby, the ripple component of the output current Iout of the constant current drive circuit 101 can be sufficiently suppressed, and the LED current Iled can be made more direct current. Furthermore, since the current control speed of the current correction circuit 102 is sufficiently faster than the current control speed of the constant current drive circuit 101, problems such as mutual interference between controls do not occur. This makes it possible to achieve high accuracy and high stability of the drive current.

Furthermore, as described above, the control target current value of the output current Iout of the constant current drive circuit 101 is set to a value slightly higher than the target current value of the LED current Iled. It is desirable to set the value to the minimum necessary value. Thereby, the bypass current Ibyp of the current correction circuit 102 also becomes the required minimum value, and the heat generation of the bypass current control FET Q10 and the current limiting resistor R15 can also be suppressed to a minimum. This makes it possible to minimize the heat generated by the parts of the LED drive circuit.

[Explanation of operating waveforms]
FIG. 3 is a diagram showing operating waveforms of each part of the LED drive circuit. Further, FIG. 4 is a diagram showing an enlarged waveform of a portion corresponding to a period when the LED current is started up. FIG. 4 shows an enlarged waveform of the period T1 in FIG. Here, description will be made assuming that the target current value of the LED current Iled is 1000 mA.

In the graphs 201, 202, 201, and 211, the horizontal axis represents the passage of time, and the vertical axis represents the voltage value. Graphs 201 and 211 represent switching waveforms of the switching element Q1 by the constant current control IC 111. Vswon represents a voltage value at which switching element Q1 is turned on. Further, graphs 202 and 212 represent waveforms of PWM signals input from the timing generation circuit 51 of the measuring device 5. Vpwmon represents a voltage value when the PWM signal is on.

In both graphs 203 to 205 and 213 to 215, the horizontal axis represents the passage of time, and the vertical axis represents the current value. Further, graphs 203 and 213 represent the waveforms of the output current Iout of the constant current drive circuit 101, and include ripple components. Further, graphs 204 and 214 are bypass current waveforms generated by the current correction circuit 102. The scale of the vertical axes of graphs 204 and 214 was set to 110 mA, which is 1/10 of the output current Iout. Further, graphs 205 and 215 represent the waveforms of the LED current Iled after the correction, which is obtained by subtracting the bypass current Ibyp from the output current Iout. The scale of the vertical axes of graphs 205 and 215 is the same as Iout.

In the graphs 206 and 216, the horizontal axis represents the passage of time, and the vertical axis represents the magnitude of voltage. Further, graphs 206 and 216 are forward voltage waveforms of the LED 21.

When the PWM signals shown in graphs 202 and 212 are input, switching element Q1 repeats switching as shown in graphs 201 and 211. As a result, the constant current drive circuit 101 outputs an output current Iout as shown in graphs 203 and 213.

Here, since the smoothing capacitor C1 has the minimum necessary capacity, the output current Iout shown in the graphs 203 and 213 includes a ripple current. Further, the current value 221 in the graph 213 represents 1000 mA, which is the target current value of the LED current Iled. That is, as shown in graphs 203 and 213, the constant current drive circuit 101 controls the output current Iout at a control target current value that is slightly higher than the target current value of 1000 mA for the LED current Iled. For example, the constant current drive circuit 101 controls the control target current of the output current Iout to be approximately 1050 mA. As shown in graphs 204 and 214, the correction circuit 102 bypasses the output current Iout by passing a current exceeding 1000 mA as a bypass current Ibyp.

As a result, as shown in the graph 215, the large delay in the rise of the LED current due to the smoothing capacitor C1 is reduced, and the current value 222 in the graph 215 represents 1000 mA, which is the target current value of the LED current Iled. That is, as shown in graphs 205 and 215, the LED current Iled becomes the target current of 1000 mA, and the ripple component is also removed. Further, as shown in graphs 206 and 216, after the current rises, the forward voltage Vf of the LED 21 is stable, and the occurrence of uneven light emission can be suppressed. Furthermore, since the bypass current Ibyp is about 1/10 or less of the LED current Iled, the heat generation of the bypass current control FET Q10 can be significantly reduced compared to a conventional linear transistor.

In addition, in the embodiment, an example was shown in which the bypass current Ibyp was about 10%, but even if it is about 25%, a heat generation reduction effect can be obtained compared to the linear type. As described above, the light source device 2 according to the first embodiment can realize fast and stable forward voltage Vf and emission intensity, and can also be used as the concentration measuring device 1 to perform measurements with good accuracy and reproducibility. be.

[About the principle of processing to improve measurement accuracy using forward voltage]
Next, the principle of processing for improving measurement accuracy using forward voltage will be explained. As described above, the measuring device 5 calculates the absorbance of the sample using the intensity of the light of a specific wavelength out of the light emitted by the light source device 2 and the intensity of the light of the specific wavelength spectrally separated by the spectrometer 4. Then, estimate the concentration of the sample from the calculated absorbance. However, the light spectrum of the light emitted from the LED 21 changes depending on the temperature.

For example, the intensity of the light emitted by the LED 21 decreases as the temperature of the LED 21 increases. Moreover, in the light emitted by the LED 21, the wavelength with the highest intensity (the wavelength that becomes the peak) shifts to a longer wavelength side as the temperature of the LED 21 increases. In this way, the intensity of the light emitted by the LED 21 changes with the temperature of the light emitting element depending on the environmental temperature, so there is a risk that the accuracy of estimating the concentration will decrease.

In order to compensate for changes in the intensity of light emitted from the LED 21 due to temperature changes, when changing the current value flowing through the LED 21, a larger current must be passed as the ambient temperature rises. This shortens the life of the light emitting element. Furthermore, since the correlation between the temperature of the LED 21 itself and its surroundings (hereinafter collectively referred to as "ambient temperature") and the intensity of light emitted from the light emitting element differs for each LED 21, the correlation is measured in advance for each LED 21. There is a need. However, changing the ambient temperature takes a lot of time and effort. Furthermore, depending on the installation location of the measuring device 5, it may be difficult to change the ambient temperature.

On the other hand, the LED 21 has a characteristic that the forward voltage (Vf) when a constant current is passed varies depending on the ambient temperature. In other words, the LED 21 has a characteristic that when a current (forward current) is passed from the anode to the cathode, the voltage decreases by the forward voltage, and such forward voltage changes depending on the ambient temperature. Further, as described above, there is a correlation between the intensity of light emitted by the LED 21 and the ambient temperature. Therefore, there is a correlation between the intensity of light emitted by the LED 21 and the forward voltage of the light emitting element.

Therefore, prior to concentration measurement, the measuring device 5 measures the forward voltage when a current is applied to the LED 21 of the light source device 2 installed in the concentration measuring device 1 while changing the current value. Then, the measuring device 5 measures the intensity of light of a specific wavelength emitted by the light emitting element when a current with a predetermined current value is applied, and the intensity of light with a specific wavelength emitted by the light emitting element when a current with a predetermined current value is applied. Correspondence information indicating the relationship with the forward voltage is generated.

Furthermore, the measuring device 5 turns on the LED 21 included in the light source device 2 to separate light of a specific wavelength from the light received through the measurement target, and measures the forward voltage of the light emitting element. Then, the measuring device 5 measures the concentration of the measurement target based on the correspondence information generated in advance, the measured forward voltage, and the intensity of light of a specific wavelength. For example, the measuring device 5 estimates the intensity of light corresponding to the measured forward voltage from the correspondence information as the intensity of the light emitted by the LED 21. Then, the measuring device 5 measures the concentration of the measurement target based on the estimated light intensity and the intensity of the spectroscopic light of the specific wavelength. For example, the measuring device 5 estimates the intensity of the light of a specific wavelength emitted by the LED 21, and calculates the absorbance of the measurement target based on the estimated intensity of the light and the intensity of the spectroscopic light of the specific wavelength. The measuring device 5 then measures the concentration of the measurement target based on the calculated absorbance.

Hereinafter, referring back to FIG. 1, the principle of a measurement method for estimating the concentration of a sample using the relationship between the forward voltage and the intensity of light emitted by a light emitting element will be explained. For example, as shown in FIG. 1, the light source device 2 includes an LED 21, a forward voltage measurement circuit 22, and an LED drive circuit 100.

The LED 21 is a semiconductor element that emits light when supplied with current. For example, the LED 21 emits light having a specific wavelength that is easily absorbed by the measurement target. Note that in the following description, the light emitted from the LED 21 may be referred to as emitted light.

Here, for example, when the current flowing through the LED 21 is constant, there is a substantially linear correlation between the ambient temperature of the light emitting element 21 and the forward voltage Vf, in which the value of the forward voltage Vf decreases as the ambient temperature increases. exist. As a result, when the current flowing through the LED 21 is constant, there is a nearly linear correlation between the intensity of the emitted light from the LED 21 and the forward voltage Vf, in which the intensity of the emitted light increases as the value of the forward voltage Vf increases. exist.

In this way, when estimating the intensity of light of a specific wavelength emitted by the LED 21 using the correlation between the forward voltage Vf and the intensity of the emitted light, it is possible to estimate the intensity of the light of the specific wavelength emitted by the LED 21 without obtaining the correlation related to the temperature of the LED 21 in advance. It is considered that the intensity of the emitted light can be estimated. In other words, if the correlation between the forward voltage Vf and the intensity of the emitted light can be obtained in advance, it is possible to estimate the intensity of the emitted light from the LED 21 during concentration measurement without changing the ambient temperature of the LED 21. becomes.

Here, it is known that when the value of the current flowing through the LED 21 is changed, the forward voltage Vf of the LED 21 changes. Therefore, in the concentration measuring device 1, the correlation between the forward voltage Vf of the LED 21 and the intensity of the emitted light is acquired in advance as correspondence information by changing the value of the current flowing through the LED 21. Then, in the concentration measuring device 1, the intensity of the emitted light is estimated from the forward voltage Vf of the LED 21 at the time of concentration measurement using the correspondence information, and the estimated intensity of the emitted light and the intensity of the light received via the measurement target are calculated. From this, the concentration of the object to be measured is measured.

Note that the correspondence information may be parameters measured for each LED 21 or may be commonly used by each light source device 2, but since the characteristics of the LED 21 vary depending on the product. , is preferably determined for each individual.

Moreover, such temperature characteristics of the LED 21 change not only due to the ambient temperature but also due to self-heating of the LED 21 itself. In addition, although LED21 has a longer lifespan than a halogen lamp, the longer it is lit or the larger the current is passed through it, the more it deteriorates and the conversion efficiency from electricity to light decreases. When doing so, the light emitted becomes dark. In order to avoid such problems, the concentration measuring device 1 measures the forward voltage value of the LED 21 using a weak current, and measures the temperature of the LED 21 from the measured forward voltage value. That is, the concentration measuring device 1 measures the temperature of the LED 21 (that is, the diode itself) using the same principle as a so-called diode thermometer. Note that the concentration measuring device 1 may perform processing such as gain calibration in addition to the processing described above.

The LED drive circuit 100 applies a voltage to the LED 21 to turn it on. Furthermore, the LED drive circuit 100 generates a plurality of currents each having a different current value, which are used to measure the correlation between the forward voltage in the LED 21 and the intensity of light emitted from the LED 21. Furthermore, the LED drive circuit 100 generates a current for measuring the value of the forward voltage at the LED 21 during concentration measurement.

The forward voltage measurement circuit 22 is a circuit that measures the forward voltage of the LED 21. For example, the forward voltage measurement circuit 22 measures the forward voltage of the LED 21 when the current generated by the LED drive circuit 100 flows through the LED 21 when generating the correspondence information. That is, the forward voltage measurement circuit 22 measures, with a predetermined resolution, the change in the forward voltage of the LED 21 when a current whose current value is changed flows. The forward voltage measuring circuit 22 then outputs each measured forward voltage value to the measuring device 5.

Further, the forward voltage measurement circuit 22 measures the forward voltage of the light emitting element 21 using the current generated by the LED drive circuit 100 during concentration measurement. For example, the forward voltage measuring circuit 22 measures the voltage of the light emitting element 21 as a forward voltage when a current flows, and outputs the value of the measured forward voltage to the measuring device 5.

Note that the value of the forward voltage output by the forward voltage measurement circuit 22 is used to predict the intensity of the emitted light. Therefore, the accuracy of the forward voltage output by the forward voltage measurement circuit 22 contributes to the accuracy of the measured concentration. Therefore, the forward voltage measurement circuit 22 measures the forward voltage with an accuracy that takes into consideration the accuracy when measuring the concentration.

For example, in order to keep the concentration estimation accuracy within ±0.1 percent, the forward voltage measurement accuracy needs to be suppressed to ±20 microvolts or less. To maintain such measurement accuracy, for example, it is necessary to measure a forward voltage of 2 volts with an effective resolution of 100,000 or more. Therefore, the forward voltage measurement circuit 22 outputs the voltage value of the measured forward voltage using, for example, an AD (Analog-to-Digital) converter having an effective resolution of 17 bits or more. To give a more specific example, the forward voltage measurement circuit 22 uses a ΔΣ type AD converter that requires a long conversion time. Note that the above-mentioned example is just an example, and for example, a forward voltage of 1 volt or less may be measured. In this way, the effective resolution changes depending on how much forward voltage is measured depending on the accuracy, and forward voltage can be measured using a circuit that realizes such effective resolution.

On the other hand, the measuring device 5 includes a timing generating circuit 51, a generating section 52, and a concentration measuring section 53. The timing generation circuit 51 outputs a PWM signal to the LED drive circuit 100. As a result, light is emitted from the LED 21, and the forward voltage measuring circuit 22 measures the value of the forward voltage Vf of the LED 21 when current flows. Further, the emitted light is transmitted to the spectroscopic device 4 via the flow cell 3, and the spectroscopic device 4 spectrally separates light of a specific wavelength.

The generation unit 52 generates correspondence information of the LED 21. For example, the generation unit 52 acquires, from the forward voltage measuring circuit 22, the value of each forward voltage when currents with different current values are passed through the LED element 21 from the LED drive circuit 100. The generation unit 52 also measures the intensity of light of a specific wavelength received by the light receiving element 42 when currents having different voltage values are applied to the LED 21 from the variable current generation circuit 22. Note that when generating the correspondence information, no sample is flowing through the flow cell 3.

Then, the generation unit 52 generates correspondence information indicating the relationship between the value of the forward voltage of the LED 21 and the intensity of light of a specific wavelength received by the light receiving element 42 when currents having different voltage values are applied. generate. For example, the generation unit 52 generates correspondence information that associates the value of the forward voltage with the intensity of light of a specific wavelength.

Note that if there are a plurality of specific wavelengths used for measurement, the generation unit 52 generates correspondence information for each specific wavelength. In such a case, for example, the LED drive circuit 100 may change the value of the current applied to the light emitting element each time the spectrometer 4 separates light of each specific wavelength and measures the intensity of the separated light. good. Further, for example, the LED drive circuit 100 may cause a variable current that changes from a first current value to a second current value to flow through the LED 21 multiple times. In such a case, the spectrometer 4 separates light of a different specific wavelength each time a variable current is applied, and measures changes in the intensity of the separated light.

The concentration measurement unit 53 determines the sample size based on the correspondence information generated by the generation unit 52, the intensity of light of a specific wavelength measured by the light receiving element 42, and the forward voltage measured by the forward voltage measurement circuit 22. Measure the absorbance of the solute and estimate the concentration of the solute from the measured absorbance. For example, for each specific wavelength, the concentration measurement unit 53 specifies the light intensity associated with the forward voltage measured by the forward voltage measurement circuit 22 in the correspondence information as the intensity of the emitted light. Subsequently, the concentration measurement unit 53 calculates the absorbance of the sample from the intensity of the light of each specific wavelength received by the light receiving element 42 and the intensity of the specified emitted light.

Then, the measuring device 5 calculates the absorbance at a specific wavelength, and measures the concentration of the solute from the calculated absorbance. For example, the measuring device 5 calculates the absorbance at each specific wavelength, and calculates the concentration of the solute contained in the sample from the calculated absorbance.

In this way, the measuring device 5 generates in advance correspondence information indicating the relationship between the forward voltage of the LED 21 and the intensity of the light emitted from the light emitting element 21. Furthermore, the measuring device 5 measures the concentration of the object to be measured based on the correspondence information measured in advance, the forward voltage of the LED 21, and the intensity of light of a specific wavelength received through the object to be measured. Therefore, the measuring device 5 can easily and accurately measure the concentration of the measurement target without changing the ambient temperature of the concentration measuring device 1.

[Effects in the first embodiment]
As explained above, in the LED drive circuit 100 according to the present embodiment, the control target value of the LED current Iled is exceeded among the output current Iout smoothed by the smoothing capacitor C1 output from the constant current drive circuit 100. The current corresponding to the amount of current is caused to flow through the bypass path as bypass current Ibyp. Further, the capacitance of the smoothing capacitor C1 can be set to the minimum necessary capacitance.

This makes it possible to suppress the delay in the rise of the LED current Iled. Furthermore, the LED current Iled can be set as the control target value. Furthermore, the ripple component of the LED current Iled can also be removed. After the current rises, a stable forward voltage can be supplied to the LED 21, and uneven light emission can be suppressed. Furthermore, the bypass current Ibyp can be suppressed to be lower than the LED current, and the heat generation of the bypass current control FETQ10, which is a current control transistor, can be significantly reduced. Therefore, it is possible to achieve higher accuracy and higher stability of the drive current, faster rise response of the drive current from the off state to the on state, and minimization of component heat generation in the LED drive circuit. .

[Second embodiment]
FIG. 5 is a configuration diagram of an LED drive circuit according to the second embodiment. In FIG. 5, a path connected to the forward voltage measurement circuit 22 is omitted. In the following description, descriptions of operations of the same parts as in the first embodiment will be omitted.

[Differences from the first embodiment]
The LED drive circuit 100 according to this embodiment uses a high-side current detection type IC as the constant current control IC 111. The output current detection resistor R1 is arranged on the high voltage side, that is, inside the constant current drive circuit 101.

The constant current control IC 111 compares the detection signal from the output current detection element R1 arranged in the constant current drive circuit 101 with an internal reference voltage, and controls the time ratio between on and off of the switching element Q1. Therefore, the output current detection element R1 is set to have an appropriate constant depending on the control target current value of the output current Iout.

By moving the output current detection resistor R1 to the high voltage side, there is no need to return the current path to the constant current control IC 111 for detecting the output current. Therefore, the other end of the LED current detection resistor R10 in the current correction circuit 102 is directly connected to the circuit GND (Ground) without going through the output current detection resistor R1 or the like.

Thereby, the non-inverting input terminal of the operational amplifier 123 that controls the bypass current Ibyp can be directly connected to the LED current detection resistor R10. Therefore, it is not necessary to provide the differential amplifier circuit 121 in the current correction circuit 102 of the LED drive circuit 100 according to this embodiment. The operational amplifier 123 receives an input of the LED current Iled flowing through the LED 21, compares the LED current Iled with a reference voltage Vref, and controls the operational amplifier 123 so that the difference between the LED current Iled and the output voltage Iout flows as a bypass current Ibyp. The comparison result is used to control the bypass current control FET Q10.

[Effects of the second embodiment]
As explained above, since the LED drive circuit 100 according to the present embodiment does not need to use the differential amplifier circuit 121, it is possible to eliminate the influence of variations in the constants of these components and temperature drift, and to improve the performance. Highly accurate current control becomes possible.

[Other embodiments]
In the first and second embodiments, an example was shown in which an LED was used as the semiconductor light emitting element, but the present invention is not limited to this, and for example, an LD (Laser Diode) may be used. Moreover, although the case where one semiconductor light emitting element is used has been described, a plurality of semiconductor light emitting elements may be used.

Further, although an example is shown in which a step-down type circuit is used as the constant current control IC 111 of the constant current control circuit 101, the constant current control IC 111 may be a step-up type circuit or a buck-boost type circuit. .

Since the operating voltage for one LED 21 is about 2V, it is preferable to use a step-down type circuit for the constant current control IC 111. On the other hand, if there are a plurality of LEDs 21, a step-up type circuit may be used for the constant current control IC 111, or a step-up/step-down type circuit may be used in consideration of battery power consumption.

Further, in the above embodiment, an example of a diode rectification type circuit using the freewheeling diode D1 has been shown, but this portion may be replaced with a switching element such as an FET to adopt a synchronous rectification type. This further improves the output efficiency of the output current Iout, making it possible to provide a constant current drive circuit with lower heat generation.

[About the sample]
Further, the concentration measuring device 1 may use not only an aqueous solution in which various solutes are dissolved, but also a solution such as an organic solvent in which various solutes are dissolved, as a sample. Further, in such a case, the concentration measuring device 1 may employ the absorbance calculated from the ratio of the absorbance of the solvent and the absorbance of the solute. Further, the concentration measuring device 1 may use not only a solution but also various gases such as a mixed gas as a sample and measure the concentration of any gas contained in the sample. Further, the concentration measuring device 1 may measure the concentration of a substance that is a solvent instead of a solute.

[About measurement]
In the example described above, the concentration measuring device 1 estimated the concentration of solutes and gas concentrations dissolved in various solutions. However, embodiments are not limited thereto. For example, the concentration measuring device 1 may determine whether a predetermined solute or gas is contained in the sample using the above-described configuration. For example, if the absorbance at a certain wavelength exceeds a predetermined threshold, the concentration measuring device 1 may determine that the sample contains a solute or gas corresponding to that wavelength. That is, the measurement process executed by the concentration measuring device 1 is a concept that includes a process of detecting an arbitrary detection target such as a solute or a gas.

[About device configuration]
Note that the device configuration of the concentration measuring device 1 is not limited to the above description. For example, the light source device 2, the spectroscopic device 4, and the measuring device 5 may constitute an integrated measuring device.

Although an example of the embodiment has been described above, these are merely examples, and the present embodiment is not limited to the above description. In addition to the aspects described in the disclosure section, the configuration and details of the embodiments can be implemented in other forms with various modifications and improvements based on the knowledge of those skilled in the art. Moreover, each embodiment can be implemented in any combination within the range not contradictory.

1 Concentration measuring device 2 Light source device 3 Flow cell 4 Spectroscopic device 5 Measuring device 21 LED
22 Forward voltage measurement circuit 41 Tunable filter for Fabry-Perot spectroscopy 42 Light receiving element 51 Timing generation circuit 52 Generation section 53 Concentration measurement section 100 LED drive circuit 101 Constant current drive circuit 102 Current correction circuit 111 Constant current control IC
121 Differential amplifier circuit 122, 123 Operational amplifier 124 Bypass circuit Q1 Switching element Q10 FET for bypass current control
R1 Output current detection element R10 LED current detection resistor R11 to R14 Resistor R15 Current limiting resistor C1 Smoothing capacitor L1 Inductor

Claims (10)

A semiconductor light emitting device,
a constant current drive circuit that supplies a constant current toward the semiconductor light emitting device;
A part of the constant current supplied from the constant current drive circuit is sent to the bypass circuit as a bypass current, the remaining current is supplied to the semiconductor light emitting device as a semiconductor light emitting device current, and the semiconductor light emitting device current is set to a predetermined target current. and a current correction circuit that corrects to reduce the bypass current when the semiconductor light emitting element current is smaller than the predetermined target current value, and to increase the bypass current when the semiconductor light emitting element current is larger than the predetermined target current value. Light source device. The light source device according to claim 1, wherein the constant current drive circuit includes a switching element and a switching control circuit that controls on/off of the switching element, and supplies the constant current according to the on/off operation of the switching element. 3. The light source device according to claim 2, wherein the current correction circuit executes the bypass current correction operation faster than the on/off operation of the switching element of the switching control circuit. 4. The light source device according to claim 2, wherein the constant current drive circuit controls the switching element based on an externally applied timing signal to intermittently supply the constant current. Any one of claims 2 to 4, wherein the switching control circuit controls an on-off interval of the switching element based on a detected value of the constant current output from the constant current drive circuit. The light source device described in . The current correction circuit calculates the magnitude of the bypass current based on a forward voltage of the semiconductor light emitting element detected by a semiconductor light emitting element current detection resistor arranged on the output side of the semiconductor light emitting element and a reference voltage. The light source device according to any one of claims 1 to 5, characterized in that the light source device is controlled. The current correction circuit includes a differential amplification circuit, and compares the voltage value of the voltage output from the differential amplification circuit with the reference voltage using the forward voltage as input, and determines the magnitude of the bypass current. The light source device according to claim 6, characterized in that the light source device is controlled. The constant current drive circuit includes a high-side current detection circuit that detects the current value of the constant current between an input terminal of an input voltage and the semiconductor light emitting element, and the current value of the constant current detected by the high-side current detection circuit. controlling the constant current based on the current value,
7. The light source device according to claim 6, wherein the current correction circuit controls the magnitude of the bypass current based on a difference between a voltage value of the forward voltage and a voltage value of the reference voltage. 9. The light source device according to claim 1, wherein the current correction circuit sets the bypass current to 25% or less of the constant current. a semiconductor light emitting element capable of emitting a specific wavelength corresponding to the concentration measurement target;
a constant current drive circuit that supplies a constant current toward the semiconductor light emitting device;
A part of the constant current supplied from the constant current drive circuit is sent to the bypass circuit as a bypass current, the remaining current is supplied to the semiconductor light emitting device as a semiconductor light emitting device current, and the semiconductor light emitting device current is set to a predetermined target current. a current correction circuit that corrects to reduce the bypass current when the semiconductor light emitting element current is smaller than the predetermined target current value, and to increase the bypass current when the semiconductor light emitting element current is larger than the predetermined target current value; ,
a spectroscopy section that spectrally spectra the light received through the measurement target;
a measurement unit that measures the forward voltage of the semiconductor light emitting device;
Correspondence information indicating a relationship between the forward voltage of the semiconductor light emitting element obtained in advance and the emission intensity of the light of the specific wavelength emitted by the semiconductor light emitting element, and the forward voltage measured by the measuring unit; and a concentration measuring section that measures the concentration of the object to be measured based on the intensity of the light of the specific wavelength that has been spectrally separated by the spectroscopic section.

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