Semiconductor laser pulse driving circuit based on super capacitor

Abstract

The invention discloses a semiconductor laser pulse driving circuit based on a super capacitor, and belongs to the technical field of electronic circuits. The circuit comprises at least one super capacitor which supplies power to the vertical cavity surface emitting laser; the current control and sampling circuit is used for controlling the current circulation and closing of the vertical cavity surface emitting laser and sampling and monitoring the discharge current of the super capacitor through the current control and sampling circuit, and the current control and sampling circuit is connected with the vertical cavity surface emitting laser and the super capacitor in series to form a laser discharge loop; and the charging circuit is used for dynamically adjusting the voltage output by the charging circuit according to the sampling result of the current sampling point so as to adjust the voltage value of the super capacitor. The super capacitor is used for supplying power to the vertical cavity surface emitting laser, millisecond-level long-pulse and large-current driving current output can be achieved, meanwhile, the average power requirement of a circuit front-end power source is lowered by means of duty ratio limitation of practical application, and then cost is lowered.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and particularly relates to a pulsed drive circuit for a semiconductor laser based on a super capacitor. Background Art

[0002] High-power VCSEL (Vertical-Cavity Surface-Emitting Laser) chips, as a highly efficient and uniform-intensity semiconductor laser light source, are widely used in fields such as laser medical beauty, solid-state laser pumping, industrial heating, and infrared lighting. Among them, in fields such as laser medical beauty, its operating state is restricted to a millisecond-level long-pulse state with a pulse width of 5 - 200 ms, a frequency of 1 - 10 Hz, and a duty cycle ≤ 40%. For example, applications such as laser hair removal require high-power VCSEL chips to operate in the above state.

[0003] In order to ensure the stability of the optical power, semiconductor lasers generally use a constant-current power supply for driving. There are mainly two implementation methods for traditional semiconductor laser constant-current drive sources. One is to maintain the stability of the optical power directly through the principle of a constant-current switching power supply, and the other is to maintain the stability of the optical power based on MOSFET constant-current modulation of a constant-voltage source. For the first method, it samples and feeds back the current output by the power supply, and adjusts the magnitude of the output current through a high-frequency switching circuit according to the feedback result, thereby achieving constant-current output; for the second method, it connects a high-power MOSFET in series in the load circuit of the semiconductor laser and controls the MOSFET to operate in the constant-current region, thereby realizing the constant-current power supply drive of the semiconductor laser.

[0004] In the prior art, high-power VCSEL chips need to operate in a long-pulse state with a pulse width of 5 - 200 ms. For the existing design methods of maintaining a constant-current source, it is necessary to ensure that the average power of the power supply is not lower than the peak power of the semiconductor laser load during operation. Therefore, for long-pulse medical applications with a low duty cycle, the design of its drive power supply has a large power redundancy, which also brings unnecessary costs. Summary of the Invention

[0005] Aiming at the problems of high required power and high duty cycle existing in the prior art, the present application mainly provides a pulsed drive circuit for a semiconductor laser based on a super capacitor.

[0006] To achieve the above object, the technical solution adopted by this application is as follows: A semiconductor laser pulse driving circuit based on a super capacitor, which includes: at least one super capacitor that powers a vertical cavity surface emitting laser; a current control and sampling circuit that controls the current flow and cut-off of the vertical cavity surface emitting laser by controlling its switch state, and at the same time, a current sampling point is provided thereon, and the discharge current of the super capacitor is sampled and monitored through the current sampling point. The current control and sampling circuit, the vertical cavity surface emitting laser, and at least one super capacitor are connected in series to form a laser discharge loop; a charging circuit that is connected to the positive and negative electrodes of at least one super capacitor and charges at least one super capacitor. Among them, the charging circuit dynamically adjusts the voltage it outputs according to the sampling result of the current sampling point of the laser discharge loop, and further adjusts the voltage value of the super capacitor, so that the super capacitor provides a constant current for the vertical cavity surface emitting laser.

[0007] Optionally, the charging circuit charges at least one super capacitor to a set voltage, and adjusts the voltage output by the charging circuit to at least one super capacitor according to the sampling result of the capacitor voltage sampling point and the driving current of the vertical cavity surface emitting laser, so as to achieve a target driving current at the vertical cavity surface emitting laser. Among them, the capacitor voltage sampling point is set on the outermost side of the super capacitor.

[0008] Optionally, the device selection method for at least one super capacitor is as follows: Calculate the loop current value of the laser discharge loop according to the open-circuit voltage of the preset super capacitor, the loop internal resistance of the laser discharge loop, the bandgap voltage of the vertical cavity surface emitting laser, and the preset capacity of the super capacitor; and determine the device type of at least one super capacitor according to the device selection standard and the loop current value.

[0009] Optionally, the current control and sampling circuit is composed of a MOSFET and a sampling resistor. Among them, the MOSFET is connected in series with the vertical cavity surface emitting laser, and the MOSFET controls the current flow and cut-off of the vertical cavity surface emitting laser by adjusting its switch state; the sampling resistor is connected in series with the MOSFET, and the other end of it is connected to an operational amplifier for voltage signal amplification and serves as a current sampling point.

[0010] Optionally, the current sampling device of the current control and sampling circuit adopts a Hall current sensor. At this time, the current sampling circuit is located at any position in the laser discharge loop.

[0011] Optionally, according to the equivalence relationship between the transient reduced charge of at least one super capacitor and the transient increased charge of the loop, and the loop current value, calculate the transient current value of the loop at any moment.

[0012] Optionally, according to a predetermined laser optical power fluctuation value and the transient current value at any moment, determine whether the current value fluctuation in the designed circuit meets the predetermined laser optical power fluctuation value, and adjust the capacitance parameter of at least one supercapacitor according to the determination result. Moreover, the larger the capacitance of the supercapacitor, the smaller the laser optical power fluctuation value.

[0013] Optionally, there is a linear relationship between the laser optical power fluctuation value of the vertical cavity surface emitting laser and its current.

[0014] Optionally, when the semiconductor laser pulse driving circuit based on supercapacitors includes multiple supercapacitors, the multiple supercapacitors are connected in series.

[0015] Optionally, when N supercapacitors are connected in series, a balancing and protection circuit is provided at both ends of the electrodes of each supercapacitor, where N is not less than 2.

[0016] Optionally, both ends of at least one supercapacitor are connected to a discharging circuit, which is used for discharging the supercapacitor when the capacitance voltage needs to be lowered or when the entire system is shut down. The discharging circuit generally consists of a high-power resistor and a switching device (such as a MOSFET), etc.

[0017] The beneficial effects that can be achieved by the technical solution of this application are as follows: Using supercapacitors to supply power to the vertical cavity surface emitting laser realizes the output of driving current with long pulses and large currents at the millisecond level. And by using the duty cycle limit in actual applications, the average power of the front-end power supply of the circuit is reduced, thereby greatly reducing the cost, and it can meet the requirements of medical devices for laser energy or peak power fluctuations. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 is a schematic diagram of the equivalent circuit of a high-power vertical cavity surface emitting laser chip in the prior art; Figure 2 is a comparison diagram of the linear relationships between VCSEL and EEL; Figure 3 is a schematic diagram of the relationship between the optical power and current of a vertical cavity surface emitting laser within the normal junction temperature; Figure 4 is a schematic diagram of a specific embodiment of the semiconductor laser pulse driving circuit based on supercapacitors in this application; Figure 5 It is a schematic diagram of module connection of a semiconductor laser pulse driving circuit based on a super capacitor according to the present application; Figure 6 It is a schematic circuit diagram of a semiconductor laser pulse driving circuit based on a super capacitor according to the present application.

[0020] Through the above-mentioned drawings, specific embodiments of the present application have been shown, and there will be more detailed descriptions hereinafter. These drawings and textual descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. Specific Embodiments

[0021] The following elaborates on the preferred embodiments of the present application in conjunction with the drawings, so that the advantages and features of the present application can be more easily understood by those skilled in the art, thereby making the scope of protection of the present application more clearly defined.

[0022] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, the elements defined by the statement "comprising..." do not exclude the presence of additional identical elements in the process, method, article or device comprising the said elements.

[0023] The basic principle of a high-power semiconductor laser is to grow a reflective DBR (Distributed Bragg Reflector), a quantum well active region, and an output DBR in sequence in a direction perpendicular to the substrate by means of epitaxial growth, thereby forming a wavelength-scale resonant cavity, and thus realizing a semiconductor laser for laser gain and output. Among them, the quantum well active region uses the recombination of electrons and holes in the P region and the N region to achieve photon radiation and complete electro-optical conversion. The light-emitting die of multiple vertical cavity surface emitting lasers often forms a high-power VCSEL (Vertical Cavity Surface Emitting Laser) light-emitting array, that is, a high-power vertical cavity surface emitting laser chip, through periodic uniform arrangement.

[0024] Figure 1 It is a schematic diagram of the equivalent circuit of a high-power vertical cavity surface emitting laser chip in the prior art. Without considering parasitic capacitance and high-frequency modulation, the equivalent circuit of the high-power vertical cavity surface emitting laser chip is as Figure 1As shown, the main impedance of the light-emitting active region of the high-power vertical-cavity surface-emitting laser chip comes from the series resistance of the p-DBR and n-DBR respectively. In addition, there are other minor series impedances such as the ohmic contacts of the positive and negative electrodes of the chip and the substrate. The voltage drop in the active region is related to the energy bandgap (Eg) of different active regions. That is, Eg = 1.24 / λ, where λ is the laser wavelength (unit: um), and E g The unit is eV.

[0025] If the total series impedance of the p-DBR and n-DBR and other series impedances is set as R, the driving current is set as I, and the bandgap voltage of the active region is g, then the voltage across the high-power vertical-cavity surface-emitting laser chip is: V = I R + g = I R + Eg / e. For example, when the required laser wavelength is 810 nm (i.e., λ = 0.81 um), the corresponding energy bandgap of the high-power vertical-cavity surface-emitting laser chip is Eg = 1.24 / 0.81 = 1.53 eV, then the theoretical voltage drop in its active region is g = Eg / e = 1.53 V.

[0026] In fact, through the regression analysis of the measured VCSEL voltage-current experimental data by experimental methods, a better linear relationship can be obtained. Figure 2 is a comparison diagram of the linear relationships of VCSEL and EEL. As Figure 2 shown, the slope coefficient of the VCSEL is 0.0082, that is, the equivalent series resistance R (unit: milliohm) of the VCSEL is 0.0082, and 1.5912 is the approximate value of the voltage drop in the active region (unit: V). It can be seen that due to the existence of the relatively large and stable internal resistance of the p-DBR and n-DBR, the voltage and current of the VCSEL have a better linear relationship. In addition, since the VCSEL is not limited by the optical damage threshold, it can withstand instantaneous surges and overshoots. The above factors make it possible to drive the VCSEL with a constant current. For the traditional edge-emitting semiconductor laser (EEL), since its equivalent internal resistance is mainly composed of the ohmic contact and the substrate internal resistance, the resistance value is small, and the resistance value of the ohmic contact is not very stable due to the influence of the manufacturing process. Therefore, the linearity of the regression curve is inferior to that of the VCSEL. Slight voltage fluctuations may lead to large current fluctuations, and the device damage threshold is low and cannot withstand instantaneous current overshoots and surges. Therefore, a strict constant-current power supply must be used for driving.

[0027] Figure 3 is a schematic diagram of the relationship between the optical power and current of the vertical-cavity surface-emitting laser within the normal junction temperature. As Figure 3As shown, within the normal junction temperature and above the emission threshold, the injection current received by the vertical-cavity surface-emitting laser (VCSEL) has a linear relationship with the number of its radiated photons. This linear relationship is often expressed by the slope efficiency (abbreviated as SE), which generally ranges from 0.8 to 1.2 W / A, that is, under normal circumstances, the output optical power corresponding to each ampere of current is 0.8 - 1.2 W / A. Based on the above characteristics of the VCSEL, in practical applications, in order to ensure the stability of the optical power, the VCSEL generally uses a constant-current power supply for driving.

[0028] Therefore, this application proposes a semiconductor laser pulse driving circuit based on a supercapacitor, which further ensures the stability of the laser emitted by the VCSEL by ensuring the stability of the current received by the VCSEL.

[0029] Next, specific embodiments will be used to elaborate in detail on the technical solution of this application and how the technical solution of this application solves the above technical problems. The specific embodiments described below can be combined with each other to form new embodiments. For the same or similar ideas or processes described in one embodiment, they may not be repeated in some other embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0030] Figure 4 An embodiment of a semiconductor laser pulse driving circuit based on a supercapacitor of this application is shown.

[0031] Figure 4 The shown semiconductor laser pulse driving circuit based on a supercapacitor includes: at least one supercapacitor 401, which supplies power to the VCSEL; A current control and sampling circuit 402 controls the current flow and shutdown of the VCSEL by controlling its switch state. At the same time, a current sampling point is provided thereon, and the discharge current of the supercapacitor is sampled and monitored through the current sampling point. The current control and sampling circuit is connected in series with the VCSEL and at least one supercapacitor to form a laser discharge loop; A charging circuit 403 is connected to the positive and negative electrodes of at least one supercapacitor and charges at least one supercapacitor. Among them, the charging circuit dynamically adjusts the voltage it outputs according to the sampling result of the current sampling point, and then adjusts the voltage value of the supercapacitor to enable the supercapacitor to provide a constant current for the VCSEL.

[0032] In this specific embodiment, a supercapacitor is used to power a vertical-cavity surface-emitting laser (VCSEL), enabling the output of driving currents with long pulses in the millisecond level and large currents. By using the duty cycle limitation in practical applications, the average power of the front-end power supply of the circuit is reduced, thereby reducing costs and meeting the requirements of medical devices for laser energy or peak power fluctuations.

[0033] Specifically, for the driving of a vertical-cavity surface-emitting laser (VCSEL), the most important thing is to control the magnitude of its current. Therefore, in this application, the current of the vertical-cavity surface-emitting laser can be further controlled by controlling the voltage across the supercapacitor, and by determining the loop current of the laser discharge loop, the magnitude of the voltage output by the supercapacitor can be determined. In order to ensure the accuracy of the voltage released by the supercapacitor, a charging circuit is used to adjust the output voltage of the supercapacitor. Furthermore, to ensure the adjustment accuracy of the charging circuit, the charging circuit obtains the information of the current sampling point in real time. Among them, the change in the capacitance of the capacitor in the circuit can adjust the current fluctuation in the circuit, and the vertical-cavity surface-emitting laser can also be other types of semiconductor lasers.

[0034] Figure 5 is a schematic diagram of the module connection of the semiconductor laser pulse driving circuit based on a supercapacitor in this application, as Figure 5As shown, a vertical cavity surface emitting laser (VCSEL), a supercapacitor, and a current control and sampling circuit are connected in series to form a laser discharge circuit. The current control and sampling circuit is divided into a current control circuit for controlling the operation of the VCSEL and a sampling circuit for sampling relevant information of the laser discharge circuit. The current control circuit generally uses a MOSFET, that is, the operation of the VCSEL is controlled by controlling the working state of the MOSFET. The sampling circuit samples and monitors the discharge current of the supercapacitor, that is, the sampling circuit collects the magnitude of the driving current of the VCSEL. Each capacitor of at least one supercapacitor is connected with a balancing and protection circuit and a discharging circuit, and the charging circuit is connected to the positive and negative electrodes of at least one supercapacitor. Capacitor voltage sampling points are provided at both ends of at least one supercapacitor for monitoring the capacitance. The charging circuit adjusts the charging voltage of the supercapacitor according to the magnitude of the sampling current to make the current value of the discharge circuit reach the target set value. The charging circuit obtains electric energy by connecting to an external circuit. The capacitor discharging circuit is used for discharging when it is necessary to reduce the voltage of at least one supercapacitor and for discharging the residual energy stored in the capacitor when the power supply system is turned off. The operation of the VCSEL is driven by a specific current to achieve a specific optical power output. At the same time, its laser pulse width and frequency are achieved through the switch control of the discharge circuit. In the medical field, the control of the optical power and pulse width further realizes the control of the single-pulse output energy of the laser. The VCSELs in this application can be one or more, and the multiple VCSELs can be connected in parallel, series, or series-parallel. The control circuit supplies power to each functional module in the control circuit according to a predetermined working mode to provide a stable current to the VCSEL.

[0035] In a specific embodiment of the present application, the charging circuit charges at least one supercapacitor to a set voltage and adjusts the voltage output by the charging circuit to at least one supercapacitor according to the sampling result of the capacitor voltage sampling point and the driving current of the VCSEL to achieve a target driving current at the VCSEL. The capacitor voltage sampling point is provided at both ends of at least one supercapacitor.

[0036] Specifically, the voltage across the supercapacitor is set by the capacitor charging circuit. The charging circuit monitors the voltage across the capacitor in real time. That is, after charging at least one supercapacitor to the set voltage, the charging circuit adjusts the voltage output to at least one supercapacitor according to the sampling result of the capacitor voltage sampling point and the drive current of the vertical cavity surface emitting laser. When it is detected that the voltage value of the supercapacitor is lower than the preset value, charging is quickly started. When it is detected that the voltage value of the supercapacitor exceeds the preset value, charging is stopped, so as to achieve the target drive current at the vertical cavity surface emitting laser. That is, after charging at least one supercapacitor to the set voltage, the sampling result of the capacitor voltage sampling point is monitored in real time. When it is necessary to reduce the voltage of at least one supercapacitor, it is necessary to accurately perform voltage discharge processing according to the sampling result of the capacitor voltage sampling point, so that the voltage of the capacitor after discharge reaches the predetermined value.

[0037] Specifically, there are a dynamic voltage during discharge and an open-circuit voltage when not discharging in voltage detection. The former is lower than the latter, but there is a corresponding relationship between the two.

[0038] In this specific embodiment, by monitoring and maintaining the preset voltage across the supercapacitor, the stability of the discharge current across the capacitor is ensured, and thus the target drive current is achieved at the vertical cavity surface emitting laser.

[0039] In a specific embodiment of the present application, the current control and sampling circuit consists of a MOSFET and a sampling resistor. Among them, the MOSFET is connected in series with the vertical cavity surface emitting laser, and the MOSFET controls the current flow and cut-off of the vertical cavity surface emitting laser by adjusting its switching state; the sampling resistor is connected in series with the MOSFET, and the far-MOSFET end is at a relative ground level, and the other end is connected to an operational amplifier for voltage signal amplification and then used as a current sampling point.

[0040] In a specific embodiment of the present application, the current sampling circuit is a Hall current sensor, and when the current sampling circuit is a Hall current sensor, the current sampling circuit is located at any position in the laser discharge circuit.

[0041] Specifically, the current control circuit generally uses a MOSFET to control the current flow and cut-off of the vertical cavity surface emitting laser. The current sampling circuit can be a circuit composed of a sampling resistor and an operational amplifier connected in series, and then the low-voltage signal collected in this circuit is amplified to a high-voltage signal for detection to obtain sampling information, or it can be a method of detecting the current magnitude by detecting the current magnetic field using a Hall current sensor with its own amplifier.

[0042] Specifically, Figure 6 is a circuit schematic diagram of a semiconductor laser pulse drive circuit based on a supercapacitor in the present application, as Figure 6As shown, when the current sampling circuit consists of a MOSFET and a sampling resistor, the negative electrode of the vertical cavity surface emitting laser is connected to the source electrode of the MOSFET, and the drain electrode of the MOSFET is connected to the sampling resistor (for large current sampling, a high-power zero-ohm resistor is commonly used as the sampling resistor). When the semiconductor laser pulse driving circuit based on supercapacitors contains multiple supercapacitors, the multiple supercapacitors are connected in series, and the series-connected capacitor group is connected in parallel with the circuit composed of the vertical cavity surface emitting laser, the MOSFET, and the sampling resistor, that is, first, multiple supercapacitors are connected in series and the series-connected supercapacitors are connected in parallel with the circuit composed of the vertical cavity surface emitting laser, the MOSFET, and the sampling resistor, and the charging circuit is connected in parallel with the circuit of the multiple series-connected supercapacitors. Among them, the other end of the sampling resistor can be connected to an operational amplifier for voltage signal amplification and then used as a current sampling point for current sampling. And the control part controls whether the vertical cavity surface emitting laser works, whether discharge processing is performed, and whether voltage regulation is required, etc.

[0043] Moreover, the MOSFET that controls the VCSEL current switch in the circuit operates in the switching state rather than the constant current region, which can reduce the heat dissipation requirement and also reduce the energy loss. Through the circuit designed above, a driving current output with long pulses and large currents can be achieved, so that the vertical cavity surface emitting laser can generate stable laser, and the average power of the front-end power supply of this application is low, which can reduce the waste of power supply cost.

[0044] When the current sampling circuit is a Hall current sensor, the Hall current sensor can be located at any position in the discharge loop of the laser. The remaining working modes and functions of the Hall current sensor in the semiconductor laser pulse driving circuit are similar or the same as those of the circuit composed of a MOSFET and a sampling resistor, and will not be elaborated here.

[0045] In a specific embodiment of this application, according to the equivalence relationship between the transient reduced charge of at least one supercapacitor and the transient increased charge of the loop, and the loop current value, the transient current value of the loop at any moment is calculated.

[0046] Specifically, when the current sampling circuit consists of a MOSFET and a sampling resistor, the loop current value when the vertical cavity surface emitting laser works is calculated according to the series impedance of the vertical cavity surface emitting laser, the internal resistance of the MOSFET, the internal resistance of the sampling resistor, the DC internal resistance of the capacitor, the bandgap voltage of the vertical cavity surface emitting laser, the capacitance and voltage of at least one supercapacitor. Then, according to the equivalence relationship between the transient reduced charge of at least one supercapacitor and the transient increased charge of the loop, and the loop current value, the transient current value of the loop at any moment is calculated.

[0047] When the current sampling circuit is a Hall current sensor, the loop current value during the operation of the vertical cavity surface emitting laser is calculated based on the internal resistance of the vertical cavity surface emitting laser, the internal resistance of the Hall current sensor, the DC internal resistance of the capacitor, the bandgap voltage of the vertical cavity surface emitting laser, the capacitance and voltage of at least one supercapacitor. Then, according to the equivalence relationship between the transient reduced charge of at least one supercapacitor and the transient increased charge of the loop, and the loop current value, the transient current value of the loop at any moment is calculated.

[0048] In a specific embodiment of the present application, based on a predetermined laser optical power fluctuation value and the transient current value at any moment, it is determined whether the current value fluctuation in the designed loop meets the predetermined laser optical power fluctuation value, and the capacitance parameter of at least one supercapacitor is adjusted according to the judgment result. Moreover, the larger the capacitance of the supercapacitor, the smaller the laser optical power fluctuation value.

[0049] In a specific embodiment of the present application, there is a linear relationship between the laser optical power fluctuation value of the vertical cavity surface emitting laser and its current.

[0050] Specifically, there is a linear relationship between the laser optical power fluctuation value of the vertical cavity surface emitting laser and its current. Therefore, when it is necessary to generate laser pulses with a large pulse width, a small duty cycle, and a stable optical power, there are also high requirements for the power supply that provides current for the vertical cavity surface emitting laser. In the present application, by using supercapacitors to provide large-current drive for the VCSEL, when the vertical cavity surface emitting laser can work in the required state, the average power demand for the front-end power supply can be reduced, thereby reducing the manufacturing cost.

[0051] In a specific embodiment of the present application, the device selection method for at least one supercapacitor is as follows: based on the open-circuit voltage of the preset supercapacitor, the loop internal resistance of the laser discharge circuit, the bandgap voltage of the vertical cavity surface emitting laser, the preset capacitance and voltage of the supercapacitor, the loop current value of the laser discharge circuit is calculated; and, according to the device selection standard and the loop current value, the device type of at least one supercapacitor is determined.

[0052] Specifically, the supercapacitor is a capacitor with a low operating voltage value, a high capacitance, and a small internal resistance. Preferably, the supercapacitor selects a farad capacitor, which is a capacitor made of a special material, and generally the capacitance can reach the order of farad (F). Further, in order to ensure that each capacitor avoids uneven charging and overcharging problems caused by impedance and capacitance differences during the charging process, a balance and protection circuit can be set at both ends of the electrodes of each capacitor to discharge in a timely manner in the case of overcharging and avoid device damage.

[0053] In a specific embodiment of the present application, when the semiconductor laser pulse driving circuit based on supercapacitors includes multiple supercapacitors, the multiple supercapacitors are connected in series.

[0054] In a specific embodiment of the present application, both ends of at least one supercapacitor are connected to a discharge circuit, and the supercapacitor is discharged when the capacitor voltage needs to be lowered or the entire system is shut down.

[0055] Specifically, for the circuit that powers the VCSEL, since the VCSEL needs to operate in a state of long pulse width and large current to excite high laser energy, and its current source is usually directly provided by the front-end power supply or a large-capacity capacitor is used for discharging to power the VCSEL. In the present application, the VCSEL is powered by multiple series-connected supercapacitors, and a capacitor voltage sampling point is provided at the outermost periphery of the series-connected supercapacitors, so that when the output voltage of the charging circuit is inconsistent with the voltage across the supercapacitor, the voltage of the supercapacitor can be adjusted in time. That is, when the capacitor voltage is insufficient, the charging circuit is started in time to charge the supercapacitor; if the capacitor voltage exceeds the preset value, the bypass circuit is started to discharge the supercapacitor. Among them, the discharge circuit generally consists of a high-power resistor and a switching device (such as a MOSFET), etc.

[0056] In a specific embodiment of the present application, in an actual application scenario, such as in a household semiconductor laser hair removal system, assuming that the electro-optical efficiency of the VCSEL is 40%, if it is necessary to generate a 10 J optical pulse within 100 ms, at this time, at least 25 J of electrical injection is required for the VCSEL. Using the method of directly powering by a switching power supply in the prior art, it is required that the designed output power of the switching power supply is at least 25 J / 100 ms = 250 W. At this time, if the working voltage of the VCSEL is 2 V, the discharge current provided by the switching power supply to the circuit is 125 A.

[0057] And in an actual application scenario, the working voltage required by the VCSEL during operation is relatively low while the required working current is relatively high. When a large-capacity capacitor is used for discharging to power the VCSEL, according to the energy storage capacity formula of the capacitor E = CU 2 / 2, under the same application conditions as described above, the capacitance of the capacitor needs to reach the joule level. However, traditional electrolytic capacitors usually have a relatively small capacitance and are more suitable for energy storage at high voltages. Therefore, in applications with low voltage and high capacitance requirements, supercapacitors with a voltage of 2.7 - 3.0V, a capacitance in the order of several hundred farads, and an internal resistance in the order of milliohms can be used to supply power to the VCSEL. By using a supercapacitor with a low operating voltage value, a high capacitance, and a small internal resistance of the capacitor to supply power to the VCSEL, a driving current with long pulses and large current can be provided to the VCSEL, the power required for the VCSEL to operate can be reduced, and high - energy pulsed lasers with a low duty cycle can be generated.

[0058] For example, assume that the operating voltage of the VCSEL is 2V when the operating current is 125A. If a supercapacitor with a capacitance of 400F, a maximum voltage of 3V, a DC resistance of 3.2mΩ, and a volume size of about D35x60mm is used to supply power to the VCSEL, when its discharge current is 125A, the voltage drop required for its internal impedance is 3.2mΩ 125A = 0.32V. If the internal resistance of the switching MOSFET in the circuit is 1mΩ and the resistance of the zero - ohm resistor used for sampling is 1mΩ, the voltage margin allowed to supply power to the VCSEL is 3 - 0.32 - 125 (0.001 + 0.001)=2.35V. At this time, the voltage value exceeds the 2V operating voltage required for the VCSEL to operate. That is to say, the supercapacitor can provide sufficient supply voltage and current to the VCSEL.

[0059] For application scenarios such as laser medicine, it is generally required that the laser optical power fluctuation does not exceed + / - 20%. Since the VCSEL current and the optical power are basically linearly related, in order to ensure that the laser optical power fluctuation meets the requirements, it is necessary to require that the driving current fluctuation does not exceed + / - 20% either. For example, when the emission threshold current of the VCSEL is 15A, based on the current value of 125A at the start of discharge, at the end of the discharge cycle, the current provided by the supercapacitor should not be lower than (125 - 15) 80%+15 = 103A.

[0060] Assume that the open - circuit voltage of the series - connected supercapacitor is U, the total internal resistance of the loop is R (including the internal resistance of the VCSEL, the internal resistance of the MOSFET, the internal resistance of the sampling resistor, and the DC internal resistance of the capacitor of the supercapacitor, etc.), the band - gap voltage of the VCSEL is g, and the capacitance of the supercapacitor is C. Then when the MOSFET is turned on, the average current I in the loop satisfies: U = I R + g.

[0061] Because there is an equivalent relationship between the transient reduction of charge in the supercapacitor and the transient increase of charge in the loop, that is, I dt=-C If dU, then the average current I=(U - g) / R in the loop is substituted into the equivalent relationship to obtain (U - g) / R dt = -C dU, that is, dt = -RC / (U - g) dU. For dt = -RC / (U - g) dU, integrating both sides of the equation dt = -RC / (U - g) gives t = -RC ln(U - g).

[0062] Then when the discharge time t starts from 0 to the end time T of the first discharge pulse, it satisfies the following constraints: T = RC [ln(U 0 - g) - ln(U 1 - g)], where U 1 - g = I 1 R From this, the transient current in the loop at time T can be obtained: I 1 = EXP[ln(U 0 - g) - T / (RC)] / R If the required value of the preset laser optical power fluctuation is (I 1 - I th ) / (I 0 - I th ) ≤ 1 - δ, where δ is the error standard and it can take values such as 5%, 10%, 20%, etc., then according to the transient current in the loop at time T and the required value of the preset laser optical power fluctuation, it can be known that: {EXP[ln(U 0 - g) - T / (RC)] / R - I th} / [(U 0 - g) / R - I th ≤ 1 - δ The above is the calculation result based on the bandgap width of one VCSEL. If there are n VCSELs connected in series in the circuit loop, then: {EXP[ln(U 0 - n g) - T / (RC)] / R - I th} / [(U 0 - n g) / R - I th ≤ 1 - δ.

[0063] When the parameters of the designed supercapacitor can enable the VCSEL to meet the above requirements, the parameters of the designed supercapacitor can be optimized, or the parameters at this time can be used as the final result. If the parameters of the designed supercapacitor cannot enable the VCSEL to meet the above requirements, modify the parameters of the supercapacitor until the VCSEL meets the limiting conditions.

[0064] For example, when the internal resistance of the VCSEL satisfies (2 - 1.53) / 125 = 3.76 mΩ, where 2 is the operating voltage of the VCSEL, 125 A is the operating current of the VCSEL, and 1.53 is the bandgap value of the VCSEL. Therefore, the total impedance R of the circuit = 3.76 + 3.2 + 1 + 1 = 0.00896 Ω. If U 0 = 2.65 V, C = 400 F, and g = 1.53 V, then at T = 0.1 s, the transient current of the circuit is: I 1 = EXP[ln(U 0 - g) - RC / T] / R = 121.56 A At this time, if the emission threshold current I th of the VCSEL is 15 A, then the decrease in optical power is 1 - (121.56 - 15) / (125 - 15) = 3.13%. The fluctuation at this time is much smaller than the conventional requirements for optical power fluctuation.

[0065] In several embodiments provided in the present application, it should be understood that the disclosed device can be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0066] The above is only the embodiment of the present application, and thus does not limit the patent scope of the present application. Any equivalent structural transformation made using the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, is similarly included in the patent protection scope of the present application.

Claims

1. A semiconductor laser pulse driving circuit based on supercapacitor, characterized in that: include: at least one supercapacitor for powering the vertical cavity surface emitting laser; A current control and sampling circuit, which controls the current flow and shutdown of the vertical cavity surface emitting laser by controlling its switch state, and is provided with a current sampling point, through which the discharge current of the supercapacitor is sampled and monitored, and the current control and sampling circuit is connected in series with the vertical cavity surface emitting laser and at least one of the supercapacitors to form a laser discharge circuit; A charging circuit is connected to the positive and negative electrodes of at least one of the supercapacitors and charges at least one of the supercapacitors, wherein the charging circuit dynamically adjusts the voltage output by the sampling result of the current sampling point, and then adjusts the voltage value of the supercapacitor so that the supercapacitor provides a constant current for the vertical cavity surface emitting laser.

2. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: The charging circuit charges at least one of the supercapacitors to a set voltage, and adjusts the voltage output by the charging circuit to at least one of the supercapacitors according to a sampling result of a capacitor voltage sampling point and a driving current of the vertical cavity surface emitting laser, wherein the capacitor voltage sampling point is set at the outermost side of the supercapacitor.

3. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: The device selection method of the at least one supercapacitor is: according to the preset open circuit voltage of the supercapacitor, the loop internal resistance of the laser discharge loop, the bandgap voltage of the vertical cavity surface emitting laser and the preset capacity of the supercapacitor, the loop current value of the laser discharge loop is calculated; and, The device type of the at least one supercapacitor is determined according to a device selection standard and the loop current value.

4. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: The current control and sampling circuit is composed of a MOSFET and a sampling resistor, wherein the MOSFET is connected in series with the vertical cavity surface emitting laser, and the MOSFET controls the current flow and shutdown of the vertical cavity surface emitting laser by adjusting its switching state; the sampling resistor is connected in series with the MOSFET, and the other end of the sampling resistor is connected to an operational amplifier to amplify the voltage signal and then serves as a current sampling point.

5. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: The current control and sampling circuit is a Hall-type current sensor, and when the current sampling circuit is a Hall-type current sensor, the current sampling circuit is located at any position in the laser discharge loop.

6. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: The transient current value of the loop at any moment is calculated based on the equivalent relationship between the transient charge reduction of at least one of the supercapacitors and the transient charge increase of the loop, as well as the loop current value.

7. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 6, characterized in that: According to the predetermined laser light power fluctuation value and the transient current value at any moment, it is judged whether the current value fluctuation in the designed loop meets the predetermined laser light power fluctuation value, and the capacity parameter of at least one of the supercapacitors is adjusted according to the judgment result, and the larger the capacity of the supercapacitor, the smaller the laser light power fluctuation value.

8. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: There is a linear relationship between the laser light power fluctuation value of the vertical cavity surface emitting laser and its current.

9. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: When the supercapacitor-based semiconductor laser pulse driving circuit includes a plurality of the supercapacitors, the plurality of the supercapacitors are connected in series.

10. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: When N supercapacitors are connected in series, a balancing and protection circuit is provided at both ends of electrodes of each supercapacitor, wherein N is not less than 2.

11. The semiconductor laser pulse driving circuit based on supercapacitor according to claim 1, characterized in that: Two ends of at least one of the supercapacitors are connected to a discharge circuit, and the supercapacitor is discharged when the capacitor voltage needs to be lowered or the entire system is shut down.

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