CN109217101B - Laser current driving circuit with maximum current protection and driving method - Google Patents
Laser current driving circuit with maximum current protection and driving method Download PDFInfo
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- CN109217101B CN109217101B CN201811150362.3A CN201811150362A CN109217101B CN 109217101 B CN109217101 B CN 109217101B CN 201811150362 A CN201811150362 A CN 201811150362A CN 109217101 B CN109217101 B CN 109217101B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
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Abstract
The invention relates to the technical field of semiconductor laser driving, and provides a laser current driving circuit with maximum current protection and a driving method. The circuit comprises a protection voltage setting unit, a comparison unit and a comparison unit, wherein the protection voltage setting unit is used for setting a reference protection voltage used as a comparison basis for a power supply voltage clamping unit; the reference protection voltage value is calculated according to the maximum current allowed by the laser; and the voltage clamping unit is used for acquiring the reference protection voltage of the protection voltage setting unit and determining the output quantity of the working current setting unit or the clamping voltage clamped by the voltage clamping unit which is output to the laser current driving unit by comparing the input quantity of the working current setting unit. The circuit of the invention has simple structure, high precision and easy realization because the intervention of an additional main controller is not needed, and can obviously protect the laser only by adding few elements, thereby improving the safety, stability and precision of the system.
Description
[ technical field ] A method for producing a semiconductor device
The invention relates to the technical field of semiconductor laser driving, in particular to a laser current driving circuit with maximum current protection and a driving method.
[ background of the invention ]
As shown in fig. 1, the conventional semiconductor laser driving circuit protects the laser by comparing the actual load current with the maximum protection current, which is a backward feedback type protection, and this protection method has the disadvantage of response lag, and when the protection action occurs, the overcurrent actually occurs, and the load may be damaged.
Another conventional semiconductor laser driving circuit is shown in fig. 2, and this driving circuit has the disadvantage that the laser is disposed at the collector of the transistor, and the sampling resistor is disposed at the emitter of the transistor, and according to kirchhoff's current law, the emitter current Ie of the transistor is Ic + Ib, which results in the actual current passing through the semiconductor laser being smaller than the expected current by an Ib value, so this driving circuit has the disadvantage of being not precise enough, and there is an error between the set value and the actual value.
In view of the above, overcoming the drawbacks of the prior art is an urgent problem in the art.
[ summary of the invention ]
The invention aims to solve the technical problems of response lag and insufficient current setting precision in the current drive backward feedback type protection technology of the existing laser.
The invention further aims to solve the technical problem of how to improve the precision of the semiconductor laser driving circuit.
The invention adopts the following technical scheme:
in a first aspect, the present invention provides a laser current driving circuit with maximum current protection, including a working current setting unit, a voltage clamping unit, a protection voltage setting unit, and a laser current driving unit, where the working current setting unit, the protection voltage setting unit, and the laser current driving unit are respectively connected to the voltage clamping unit, specifically:
the protection voltage setting unit is used for setting a reference protection voltage for the voltage clamping unit to be used as a comparison basis; the reference protection voltage value is obtained by calculation according to the maximum current allowed by the laser;
the voltage clamping unit is used for obtaining the reference protection voltage of the protection voltage setting unit and determining the output quantity of the working current setting unit or the clamping voltage clamped by the voltage clamping unit to be output to the laser current driving unit by comparing the input quantity of the working current setting unit.
Preferably, the voltage clamping unit includes an operational amplifier U1 and an operational amplifier U2, specifically:
the working current setting unit is connected to the inverting input end of the operational amplifier U1 through a resistor R3, and the protection voltage setting unit is respectively connected to the non-inverting input ends of the operational amplifier U1 and the operational amplifier U2 through a resistor R1 and a resistor R2;
the output end of the operational amplifier U1 is fed back to the inverting input end through a resistor R4; the output end of the operational amplifier U1 is also fed back to the inverting input end of the operational amplifier U2 through a resistor R5;
the output end of the operational amplifier U2 is fed back to the inverting input end of the operational amplifier U2 through a resistor R6; the output end of the operational amplifier U2 is connected with the input end of the laser current driving unit.
Preferably, the corresponding relationship among the resistor R3, the resistor R4, the resistor R5 and the resistor R6 is as follows: r3 ═ R4, R5 ═ R6.
Preferably, the laser current driving unit includes an operational amplifier U3 and a transistor Q1, specifically:
the output end of the voltage clamping unit is connected to the non-inverting input end of an operational amplifier U3 in the laser current driving unit through a resistor R7;
the output end of the operational amplifier U3 is connected to the base electrode of a triode Q1 through a resistor R11, the collector electrode of the triode Q1 is connected to the cathode of a laser LD1 through a sampling resistor RS, the anode of the laser LD1 is connected to a power supply VCC, the emitter electrode of the triode is grounded, and a feedback resistor R10 is connected between the collector electrode of the triode Q1 and the inverting input end of the operational amplifier U3 to form current type negative feedback.
Preferably, the capacitor C1 is arranged between the output end of the operational amplifier U3 and the inverting input end of the operational amplifier U3, and the bandwidth of the current limiting driving unit is within the interval of 800kHz-1.2 MHz.
Preferably, the value range of the capacitor C1 is 80-120 pF.
In a second aspect, the present invention further provides a laser current driving method with maximum current protection, where the laser current driving circuit with maximum current protection in the first aspect is used, specifically:
at the output voltage Vin of the working current setting unit<At 2Vmax, the output voltage Vo2 of the operational amplifier U2 is Vin, and the driving current flows through the laser LD1
At this time, the voltage is clampedThe unit is in normal working state, the laser LD1 drives the current I and the output Vin of the current setting unit according to a proportionality coefficient
A corresponding change; the Vmax is the output of the protection voltage setting unit and the reference protection voltage of the voltage clamping unit; the resistor R8 is a resistor connected between the collector of the transistor Q1 and the forward input port of the operational amplifier U3;
at the output voltage Vin of the working current setting unit>When the voltage is 2Vmax, the output voltage Vo1 of the operational amplifier U1 is 0V, the output voltage Vo2 of the operational amplifier U2 is 2Vmax, and the driving current flows through the laser LD1
At this time, the voltage clamping unit is in a clamping operation state, and the laser LD1 driving current I is only related to the output voltage Vmax of the protection voltage setting unit.
Preferably, the method further comprises:
according to the virtual short characteristic of the operational amplifier, the voltages of the in-phase end and the anti-phase end of the operational amplifier are basically equal, the output voltage Vo1 of the operational amplifier U1 is 2Vmax-Vin, and the output voltage Vo2 of the operational amplifier U2 is 2Vmax-Vo1 according to the set values of R3 and R4 and R5 which are R6.
Preferably, the driving current flows through the laser LD1
The relationship of (a) is derived as:
according to the principle of the virtual break of the operational amplifier, no current flows between the non-inverting terminal and the inverting terminal of the operational amplifier U3, the following transmission equation can be derived:
equation 1:
equation 2:
equation 3:
wherein Va is the input voltage of the laser driving unit, Vb is the same-phase input end voltage of the operational amplifier U3, Vc is the opposite-phase input end voltage of U3, Vd is the high-side voltage of the sampling resistor Rs, and Ve is the low-side voltage of the sampling resistor Rs;
according to the preset conditions of R7 ═ R9 and R8 ═ R10, where a scaling factor k exists between R8, R10 and R7, R9, then R8 ═ R10 ═ k R7;
the equation 1 is converted into equation 4: ve ═ k +1) Vb-kVa;
the equation 2 is converted into equation 5: vd ═ K +1 × Vc;
substituting said equation 3 results in equation 6:
vb ═ Vc can be obtained from the imaginary short principle of the operational amplifier, and substitution into the above equation 6 can result in equation 7 of the relationship between the current I finally flowing through the semiconductor laser LD1 and the set voltage:
since Va and Vo2 are the same point voltage, equation 7 can be translated to:
preferably, the method further comprises:
when the maximum current allowed to pass through the laser is Imax, the maximum current is obtained according to the equation
And calculating a reference protection voltage value of the protection voltage setting unit.
The invention provides a laser current driving circuit with maximum current protection, which is characterized in that a protection voltage setting unit and a voltage clamping unit are added in front of a conventional laser current driving unit. And the input value of the laser driving unit is limited by the combined action of the protection voltage setting unit and the voltage clamping unit. Simple structure because need not plus main control unit's intervention, therefore precision is higher, easily realizes, only need add few component, just can show the guard action to the laser instrument, has improved the security, the stability and the precision degree of system.
In the preferred scheme of the invention, the traditional laser current driving unit is partially improved, the semiconductor laser and the sampling resistor are serially arranged on a collector current path of the triode, and the semiconductor laser and the sampling resistor are in serial connection, so that the current value flowing through the semiconductor laser is equal to the current value flowing through the sampling resistor, the actual working current of the semiconductor laser is strictly equal to the set value, and the precision of the semiconductor laser driving circuit is improved.
[ description of the drawings ]
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly described below. It is obvious that the drawings described below are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
Fig. 1 is a schematic diagram of a current protection structure of a conventional backward feedback laser;
FIG. 2 is a schematic diagram of a current-driven circuit of a conventional semiconductor laser;
fig. 3 is a schematic structural diagram of a laser current driving circuit with maximum current protection according to an embodiment of the present invention;
FIG. 4 is a schematic circuit diagram of a voltage clamping unit according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a current-driven circuit of an improved semiconductor laser according to an embodiment of the present invention;
fig. 6 is a schematic diagram of a laser current driving circuit with maximum current protection according to an embodiment of the present invention.
[ detailed description ] embodiments
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the description of the present invention, the terms "inner", "outer", "longitudinal", "lateral", "upper", "lower", "top", "bottom", and the like indicate orientations or positional relationships based on those shown in the drawings, and are for convenience only to describe the present invention without requiring the present invention to be necessarily constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1:
the embodiment 1 of the present invention provides a laser current driving circuit with maximum current protection, as shown in fig. 3, including a working current setting unit, a voltage clamping unit, a protection voltage setting unit, and a laser current driving unit, where the working current setting unit, the protection voltage setting unit, and the laser current driving unit are respectively connected to the voltage clamping unit, specifically:
the protection voltage setting unit is used for setting a reference protection voltage for the voltage clamping unit to be used as a comparison basis; the reference protection voltage value is obtained by calculation according to the maximum current allowed by the laser;
the voltage clamping unit is used for obtaining the reference protection voltage of the protection voltage setting unit and determining the output quantity of the working current setting unit or the clamping voltage clamped by the voltage clamping unit to be output to the laser current driving unit by comparing the input quantity of the working current setting unit.
The invention provides a laser current driving circuit with maximum current protection, which is characterized in that a protection voltage setting unit and a voltage clamping unit are added in front of a conventional laser current driving unit. And the input value of the laser driving unit is limited by the combined action of the protection voltage setting unit and the voltage clamping unit. Simple structure because need not plus main control unit's intervention, therefore precision is higher, easily realizes, only need add few component, just can show the guard action to the laser instrument, has improved the security, the stability and the precision degree of system.
The invention provides a laser current drive circuit with maximum current protection, which is characterized in that a laser current detection unit is removed on the basis of a conventional backward feedback type laser current drive unit, and a protection voltage setting unit and a voltage clamping unit are added in front of the laser current drive circuit. When the value of the working current setting unit is lower than that of the protection voltage setting unit, the voltage clamping unit does not work, and the circuit works normally according to the value output by the working current setting unit; when the value of the working current setting unit is higher than that of the protection voltage setting unit, the voltage clamping unit is triggered, so that the laser works according to the value output by the voltage clamping unit, and the protection effect is achieved. The whole control process is continuous and smooth, no impact and fluctuation are generated, and the value of the protection voltage setting unit and the maximum current value allowed by the laser can be accurately converted and can be easily obtained, so that the method is particularly suitable for the application of the laser drive which requires particularly precise protection current.
In combination with the embodiment of the present invention, a simple voltage clamping unit structure with high response speed is provided, as shown in fig. 4, including an operational amplifier U1 and an operational amplifier U2, specifically:
the working current setting unit is connected to the inverting input end of the operational amplifier U1 through a resistor R3, and the protection voltage setting unit is respectively connected to the non-inverting input ends of the operational amplifier U1 and the operational amplifier U2 through a resistor R1 and a resistor R2;
the output end of the operational amplifier U1 is fed back to the inverting input end through a resistor R4; the output end of the operational amplifier U1 is also fed back to the inverting input end of the operational amplifier U2 through a resistor R5;
the output end of the operational amplifier U2 is fed back to the inverting input end of the operational amplifier U2 through a resistor R6; the output end of the operational amplifier U2 is connected with the input end of the laser current driving unit.
In the voltage clamping unit structure shown in fig. 4, in order to facilitate precise control and matching of related electrical components, there is a preferred implementation manner, wherein the corresponding relationships among the resistor R3, the resistor R4, the resistor R5 and the resistor R6 are as follows: r3 ═ R4, R5 ═ R6.
In combination with the embodiment of the present invention, a laser current driving unit in the prior art is further improved, as shown in fig. 5, the improved laser current driving unit in the embodiment of the present invention includes an operational amplifier U3 and a transistor Q1, specifically:
the output end of the voltage clamping unit is connected to the non-inverting input end of an operational amplifier U3 in the laser current driving unit through a resistor R7;
the output end of the operational amplifier U3 is connected to the base electrode of a triode Q1 through a resistor R11, the collector electrode of the triode Q1 is connected to the cathode of a laser LD1 through a sampling resistor RS, the anode of the laser LD1 is connected to a power supply VCC, the emitter electrode of the triode is grounded, and a feedback resistor R10 is connected between the collector electrode of the triode Q1 and the inverting input end of the operational amplifier U3 to form current type negative feedback.
In the improved laser current driving unit, the semiconductor laser and the sampling resistor are serially arranged on a collector current path of the triode, and the semiconductor laser and the sampling resistor are in series connection, so that the current value flowing through the semiconductor laser is equal to the current value flowing through the sampling resistor, the actual working current of the semiconductor laser is strictly equal to the set value, and the precision of the semiconductor laser driving circuit is improved.
As shown in FIG. 5, the capacitor C1 is arranged between the output end of the operational amplifier U3 and the inverting input end of the operational amplifier U3, and the bandwidth of the current limiting driving unit is within the range of 800kHz-1.2 MHz. Preferably, the value range of the capacitor C1 is 80-120 pF.
Example 2:
after providing the laser current driving circuit with maximum current protection described in embodiment 1, the present invention further provides a laser current driving method with maximum current protection, which explains the principle of the laser current driving circuit with maximum current protection provided by the present invention from the implementation process, and specifically:
at the output voltage Vin of the working current setting unit<At 2Vmax, the output voltage Vo2 of the operational amplifier U2 is Vin, and the driving current flows through the laser LD1
At the moment, the voltage clamping unit is in a normal working state, and the laser LD1 drives the current I to be proportional to the output Vin of the current setting unit
A corresponding change; the Vmax is the output of the protection voltage setting unit and the reference protection voltage of the voltage clamping unit; the resistor R8 is a resistor connected between the collector of the transistor Q1 and the forward input port of the operational amplifier U3;
at the output voltage Vin of the working current setting unit>When the voltage is 2Vmax, the output voltage Vo1 of the operational amplifier U1 is 0V, the output voltage Vo2 of the operational amplifier U2 is 2Vmax, and the driving current flows through the laser LD1
At this time, the voltage clamping unit is in a clamping operation state, and the laser LD1 driving current I is only related to the output voltage Vmax of the protection voltage setting unit.
Preferably, Vmax can be obtained by obtaining the maximum current value Imax allowed by the laser according to the equation
And calculating a reference protection voltage value of the protection voltage setting unit.
In the embodiment of the invention, the voltages of the in-phase end and the anti-phase end of the operational amplifier are basically equal according to the virtual short characteristic of the operational amplifier, the output voltage Vo1 of the operational amplifier U1 is 2Vmax-Vin, and the output voltage Vo2 of the operational amplifier U2 is 2Vmax-Vo1 according to the set values of R3-R4 and R5-R6.
The current flowing through the laser LD1
The relationship of (a) is derived as:
according to the principle of the virtual break of the operational amplifier, no current flows between the non-inverting terminal and the inverting terminal of the operational amplifier U3, the following transmission equation can be derived:
equation 1:
equation 2:
equation 3:
wherein Va is the input voltage of the laser driving unit, Vb is the same-phase input end voltage of the operational amplifier U3, Vc is the opposite-phase input end voltage of U3, Vd is the high-side voltage of the sampling resistor Rs, and Ve is the low-side voltage of the sampling resistor Rs;
according to the preset conditions of R7 ═ R9 and R8 ═ R10, where a scaling factor k exists between R8, R10 and R7, R9, then R8 ═ R10 ═ k R7;
the equation 1 is converted into equation 4: ve ═ k +1) Vb-kVa;
the equation 2 is converted into equation 5: vd ═ K +1 × Vc;
substituting said equation 3 results in equation 6:
vb ═ Vc can be obtained from the imaginary short principle of the operational amplifier, and substitution into the above equation 6 can result in equation 7 of the relationship between the current I finally flowing through the semiconductor laser LD1 and the set voltage:
since Va and Vo2 are the same point voltage, equation 7 can be translated to:
example 3:
based on the laser current driving circuit with maximum current protection described in embodiment 1, the embodiment of the present invention further describes the optimal setting of the matching parameters and the corresponding implementation process in a specific application scenario.
The complete driving circuit diagram including the improvement point of the present invention is shown in fig. 6, wherein the current I1 is the current flowing through the resistor R8, the current I2 is the current flowing through the resistor R10, and the current I is the current flowing through the laser LD1 and the sampling resistor RS. Between the output end and the inverting input end of the integrating capacitor C1, the value of C1 is 100pF, the value of R1 is 1K, and the action of C1 can limit the bandwidth of the current driving unit to be about 1MHz and is used for forcing the voltage between the inverting end and the inverting end of the operational amplifier to tend to be consistent. The value of R11 is preferably set above 100 Ω, and the effect is that the base current of the restriction triode is not too big, carries out current-limiting protection to the operational amplifier U3.
The operational amplifiers U1, U2 and U3 are rail-to-rail, low offset voltage and single power supply operational amplifiers, and have resistance values of R3-R4, R5-R6, R7-R9 and R8-R10. The values of the resistor R3, the resistor R4, the resistor R5 and the resistor R6 are 10K omega, and the precision is 1%; r7, R9 takes 20K and the precision is 1%, R8 and R10 take 100K and the precision is 1%; the value of R11 is 1K omega, and the precision is 1%.
The protection voltage setting unit can ensure that the driving current of the laser works within a safety value only by outputting according to the calculation result, and even if the output of the working current setting unit is out of limit, the voltage clamping unit can quickly respond, the whole circuit can normally work.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. The utility model provides a take laser instrument current drive circuit of maximum current protection which characterized in that, includes working current setting unit, voltage clamping unit, protection voltage setting unit and laser instrument current drive unit, wherein working current setting unit, protection voltage setting unit and laser instrument current drive unit respectively in voltage clamping unit connects, and is specific:
the protection voltage setting unit is used for setting a reference protection voltage for the voltage clamping unit to be used as a comparison basis; the reference protection voltage value is obtained by calculation according to the maximum current allowed by the laser;
the voltage clamping unit is used for acquiring the reference protection voltage of the protection voltage setting unit and determining the output quantity of the working current setting unit or the clamping voltage clamped by the voltage clamping unit to be output to the laser current driving unit by comparing the input quantity of the working current setting unit;
the voltage clamping unit comprises an operational amplifier U1 and an operational amplifier U2, and specifically comprises:
the working current setting unit is connected to the inverting input end of the operational amplifier U1 through a resistor R3, and the protection voltage setting unit is respectively connected to the non-inverting input ends of the operational amplifier U1 and the operational amplifier U2 through a resistor R1 and a resistor R2;
the output end of the operational amplifier U1 is fed back to the inverting input end through a resistor R4; the output end of the operational amplifier U1 is also fed back to the inverting input end of the operational amplifier U2 through a resistor R5;
the output end of the operational amplifier U2 is fed back to the inverting input end of the operational amplifier U2 through a resistor R6; the output end of the operational amplifier U2 is connected with the input end of the laser current driving unit.
2. The laser current driving circuit with maximum current protection as claimed in claim 1, wherein the corresponding relationship among the resistor R3, the resistor R4, the resistor R5 and the resistor R6 is: r3 ═ R4, R5 ═ R6.
3. The laser current driving circuit with maximum current protection as claimed in claim 1, wherein the laser current driving unit comprises an operational amplifier U3 and a transistor Q1, specifically:
the output end of the voltage clamping unit is connected to the non-inverting input end of an operational amplifier U3 in the laser current driving unit through a resistor R7;
the output end of the operational amplifier U3 is connected to the base electrode of a triode Q1 through a resistor R11, the collector electrode of the triode Q1 is connected to the cathode of a laser LD1 through a sampling resistor RS, the anode of the laser LD1 is connected to a power supply VCC, the emitter electrode of the triode is grounded, and a feedback resistor R10 is connected between the collector electrode of the triode Q1 and the inverting input end of the operational amplifier U3 to form current type negative feedback.
4. The laser current driving circuit with maximum current protection as claimed in claim 3, wherein a capacitor C1 is disposed between the output terminal of the operational amplifier U3 and the inverting input terminal of the operational amplifier U3, and the bandwidth of the current driving unit is limited to be within the interval of 800kHz-1.2 MHz.
5. The laser current driving circuit with maximum current protection as claimed in claim 4, wherein the capacitance C1 has a value range of 80-120 pF.
6. A laser current driving method with maximum current protection, characterized by using the laser current driving circuit with maximum current protection according to claim 4, specifically:
at the output voltage Vin of the working current setting unit<At 2Vmax, the output voltage Vo2 of the operational amplifier U2 is Vin, and the driving current flows through the laser LD1
At the moment, the voltage clamping unit is in a normal working state, and the laser LD1 drives the current I to be proportional to the output Vin of the current setting unit
A corresponding change; the Vmax is the output of the protection voltage setting unit and the reference protection voltage of the voltage clamping unit; the resistor R8 is a resistor connected between the collector of the transistor Q1 and the forward input port of the operational amplifier U3;
at the output voltage Vin of the working current setting unit>When the voltage is 2Vmax, the output voltage Vo1 of the operational amplifier U1 is 0V, the output voltage Vo2 of the operational amplifier U2 is 2Vmax, and the driving current flows through the laser LD1
At this time, the voltage clamping unit is in a clamping operation state, and the laser LD1 driving current I is only related to the output voltage Vmax of the protection voltage setting unit.
7. The laser current driving method with maximum current protection according to claim 6, further comprising:
according to the virtual short characteristic of the operational amplifier, the voltages of the in-phase end and the anti-phase end of the operational amplifier are basically equal, the output voltage Vo1 of the operational amplifier U1 is 2Vmax-Vin, and the output voltage Vo2 of the operational amplifier U2 is 2Vmax-Vo1 according to the set values of R3 and R4 and R5 which are R6.
8. The laser current driving method with maximum current protection as claimed in claim 6, wherein the driving current flowing through the laser LD1
The relationship of (a) is derived as:
according to the principle of the virtual break of the operational amplifier, no current flows between the non-inverting terminal and the inverting terminal of the operational amplifier U3, the following transmission equation can be derived:
equation 1:
equation 2:
equation 3:
wherein Va is the input voltage of the laser driving unit, Vb is the same-phase input end voltage of the operational amplifier U3, Vc is the opposite-phase input end voltage of U3, Vd is the high-side voltage of the sampling resistor Rs, and Ve is the low-side voltage of the sampling resistor Rs;
according to the preset conditions R7 ═ R9, R8 ═ R10, where a scaling factor k exists between R8, R10 and R7, R9, that is, R8 ═ R10 ═ k ═ R7;
the equation 1 is converted into equation 4: ve ═ k +1) Vb-kVa;
the equation 2 is converted into equation 5: vd ═ K +1 × Vc;
substituting said equation 3 results in equation 6:
vb ═ Vc can be obtained from the imaginary short principle of the operational amplifier, and substitution into the above equation 6 can result in equation 7 of the relationship between the current I finally flowing through the semiconductor laser LD1 and the set voltage:
since Va and Vo2 are the same point voltage, equation 7 can be translated to:
9. the laser current driving method with maximum current protection according to claim 6, further comprising:
when the maximum current allowed to pass through the laser is Imax, the maximum current is obtained according to the equation
And calculating a reference protection voltage value of the protection voltage setting unit.
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