Laser current drive circuit with protection function

Abstract

The laser current driving circuit with protection function can avoid the instantaneous voltage signal or the surge current signal formed by the DAC due to the fact that the DAC is not controlled by the main control chip and added to the subsequent circuit and the laser during the power-on moment of the system, so that the laser is more comprehensively protected during use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser current driving, in particular to a laser current driving circuit with a protection function. BACKGROUND

[0002] The nature of the semiconductor laser itself determines its poor surge impact resistance. Statistics show that more than half of the sudden failures of semiconductor lasers are due to surge breakdown. This requires a high stability and small surge impact of the driving power supply, so various protection circuits are needed in the driving power supply to meet the actual requirements. Figure 4 As shown in the prior art, Figure 4 The main control module connects the laser through a digital-to-analog conversion module, a voltage-controlled current source module, and a protection circuit module connected in series. The laser current driving circuit usually uses a slow start circuit, a TVS (Transient Voltage Suppressor) absorption circuit, and a current limiting circuit to prevent surge impact and excessive current.

[0003] The semiconductor laser current driving circuit is generally composed of a high-precision DAC module (DAC, digital analog convertor), a voltage-controlled current source module, and a protection circuit module. The high-precision DAC module generates a voltage signal under the control of the main control chip, which is converted into a current signal by the voltage-controlled current source through V-I conversion. The protection circuit is in the form of an RC low-pass filter network between the DAC chip and the voltage-controlled current source to realize the delay soft start of the voltage signal and filter out the surge voltage. The TVS device is connected in parallel across the laser, which uses its high-speed response characteristic to suppress high grid surge voltage and lightning-induced voltage, and performs current limiting and surge protection. A current limiting resistor is connected in series with the laser for current limiting protection (such as Figure 3 or Figure 4 ). Figure 3 The prior art is a laser current driving circuit. Figure 3 The main control module connects the laser through a digital-to-analog conversion module, an RC filter delay module, and a voltage-controlled current source module connected in series. Figure 4 The prior art is a laser current driving circuit with a protection circuit module.

[0004] Parallel TVS devices are arranged at both ends of the laser to carry out current limiting and surge protection, but are limited by the response speed of the TVS, and if the response speed cannot meet the requirements, the surge impact cannot be well inhibited. The RC low-pass filter network is effective for reducing power ripple and absorbing small surges (RC is resistance R and capacitance C), but for large surges, the circuit will fail. The entire circuit does not consider the system power-on instant, the DAC is not controlled by the master control chip, and a large instantaneous voltage signal can also be generated, which is added to the subsequent circuit and the laser, causing the laser to be damaged. SUMMARY

[0005] The present application aims at the defects or deficiencies in the prior art, and proposes a laser current driving circuit with protection function, by adding a programmable switch between the DAC circuit and the V-I conversion circuit, the programmable switch is selected to the ground of the pull-down resistor during system power-on, so that the instantaneous voltage signal or the surge current signal generated by the DAC due to not being controlled by the master control chip is added to the subsequent circuit and the laser during the system power-on instant, so that the laser is more comprehensively protected during use.

[0006] The technical solution of the present application is as follows:

[0007] The laser current driving circuit with protection function comprises a master control module, the master control module is connected with a laser through a digital-to-analog conversion module DAC, an RC filter delay module and a voltage-controlled current source module connected in sequence, characterized in that a programmable switch is inserted between the digital-to-analog conversion module and the RC filter delay module, the programmable switch is selected to the ground of the pull-down resistor during system power-on, so that the instantaneous voltage signal or the surge current signal generated by the DAC due to not being controlled by the master control chip is added to the laser during the system power-on instant, so that the laser is more comprehensively protected during use.

[0008] The input end of the programmable switch is connected with the output end of the DAC and the master control module respectively, the master control module transmits a switch signal SW to the input end of the programmable switch, the input end of the DAC is connected with the master control module through a serial digital interface SDI, the master control module transmits a digital quantity to the DAC through the SDI, so that the DAC outputs an analog voltage signal U to the input end of the programmable switch, the output end of the programmable switch comprises a first selection end SW_NO and a second selection end SW_NC, the SW_NC is connected with the ground end through a first resistor R1, the SW_NO is connected with the ground end through a tenth resistor R10 in one way, and is connected with the RC filter delay module in another way.

[0009] The RC filter delay module comprises a ninth resistor R9 and an eighth resistor R8, one end of the R9 is connected to the SW_NO, the other end is grounded through a second capacitor C2, one end of the R8 is grounded through the second capacitor C2, the other end is grounded through a first capacitor C1 in one way, and is connected to the voltage-controlled current source module in another way.

[0010] The voltage-controlled current source module comprises a first operational amplifier and a second operational amplifier, the negative input end of the first operational amplifier is interconnected with the output end, and the interconnected end is connected to the positive input end of the second operational amplifier through a sixth resistor R6, one end of the positive input end of the second operational amplifier is connected to one end of a seventh resistor R7, the other end of the R7 is grounded through the first capacitor C1, the positive input end of the first operational amplifier is connected to a laser through a fifth resistor R5, and the output end of the second operational amplifier is connected to the positive input end of the first operational amplifier in one way through a fourth resistor R4, and is connected to the negative input end of the second operational amplifier in another way and then grounded through a third resistor R3.

[0011] The current output by the voltage-controlled current source module is I, I=U / R4, a constant current I generated by the voltage-controlled constant current source drives the laser to work, and the R5 plays a current-limiting protection role.

[0012] The laser is connected in parallel with a transient voltage suppressor (TVS), and the TVS adopts a diode structure.

[0013] The technical effect of the application is as follows: the laser current driving circuit with a protection function in the application adds a program-controlled switch between a DAC circuit and a V-I conversion circuit, so that the instantaneous voltage signal generated by the DAC not controlled by a master control chip can be avoided from being added to subsequent circuits and a laser during system power-on, and the laser is damaged. The application considers the uncontrolled inrush current signal that can cause damage to the laser and circuits during system power-on, so that the circuit is safer, and the laser is more comprehensively protected during use. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a structural schematic diagram of the laser current driving circuit with a protection function. Figure 1 The main control module is connected to the laser through a digital-to-analog conversion module, a program-controlled switch, an RC filter delay module and a voltage-controlled current source module connected in sequence.

[0015] Figure 2 It is a principle schematic diagram of the laser current driving circuit with a protection function. Figure 2 The main control chip, a digital-to-analog converter, a program-controlled switch, a first operational amplifier, a second operational amplifier, a laser, resistors and capacitors and the like are included.

[0016] Figure 3 is a laser current driving circuit in the prior art. Figure 3 The main control module is connected with the laser through a digital-to-analog conversion module, an RC filter delay module and a voltage-controlled current source module connected in series.

[0017] Figure 4 is a laser current driving circuit in the prior art. Figure 4 The main control module is connected with the laser through a digital-to-analog conversion module, an RC filter delay module and a voltage-controlled current source module connected in series.

[0018] The reference signs are listed as follows: SDI-serial digital interface (Serial Digital Interface, the main control chip transmits digital quantity to the DAC through the SDI, and the DAC outputs an analog voltage signal U) ; SW-switch signal (switch, the main control chip transmits the SW signal to the program-controlled switch) ; DAC-digital analog converter (digital analog convertor) ; U-analog voltage signal; SW_NO-first gate terminal; SW_NC-second gate terminal; GND-ground terminal; R1-R10-first resistor to tenth resistor; C1-C2-first capacitor to second capacitor; I-current (constant current) ; TVS-transient voltage suppressor (Transient Voltage Suppressor, the TVS adopts a diode structure, and the TVS is connected in parallel with the laser). DETAILED DESCRIPTION

[0019] The present application will be described below in conjunction with the accompanying drawings (Fig. Figures 1-2 ) and examples.

[0020] Figure 1 is a structure schematic diagram of the laser current driving circuit with the protection function according to the present application. Figure 2 is a principle schematic diagram of the laser current driving circuit with the protection function according to the present application. Reference is made to Figures 1 to 2The laser current drive circuit with protection function is shown, including a master control module, the master control module connects the laser through the digital-to-analog conversion module DAC, RC filter delay module and voltage-controlled current source module connected in series, a programmable switch is inserted between the digital-to-analog conversion module and RC filter delay module, the programmable switch is gated to the ground through a pull-down resistor when the system is powered on, so as to avoid the laser damage caused by the instantaneous voltage signal or the surge current signal formed by the DAC when the system is powered on and the laser is not controlled by the master control chip. The input end of the programmable switch is connected with the output end of the DAC and the master control module respectively, the master control module transmits a switch signal SW to the input end of the programmable switch, the input end of the DAC is connected with the master control module through a serial digital interface SDI, the master control module transmits a digital quantity to the DAC through the SDI, so that the DAC outputs an analog voltage signal U to the input end of the programmable switch, the output end of the programmable switch includes a first gating end SW_NO and a second gating end SW_NC, the SW_NC is connected with the ground through a first resistor R1, the SW_NO is connected with the ground through a tenth resistor R10 in one way and connected with the RC filter delay module in another way.

[0021] The RC filter delay module includes a ninth resistor R9 and an eighth resistor R8, one end of the R9 is connected with the SW_NO, and the other end is connected with the ground through a second capacitor C2, one end of the R8 is connected with the ground through the second capacitor C2, and the other end is connected with the voltage-controlled current source module in one way and connected with the ground through a first capacitor C1 in another way. The voltage-controlled current source module includes a first operational amplifier and a second operational amplifier, the negative input end and the output end of the first operational amplifier are interconnected, and then the positive input end of the second operational amplifier is connected with the sixth resistor R6, one end of the positive input end of the second operational amplifier is connected with the seventh resistor R7, the other end of the R7 is connected with the ground through the first capacitor C1, the positive input end of the first operational amplifier is connected with the laser through the fifth resistor R5, the output end of the second operational amplifier is connected with the positive input end of the first operational amplifier in one way and connected with the negative input end of the second operational amplifier in another way, and then the ground is connected through the second resistor R2. The current output by the voltage-controlled current source module is I, I=U / R4, a constant current I is generated by the voltage-controlled constant current source to drive the laser to work, and the R5 plays a current limiting protection role. The laser is connected in parallel with a transient voltage suppressor TVS, and the TVS adopts a diode structure.

[0022] The laser current driving circuit with protection function adds a program-controlled switch between a DAC module and a V-I conversion module, when the system is powered on, the switch is connected to ground through a pull-down resistor, and in the program, the variable controlling the output of the DAC module is written as zero, so as to ensure that the output of the DAC module is 0, and then the switch is connected to the subsequent V-I conversion circuit and the laser, thereby avoiding that the instantaneous voltage signal generated by the DAC not controlled by the master control chip is added to the subsequent circuit and the laser at the moment when the system is powered on, and the laser is damaged. Figure 1 and Figure 2 As shown in the figures, the master control chip controls the on state of the program-controlled switch (SW, switch) through the SW signal, and protects the circuit and the laser during the period when each chip is not controlled at the moment when the system is powered on. The master control chip transmits digital quantity to the DAC chip through the SDI data transmission signal line (SDI, Serial Digital Interface, serial digital interface). At the moment when the system is powered on, the SW signal controls the program-controlled switch to connect SW_NC (the second selection end), the DAC chip is connected to ground through the resistor R1, and the subsequent voltage-controlled constant current source circuit is connected to ground through the resistor R10, so that the input of the current source circuit is 0V voltage, and thus the laser tube will not be damaged due to unstable output of the circuit. The master control chip inputs the signal of 0 to the DAC chip through the SDI signal line, so as to ensure that the output of the DAC chip is 0, and then the SW signal controls the program-controlled switch to connect SW_NO (the first selection end), and the DAC chip outputs an analog voltage signal U according to the received digital quantity, realizes the soft start effect through the second-order RC filter circuit, and filters out high-frequency noise in the signal, and then outputs the signal to the voltage-controlled constant current source circuit. The RC low-pass filter circuit is composed of two resistors (R8, R9) and two capacitors (C1, C2). The voltage-controlled constant current source circuit is composed of two operational amplifiers and five resistors (R2, R3, R4, R6, R7), according to the superposition theorem, when R3 / R2=R6 / R7, the current I=(R6U) / (R7R4), and when R6=R7, the current I=U / R4. The constant current generated by the voltage-controlled constant current source drives the laser to work, the resistor R5 plays a current limiting protection role, and the TVS diode connected in parallel with the laser mainly protects the laser from static electricity and surge. The use of the program-controlled switch can make up for the deficiency of the TVS diode and the current limiting resistor in the surge protection capability.

[0023] The contents not described in detail in the specification of the present application belong to the prior art known to those skilled in the art. It is indicated herein that the above description is helpful for those skilled in the art to understand the present application, but does not limit the protection scope of the present application. Any implementation of equivalent replacement, modification, improvement and / or deletion of the above description without departing from the essential content of the present application falls within the protection scope of the present application.

Claims

1. A laser current drive circuit with protection function, comprising a main control module, wherein the main control module is connected to the laser via a digital-to-analog converter (DAC), an RC filter delay module, and a voltage-controlled current source module connected in series, characterized in that, A programmable switch is inserted between the digital-to-analog converter module and the RC filter delay module. The programmable switch is turned on to ground by the pull-down resistor when the system is powered on, so as to avoid the instantaneous voltage signal or surge current signal generated by the DAC due to not being controlled by the main control chip being applied to the laser at the moment of system power-on, which would damage the laser. The input terminals of the programmable switch are respectively connected to the output terminal of the DAC and the main control module. The main control module transmits the switch signal SW to the input terminal of the programmable switch. The input terminal of the DAC is connected to the main control module through the serial digital interface SDI. The main control module transmits digital signals to the DAC through SDI, so that the DAC outputs an analog voltage signal U to the input terminal of the programmable switch. The output terminal of the programmable switch includes a first gating terminal SW_NO and a second gating terminal SW_NC. The SW_NC is connected to the ground terminal through the first resistor R1. One path of the SW_NO is connected to the ground terminal through the tenth resistor R10, and the other path is connected to the RC filter delay module. The RC filter delay module includes a ninth resistor R9 and an eighth resistor R8. One end of R9 is connected to the SW_NO, and the other end is grounded through the second capacitor C2. One end of R8 is grounded through the second capacitor C2, and the other end is grounded through the first capacitor C1 and connected to the voltage-controlled current source module. The voltage-controlled current source module includes a first operational amplifier and a second operational amplifier. The negative input terminal and output terminal of the first operational amplifier are interconnected and then connected to the positive input terminal of the second operational amplifier through a sixth resistor R6. The positive input terminal of the second operational amplifier is connected to one end of a seventh resistor R7, and the other end of R7 is grounded through a first capacitor C1. The positive input terminal of the first operational amplifier is connected to a laser through a fifth resistor R5. One output terminal of the second operational amplifier is connected to the positive input terminal of the first operational amplifier through a fourth resistor R4, and the other output terminal is connected to the negative input terminal of the second operational amplifier through a third resistor R3 and then grounded through a second resistor R2.

2. The laser current drive circuit with protection function according to claim 1, characterized in that, The voltage-controlled current source module outputs a current I, where I = U / R4. This constant current I is generated by the voltage-controlled constant current source to drive the laser. R5 serves as a current limiting protection.

3. The laser current drive circuit with protection function according to claim 1, characterized in that, The laser is connected in parallel with a transient voltage suppressor (TVS), and the TVS adopts a diode structure.

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