Design of Laser Driving Power Supply Based on CPLD

introduction

Laser processing mainly uses CO2 laser beam to focus on the surface of the material to melt the material, and at the same time uses compressed gas coaxial with the laser beam to blow away the melted material to complete the cutting of the required trajectory graphics or the engraving of the surface of the corresponding crafts. Laser processing is a non-contact processing with the advantages of multiple processing methods, strong adaptability, high processing accuracy, good quality and high processing efficiency. As the direct control unit of the laser, the maximum frequency of the optical switch response and the stability and reliability of the light output power of the laser driver will directly affect the final processing effect. Based on the needs of fast response and stable light output, Lechuang Automation Technology Co., Ltd. has developed a digital high-power laser driver based on CPLD.

2 System composition and working principle

2.1 System composition

The system structure of the digital high-power CO2 laser driver based on CPLD is shown in Figure 1. The system is mainly composed of the main power supply, voltage-stabilized power supply, auxiliary power supply, drive bridge, inverter boost, feedback circuit and digital control circuit. The main power supply and voltage-stabilized power supply mainly complete the stable output of 310V DC voltage from AC20V input, ensuring that the inverter boost part works stably and reliably under reasonable parameters. The auxiliary power supply mainly converts 310V DC voltage into SV and 12V DC voltage for use by the digital control part and the feedback comparator part. The drive bridge and inverter boost mainly complete the output of about 200V high voltage required by the load. The feedback circuit mainly plays a protective role and controls the range of output current.

2.2 Working Principle

In the principle block diagram of the laser drive power supply, AC202V generates a 310V DC voltage after rectification and filtering. The 310V DC voltage is output through a voltage regulator to supply the inverter boost part and the auxiliary power supply. The auxiliary power supply converts the 310V DC voltage into 12V and SV DC voltage to provide a reference voltage for the digital control part and the feedback part. The digital control part controls the power by controlling the conduction time of the drive bridge. The feedback circuit protects the output current from not exceeding 30MA by sampling the current at the output source end.

3. Function Implementation Methods

3. Main circuit and voltage stabilizing circuit

After rectification and filtering, AC220V obtains a DC voltage of about 301V, and then passes through a switching power supply to obtain a stable DC voltage of 310V.

3.2 Drive bridge circuit and inverter boost part

The 310 V DC voltage is converted to a high-frequency square wave voltage through a half-bridge inverter. In order to ensure the luminescence of the low-current laser, series resonance and parallel resonance technology are used in the inverter circuit. The boost part composed of a high-frequency boost transformer and a high-voltage rectifier circuit is packaged into an independent component high-voltage package. In the design, two high-voltage packages are connected in series to output power to the laser.

3.3 Digital control part and feedback part

The digital part is controlled by CPLD. On the one hand, CPLD completes the logic control of switching light, water protection, over-current and over-voltage feedback signals, and on the other hand, it mainly completes the output of PWM wave.

3.4 Auxiliary power supply

Based on the auxiliary power supply of VIPer22 A converter and high-frequency power transformer, the output voltage waveform is stable without large spikes.

4. Features

4.1 Good stability, strong resistance to external voltage fluctuations, and large adjustment range

A first-stage switching regulated power supply is designed before the inverter boost circuit. This regulated power supply can ensure that when the external grid voltage changes between -15% (187V) and +10% (242V), the reference voltage of the inverter boost part is stable at 30V. This ensures that the inverter boost part can operate under a stable parameter and improves its working stability.

4.2 High frequency response

Since the control part adopts the digital control method based on CPLD, it can handle the control pulse of lokb/s in the laser engraving process, and can well complete the slope engraving and small character engraving.

4.3 Accurate Power Control

In laser cutting, the duty cycle of the driving pulse output by the digital control module is not affected by external non-control signals, which can ensure stable power output under long-term operation. In laser engraving, it can respond to the power data of the control system in real time. At the same time, since the relationship between the output power of the laser and the working current is not linear, when engraving on a slope, the optical power can be corrected by the digital control part so that it changes linearly to ensure the slope requirements in the engraving slope.

4.4 Customizable control methods

In laser processing applications, there are sometimes many special processing requirements, such as requiring a larger light output power at the beginning of cutting. Digital control methods can easily modify the program to meet the corresponding new requirements.

5 Conclusion

Through long-term testing on a 1.6M laser produced by Chengdu Weiju Technology Co., Ltd., it was found that the laser driver power supply has high frequency response, precise control, and small output current ripple, which can ensure long-term stable operation of the laser.