High-power semiconductor laser drive power protection circuit scheme - Power Circuit - Circuit Diagram

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Photocoupler

1 Introduction

Semiconductor lasers (LD) have the advantages of small size, light weight, high conversion efficiency, long working life, etc., and have been widely used in industrial, military, medical and other fields. LD is a kind of laser with current injection as the excitation mode. Its service life and working characteristics depend to a large extent on the performance of the driving power supply used.

It is necessary to design a drive power that meets the requirements of LD technology, stable performance and reliable operation. In recent years, many research institutes have researched and developed a series of LD current sources to ensure the normal operation of LD.

The nature of the semiconductor laser itself determines its ability to withstand surge surges. This requires high stability of the drive power supply and low surge impact. Therefore, various protection circuits are required in the drive power supply to meet actual requirements. Slow start circuits, TVS (transient suppressor) absorption circuits, current limiting circuits, etc. are usually used to prevent surge surges and excessive currents. However, the operating current of high-power semiconductor lasers is large, and the semiconductor lasers are relatively fragile. The conventional slow-start circuits and TVS absorption circuits cannot meet the actual requirements well. Based on various practical protection circuits, this paper designs a high-power device to force absorption or isolation surge surge and dual current-limit protection circuit to effectively protect the semiconductor laser from damage, which has a good practical application prospect.

2 Principle analysis

2.1 Analysis of damage mechanism of semiconductor laser

Semiconductor lasers used under normal conditions have a long working life. However, under inappropriate working conditions, it will cause a sharp deterioration or even failure of performance. Statistics show that semiconductor lasers suddenly fail, and more than half of the chances are due to surge breakdown. Therefore, how to protect the semiconductor laser and extend the service life of the semiconductor laser is an important issue in the development of a high power semiconductor laser drive power protection circuit. Mainly should consider:

1) The laser must work within the limiting current. A safe and reliable current limiting circuit is indispensable.

2) In order to prevent the surge of the driving power supply, a strong surge absorbing circuit must be provided.

3) Since the laser is a sensitive current component, the drive current cannot be directly applied to both ends of the laser. The slow start circuit is also essential for laser protection.

2.2 Characteristics of traditional protection circuits

1) The TVS device is added to the primary and secondary sides of the isolation transformer, and its high-speed response characteristics are used to suppress excessive grid surge voltage and lightning induced voltage. This kind of measure is more effective, but it is limited by the response speed of TVS. If the response speed is not up to the requirement, the surge impact cannot be well suppressed.

2) Add a π-type low-pass filter network between the DC power supply and the laser to further filter out the surge voltage. Better performance if shielded inductors and non-inductive surge absorbers are used. This is actually passive filtering, which is effective for reducing power supply ripple and absorbing relatively small surges. But for large surges, this circuit will fail.

3) Add a slow start circuit between the DC power supply and the laser to slowly increase the voltage supplied to the laser to avoid the impact on the device when the power is suddenly turned on or off. At the same time, this can also avoid the distributed inductance caused by the circuit. Surge impact. This circuit is indispensable and practical.

4) Current limiting circuit. This type of circuit is also essential, but conventional current limiting circuits are typically single current limited.

2.3 Main features of this circuit design

1) Fully consider and absorb some excellent design ideas of traditional protection circuits, and design a soft-start circuit when the power is turned on to prevent damage to the device and the semiconductor laser from the startup surge. Because this circuit is relatively mature, this article did not elaborate.

2) A dual current limiting circuit is designed to ensure that the current through the semiconductor laser does not overcurrent.

3) Use power devices (MOS transistors) to turn on or off to force absorption or isolation of surges to prevent damage to semiconductor lasers caused by surges.

4) Establish a slow start process in the laser turn-on and turn-off operation to reduce the surge generated by the work and adversely affect the laser.