Technology sharing: Design and development of nonlinear pulse laser power supply

1 Introduction

Although the traditional pulse laser power supply has achieved nonlinearization and replaced the old linear voltage doubler rectification technology, the overall conversion efficiency, volume, weight, charge and discharge time and other important parameters have been greatly improved. In addition, the continuous improvement of the reliability and productization of nonlinear laser power supplies have brought the application of laser technology to a new level. However, this nonlinear laser power supply still has the disadvantage that the operating frequency is always below 20kHz and cannot be further improved. This leads to the conversion efficiency, volume, weight, charge and discharge time of the traditional nonlinear laser power supply cannot be improved to the ideal state. At the same time, there is very annoying audio noise. In order to solve these problems, we have designed and successfully developed a nonlinear pulse laser power supply with an operating frequency of 100kHz.

2 Circuit composition

The principle block diagram of the pulse laser power supply is shown in Figure 1. It consists of three parts: trigger circuit, main converter circuit and high-voltage charging and discharging circuit. Its circuit principle diagram is shown in Figure 2.

Figure 2 Schematic diagram of pulse laser power supply circuit Figure 3 Working principle of the circuit

3.1 Working Principle of Trigger Circuit

As can be seen from Figure 2, the trigger circuit is mainly composed of the trigger indication circuit and the trigger circuit, which are specifically completed by the LBI and LBO terminals of IC1, V1, LED, VD1, K1 and K2. When the converter charges the capacitor through the transformer T1, diodes VD2 and VD3, the sampling circuit (composed of R10, R9, W1, W2, W3, R1) feeds back its charging voltage value to the LBI and VFB terminals of IC1. Once the voltage is charged to the required voltage value (about 1kV), the voltage value of the LBI terminal will be greater than 1.3V, the LBO terminal will become a high level, V1 will be turned on, and the LED will light up, indicating that the voltage has been charged to a state that can be triggered. In addition, the sampling circuit also sends the feedback signal to the VFB terminal of IC1. If the voltage value of the feedback signal is ≥1.3V, the converter will be turned off immediately to maintain the high voltage to the required value. The trigger device is a high-voltage, high-current automotive-grade thyristor BT151/800R.

3.2 Working Principle of Main Converter

The main converter circuit is a single-ended flyback boost circuit composed of IC1 (MAX641/642/643), transformer T1, V2 and other components. The core of the circuit is MAX641/642/643. Here we only give the technical data of the high-frequency auto-boost transformer for reference by colleagues in production. The core uses 4kBEE ferrite, and the frame uses EE19 vertical frame that matches the core. Its technical parameters are shown in Figure 3.

Figure 3 Technical parameters of T1 transformer

3.3 Working Principle of Charge and Discharge Circuit

The charging and discharging circuit is mainly composed of capacitors C7∥C10, C8∥C11, C9∥C12, C13, R14, step-up transformer T2, etc. When capacitors C7∥C10, C8∥C11, and C9∥C12 are charged to the set high voltage value, the voltage in capacitor C13 is also charged to the required voltage value (about 300V). At this time, K1 or K2 is closed, and thyristor V3 is triggered to turn on. The energy stored in capacitor C13 is discharged through the primary winding of transformer T2, causing the secondary winding to induce a high voltage of about 10kV, ionizing the gas in the laser. During ionization, the energy stored in capacitors C7∥C10, C8∥C11, and C9∥C12 maintains the ionization process for a certain period of time, thereby obtaining the required laser pulse. 4 Selection of important components and technical requirements

1) Energy storage capacitors Since the energy storage capacitors C7∥C10, C8∥C11, and C9∥C12 need to provide enough energy for the laser in a very short time, when selecting the capacitors, in addition to requiring them to have a sufficiently high withstand voltage (≥350V), they must also have the characteristics of fast charging and discharging, that is, photoflash capacitors printed with "PHOTOFLASH" should be selected.

2) Step-up transformer In addition to the primary winding of the step-up transformer supplying capacitor C13 to discharge so that the secondary voltage is increased to more than 10kV, it must also meet the requirement that after the gas is ionized, all the energy in capacitors C7∥C10, C8∥C11, and C9∥C12 is released to the laser through the secondary winding so that a strong laser beam can be stimulated. Therefore, the secondary winding must have a large number of turns and a small resistance, and at the same time meet the requirements of high voltage resistance. The transformer core uses a ring-shaped 3kB ferrite material, the primary winding is wound with a polytetrafluoroethylene silver-plated high-voltage wire of 1.0, the secondary winding is wound with a polytetrafluoroethylene silver-plated high-voltage wire of 0.32, and the core magnetic ring uses a soft magnetic ferrite with an outer diameter of 35, an inner diameter of 12, and a thickness of 10. Its technical parameters are shown in Figure 4.

Figure 4 Technical parameters of T2 step-up transformer

3) A few notes on choosing MAX641/642/643

(1) The PWM signal output by MAX641 drives V2 to output a square wave with an amplitude of 5V;

(2) The PWM signal output by MAX642 drives V2 to output a square wave with an amplitude of 12V;

(3) The PWM signal output by MAX643 drives V2 to output a square wave with an amplitude of 15V.