Modular Switched Mode Power Supply For Diode-Pumped Lasers
To solve various problems associated with conducting scientific research, technical measurements, processing and obtaining new materials, transferring information, etc., a large number of models of optical quantum generators (lasers) have been developed and are being produced globally [1–2]. The most effective way to create population inversion in lasers is diode pumping, for both continuous and pulsed radiation [1–4]. In modern models of lasers, diode pumping is performed using diode arrays. Various power supplies are developed by both foreign and domestic manufacturers for these purposes. Depending on the tasks for which lasers are used , power supplies differ in operating modes, technical characteristics, design and dimensions.
The greatest difficulties arise in the development of power supplies for pulsed diode-pumped lasers, which are used on moving objects in various technical devices. Such devices include, e. g., rangefinders or infrared night-vision devices installed on machines, ships or aircraft [2, 5], automated mobile complexes for laser welding in difficult conditions (inside the pipeline or ship hold, etc.) In these cases, there are significant limitations on the weight and size characteristics of the power supply and its cooling capabilities. The most accessible refrigerant, as a rule, in such conditions is only air.
However, the most widespread in the Russian market were pulse matrices produced by "Inject", which is connected both with the specifics of the tasks being solved, and with their availability and the possibility of manufacturing the customized matrices with specified characteristics. At the same time, the electrical parameters of these matrices differ significantly from their western counterparts towards a higher operating voltage, lower currents and the need to supply several matrices from one source at once (as a rule, from 3 to 9 per quantron). This makes it impossible to use ready-made western supplies without significant changes and modifications.
Until recently, to solve these problems, FEDAL offered ready-made complete solutions based on commercially available SF3XX series supplies with operating voltages up to 140–160 V and currents up to 250–3300 A. In this case, the matrices were connected in parallel through an additional current equalization board. The advantage of this solution was the simplicity and low cost of the supply in terms of the matrix and the principle: "one supply one laser". Among the shortcomings, the current spread between the matrices up to 5% can be distinguished, which did not allow them to be used at maximum modes, additional power losses on the alignment board, and a large number of wires going directly to the laser quantum.
However, a further increase in laser power, accuracy requirements for current stabilization, small front and cut-off pump pulses (no more than 15–20 µs), dimensions and weight, operating temperature range and inexpediency of further increasing the average power supply power over 5 kW required to significantly rethink approaches to data construction systems.
Therefore, in these cases it is more logical to use the sequential inclusion of diode arrays for the pumping. With this inclusion, the current in each matrix will be the same, but limited by the operating voltage, which currently is 500 V. At high voltages, the housing breakdown occurs within the matrix. In conditions of limited space in the laser design, e. g., for a range finder that is mounted on a movable carrier, it is very difficult to ensure the required insulation voltage of the matrix from the housing. At the same time, the average power of the diode array produced by "Inject" is relatively low. Therefore, 9 or more arrays are usually used for pumping in a high-power pulsed laser. Our studies have shown that the effective operation of the pumping system of the three series-connected diode arrays by "Inject" requires operating voltages from 400 to 500 V at currents from 30 to 50 A. The most appropriate solution to this problem is to develop a compact air-cooled switched mode power supply with a configuration allowing to assemble modules for pulsed lasers of different power (e. g., 100 W, 500 W, 1000 W, etc.). This circumstance will make this power supply versatile for various designs of laser systems on moving objects.
One of the variants of such a small-sized switched mode power supply is proposed by the FEDAL team in this article based on the conducted research. When interacting with manufacturers of laser systems as the final product, manufacturers of laser electronics developed the idea of applying the principle of modularity, which was first widely and successfully applied by IPG Photonics in their products.
MODULAR SWITCHED MODE POWER SUPPLY AND ITS FEATURES
The construction of laser systems according to the modularity principle implies the presence of one spent general-purpose power supply unit of medium or low power (e. g., for a power of 500 W). In this case, the required power of the finished laser system is gained due to the number of power supplies. Each general-purpose power supply is optimized for a specific range of currents and voltages, which makes its parameters more qualitative in terms of the stability of the pump current pulse, pulse front and efficiency.
Thus, when building different laser systems for different power, one general-purpose solution is sufficient, covering a large power range (the boundary values of which may differ tenfold). Such general-purpose power supplies have a serial interface, this allows you to easily and conveniently integrate them into multichannel systems. Thus, a single quantron can be pumped with a single power supply or with several supplies depending on the required power.
Also, a necessary requirement, which is caused by the operation on the principle of modularity, is the constructive implementation of this unit in the form of an OEM (embedded) solution. This allows its simple integration into laser systems.
The second necessary feature of these power supplies, due to the need of the market, is its "completeness". Unlike half-finished solutions, like drivers that manufacturers sometimes use to equip their products, the power supply unit already constructively includes a diode driver, an AC / DC converter, storage capacities and a control system. Since the power supply is designed as an OEM solution (both in the housing and in the form of open printed circuit boards), this construction simplifies the task of assembling the laser system and allows laser manufacturers to significantly reduce the dimensions of the finished product, without delving into the power supply of laser diodes and tuning drivers. As an example, the table shows the main characteristics of the already released power supply SF305M, which satisfies all the principles listed above.
As a result of study of the market of diode-pumped lasers, it was found that the Russian and foreign manufacturers of laser systems have completely different requirements for the power supply units of the diode arrays. The products of foreign companies are mainly designed for diode arrays that feed on low voltage and high currents. Therefore, for pumping these matrices, circuit solutions are used based on step-down converters operating in current stabilization mode (drivers) and ready-made commercially available AC / DC sources. The Russian manufacturers, on the contrary, consume matrices that feed on high operating voltages and lower currents. This creates conditions for domestic producers that it is impossible to use ready-made western supplies without additional significant changes and improvements.
Therefore, to solve the problem of using domestic laser arrays, a compact air-cooled switched mode power supply unit has been developed. Its design allows you to assemble power supplies for pulsed lasers of different power (100, 500, 1000 W) in a modular way.
The power supply operates with high-power lasers, has high accuracy of current stabilization, short pulse front duration (no more than 15–20 µs), low weight and size characteristics, and functions in a wide temperature range. In the future, FEDAL plans to expand the model series, releasing similar power supplies with different values of the parameters of the pump current pulses.