Spie Press Book • newPowering Laser Diode Systems
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Table of Contents
- 1 Introduction
- 1.1 Photonics Revolution and Power Electronics
- 1.2 Audience
- 1.3 Equation Derivation, Numerical Calculations, and Units
- 1.4 Schematic Plotting and Circuit Computer Simulation
- 1.5 Power-Supply Development
- 2 Power-Electronics Design Rules to Save Time and Avoid Frustration
- 2.1 Start with a Clearly Written Technical Specification
- 2.2 Attentively Study the Characteristics of the Load
- 2.3 Choose the PS Topology Carefully
- 2.4 Choose a Topology that Efficiently Uses the Parasitic Elements of the Circuit Components
- 2.5 Use MathCad for Circuit Calculation and Mathematical Modeling
- 2.6 Perform a Computer Simulation of the Power-Electronics Circuits
- 2.7 Verify the Correctness of the Component Kit and the Soldering Quality
- 2.8 Test Offline Power Sources Carefully
- 2.9 Offline Devices Not Connected to the AC Mains Do Not Work
- 2.10 Skillful Measurements Obtain the Required Results
- 2.11 LD-Driver Design Priorities
- 3 Similarities and Differences between LDs and LEDs
- 4 Laser Diodes: Electrical Loads and Driving Requirements
- 4.1 Electrical Load Types
- 4.2 Characteristics of Laser Diodes
- 4.3 Aging and Temperature Effects on LDs
- 4.4 Ideal and Real Sources of Electrical Energy
- 4.5 Requirements for LD Powering
- 5 Primary and Secondary Sources of Electrical Energy
- 5.1 Primary Sources of Electrical Energy
- 5.1.1 Electrical batteries
- 5.1.2 Electrical-energy generation and distribution
- 5.2 Secondary Sources of Electrical Energy
- 5.2.1 Active secondary converters
- 5.3 Passive Voltage-to-Current Converters
- 5.4 Passive Linear DC VtoI Converter with a Ballasting Resistor
- 5.5 Passive Sinusoidal AC VtoI Converter with a Ballasting Inductor
- 5.6 Passive Sinusoidal AC VtoI Converter with a Ballasting Capacitor
- 5.7 Capacitors and Inductors in Laser Systems
- 6 High-Frequency Switch-Mode Passive DC-to-DC Converters in LD Systems
- 6.1 Passive Converter with a Ballasting Inductor and Capacitive Output
- 6.2 Converter Circuit Description and Calculation
- 6.3 Conduction Losses and Optimization in VtoV Converters
- 6.4 Switching Losses in Converters with Pulse-Width Modulation
- 6.5 Resonant and Quasi-resonant Converters
- 6.6 Reducing Switching Losses in HF VtoV Converters
- 6.7 Utilizing Converter Parasitic Elements
- 6.8 Transformer in a HF Converter
- 7 High-Frequency Switch-Mode LD Driver Topology
- 7.1 Calculating the Filter Inductor
- 8 Powering Medium-Power LD Systems
- 8.1 Powering a LDD with a Battery
- 8.2 Powering a LDD with a One-Phase AC Line
- 8.3 One-Phase Compound Converter as a LDD
- 9 Powering High-Power LD Systems
- 9.1 Three-Phase AC Line
- 9.2 LD Bars and Stacks
- 9.3 Powering Multiple LD Strings from a Single Inverter
- 9.4 Powering RGB Lasers in Movie Projection Systems
- 9.5 Programmable LED Color-Lighting Systems
- 9.6 Powerful Modular DC-Voltage Source
- 10 LD Drivers Based on Other Topologies
- 10.1 Buck Converter as a LDD
- 10.2 Active Linear DC VtoI Converter
- 11 Passive Switch-Mode Voltage-to-Power Converters in Laser Systems
- 11.1 Passive VtoP Converter as a LDD
- 11.2 Passive VtoP Converter as a Capacitor Charger
- 12 Powering Other Components of LD Systems
- 12.1 Thermoelectric Cooler
- 12.2 High-Voltage Power Supply with a Pockels Cell
- Appendix: LTspice Circuit-Simulation Examples
- A.1 VtoV Converter Circuit
- A.2 VtoI Converter Circuit and Load-Curve Plotting
- A.3 VtoP Converter Circuit
- A.4 VtoP Converter as a Capacitor Charger Circuit
In February 2015, SPIE Press offered Dr. Ilya Bystryak and me the opportunity to write a book based on our professional development course "Powering and Integration of Laser Diode Systems," presented by both of us at the Photonics West conference. The course material was the result of our lengthy collaboration, initially in the Soviet Union, where we worked for the same research laboratory for an extended period of time, and later in the U.S.
Professional collaboration and the sharing of ideas are important factors of our successful careers in the field of power electronics. Such communication multiplies the engineering effectiveness of each other. The best-known examples of similar fruitful cooperation are the joint work of Steve Jobs and Steve Wozniak, Larry Page and Sergey Brin, and Bill Gates and Paul Allen. Constant, critical face-to-face or telephonic discussions around ongoing projects and emerging problems enables the fast and efficient resolution of these challenges. This form of cooperation is rarely achieved by project formal discussions at scheduled company meetings, design reviews, etc. Therefore, I recommend to my young colleagues to find a partner and a formidable opponent to cooperate with and to maintain this kind of professional relationship throughout their career.
Because the book is based on an instructional course, I decided to present it to a certain extent as a textbook; however, because strict technicalities are often not very useful and boring to read, the material is not written in the traditional textbook style. This Tutorial Text discusses the competent design and skilled use of laser diode drivers (LDDs) and power supplies (PSs) for the electrical components of laser diode systems. It is intended to help power-electronics design engineers during the initial design stages: the choice of the best PS topology, the calculation of parameters and components of the PS circuit, and the computer simulation of the circuit. Readers who use laser diode systems for research, production, and other purposes will also benefit. The book will help readers avoid errors when creating laser systems from ready-made blocks, as well as understand the nature of the "mystical failures" of laser diodes (and possibly prevent them).
The following questions guided the compilation of this book:
- What is the basis of choosing one or another technical solution?
- Which converter topologies are better suited than others for powering certain LD system parts?
- Why should soft-switching topologies be used when developing switch-mode PSs?
- Why must one contend with the parasitic elements of the circuit components in some topologies, whereas other topologies can use parasitic elements beneficially?
- How does the choice of topology influence LD and LDD reliability?
- How can the right topology protect against overload and avoid the premature death of the LD (which usually costs more than the LDD)?
- Which topologies generate less electromagnetic interference (EMI) noise and therefore require fewer measures of protection against penetration EMI in the AC mains and the environment?
I tried not to overload the book with complex mathematical formulas. In my experience, most converter calculations are straightforward, and well-known mathematical formulations of the electrical circuit laws are sufficient. Excessive math does not promote but rather hinders understanding the essence of things.
The electrical characteristics of laser diodes and the specifics of the sources for their powering are discussed herein. It has been shown that laser diodes require electrical sources with the characteristic of either a constant current or a constant power source. Because the primary sources of electrical energy are voltage sources, the methods of converting voltage sources into a constant current or a constant power source are the main subject of the book.
Detailed attention is paid to the passive methods of conversion (Chapter 5). Passive conversion of the voltage to the current has several advantages when designing LDDs:
- Because there is no need for a feedback loop in passive converters, their circuits are less complicated than those of active converters.
- An inherent current limit prevents an overcurrent that could destroy the laser diode.
- It is simple to create powerful sources with the direct parallel connection of conversion modules.
- Multiple laser diode strings can be driven by a single converter.
- Pulse modulation of the laser diode current in the pulsed laser system is simple.
Modern power supplies are based on switching converters. The main problems that afflict these converters are switching losses and EMI noise generation, which can be eliminated or reduced by soft-switching. Soft-switching is the hallmark of professional PS design, so Chapter 6 addresses the design of quasi-resonant circuits and the calculation of lossless snubbers, which allows one to organize soft-switching.
Another problem facing power electronics designer involves the parasitic elements of the converter circuit. Section 6.7 demonstrates the proper topology that derive a benefit from parasitic elements instead of fighting them.
The initial stages of PS design are reflected in the book via examples. MathCad is used for calculations, and LTspice is used for electrical schematic plots and the computer simulations. In some complex cases, the purely mathematical calculation of circuits is impossible, so a combination of calculation and simulation is necessary.
Readers should understand the basic concepts and definitions used in power electronics. Sufficient context is provided to explain the topics at hand, but other publications should be consulted for an overview of laser-diode power design. Furthermore, some common design issues are not covered here, e.g., the design of synchronous rectifiers in PSs with a low voltage output, EMI filters, gate drivers for MOSFETs, and how to protect PSs from instabilities in the AC line. A list of references is provided for further reading regarding these matters.
Grigoriy A. Trestman