| back to top2008-2009 Power Seminars |
BLDC Ripple Torque Reduction via Modified Sinusoidal PWM
A brushless direct current (BLDC) fan motor driver system using sinusoidal PWM (SPWM) is introduced. The driver board is assembled in the motor to minimize the system size. Based on the signal from the hall position sensor on the board, the controller generates the SPWM input for the power module to drive the BLDC motor. Because it is a sinusoidal PWM instead of a square PWM, both vibration and noise are lower. Experimental results are presented to verify the stability of the driver system.
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Board Level Evaluation of Power Quad Flat No-Lead (PQFN) Packages
Evaluations in surface mount board assembly are conducted for two advanced packages, the PQFN3x3 and PQFN5x6. These packages offer very low inductance for better circuit performance. This paper will provide practical guidance about PCB mounting and thermal management. It will evaluate processes such as stencil printing, component placement and reflow. Stencil design has shown to be the most critical. In the reflow process, exposure to temperature above its rating will result in reliability risks. Because of this risk, the thermocouple location must be considered in temperature profiling. Temperature cycle test, drop test, vibration and bending tests are conducted to determine reliability of the assembly process. Thermal simulation is conducted using ANSYS® software, showing the effect if voids are present in the solder between the package terminals and the land pad. Finally, recommendations are presented to ensure successful assembly.
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Design Considerations for Asymmetric Half-Bridge Converters
Among various kinds of soft-switching converters, the asymmetric PWM half-bridge converter has drawn considerable attention due to its simplicity, inherent zero voltage switching (ZVS) capability and fixed-frequency operation. This paper presents an analysis and reviews practical design considerations for the asymmetric half-bridge converter. It includes designing the transformer and selecting the components. The step-by-step design procedure explained with a design example will help engineers design the asymmetric half bridge converter.
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Designing Auxiliary Power Supplies for High Efficiency and Low Standby Power
Auxiliary power supplies are required to have low standby power consumption at light load conditions. These power supplies also offer desirable features such as low cost, high efficiency and a Line Under Voltage Lockout (UVLO) function to detect the input voltage so the main power supply will not have to operate at low input voltage ranges. Fairchild’s FSQ510 has been specifically designed for low power consumption and valley switching control and is ideal for auxiliary power supplies. This paper will outline a design procedure for an auxiliary power supply using the FSQ510.
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From Powder to Transformers
The design of the main transformer is a critical part of designing a switch mode power supply. Understanding the process of making cores from powder into a final core shape, and understanding the effects of parameters like core loss, permeability and flux density, designers are better able to choose the right material to achieve the smallest size with lowest losses and reduced cost. With the additional understanding of AC losses and layer arrangements, designers can also optimize the windings to create a solid magnetic design with small size and high efficiency.
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Understanding Interleaved Boundary Conduction Mode PFC Converters
Boundary conduction mode power factor converters are widely used in lower power off-line power supplies. Their application at higher power levels is less practical due to the high amplitude of the inductor ripple current that puts a burden on the EMI filter and can be a significant source of power dissipation in the boost inductor and power switch of the converter. Interleaving two of these boundary conduction mode converters mitigates the input filter problem and to a certain extent the issue of high RMS currents of the semiconductor devices. Interleaved BCM PFC circuits are becoming popular in the industry. This paper analyzes the advantages of such a solution, highlights critical design issues related to power factor correction in general, and addresses the specific requirements and potential solutions to control an interleaved boundary conduction mode power factor converter.
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Using MOSFET Selection to Minimize Losses in Low-Output-Voltage DC-DC Converters
The role of the Power MOSFET in achieving high efficiency converter design is the focus of this paper. It gives a brief overview of current low voltage MOSFET trench technologies, along with a discussion of on resistance versus gate charge tradeoffs for MOSFETs optimized for use as either control or synchronous switches. It also covers the importance of the integrated Schottky diode (SyncFET™) in synchronous rectification, and the necessity of packaging technologies with low parasitic inductance and resistance.
The MOSFET-to-circuit interaction will be discussed in detail with the aid of TCAD mixed-mode simulations. All relevant MOSFET switching events will be analyzed: common source inductance versus drain current rise and fall, body diode conduction and reverse recovery, external Schottky diode layout challenges versus SyncFET™ advantages, and elimination of shoot-through currents from gate bounce. The simulation of these MOSFET power losses is compared for different amounts of circuit inductance and used as background for discussing measured converter efficiency data. A review of popular MOSFET loss equations is also included.
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| back to topPower Supplies |
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Application Review and Comparative Evaluation of Low-Side MOSFET Drivers (2007)
Power MOSFETs require a gate drive circuit to translate the on/off signals from an analog or digital controller into the power signals necessary to control the MOSFET. This topic provides details of MOSFET switching action in applications with clamped inductive load, when used as a synchronous rectifier, and driving pulse/gate drive transformers. Potential driver solutions including discrete and integrated driver designs are discussed. MOSFET driver datasheet current ratings are examined and circuits are presented to assist users in evaluating the performance of drivers on the lab bench.
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Applying Power MOSFETs in an Unclamped Inductive Switching Environment (2006)
• What is Unclamped Inductive Switching and why is it important to the designer?
• Terminology and definitions
• Understanding the UIS failure mechanism within a power MOSFET
• Determining the UIS capability of a power MOSFET
• Understanding and interpreting the Fairchild single pulse UIS data sheet graph
• Design Example #1 -- Choosing the correct power MOSFET for a single pulse UIS condition
• Design Example #2 -- Choosing the correct power MOSFET for a repetitive pulse UIS condition
• Conclusions
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Design Consideration of LLC Resonant Converter (2007)
Recently the, LLC resonant converter has drawn a lot of attention due to its advantages over the conventional series resonant converter and parallel resonant converter; narrow frequency variation over wide load and input variation and Zero Voltage Switching (ZVS) of the switches for entire load range. This topic will discuss the analysis and practical design considerations of a LLC-type resonant converter. Included in this discussion will be the design of a transformer and the selection of components, a step-by-step design procedure, and a design example that will help engineers design the LLC resonant converter easily.
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Design Review: Power Stage Design for a 200W Off-Line Power Supply (2007)
New AC power supply designs in the range of 200W - 500W increasingly require power factor correction (PFC) which reduces the energy wasted in the power utility supply lines and increases the maximum power which can be drawn from a power outlet. This paper describes the design of a two switch forward power supply with a continuous PFC front end based on the FAN4800. Design options for such a power supply are reviewed. Practical topics including layout, EMI, magnetic design are discussed with the aim of helping practicing engineers to accelerate and improve their designs.
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Low Cost, Isolated Current Source for LED Strings (2007)
Learn "how to" design an isolated constant current source to drive high power LED’s from an AC power line. The constant current source is built using a flyback topology and has an efficiency greater than 80%. Conventional current sources need many components for this. This application is a low-cost solution based on an innovative circuit (patent filed) using a Fairchild Power Switch (FPS). The converter is a primary side regulated removing the need for an optocoupler and other additional components.
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Practical Power Application Issues for High Power Systems (2006)
Choosing the right products for high power systems is a critical challenge. This presentation will introduce new products for the system design of a power supply and frequency inverters that offer better reliability, higher efficiency and a reduction of board space.
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Practical Power Application Issues for Switch-Mode Power Supplies (2006)
• EMI Reduction Techniques for Power Supplies: layout, input filter resonance, measuring common mode and differential mode noise separately, comparison of SEPIC and buck converters
• Stability of synchronous buck converters: how to design the compensation network
• What non-magnetics designers need to know about transformers: understanding transformer and core datasheets, what it takes to design a transformer yourself, how to specify a transformer so that you get what you want
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Tips and Tricks to get More out of your SPICE Simulations (2007)
Circuit simulation tools are useful supplements to breadboarding for gaining fast and detailed design insight. A collection of simulation tips and tricks used by Fairchild’s Global Power Resource support group is presented. Interactive on-line design simulation tools and device models for off-line solutions are available on the Fairchild website.
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Understanding Diode Reverse Recovery and Its Effect on Switching Losses (2007)
Half-bridge structures are extensively used in power electronics applications: lighting, power supplies, UPS and motor drives. When these half-bridge circuits are hard switched, the low side diode reverse recovery affects system performance. This topic reviews the principle of diode reverse recovery and how this affects the semiconductor switch performance. Practical tests showing how di/dt and temperature affect performance are presented. Finally measurements using different devices are compared showing the curves for fast and soft recovery diodes, showing that in some cases, efficiency can be improved by adding capacitance in parallel with the diode.
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Understanding Modern Power MOSFETs (2006)
Driven by new energy efficiency regulations, system designers are increasingly adopting synchronous buck controllers and half-bridge structures. This presents them with the new challenge of designing with power MOSFETs. This presentation provides a basic understanding of MOSFETs with more detailed explanation of synchronous buck and half-bridge structures.
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