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ZVS and ZCS High Efficiency Low Profile Adapter

The paper presents an innovative design that delivers 65W of power at more than 91% efficiency in a footprint of a business card using a high frequency quasi-resonant fly-back topology with synchronous rectification, while maintaining a reasonable low cost of the AC/DC adapter. Topology and techniques for obtaining ZVS and ZCS for high frequency and high voltage switching are described. The goal of the design is maintaining a reasonable temperature rise of the case while delivering 65W power in a reduced volume. The resulting product increases more than twice the power density compared to the standard notebook adapters.


Increasing The Efficiency In High Current And Low Voltage Application

The paper will present a converter design targeted to push the performance in respect of efficiency and power density while reducing the cost. The innovation will come from the topology, magnetic structure, drive circuit and the control method. It will present a group of innovation which together lead to a design with outstanding performance.These technologies will be implemented in a 12V output voltage bus converter for HP , delivering 450W with limited airflow.


Magnetic Integration For High Density And High Efficiency Applications

The tutorial will present a comprehensive overview of the integrated and quasi-integrated magnetic concepts and implementations. In the quest for higher power densities and higher efficiency integrated magnetic structures have become more popular. There will be presented many forms of integrated magnetic in close correlation with converter topologies. Included are several structures wherein the transformer and the storage elements are placed on the same magnetic core, forming the traditional integrated magnetic with emphasis on the latest trends. In addition to this will be presented structures wherein two independent power trains are placed on the same standard magnetic core and structures wherein the main transformer and a signal transformer are sharing the same magnetic core without interference. The focus for the integrated magnetic will be for low profile and or planar magnetic structures. Ripple steering in new applications will also be presented. There will be presented the advantages of different forms of magnetic integration in very high current and low voltage application. The seminar will also show present and future trends in magnetic integration and new forms of planar magnetic.


Increasing The Efficiency In High Current And Low Voltage Application

The continuous quest for lower voltage and higher current has created some challenges for the power designers especially if the high efficiency and high power density is pursued. This paper will underline the challenges associated with very low voltage and high current application. It will focus mostly on the reduction of effective duty cycle due to the leakage and stray inductance. It will present a magnetic structure which actually minimizes not only the leakage inductance but also the stray inductance which plays a crucial role in this application. In addition to that the magnetic structure reduces by a factor of two the footprint of the magnetic core, using a special layout structure which leads to cancellation of the magnetic filed created by the flowing current outside of the transformer the stray inductance is practically eliminated. These concepts were implemented in a 1.2V @100A quarter brick isolated DC-DC Converter which has an efficiency 2% higher than the competition at full load and reached 90% for 1.2V @ 60A, higher than many VRMs.


Magnetic Integration Through Multiple Functions In The Magnetic Cores

The paper presents a method of employing a magnetic core for multiple functions. For some magnetic cores shapes such EE and EI, we can implement two independent functions. These functions can be two independent power processing, can be a signal processing and power processing, or can be a power transfer and energy storage. In the continuous quest for miniaturization and cost reduction, these technologies offer a significant advantage. Several example of such implementation in high density DC-DC Converters will be presented.


Constant Voltage Reset Circuit

This paper presents a reset mechanism, which combines the advantages of the active clamp reset and the traditional third wire reset technique. In this concept the reset voltage is constant similar to the third wire reset, wherein a constant voltage is applied to the transformer during the reset cycle. The technology has several key advantages from the active clamp reset mechanism. The energy contained in the leakage and magnetizing inductance is recycled, and the voltage across the main switch is clamped. In addition to this, the flux through the transformer is symmetrical to zero and the duty cycle can be higher than 50%, similar to the active clamp circuit. Though this circuit contains most of the active clamp circuit’s key features it does not exhibit its limitations. One of the drawbacks of the active clamp circuit is its behavior during transients wherein the duty cycle changes. During transients, until the reset capacitor charges to its optimum level, the voltage across the switch may reach uncontrollable levels. In this reset technique the voltage across the switch is constant regardless of the duty cycle and reacts to transients without any limitations. In addition to this the implementation is very simple; it does not require any additional driving and timing circuits for the reset switch. The reset switch is driven directly form the transformer by a driving winding and the reset voltage can be easily adjusted by a resistor divider. Using this technology a DC-DC converter was implemented, providing 1.2 V @ 20A, from an input voltage range of 36 V to 60 reaching an efficiency of 86% at full load. Another application of this technology in a 1/8 brick DC-DC Converter is also presented.


Self-driven Constant Voltage Reset Circuit

This paper presents a reset mechanism, which combines the advantages of the active clamp reset and the traditional third wire reset technique. In this concept the reset voltage is constant similar to the third wire reset, wherein a constant voltage is applied to the transformer during the reset cycle. The technology has several key advantages from the active clamp reset mechanism. The energy contained in the leakage and magnetizing inductance is recycled, and the voltage across the main switch is clamped. In addition to this, the flux trough the transformer is symmetrical to zero and the duty cycle can be higher than 50%, similar to the active clamp circuit. Though this circuit contains most of the active clamp circuit’ key features it does not exhibit its limitations. One of the drawbacks of the active clamp circuit is its behavior during transients wherein the duty cycle changes. During transients, until the reset capacitor charges to its optimum level, the voltage across the switch may reach uncontrollable levels. In this reset technique the voltage across the switch is constant regardless of the duty cycle and reacts to transients without any limitations. In addition to this the implementation is very simple; it does not require any additional driving and timing circuits for the reset switch. The reset switch is driven directly form the transformer by a driving winding and the reset voltage can be easily adjusted by a resistor divider. Using this technology a DC-DC converter was implemented, providing 1.2 V @ 20A, from an input voltage range of 36 V to 60 reaching an efficiency of 86% at full load.


High Efficiency Flyback Converter Using Synchronous Rectification

This paper presents a method of driving a synchronous rectifier in a flyback topology. For optimum driving of the synchronous rectifier in a flyback converter, the primary side gate signal has to be transferred to the secondary with minimum delay. This paper presents a method of signal transfer through a power transformer without interference with the main power train. In this concept, the main transformer of the flyback converter is used to store and transfer energy to the secondary and, at the same time, to transfer the gate signal from the primary side to the secondary side with minimum delay. Both the power winding and the signal transfer winding are incorporated in a multilayer PCB, reducing the labor cost. Incorporating the signal winding and the power winding on the same magnetic core decreases the cost and increases the power density, which is a very important feature for the latest generation of DC-DC power converters. This technology is implemented in a 15 W 3.3 V@ 4.5A DC-DC converter, with an efficiency reaching 90% at full load. The power density of the converter reaches 40 W/inch3


High Efficiency Flyback Converter Using Synchronous Rectification

This paper presents a method of driving a synchronous rectifier in a flyback topology. For optimum driving of the synchronous rectifier in a flyback converter, the primary side gate signal has to be transferred to the secondary with minimum delay. This paper presents a method of signal transfer through a power transformer without interference with the main power train. In this concept, the main transformer of the flyback converter is used to store and transfer energy to the secondary and, at the same time, to transfer the gate signal from the primary side to the secondary side with minimum delay. Both the power winding and the signal transfer winding are incorporated in a multilayer PCB, reducing the labor cost. Incorporating the signal winding and the power winding on the same magnetic core decreases the cost and increases the power density, which is a very important feature for the latest generation of DC-DC power converters. This technology is implemented in a 15 W 3.3 V@ 4.5A DC-DC converter, with an efficiency reaching 90% at full load. The power density of the converter reaches 40 W/inch3


Signal Transfer Through Power Magnetics

This paper presents a method of signal transfer through a power magnetic without interference with the main power train. There will be described two implementations of this concept. In the first application the concept is applied in a 15W DC-DC Converter using flyback topology. The main transformer of the flyback converter is used to store and transfer energy to the secondary and at the same time to transfer the gate signal from the primary side to the secondary side with minimum delay. Incorporating the signal winding and the power winding on the same magnetic core decrease the cost and increases the power density, which is a very important feature for the latest generation of DC-DC Converters. In the second application of this technology is implemented in a quarter brick DC-DC Converter, using a half bridge topology. In this implementation the gate signal for the primary switchers is transferred from the secondary to the primary side through the output chokes. The output chokes are used to store energy and in the same time to transfer signal from the secondary to the primary. The technology is implemented in a DC-DC Converter 132W, 3.3V @ 40A DC-DC Converter, with an efficiency of 91.5% at full load and reaching a power density of 146W/inch3