Published papers

Our List of Published Papers from Many Conference Presentations Over the Years.

Ideal Flyback

Date: May 10, 2021

Conference/Proceedings: PCIM Europe conference 2021

Abstract:
Two simple circuit modification which are designed to correct the main drawbacks of the Flyback topology are presented. The flyback topology it is the simplest topology used in power conversion field and as result has the largest utilization, especially in low and medium power applications. The first drawback of the flyback topology is the hard switching operation. This leads to high switching losses and also leads to large voltage spikes across the secondary rectifier, at the time when the primary switch turns on. Another drawback of the conventional flyback topology is the lack of utilization of the leakage inductance energy from the transformer which creates voltage spikes across the primary switch when the primary switch turns off. In this paper are presented two simple modification of the conventional flyback topology which converts the flyback topology in a soft switching topology, wherein the primary switch turns on at zero voltage in any operating conditions, and the energy from the leakage inductance which is not recycled in the secondary is used to discharge the parasitic capacitance across the main switch creating zero voltage switching conditions.

A Family of High Efficiency Variable Frequency Soft-Switching Off-line DC-DC Converters

Date: May 12, 2009

Conference/Proceedings: International Conference for Power Conversion, Intelligent Motion & Power Quality. PCIM Europe ‘09. Conference Proceedings 2009

Abstract:
The paper presents a family of off-line DC-DC converters for medium to high power delivering more than 95% efficiency for output levels of 12 to 48 V. The multi-layer PCB solution allows for low profile converters with multiple applications, from AC-DC adapters to TELECOM and computing. The main gain of this new design approach consist in using variable frequency topology with high frequency zero voltage switching (ZVS) and zero current switching (ZCS) for primary switchers. Theoretical considerations and practical results are presented for high frequency and high voltage soft-switching. The goal of the designs is to maintain a reasonable temperature rise of the multi-layer PCB board while delivering up to 90 W and respective 750 W power in a reduced volume and low cost.

750W High Efficiency and Soft-Switching Off-Line 12V Converter

Date: February 15, 2009

Conference/Proceedings: Applied Power Electronics Conference and Exposition, February 2009. APEC ’09. Conference Proceedings 2009, Twenty-fourth Annual

Abstract:
The paper presents an innovative off-line low profile converter design that delivers 750 W of power at 95%-96% efficiency for nominal input range, using variable frequency topology with high frequency zero voltage switching (ZVS) and zero current switching (ZCS) for primary switchers. Theoretical considerations and practical results are presented for high frequency and high voltage soft-switching. The goal of the design is to maintain a reasonable temperature rise of the multi-layer PCB board while delivering 750 W power in a reduced volume and low cost. The resulting product increases more than twice the power density compared to the standard two stages 400V to 12V power converters and outperforms other one stage solutions in a 125 x 70 mm² footprint with only a 18 mm profile.

High Efficiency Adapter Using Dual Switch PFC-Flyback Single Stage

Date: May 27, 2008

Conference/Proceedings: International Conference for Power Conversion, Intelligent Motion & Power Quality. PCIM Europe ‘08. Conference Proceedings 2008

Abstract:
The paper presents an innovative design that delivers 85W of power at more than 91% efficiency in a low profile using a high frequency quasi-resonant fly-back topology with synchronous rectification, and improved power factor based on dual switch method. A closed to 0.9 power factor is achieved employing only one magnetic element and two primary side switchers. A significant power density increase is obtained due to a combination of smaller bulk capacitor and a smaller magnetic element.

High Efficiency 100W Quasi-Resonant Multi-Phases Interleaved PFC Using Planar Magnetic Components

Date: February 23, 2008

Conference/Proceedings: Applied Power Electronics Conference and Exposition, February 2008. APEC ’08. Conference Proceedings 2008, Twenty-third Annual

Abstract:
The paper presents an innovative PFC design that delivers 100 W of power at 96%-97% efficiency for nominal input range, in low profile using a high frequency quasi-resonant interleaved boost topology, while maintaining a reasonable low cost of the ac-dc adapter. Theoretical considerations and practical results for high frequency interleaved boost converters are described. The goal of the design is maintaining a reasonable temperature rise of the case while delivering 100W power in a reduced volume. The resulting product increases more than twice the power density compared to the standard notebook universal adapters.

ZVS and ZCS High Efficiency Low Profile Adapter

Date: March 3, 2007

Conference/Proceedings: International Conference for Power Conversion, Intelligent Motion & Power Quality. PCIM China.

Abstract:
The paper presents an innovative PFC design that delivers 100 W of power at 96%-97% efficiency for nominal input range, in low profile using a high frequency quasi-resonant interleaved boost topology, while maintaining a reasonable low cost of the ac-dc adapter. Theoretical considerations and practical results for high frequency interleaved boost converters are described. The goal of the design is maintaining a reasonable temperature rise of the case while delivering 100W power in a reduced volume. The resulting product increases more than twice the power density compared to the standard notebook universal adapters.

Increasing The Efficiency In High Current And Low Voltage Application

Date: February 10, 2006

Conference/Proceedings: Delta Power Electronics Center, DPEC Seminar Proceedings

Abstract:
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

Date: September 15, 2005

Conference/Proceedings: European Center for Power Electronics e. V., ECPE ‘05. Seminar: “Power Supplies”

Abstract:
This tutorial presents 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.

Magnetic Integration Through Multiple Functions In The Magnetic Cores

Date: January 18, 2005

Conference/Proceedings: Delta Power Electronics Center, DPEC Seminar Proceedings

Abstract:
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

Date: May 20, 2003

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ‘03, Fourty-Seventh International

Abstract:
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.

Signal Transfer Through Power Magnetics

Date: September 17, 2002

Conference/Proceedings: IBM Power Technology And Qualifications, 2002 Power Technology Symposium; Theme: Future Technology

Abstract:
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

High Efficiency Flyback Converter Using Synchronous Rectification

Date: May 14, 2002

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ’02, Forty-Fifth International

Abstract:
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

Self-driven Constant Voltage Reset Circuit

Date: February 9, 2002

Conference/Proceedings: Applied Power Electronics Conference and Exposition, APEC ’03, Eighteenth Annual

Abstract:
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.

A 3kW Soft Switching DC-DC Converter

Date: June 19, 2001

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ‘01, Conference Proceedings 2001, Forty-Third International

Abstract:
This paper will present a circuit technique designed to reduce the negative impact of reverse recovery in the rectifiers for high output voltage converters. This technique works by combining reduced amplitude of the reverse recovery current and a lower voltage across the rectifier during the turn off commutation. Another major advantage of the proposed circuit is the fact that the current reflected in the primary is shaped to a triangular form with a low dI/dt during the turn on of the main switch. This will allow the completion of the resonant transition to zero voltage across the primary switchers. In the secondary section the reverse recovery current is reduced due to low dI/dt current slope at turn off and the reverse voltage is clamped to the output voltage. The maximum reverse recovery voltage does not exceed the output voltage. The soft commutation in the primary section and the secondary allows a higher frequency of operation without penalty in efficiency. A 3kW converter for on board battery charger in electric vehicles provides an output voltage between 170V to 380V. Efficiency above 96% is obtained at a switching frequency of 250 kHz while the power density of the converter exceeds 100W/inch³

Distributed Magnetics In High Power Converters

Date: May 1999

Conference/Proceedings: High Frequency Magnetic Material

Abstract:
This paper presents an actual avenue in magnetics topic, especially planar technology, related with DC-DC Power Converters. Starting from basic electric laws simple ideas could be derived and applied to practice. This leads to final interesting results that fulfill most of the initial technical requirements.

Very High Power Density Flyback Converter

Date: May 26, 1998

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ’98, Thirty-Eighth International

Abstract:
The paper states the concept of a very high power density flyback converter. Due to its less complex schematic flyback converters are recommended for power supplies providing low output power with inputs from low level DC voltages to high DC voltages (off-line SMPS). Main innovations are used: planar magnetics-PCB transformer and proprietary special packaging. As a result the parasitic are highly reduced and the almost ideal DC-DC converter, of 25 W, 12 V input to 48 V output reaches a power density of 100 W/inch³

Power Conversion Technology For Power Levels Under 3kW

Date: May 26, 1998

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ’98, Thirty-Eighth International

Abstract:
We have witnessed in the last several years a transition from a technological driven to a price driven market. The power technology development was de-emphasized unless it targeted cost reduction. Though the cost is still one of the first priorities, quality and reliability made strong headway being named number one and two priority. The paper will present several technological advances, which can offer better performance in respect of reliability and quality, at a lower total cost. Different standardization techniques will be also presented. Standardization becomes the main avenue to improve the design and product quality, the reliability, to lower NRE and to reduce time-to-market.

Small-signal Characterization Of The Forward-Flyback Converters With Active Clamp

Date: February 15, 1998

Conference/Proceedings: Applied Power Electronics Conference and Exposition, APEC ’98, Thirteenth Annual

Abstract:
Linear equivalent models of the forward-flyback converters with active clamp are deduced, using the Vorperian model of the PWM switch. Control-to-output transfer functions are plotted against frequency, for a 36-72V to 5V converter, for different load resistances, thus allowing the design of error amplifier as to ensure circuit stability. Experimental results confirm model validity.

Increasing the Utilization Of The Transformer’s Magnetic Core By Using Quasi-integrated Magnetics

Date: October 14, 1997

Conference/Proceedings: Power Conversion & Intelligent Motion, PCIM ’97, Conference Proceedings 1997

Abstract:
Several topologies leading to a better utilization of transformer’s magnetic core are investigated. To reduce the size of the output filter these topologies uses the main transformer as a storage element too. Thus a quasi-integrated magnetic is established as an intermediate step between conventional and fully integrated magnetic underlying its advantages and limitations. A quasi-integrated magnetic topology using a tap or not in the secondary side is analyzed. Two methods of eliminating the secondary winding tap will be suggested, one by using current-doubler and the second by employing two symmetrical transformers. Two 100W 5V@20A experimental converters were built and evaluated using quasi-integrated magnetic under two different implementations.

Quasi-Integrated Magnetic an Avenue For High Power density and Efficiency In Power Converters

Date: February 23, 1997

Conference/Proceedings: Applied Power Electronics Conference and Exposition, APEC ’97, Twelfth Annual

Abstract:
In order to utilize better the magnetic core of the transformer in DC-DC converters there are investigated some topologies that could fulfill this aim. The main idea is to use the transformer, usually an isolation component in a DC-DC converter, as a storage element too thus reducing the size of the choke from the filtering stage. In this way a quasi-integrated magnetic approach is set that can be seen as an intermediate step between conventional and fully integrated magnetic. Advantages and limitations are underlined. A topology using quasi-integrated magnetic was investigated with and without tap in the secondary side. As a result two methods that could eliminate the secondary winding tap are presented, one using a current doubler and the other one using two symmetrical transformers. Two experimental 100W converters providing 20A under 5V were built and evaluated using quasi-integrated magnetic approach under two different implementations.

The Impact Of Low Output Voltage Requirements On Power Converters

Date: June 20, 1995

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ’95, Thirtieth International

Abstract:
Today’s power conversion trend is to use lower output voltages. This avenue sets new challenges that must be faced. The paper presents several techniques applied in power converter circuits when using low voltage Schottky rectifiers. Also it will discuss the advantages and limitations associated with synchronized rectification. A comparison between Schottky rectifiers and synchronized rectifiers made by experimental results is presented. Further the negative impact of the leakage inductance and circuit parasitic inductance on the performance is analyzed. Special care is dedicated to the copper loss minimization in the secondary winding of the transformer and the output choke. Using circuit topologies doing this one arrives to a better copper utilization especially for low output voltage applications. The paper concludes with experimental results of Rompower’s 75W 3.3V output DC-DC converter operating from an input voltage of 36V to 60V.

High Efficiency DC-DC Converter

Date: April 17, 1994

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ’94, Twenty-Eighth International

Abstract:
The paper presents a whole family of converters using two complementary switches in the primary side and two MOSFET synchronous rectifiers in the secondary side. These devices together with the main transformer and the filtering choke are coupled in large number of topologies. Using complementary switches one can obtain soft transitions across switching elements. Also the complementary square waveforms reflected in the secondary side offers a simple and efficient driving signal command for the synchronous rectifiers. Starting from one topology from the specified range a very efficient high-density 100W power converter was built. The converter operates from an input voltage of 35Vdc to 72Vdc, providing 5V at 20A, with efficiency above 90% at full load. High efficiency combined with the use of a full-integrated multilayer PCB magnetic technology has allowed a power density of 52W/inch³

Soft Transitions Power Factor Correction Circuit

Date: June 22, 1993

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ’93, Twenty-Sixth International

Abstract:
Reverse recovery of the diode rectifier has a negative effect on power converters’ performance when operating at high frequency. Due to the low impedance across the voltage source when the diode commutes this negative effect becomes worse in non-isolated converters using buck and boost topologies. Today’s industry requests for better power diodes rectifier regarding switching speed and low conduction losses seems to touch the technology limits. Thus the paper presents circuit techniques that minimize the negative effects of silicon power rectifiers’ reverse recovery. Two “soft" switching techniques applied to buck and boost topology are presented together with experimental results in a power factor correction application.

High Frequency, Soft Transitions Converter

Date: March 07, 1993

Conference/Proceedings: Applied Power Electronics Conference and Exposition, APEC ’93, Eighth Annual

Abstract:
A high efficiency, high power density power conversion technology is presented. This topology is compatible with high output voltage applications such as 24V and 48V, where Schottky rectifiers cannot be used. The converter combines zero voltage switching across the primary switches, continuous energy transfer from the primary to the secondary and soft commutations of the output rectifiers. The soft switching of the output rectifiers minimizes the reverse recovery losses associated with ultra fast rectifiers operating at high frequency. An experimental converter using this concept is evaluated. The converter operates from an input voltage of 200V to 430V at 300 KHz, providing 400W (50V@8A) with efficiency of 95% at full load.

Constant Frequency Zero Voltage PWM Converters

Date: April 28, 1992

Conference/Proceedings: International Power Conversion & Intelligent Motion, PCIM ’92, Twenty-Fourth International

Abstract:
By utilizing a supplementary control switch, which steers the primary current back to the input source to achieve zero voltage switching conditions, a new family of ZVS-PWM converters is derived. The forward ZVS-PWM in single ended configuration is analyzed. High frequency, zero voltage switched, PWM technique is combined with continuous transfer of energy to the secondary, for double ended secondary, for double ended configuration, offering very high power density capability. Experimental results are presented for 300W converter, operating from a large input voltage range of 200V to 400V at 400 KHz switching frequency.

A New High Frequency, Zero Voltage Switched, PWM Converter

Date: February 23, 1992

Conference/Proceedings: Applied Power Electronics Conference and Exposition, APEC ’92, Seventh Annual

Abstract:
A high efficiency, high power density converter, operating at constant frequency and switching at zero voltage is presented. Zero voltage switching conditions are achieved over a broad input voltage and output current range. Continuous power transfer from the input to the output minimizes the output filter requirements and by using integrated magnetic technique, high power density can be achieved. By employing the same configuration to classical PWM topologies, a new family of ZVS-PWM converters can be derived. An experimental 5V, 100A converter was designed and built. The converter operates from an input voltage of 200Vdc to 400Vdc, at 400 KHz switching frequency.

Constant Frequency, Forward Converter With Resonant Transition

Date: June 9, 1991

Conference/Proceedings: High Frequency Power Conversion, HFPC ’91, Sixth International

Abstract:
A single ended forward converter, operating at constant frequency and switching at zero voltage is presented. By using a secondary switch, the main transformer’s core is symmetrically reset and a part of magnetizing energy is used to discharge the parasitic capacitance of the primary switch to zero. Zero voltage switching conditions are achieved over a broad input voltage and output current range. An experimental 500 KHz converter, which delivers an output power of 200W at 5V, is presented. Operating from an input voltage of 180 to 400 Vdc, the converter exhibits efficiency greater than 88% at full load.