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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


A 3kW Soft Switching DC-DC Converter

On page(s) 427-435
Location Nuremberg, Germany
Meeting date 06/19/2001 – 06/21/2001
Conference/Proceedings International Power Conversion & Intelligent Motion, June 2001. PCIM ‘01. Conference Proceedings 2001, Forty-Third International

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


A 3kW Soft Switching DC-DC Converter

On page(s) 86-92
Location New Orleans, Louisiana, USA
Meeting date 02/06/2000 – 02/10/2000
Conference/Proceedings Applied Power Electronics Conference and Exposition, February 2000. APEC ’00. Conference Proceedings 2000, Fifteenth Annual

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

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

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


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

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.