Showing papers on "Flyback transformer published in 2003"

Single-inductor multiple-output switching converters with time-multiplexing control in discontinuous conduction mode

Abstract: An integrated single-inductor dual-output boost converter is presented. This converter adopts time-multiplexing control in providing two independent supply voltages (3.0 and 3.6 V) using only one 1-/spl mu/H off-chip inductor and a single control loop. This converter is analyzed and compared with existing counterparts in the aspects of integration, architecture, control scheme, and system stability. Implementation of the power stage, the controller, and the peripheral functional blocks is discussed. The design was fabricated with a standard 0.5-/spl mu/m CMOS n-well process. At an oscillator frequency of 1 MHz, the power conversion efficiency reaches 88.4% at a total output power of 350 mW. This topology can be extended to have multiple outputs and can be applied to buck, flyback, and other kinds of converters.

Primary-side controlled flyback power converter

Abstract: The present invention provides a primary-side flyback power converter that supplies a constant voltage output and a constant current output. To generate a well-regulated output voltage under varying load conditions, a PWM controller is included in the power converter in order to generate a PWM signal controlling a switching transistor in response to a flyback voltage sampled from a first primary winding of the power supply transformer. Several improvements are included in this present invention to overcome the disadvantages of prior-art flyback power converters. Firstly, the flyback energy of the first primary winding is used as a DC power source for the PWM controller in order to reduce power consumption. A double sample amplifier samples the flyback voltage just before the transformer current drops to zero. Moreover, an offset current is pulled from a detection input of the double sample amplifier in order to generate a more accurate DC output voltage. The offset current is generated in response to the temperature in order to compensate for temperature-induced voltage fluctuations across the output rectifier. Ultimately, in order to maintain a constant output current, the PWM controller modulates the switching frequency in response to the output voltage.

Power converter controller having event generator for detection of events and generation of digital error

Abstract: A power converter comprises an event detection module detecting various events of the power converter in real time at the switching frequency of a switch in the power converter according to predetermined criteria. A pulse generator generates control signals for controlling the on-times and off-times of the switch based on the various detected events. The events detected by the event detection module include a detection of a “knee” in the reflected secondary voltage on the auxiliary windings of the transformer in a primary side sensing flyback power converter, and detection of a digital error quantifying the difference between the reference voltage and the reflected secondary voltage on the auxiliary windings of the transformer in time domain.

Flyback power converter having a constant voltage and a constant current output under primary-side PWM control

Abstract: A primary-side flyback power converter supplies a constant voltage and a constant current output. To generate a well-regulated output voltage under varying load conditions, the power converter includes a PWM controller. The PWM controller generates a PWM signal to control a switching transistor in response to a flyback voltage detected from the first primary winding of the power supply transformer. To reduce power consumption, the flyback energy of the first primary winding is used as a DC power source for the PWM controller. The flyback voltage is sampled following a delay time to reduce interference from the inductance leakage of the transformer. To generate a more accurate DC output voltage, a bias current is pulled from the detection input to form a voltage drop across a detection resistor for compensating for the voltage drop of the output rectifying diode.

Power converter method and apparatus having high input power factor and low harmonic distortion

Abstract: The invention proposes a single stage, single switch, input-output isolated converter configuration using a hybrid combination of forward and flyback converters. The converter operates at a high input power factor with a regulated DC output voltage. It makes use of a novel control scheme utilizing duty cycle control at two discrete operating frequencies. Although the invention employs two frequencies, it does not use a continuous frequency variation. The proposed configuration has the advantage of reduced peak current stresses on the components and is specifically suited for ‘buck’ applications where low DC output voltages (e.g. 24V, 48V) are needed. The proposed configuration will be of specific interest to industries associated with battery charging and uninterruptible power supply (UPS) systems. Apart from having several competitive features compared with prior art techniques, the proposed dual frequency operation scheme reduces the amplitude of its noise spectrum by spreading it over a wider frequency range thus making it more electromagnetic compatible.

Next generation distribution transformer: to address power quality for critical loads

Abstract: A new single phase distribution transformer concept is proposed to improve power quality for critical loads. The secondary of the proposed transformer is composed of two windings, one of them equipped with a power electronic ac-ac converter. With the choice of proper turns ratio and the design of the PWM ac-ac converter, the proposed transformer has the following capabilities: (a) can compensate for 50% voltage sag and swells (b) can continuously shape the output voltage to be sinusoidal (low THD) even when the input voltage is distorted (c) can disconnect the load rapidly under fault conditions. The proposed approach does not employ any energy storage devices, such as large capacitors or inductors. The PWM ac-ac converter consists of four switching devices (IGBT) and is controlled with a four-step switching technique to achieve snubber-less operation. A design example is presented for a 480V/120V, 5 kVA transformer. Simulation results are discussed and experimental results on a 2kVA unit are presented.

Coupler between different phase lines, mounting method therefor, and coupling method between different phase lines

Abstract: PROBLEM TO BE SOLVED: To provide a coupler between different phase lines that can simply and safely be installed in order to obtain power communication between different phase lines of a single phase three-wire system. SOLUTION: In the coupler between the different phase lines, a first high frequency signal transmission transformer 21 is configured by winding a secondary coil of the first high frequency signal transmission transformer 21 spirally to a first phase power line U acting as a primary coil of the first high frequency signal transmission transformer 21 with a sheath layer of the power line U interposed therebetween. A second high frequency signal transmission transformer 22 is configured by winding a secondary coil of the second high frequency signal transmission transformer 22 spirally to a second phase power line W acting as a primary coil of the second high frequency signal transmission transformer 22 with a sheath layer of the power line W interposed therebetween. The secondary coil of the first high frequency signal transmission transformer 21 is connected in series with the secondary coil of the second high frequency signal transmission transformer 22. COPYRIGHT: (C)2005,JPO&NCIPI

Performance comparison of continuous conduction mode (CCM) and discontinuous conduction mode (DCM) flyback converters

Abstract: This paper presents performance comparison of continuous conduction mode (CCM) and discontinuous conduction mode (DCM) flyback converters The comparison is conducted through experiment on the 5 V/25 W, 50 kHz prototype CCM and DCM flyback converters, which have been designed and built with similar circuit layouts, components, and power ratings Aspects to be compared are component stress, output voltage regulation and transient response due to a step-load, and efficiency The pros and cons for each mode of operation are discussed based on the experimental results

Soft switching high efficiency flyback converter

Abstract: DC-DC converters such as flyback converters achieve self-regulation by communication information between primary and secondary circuits through the power transformer. Operating in accordance with a generalized concept or algorithm, the converter can be bi-directional and self-regulating. Control of the turn OFF times of semiconductor switches in first and second circuits coupled to first and second windings of the power transformer determines whether power flow is in one direction through the converter or the other direction. Turn ON timing of each semiconductor switch is when there is a reverse current through the switch and voltage across the switch is at or near zero. Turn OFF of a switch can be controlled from one or more operating parameters of the converter such as output voltage, in which case the converter's self-regulation is affected through duty cycle variation with variations in output voltage.

Regulation of bi-directional flyback converter

Abstract: A bi-directional flyback circuit includes a primary side switch (106) that regulates the re-circulated energy to achieve substantially zero voltage switching and a secondary-side switch (107) that regulates the output voltage. No feedback circuit between an output side and an input side of the bi-directional flyback circuit is needed for regulating the output voltage (v1).

Highly Efficient Contactless Electrical Energy Transmission System.

Abstract: This paper proposes a new concept for a contactless electrical energy transmission system for an elevator and an automated guided vehicle. The system has rechargeable batteries on the car and electrical energy is supplied at a specific place. When electric power is supplied to the car, it runs automatically and approaches the battery charger. Therefore, a comparatively large gap is needed between the primary transformer at the battery charger and the secondary transformer on the car in order to prevent damage which would be caused by a collision. In this case, a drop of the transformer coupling rate due to the large gap must be prevented. In conventional contactless electrical energy transmission technology, since electric power is received by a pick-up coil from a power line, a large-sized transformer is required. And when the distance over which the car runs is long, the copper loss of the line also increases. The developed system adopts a high frequency inverter using a soft switching method to miniaturize the transformer. The system has a coupling rate of 0.88 for a transformer gap length of 10mm and can operate at 91% efficiency.

Backlight inverter for liquid crystal display panel with self-protection function

Abstract: A backlight inverter for an LCD panel which is capable of detecting a fault in a transformer device including two transformers driven in tandem or an open-lamp condition and performing a control operation to stop its operation upon detecting the fault in the transformer device or the open-lamp condition. The inverter supplies a PWM signal through a switch in normal operation. The inverter also detects a voltage corresponding to current flowing through each lamp in a lamp device and determines from the detected voltage whether the open-lamp condition has occurred. The inverter further detects a voltage at a midpoint of secondary windings of the transformer pair in the transformer device and determines from the detected voltage whether the fault exists in the transformer device. In the event of the open-lamp condition or the fault in the transformer device, the inverter turns off the switch. Therefore, an enhanced self-protection function can be carried out in the event of a malfunction, such as the fault in the transformer device or the open-lamp condition, to more securely prevent the internal components and circuits of the inverter from being damaged due to such a malfunction.

Power measurement mechanism for a transformer coupled plasma source

Abstract: An apparatus is described. The apparatus includes a vacuum chamber and an electrical transformer to induce an electromagnetic field within the vacuum chamber. The transformer includes a primary winding, a secondary winding formed by the plasma loop, and a separate secondary winding implemented to measure the voltage along the plasma loop. The apparatus also includes a current transformer to measure the current flow through the plasma loop.

Analysis and design of the flyback transformer

Abstract: A practical design method, which is based on the current shape, is presented to achieve the appropriate parameters of the flyback transformer. Through this method, a practical transformer is achieved, and its performance is verified by a step-up flyback converter, experimental waveforms and result are presented.

X-ray generator and x-ray ct apparatus comprising same

Abstract: In an X-ray generating device of the neutral grounding system, to remove an unbalance voltage generated due to difference in impedance of parallel transformer coils of the high voltage transformer and particularly an unbalance voltage involved with difference in impedance above and below the neutral points generated in a metal X-ray tube, a plurality of currents flowing in opposite directions through primary windings of the parallel transformer coils in the high voltage transformer are passed through by or wound around a common toroidal coil or wound around an outer circumference of the toroidal coil at a predetermined ratio of winding number, and the unbalance voltage occurring to the secondary side is cancelled by changing primary current with magnetic behavior.

Current detecting circuit AC/DC flyback switching power supply

Abstract: A current detecting circuit connects to a secondary side of a transformer, including a first, second transistors and a field-effect transistor (FET). The first transistor has a base connecting with the base and emitter of the second transistor to form a common base terminal, an emitter forming a first detecting terminal and a collector forming a feedback terminal. The second transistor has a collector forming a second detecting terminal. The FET is used to replace a prior current rectifying diode. The FET has a source connecting to an output terminal of the transformer and a drain connecting to a direct current (DC) output terminal. The first, second detecting terminals and feedback terminal are connected with the source, drain and gate of the FET, respectively. Via detecting the current of the DC output terminal, the FET is timely turned on and off to release the energy stored in the transformer.

Method and apparatus for transformer bandwidth enhancement

Abstract: A method and apparatus for transformer bandwidth enhancement is disclosed. In one embodiment, a transformer is provided for use in a high frequency communication environment. In one configuration, the transformer is configured with one or more compensation networks to improve high frequency operation and to reduce insertion loss at all frequencies. The compensation networks may be designed, in combination with a transformer, to create an equivalent all-pass symmetric lattice network having a frequency response in the desired range. In one embodiment, the compensation networks comprise a capacitance creating device which, when cross-connected to the transformer, increases transformer bandwidth.

High efficiency flyback converter

Abstract: A DC-DC flyback converter that has a controlled synchronous rectifier in its secondary circuit, which is connected to the secondary winding of a main transformer. A main switch (typically a MOSFET) in the primary circuit of the converter is controlled by a first control signal that switches ON and OFF current to the primary winding of the main transformer. To prevent cross-conduction of the main switch and the synchronous rectifier, the synchronous rectifier is turned ON in dependence upon a signal derived from a secondary winding of the main transformer and is turned OFF in dependence up a signal derived from the first control signal. In one embodiment the first control signal is inverted and delivered to a logic circuit along with the voltage across the main transformer secondary winding and the voltage across the synchronous rectifier. In a further embodiment the first control signal is differentiated and supplied to a control primary winding wound on the outer flux paths of a main transformer core that has a center flux path on which is wound the main transformer primary and secondary windings. A control secondary winding is wound on the outer flux paths in current canceling relation as to flux conducted from the center flux path into the outer flux paths. The control signal for the synchronous rectifier is taken from the output of the control secondary winding in this latter embodiment.

Copper losses of flyback transformer: search for analytical expressions

Abstract: Because analytical expressions are required to run optimization software, this subject is very topical. This work uses equivalent permeability to homogenize the winding structure and approximations for the window field. A progressive approach leads to the needed expressions for a transformer built around a gapped ferrite core. At every step, analytical expressions are compared to Flux3D simulation.

Data access arrangement using a high frequency transformer for electrical isolation

Abstract: An electrical isolation barrier for use in a Data Access Arrangement uses a high frequency (HF) transformer (24) to provide isolation. An input signal (21), which may be analog or digital, is connected to a modulator (22). The analog output of the modulator (22) is connected to the input of the HF transformer (24). The output of the HF transformer (24) is connected to the input of a demodulator (26). Simple amplitude modulation can be used in the modulator (22) to modulate the input signal (21) to the frequency range of operation of the HF transliormer (24). A simple low pass filter may be incorporated in the demodulator (26) to remove harmonic distortion caused by the HF transformer (24). The output signal (27) of the demodulator (26) is substantially the same as input io signal (21).

Current controlled contact arc suppressor

Abstract: The arc suppression system for electrical contacts includes a transistor, such as an IGBT, which is connected across the contacts. A control circuit controls the operation of the transistor such that the turning on of the transistor results in a current path around the contacts, thereby tending to prevent arcing across the contacts. A current sensor, such as a flyback transformer, is positioned in series with the contacts, wherein when the contacts open, current is interrupted through the contacts and the transformer, a secondary voltage results which is applied to the transistor, which tends to maintain the transistor on for a time which is sufficient to allow the contacts to either open or close without an arc.

Design of a Circular Piezoelectric Transformer with Crescent-Shaped Input Electrodes

Abstract: In this study, a new disk-type piezoelectric transformer design is proposed. The input side of the transformer has a crescent-shaped electrode and the output side has a focused poling direction. The electrodes and poling directions on commercially available piezoelectric ceramic disks were designed so that the planar or shear mode coupling factor (kp or k15) becomes effective rather than the transverse mode coupling factor (k31). ATILA finite element code was used to analyze transformer behavior and to optimize electrode and poling configurations. The voltage step-up ratio of the proposed transformer has been markedly improved in comparison with that of the equivalent rectangular type. A single layer prototype transformer, 25.4 mm in diameter and 1.0 mm thick, operated at 92.8 kHz, was fabricated and its characteristics, such as step-up ratio and power transformation efficiency were measured. While the transformer was driving a cold cathode fluorescent lamp (CCFL), the temperature field of the transformer was also observed.

Method for testing a transformer and corresponding test device

Abstract: Testing a transformer by applying to the transformer a test signal, the frequency of which may be lower than the nominal frequency of the transformer. The voltage of the test signal may also be lower than the nominal voltage of the transformer. A number of frequency-dependent parameters are measured, particularly the eddy current resistance and the hysteresis curve of the transformer, in order to derive a simulation model which simulates the behavior of the transformer at different frequencies. Using this simulation model, it is possible to predict operating parameters of the transformer, such as the terminal voltage on the secondary and the terminal current in the secondary, during operation with a frequency deviating from the frequency of the test signal, particularly during operation with the nominal frequency of the transformer.

A high-quality rectifier based on the forward topology with secondary-side resonant reset

Abstract: The use of buck-derived topologies for unity power factor AC-to-DC applications is limited by their inherent inability to draw current from the line in those intervals, during the line half period, in which the input voltage is lower than the output one. This drawback is overcome in the proposed high-quality rectifier based on the forward topology with secondary-side resonant reset. The employed secondary side reset capacitor is able to provide proper transformer reset by recycling the transformer stored energy to the load and, at the same time, it allows to draw energy from the line even when the input voltage is lower than the output one. Consequently, besides a better utilization of the transformer core (bipolar core excitation), a low distorted input current waveform can be obtained with a power factor close to unity. Experimental results of a 200 W prototype confirm the theoretical expectations.

Design and experimental results of an input-current-shaper based electronic ballast

Abstract: This paper presents some design issues and experimental results regarding the use of the input current shaper (ICS) technique to implement high power factor electronic ballasts. The ICS is placed between main rectifier and bulk capacitor to increase the conduction angle of the main rectifier diodes up to a minimum value to obtain low current harmonics injected to the mains. Two possibilities to implement ICS-based ballast are considered in this paper: the forward-based ICS and the flyback-based ICS. Experimental results obtained from two 40-W fluorescent lamp ballasts are also presented.

Synchronous rectifyier controlled by a current transformer

Abstract: A power converter with synchronous rectifying through the control of a current transformer is disclosed. The basic architecture of the power converter includes a flyback transformer ( 10 ), a switch controller ( 20 ) and a current transformer ( 30 ). The secondary winding of the flyback transformer ( 10 ) is connected to the primary winding of the current transformer ( 30 ) used to control the switch controller ( 20 ). The primary winding of the current transformer ( 30 ) is connected to a synchronous rectifying switch (Q 7 ). If a current change occurs on the secondary winding of the flyback transformer ( 10 ), the current transformer ( 30 ) detects the phase change and enables the switch controller ( 20 ) to switch off the synchronous rectifying switch (Q 7 ). The current transformer ( 30 ) turns off the synchronous rectifying switch (Q 7 ) anticipatorily in the continuous current output mode to prevent any power loss from crossovers.

Ac-dc power converter having high input power factor and low harmonic distortion

Abstract: The invention proposes a single stage, single switch, input-output isolated converter configuration using a hybrid combination of forward and flyback converters. The converter operates at a high input power factor with a regulated DC output voltage. It makes use of a novel control scheme utilizing duty cycle control at two discrete operating frequencies. Although the invention employs two frequencies, it does not use a continuous frequency variation. The proposed configuration has the advantage of reduced peak current stresses on the components and is specifically suited for “ buck” applications where low DC output voltages (e.g. 24V, 48V) are needed. The proposed configuration will be of specific interest to industries associated with battery charging and uninterruptible power supply (UPS) systems. A part from having several competitive features compared with prior art techniques, the proposed dual frequency operation scheme reduces the amplitude of its noise spectrum by spreading it over a wider frequency range thus making it more electromagnetic compatible.

Soft switching converter using current shaping

Abstract: A converter (40) topology that eliminates reverse recovery losses in its output rectifying semiconductor devices (Sr1, Sr2) employs an AC injection voltage source (Vinj) in series with a power transformer primary winding (16). Input semiconductor switches (M1, M4) in the converter's primary circuit are controlled to provide in the power transformer secondary a voltage across the winding or windings in a first direction forward biasing one of the output rectifying devices followed by a lower level reverse biasing voltage produced by the injection voltage. This lower level voltage across the secondary turns off the previously conducting rectifier device and drives carriers out of its semiconductor junction or junctions to eliminate reverse recovery losses occurring when the secondary applies a higher level reverse bias across the non-conducting rectifier device. The injection voltage source can be a transformer (20) in addition to the power transformer having a primary winding (23) in series with the primary winding of the power transformer and a secondary winding (24) connected to ground through a capacitor (22). In addition to preventing reverse recovery losses in the rectifying devices in the secondary, the injection voltage transformer also injects an AC triangular waveform current (Vinj) into the current in the converter primary input circuit to the junction of the semiconductor switches where they are connected in a bridge circuit supplying the power transformer primary. By this, the injection voltage source assures zero voltage switching of the semiconductor switches even at light loads.

Power converter employing a planar transformer

Abstract: A power converter may employ a planar transformer to minimize winding conduction loss, and the switching devices of the power converter may be aligned in lines parallel to an edge of the planar transformer to minimize the termination leakage inductance. The windings of the planar transformer may be thermally conductively coupled to one or more heat sinks carried by a circuit board which are with respective ones of the switching devices, to provide a cooling path for the planar transformer.

High Frequency Model of Transformer Winding

Abstract: A high frequency model of transformer winding is used to analyze the voltage oscillations due to various excitations such as the very fast transient overvoltage which occurs at the time of disconnecting switch operations. Usually, a circuit of interlinked inductances and capacitances is used for this purpose, in which circuit parameters have to be properly determined. Previously, those constants have been estimated taking the coil section pair as a unit. In the method proposed here, the section pair can be further subdivided. The time-domain calculation is conducted combining the frequency analysis and FFT technique. The voltage oscillations of the winding subjected to the lightning impulse are calculated. The correspondence with the experimental results is satisfactory. The response to a chopped impulse shows this method's applicability to high frequency analysis. Since the constants are calculated directly from the design parameters of transformer winding, this technique is particularly useful in developing and designing transformers. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 8–16, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10280