Showing papers on "Flyback transformer published in 2001"

A topology survey of single-stage power factor corrector with a boost type input-current-shaper

Abstract: A topological review of the single stage power factor corrected (PFC) rectifiers is presented in this paper. Most reported single-stage PFC rectifiers cascade a boost-type converter with a forward or a flyback DC-DC converter so that input current shaping, isolation, and fast output voltage regulation are performed in one single stage. The cost and performance of single-stage PFC converters depend greatly on how its input current shaper (ICS) and the DC-DC converter are integrated together. For the cascade connected single-stage PFC rectifiers, the energy storage capacitor is found in either series or parallel path of energy flow. The second group appears to represent the main stream. Therefore, the focus of this paper is on the second group. It is found that many of these topologies can be implemented by combining a two-terminal or three-terminal boost ICS cell with DC-DC converter along with an energy storage capacitor in between. A general rule is observed that translates a three-terminal ICS cell to a two-terminal ICS cell using an additional winding from the transformer and vice verse. According to the translation rule, many of the reported single-stage PFC topologies can be viewed as electrically equivalent to one another. Several new PFC converters were derived from some existing topologies using the translation rule.

Dc-to-dc converter

Abstract: A transformer has a primary winding connected between a pair of dc input terminals via an on-off switch, and a secondary winding connected between a pair of dc output terminals via a rectifying and smoothing circuit The output voltage applied from the rectifying and smoothing circuit to the load is held constant by switching the input voltage through feedback control The switch is driven in either of two different prescribed modes depending upon whether the converter is under normal or light load In order to ascertain the load magnitude a flyback period determination circuit is connected to a tertiary winding of the transformer for providing a signal indicative of a flyback period during which a flyback voltage exists across the transformer tertiary after the switch is turned off each time Each flyback period is compared with two different reference periods of time for hysteretic determination of whether the converter is under normal or light load Several other embodiments are disclosed

A zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation

Abstract: A new primary-side-assisted zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation is proposed. The proposed DC-DC converter uses only one auxiliary transformer and two diodes to obtain ZCS for the leading leg. It has a simple and robust structure, and load current control capability even in short circuit conditions, The possibility of magnetic saturation due to asymmetricity of circuits or transient phenomena is greatly reduced, which is a very attractive feature in DC-DC converters with transformer isolation. The power rating of the auxiliary transformer is about 10% of that of the main transformer. Operation of a 12 kW prototype designed for welding application was verified by experiments.

A new low-stress buck-boost converter for universal-input PPC applications

Abstract: In converters for power-factor-correction (PFC), universal-input capability (ability to operate from any AC line voltage, world-wide) comes with a heavy price in terms of component stresses and losses, size of components, and restrictions on the output DC voltage. A new two-switch topology is proposed to offer very significant performance improvements over the single-switch buck-boost converters (including flyback, SEPIC, and Cuk topologies) and conventional two-switch buck-boost cascaded converters. The proposed converter has buck-boost conversion characteristic, switch conduction losses comparable to the boost converter, no inrush current problem, and potential for smaller inductor size compared to the boost converter.

A low-profile power converter using printed-circuit board (PCB) power transformer with ferrite polymer composite

Abstract: A new design of low-cost and low-profile power transformer is presented in this paper. The manufacturing cost of a power transformer can be reduced using the proposed printed-circuit board (PCB) transformer. The transformer windings are etched on the opposite sides of a double-sided PCB. Self-adhesive ferrite polymer composite (FPC) sheets are stuck on the two PCB surfaces to shield the magnetic flux induced from the transformer windings. The PCB transformer does not require manual winding and bobbin. A power converter prototype employing the PCB transformer has been implemented. The technique of choosing the optimum switching frequency of the power converter using the PCB transformer is addressed in this paper. The maximum power delivered from the prototype is 94 W. The maximum efficiency of the power converter is 83.5%.

Switch-mode power supplies

Abstract: A family of switch-mode power supplies with low current stresses on switches and capable of producing an output voltage higher than the input voltage, incorporating a multiple-tap transformer driven by at least one ground-referenced switch. When the transformer is center-tapped, it is driven by two ground-referenced switches. The current stress in each switch is equal to the difference between the source current and the load current. The converters can operate in zero current switching and zero voltage switching. Integrated magnetics can be used to reduce further component count.

Cross regulation in flyback converters: analytic model and solution

Abstract: An analytical model for studying cross regulation among the multiple outputs of flyback converters is presented in this paper. Both the theoretical and experimental results show that the cross regulation can be improved by lowering the clamp voltage, which has not been previously reported. Many other factors, such as the leakage inductance in primary and secondary windings, the magnetizing inductance, and the air gap can also affect the cross regulation. Detailed analysis and test results are provided. Based on this model, a cost-effective passive energy regenerative clamp is proposed that allows the clamp voltage to be much lower than that of traditional RC clamps, thus improving the cross regulation and energy efficiency.

X-ray computer tomography apparatus

Abstract: An X-ray computer tomography apparatus comprises a high-voltage transformer which performs the increase and noncontacting transmission of the power simultaneously and outputs a desired high voltage for causing X rays to be generated at the rotatable gantry section. The high-voltage transformer is divided into a primary-side which is provided on the static gantry section and to which the output of a frequency converting circuit is supplied and a secondary-side which generates a high voltage. A capacitor is connected to a secondary coil of the high-voltage transformer, thereby forming a resonance circuit.

Primary side control circuit of a flyback converter

Abstract: Voltage feedback in flyback converters is typically done with the assistance of opto-couplers, to preserve electrical isolation. However the output voltage also exists (in part) across the primary side switch when in its off state. This paper investigates the extraction of the output voltage within one switching cycle. Good results are obtained from a flyback converter with a novel control circuit using cycle by cycle control. The converter works in both continuous and discontinuous mode of operation.

Flyback power converter with secondary-side control and primary-side soft switching

Abstract: A flyback power converter is described which provides multiple independently regulated outputs. Zero-volt primary side switching is achieved at a resonance minimum which occurs at the end of each energy cycle between a primary side capacitor and an isolation transformer primary winding.

Power electronic circuits with all terminal currents non-pulsating

Abstract: Three terminal PWM DC to DC converter networks which accomplish both non-pulsating input and non-pulsating output currents using a single simple coupled inductor is revealed. The DC to DC converter networks accomplish buck, boost, buck boost (flyback), buck complement, boost complement, or flyback complement (SEPIC) conversion using a simple circuit requiring only two switches, one of which may be a simple diode rectifier, one or two capacitors, and three or four inductors, which may be co-located on a single common magnetic core. Also revealed are techniques to accomplish isolation, high order (quadrature) transfer functions, methodology for reducing current ripple to near zero levels at all terminals simultaneously, and methodology for generalizing the process of changing three terminal networks with pulsating terminal currents into three terminal networks with non-pulsating terminal currents.

Step-Down Piezoelectric Transformer for AC-DC Converters

Abstract: In this paper, a new piezoelectric transformer for AC-DC converters is presented. This piezoelectric transformer, with a multilayered construction in the thickness direction, operates in a fundamental contour-extensional vibration mode. Output impedance is designed to be low, approximately several tens of ohms. First, we simulated the design of the transformer using equivalent circuit method and finite element method (FEM) analyses. We calculated that the transformer could work with an eficiency higher than 95% and a gain of 0.4 at a resonant frequency of 140 kHz. Second, we fabricated a transformer of 14 mm length, 14 mm width and 5.8 mm thickness and examined it. It was found that the transformer exhibited a 0.4 gain and 96.3% efficiency at 135 kHz, when the temperature increase was 30°C. We applied the transformer to the fabrication of an AC-DC converter using a half-bridge zero voltage switching circuit, and examined the converter. It was found to achieve good line and load regulation, and the highest efficiency of 90% was obtained for Vin=80–120 Vac, Vout=13 Vdc, and Iout= 0.8–1.5 A.

A novel prototype design for a transformer for high voltage, high frequency, high power use

Abstract: A prototype transformer has been designed and built which is novel in its combination of high voltage (50 kV), high frequency (20 kHz) and high power (25 kVA) specifications. The design technique utilized a spreadsheet approach which facilitated an iterative design procedure. The transformer used a ferrite core, nylon insulated secondary bobbins and pressurized sulfur hexafluoride encapsulation. It was designed as part of a high-voltage switched-mode power supply for driving electrostatic precipitators. The transformer was field tested at a large coal-fired power station and was found to have an efficiency of better than 98%.

Zero voltage switching cells for power converters

Abstract: Zero voltage switching cells using a small magnetic circuit element, a pair of switches, and a capacitor are revealed. The application of the zero voltage switching cells to any of a wide variety of hard switching power converter topologies yields equivalent power converters with zero voltage switching properties, without the requirement that the magnetizing current in the main magnetic energy storage element be reversed during each switching cycle. The new switching cells either provide integral line filtering or a means to accomplish zero voltage switching with no high side switch drive mechanism. In the subject invention the energy required to drive the critical zero voltage switching transition is provided by the small magnetic circuit element, either a single winding choke or a two winding coupled choke, that forms part of the zero voltage switching cell. The application of the zero voltage switching cells to buck, buck boost, Cuk, flyback, and forward converters is shown. A variation of the zero voltage switching cell which adds a single diode to clamp ringing associated with the magnetic circuit elements and parasitic capacitance of off switches is also revealed.

Method and apparatus for reducing standby power in power supplies

Abstract: Power consumption of a low-power flyback power converter under standby-load or no-load conditions is reduced by modulating the OFF time of the flyback transformer's main switch as a function of the feedback control current when the load drops below a predetermined level. This modulation overcomes the conventional frequency-increasing modulation of the ON time at low output power levels so as to reduce the switching frequency, and hence the switching losses, to minimal levels as the load is reduced. Excessive frequency reduction can optionally be avoided by a clamping feature that limits the expansion of the OFF time.

Power electronic circuits with ripple current cancellation

Abstract: PWM DC to DC converter circuits which accomplish ripple cancellation at one or more terminals are revealed. Four or more inductors are required in each case, however, in all cases multiple inductors can be combined into a single simple coupled inductor to accomplish the ripple cancellation. Some of the circuits revealed accomplish ripple cancellation at all terminals and some also provide zero voltage switching and galvanic load isolation. The non-isolated DC to DC converter networks revealed accomplish buck, boost, buck boost (flyback), buck complement, boost complement, or flyback complement conversion using a simple circuit requiring only two switches, one of which may be a simple diode rectifier, two or more capacitors, and four or more inductors, which may be co-located on a single common magnetic core. The isolated converters revealed provide continuous and discontinuous forward converter and continuous flyback converter transfer functions. Also revealed are techniques to accomplish isolation, high order (quadrature) transfer functions, zero ripple tapped inductor topologies, and methodology for generalizing the process of changing three terminal networks with pulsating terminal currents into three terminal networks with zero ripple terminal currents.

Synchronous rectification in a flyback converter

Abstract: A flyback converter (100) has a primary side (112) comprising a main switch (Q1) and a control device (116) and a delay circuit (110). The converter has a secondary side (114) comprising a drive circuit controlling a rectifying switch (Q4). The drive circuit comprises a first part including a first transistor (Q2), a first discharge diode (D2) and an on-node (D_ON) and a second part including a second transistor (Q3), a second discharge diode (D3) and an off-node (D_OFF). The control device is connected to the drive circuit via at least one drive capacitor (C1, C2) to the on- and off-nodes. The control device issues drive pulses to the main switch through the delay circuit and to the drive circuit. The drive circuit has a first mode of operation in a flyback phase, which is triggered when the main switch is turned off and the rectifying switch is rendered conducting. A second mode of operation is a forward phase, which is triggered when the main switch is turned on and the rectifying switch is rendered non-conducting. The flyback converter comprises few components and the main switch is efficiently prevented from conducting simultaneously with the rectifying switch.

Battery charger circuit with low standby power dissipation

Abstract: A battery charger circuit is provided. One battery charger circuit in accordance with the present invention includes a switching element in series with a primary winding of a transformer. Control circuitry renders the switching element conductive during an on period so as to produce a current through the series arrangement and renders the switching element non-conductive during an off period. A method to reduce standby current in a battery charger circuit is also provided. One method in accordance with the present invention includes the steps of defining a current path in series with a first winding of a transformer, and sensing current flowing through the current path. The method also includes the steps of allowing the current to flow to the first winding when the current includes a load current and a magnetizing current, and preventing the current from flowing to the first winding when the current includes only a magnetizing current.

Systems and methods for providing voltage regulation externally to a power transformer

Abstract: Voltage regulation of power transformers by the use of a separate, removable, detachably coupled device external to the main transformer that can be attached to a main transformer unit when voltage regulation is desired. The device is connected to the three neutrals of the main transformer and can comprise: (a) a bank of three capacitors connected in wye, (b) a bank of three medium voltage (MV) or low voltage (XV) transformers, (c) one three-phase low voltage or medium voltage transformer, or (d) a combination of a XV/MV transformer and a capacitor bank.

Digital control of a single-stage single-switch flyback PFC AC/DC converter with fast dynamic response

Abstract: This paper presents the DSP control of single-stage single-switch (S4) flyback AC-DC converter with fast output voltage regulation. Active current shaping technique using flyback AC-to-DC converter has been employed for the power factor control and DC voltage regulation. The proposed control scheme possesses the following characteristics: high power factor, fast regulation of the output DC voltage, high efficiency, low cost, galvanic isolation, and the most important is that all the control functions are realized by using software control which provides great flexibility for system modification and applications. An adaptive voltage ripple estimator has been proposed to compensate the measured DC-link voltage ripples. The proposed control scheme for the S4-PFC flyback converter was realized by using a single-chip DSP controller. Simulations and experimental results have been given to illustrate the performance of the implemented DSP-controlled PFC converter.

Transformer assembly for implantable cardiac stimulation device

Abstract: The transformer assembly is coupled between a power supply and a pulse delivery circuit of the implantable cardiac stimulation device for charging a pair of defibrillation capacitors for delivering defibrillation pulses. The power transformer assembly is formed from a printed circuit board (PCB) having a set of transformer coil turns embedded therein and a transformer core mounted adjacent to the windings of the PCB. By embedding the coil of the transformer within the PCB, the transformer may be more easily integrated with other components of the stimulation device so that the overall size of the stimulation device may be reduced. Moreover, the use of a PCB helps avoid reliability problems that might otherwise occur in the fabrication, assembly and operation of the device. In one specific configuration described herein, the transformer assembly includes a primary and two secondary transformers. The primary transformer is used as a flyback transformer for charging the pair of defibrillation capacitors. The two secondary transformers are used to provide voltage for selectively switching on a set of transistors formed in an H-bridge configuration so as to apply charge stored in the capacitors in biphasic pulse waveform to the heart. The coils of the primary and secondary transformers are all embedded within a single PCB. In another configuration, only the coil of the primary transformer is embedded within the PCB. The coils of the two secondary transformers are affixed to the surface of the PCB.

Resonance type switching power supply unit

Abstract: An object of the present invention is to create the optimum resonating condition to constantly decrease switching losses. A converter transformer capable of varying the leakage inductance is employed as a converter transformer, and a control circuit is arranged to detect an input voltage applied to a switching circuit and a voltage drop brought about in a current detecting resistor which allows a load current to flow. Thus, the leakage inductance of the converter transformer can be controlled.

Partial-core transformer design using reverse modelling techniques

Abstract: Equivalent circuit components are developed for a partial-core transformer using a new technique called reverse transformer design. Components requiring special consideration include the core-loss resistance, magnetising reactance and the winding leakage reactance. Three sample transformers were built and tested in order to verify and determine the equivalent circuit parameters. A fourth transformer was also designed, built and tested. The measured performance of the transformer confirmed the validity and accuracy of the model.

Miniaturized ac/dc power supply and battery charger

Abstract: A transformer (T1) connected to a power source (AC), which consists of a primary coil (16 and 18), a secondary coil and a magnetic core, the secondary coil being configured to provide a regulated DC output (12) voltage and/or current. The primary coil contains two portions, one portion being used to operate the transformer as a low voltage input (16) converter and both portion being used when the transformer is used as a high voltage input (18) converter.

High frequency transformer modeling

Abstract: This paper presents a technique of indirect measurement of linear and nonlinear elements of a wideband transformer using the reflection coefficient technique with the scattering matrix (S-parameters) The S-parameter frequency domain measurement method of the wideband RF transformer and conversion into a discrete model is discussed The leakage and the magnetizing inductances, the winding and magnetic losses, and the winding capacitances are calculated using the "parameter extraction" technique Experimental results of a ferrite wideband transformer over the range 50 to 300 MHz, confirmed that the scattering matrix is a precise and efficient method to obtain a nonlinear transformer model

Method and apparatus for soft switched AC power distribution

Abstract: An improved soft switched AC power distribution system for minimizing electromagnetic interference and AC losses in an AC power distribution system. The improved AC power distribution system comprises a flyback transformer comprising a primary winding and at least one intermediate secondary winding. A synchronization control circuit is connectable to the primary winding while at least one load transformer is connectable to the at least one intermediate secondary winding. The at least one load transformer connectable to the at least one intermediate secondary winding is connectable via an EMI shielded connection with controllable voltage and current rise times.

Magamp post regulation for flyback converter

Abstract: In this paper, a new magamp technique for flyback converters is proposed. The operation principle of the proposed approach is described and design guidelines are provided. Experimental verifications on a 50 W two-output flyback converter are conducted. Recordings show that the proposed approach is effective and voltage regulation of the auxiliary output is excellent.

Method and unit for driving piezoelectric transformer used for controlling luminance of cold-cathode tube

Abstract: A method and unit for driving a small high-efficiency piezoelectric transformer allowing a cold-cathode tube to have stable luminance by detecting only an active current flowing in the cold-cathode tube based on a phase difference between an output current and voltage of the piezoelectric transformer, removing a reactive current caused by stray capacitance formed between the cold-cathode tube and a reflector, and accurately controlling driving of the piezoelectric transformer so that a constant active current is detected.

Optimization of a flyback transformer winding considering two-dimensional field effects, cost and loss

Abstract: The largest loss in an example litz-wire flyback transformer is found during current commutation between windings. In order to reduce this loss, a new optimization method is introduced. The new method optimizes strand size and number in litz wire considering cost and loss. Unlike previous methods, it is valid with two- or three-dimensional field geometry and with different nonsinusoidal waveforms in any number of windings. The result of applying this method to the example flyback transformer is less expensive designs with lower loss, as confirmed by experimental measurements.