Showing papers on "Flyback transformer published in 1998"

Optimized transformer design: inclusive of high-frequency effects

Abstract: Switching circuits, operating at high frequencies, have led to considerable reductions in the size of magnetic components and power supplies. Nonsinusoidal voltage and current waveforms and high-frequency skin and proximity effects contribute to power transformer losses. Traditionally, power transformer design has been based on sinusoidal voltage and current waveforms operating at low frequencies. The physical and electrical properties of the transformer form the basis of a new design methodology while taking full account of the current and voltage waveforms and high-frequency effects. Core selection is based on the optimum throughput of energy with minimum losses. The optimum core is found directly from the following transformer specifications: frequency; power output; and temperature rise. The design methodology is illustrated with a detailed design of a push-pull power converter.

Reduction of power converter EMI emission using soft-switching technique

Abstract: Measurements of conducted and radiated electromagnetic interference (EMI) emission from hard-switched and soft-switched buck, boost, and flyback converters of similar power ratings are presented. Results indicate that EMI emission can be substantially reduced by using a soft-switching technique in power converters. Thus, the soft-switching technique provides a practical and useful solution to reduce EMI emission from switched-mode power circuits. A comparison of EMI emission on the three classes of converters is also included. The flyback converter is found to be the least EMC friendly among the converters tested.

Nonlinear-carrier control for high-power-factor rectifiers based on up-down switching converters

Abstract: In this paper, nonlinear-carrier (NLC) control is proposed for high-power-factor rectifiers based on flyback, Cuk, Sepic, and other up-down power converters operated in the continuous conduction mode (CCM). In the NLC controller, the switch duty ratio is determined by comparing a signal proportional to the integral of the switch current with a periodic nonlinear-carrier waveform. The shape of the NLC waveform is determined so that the resulting input-line current follows the input-line voltage, as required for unity power factor rectification. A simple exponential carrier waveform generator is described. Using the NLC controller, input-line voltage sensing, error amplifier in the current-shaping loop, and multiplier/divider circuitry in the voltage feedback loop are eliminated. The simple high-performance controller is well suited for integrated-circuit implementation, Results of experimental verification on a 150 W flyback rectifier are presented.

Design considerations and performance evaluations of synchronous rectification in flyback converters

Abstract: Design tradeoffs and performance comparisons of various implementations of the flyback converter with a synchronous rectifier (SR) are presented. Specifically, the merits and limitations of the constant-frequency (CF) continuous-conduction mode (CCM), CF discontinuous-conduction mode (DCM), variable-frequency (VF) DCM, and zero-voltage-switched (ZVS) DCM flyback converters with SRs are discussed. The theoretical efficiency improvements of the discussed synchronous rectification approaches relative to Schottky diode implementations are derived. Finally, theoretical results are verified on an experimental universal-input off-line 15 V/36 W flyback prototype.

A multiple-winding magnetics model having directly measurable parameters

Abstract: A general model of the multiple-winding transformer and coupled inductor is presented, in which all parameters can be directly measured. The approach is suitable for all winding geometries, and simplifying approximations can be easily made. This model can be applied in the determination of cross-regulation, current ripple and small-signal dynamics of multiple-output DC-DC power converters. An experimental four-winding flyback transformer example is investigated. Observed leakage inductance parameter measurements are interpreted physically, and are related to observed flyback converter waveforms. It is also shown that the model correctly predicts small-signal dynamics.

Asymmetrical duty cycle flyback converter

Abstract: An asymmetrical duty cycle flyback converter comprising a main transformer for transforming an input voltage at a desired ratio, the main transformer including a primary winding connected to an input stage and a secondary winding connected to an output stage, a switching circuit for switching the input voltage to the main transformer, the switching circuit including first and second switches, a rectifying/smoothing circuit for rectifying and smoothing an output voltage from the main transformer, a controller for generating a control signal in response to an output voltage from the rectifying/smoothing circuit to control the switching operation of the switching circuit, and a switch driver for generating first and second drive signals in response to the control signal from the controller to drive the first and second switches in the switching circuit in such a manner that they can complementarily be switched on the basis of on-time duties asymmetrical with respect to each other and at an interval of a dead time therebetween to perform a zero voltage switching operation. With this construction, the present invention has the effect of realizing a miniaturation and improvement in power efficiency.

Analysis and experimental results of a single-stage high-power-factor electronic ballast based on flyback converter

Abstract: A new single-stage high-power-factor electronic ballast based on a flyback power converter is presented in this paper. The ballast is able to supply a fluorescent lamp, assuring a high input power factor for the utility line. Other features are lamp power regulation against line voltage variations and low lamp current crest factor, both assuring long lamp life. The ballast is analyzed at steady-state operation and design equations and characteristics are obtained. Also, a procedure for the ballast design is presented. Finally, simulation and experimental results from a laboratory prototype are shown.

Single-switch two-output flyback-forward converter operation

Abstract: A double power converter with fully independent regulated outputs is introduced. The proposed topology results from magnetic integration of flyback and forward power converters. The derived converter shares a single power switch having a single magnetic component. Also, only one standard pulsewidth modulation (PWM) integrated modulator is needed in order to keep independent closed-loop control of both output voltages. The double regulation may be sustained over a wide spread of current loads. Boundaries of full regulation and experimental results are presented.

PWN controller use with open loop flyback type DC to AC converter

Abstract: A controller and ring generator circuit realized therefrom utilizing an open loop flyback topology to achieve a desired output voltage waveform. A characteristic feature of the controller is that it provides the required signals to control a ring generator circuit having an open loop fly back topology. The controller functions to generate a PWM signal that is used to switch the primary of a transformer on and off. The controller includes the necessary functionality to control the duty cycle of the generated PWM signal so as to produce a sine wave output on the secondary of the transformer. The controller also includes overcurrent protection circuitry that tracks the load current by sensing the current through the primary winding. In addition, the circuit permits negative current in the secondary by use of a synchronous rectifier circuit coupled to an additional secondary transformer winding. An output bridge circuit creates a full sine wave from the generated half wave output.

AC/CD converter with a piezoelectric transformer

Abstract: An AC/DC converter of the present invention includes a transformer implemented by a piezoelectric transformer. Power fed from a commercially available power source (14) is converted to a DC voltage by rectification and smoothing. The DC voltage is transformed to a high frequency (about 100 kHz) pulse voltage by switching FETs (Field Effect Transistors) (5) and 6. The pulse voltage is applied to the input of a piezoelectric transformer (9). The transformer (9) has its vibration mode and dimension selected such that the resonance frequency of the transformer is substantially identical with the frequency of the above pulse wave. A high frequency AC voltage is produced from the output side of the transformer (9). The AC voltage is transformed to a DC voltage by rectification and smoothing and then fed to a load resistor (13). The piezoelectric transformer is easy to miniaturize, compared to an electromagnetic transformer. The entire AC/DC converter can therefore be reduced in size.

Three-phase electrical power measurement system including three transformers and a measurement circuit to calculate the power thereof

Abstract: A measurement system includes a first transformer enclosed within a first housing and magnetically linked to a first cable where the first transformer senses changing current within the first cable and in response produces a first output voltage. A second transformer is enclosed within a second housing and magnetically linked to a second cable where the second transformer senses changing current within the second cable and in response produces a second output voltage. A third transformer is enclosed within a third housing and magnetically linked to a third cable where third transformer senses a changing current within the third cable and in response produces a third output voltage. A measurement circuit is electrically connected to the combination of the first transformer to receive a first input signal representative of the first output voltage, the second transformer to receive a second input signal representative of the second output voltage, and the third transformer to receive a third input signal representative of the third output voltage. The measurement circuit calculates an output value representative of electrical power within the first, second, and third cables in response to receiving the first, second, and third input signals. The measurement circuit is enclosed within at least one of the first housing, the second housing, and the third housing.

Integrated protection from the effects of a short circuit of the output of a flyback converter

Abstract: A method of protection from the effects of a persistent short circuit of the output of a DC-DC flyback converter self-oscillating either at a variable frequency or functioning at a fixed frequency in a discontinuous manner, using a transformer for storing and transferring energy to a load, having an auxiliary winding (AUS) for synchronizing the turning on of the power switch (POWER) that drives the winding (N1) of the transformer under a condition of null current in the primary winding when self-oscillating at a variable frequency, wherein the voltage induced back from the current flowing in a secondary winding (N2) of the transformer on said auxiliary winding (AUS) is rectified and filtered (D2, C2) to power, during a steady state of operation, the control circuitry (CONTROL) of the converter, the turning on of the power switch (POWER) being driven during a start-up or recovery phase by a primary control loop, when the supply voltage (VDD) of the control circuit reaches or is over a preestablished enabling threshold of the control circuit, a secondary control loop comprising a photocoupler of the output error voltage (ERROR AMP) to an input (COMP) of the control circuitry (CONTROL) to which it is connected a compensation capacitor (CCOMP), includes the steps of discriminating an output short circuit condition from a start-up or recovery condition by comparing (COMP1) the voltage (VAUS) present on said auxiliary winding (AUS) with a preestablished threshold (Vref1) higher than the voltage (VAUS) that is induced on the auxiliary winding (AUS) under a short circuit condition of the secondary winding (N2) of the flyback transformer and by comparing the voltage existing on said compensation capacitor (CCOMP) with a second threshold (Vref2) of value equal or close to the value of maximum charge of said compensation capacitor (CCOMP), within a time interval sufficiently delayed from the turn-off instant of the power switch (POWER); conditioning, by means of a (SET CC) signal resulting from the logic combination (AND) of the signal originating from said two comparisons (OUTZC, OUTCOMP), in said interval of definite time (MONO1), the enabling upon turning on (FF2, FF1, DRIVER) of the Power switch (POWER).

DC to DC power converter including synchronous output rectifier circuit

Abstract: A DC to DC power converter which can suitably be used, for example, in a charger device for rechargeable batteries has an input and a load output, a resonant transformer provided with a transformer input and a transducer output coupled to the load output, an output rectifier circuit coupled to the load output, a controllable transformer control circuit, in the form of a pulse providing circuit, coupled between the input of the converter and the transformer input, and a synchronous output rectifier circuit coupled between the transformer output and the load output. The transformer control circuit receives a control signal derived from a signal constituting or proportional a signal at the transformer output. The output rectifier circuit shows a variety of possible embodiments, each embodiment including at least two transistor switches which are connected between a different end of the transformer output and a same end of the load output.

Small-signal characterization of the forward-flyback converters with active clamp

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 36-72 V-to-5 V converter, for different load resistances, thus allowing the design of the error amplifier as to ensure circuit stability. Experimental results confirm the models' validity.

Active clamp for buck-based converter and method of operation thereof

Abstract: For use with a buck-based converter having a rectifier that receives current from a secondary side of a isolation transformer, an active clamp and a method of operating the buck-based converter to manage reverse recovery energy therein. In one embodiment, the active clamp includes: (1) an auxiliary transformer coupled across the isolation transformer and (2) an auxiliary switch, interposed between the auxiliary transformer and the rectifier, that: (2a) closes as a function of an output voltage of the rectifier to cause the auxiliary transformer to receive reverse recovery energy from the rectifier and deliver the reverse recovery energy to a primary side of the isolation transformer and (2b) opens to limit a magnetic flux of a core of said auxiliary transformer.

A single-switch flyback-current-fed DC-DC converter

Abstract: This work presents a novel DC-DC converter, whose significant advantages are the single power switch, single-input inductor, purely capacitive output filter, isolation, low current ripple through the output capacitor, and operation at constant frequency in a conventional pulse-width-modulation scheme. The new converter operates over a wide input-voltage range and can be employed in power factor correction and multiple-output power supplies. Theoretical analysis is presented along with experimental results taken from a laboratory prototype rated at 300 W/50 kHz.

Compact solid state klystron power supply

Abstract: A high voltage pulse generating circuit for powering klystrons, and the like. The circuit includes a source of D.C. power having positive and negative terminals, a flyback transformer having a primary winding and a secondary winding, the primary winding having first and second terminals for connection to the source of D.C. power, a sensor for generating a signal indicating the amplitude of the current in the primary winding, and a solid state switching circuit for coupling the source of D.C. power to the primary winding of the flyback transformer. The primary winding is coupled to the power source in response to a control signal, and decoupled from the power source when a predetermined level of current is detected in the primary winding.

Modulator for generating high voltage pulses

Abstract: A topology for combining an array of low voltage, low current components to form a high voltage, high current pulse modulator. Each module of the MIA is composed of an inductive adder cell and a plurality of energy storage capacitors, a plurality of solid-state switches, and ancillary components to form a high current but a low voltage modulator. By using a large number of energy-storage/switch combinations in parallel, a highly redundant (reliable) module is formed. High voltage is obtained by inductively adding the voltage of a plurality of modules. Each module drives a single turn primary of a transformer (inductive adder cell). Each transformer has a single turn secondary. The single turn secondary of each transformer is connected in series. The advantage to this transformer topology (as opposed to a multi-turn secondary) is greatly reduced secondary capacitance which allows the transformer to operate at much higher bandwidth than otherwise possible.

An isolated ZVS/ZCS flyback converter using the leakage inductance of the coupled inductor

Abstract: This paper describes a simple and effective way to modify an existing hard-switched flyback power converter into a circuit with zero-voltage switching (ZVS) and zero-current switching (ZCS). The key improvement is to turn the unattractive features of the coupled inductor leakage inductance and snubber capacitor into attractive ones. The coupled inductor leakage inductance and snubber are used to form a quasi-resonant circuit to facilitate ZVS/ZCS of all power devices. The operating principles of the power converter and experimental results are presented.

Frequency modulated ballast with loosely coupled transformer

Abstract: A frequency dependent controller utilizes a loosely coupled transformer, which controller is adapted to change the operating characteristics of the transformer by varying its operating frequency in accordance with the requirements of a load to be supplied with power. If the transformer is operated at a single frequency, the maximum current that can be delivered is limited by the reactance of the transformer. If the transformer is operated over a frequency range by the controller, the maximum current and other operating characteristics of the transformer are a function of both the magnetic shunt and its then current operating frequency. Frequency control of a loosely coupled transformer permits precision electronic regulation of the transformer's operating characteristics and is suitable for control of a variety of devices, such as gas discharge lamps, DC to DC converters, AC to DC power and high voltage supplies, motor control and variable heaters.

Electric rotational machine arrangement e.g. for wind-power generator

Abstract: An electrical rotary machine (1) including a stator (3) and a rotor (4), in which the stator has a stator transformer winding (7) and the rotor (4) a rotor transformer winding. The transformer windings (3,4) form an electrical transformer (10) and are designed for operation with alternating current (AC). The electrical rotational machine (1) can be operated with a rotor (4) frequency of between 0.01 Hz and 500 Hz. During operation of the rotational machine, an AC with a frequency greater than the frequency of rotation of the rotor, is transformed by the transformer (10).

Line harmonic correcting flyback power converter

Abstract: Effective harmonic correction without frequency, power or voltage limitations is achieved in a single-stage DC-to-DC converter by disconnecting the bulk capacitor of a typical single-stage converter during low voltage conditions, and by using various phase and cycle modulation techniques associated with a switchable auxiliary transformer winding which charges the bulk capacitor to control its voltage. A means is thus provided to control the level of harmonics generated depending upon the level of the AC output voltage. When the auxiliary winding is used as a clamp winding, full ZVS conditions are provided for both the auxiliary winding switch and the converter's primary winding switch. Energy can then also be directed, under independent control of the switched auxiliary winding, to independent power nodes, i.e., either the output capacitance and load, or the bulk capacitor. This ensures that the output voltage will not be affected during any period needed to recharge the bulk capacitor.

Modelling of resonant switched-mode converters using SIMULINK

Abstract: A method of modelling DC-DC converters has been developed using SIMULINK. For the flyback quasiresonant converter, the equations for the state variables and the active and passive switches have been derived and a corresponding SIMULINK model has been constructed. Submodels for the different parts of the controller have also been constructed, and the complete system has been simulated. This modelling technique requires less memory and CPU time than SPICE.

Zero voltage soft-commutation PWM DC-DC converter with saturable reactor switch-cascaded diode rectifier

Abstract: An improved single-ended push-pull (SEPP) half-bridge type zero-voltage soft-switching pulse width modulation (ZVS-PWM) DC-DC power converter is presented in this paper, which makes use of a saturable reactor-assisted lossless capacitor type zero voltage soft-switching method. The SEPP power converter with a high-frequency forward and flyback hybrid transformer link has some advantages such as lowered switching and conduction losses, soft-switching transition operation over a wide load range, constant frequency PWM regulation and minimized Electro Magnetic Interference (EMI) as well as Radio Frequency Interference (RFI) noises. Its operating principle is illustrated and its periodic steady-state circuit analysis is implemented. In order to demonstrate the remarkable effectiveness of this converter's characteristics, feasibility experiments are conducted with a 150 W/200 kHz prototype of a high-frequency link ZVS-PWM DC-DC converter using power MOSFETs with an ultrafast soft-recovery diode.

A photomultiplier high-voltage power supply incorporating a ceramic transformer driven by frequency modulation

Abstract: This paper describes the circuit and operation of a photomultiplier high-voltage power supply incorporating a ceramic transformer instead of a conventional magnetic one. The ceramic transformer, being constructed from a ceramic bar, utilizes the piezoelectric effect to generate high voltage. As no magnetic material is present, no leakage of magnetic flux occurs such that the power supply can be operated under a strong magnetic field. The transformer shows a sharp resonance, after which voltage amplification is dependent on frequency. Transformer output is stabilized by feedback utilizing frequency dependence, i.e., after rectification, the output high voltage is fed back to a voltage-controlled oscillator that adjusts the oscillation frequency according to the output voltage of an error amplifier that compares the output high voltage with a reference voltage. This photomultiplier high-voltage power supply provides high voltage from 1500 to 2500 V at a 20-M/spl Omega/; load, where the load is a breeder of the photomultiplier. The magnitude of voltage ripples is at a prescribed level when the load is 20 M/spl Omega/. Ripple magnitude is proportional to load current. Voltage ripples limit the load current to the photomultiplier.

Piezoelectric transformer with voltage feedback

Abstract: A piezoelectric transformer (200) with voltage feedback is disclosed. The transformer comprises a piezoelectric plate of predetermined length (L), width (W) and height (H) with a driving section (202) having alternatingly stacked plurality of piezoelectric ceramic layers having internal interdigitated layers. A driven section (206) including an unpolarized dielectric section (208), a voltage feedback section (220) in the form of a multilayer electrode structure or an outer strip, and a normally unpolarized dielectric section (222) is also disclosed. The transformer generates an output voltage at an output terminal by the piezoelectric vibration transmitted from the driving section. A feedback control circuit is connected to the voltage feedback section. The isolated voltage feedback provides feedback control to keep the transformer operating at the proper resonant frequency even if there is a change in output load of the transformer.

Switch-mode supply with power factor correction

Abstract: A circuit for providing a rectified voltage to a flyback switch-mode supply circuit comprises a rectifying bridge having output terminals; a primary winding of the switch-mode supply having an intermediate tap; a switch serially connected with the primary winding; the serial connection between the output terminals, of a first diode and a capacitor, the first diode being biased so as to allow the charging of the capacitor; a second diode between a first output terminal of the winding, the second and third diodes being biased so as to let the current flow towards a second terminal of the winding.

Small-signal modeling of multiple-output flyback converters in continuous conduction mode with weighted feedback

Abstract: A small-signal model of multiple-output flyback power converters is developed. From the model, closed-loop power converter performances, such as line regulation and load regulation, can be predicted. Based on the model, a design procedure for feedback compensation is suggested. The model is experimentally verified.

Modeling a power transformer for investigation of digital protection schemes

Abstract: A three-phase transformer model for the calculation of electromagnetic transients for differential protection studies is presented. The ATP-EMTP was chosen as a computer tool for modeling the following situations: internal faults; transformer energization and removal of external faults. An application of the methodology is exemplified for a 138/13.8 kV-25 MVA transformer, where some transient results are presented.

Dynamic circuit modeling of a high frequency transformer

Abstract: This paper presents a generalized dynamic circuit model of high frequency transformers, which includes all types of core losses and thermal effects on magnetic hysteresis. This transformer model provides accurate core loss prediction and is suitable for the simulation of transformers used in high frequency switching-mode power converters. Simulation results of a 500 W/25 kHz transformer supplied by a full-bridge inverter are confirmed with measurements.