Showing papers on "Flyback converter published in 2001"

Buck-boost PWM converters having two independently controlled switches

Abstract: Single-switch step-up/step-down converters, such as the buck-boost, SEPIC and Cuk, have relatively high voltage and current stresses on components compared to the buck or the boost converter. A buck-boost converter with two independently controlled switches can work as a boost or as a buck converter depending on input-output conditions, and thus achieves lower stresses on components. Using the converter synthesis method from D. Zhou (1995), families of two-switch buck-boost converters are generated, including several new converter topologies. The two-switch buck-boost converters are evaluated and compared in terms of component stresses in universal-input power-factor-corrector applications. Among them, one new two-switch converter is identified that has low inductor conduction losses (50% of the boost converter), low inductor volt-seconds (72% of the boost converter), and about the same switch conduction losses and voltage stresses as the boost converter.

Apparatus and method for efficiently amplifying wideband envelope signals

Abstract: Systems and methods for amplifying an RF input signal include employing a moderately power efficient wide bandwidth device, such as an AB-type amplifier, to amplify the power residing in the high frequency components of the input signal, and a highly power efficient narrow bandwidth device, such as a synchronous buck DC/DC converter, to amplify the power residing in the low frequency components of the input signal. The amplified low frequency components and high frequency components are then combined to produce an amplified replica of the RF input signal. A positive feedback loop is provided between the output of the AB-type amplifier and the input of the DC/DC converter to provide stability to the amplified RF signal. A negative feedback loop is provided between the output of the DC/DC converter and the input of the AB-type amplifier to minimize interference introduced by the DC/DC converter.

Design and performance evaluation of low-voltage/high-current DC/DC on-board modules

Abstract: The topology selection, design, and performance evaluation of an on-board DC/DC converter, which delivers power from a 48 V input to a 1.2-1.65 V/70 A microprocessor load, are presented. It was shown that the symmetrical half-bridge topology with the current doubler and synchronous rectifiers is a suitable approach for this application. The measured full-load efficiency of a 200 kHz experimental half-bridge converter was higher than 82% in the entire output and input voltage range.

Start-up circuit for flyback converter having secondary pulse width modulation control

Abstract: An output isolated, switching power supply (100) has a transformer (73) with a primary (91) and two secondaries (92, 93), and electronic switch (75) in series with the primary, a first rectifier (87) and filter (88) on the first secondary (93) to provide bias power during both startup and operating modes, and a second rectifier (80) and filter (82) on the second secondary (92) to provide regulated output power. A resistor-capacitor network (78, 74) on the primary side provides an initial operating condition, such as a single control pulse, to the electronic switch which causes sufficient energy to be transferred through the first secondary to supply sufficient startup energy to operate a current control integrated circuit (89) on the secondary side in a staged fashion. After the initial operating condition, the current control integrated circuit generates and applies a control signal to the electronic switch through an isolation circuit (77) to cause the electronic switch to turn on and off in controlled fashion in order to deliver regulated power to the output of the supply. The low voltage, secondary side, current control integrated circuit provides a further aspect of the present invention.

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.

Sample and hold method to achieve square-wave PWM current source for light emitting diode arrays

Abstract: An apparatus for controlling overshoots in the switching of LED arrays in a system having a switching voltage converter providing the biasing voltage for the LED array. By synchronizing a switching converter to an LED turn-on signal, loading on the voltage converter can be controlled such that output conduction of the converter only occurs when LEDs that are to be displayed are switched on to provide loading to the output of the converter. A Sample and hold method is employed to effectively store the current information in a previous “on” interval and use it for the current control in a following interval with inhibited current overshoot.

Symmetrical DC/DC converter

Abstract: A symmetrical DC/DC converter selects an energy transferring direction and a step-up or a step-down operation as well as a desired step-up or a step-down ratio. The converter includes a single inductor with a pair of switching devices connected to its terminals in a symmetrical arrangement with respect to the inductor. The converter is operable as a step-up converter and a step-down converter in a manner such that one and the other of the switching devices are used as an input switch and an output switch, respectively, and that one and the other of the switching devices are conversely used as an output switch and an input switch, respectively.

A double ZVS-PWM active-clamping forward converter: analysis, design, and experimentation

Abstract: This paper presents an isolated DC-DC converter based on two ZVS-PWM active-clamping forward converters connected in series and coupled by a single high-frequency transformer. The proposed converter features no switching losses from no-load to full-load operation and low conduction losses. This converter is suitable for high input voltage (>400 VDC) and high power applications. Operation principles, theoretical analysis and design example, are presented, as well as experimental results taken from a 3 kW laboratory prototype.

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.

Range winding for wide input range front end DC/DC converter

Abstract: Hold up time requirement is a special requirement for a front end (FE) converter. The converter needs to provide output voltage within regulation for 20 ms after the AC input is lost. When designing the FE DC/DC converter, we want it to operate over a wide input range so that we can use less high voltage bus capacitor to meet the requirement. The converter efficiency is reduced at normal operating conditions, in order to cover wide input range. This paper demonstrates a new method to cover wide input range while also optimizing the normal condition operation with range winding.

A new generalized direct matrix converter

Abstract: In this paper, the authors attempt to introduce a new modulation algorithm for matrix power converters, with an alternative PWM strategy, regardless of type of input and output (AC or DC), and also the number of input and output phases, by using suitable toggling matrix switches, such that favorable output patterns are achieved (with variable amplitudes and frequency). The switch functions in such a converter ensure that the switches do not short-circuit the voltage sources, and do not open-circuit the current sources, thus yielding continuous currents at output terminals. Also if the number of input-phases are equal or less than the number of output-phases, then continuous current is available at input terminals. The advantage of this approach is that it can be developed for any kind of matrix converter. It is illustrated that, even under unbalanced and highly distorted input voltage waveforms, the output waveforms are reasonably clean and balanced. Here, the topology of a DC to single-phase AC power converter and single-phase to three-phase AC/AC power converter are presented.

A front-end DC/DC converter for network server applications

Abstract: Network server power supplies call for a dual universal AC line input and 48V DC input front-end converters to generate the 380 V DC bus. To realize the DC input front-ends, nonisolation DC/DC power converters, such as continuous current mode (CCM) boost converters, are not good candidates because of their power limitations under extreme duty cycles. Cascade DC/DC power converters can meet this specific application requirement with the deficiency of extra complexity and higher cost. Although coupled inductor DC/DC converters can provide high step-up voltage gain without the penalty of extreme duty ratio, their efficiency is poor due to the losses associated with the leakage inductors. In this paper, a clamp mode coupled inductor boost converter with no extreme duty ratio is presented. The proposed topology utilizes coupled inductor to achieve high step-up gain as well as to alleviate the output rectifier reverse recovery problem. The efficiency of a 1 kW prototype is higher than 90% under nominal operation condition.

System and method for regulating multiple outputs in a dc-dc converter

Abstract: A multiple output flyback converter provides independently controlled high-bandwidth secondary side voltage regulation for rapid response to small signal changes at the multiple outputs on the secondary side. Each of the multiple output circuits includes a fast local feedback loop to perform rapid and precise secondary side voltage regulation. The fast local secondary side feedback loops compensate for small changes in the load on the order of 1 to 5 percent. By providing each output circuit with independent secondary-side control, the last or final voltage output is controlled from the primary side. A further feature of the inventive circuit is that the input circuit of the converter includes an active clamp circuit for recovering both energy in the leakage inductance and additionally recovers residual energy in the magnetic field of the secondary winding of the transformer at the end of each energy cycle.

An improved boost PWM soft-single-switched converter with low voltage and current stresses

Abstract: This paper presents an improved regenerative soft turn-on and turn-off snubber applied to a boost pulsewidth-modulated (PWM) converter. The boost soft-single-switched converter proposed, which has only a single active switch, is able to operate with soft switching in a PWM way without high voltage and current stresses. This is achieved by using an auxiliary inductor, which is magnetically coupled with the main inductor of the converter. In order to illustrate the operating principle of this new converter, a detailed study, including simulations as well as experimental results, is carried out. The validity of this new converter is guaranteed by the obtained results.

Multi-phase switching converters and methods

Abstract: Multi-phase switching converters and methods that provide fast response and low ripple on the converter inputs and outputs. The converters include multiple converter stages that are normally operated in sequence into a common load. However upon sensing that operation of one of the converter stages does not bring the converter back into regulation, multiple converter stages are operated until regulation is reestablished, after which the converter stages are operated in sequence again. In the embodiment disclosed, upon sensing that operation of one of the converter stages does not bring the converter back into regulation, all converter stages are operated until regulation is reestablished, after which the converter stages are operated in sequence again starting with the stage with the lowest inductor current.

Power factor correction (PFC) circuit that eliminates an inrush current limit circuit

Abstract: Aspects for a power converter with power factor correction (PFC) circuit are described. The aspects include a buck/boost circuit for achieving a DC voltage from an AC input voltage signal line without developing an inrush current from the AC input voltage line, and a DC/DC converter circuit coupled to the buck/boost circuit for converting the DC voltage to a desired voltage level. The aspects are achieved in a straightforward, cost effective, and adaptable manner.

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.

Inductor current synthesizer for switching power supplies

Abstract: A circuit and method for sensing the inductor current flowing to a load from a switching power supply without using a sense resistor in the path of the inductor current. In a synchronous buck converter topology, the inductor current is derived by sensing the voltage drop across the synchronous MOSFET of the half-bridge and reconstructing the current using a sample and hold technique. A ripple current synthesizer is employed to reconstruct inductor current outside the sample and hold window. The sampled product I Load ×R DSon is used to update the ripple current estimator with dc information every switching cycle. The resulting voltage waveform is directly proportional to the inductor current. The inductor current synthesizer of the present invention can also be used in boost converter, flyback converter and forward converter topologies.

A controlled multi-output dc/dc converter

Abstract: A multi-output DC/DC converter (1;10;30;40;50;60), comprising inductive electrical energy storage means (L), switching means (S0-S7) and control means (6;9;31;41;51;61). The control means (6;9;31;41;51;61) are arranged for selectively operating the switching means (S0-S7) for transferring an amount of electrical energy from the energy storage means (L) to an output (A;B;C;D) of the DC/DC converter (1;10;30;40;50;60) providing an output voltage in accordance with a switching sequence based on comparing, by the control means (6;9;31;41;51;61) of the output voltage of each output (A;B;C;D) with an associated reference voltage. The control means (6;9;31;41;51;61) are arranged for operatively controlling the switching means (S0-S7) for each output (A;B;C;D) in accordance with an output individual switching cycle, wherein the switching sequence is comprised of the output individual switching cycles for transferring electrical energy to the outputs (A;B;C;D) of the multi-output DC/DC converter (1;10;30;40;50;60) in a predetermined order of priority.

Modeling, simulation, and experimental verification of soft-switched bi-directional DC-DC converters

Abstract: In this paper, an extended averaged model is developed for a soft-switched bi-directional DC-DC converter for high-power applications. The proposed technique can be applied to other bi-directional DC-DC power converters with a high-frequency isolation transformer. Simulation results of Matlab/Simulink using the proposed average model are compared to those of detailed circuit simulation and experimental results to confirm the validity of this technique.

Leakage energy recovering system and method for flyback converter

Abstract: A switching converter, having a transformer having primary, secondary and auxiliary windings, an actively controlled switch, a capacitor and a first passive switch in series across the primary, the auxiliary winding of the transformer and a second passive switch being connected in series to the node between the capacitor and first passive switch, with the active switch being connected to a side of the primary winding opposite the first passive switch. The method energizes a transformer core with the primary winding and discharges a capacitor during an ON state; and clamps a voltage across the active switch with the capacitor, and transfers magnetizing energy to the secondary winding during an OFF state, to efficiently transfer energy corresponding to a switching transient to the load while limiting maximum active switch voltage.

Lossles switching converter with dc transformer

Abstract: A new switching converter operates at record high efficiency despite its small size and light weight and enables ultra high overload current capability owing to two novel methods: new Lossless Switching method eliminates switching losses by use of a precise sequence and timing of the four controllable switches, while novel DC Transformer structure provides a method to eliminate the stored DC energy in magnetics, which further increases efficiency and reduces the magnetics and converter size.

Preventing instability in DC distribution systems by using power buffering

Abstract: Negative incremental impedance of regulated converter loads can cause stability problems in distributed DC power systems. Since the load-side converters usually contain energy storage elements, it is possible to avoid instability through transient control of the load-side converter input impedance. In this paper, bus-side stability is used as a control constraint. It is shown that load-side converter control-loop gain can be modified to improve stability characteristics, or even actively controlled to meet given impedance specifications.

Power supply for both AC and DC

Abstract: A power supply for both alternating current (AC) and direct current (DC) which has an AC/DC converter and DC/DC converter detachably coupled with each other. The AC/DC converter is adapted to convert an AC input voltage into a DC signal, and the DC/DC converter is adapted to convert a DC input voltage into a DC signal. An output voltage selector is provided to obtain a DC output voltage appropriate to an associated device. The present power supply can be conveniently carried, supply power to an associated device regardless of AC and DC input voltages and select a level of an output DC voltage. Therefore, the present power supply can be used universally irrespective of the types of associated devices and manufacturers.

Integrated traction inverter module and bi-directional DC/DC converter

Abstract: Integrated power systems and methods for use in an electric vehicle having a fuel cell and an electric motor, the integrated power systems and methods including a common casting, a traction inverter module operable for converting DC current generated by the fuel cell into AC current capable of powering the electric motor, and a DC/DC converter operable for stepping-down the voltage of the fuel cell. The traction inverter module and the DC/DC converter are disposed within the common casting.

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.

Input-current-shaper based on a modified SEPIC converter with low voltage stress

Abstract: The boost topology is often the designer's first choice when dealing with PFC front-ends. This topology is well documented in the literature and has obvious advantages like continuous input current and low voltage- and current-stress compared to other PFC topologies. The PFC SEPIC converter also has the advantage of the continuous input current but suffers from high voltage- and current stress. In this paper a modified SEPIC converter is presented with reduced voltage stress, comparable to that of the boost converter. Experimental result of a 200 W prototype for 185-270 V line voltage are also presented.

MMIC DC-to-DC converter

Abstract: An improved Monolithic Microwave Integrated Circuit DC-to-DC voltage converter fabricated in GaAs MESFET technology is introduced. The converter comprises a differential oscillator having crossed-coupled symmetrical inductors that ensure low-noise operation. The converter further comprises a highly-efficient synchronous rectifier and a start-up enable circuit.