Showing papers on "Flyback converter published in 1994"

Utilization of an active-clamp circuit to achieve soft switching in flyback converters

Abstract: Flyback derived power convertor topologies are attractive because of their relative simplicity when compared with other topologies used in low power applications. Incorporation of active-clamp circuitry into the flyback topology serves to recycle transformer leakage energy while minimizing switch voltage stress. The addition of the active-clamp circuit also provides a mechanism for achieving zero-voltage-switching (ZVS) of both the primary and auxiliary switches. ZVS also limits the turn-off di/dt of the output rectifier, reducing rectifier switching losses, and switching noise due to diode reverse recovery. This paper analyzes the behavior of the ZVS active-clamp flyback operating with unidirectional magnetizing current and presents design equations based on this analysis. Experimental results are then given for a 500 W prototype circuit illustrating the soft-switching characteristics and improved efficiency of the power converter. Results from the application of the active-clamp circuit as a low-loss turn-off snubber for IGBT switches is also presented.

Inductorless DC-to-DC converter with high power density

Abstract: A new type of switching-mode power supply containing no inductors or transformers is proposed. The controlled transfer of energy from a unregulated DC source to a regulated output voltage is realized through a switched-capacitor (SC) circuit. A duty-cycle control is used; the driving signals of the transistors in the SC circuit are determined by the feedback circuit. The absence of magnetic devices makes possible the realization of power converters of small size, low weight and high power density, able to be manufactured in IC technology. High efficiency, small output voltage ripple and good regulation for large changes in the input voltage and/or load values are other positive features of the new type of DC-to-DC power converter. The input-to-output voltage conversion ratio is flexible; the same converter structure can provide a large range of constant desired values of the output voltage for a given input voltage, by predetermining the steady-state conversion ratio. The frequency response shows good stability of the designed converter. The experimental results obtained by using a prototype of a step-down SC-based DC-to-DC converter confirmed the theoretical expectations and the computer simulation results. >

Analysis and design of LCL-type series resonant converter

Abstract: A series resonant converter modified by adding an inductor in parallel with the transformer primary (or secondary) is presented. This configuration is referred to as an "LCL-type series resonant converter". A simplified steady-state analysis using complex AC circuit analysis is presented. Based on the analysis, a simple design procedure is given. Detailed experimental results obtained from a MOSFET-based 640 W converter are presented to verify the analysis. A narrow variation in switching frequency is required to regulate the output voltage for a very wide change in load, and the converter has load short-circuit capability. It is shown that by placing the parallel inductor on the secondary side, the parasitics of the high-frequency transformer can be used profitably. >

Optimum ZVS full-bridge DC/DC converter with PWM phase-shift control: analysis, design considerations, and experimental results

Abstract: By adding a simple external commutating aid circuit to the full-bridge DC/DC converter with phase-shift control and by reducing the magnetizing inductance, optimum performance (i.e. ZVS operation and high conversion efficiency) can be achieved from full load down to almost zero load. An analysis is presented to determine the required and available commutation energies. The analysis is complemented with design considerations and experimental results taken from a 3-kW converter operating at 200-kHz clock frequency. >

Novel full bridge zero-voltage-transition PWM DC/DC converter for high power applications

Abstract: A novel full-bridge (FB) zero-voltage-transition (ZVT) PWM DC/DC converter for high power applications is proposed. An auxiliary network which consists of two small switches and one small inductor provides zero-voltage-switching (ZVS) for entire line and load ranges without increasing device voltage and current stresses. Since the ZVS range is independent of the switch capacitance, IGBTs can be used instead of MOSFETs by adding external capacitors to the switches without increasing switching losses, which allows the proposed converter to handle higher power. Operation, analysis, and features are described and verified experimentally. A 1.8 kW ZVT PWM converter prototype is compared with a ZVS PWM converter prototype of the same power rating. >

Synchronously rectified buck-flyback DC to DC power converter

Abstract: A synchronously rectified buck-flyback converter is described which provides multiple synchronous regulated outputs. A synchronous buck converter provides the main output and a synchronous flyback converter, utilizing the primary inductor of the buck converter, provides the secondary output. The converter utilizes a split-feedback signal, whereby each of the regulated outputs provides a component of the signal and a switch controller synchronously activates and deactivates rectification switches based on the feedback signal, required output levels and load. The switches are synchronously controlled such that a power input switch is operated in anti-phase to a control switch for each regulated output.

Design of a piezoelectric transformer converter and its matching networks

Abstract: The feasibility of using the piezoelectric material for power transformation has been investigated for low profile DC/DC power converter design. This paper presents a systematic way to design a DC/DC power converter with a piezoelectric transformer (PT). The electrical equivalent circuit for the PT is developed. This model explains why the loss of the PT strongly depends on load and switching frequency. The two-port power flow method is employed to calculate the maximum efficiency of the PT. A complete PT converter, composed of amplifier, the PT and its matching networks, is built. Both experimental and simulated results of PT converter demonstrated that the above study is truly useful for designing the PT converters. >

Clamped continuous flyback power converter

Abstract: Size reduction in a clamped power converter can be achieved, and stability of the converter under no-load and transient loads can be substantially improved, by operating the converter in a continuous flyback mode.

A novel three-phase single-switch discontinuous-mode AC-DC buck-boost converter with high-quality input current waveforms and isolated output

Abstract: In this paper, a new three-phase single-switch AC-DC flyback converter system is presented. The system operates in the discontinuous mode. The simple structure of its power and control circuit, low mains current distortion, and resistive fundamental behavior, as well as the high-frequency isolation of the controlled output voltage, have to be pointed out. Besides the analysis of the stationary operating behavior, the dependencies of the peak values, average values, and rms values of the device currents, and of the maximum blocking voltages across the power electronic devices on the circuit parameters, are given as analytic approximations. The theoretical analysis is verified by digital simulation. >

Development of a DC distributed power system

Abstract: This paper presents design considerations for power converter modules used in a distributed power system, including front-end power converter modules and load power converter modules. The system is designed for a universal input voltage of 90-260 V AC, with a bus voltage of 48 V DC. Several versions of the 600 W power factor corrected front-end power converter modules have been evaluated. One configuration includes a zero-voltage-transition PWM boost PFC circuit followed by a zero-voltage-switched active-clamp forward power converter. The second configuration uses an interleaved active-clamp flyback power converter for both the power factor correction and bus voltage regulation. 150 W and 300 W load power converter modules with 5 V output have been developed using the active clamp forward power converter topology and low-profile magnetics. >

2 MHz Power Converter with Piezoelectric Ceramic Transformer

Abstract: A power converter with a new piezoelectric transformer is presented. The piezoelectric transformer, made of lead titanate solid solution ceramic, is operated with a thickness extensional vibration mode. This transformer can operate at high frequency, over several megahertz, with about 90% efficiency. The resonant frequency for the transformer is 2 MHz. The power converter with the transformer applies the theory for a class-E switching converter using an electromagnetic transformer. Maximum output power is obtained when the switching frequency is slightly higher than the resonant frequency. A 4.4 W output power is successfully obtained with 52% efficiency at 2.1 MHz switching frequency.<>

An isolated DC-DC converter using two zero current switched IGBTs in a symmetrical topology

Abstract: A symmetrical, current-fed DC-DC boost converter was investigated theoretically and experimentally on a 300 W prototype in the frequency range: 40 to 110 kHz. The converter is built around an L-type half-bridge IGBT inverter. Zero-current-switching is achieved by a series resonant LC-network placed between the collectors of the IGBTs. >

Uninterruptable off-line, isolated flyback topology switch-mode power supply

Abstract: An all-ranging DC output uninterruptible switched mode power supply (SMPS) of off-line flyback topology is capable of operating with an input voltage between 90 v AC and 270 v AC and an input frequency range of 40 Hz-70 Hz for operation throughout the world. Provided with a battery backup, the SMPS gives DC output without interruption even during AC power failures. The battery and the regulated AC main's supply outlet are connected through an "OR" connection comprising Shortsky rectifier diodes. A pulse width modulator whose conductive duty cycle is responsive to the condition of a voltage, Vcc, provides a reference voltage. An isolated flyback converter includes MOSFET transistor switch and power transformer. The power transformer stores energy in its primary winding when transistor is conductive and transfers energy to the secondary winding when transistor is nonconductive. The pulse width modulator controls the conduction of the transistor. A snubber circuit allows slow decay of current in the power transformer. An opto-coupler acts as a feedback or the pulse width modulator. Inductor is used for storing energy and transferring energy to the negative voltage regulator when control IC, is off, to provide -12 v at the output of negative voltage regulator.

Power distribution system for generating regulated DC output voltages using a dual active bridge converter driven from an unregulated DC source

Abstract: A power distribution system including a dual active bridge converter (DABC) distributes a regulated high-frequency, edge-resonant, square wave ac output voltage from an unregulated dc voltage source. The DABC-includes a primary-side half-bridge connection of switching devices and a secondary-side half-bridge connection of switching devices which are coupled by an intermediate high-frequency transformer. An ac distribution bus is connected to the regulated secondary side of the transformer. The primary-side and secondary-side connections of switching devices are phase-shifted in a manner to provide a regulated high-frequency square-wave voltage on the ac distribution bus, which is distributed via a low-impedance distribution bus to a plurality of simple point-of-load converters. Alternatively, a plurality of DABC's is configured in a high-frequency ac power distribution system such that a primary-side half-bridge of switching devices converts an unregulated dc voltage source to an unregulated high-frequency, square wave ac voltage which is distributed to a plurality of point-of-load converters. Each point-of-load converter has a high-frequency transformer and secondary-side switching devices, such that each point-of-load converter forms a DABC pair with the primary-side half-bridge.

Symmetrical, phase-shifting, fork transformer

Abstract: In 12-pulse and 18-pulse AC/DC converter systems a single wye connected auto transformer using appropriate segments of voltage from each phase connected in fork fashion is used to develop 6-phase and 9-phase voltages in a symmetrical manner such that inherent compensation is made for the dc converter output voltage to be within 4.2% of that of a 6-pulse converter. Additional design adjustments for step-up or step-down of voltage can be made without compromising the transformer symmetry. An unconnected but closed delta winding provides a path in which third harmonic currents, and multiples thereof can flow.

A BIFRED converter with a wide load range

Abstract: In this paper, the boost integrated flyback rectifier energy DC-DC (BIFRED) power converter which incorporates power factor correction, output voltage hold-up and input-to-output isolation is examined The particular problem of high bulk capacitor voltage at light loads is addressed and it is shown how this may be resolved if the boost and flyback sections of the power converter are allowed to operate discontinuously The criteria for ensuring correct operation in the discontinuous mode are investigated It is shown that operating in this mode places no restrictions on the minimum load and simplifies the control loop design >

PWM converters for three phase AC power control and AC to DC conversion

Abstract: PWM converters provide buck, boost, buck-boost, flyback, and Cuk configurons for three phase AC-AC power control. In an AC-DC embodiment, only a single power conversion circuit is used in a configuration including a pair of series connected gate turn off devices which are oppositely poled and oppositely timed, are connected directly to an AC input source, and provide an output to a high frequency isolating transformer. The transformer provides an output to a rectifier, which thus provides the DC output.

Parallel control type dc/dc converter

Abstract: A parallel control type DC--DC converter supplies an output voltage to a load based on voltages supplied from independent power sources. The DC--DC converter is provided with at least first and second converters powered by the independent power sources and commonly grounded and including a switching element, a control circuit driving the switching elements within the first and second converters by ON-pulses having the same width depending the output voltage, and a circuit coupling outputs of the first and second converters in parallel and producing the output voltage.

A choppingless converter for switched reluctance motor with unity power factor and sinusoidal input current

Abstract: This paper describes a new converter topology for switched reluctance motor drives. The new topology consists of a pair of boost-buck power converters and a machine converter. The boost converter lets the system deliver sinusoidal input current and enhances the DC source voltage having the capability of fast current rise/decay of the stator windings. It also provides DC voltage regulation. The buck converter is used to regulate the DC source voltage responding to the motor speed variations. The wide pre-voltage regulation by the two power conversion stages eliminates the high voltage-choppings to control the stator winding currents. This enables the machine-drive converter to work in single pulse-current mode, hence, removing the switching losses. >

Voltage converter with frequency shift protection against overload current

Abstract: A voltage converter has a control circuit that generates a PWM voltage from a DC input voltage, a housekeeping coil and a first voltage rectifier-filter which supply power to the control circuit from an induced voltage in the housekeeping coil, and a second voltage rectifier coupled to the housekeeping coil to rectify flyback (or reset) voltages in the housekeeping coil. The rectified flyback voltage controls the frequency of the PWM voltage generated by the control circuit. During an overload, the control circuit reduces the duty cycle of the PWM voltage. In response, the magnitude of the rectified flyback voltage falls which causes the frequency of the PWM voltage to be reduced. The first and second voltage rectifiers may be coupled to different taps of the housekeeping coil, so that both voltage rectifiers provide positive voltages relative to a ground tap even though the two voltage rectifiers rectify pulses of opposite polarity on the secondary coil. In an alternative embodiment, a flyback voltage in a secondary coil other than a housekeeping coil is rectified to control the PWM frequency.

DC/DC Conversion Circuit

Abstract: DC/DC conversion circuit (1), comprising a transformer (2) having a primary winding (3), a secondary winding (4), and an auxiliary winding (5); a switching transistor (T), in a series circuit with the primary winding (3) between first and second direct current input terminals (6; 7); a start circuit (R1, C1) for switching the switching transistor (T) on at power - on a control transistor for switching off the switching transistor in dependence on a current flowing through the series circuit during operation. The auxiliary winding and the control transistor (Q) connect to a voltage control circuit (8) for setting an output power at the secondary winding by controlling switching-on of the switching transistor in dependence on the magnitude of a primary current. Via the auxiliary winding, a conversion circuit (1) builds - up the bias voltage for turning on the switching transistor in a time period inversely proportional to the amount of the secondary-side output power.

Method and apparatus for increasing switching regulator light load efficiency

Abstract: A method and apparatus for increasing the light load efficiency of a DC-DC converter by reducing the quiescent power of the control section. In accordance with the invention, the DC-DC conversion is first started using a first regulator circuit to power the converter controller. When the converter output reaches an adequate level, the converter controller power input is switched to the output of the converter. At the same time, the first regulator circuit is turned off, whereby the converter controller continues to operate from the converter output, which has a voltage substantially less than the power supply input voltage. Because controllers all draw about the same current, the lower input voltage to the controller lowers the power consumption thereof, improving the efficiency of the regulator, particularly when subjected to light loads. Various embodiments are disclosed.

Performance comparison of output power estimators used in AC/DC/AC converters

Abstract: In the paper various methods of power estimation used in AC/DC/AC converters are compared. To maintain constant DC bus voltage using only small electrolytic capacitors which is one of the design targets in these systems, the input bridge reference currents must be generated on the basis of the system power flow. Since this method is not sufficient for tight regulation, an inner DC bus voltage control loop is usually added. The design procedure of the DC bus voltage regulator is also presented. The performance of three estimation methods is compared in terms of DC bus voltage fluctuation in dynamic conditions for a 15 kW AC/DC/AC converter. >

Thin type DC/DC converter using a coreless wire transformer

Abstract: A 10 W class thin type DC/DC power converter is developed which uses a new type of coreless wire transformer. The power converter is intended for portable equipment use. The coupling factor of the wire transformer is more than 95% at frequencies higher than 100 kHz. When applied in a 3 output DC/DC power converter, the power converter is only 5.5 mm thick and has 70% efficiency. >

Power factor corrected switching power supply

Abstract: In an AC to DC power converter (off line switcher) and a method of converting AC power to DC power in high voltage systems the flyback converter's low side semiconductor switch has a lower breakdown voltage than its high side semiconductor switch. The lower breakdown voltage is achievable by means of a shunt regulator that controls a clamp voltage across the low side switch. The efficiency of the converter's post regulator is improved by processing only a fraction of the system's total power output.

Flyback power supply having a VCO controlled switching rate

Abstract: A DC-DC current-mode controlled flyback switching power supply provides a high efficiency of operation throughout a wide range of input voltages. An error amplifier produces an error signal from the difference between a reference voltage and an output voltage feedback signal. The error signal controls a VCO that sets a latch to enable a power switch to store power in a flyback transformer. A comparator compares the error signal against a current sense feedback signal indicating the current flowing through the power switch. The comparator resets the latch and disables the power switch to transfer the stored energy in the flyback transformer to the output of the power supply. The extended input range of operation is achieved by varying the switching frequency of the DC-DC converter through the use of the VCO to accommodate varying input voltages and loading.

Analysis and implementation of a full-bridge constant-frequency LCC-type parallel resonant converter

Abstract: A comprehensive analysis of the full-bridge constant-frequency LCC-type parallel resonant converter (LCC-PRC) is presented. Owing to operation under constant frequency, the filter designs are simplified and utilisation of magnetic components are improved. The LCC-PRC takes on the desirable characteristics of the pure series and the pure parallel converter, thus removing the main disadvantages. A useful analytic technique, based on classical AC complex analysis, is introduced for designing the LCC-PRC. By using a proper transformation on the state variable, the converter is analysed by means of a two-dimensional state-plane diagram, which shows that the converter possesses three operation modes (I, II, III). It is shown that operating the converter in mode II provides the desirable higher efficiency for a wide load range. A CPU (8031) is used to control the phase-shift time. Its control characteristic is very accurate and the cost is low. Finally, a constant-frequency controlled full-bridge LCC-type parallel resonant converter (LCC-PRC) using the CPU (8031) control is implemented.

Flyback power converter with spike compensator circuit

Abstract: An improved electrical power converter is disclosed. The electrical power converter utilizes a pulse width modulator responsive to the voltage across a tertiary winding of the power transformer. The electrical power converter includes a feedback control circuit for providing a regulating voltage to the pulse width modulator that is substantially proportional to the voltage across the tertiary winding with the voltage spikes caused by any leakage inductance in said power transformer removed. The feedback control circuit includes a spike compensator circuit that utilizes leakage inductance produced voltage spikes to compensate for output voltage degradation due to heavy loads.

DC/DC converter for a variable voltage load

Abstract: The invention relates to a circuit for converting input source energy into output load energy, for example a flyback converter for charging a storage capacitor for defibrilation from a low-voltage battery in an implantable defibrilator. The invention allows the input current to pass through the flyback inductor for a fixed duration and it allows the output current to pass for a duration which is directly proportional to the average voltage of the battery and inversely proportional to the voltage of the capacitor which is charged. When the invention is used in proximity to an electromagnetic communications system, a control circuit, in order to avoid interference, enables and inhibits the converter with a maximum frequency which is substantially below the operating frequency of the system. Moreover, the control circuit drives the converter in such a way that the cycles of energy transfer from the source to the storage capacitor take place at a minimum fundamental frequency which is substantially above the frequency of the system.

Novel soft-switching full-bridge converter with magnetic amplifiers

Abstract: A novel full-bridge DC-to-DC converter combines the functions of the lossless soft-switching and secondary side PWM output voltage regulation at constant-switching frequency. The primary side switches of the bridge are driven at constant frequency and near 50% duty ratios with small dead-times, while the output voltage is regulated by PWM control of the magnetic amplifiers on the secondary side. The proposed converter exhibits soft-switching for no-load to full load conditions and maintains high overall efficiency. Experimental results obtained on 300 W, 48 V prototype operated from 300 VDC confirm those features. >