Showing papers on "Flyback converter published in 1992"

Small-signal analysis of the phase-shifted PWM converter

Abstract: The specific circuit effects in the phase-shifted PWM (PS-PWM) converter and their impact on the converter dynamics are analyzed. The small-signal model is derived incorporating the effects of phase-shift control and the utilization of transformer leakage inductance and power FET junction capacitances to achieve zero-voltage resonant switching. The differences in the dynamic characteristics of the PS-PWM converter and its PWM counterpart are explained. Model predictions are confirmed by experimental measurements. >

Pulse width modulated DC/DC converter with reduced ripple current coponent stress and zero voltage switching capability

Abstract: An improved DC to DC converter is provided in particular for converters with high power density requirements. The converter comprises an input voltage source and a capacitor connected in series to the voltage source. A switching transistor configuration connects the voltage source and the capacitor alternatively to the primary windings of a transformer. The secondary windings of the transformer are connected to a full-wave rectifier and a filter. The output voltage provided at the output of the filter is modulated by a controlling means.

Soft-switching full-bridge dc/dc converting

Abstract: The addition of an external commutating inductor and two clamp diodes to the phase-shifted PWM full-bridge dc/dc converter substantially reduces the switching losses of the transistors and the rectifier diodes, under all loading conditions. We give analyses, practical design considerations, and experimental results for a 1.5-kW converter with 60-V, 25-A output, operating at 100-kHz clock frequency and 95% efficiency.

Power system for parallel operation of AC/DC converters

Abstract: A plurality of AC/DC converters (11) connected in parallel, are provided in which any one of the power converters can fail with-out affecting the operation of the machine which the plurality of converters are providing power. The failed AC/DC converter can be removed and replaced by another converter without shutting down the system. The output voltage of each converter is sensed on the power supply side of a decoupling diode (17, 19, 21). This allows each one of the converters to operate with its own sense loop (25, 27, 31, 33, 35, 41, 43) and, therefore, the feedback loop does not open when a converter is removed and another used in its place. Via power limit circuit (45) each of the parallel connected AC/DC converters (11) is designed to provide a preset maximum power which is independent of AC line voltage variation. To limit the power, the control voltage is made inversely proportional to the average input AC line voltage. The output voltage of the AC/DC converter is made to vary as a function of the load. This allows all the converters in parallel to provide power to the load all the time.

Steady-state performance of DC motors supplied from photovoltaic generators with step-up converter

Abstract: A simple step-up converter circuit consisting of a single power transistor and an inductor is used as an interface between a PV (photovoltaic) generator and a shunt DC motor driving a centrifugal water pump. The step-up converter allows maximum power output from the PV generator to the motor at all insolation levels. Steady-state performance of the motor is vastly improved as its input voltage and current are stabilized by the regenerative action of the converter. The PV generator operates at maximum power regardless of insolation variations. The converter duty ratio can be set at a fixed optimal value which is valid for all insolation levels. This remarkable property makes this device economically attractive since it is easy to build and does not require any insolation-dependent control as compared to other peak-power tracking devices. >

Zero voltage switching approach for flyback converter

Abstract: A zero voltage switched flyback power converter which realizes soft switching for every semiconductor is proposed. The sinusoidal resonant current flows through the secondary side rectifier diode and zero current switching of the diode is realized. Diode recovery is not generated. The proposed converter can operate with constant frequency pulse width modulation. High frequency switching and low noise are achieved. >

Polyphase AC/DC converter

Abstract: A power converter for converting input AC power comprising N phase-to-phase input AC waveforms at a first frequency into overall output DC power, where N is an integer greater than two, includes N phase-to-phase AC/DC converters each receiving a phase-to-phase waveform and having outputs connected in series whereby the converter outputs are combined to develop the overall output DC power. The AC/DC converters are operated such that a parameter of the input AC power and a parameter of the overall output DC power are controlled.

High power factor AC/DC converter

Abstract: A high power factor AC/DC converter is disclosed. In the AC/DC converter in which a rectifying circuit RC1 rectifies a commercially available AC power supply Ei, a switching device turns on and off so that the rectified voltage is applied across the primary winding n1 of the transformer Tr1 to provide a high frequency voltage across the secondary winding n2, and the high frequency voltage is rectified by means of a rectifying circuit connected across the secondary winding so as to generate a predetermined DC output, a choke coil (L1) and a diode (D1) are interposed between the rectifying circuit (RC1) and a smoothing capacitor (C1) and a capacitor (C3) is interposed between a first junction and a second junction. The first junction connects the choke coil (L1) to the diode (D1) and the second junction connected the switching device (Q1) to the primary winding (n1) of the transformer (Tr1).

DC-DC power converter including sensing means for providing an output when the reserve power of the converter falls below a predetermined amount for a given input voltage

Abstract: A DC to DC power converter in the form of a pulse-width modulator is shown which can sense via an indication of duty cycle how much reserve power is available for loads using the present input voltage. The device is for use at the end of a telephone line where the input voltage power supply impedance can be appreciable. When the reserve power, as detected in the power converter, reaches a minimum critical level, a signal is sent out requesting the voltage supply to increase the available voltage to the power converter.

PWM control and input characteristics of three-phase multi-level AC/DC converter

Abstract: The authors discuss the current control and pulse width modulation (PWM) pattern generation of a multilevel power converter which is capable of producing three levels of phase voltage. In the proposed current control, fast response is realized by introducing a converter model in the control algorithm and the effect of parameter difference between the model and an actual system is compensated for through proportional-plus-integral control of current difference. In PWM pattern generation, the balance of two capacitor voltages is taken into account. For the same sampling period, the current distortion factor of the proposed system can be approximately reduced to 60% of that of a conventional two-level power converter. The prototype was made using a digital signal processor, and simulation and experimental results were compared. >

Fixed frequency DC to DC converter with a variable inductance controller

Abstract: A DC to DC converter (50, 60, 70) that includes a switching circuit (10) responsive to a DC input, a magnetic amplifier controller (20) responsive to the switching circuit for providing an AC output, and an AC current to DC voltage rectifying circuit (30) responsive to the output of the magnetic amplifier controller for providing a DC output voltage. The magnetic amplifier controller includes a variable inductance (L1) that cooperates with the switching circuit to form a resonant DC to AC inverter (110) that provides to the magnetic amplifier controller a current whose amplitude is controlled by the variable inductance. The magnetic amplifier controller provides an approximately sinusoidal output current which is a function of the current input thereto, and the DC voltage output of the AC current to DC voltage rectifier is a proportional to the input current provided by the magnetic amplifier controller. Thus, the DC voltage output of the DC to DC converter is controlled by the control current to the magnetic amplifier controller.

DC to DC/DC to AC power conversion system

Abstract: A pulse width modulation DC to DC converter operates in an open loop mode to convert the DC output of the AC to DC converter (36) to a desired, predetermined DC level (221) using pulse width modulation techniques and a switching configuration (32) substantially similar to that of the AC to DC converter (36).

VCO driven flyback converter for implantable cardoverter/defibrillator

Abstract: A battery powered cardioverter or defibrillator employing output capacitors for delivery of cardioversion or defibrillation pulses. The capacitors are charged by means of a step-up transformer, coupled and uncoupled from the battery by means of a voltage controlled oscillator which varies its off and on times as a function of the voltage on the battery and the voltage stored on the output capacitor to allow for rapid charging of the capacitor even under conditions of battery depletion. The voltage controlled oscillator is constructed to provide a highly accurate timing signal with a low current drain.

High power factor power supply

Abstract: An off-line switching power supply includes an ac rectifier and a dual-output switching converter having one output coupled between the ac rectifier and the input to the dual-output converter in order to provide a high power factor, the other output of the dual-output switching converter providing a dc voltage as the power supply output. The outputs of the dual-output converter are fully decoupled so as to allow independent control of the ac input current and the power supply output voltage. In a preferred embodiment, a full-wave ac rectifier bridge is coupled in series with the second output of the power converter via an input resonant boosting converter. A full-bridge dc-to-ac converter is coupled between the dc link and ground for providing an ac signal to excite the boosting converter and for providing another ac voltage through a transformer to an output rectifier to generate a regulated dc output voltage. The amplitude of the regulated output voltage is controlled by pulse width modulation, while active frequency control of the boosting converter is provided to control the amplitude of the ac input current. Alternatively, frequency control of the boosting converter is passive, i.e., depends on the gain characteristics of the boosting converter resonant circuit. As a result of the complete decoupling of the input boosting converter and the power supply output voltage, the off-line switching power supply is capable of drawing high quality current waveforms from the ac source while producing a regulated dc output voltage with fast transient response.

Noise Analysis of DC-to-DC Converter with Random-Switching Control

Abstract: The effectiveness of random-switching control, by which the switching-noise spectrum is spread and its level is reduced, is briefly described through experimental results. The noise spectrum by random switching is analyzed in a general approach including a noise-generation model and a switching function with a random process. Taking the normal distribution as an instance, the amount of random perturbation is quantitatively analyzed. The validity of the analysis was confirmed experimentally by a series of pulses serving as an ideal switching-noise. >

Analysis and design of a fixed frequency LCL-type series resonant converter

Abstract: A fixed-frequency LCL-type series resonant power converter which uses an inductive output filter is proposed. Steady-state analysis of the converter is presented using complex AC circuit analysis. Based on the analysis, a simple design procedure is given. Detailed experimental results obtained from a MOSFET-based 500 W converter are presented to verify the analysis. The proposed converter requires a narrow variation in pulse-width while maintaining a lagging power factor mode of operation for very wide variation in the load. >

Linear circuit models of PWM flyback and buck/boost converters

Abstract: A method for modeling PWM converters operating in continuous conduction mode (CCM) is introduced. First, static voltage and current transfer functions of the idealized switching part of the converters are found. Second, the linearization of these transfer functions at the operating point is carried out, and the idealized switching part is replaced by dependent current and voltage sources. Third, the equivalent average resistance of parasitic resistances and equivalent average voltage of offset voltage sources of switches are determined using the principle of energy conservation. The method leads to linear DC and small-signal circuit models of a PWM converter. To illustrate the method, the analysis of the PWM flyback converter is given. Design equations for DC voltage transfer function, efficiency, and small-signal characteristics are derived. >

Single-switch three-phase AC/DC converter with high power factor and wide regulation capability

Abstract: A single-ended pulse width modulated (PWM) three-phase rectifier is presented. It is capable of high power factor and wide output voltage regulation while using high-frequency transformer insulation. The circuit behavior is investigated with the assumption of discontinuous input current operation. Design criteria are derived. The actual converter performances are verified on a 1.5 kW prototype, fed by a 380 V AC supply, in which insulation and voltage adaptation are realized by a 50 Hz transformer. Resulting AC current distortion is below 7%, efficiency is better than 90%, and power density is in the range of 0.4 kW/1. >

Universal power adapter for converting AC/DC voltage to DC voltage

Abstract: A universal power adapter comprised of a standard IEC three-wire socket, an AC/DC power supply detector circuit, an AC/DC power supply selector circuit, an AC/DC power supply pre-treating circuit, a DC power supply transformer circuit, a feedback and regulating circuit, and a DC output circuit, wherein said standard IEC three-wire socket connects an AC or DC input voltage to said AC/DC power supply selector circuit and said AC/DC power supply pre-treating circuit for converting into a DC voltage via said AC/DC power supply detector circuit, said DC voltage being treated through said DC power supply transformer circuit and said feed back and regulating circuit to provide a DC working voltage for output through an output device.

A new active power factor correction method for single-phase buck-boost AC-DC converter

Abstract: A current mode control technique suitable for a single-phase AC-DC converter is presented. It is shown that application of this technique to a single-phase AC fed buck-boost AC-DC converter yields a sinusoidal input current waveform at unity input power factor. The proposed converter retains this property even under distorted AC input voltage conditions. In addition, the proposed technique offers definite advantages over the conventional boost converter and it is easy to understand, is easy to implement, and draws sinusoidal input current from the AC source for any DC output voltage condition. That is, the DC output voltage may be less than the peak AC input voltage. Furthermore, the proposed technique attenuates substantially the low-frequency harmonic components of the rectifier input current while shifting the unwanted harmonic components near the switching frequency. These unwanted high-frequency components can be easily filtered out using lightweight filter components. >

Series resonant converter with third-order commutation network

Abstract: To compensate for the poor output voltage regulation of the series resonant converter (SCR), a converter is derived by adding an inductor in parallel with the resonant capacitor of the conventional SCR. The resulting converter is called the LLC-SRC. This converter is analyzed via a two-dimensional state-plane diagram through a proper transformation of its state variables. Based on the analysis results, a set of characteristic curves is derived showing that the control characteristics and component stresses of the new converter are improved compared with those of a conventional SRC. Based on these curves, the design procedure for the LLC-SRC is formulated. The experimental results from the breadboard model were used to verify the theoretical work. >

AC to DC converter having an enhanced power factor

Abstract: The invention relates to an AC to DC converter having an improved power factor achieved by combining boost converter operation at the beginning and ending of each half wave of the AC input waveform, with passive operation at the middle portion of each half wave. The timing of the operation is based on comparing the instantaneous voltage with a stored average voltage, which has the effect of making boost converter operation go off at a fixed angle after the beginning of each half wave and go on at a fixed angle before the ending of each half wave, the angles being independent of the average AC voltage. The converter increases the power factor to a value between 90 and 97% and reduces the current waveform distortion to between 15 and 29%.

A phase-shift modulated double tuned resonant DC/DC converter: analysis and experimental results

Abstract: Analysis, design, and experimental results of a double-tuned resonant DC/DC converter are presented. The resonant circuit employed in the converter consists of a series branch in which an inductor and a capacitor are connected in parallel. The components of both branches are tuned at the operating frequencies of the converter. The proposed resonant circuit provides reduced switching and conduction losses for a wide range of input voltage and output load variations. A detailed description of the converter circuit, explaining operating modes, it is given. A prototype converter was built. It operates at a 256 kHz clock frequency and delivers 5 V, 100 A DC from a nominal 48 V DC input. Experimental results show an overall efficiency of about 86% from full-load to 1/4 load. >

Independent control of the AC line current and output DC voltage of a high power factor AC-to-DC converter

Abstract: A method and system for controlling a dual output power converter of the type having a pair of input terminals connectable to a source of rectified AC power of variable voltage amplitude, a boosting circuit including a secondary winding of a boost transformer operatively coupled in circuit with the pair of input terminals for providing a boosted voltage onto a DC power bus, and a full-bridge inverter including at least one controllable switching device serially connected in each leg of the inverter. The inverter has an input connected to the DC bus and a pair of output terminals connected to respective ends of a primary winding of an output transformer, at least one of the pair of output terminals being connected in circuit with the primary winding of the boost transformer. The control system compares signals representative of the magnitude of the AC power voltage to signals representative of the DC bus voltage and varies the inverter frequency of operation in a manner to adjust the magnitude of the DC bus voltage to establish a preselected ratio of DC bus voltage to AC power voltage.

Synchronized switch tapped coupled inductor regulation circuit

Abstract: A synchronized switch tapped coupled inductor circuit which couples a first closed-loop regulated output of a forward converter switching power supply to a second output to assist in regulating the voltage of the second output. The switched power supply includes a converter transformer which is implemented as a forward converter providing the multiple outputs. The second output includes a storage inductor which is coupled to a storage inductor of the first output. The second coupled inductor includes a center tap which is connected to a synchronized switch. The synchronized switch is further connected to the first output and coupled to the converter transformer to detect the forward and flyback portions of each cycle. During the flyback portion of each cycle, the switch is turned on coupling the center tap to the first output. During the forward portion of each cycle, the switch is turned off, isolating the outputs from each other.

A resonant DC-DC transformer

Abstract: The characteristics of a push-pull parallel resonant converter (PPRC) when operated as a DC-DC transformer were investigated theoretically and experimentally. In the DC-DC transformer region, the voltage transfer ratio was found to be practically constant and independent of the input voltage and load. In this mode, all the switching elements operate in the zero voltage switching (ZVS) conditions. This helps to achieve high efficiency at high switching frequencies Another important feature of the proposed DC-DC transformer is the ability to be driven by an arbitrary switching frequency, provided that it is lower than the self-oscillating frequency. This permits the synchronization of the converter to a master clock to obtain a stable signal spectrum of a desired base frequency. The analytical expressions for the peak voltages and currents derived are applied to the converter. The proposed topology was tested experimentally on a 100 W unit which was run in the 200 kHz frequency region. >

Novel constant frequency PWM DC/DC converter with zero voltage switching for both primary switches and secondary rectifying diodes

Abstract: A zero-voltage-switching (ZVS) DC/DC converter operating at constant frequency and having wide linearity is proposed. ZVS operation is achieved not only for the primary switches but also for the secondary rectifier diodes to reduce the switching stresses and losses. The converter overcomes other shortcomings of the conventional resonant DC/DC converters, among which are the high VA ratings of devices and passive components and load-dependent DC characteristics. >

High performance AC/DC converter for high frequency power distribution systems: analysis, design considerations and experimental results

Abstract: This paper presents a description and analysis of a new AC/DC converter topology for use in the high-frequency power distribution system in Space Station Freedom. Steady-state analysis of the converter is provided, the performance characteristics presented, and transient behavior studied. The proposed converter has close-to-unity rated power factor (greater than 0.98), low total harmonic distortion in input current (less than 5%), and high conversion efficiency (greater than 96%). Finally, to verify the proof of-concept, a bread-board converter was built. >

Electric fence charger

Abstract: The invention provides an electric fence charger of the type that periodically provides high voltage electrical shock pulses through an electric fence wire. The fence charger has a low voltage power source that powers the fence charger and supplies a charging current. An energy converter converts the low voltage and charging current of the power source to high voltage for storage in a high voltage storage means. A timer emits pulse discharge control signals on a periodic basis and these control signals are used to control discharge of the stored high voltage for delivering shocking pulses into the fence wire. A regulator adjusts operation of the energy converter to provide a minimum high voltage energy level as long as the power source voltage exceeds an established power source voltage reference. In another embodiment of the invention, a fence charger employs a DC-DC flyback converter for charging a high voltage storage means to a discharge voltage level which provides a minimum shock energy pulse. This embodiment includes means for operating the flyback converter at a constant frequency and means responsive to battery voltage for changing the flyback converter duty cycle to regulate the discharge voltage level.

Optimal control and appropriate pulse width modulation for a three-phase voltage DC-link PWM converter

Abstract: Novel control strategies are presented which use all allowed switching operations of the three-phase voltage DC-link pulse width modulation (PWM) converter such that the converter has a line-friendly performance from the point of view of the utilities or the consumer In the case of an ideal converter and a distortion-free supply network, the power factor becomes equal to unity under steady-state conditions and the dynamic characteristics of the control system are sufficient In order to reach this line friendly performance with an existing converter and to keep the expenditure for the line-side filter low, appropriate PWM at a high switching frequency (>10 kHz) is necessary The theory of the control strategies and appropriate PWM are presented Practical results obtained with an insulated-gate bipolar transistor (IGBT) converter illustrate the dynamic and steady-state performance of the new control system in both energy-flow directions >