Showing papers on "Flyback transformer published in 1993"

Magnetically integrated full wave DC to DC converter

Abstract: A full wave DC to DC converter that is magnetically integrated so that the function of the output filter inductor is magnetically included in the transformer assembly. Two essentially symmetrical transformers have their primary windings connected in series and are driven by a full wave switched primary circuit such as a full bridge. The transformer secondaries are polarized so that their rectifying diodes conduct on opposite phases, so only one transformer secondary conducts for each half cycle. The conducting secondary winding conducts for each half cycle. The conducting secondary winding conducts both forward current reflected from the primary and flyback current from collapsing core flux. The transformer having the non-conducting secondary stores energy as magnetic flux. On the other half-cycle, the transformers reverse roles. Because stored transformer flux energy is released to the load through the secondary windings, continuous current is maintained and no separate output smoothing inductor is required.

Power factor correction with flyback converter employing charge control

Abstract: The charge control concept is applied to a flyback power converter for the purpose of power factor correction (PFC). Using charge control, a flyback converter can operate in continuous conduction-mode (CCM) with unity power factor. The simplicity of the flyback circuit is maintained and the power handling capacity is increased. The properties of charge control related to flyback PFC application are studied. The design guidelines are presented. A 200 W prototype circuit is built. Experimental results show good application prospects. >

Design of the zero-voltage-switching quasi-square-wave resonant switch

Abstract: Zero-voltage-switching, quasi-square-wave (ZVS-QSW) power converters with controllable rectifiers feature constant-frequency, PWM-like operation with low voltage and relatively low current stresses on active devices. New closed-form analytic results are derived and applied to construct a detailed design procedure for the ZVS-QSW switch. Starting with usual design constraints, resonant elements are selected so that zero-voltage switching is achieved under all operating conditions, with favorable tradeoff between switching and conduction losses. Results are derived in a form applicable to a wide variety of ZVS-QSW power converter topologies. The design procedure is illustrated on a flyback power converter example and is supported by simulation results. >

Compact low noise low power dual mode battery charging circuit

Abstract: A low noise battery charger includes a rectifier to convert AC line voltage to a rectified sinusoidal voltage that is applied to a primary winding of a transformer. Another rectifier coupled to a first secondary winding applies a charging current to a battery. A switch coupled in series with the primary winding controls current therein. A rectifier coupled to another secondary winding produces a battery condition voltage. An incrementing signal synchronized with the rectified sinusoidal voltage increments a ratchet DAC until its output voltage exceeds the battery condition voltage. A low charging mode signal is produced when the battery condition voltage falls a certain amount below the DAC output voltage. Flow of current through the primary winding is controlled by operating the switch at a relatively high frequency and by producing constant turn off times for the switch which are proportional to the resonant period of the primary winding circuit and also by modulating turn on times for the switch in response to the signal indicative of primary winding current. Maximum power transfer across the transformer is thereby achieved without flyback voltage of the transformer exceeding breakdown voltage of the switch, and zero current switching is achieved.

Galvanic isolation device for direct current electrical signals or electrical signals likely to include a direct current component

Abstract: Galvanic isolation device for direct current electrical signals or electrical signals likely to include a direct current component, which includes a transformer (T), reversible switch I for chopping the incident signal applied to one wind of this transformer reversible switch I' for chopping the signal obtained at the other winding of this transformer, controlled either in phase or in phase opposition with each other and filters (F1,F2) for filtering the chopped signals respectively obtained at windings of the transformer.

Pulse generator for use in an implantable atrial defibrillator

Abstract: A pulse generator (66) for use in an implantable atrial defibrillator (30) provides cardioverting electrical energy to the atria of a heart through at least one lead (36) having a pair of electrodes (44,46) associated with the atria of the heart. The pulse generator includes a depletable, low voltage, power source (67) such as a battery. A charging circuit coupled to the battery includes a flyback transformer for converting the battery voltage to pulsating high voltage electrical energy to store the high voltage electrical energy in a storage capacitor coupled to the charging circuit. A crosspoint switch selectively couples the storage capacitor to the electrodes (44,46) for applying a portion of the stored electrical energy to the atria of the heart for cardioverting the atria of the heart.

High voltage regulator for an integrated horizontal sweep system

Abstract: A voltage regulator for a flyback-type high voltage supply having: a pulse transformer with its secondary interconnected in series with the primary of a flyback transformer; a control circuit for sensing the generation of a flyback pulse, a reference voltage, and a feedback voltage signal appearing at the output of the flyback transformer; and a switch for selectively applying energy to the primary of the pulse transformer while uniformly maintaining the flow of current through the primary of the flyback transformer.

Piezoelectric transformer converter for power use

Abstract: In a piezoelectric transformer converter for power use that includes a switching circuit that generates alternating current, a power-use piezoelectric transformer, and a rectification-smoothing circuit, the alternating current output of the power-use piezoelectric transformer is directly phase-inverted and amplified by a phase inversion-amplification circuit, and by way of a driving circuit, produces self-excited oscillation. In addition, the output voltage of the rectification-smoothing circuit is compared with a reference voltage by means of an error amplifier, and based on the resulting amplified voltage difference, the output voltage is controlled by using PWM control or frequency modulation control without the need for an additional electrode for self-excited oscillation. In addition, when controlling the output voltage to be constant, stable control is enabled that is unaffected by variance in the frequency characteristics of the power-use piezoelectric transformer.

DC-To-DC converter with secondary flyback core reset

Abstract: A secondary flyback core reset (SFCR) scheme for single-ended forward DC-to-DC converters is disclosed. The transformer secondary magnetizing inductor and a parasitic reset capacitance of the output forward rectifier diode form a secondary flyback reset circuit. The magnetic flux built up through the primary winding when the main switch is turned on is reset through this secondary flyback reset circuit when the main switch is turned off. The secondary flyback reset circuit initiates a half resonant cycle and resets the transformer. With proper design of the reset time, the maximum duty cycle of the main switch can go beyond 50%, while still using the first and third quadrants of the core B-H loop characteristics for optimum use of the core power density, and reduced RMS switching current and rectifier blocking voltages and power switch blocking voltage.

High voltage integrated flyback circuit in 2 μm CMOS

Abstract: When a field effect transistor is used to control the current through an inductive load, the flyback voltage is felt through the vertical pnp transistor at the drain, which onducts to the substrate. This current represents a power loss and a source of heat. This invention supplies a second lateral transistor which conducts this current back to the power supply.

Parallel-resonant inverter-type fluorescent lamp ballast

Abstract: A push-pull inverter is supplied from an inductively current-limited DC voltage source by way of a center-tap on a transformer having significant inductance. This transformer inductance is parallel-coupled with a capacitance means. The inverter is made to self-oscillate through positive feedback provided by way of a saturable current transformer. The inverter frequency is determined by the saturation time of this current transformer, which saturation time is designed to be somewhat longer than the half-cycle period of the natural resonance frequency of the transformer inductance combined with the capacitance means. By controlling the length of this saturation time, the magnitude of the current provided to the fluorescent lamp is controlled, thereby permitting control of the light output in response to changes in the magnitude of the power line voltage.

Display apparatus for displaying pictures virtually instantaneously

Abstract: A display apparatus for displaying pictures virtually instantaneously adopts a direct-heating type cathode of an impregnated structure, and includes a cathode ray tube having a dispenser cathode wherein a cathode material is filled in pores of a porous body and a porous heater is directly connected to the cathode material. A voltage generator of the apparatus produces a first voltage for driving the heater. A video signal supply portion supplies a video signal to the cathode, while a deflector deflects horizontally and vertically an electron beam generated from the cathode to produce a raster by scanning the fluorescent surface of the cathode ray tube. A flyback transformer generates a second voltage to be supplied to the anode and one or more grids of the cathode ray tube using a horizontal deflection output signal supplied from the deflector. With the described arrangement, an electron-emitting velocity of an electron gun reaches its maximum value within about one second after power is applied. Thus, the display apparatus can be adapted to an HDTV requiring high current density electron-emitting characteristics.

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 of the PPRC 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) condition. Another important feature of the proposed DC-DC transformer is the ability to drive it by an arbitrary switching frequency, provided that the latter is lower than the self-oscillating frequency. This permits the synchronization of the converter to a master clock. The analytical expressions for voltage and current stresses, as well as the other key parameters derived, are applied to develop design guidelines for the DC-DC transformer. The proposed topology was tested experimentally on a 100-W unit which was run in the 200-kHz frequency region. >

Push-pull output stage for driving motors which generates auxiliary voltage supply

Abstract: A push-pull output stage for driving a motor which provides an auxiliary power supply Vaux above supply voltage Vcc by using highside MOSFETs which do not have source-body shorts, and by connecting a capacitor to the poles of the motor through rectifying diodes which output flyback pulses to the capacitor. Damage to the highside MOSFETs is prevented by limiting the voltage on the capacitor using a zener diode. The push-pull output stage increases the driving potential applied to the motor be eliminating the need for an isolating Schottky diode between the output stage and a power source. Back emf continues to supply energy to Vaux even after Vcc is removed.

A small-signal model for SEPIC, Cuk and flyback converters as power factor preregulators in discontinuous conduction mode

Abstract: The authors describe small-signal models for SEPIC, Cuk, and flyback converters as power factor preregulators in discontinuous conduction mode (voltage follower approach) and constant frequency, using CIECA (current injected equivalent circuit approach). Implementations with and without input voltage feedforward, using resistive load, constant power and constant current loads, are analyzed, and their respective transfer functions are obtained. The applicability of an integrated circuit (usually used in continuous conduction mode) in the control loop is also presented. Simulation results are presented, validating the models to be used in control loop design. >

Using SEPIC Topology for Improving Power Factor in Distributed Power Supply Systems

Abstract: The Single Ended Primary Inductance Converter (SEPIC) presents several advantages over boost and flyback topologies which make this converter very convenient to be used as Power Factor Preregulator...

Synchronous rectifying circuit

Abstract: A method of efficiently turning off inductive loads includes turning off a driving switch, monitoring a circuit output during turn-off, and activating a control circuit in response to an inductive flyback voltage at the output which turns on a recirculation switch and recirculates residual load current and clamps the output thereby substantially decreasing power dissipation during inductive load turn-off.

Power converter apparatus for defibrillating cardiac pacemaker

Abstract: A power converter apparatus adapted for use in a defibrillating cardiac pacemaker, to selectively provide a prescribed high voltage useful in treating a cardiac fibrillation. A pulse generator-cyclically applies a relatively low battery voltage V s to a step-up transformer, to controllably charge a high-voltage capacitor. The time durations of the cyclic applications of the battery voltage V s are controlled by digital feedback of several parameters, including peak transformer current, average transformer current., battery voltage V s , and the voltage on the high-voltage capacitor. If any of the measured parameters is determined to be outside a predetermined limit, the pulsing of the transformer is incrementally modified. A smooth, efficient charging of the high-voltage capacitor thereby is provided.

An AC power supply with sliding-mode control

Abstract: A sliding-mode control in electronic AC power supplies is presented. This control technique makes it possible to satisfy the increasing demand for the high-level performance of these systems, which include uninterruptible power supplies, test supplies, and fuel cell, and solar cell supplies. The existence and hitting conditions are discussed, and criteria for the selection of the control parameters which define the sliding surface and determine the quality of response are described. Improvements of the method are introduced to accommodate for the time-varying voltage reference and in the presence of an insulation transformer. A three-level, constant-frequency, variable-band dead-beat modulation technique is associated with the sliding control, producing ultrasonic, low-ripple modulation. Tests performed on an experimental prototype confirm the outstanding performance of the adopted control. >

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

Abstract: A new three-phase single-switch AC-DC flyback power 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 are 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. >

Switch mode power supply with reduced input current distortion

Abstract: In a switch mode power supply, a full wave rectified AC mains supply voltage is produced from an AC mains supply voltage without low-pass filtering. The unfiltered rectified voltage is applied to a winding of a flyback transformer that is coupled to a switching transistor. A first plurality of current pulses are generated in the winding from the rectified voltage at a frequency that is higher than the frequency of the mains supply voltage and at peak amplitudes that vary in accordance with the rectified voltage in a manner to increase a power factor. The rectified voltage is further rectified via a rectifier coupled in series with a resistor and a low-pass filter capacitor and produces current pulses in the capacitor. A voltage in the capacitor is coupled via a second switching transistor to the winding to produce in the winding a second plurality of current pulses that reduce a ripple component at an output of the power supply. The resistor increases the pulse-width and decreases the magnitude of the capacitor current pulses in a manner to reduce input harmonic contents and increase the power factor.

Delivery point voltage regulation in electric energy distribution networks

Abstract: A method for regulating the voltage at which electric energy is supplied at the delivery points in a network for distributing electricity. The voltage of electric energy supplied through a high-voltage network is reduced to a voltage suitable for a medium-voltage network by means of at least one variable transformer. The voltage of the electric energy in the medium-voltage network is reduced, by means of at least one transformer, to a voltage suitable for a low-voltage network supplying the electric energy to the consumers. The adjustment of the variable transformer between a high-voltage network and a medium-voltage network is influenced by the actual voltage measured and the current or load at the output side of the variable transformer. The voltage prevailing at the delivery point is measured at the location of at least a number of consumers and the variable transformer is set partly in dependence on the voltage thus measured at the consumers' location.

Constant charge time of defibrillation capacitor

Abstract: A capacitor charging circuit for charging a defibrillation capacitor in a constant period of time regardless of battery voltage by employing a controlled duty cycle charging technique The defibrillation capacitor is charged in a piecemeal manner through a transistor and flyback transformer circuit The gate of the transistor is driven by a constant frequency pulse train inverter drive signal in which voltage is conveyed to the capacitors during one-half of the full cycle of the pulse train The primary of the transformer is controlled by each pulse of the inverter drive signal so that the secondary of the transformer supplies current to the defibrillation capacitors during the off half cycle of the drive signal, the charge being built up in the defibrillation capacitors incrementally during the off half cycle of the inverter drive signal until the predetermined voltage is reached

A low input harmonic induced multiple use AC synchronous generator starter converter

Abstract: A synchronous generator start converter offers power conversion for performing multiple functions such as starting AC generators as a motor, charging batteries and also providing regulated DC output without degradation of input power quality. The converter utilizes common magnetic components and common semiconductor rectifiers within its three subcircuits. The three subcircuits include flyback converters, a square wave inverter and a field excitation controller.

Forward converter regulator using PWM controlled transformer

Abstract: A new control scheme is proposed for a forward power converter regulator using a controlled transformer. Pulse width modulation (PWM) control is used to reset the control core of the controlled transformer. As a result, a low-cost ferrite core can be used for the controlled transformer to achieve good regulation and high efficiency. Overall efficiency of 82-86% is achieved in a 200 kHz, 500 W, 5 V output regulator. A PWM-controlled transformer regulator is particularly suited for high-output-current and/or high-output-voltage postregulator applications.

Liquid crystal driving circuit

Abstract: PURPOSE: To reduce power consumption of a driving circuit of a liquid crystal display device by cutting off a current flowing in a buffer circuit in a vertical flyback period and a horizontal flyback period. CONSTITUTION: An output line of a buffer circuit is connected to a drain line of a liquid crystal display device through a resistor 18. And an N channel MOS 19 for controlling operation of a buffer circuit is connected between the buffer circuit and the ground potential, the MOS 19 is controlled by a control signal HE. Therefore, when the control signal HE is in an H level, the buffer circuit is operated, but when the control signal HE is in an L level, a current flowing in the buffer circuit is cut off. The control signal HE is made an L level in a period excluding a horizontal scanning period displayed in an effective display line of dot lines located from the uppermost section of the liquid crystal display device to the lowermost, that is, a vertical flyback period, and a period in which the liquid crystal display device is shifted from a line to a next line, that is, a horizontal flyback period, and the control signal HE is made an H level in a period in which a video signal of one horizontal scanning period is displayed. COPYRIGHT: (C)1994,JPO

Current limiters in power utility applications

Abstract: A current limiting method and apparatus for preventing fault overload in a utility power transmission system (10) employs a high power, superconducting coil based pulse transformer (36) for saturating the core of the utility power transformer (30) thereby limiting its current carrying capacity. The utility transformer core (54) is biased to a disadvantageous portion of its B-H curve. A fault condition is detected and as a result the superconducting coil (48) is quenched thereby sending a high energy pulse of current into the utility transformer magnetic core (54). The core, while heating, does not exceed its capability to maintain a stable thermal condition while at the same time limiting the current being transformed from its input (32) to output (34) lines, until a transformer circuit breaker activates.

Series-parallel active power line conditioner utilizing reduced-turns-ratio transformer for enhanced peak voltage regulation capability

Abstract: The present invention provides an improved active power line conditioner which achieves a significant improvement in peak voltage regulation capability when compared with a similarly-sized device of the prior art. Enhanced peak voltage regulation capability is achieved by reducing the number of turns on the transformer winding connected to the series inverter. As a result, the AC regulation voltage induced across the transformer primary and added to or subtracted from the AC supply voltage will be capable of achieving higher peak levels of short duration. When a reduced-turns-ratio transformer is utilized according to the invention, variations of the AC supply voltage which are within the sinusoidal regulation range of a prior art active power line conditioner having a similarly-sized transformer, the output voltage will remain sinusoidal. When, however, the input voltage variation is outside of this sinusoidal regulation range, the reduced-turns-ratio transformer will create a peaking but nonsinusoidal AC output voltage. This allows rejection of higher magnitude input voltage disturbances of short duration.

Design of power factor corrector for the off-line isolated buck/boost converter by a voltage-follower technique

Abstract: A voltage-follower controller (VFC) formed by the usual PWM controller is proposed that improves the power factor of the isolated buck/boost (flyback) power converter in the discontinuous conduction mode (DCM). The presented VFC can adaptively control the line current in phase with the input line voltage to achieve nearly unity power factor under the full-load condition. An isolated 50 W buck/boost power converter with VFC in DCM is realized that improves the power factor to 0.994. >

High-voltage generating circuit

Abstract: A high-voltage generating circuit for use in a CRT display apparatus has a horizontal drive circuit which is supplied with a horizontal frequency signal synchronous with a horizontal synchronizing signal in an input signal, a high-voltage converter output circuit which can be turned on and off by an output signal from the horizontal drive circuit, and a flyback transformer connected to an output terminal of the high-voltage converter output circuit. A frequency multiplier connected between the horizontal drive circuit and a terminal supplying the horizontal frequency signal to the horizontal drive circuit multiples the frequency of the horizontal signal at the terminal by a multiplication factor variable depending on the frequency of the horizontal frequency signal.