Showing papers on "Flyback transformer published in 1991"

Multi-loop control for quasi-resonant converters

Abstract: A multiloop control scheme for quasi-resonant converters (QRCs) is described. Like current-mode control for pulse width modulation (PWM) converters, this control offers excellent transient response and replaces the voltage-controlled oscillator (VCO) with a simple comparator. In this method, referred to as current-sense frequency modulation (CSFM), a signal proportional to the output-inductor current is compared with an error voltage signal to modulate the switching frequency. The control can be applied to either zero-voltage-switched (ZVS) or zero-current-switched (ZCS) QRCs. Computer simulation is method applied to a ZCS buck QRC. A circuit implementation is presented that allows multiloop control to be used on circuits switching up to 10 MHz. This circuit requires few components and produces clean control waveforms. Experimental results are presented for zero-current flyback and zero-voltage buck QRCs, operating at up to 7 MHz. Good small-signal characteristics have been obtained. >

Improving power factor correction in distributed power supply systems using PWM and ZCS-QR SEPIC topologies

Abstract: The single-ended primary inductance converter (SEPIC) presents several advantages over boost and flyback topologies which make this converter convenient for use as a power factor preregulator (PFP). Due to this fact, both the pulsewidth modulation (PWM) and the zero-current switched quasi-resonant (ZCS-QR) SEPIC used as PFPs are studied. Stress in components and operation in continuous and discontinuous conduction mode are considered in the PWM case, while the use of full-wave and half-wave resonant switches is considered in the ZCS-QR case. The study of the PWM SEPIC used as a PFP reveals that both types of PFP control, multiplier approach and voltage-follower approach, can be used in PWM SEPIC, the first one when it operates in continuous conduction mode and the second one when it operates in discontinuous conduction mode. Regarding the ZCS-QR SEPIC used as PFP, both types of resonant switch (half-wave and full-wave) can be used. >

Use of leading-edge modulation to transform boost and flyback converters into minimum-phase-zero systems

Abstract: In leading edge modulation, the pulse width modulated (PWM) signal is turned off at the clock signal and turned on when the error signal crosses the ramp waveform. It is shown that the positive zero in the power stage transfer function of boost and flyback regulators can be shifted into the left-half-plane under suitable conditions. These conditions are as follows: (1) leading edge modulation must be used in the pulse width modulator; (2) the feedback compensation must not average the capacitor EST-generated output voltage switching ripple; and (3) appropriate power stage parameter values are necessary. The design procedure for shifting the positive zero into the left-half-plane is presented. Experimental verification is provided. >

Design of a high-frequency planar power transformer in multilayer technology

Abstract: A high-frequency power transformer using multilayer printed circuit board (ML-PCB) technology is presented for applications in switched-mode power supplies operating at frequencies up to several megahertz. The mechanical configuration of laboratory prototypes is discussed, as well as the electrical, parasitic, and thermal behavior. The focus is on the leakage inductance, since the analysis of other aspects is relatively simple. Test results show that the transformer has high efficiency, low leakage inductance, good thermal behavior, and good line insulation properties. The topology enables the designer to make a trade-off between leakage inductance and interwinding capacitance. Due to the well-defined geometry, parasitic interwinding capacitance and leakage inductance are reproducible and can be computed relatively easily. >

Transformer isolated drive circuit

Abstract: A transformer isolated circuit for driving a semiconductor power switch includes a transformer which is driven with a high frequency Pulse Width Modulated (PWM) signal in such a way that the constantly present PWM carrier supplies the power needed for high gate current pulses, while different duty cycles determine the "on" or "off" state of the power device under control. Transformer saturation is prevented by sensing primary current and returning it to zero once per PWM cycle. Because of the high PWM carrier frequency used, the average transformer power is low, yet the secondary side is able to deliver high pulse currents for fast "on-off" switching of the gate of even the largest N- or P-channel device, without need for auxiliary power supplies. Also included are provisions for extremely fast output current limiting, for use where short circuit protection is necessary. Discussion of a monolithic implementation is included.

Bootstrap modified topologies for wide-input range switchmode DC to DC converters

Abstract: A bootstrap circuit that operates in combination with switchmode DC to DC converter topologies that are based on forward (10), half-bridge/full-bridge (40) and flyback (60) configurations. Each configuration consists of an output circuit (18) and a bootstrap modified input circuit (12) that further consists of a bootstrap circuit (14) and a converter input circuit (16). The bootstrap function is achieved by charging a bootstrap inductor (L1) from current derived from the input voltage source and subsequently discharging the inductor through a bootstrap capacitor (C1) where an augmented voltage that is higher than the input voltage is developed. The converter then operates from the augmented voltage rather than from the input voltage. Thus, the invention is able to provide a constant output when operated over a wide-input voltage range while at the same time reducing the voltage stresses on the converter's primary switches and output rectifiers. Furthermore, reduction of input RF noise is accomplished by judicious choice of size and location of the bootstrap capacitor C1.

Three-phase flyback AC-DC convertor with sinusoidal supply currents

Abstract: A three-phase flyback AC-DC convertor which has the step-up and step-down characteristics of output voltage, is described. The introduction of pulsewidth modulation makes it possible to obtain the sinusoidal supply currents with a near unity power factor. Three gate-turn-off thyristors provide the necessary control over the currents for unidirectional power flow. To improve upon the oscillatory transient operations, the tested system includes the digital PID controller using a microcomputer for output voltage regulations. The experimental results and state-space simulations confirm the usefulness of the presented convertor. >

A new type high frequency transformer

Abstract: In order to realize small power supplies, the authors propose a type of coreless high-frequency transformer. This transformer is composed of simple twisted coils and its operating principle is based on the skin effect of current carrying conductors. Approximate analysis based on the symmetrical current distributions in each of the coil axes has been applied to this transformer. As a result, it has been clarified that the simple analytical model can be used to estimate the rough performance of the transformer. Analytical and experimental studies suggest that twisted coils have versatile possibilities as a high-frequency transformer. >

Power conversion system, method for controlling the same, and uninterruptible power supply using the same

Abstract: A three-phase a.c. uninterruptible power supply includes a transformer needing insulation, a single-phase inverter (2), and a cycloconverter (4). The uninterruptible power supply operates to convert a d.c. voltage into a high-frequncy a.c. voltage in the single-phase inverter (2), transmit the output voltage of the single-phase inverter (2) in an insulating state, and convert the output of the transformer into a three-phase voltage having a lower frequency such as 50 or 60 Hz than the frequency of the output voltage of the single-phase inverter (2). It results in allowing the transformer needing insulation to use a high-frequency signal, thereby reducing the transformer itself in size.

Current chopping strategy for generating action in switched reluctance machines

Abstract: A method and apparatus are provided for controlling the switching devices in a switched reluctance machine bridge inverter, which inverter has at least two switching devices per phase leg, during generating operation. At the start of the conduction interval for a particular machine phase, both switching devices of that phase are turned on, causing the phase current to build up. When the phase current reaches an upper hysteresis band level, both switching devices are turned off, resulting in the application of a reverse voltage across the phase winding and directing the phase current into the power source via flyback diodes. At relatively low and medium speeds, the phase current decreases until it reaches a lower hysteresis band level, at which point only one switching device is turned back on to form a freewheeling loop through that device and the corresponding flyback diode. The process repeats until the turn-off angle of the active phase is reached, at which point both switches are turned off in order to discharge the corresponding phase winding.

A high efficiency power converter employing a synchronized switching system

Abstract: A synchronized switching system for use in a power converter. A pulse-width modulation controller is provided to alternately turn on and off a switching device and control the on/off duty cycle. When the switching device is turned off, initial commutating or flyback current from an inductor is conducted by a protective diode connected to ground. The diode is paralleled by a more efficient secondary switching device that is synchronized to conduct during the nonconduction period of a main switching device. A sense winding is added on the inductor for synchronizing the secondary switching device. A digital logic circuit controls the conduction time of the secondary switching device based on signals from a pulse-width modulation controller and from the sense winding of the inductor. After the main switching device has been conducting for the required time, the pulse-width modulation controller turns it off. The digital logic circuit senses the voltage level on the inductor and causes the secondary switching device to conduct, just after the main switching device stops conducting. The digital logic circuit prevents the main and secondary switching devices from conducting simultaneously.

AC current detector and power supply circuit

Abstract: An full bridge Zero-Voltage-Switched DC/DC converter with the four MOSFET snitches feeding the primary winding (T1) of the output transformer (T1) through a series inductance (L) and a series DC blocking capacitance (C) uses two MOSFET asynchronous rectifiers ((Q2) in its full wave output section. Each ((Q2) is serially connected between the output transformer (T1) and the output shunt capacitance (C') through the primary winding (T21) of a transformer detecting its drain current. The secondary winding (T22) of the detector transformer is shunted by a pair of resistances (R1/R'1) each in series with the base-emitter junction of a bipolar transistor (Q1/Q'1), the two transistors of complementary polarity forming a totem-pole branched across an auxiliary winding (T12) of the output transformer. The totem-pole output coupled (R2) to the gate of the MOSFET (Q2) switches its state upon the drain current value crossing the adjustable (R1/R'1) low value of the detector transformer magnetising current.

Transformer fault protection device

Abstract: A transformer ground fault protector is provided and includes sensing means to be positioned adjacent but spaced from the output of each secondary winding in a transformer having its secondary windings connected in series and at the midpoint of the series circuit to ground. The sensing means forms a capacitive circuit with the windings and generates an output voltage when the secondary windings are energized. The output voltages generated by the sensing means are combined which in normal operation of the transformer, results in a voltage having a magnitude substantially equal to zero volts. However, when a fault occurs in the transformer, the output voltages induced in the sensing means are unequal and opposite in polarity resulting in a voltage having an absolute value greater than zero when combined. The resultant voltage in turn is conveyed to a comparator which compares the magnitude of the resultant voltage with a predetermined threshold voltage. When the resultant voltage is greater than the predetermined threshold voltage, the comparator provides a positive output voltage which is used to bias a switch connected in series with the transformer primary winding to an open condition thereby to isolate the primary winding from its power supply. An LED is illuminated when the primary winding is isolated from the power supply to provide a visual indication of the transformer fault condition.

Interrogation of a conventional current transformer by a fiber-optic interferometer

Abstract: A new approach to the measurement of large currents at high potential is presented in which the output signal from a conventional current transformer is measured by transducing the voltage developed across the transformer secondary into phase modulation in a fiber-optic interferometer through a piezoelectric element. The demonstrated current range was 140 A, although the system is capable of measuring current as great as 3000 A. The current resolution is >10−1A/Hz over a frequency range of 30–104 Hz.

Inverter and power supply systems including same

Abstract: An inverter for supplying electrical energy from a DC supply to a load, includes a flyback transformer having a primary winding circuit coupled to the DC supply, and a secondary winding circuit coupled to the load. The primary winding circuit includes a first switch for interrupting the DC supply causing energy to be stored in the transformer, and the secondary winding circuit includes a second, unidirectional switch to produce an output of one sign when closed. The primary winding circuit further includes an electrical device effective to return energy to the DC supply only when the first and second switches are open.

Complementary electronic power converter

Abstract: Minimal energy storage is required in complementary converters, a family of zero-voltage switching circuits which achieve non-pulsating input and output currents by employing a ripple-cancelling technique instead of conventional filtering. The input voltage in these circuits is divided between a primary winding of a main transformer and a primary winding of a second transformer referred to as a complement transformer. The turns ratios of the two transformers are adjusted so that the secondary voltage of the complement transformer cancels the ripple in the rectified output of the main transformer. The symmetry of these circuits allows an AC voltage waveshape to be impressed upon the main transformer, independent of the load current passing through it. If desired, a sinusoidal voltage can be produced across the main transformer with only a small resonant current, which can be achieved with minimal energy storage. The complement transformer also requires minimal energy storage because the flux produced by the DC primary currents is cancelled by the DC secondary currents. The symmetry of these circuits allows them to have bidirectional power flow if synchronous rectification is used. Further, if bidirectional switches are used, reversing the input voltage will reverse the output voltage. Thus, complementary converters can be made to emulate an ideal transformer, passing both AC and DC if the input frequency is well below the switching frequency.

Using zero-current-switched quasiresonant converters as power factor preregulator

Abstract: Th use of zero-current-switched quasiresonant power converters (ZCS-QRCs) as power factor preregulators (PFPs) is studied The study is applicable to boost, buck-boost, flyback, SEPIC, and Cuk topologies The main conclusion obtained is that the switching frequency variation range using a half-wave resonant switch is lower than that using a full-wave resonant switch if the load connected to the output is almost constant Moreover, using topologies with power transformers (flyback, SEPIC, or Cuk), this variation range can be minimized by choosing an adequate value of the normalized switching frequency at the peak of the sinusoidal input voltage However, this range increases greatly when the load changes in the same manner In this case, a smaller switching frequency variation range is obtained using the full-wave switch However, this type of resonant switch decreases the efficiency because it handles reactive energy and then a tradeoff between switching frequency variation range and efficiency must be considered >

Flyback converter having a high efficiency irrespective of magnitude of a load

Abstract: In a converter which is usable as a kind of DC--DC converter and which comprises a transformer for processing an exciting current into an excited current under influence of an inductance value of the transformer, the inductance value is controlled in compliance with a value of the exciting current. The exciting current is controlled by a current control circuit with reference to the excited current so that exciting current is intermittently supplied to the transformer. While the exciting current is absent during intermittent supply to the transformer, the transformer produces the excited current.

Balun transformer with common mode coil

Abstract: A balun transformer with a common mode coil is formed by parallel two-strand cable wound around a common core having through-holes through which the cable passes. The common mode coil can be connected either on the input side or the output side of the balun transformer. Because only one core is used to form both the balun transformer and the common mode coil, the outer dimensions of the transformer can be reached, along with manufacturing costs, to reduce the number of man-hours required to manufacture the transformer by this invention. This configuration also permits shorter connections between the balun transformer and the common mode coil.

Voltage regulator with active turnoff

Abstract: A base voltage of a regulator transistor (Q2) is developed during normal operation in a filter capacitor (C2) coupled to a flyback transformer (24) of a horizontal deflection circuit (Q5,LY,CS). After a transition to a standby mode of operation, the deflection circuit is disabled and the capacitor begins discharging. The emitter of the transistor is coupled to a load circuit (L3). A supply voltage (+V₁) is coupled to the collector of the transistor during both standby and normal mode. To reduce the loading of a standby power supply that generates the collector voltage as long as the capacitor is not fully discharged, an active turnoff (Q3) of the regulator transistor is provided immediately after the receiver goes into the standby mode of operation so as to actively turnoff the current drawn by the transistor.

Raster distortion correction circuit

Abstract: An East-West switching transistor is coupled between a flyback transformer primary winding and a horizontal deflection output transistor circuit to control retrace energy to obtain an East-West modulation of the deflection current amplitude as required for East-West pincushion raster correction. The East-West switching transistor isolates a retrace resonant circuit that includes a horizontal deflection winding from a flyback resonant circuit that includes the flyback transformer during a portion of retrace. The deflection winding is coupled to a common conductor to permit the use of a retrace voltage sample developed in the deflection winding as a feedback signal to synchronize the deflection current to the video signal. The arrangement reduces phase modulation of the deflection current as a function of beam current variations, that could be visible as a beam current dependent horizontal picture shift or a raster bending in a horizontal direction.

High frequency lamp transformer for linear lighting fixture

Abstract: A lamp power transformer circuit which is packaged in a module housing having the same size, shape and cross section as a linear lighting fixture to which it is attached. The transformer circuit is designed to rectify input 60 Hz power and to switch the DC at a high frequency through a small stepdown magnetic transformer, to produce a lamp supply voltage of 12 volts, 30 KHz. The invention produces a light weigth lamp transformer, having a high operating efficiency, and sized for attaching to a previous invention, linear lighting fixture which incorporates low voltage halogen lamps.

Transformer, in particulier switch mode transformer

Abstract: The transformer is preferably used as a switch mode transformer, primarily for the transmission of electrical signals in the form of pulses in an information transmission system. In this case, it is simultaneously used for DC isolation of the signal source and signal sink. This transformer is intended to be of simple construction and nevertheless to ensure extremely reliable signal transmission or, if applicable, power transmission or transmission of measured variables. This is achieved in that its primary and its secondary winding are fitted in each case as a conductor track (14, 16) on mutually congruent and mutually superimposed surfaces of at least one insulating body (14, 15), and in that these conductor tracks (14, 16) are separated from one another by an insulating layer (3).

Electronic ballast with leakage transformer

Abstract: In an electronic ballast, a half-bridge inverter is powered from a constant DC voltage and provides an AC output voltage having a waveform with trapezoidally shaped half-cycles. This AC voltage is applied across the primary winding of a leakage transformer, whose loosely coupled secondary winding is connected across a gas discharge lamp. The internal inductive reactance of the secondary winding constitutes a lamp ballasting means by way of limiting the magnitude of the resulting lamp current to a pre-established desired level. The ballast is enclosed in a steel housing of conventional shape and size (i.e., rectangular: about 2.3" wide, 1.5" high, and 8.2" long). Significant power losses may result from magnetic coupling to the walls of the steel housing of the substantial leakage flux surrounding the leakage transformer. A significant reduction of these losses is attained by orienting the leakage transformer within the elongated steel housing in such manner as to have the main plane of the leakage transformer (i.e., the plane parallel with the flux lines in the magnetic core of the leakage transformer) positioned such as to be perpendicular to the main longitudinal axis of the steel housing and well removed from its end walls.

H-bridge flyback recirculator

Abstract: A circuit for discharging an inductive load of an H-bridge circuit at a controlled rate has been provided. When a first half of the H-bridge circuit is switched from a conductive state to a non-conductive state, the circuit clamps a first side of the inductive load, while creating a recirculation path to discharge the inductive load at a controlled rate. A similar circuit may be utilized when a second (complementary) half of the H-bridge circuit is switched from a conductive state to a non-conductive state wherein the similar circuit clamps a second side of the inductive load, while creating a recirculation path to discharge the inductive load at a controlled rate.

Design and operation of a fully integrated BiC/DMOS head-actuator PIC for computer hard-disk drives

Abstract: A fully integrated head-actuator power integrated circuit (PIC) for computer hard-disk drives is described including a 1-A, 10-W CMOS H-bridge class-B amplifier. Operation of the complementary MOS-transistor power output stage includes a small-signal on-track mode and a five-interval high-speed large-signal seek mode. Analysis of a seek event reveals that maximum power dissipation occurs during the acceleration and deceleration intervals. Inductive flyback during break-before-make operation is clamped by integral multicollector bipolar transistors as confirmed by measurements and PISCES simulations. The mechanisms, occurrence, and device design considerations of the output transistor's flyback current partitioning into type A (source) and type B (N/sub well/) collector and base (body) current components are analyzed. The concept and implementation of a synchronous clamp are introduced. Finally, performance and parasitic suppression considerations of an advanced self-isolated BiC/DMOS process and device arsenal are discussed. >

A Compact 200 kV Pulse Transformer System

Abstract: Compact, lightweight pulse power systems are being developed to drive RF generators. The most feasible method of meeting these requirements is with high voltage PFN-Pulse Transformer (PPT) systems capable of driving the microwave tubes directly from the output of the transformer. To test the feasibility of this approach, a PPT system was designed and tested with an Split Cavity Oscillator (SCO) microwave generator. Results of the tests demonstrated satisfactory performance with this load and driver combination. The PPT system was designed with a 10X voltage step-up transformer and a 0.5 ohm, 2 /spl mu/s PFN. The maximum rated output voltage of the transformer was 200 kV with a 50 ohm load.

Horizontal deflection circuit

Abstract: PURPOSE:To afford optimum S-shaped correction without internal pin cushion distortion when left right pin cushion distortion correction is applied with simple circuit constitution by providing a control means controlling a voltage across an S-shaped correction capacitor for each horizontal deflection period and optimizing the S-shaped correction for a vertical deflection period to the horizontal deflection circuit CONSTITUTION:A modulation voltage source 8 supplies a +B voltage subject to vertical period parabolic modulation to the circuit Since the +B voltage is increased as the time approaches toward the center of the vertical period, a voltage divided by power voltage division resistors 9, 10 is increased This voltage is sampled and held by a sample-and-hold circuit 11 for each horizontal deflection period by using a pulse resulting from shaping a flyback pulse with a low peak level divided by resonance capacitors 3, 23 through a pulse shaping circuit 12 Since this voltage is inputted to an inverting input terminal of an inverse amplifier 17, the output voltage is lowest in the vicinity of the center of the vertical period Since an emitter voltage of control transistors 21, 22 is low, a voltage across the Sshaped correction capacitor 6 is increased Thus, the amplitude of the parabolic voltage of the S-shaped correction capacitor 6 in the middle of the vertical period is optimized

Flyback transformer including a plated metal coil and having reduced leakage flux

Abstract: A flyback transformer includes at least one primary coil and at least one secondary coil formed thereon. Each primary and secondary coil may be a metal plating coil with an insulating bobbin and a conductor formed thereon. Secondary coils may be formed of pairs of metal plating coils connected in series. One to three primary coils may have secondary coils sandwiched therebetween. The transformer may also have a resonance capacitor integrally formed therein, and may have respective rectifying diodes connected between the secondary coils.

Pulse width regulated high voltage power supply using ringless flyback transformer

Abstract: A flyback transformer operable over a broad frequency range is used as a regulated high voltage power supply. A ringless, layer-wound transformer is operated far below its natural resonant frequency in response to a pulse width modulator which may be synchronized with a video display in order to prevent beat frequency images in a video display. Diodes are coupled between the layers of windings to reduce the leakage inductance and stray capacitance. The supply is particularly suitable for TV or monitor use but not exclusively, so any apparatus requiring a regulated high voltage supply may use the invention.