Showing papers on "Flyback transformer published in 1988"

A novel approach for minimizing high-frequency transformer copper losses

Abstract: A graphical and numerical method of calculating and minimizing losses in windings, that generalizes previous findings, has been introduced Using electromagnetic theory and MMF diagrams in both space and time a method is proposed that provides insight into the mechanism of skin and proximity effect losses and that also yields quantitative results Using this method, several winding geometries for various topologies are covered The analysis and optimization process is experimentally verified using an interleaved flyback transformer The mathematical treatment justifying the use of the field method and which is essential in arriving at any numerical result is presented are more general equations for the calculation of copper losses are derived The relation between the fields in the transformer and copper losses is emphasized Also, the tools necessary to derive optimization diagrams are provided >

D. C. to D. C. converter

Abstract: A d.c. to d.c. converter system converts a d.c. signal into a pulsating a.c. signal, which is applied to the primary of a power transformer. A transformer in which the primary and secondary windings are planar is employed to generate the output pulse signal. The planar transformer design provides the inductance required to filter the output signal and reduce the ripple therein, while simultaneously providing tight coupling between the primary and secondary windings. A single turn secondary winding is provided to reduce the number of turns in the transformer and thereby reduce the associated power loss.

Power supply having combined forward converter and flyback action for high efficiency conversion from low to high voltage

Abstract: In a switching power supply including a step-up transformer having primary and secondary windings, wherein in each successive cycle of operation, during a first period of time a voltage pulse is applied across the primary winding for causing forward current in the secondary to flow through a shuttle capacitor and output capacitor connected in series with the secondary winding at this time, for charging the output capacitor to a voltage level approaching the voltage across the series circuit of the shuttle capacitor and secondary winding, and in an immediately following second period of time terminating the voltage pulse across the primary winding, and allowing flyback energy in the secondary winding to charge and be captured only by the shuttle capacitor for transfer to the output capacitor during the next cycle of operation.

Analysis of a resonant reset condition for a single-ended forward converter

Abstract: The reset condition of a transformer core flux is analyzed for a single-ended forward converter operating in a resonant reset mode. Relationships between reset time and device parameters such as the main switch output capacitance are derived. As a result, the maximum frequency in a resonant reset mode can be predicted. The main results are: the resonance period of the main transformer flyback voltage is mainly determined by transformer magnetizing inductance, main switch output capacitance, and diode junction capacitance; the main transformer flux excursion is between the first and third quadrant in B-H characteristics; and the maximum operating frequency in the resonant reset mode is determined by the above parameters and volt-second products during main switch on-time. The validity of the analysis is confirmed by comparison with experimental results for a low-power DC-to-DC converter with a 50 V input and a 5 V, 2 A maximum output. >

Transformer for a flyback type converter

Abstract: A pulse transformer for a flyback converter type switching power source has a ferrite core (10,11) with a pair of side legs (10a, 11a) and a center leg (10b, 11b) which is shorter than said side leg so that an air gap G is provided in the magnetic path along the center leg, and the windings on a bobbin (15) on said ferrite core is improved by positioning said gap G at the end portion of the center leg close to the end of the bobbin, and a dielectric belt (16b) on the bobbin (15) so that no winding exists around said gap. Thus, leakage flux around said gap does not interlink with the windings, and no eddy current flows in the windings, and a partial temperature raise in the windings is prevented.

Design of high-frequency hybrid power transformer

Abstract: Fabrication of a high-frequency power transformer/inductor using multilayer thick-film hybrid technology is presented. An experimental 6 MHz, 40 W miniature transformer is fabricated with windings printed on the ferrite substrate. Half of a conventional low-profile pot core is used to close the magnetic path. Issues related to power density, thermal management, and efficiency of this hybrid power-magnetic integrated circuit (HPMIC) are discussed. >

Capacitor switching and transformer transients

Abstract: The impact of capacitor switching on transformer transients is evaluated. Two specific transformer failure events are described. Each of these failures coincided with the switching of a capacitor bank some distance away from the transformer. The causes of these failures are evaluated, and field-test transient voltage waveforms are duplicated by computer simulations. The simulation capability is extended to determine system conditions that are susceptible to these transient voltages as well as the means to minimize them. >

High efficiency converter

Abstract: A new principle for high efficiency power conversion at high frequencies is described. The principle provides zero voltage switching by using the magnetising current of a transformer or parallel inductance to charge the switch adjunct capacitance and other capacitance during the dead time. The transformer is prevented from being loaded during the dead time. An embodiment of the invention is described where loading of the transformer during the dead time is prevented by directing the output inertial current to a capacitor instead of through the rectifiers to the secondary of the transformer. This can also be achieved by using synchronised rectification that provides pulse width modulated regulation on the output and ensures that the transformer secondary is separated from the inertial current of the output during the dead time. Voltage and current stresses on the switching devices and rectifiers are minimised. The principle may be applied to inverters where the load is resistive.

Integrated current sensor torque control for ac motor drives

Abstract: A method and apparatus for operating a current-controlled pulse width modulated inverter for driving a polyphase AC load includes using partial current feedback information, obtained from the inverter lower phase-leg switches and flyback diodes only, to regulate current flow in each phase of the load by synthesizing an analog feedback signal from the partial current feedback information.

Push-pull current-fed dc-dc converter

Abstract: A push-pull transformer of a push-pull current-fed DC-DC converter is arranged so that the inductance of the primary side of the transformer diminishes equivalently, thereby reducing a conversion loss attributable to a distributed capacitance of the transformer. To equivalently reduce the inductance of the primary side, for instance, a gap is formed in the core of the transformer and/or an inductor is connected in parallel to any one of the windings of the transformer.

Low-voltage-side current-surge phenomena in single-phase distribution transformer systems

Abstract: Lightning current surges entering the secondary windings of distribution transformers can be a cause of transformer failure. Proposed solutions have included interlacing the secondary windings and applying low-voltage arresters. Tests have been proposed to verify the ability of a transformer to withstand these surges. It is shown that the amount of current varies significantly for different sizes and designs of transformers, loads, and secondary cables. It is also shown that the entire secondary circuit must be treated as a system. Measures taken to protect the transformer generally increase the surge voltage stress on the load equipment. The source of the problem is the voltage drop along the secondary cable. Minimizing that voltage can effectively alleviate the problem of both transformer and load. These facts must be taken into consideration before developing transformer test standards to address the low-voltage-side current surge problem. >

Method for measuring insulation resistance of electric line

Abstract: A method of measuring an insulation resistance of an electric line. An AC signal voltage having a frequency of f i is applied to the electric line through a voltage transformer or a current transformer coupled to a grounding conductor or to the electric line. Phase measuring currents having frequencies (f 1 -f S ) and (f 1 +f S ) are also applied to the electric line through a winding of the current transformer or voltage transformer. A leakage current component and the AC signal voltage are synchronously detected to obtain a synchronously detected output and the phase of the AC signal voltage of the frequency f 1 necessary for the synchronous detection is automatically adjusted so that a component of the synchronously detected output having a frequency f S becomes zero.

Current density measurement system by self-sustaining magnetic oscillation

Abstract: A system for measuring parameters in an environment having a metallic body positioned in an electrolytic medium includes a current density sensing device positioned adjacent the metallic body in a non-invasive manner. The device is sufficiently sensitive to measure current density in the milliamp per square centimeter range. A housing is provided for enclosing at least a portion of the current density sensing device in an electrically and thermally non-conductive manner. A computer is used for processing the data from the current density sensing device and wiring is provided for electrically interconnecting the two. The current density sensing device, which can be used separately from the apparatus, includes a toroidal transformer and a square wave magnetically coupled oscillator which drives the transformer. A pair of multi-section low pass filters are provided for monitoring the transformer. A fixed gain differential instrumentation amplifier is utilized for processing an output of the transformer. The processed transformer output is proportional to a current sensed by the transformer.

High voltage DC power supply

Abstract: A DC power supply for a traveling wave tube having cathode, collector and helix electrodes responds to a DC power source and a high frequency switching source. A switch controlled by the switching source is opened and closed at a fixed frequency and variable duty cycle determined by the helix-cathode voltage. A flyback choke is connected to the switch and DC power supply so current flows between the power source via the choke to the switch and a series resonant circuit while the switch is closed. First and second capacitors in separate branch circuits of the resonant circuit are respectively connected to first and second AC to DC converter and voltage multiplier stacks; each multiplier in the stacks includes a pair of branches with oppositely poled plural signal switching diodes and a capacitor. The cathode and helix are respectively connected to output terminals of the first and second stacks, while the collector is connected to a terminal between the first and second stacks. The resonant circuit is connected with the switch, flyback choke and voltage multipliers so that while the switch is closed a half-wave rectified current waveform at the resonant circuit resonant frequency flows in the resonant circuit and a ramping current having a first polarity direction flows in the choke. A ramping current having a second plurality direction flows in the choke and resonant circuit while the switch is open.

MOS-transistor bridge circuit

Abstract: In this MOS-transistor bridge circuit, for obtaining a fast flyback conduction of the current after a normal operation of the circuit, instead of the flyback diodes associated with each transistor of the bridge, the MOS transistors themselves are employed, driven so as to conduct current from the ground to the power supply, that is in the opposite direction with respect to that of normal operation. For this purpose a control section is provided receiving at the input a fast flyback signal and comprising delay gates connected to the disable inputs of the transistors, so as to delay switching off thereof, and to maintain in the on state two diagonally opposed transistors so as to allow current to flow from the ground to the power supply through these diagonally opposed transistors and the load until the current decreases to zero.

Switch-mode power supply

Abstract: An input supply voltage is coupled via a primary winding of a flyback transformer to a collector of a chopper transistor switch that operates at a given frequency. During a portion of each period when the chopper transistor switch is conductive, a second switch applies a short-circuit across a secondary winding of the transformer at a controllable instant that causes the emitter current of the chopper transistor switch to increase at a significantly higher rate. When the emitter current exceeds a predetermined threshold level, a one-shot arrangement is triggered. Consequently, a pulse is produced that turns off the chopper transistor switch and that maintains it nonconductive for the duration of the pulse. A flyback pulse produced in a winding of the transformer is rectified to produce a DC output supply voltage. The length of the interval when the chopper transistor switch is conductive is controlled by the second switch in accordance with the level of the output supply voltage in a negative feedback manner for regulating the output supply voltage.

Voltage resonance type switching power source apparatus

Abstract: In a voltage resonance type switching power source apparatus, which has a step-up transformer, a resonance capacitor connected in series with a primary winding of the transformer, and a transistor connected in parallel with the capacitor to cause a resonant oscillation current by the on-off operation thereof, an on signal of the transistor is produced in synchronism with a second signal, which is obtained by delaying a first signal depending on a voltage induced in a detecting winding provided in the transformer by a predetermined delay time.

RF transformer and diagnostic technique therefor

Abstract: An RF transformer employs at least three elongated conductive elements in generally parallel spaced relationship. At least a first inductive element is connected between a pair of the conductive elements to provide a desired field distribution. A diagnostic technique for determining the frequency shift of the transformer employs a perturbing object which is selectively longitudinally positioned within the transformer. The transformer has particular utility as an RF excited gas laser.

High voltage generator

Abstract: High voltage generators are generally arranged to step up flyback pulses from a horizontal deflection circuit by means of a flyback transformer consisting of a primary low voltage coil and a secondary high voltage coil, rectifying the high voltage output through a rectification circuit for application to the anode of a cathode-ray tube. However, such a flyback transformer construction has an inherent drawback that the voltage of the high voltage output is varied by variations in the high voltage output current due to leakage inductance, resulting in load fluctuations. To overcome this problem, the high voltage generator is provided with a tertiary coil for generating an output voltage corresponding to 1/n of the maximum variation of the load fluctuations, a summing control circuit for controlling the rate of the high voltage output to be additively supplied to the secondary coil from the tertiary coil on the basis of a variation detection signal from a high voltage, variation detector circuit which serves to detect the load fluctuations, and a multiplying circuit for multiplying the voltage received from the summing control circuit by n-times for supply to the low voltage end of the secondary coil, thereby stabilizing the voltage of the high voltage output substantially at a constant level irrespective of the variations in the high voltage output current.

High frequency transformer with a printed circuit winding in particular for a very high voltage power supply

Abstract: A high frequency transformer is made on a magnetic circuit which can be of a generally square shape. The secondary windings are made on printed circuit plates, separated by insulators and traversed perpendicularly by the core or cores of the magnetic circuit. The primary winding can be wound directly on such a core. The transformer is applicable in particular to high frequency very high voltage power supplies, in particular of the type termed "flyback" power supplies.

Dual voltage distribution transformer with internal varistor surge protection

Abstract: This dual voltage transformer comprises a primary winding having a tap at a location intermediate its length, a first termination for connection to line voltage, and a second termination for connection to ground. When the transformer is to be operated at a relatively high voltage, the first termination is connected through a dual voltage switch to line voltage; and when the transformer is to be operated at a relatively low voltage, the tap is connected through said switch to line voltage. First varistor means is connected across the primary winding between said first and second terminations both when the transformer is operated at high voltage and at low voltage; and second varistor means having a lower breakover voltage than the first varistor means is connected between said tap and ground when the transformer is operated at low voltage.

Control circuit for a switching DC to DC Power converter including a multi-turn control transformer

Abstract: A control circuit for a power converter which includes a power transformer having a primary transformer winding for receiving an input voltage signal and a secondary transformer winding for generating an output signal provides control of the on and off time of the power transformer by utilizing a control transformer having a plurality of windings. A switch is provided which is coupled to the control transformer. The switch is conductive to render the power transformer on and when non-conducting renders the powder transformer off. Activacation of the switch is controlled through magnetic coupling between the windings of the control transformer to thereby render the output voltage of the power transformer constant while the switch on time remains constant and the switch off time is variable.

No-break current supply system

Abstract: A no-break current supply system working with high efficiency and high input power factor comprises a first converter (20) connected to a commercial AC mains (2) and delivering alternating current with predetermined voltage and the highest possible frequency to the input winding of a transformer (30). A second converter (40) is connected to an output winding of the transformer (30) and supplies a load (60) with alternating current having the desired voltage and frequency. The AC side of a current converter (50) is connected to a third winding of the transformer (30) which is isolated from the input winding and output winding, a back-up battery (10) being connected to the DC side of this current converter which, as required, acts as a rectifier for charging the battery or as a DC-AC converter for delivering energy from the battery to the load. Since the transformer (30) is driven at a frequency which is markedly higher than the mains frequency, the transformer can be constructed with small dimensions and low weight.

Notch gap transformer and lighting system incorporating same

Abstract: The invention is directed to a transformer having notch gaps extending partially across the flux path of the transformer core and having a total gap volume which stores sufficient magnetic energy to substantially eliminate inductive voltage spikes in a clipped sinusoidal waveform applied to the primary of the transformer. As used in a low voltage lighting system in which the intensity of a filament lamp is regulated by a dimmer control which selectively clips the voltage applied to the transformer primary winding by an ac source, the invention substantially eliminates filament ringing.

Spray-coating device

Abstract: A spray-coating device for spraying liquid or powdered coating material on articles includes a transformer for stepping up an alternating voltage and a voltage multiplier circuit for converting the output of the transformer to a high DC output for driving a charging electrode in the spray-coating device. The alternating voltage for the transformer is obtained from a controllable source of alternating voltage which produces a sinusoidal voltage whose frequency is constantly adjusted such that the voltage and current flowing through the transformer are in phase with one another. This assures that the transformer is operated at its resonant frequency.

Electrical power supply circuit, in particular for a wave generator for a pulse radar

Abstract: An electrical power supply circuit, in particular for a pulse radar wave generator, includes a chopper regulation circuit and a transformer which is fed from a low voltage source. The primary winding of the transformer of the circuit has a plurality of primary windings wound on a common transformer core. Each of the primary windings is connected to the low voltage source via an electronic power switch controlled by a voltage regulation signal at the repetition frequency of the radar pulses or at a multiple of the frequency. The transformer secondary includes a plurality of secondary circuits with their outputs connected in series between the very high voltage output terminals of the power supply circuit as a whole. Each secondary circuit includes a secondary winding wound on the common transformer core and connected in series with a rectifier connected to oppose the voltage induced by the primary current, together with a filter capacitor connected in parallel with the series circuit consituted by each secondary winding and each rectifier.

Dual mode flyback power supply

Abstract: A dual mode flyback power supply 10 capable of automatically transitioning between operational modes in response to changes in the impedance of a load 12 connected thereto. The dual mode power supply 10 of the present invention includes an input voltage source 15 for providing input voltage and current. The power supply 10 also includes a first transformer 20 having primary N1, secondary N2 and tertiary N3 windings for supplying a first current to a load 12 operatively coupled to the secondary winding N2. The primary winding N1 is coupled to the input voltage source 15. A feedback circuit 50 provides a first signal in response to the current through the load 12 and a second signal in response to the load voltage exceeding a threshold voltage. The power supply 10 of the present invention further includes a switch 30 for controlling the input current through the primary winding N1 of the first transformer 20 in response to the first and second signals. A second transformer 25 having a primary winding operatively coupled to the tertiary winding N3 of the first transformer 20 supplies a second current to the load 12 in response to the current through the tertiary winding N3.

Method and apparatus for detecting a reduction in the input voltage to a power supply

Abstract: A scheme for detecting reduced source of voltage of a controlled switching power supply including a transformer employs the inherent insolation characteristics of the transformer to yield an isolated alarm signal indicative of a failed or inadequate source voltage.

Circuitry for limiting an operating voltage obtained by way of a rectifier from a secondary winding of a transformer

Abstract: Circuitry for limiting a rectified operating voltage To recover energy from unutilized power from the secondary winding of a switching-network transformer, it is recirculated to the primary winding through a diode When appliances fail, the excess energy component can increase to the extent that components are destroyed because the operating voltage increases To prevent this situation the excess energy is recirculated into a higher operating voltage U S through a diode and through another secondary winding of the transformer The number of turns in the second secondary winding and its polarity ensure that the flyback voltage U R will be higher than the difference between U S and U B Switching-network components in conjunction with rectifier modulators in television receivers

High voltage generator

Abstract: In a high voltage generator comprising a flyback transformer having a primary winding and a secondary winding, a horizontal deflection circuit connected to the primary winding of the flyback transformer, and a rectifier diode connected to the secondary winding of the flyback transformer, a resonance circuit including a saturable transformer and a capacitor is inserted between the primary winding of the flyback transformer and a power source, and a signal corresponding to the value of a high voltage load current is applied to a control winding of the saturable transformer. When the value of the high voltage load current is very small, the resonance circuit resonates with a higher harmonic of a flyback pulse to remove this higher harmonic component. As the value of the high voltage load current increases, the inductance value of the secondary winding of the saturable transformer changes to change the resonance frequency of the resonance circuit. As a result, the proportion of removal of the higher harmonic component decreases to increase the peak value of the high voltage thereby suppressing a voltage drop of the high voltage.