Showing papers on "Flyback transformer published in 1987"

High-Speed Drive System with Ultrasonic MOSFET PWM Inverter and Single-Chip Microprocessor Control

Abstract: The design of high-current high-voltage MOSFET inverters requires measures to reduce the switching losses of the flyback diodes. Saturable reactances have been used in the case of a 4.5-kVA MOSFET inverter to limit the di/dt during commutations. The switching overvoltages of the reactances are absorbed by one common clamping circuit per bridge leg. The drive control system and the space vector modulator for the generation of the PWM switching sequences are implemented in a single-chip microcomputer.

Resonant forward converter

Abstract: A resonant forward converter at a switching frequency of 10 MHz provides a small volume point-of-load converter for distributed power systems. The leakage inductance of a transformer is made negligibly small relative to the magnetizing inductance of the transformer. This enables a resonant controllable switch on the primary side of a transformer and a secondary side rectified diode to be switched either on or off at the same time. The capacitance across the primary side switch and the secondary side diode rings with a resonant inductor connected in parallel with the transformer. Both the switch and diode, therefore, have zero voltage switching transitions. Further, the resonant inductor being connected in parallel with the transformer provides a resonant ring that is independent of load.

Two transistor flyback switching converter with current sensing for discontinuous operation

Abstract: Disclosed is a dual transistor flyback converter having a pair of synchronously driven switching transistors (20, 36) for switching voltage to a primary (12) of a flyback transformer (10). When driven into a cutoff state, transistor (36) isolates switching transistor (20) from the supply voltage (V1), thereby preventing a transformer reflected voltage from being superimposed on the supply voltage and imposing such voltage across the transistor (20). Clamp diodes (40, 42) maintain the switching transient voltage across the flyback transformer primary (12) between prescribed limits. Capacitor (48) allows the switching transient to pass and be clamped by the diodes (40, 42), but prevents the reflected secondary voltage from being clamped when the input voltage is low. A current sensing circuit (50) in series with the flyback transformer secondary (14) senses current flow during the power conversion cycle, and provides a digital indication to a PWM control circuit (66) to facilitate reliable discontinuous operation of the flyback converter.

A novel approach for minimizing high frequency transformer copper losses

Abstract: As power supply frequencies approach the megahertz level, skin and proximity effects become significant factors to consider when calculating copper losses in transformers. Using electromagnetic theory and mmf diagrams in both space and time, a method that provides insight into the mechanism of skin and proximity effect losses and also yields quantitative results is proposed. Using this method several winding geometries for various topologies are covered. The analysis and optimization process is experimentally verified using an interleaved flyback transformer.

High power flyback, variable output voltage, variable input voltage, decoupled power supply

Abstract: There is disclosed herein a modular, high power, flyback transformer based power supply with step up and step down capability. The power supply uses multiple flyback transformers having switching transistors which may be either connected to one terminal of the primary winding or which may be placed in the center of the primary winding. The switching transistors are driven by pulse trains which are out of phase with each other. This results in lowered RMS values for ripple current through the input and output capacitors. The flyback voltage transients may be used to step up or step down the input voltage by varying the pulse width of the pulse in the switching pulse trains. In embodiments where the switching transistors are placed in the middle of the primary windings, better suppression of radio frequency emissions and current in safety ground wires is achieved. There is also disclosed a combination of such power supply modules in series or parallel on either the input or output to deliver higher power or higher output voltage or to be able to handle higher levels of D.C. input voltage. There is also disclosed an improved an improved flyback transformer design having substantially lower leakage inductance using coaxial cable as the wire from which the primary and secondary windings are made.

Zero-voltage-switched quasi-resonant buck and flyback converters — Experimental results at 10 MHz 1

Abstract: Experimental results of buck and flyback zero-voltage-switched quasi-resonant converters (ZVS-QRCs) operating above 5 MHz are presented. A design procedure is presented that minimizes voltage stress to the transistor while maintaining zero-voltage-switching for all loads. A novel, quasi-resonant gate drive scheme is proposed and implemented in a buck converter. The drive is simple and provides high switching speed. Power dissipation in the gate drive is substantially reduced due to the quasi-resonant operation. Due to a much reduced switching losses, dv/dt, and di/dt, the ZVS-QRCs are particularly suitable for very-high-frequency distributed power supply applications.

Harmonic Norton equivalent for the magnetising branch of a transformer

Abstract: In the analysis of harmonic power flows, the transformer is generally represented as a passive component. However, due to the magnetisation nonlinearity, the transformer constitutes a source of harmonic currents which can aggregate and cause substantial waveform distortion. This paper describes the development of a Norton equivalent circuit which accurately represents the transformer magnetising branch in harmonic power-flow studies. It is shown that even in the absence of other nonlinearities in the system, the transformer magnetising current can give rise to considerable harmonic voltage levels.

Modular power supply with variable input voltage and output voltage flyback power modules

Abstract: There is disclosed herein a modular, high power, flyback transformer based power supply with step up and step down capability. The power supply uses multiple flyback transformers having switching transistors which may be either connected to one terminal of the primary winding or which may be placed in the center of the primary winding. The switching transistors are driven by pulse trains which are out of phase with each other. This results in lowered RMS values for ripple current through the input and output capacitors. The flyback voltage transients may be used to step up or step down the input voltage by varying the pulse width of the pulses in the swicthing pulse trains. In embodiments where the switching transistors are placed in the middle of the primary windings, better suppression of radio frequency emissions and current in safety ground wires is achieved. There is also disclosed a combination of such power supply modules in series or parallel on either the input or output to deliver higher power or higher output voltage or to be able to handle higher levels of D.C. input voltage. There is also disclosed an improved flyback transformer design having substantially lower leakage inductance using coaxial cable as the wire from which the primary and secondary windings are made.

Transformer coupled power switching circuit

Abstract: A power switching circuit for switching power repetitively to a load at a relatively low frequency employs a power switching device which is driven across an isolating transformer interface. The drive signals are high frequency pulse signals which are modulated with the low frequency switching information, the modulations being detected in the secondary circuit of the transformer. Such an arrangement affords isolated driving with fast switching edges and requires only a small transformer. Power for the detection circuit is derived by rectification of the high frequency signals induced in the transformer secondary.

Integrated device for shielding charge injection into the substrate, in particular in driving circuits for inductive and capacitive loads

Abstract: This integrated device for shielding injected charges in driving circuits for inductive and/or capacitive loads comprises four integrated structures including a first barrier region with high resistivity which surrounds the buried layer of the epitaxial flyback pocket which may be set at a potential lower than ground on the side of the buried layer which faces the driving circuit pocket; a first charge collecting region provided in the epitaxial flyback pocket; a third low-loss diode structure, formed in an epitaxial pocket which is isolated from the flyback pocket and is arranged between the latter and the driving circuit, and connected so as to clamp the voltage between the epitaxial flyback pocket and the substrate to the diode direct conduction voltage; and, finally, a last barrier structure formed by a charge collecting region connected to the supply voltage.

Pulse width modulator used for a power converter with a transformer

Abstract: This apparatus is a power converter which delivers a pulse produced based on a dc voltage to the primary side of a transformer with its polarity being changed per half cycle to take out an ac power from the secondary side thereof. By modulating the pulse width of a pulse delivered, the output power becomes adjustable. By detecting a current on the primary side of the transformer, current change rates at positive and negative half cycles are calculated. By comparing these change rates at the both cycles, magnetic deviation of the transformer can be detected. With the pulse width correcting means, pulse widths of pulse delivered at positive and negative cycles are adjusting so as to cancel such a magnetic deviation. The control for preventing magnetic deviation described above is realized as a control having a very fast response. In addition, such a control enables the transformer to be operative in a range extremely close to the range where the transformer is saturated.

D.C. voltage converter with overload protection

Abstract: In a d.c. voltage converter 1 including a series arrangement of a transformer 3 and a pulse-switched current source 7 the power converted by means of the transformer 3 is kept constant with the aid of a control circuit 13. In the event of a short-circuit in one of the secondary windings 5-1, 5-2 a voltage drop across an auxiliary winding 6 of the transformer 3 is used to limit the converted power during the short-circuit.

AC voltage regulator

Abstract: An AC voltage regulator includes a transformer arrangement having a plurality of taps so that an input line voltage is passed to an output line with the output line voltage being determined by the nominal value of the input line voltage together with an amount contributed by the transformer. The device is switched by a network of relays one of which acts as a polarity reversal switch so that the voltage generated by the transformer is either added or subtracted to the nominal voltage. Further relays used in two series control the selection of the transformer tap. A transient suppression circuit uses a triac and resistor to communicate current from the input line to the output line with the triac gated into conduction on breaking of a relay contact. The input line voltage is measured by a comparator using a plurality of op-amps in series with the outputs therefrom passing through a logic circuit to control the relays.

Inductor with centertap switching transistor for reduced radio frequency emissions

Abstract: There is disclosed herein a modular, high power, flyback transformer based power supply with step up and step down capability. The power supply uses multiple flyback transformers having switching transistors which may be either connected to one terminal of the primary winding or which may be placed in the center of the primary winding. The switching transistors are driven by pulse trains which are out of phase with each other. This results in lowered RMS values for ripple current through the input and output capacitors. The flyback voltage transients may be used to step up or step down the input voltage by varying the pulse width of the pulses in the switching pulse trains. In embodiments where the switching transistors are placed in the middle of the primary windings, better suppression of radio frequency emissions and current in safety ground wires is achieved. There is also disclosed a combination of such power supply modules in series or parallel on either the input or output to deliver higher power or higher output voltage or to be able to handle higher levels of D.C. input voltage. There is also disclosed an improved flyback transformer design having substantially lower leakage inductance using coaxial cable as the wire from which the primary and secondary windings are made.

Design of a Pulsewidth-Modulated Resonant Converter for a High-Output-Voltage Power Supply

Abstract: The design and fabrication of a parallel resonant converter circuit and a high-frequency step-up transformer used to supply an adjustable dc voltage to a load is described. The 500-W system is operated from 115/230 V single-phase 60-Hz power, which is rectified and filtered to form a 310-V dc link. A two-transistor half-bridge circuit operating at a fixed frequency above the circuits resonant frequency converts the dc voltage to an ac voltage at approximately 20 kHz. This high-frequency voltage is transformed with a low-capacitance oil-impregnated ferrite transformer. The output voltage is rectified to form a dc voltage with a maximum value of 90-kV peak. The output voltage is adjustable using pulsewidth modulation of the conduction time of the two transistors in the power circuit. The energy stored in the resonant circuit provides a sinusoidal transformer voltage at fixed frequency over a wide range of control. The system is provided with a closed-loop peak-voltage regulator and an on-off capability from the control electronics. The transformer is designed for a specific value of inductance and capacitance to operate at the desired resonant frequency and characteristic impedance.

Single-ended flyback converter or forward converter having a low blocking voltage, for the switching transistor

Abstract: A single-ended flyback or forward converter having a low blocking voltage for the switching transistor. Transistorised converters and forward converters produce a high flyback voltage in the phase when the transistor is switched off, which flyback voltage must be reduced to less than the maximum permissible transistor reverse voltage Uce by means of damping components (C,CR or RCD elements). The new solution (see figure) allows the flyback voltage to be limited without any power losses in separate damping elements by arranging two diodes and a capacitor as a collector network.

Method and circuit arrangement for the insulation testing of test pieces with large intrinsic capacitance and for the localisation of faults in power cables

Abstract: A description is given of a method and circuit arrangement for the insulation testing of test pieces with large intrinsic capacitance and for the localisation of faults in power cables The method is characterised in that the high-voltage transformer is electronically driven on its primary side via a charging capacitor with a very low frequency voltage, which is overlaid with a higher frequency, and that on the secondary side of the high-voltage transformer, the component with the higher frequency is synchronously filtered out (demodulated), and that the high secondary voltage with low frequency is fed to the test piece, and that the measuring device is connected with the test piece via a switching device in the pulse-free period to the high-voltage transformer. The circuit arrangements for carrying out the method provide essentially for the primary-side driving of the high-voltage transformer in the form of pulse packets or in the form of a slowly changing voltage with superimposed square-wave pulses. Provided for demodulation on the secondary side of the high-voltage transformer is either a voltage-dependent resistor or spark gaps or a motor-driven, rotating synchronous switch.

Electronic hybrid circuit

Abstract: An analog electronic hybrid circuit having a complex internal impedance includes a coupling transformer. The loss resistances of the transformer are used together with a measuring resistor to establish a predetermined complex internal impedance, thereby providing a balancing network. In one embodiment, nonideal characteristics of the transformer (nonlinearities, parasitics) have only very little effect because the transformer is contained in a feedback loop.

High voltage protecting circuit

Abstract: A high voltage protecting circuit in a cathode ray tube apparatus which comprises a main power switch adapted to be connected in series with an electric power source, a flyback transformer having primary, secondary and third windings, a rectifying circuit connected with the main power switch for rectifying a power source voltage originating from the power source and to be supplied to the flyback transformer, a switching device connected between the main power switch and rectifying circuit and provided with a control terminal, and a high voltage detecting and controlling device for comparing an output voltage, produced across the third winding of the flyback transformer, with a reference voltage and for generating a control signal when the output voltage exceeds the reference voltage. The control signal is utilized to hold the switching device in an OFF position.

Switched-mode DC-to-DC power converter

Abstract: A switched mode DC/DC power converter for high outputs includes two parallel channels. Each channel consists of a flyback transformer (Fb-Tr1, Fb-Tr2) with a timed primary switch (S1, S2) on the primary side and a secondary switch (S3, S4) on the secondary side. The output flow within one channel from the primary supply voltage Ub through the primary power switch (S1; S2), the flyback transformer (Fb-Tr1, Fb-Tr2), and the secondary power switch (S3; S4) to the secondary output voltage (Ua1, Ua2) occurs, respectively, during the blockage phase. The two flyback transformers (Fb-Tr1, Fb-Tr2) are loosely linked with each through a link circuit (L.C.). The link circuit (L.C.) transmits energy from the transformer which is, respectively, in the forward phase to the other transformer. The power switches (S1, S3; S2, S4) are actuated by a control unit (C.U.) so as to be of correct frequency and phase.

Circuit for generating a constant high voltage for CRT deflection in response to multi-frequency horizontal sync input signal

Abstract: A circuit for generating a constant DC high voltage responsive to an input signal having various frequencies, having a frequency-voltage converter responsive to the input signal to generate a voltage signal corresponding to the frequency of the input signal. The voltage signal is applied to an oscillation circuit and a voltage control circuit, respectively, as a control signal. The output from the oscillation circuit is coupled to one terminal of a primary coil of a flyback transformer (FBT), and the output from the voltage control circuit is coupled to the other terminal of the primary coil of the flyback transformer (FBT).

On the correct choice of transformer ratio in low noise preamplifiers for large detector capacitances

Abstract: In the design of transformer coupled preamplifiers for large detector capacitances the transformer ratio is customarily made equal to the value which meets the capacitive matching condition. If, however, parallel noise as well as series noise external to the amplifying device are present, the optimum choice of the transformer ratio may differ substantially from the previous one. The paper aims at investigating the optimum transformer ratio with a quite general configuration of noise sources, yet sticking to the model of ideal transformer.

Automatic gain controller

Abstract: PURPOSE:To suppress increase of the capacity of a circuit and to efficiently execute an AGC action by using a horizontal synchronizing signal for synchronizing the phase during the most periods of a picture, and using the said signals for an amplitude-detection for the AGC during a vertical flyback period or only several H-periods in the vicinity of the said period. CONSTITUTION:An amplitude controlling amplifier circuit whose magnitude of amplification is variable 21 is provided in a prestage of an A/D converter 23. During the vertical flyback period or several H-periods in the vicinity of the said period, an adding circuit to add the values of the front porch and the back porch of a horizontal synchronizing signal 30 is controlled to inverse the polarity of one data. Therefore, the circuit 30 functions virtually as a subtraction circuit. Also, a value generated by doubling the median of the edge of the data pulse is forcively substituted for a reference value, to obtain the value of difference between the values of the front and the back porches. By using a resulting value for a control voltage, the circuit 21 is controlled for feedback. In such a way, the amplitude-value of a television signal which is in form of a digital signal outputted from the A/D 23 is made constant at all time.

Display device including flyback transformer constructed to control leakage currents

Abstract: A stacked or laminated-layer type of flyback transformer includes a plurality of high voltage windings wound in regular order in a direction of the winding axis and arranged on the same core cylinder. The high voltage windings in the respective layers are connected in series with each other by diodes and so that a voltage is generated with a direction of stacking of these windings. A winding start position of the first layer high voltage winding nearest a primary winding is lagged with respect to the winding start positions of the second layer winding and subsequent layer winding. The winding start position of the first layer winding is selected to be the position of, for example, 0 to 25% when the winding width on the core cylinder is 100%.

CRT focus tracking arrangement

Abstract: A video display apparatus includes a cathode ray tube and a high voltage transformer. The high voltage transformer incorporates a high voltage winding having a tap which provides a focus voltage for the electron gun assembly of the cathode ray tube. The transformer also includes a supply winding which provides power to the electron gun assembly drive circuit. The supply winding is wound to be closely coupled to the portion of the high voltage winding not associated with the generation of focus voltage so that increasing beam current produces nonuniform loading of the high voltage winding.

Raster distortion correction for a deflection circuit

Abstract: East-West modulated current that is generated in an East-West control circuit is coupled to a deflection circuit output stage via a Class A operated amplifier serving as a current source having a high output impedance during retrace. The current source prevents coupling of a signal at a retrace frequency during retrace between a high voltage winding of the flyback transformer and a retrace resonant circuit that includes the deflection winding. The high output impedance of the amplifier current source during retrace maintains the average value of the modulated current during retrace unaffected by an amplitude of a retrace voltage that is developed in the retrace resonant circuit. In this way ultor voltage loading variation is prevented from causing "mouseteeth" distortions.

Transmission line pulsed transformer

Abstract: A pulsed transformer capable of providing up to 500 kilovolt or higher, 10 nanosecond rise time, and 1000 joule or higher pulses comprising non-conducting or insulated transformer cores each separated by conductive grading rings wherein n coaxial cables in combination with the grading rings are connected in parallel at one end and in series at their other ends. The transformer may function as either an inverting or non-inverting transformer. In a transformer with n cables, if a pulse voltage of V is applied to the input, an output voltage of nV will appear at the output. The cores function to isolate the coxial cables and permit them to be connected in series at their one end. Weight may be minimized by operating the transformer in gaseous Freon rather than transformer oil.

Problems in Analysis, Control, and Design of Switching Inverters and Rectifiers

Abstract: Control and analysis techniques in switched-mode inversion (dc-ac) and rectification (ac-dc) are examined in this thesis. Current programming and sliding mode control are used to provide regulation and obtain desired dynamic responses. The basic buck, boost, flyback, and buck-boost topologies are used to illustrate the different methods of control and analysis. For illustration, embodiments employ fast switching converters, but the techniques described can be applied to any general converter. Different possibilities for the current programming of dc-ac inverters and ac-dc rectifiers are explored and the more practical and advantageous methods noted. Current reference programming improves the dynamic response of the converter and simplifies the design of the main regulatory loop. It also protects the switches from excessive current stresses and enables the parallel operation of many converters to support a common load. Constant frequency current reference programmed converters are, however, subject to oscillations under certain operating conditions. Describing equations are used to obtain the low frequency characterization of current programmed converters. The system representation is first obtained in the stationary abc reference frame and then transformed to the rotating dq coordinate frame. In the dq coordinate system, the low frequency characterizations of all balanced, polyphase ac converter systems are represented by a set of continuous, time-invariant differential equations. The steady-state and linearized, small signal dynamic responses are then obtained in this rotating reference frame. Sliding mode control is applied to inverters and rectifiers to provide regulation and ensure the stability of the system in the presence of small and large signal disturbances. This is a natural method of control for variable structure systems and enables the design of a robust controller that can provide stability and performance in the face of plant uncertainities. However, it requires that all or many of the states of the system be accessible and results in a variable switching frequency in the converter. The equivalent control method is used to obtain the low frequency properties of the sliding mode system, and can also be used to obtain the low frequency models of duty ratio programmed converters. Different switching strategies can be used to provide sliding mode control, as well as to optimize responses, maximize efficiency, or minimize switching losses. Practical aspects such as hardware implementation, switch realization, and measurement techniques are also discussed.

High voltage circuit

Abstract: PURPOSE:To independently operating a distortion correcting control and a high voltage stabilizing control by addition voltage source in the low voltage terminal of the secondary side of a flyback transformer and controlling a high voltage detecting signal and a distortion correcting signal. CONSTITUTION:An amplifying circuit 18 is a grounded emitter type inversion amplifying circuit consisting of a transistor 47. Then, the distortion correcting signal applied to a distortion correcting signal input terminal 20 is inverted and amplified and applied to the base of the error amplifying differential amplifying transistor 42 of an addition voltage source control circuit 12. Consequently, the circuit is modulated by the distortion correcting signal and the output voltage of the addition voltage source 13 is modulated. The modulation of the output voltage of the addition voltage source 13 is offset by the modulation of a high voltage generated in the secondary side of the flyback transformer 6 according to a distortion correcting power source modulating circuit 17. Accordingly, the distortion correcting control and the high voltage stabilizing control can be independently operated.