Showing papers on "Flyback transformer published in 1992"

Integrated high quality rectifier-regulators

Abstract: A family of AC-to-DC converters which integrate the functions of low harmonic rectification, low frequency energy storage, and wide bandwidth output voltage control into a single converter containing one, two, or four active switches is presented. These converters utilize a discontinuous conduction mode input inductor, an internal energy storage capacitor, and transformer secondary circuits which resemble the bridge, forward, flyback, or Cuk DC-DC converters. A large-signal equivalent circuit model for this family which uses the loss-free resistor concept is presented. Design strategies and experimental results are given. High performance regulation with satisfactory line current harmonics is demonstrated with conventional duty ratio control. Further improvements in line current are possible by simultaneous duty ratio and switching frequency control. >

Piezoelectric ceramic transformer operating in thickness extensional vibration mode for power supply

Abstract: A new kind of multilayer piezoelectric ceramic transformer for switching regulated power supplies is described. This transformer operates in the second thickness extensional vibration mode. Its resonant frequency is higher than 1 MHz. Theoretical calculations are implemented using a distributed constant electromechanical equivalent circuit method. It is calculated that this transformer can operate with higher than 90% efficiency. A fabricated transformer is examined. PbTiO/sub 3/ family ceramics are used because of the large anisotropy between electromechanical coupling factors. Results indicate that the piezoelectric transformer has good resonant characteristics, with little spurious vibration, and exhibits 16 W/cm/sup 3/ power density with high efficiency at 2 MHz. A switching regulated power supply, applying the piezoelectric transformer, is built and examined. >

Apparatus for suppressing field radiation from display device

Abstract: s7 In order to eliminate such a possibility that field radiation in a VDT exerts a bad influence on the human body, field radiation from a front surface of a cathode ray tube is reduced. A degaussing coil (3) arranged in proximity to the peripheral edge of a front surface (2) of a cathode ray tube (1) is so advantageously employed that this degaussing coil (3) is supplied with a voltage which is reverse in polarity to an electric field (12) radiated from the front surface (2) of the cathode ray tube (1). The voltage of reverse polarity is provided by an output signal (18) obtained from an output signal (16) of a horizontal deflection circuit (15) by a flyback transformer (17) and/or a voltage obtained by phase-inverting an anode voltage fluctuating in vertical synchronization. After a degaussing operation is completed, relay contacts (7, 8) are opened on the basis of a timer-controlled relay switch (9), thereby completely cutting connection between the degaussing coil (3) and a degaussing power source (4) generating an alternating current which is supplied to the degaussing coil (3) for the degaussing operation.

Zero voltage switching approach for flyback converter

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

Zero voltage switching power converter

Abstract: A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch is disclosed. The power converter includes a transformer having a primary winding and a second winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch. A second switch means is connected in series with the secondary winding of the transformer and is operated to prevent the loading effects of the secondary from interrupting the creation of the zero-voltage switching condition.

2 MHz power converter with piezoelectric ceramic transformer

Abstract: A power converter with a new piezoelectric transformer is presented. The piezoelectric transformer, made of lead titanate solid solution ceramic, is operated with a thickness extensional vibration mode. This transformer can operate at high frequency, over several megahertz, with about 90% efficiency. The resonant frequency for the transformer is 2 MHz. The power converter with the transformer applies the theory for a class-E switching converter using an electromagnetic transformer. Maximum output power is obtained when the switching frequency is slightly higher than the resonant frequency. A 4.4 W output power is successfully obtained with 52% efficiency at 2.1 MHz switching frequency. >

Method and apparatus for a cardiac defibrillator high voltage charging circuit

Abstract: A variable rate defibrillator charging circuit includes a power transformer that accepts an internal battery output and the output from an AC-to-DC converter on separate primary windings. The secondary winding of the transformer is coupled through a rectifier to a storage capacitor. The transformer operates in a fly-back mode whereby energy is discharged into the storage capacitor when the power supplies discontinue charging the transformer. After energy in the transformer is discharged into the storage capacitor, the power supplies are reactivated, recharging the transformer. The separate primary windings of the transformer provide a fast, reliable, low cost means for charging the storage capacitor with multiple power supplies. The AC power source feeding the AC-to-DC converter is detachable allowing the defibrillator to be operated remotely whereby the storage capacitor is charged solely from the internal battery. The charging circuit monitors the output voltage levels of both the battery and the AC-to-DC converter and enables or disables the power supplies in accordance to their ability to charge the storage capacitor within a predetermined amount of time. The energy in the storage capacitor, which is eventually discharged into a patient, is monitored to prevent overcharging.

Synchronous rectification method for reducing power dissipation in motor drivers in PWM mode

Abstract: Pulse Width Modulation (PWM) techniques, often used to reduce the power dissipation in polyphase motors, chop the current in the coils of the motor at their peak current levels, to achieve maximum torque, to allow rapid accelerations, and to reduce the power dissipated in the chip to a level proportional to the duty cycle. During the time the current is switched off, the current which has been established in the coils of the motor is allowed to be dissipated. Accordingly, when the switching transistors of the active coils are turned off during PWM mode chopping, a non-rectifying ground return path is provided for flyback energy in the active driving coil. This non-rectifying ground return path is provided by switching transistors in parallel with flyback diodes, operated in a form of synchronous rectification. This gives an alternate current path for the coil current to reduce the voltage drop across the diodes, and thereby reduce the power dissipation and heat in the chip.

Linear circuit models of PWM flyback and buck/boost converters

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

Zero voltage switching power converter with secondary side regulation

Abstract: A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch and to regulate the output voltage is disclosed. The power converter includes a transformer having a primary winding and a secondary winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch. A second switch means is connected in series with the secondary winding of the transformer and is operated to prevent the loading effects of the secondary from interrupting the creation of the zero-voltage switching condition. A secondary side regulation circuit is included to both regulate the output voltage and to prevent the loading effects of the secondary circuit from interfering with zero-voltage switching in the primary circuit.

A new synchronous rectifier using bipolar transistor driven by current transformer

Abstract: A new synchronous rectifier (SR) unit is proposed. SR has low offset voltage, which improves the efficiency oflow-voltage power supplies. The SR consists of a bipolar junction transistor (BJT) with a low on-resistance and a current transformer (CT). It is turned on by the free-wheeling current due to positive feedback through the CT. This unit needs no extra drive-circuit for BJT. Analysis and practical design considerations for the SR are presented. The lower offset voltage and higher conversion efficiency are obtained experimentally, and the proposed SR is compared with the case of Schottky diode for a 2 V power supply. >

Design issues for the transformer in a low-voltage power supply with high efficiency and high power density

Abstract: Circuit model, design feasibility, and design tradeoffs are investigated for the transformer in 1.5-5 V power supplies with high efficiency and high power density. The transformer is constructed from a single or a matrix of pot cores and from interleaved planar windings. It has been determined theoretically and verified experimentally that such a transformer is realizable as long as the loss constraint is not severe (e.g. less than 0.5 W transformer loss per 100 W output). The primary source of loss is the winding, not the core, in 1.5 V/turn design. Measures to reduce the transformer height tend to increase transformer loss or volume. >

Ground fault detector and associated logic for an electronic ballast

Abstract: An embodiment of the present invention is a lighting system including a sense transformer with two primaries and a secondary for receiving alternating current (AC) from a power source, a low ohmage resistor placed across the sense transformer secondary winding for preventing saturation of the core of the sense transformer, an analog comparator for detecting when ground-fault signals in the sense transformer secondary winding exceed a threshold voltage and digital counters for testing whether or not a ground-fault condition persists longer than three consecutive half-cycles of the received alternating current from the power source.

Synchronized switch tapped coupled inductor regulation circuit

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

Power factor matching in an ac power meter

Abstract: A solid-state AC energy consumption meter includes an array of AC signal transducers which provide voltage and current signals to a watt transducer chip. The watt transducer chip operates on the multi-phase voltage and current signals to produce AC energy consumption data which is fed to a register for visual display. In one aspect of the invention, a calibrating resistive component is placed in series with the input to the primary coil of the potential transformer for each phase. The value of the resistive component is calibrated to produce an appropriate change in the phase angle difference between the potential transformer secondary voltage and current transformer secondary current. More particularly, the addition of the resistance of the primary of the potential transformer provides the necessary amount of phase lead to the potential transformer to account for this phase error difference.

Run/standby control with switched mode power supply

Abstract: A television receiver has a switched mode power supply for regulating output voltages including the B+ output to a flyback transformer, by generation of output pulses to a power transformer. A controller for the power supply is coupled in two feedback loops, one responsive to a pulse width modulator coupled to the flyback transformer and the other comparing the output voltage with an internal reference for free running operation. The first feedback loop takes precedence and is active in the run mode of the television receiver. In the standby mode when horizontal rate pulses are absent, the second feedback loop takes over. The second feedback loop has a different reference level than the first, such that when switching from the run mode to the standby mode a transition interval occurs in which no pulses are output by the controller, thereby causing the B+ voltage to the flyback transformer to fall. During this transition interval, horizontal scanning signals continue at falling amplitude, and a signal is input to the kinescope drivers, thereby collapsing the picture and draining the ultor voltage on the screen anode. The reoccurrence of controller pulses when the output voltage of the power transformer has fallen to the new lower reference level is used to positively switch operation of the receiver at the conclusion of the transition interval.

Control system for motors and inductive loads

Abstract: The present invention provides a system for controlling current through inductive elements by automatically switching between a pulse width modulation mode and a linear mode, depending upon the current demands of the inductive elements. A time-base circuit provides periodic pulses that allow current to flow through an inductive device. The current through the inductive device increases over time. If the current through the inductive device exceeds a specified value, the current is shut off until the next pulse from the time-base circuit. After the power supply current has been shut off, current through the inductive device continues to flow through flyback diodes, gradually decreasing over time. Another pulse is provided by the time-base circuit before the current is allowed to reach zero. By controlling the duration and rate of increase and decrease of current through the inductive device, a method of current control for inductive elements has been provided.

Half-bridge converter switching power supply for magnetron

Abstract: A power source apparatus for microwave oven includes a half-bridge converter including a series connection of switching elements, a series connection of resonance capacitors, and a high frequency transformer having a primary winding and a secondary winding, and the half-bridge converter is driven by an output of a diode bridge which receives a commercial power source of 200 V. A current transformer detects a current of the primary winding. A control circuit compares a voltage equal to an average value of the current detected by the current transformer and a voltage set by a microcomputer, and controls the switching elements at a frequency in proportion to a magnitude of a difference of the both voltages, whereby a high frequency high voltage is induced on the secondary winding and applied to a voltage doubler rectifying circuit, and then a direct current high voltage is applied to a magnetron.

A method and a coupling for decreasing the detrimental radiation caused by a cathode-ray tube

Abstract: The object of the disclosure is a method and a coupling for decreasing the alternating current field produced by a cathode-ray tube in the environment. The said field or radiation is at least partly due to the capacitances (C1, C2) of the anode (A) with respect, on one hand, to the deflection coil (DY) and, on the other hand, to the ground. These capacitances produce, mainly because of the return pulse of the deflection coupling, a line rate noise voltage to the anode. According to the invention, a back-off voltage (U2) opposite to the noise voltage is fed to the anode (A) of the tube either directly or via a graphitizing (G). In cases where the same high-voltage transformer (TR) functions for both the high voltage of the anode and the horizontal deflection, the winding (L) of this transformer can also be used in generating the back-off voltage (U2). The back-off voltage can thus be coupled to the anode (A) via the high-voltage capacitor (C3) of the transformer.

Transformer driver having unlimited duty cycle capability by inserting narrow pulses during unlimited duty cycles

Abstract: A transformer driver having an unlimited duty cycle capability is disclosed herein. The transformer driver 10 of the present invention is coupled to an output circuit 20 and includes a transformer 32 having primary winding and secondary windings 30 and 34. The inventive driver 10 further includes a generator 26 for applying a plurality of charging pulses P1, P2 to the primary transformer winding 30 to keep the transformer from being saturated. A transistor buffer network 36 selectively electrically isolates the output circuit 20 from the transformer. In a particular embodiment the charging pulses P1, P2 serve to maintain the voltage at the control terminal 38 of a power transistor included within the output circuit.

Analog control of inductive flyback voltages in a full bridge circuit

Abstract: A voltage regulation circuit for use in "H" bridge circuit applications utilizes feedback networks to provide analog voltage regulation of the output nodes during switching of inductive loads. The regulation of the ouptut nodes during switching of inductive loads eliminates substrate current injection.

High voltage generating circuit

Abstract: The objects of the present invention are achieved by forming a high voltage generating circuit which comprises: a flyback transformer having a primary winding and a secondary winding; means for supplying pulses of first frequency to the primary winding; a smoothing capacitor connected across the secondary winding; an output line connected to one terminal of the smoothing capacitor; means for detecting a variation of high voltage on the output line to generate compensating voltage pulses of a second frequency which is higher than the first frequency for compensating the variation of high voltage to supply the compensating voltage pulses to the other terminal of the smoothing capacitor. Additionally, a low pass filter is connected between the other terminal of the smoothing capacitor and the secondary winding, which prevents the compensating voltage pulses from being supplied to the secondary winding. Further, a capacitor is connected between the other terminal of the smoothing capacitor and a reference potential. Moreover, the first frequency is equal to a horizontal deflection frequency of a cathode ray tube, and the second frequency is N times as large as the first frequency, wherein N is integer larger than 1. The first frequency could also be 1/N times as small as a horizontal deflection frequency, wherein N is integer larger than 1, and the second frequency is equal to the horizontal deflection frequency. Finally, the output line is connected to an anode of a cathode ray tube.

Auto scan horizontal deflection apparatus

Abstract: An auto scan horizontal deflection apparatus comprising a voltage detecting circuit as an amplitude detecting winding arranged at a secondary side of a choke transformer and detects amplitude of a flyback pulse. A frequency discriminating circuit (frequency/voltage converting circuit) discriminates frequency of horizontal synchronizing signal, and a control signal generating circuit (adding circuit) generates a control signal controlling the power source voltage of a variable power circuit supplying a power source voltage to a horizontal output circuit through a primary winding of the choke transformer on the basis of the outputs of both circuits. It becomes possible for the apparatus to keep horizontal deflection width constant regardless of the horizontal deflection frequency without using a conventionally-used detection resistance whose electric power loss is large, thereby decreasing electric power loss and keeping the horizontal amplitude almost constant even when the horizontal deflection frequency is changed.

Analysis of the zero-current-switched quasiresonant converters used as power factor preregulators

Abstract: The use of zero-current-switched quasi-resonant 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 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 a transformer (flyback, SEPIC or Cuk), this variation range can be minimized 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 reduced switching frequency variation range is obtained using a full-wave switch However, this type of resonant switch decreases the efficiency because it handles reactive energy, and then a trade-off between switching frequency variation range and efficiency must be considered >

High voltage converter

Abstract: High voltage converters are disclosed. The converters include at least a pair of transistor switches provided on the secondary windings of a flyback transformer. The transistor switches are controlled to be conducting, variably conducting and non-conducting so that the power flow between the transformer and a load can be controlled. Various configurations of a connection switch network are also disclosed.

High voltage regulating circuit

Abstract: A coil (11) is connected in series to a primary winding (1a) of a flyback transformer (1). A series circuit of a capacitor (15) and a switching circuit (12) is connected in parallel to the coil (11). By turning on and off the switching circuit (12), the connection of the capacitor (15) to the coil (11) is switched, to thereby connect or disconnect the coil (11) in an AC fashion. Therefore, it is possible to realize a high voltage regulating circuit which can be made inexpensive.

Technique to drive transformer coupled line amplifier

Abstract: The invention relates to a circuit for driving a transformer coupled line amplifier. The present invention uses a high impedance differential negative feedback from the secondary of the transformer and uses positive feedback from the primary winding of the transformer. This enables the transformer to be smaller in size while still reducing the harmonic distortion, improving the frequency response, eliminating ringing, lowering the output impedance, improving the longitudinal balance, and also improving the overall stability and phase response of the transformer.

Synchronous rectifier using bipolar transistor driven by current transformer

Abstract: In the power supplies to obtain a low output voltage and a high current, it is difficult to obtain high efficiency due to the forward voltage of the diode for output rectification. A method has been reported for improving the efficiency of the power supply by using bipolar transistors (BJT) with a low saturation voltage as a rectifier so that the forward voltage is reduced. However, in general, a driving circuit for the BJT is required and the application of the latter to a power supply is not straightforward. This paper proposes a synchronous rectifier system which drives a BJT by a positive feedback by a current transformer. The operating principle of this circuit is described. The reset condition of the magnetization energy of the current transformer is clarified. The present method has a simple circuit configuration in which a part of the emitter current of the BJT is used as a base-driving current by means of a current transformer. No special BJT driver circuit is needed. The present synchronous rectifier was installed in an actual power supply. It was confirmed that the efficiency is improved over the circuit using Schottky diodes.

Horizontal focus circuit in an image display

Abstract: A horizontal focus circuit in an image display for improving the focus characteristics at the edges of a planar CRT screen or a CRT screen used in a multi-sync mode. The horizontal focus circuit comprises a horizontal output portion for generating a flyback pulse, a horizontal dummy transformer for transforming the flyback pulse supplied from the horizontal output portion, a parabolic output circuit for generating a parabolic signal from the transformed flyback pulse supplied from the horizontal dummy transformer, a voltage circuit for rectifying and integrating the transformed flyback pulse supplied from the horizontal dummy transformer to generate a direct current (DC) voltage, a mode selection portion for generating a mode selection signal according to the sync frequency, a differential amplifying circuit for combining the mode selection signal supplied from the mode selection portion and the parabolic signal supplied from the parabolic output circuit, leveling up the DC voltage of the combined signal by a DC voltage supplied from the voltage circuit, and amplifying the combined and leveled-up parabolic signal, and a cascode amplifying circuit for controlling and amplifying the amplitude and frequency characteristics of the parabolic signal supplied from the differential amplifying circuit and supplying the amplified parabolic singal to a focusing grid of the CRT.

System and method for detecting D.C. motor circuit failures

Abstract: Apparatus and method are provided for determining and indicating if certain types of circuit failures have occurred in a D.C. motor circuit such as a locked rotor condition, a short-circuit or an open circuit. The method includes the steps of, and the apparatus involves applying a voltage to two leads of the D.C. motor sufficient to cause motor rotation, determining if flyback exists, determining if back EMF exists, and, finally, if a back EMF does not exist and flyback does exist then indicating a locked rotor condition. However, if a back EMF does not exist and flyback does not exist then an indication is provided that either an open-circuit or short-circuit condition exists. The same apparatus and method can be used with a voltage not sufficient to cause motor rotation, although given this limitation only flyback can be detected, so that only an open-circuit or short-circuit condition can be indicated.