Showing papers on "Flyback transformer published in 1997"

H/sup /spl infin// control applied to boost power converters

Abstract: The controller in a pulse-width-modulation (PWM) power converter has to stabilize the system and guarantee an almost constant output voltage in spite of the perturbations in the input voltage and output load over as large a bandwidth as possible. Boost and flyback power converters have a right-half-plane zero (RHPZ) in their transfer function from the duty cycle to the output voltage, which makes it difficult to achieve the aforementioned goals. Here, the authors propose to design a controller using H/sup /spl infin// control theory, via the solution of two algebraic Riccati equations. The almost optimal H/sup /spl infin// controller is of the same order as the converter and has a relatively low DC gain. The closed-loop characteristics of a typical low-power boost power converter with four different control schemes were compared by computer simulation. The H/sup /spl infin// control was found to be superior in a wide frequency range, while being outperformed by the others at extremely low frequencies. Good agreement was found between simulation results and experimental measurements.

Interleaved continuous flyback power converter system

Abstract: An interleaved flyback electrical power converter system having a plurality of flyback power converters operated in continuous mode, each converter utilizing a power switch operated under zero voltage switching conditions. The interleaved flyback power converter system is highly efficient and compact, and is suitable for use in high power, high frequency applications.

A three-phase three-winding core-type transformer model for low-frequency transient studies

Abstract: A topology-based and duality-derived three-phase, three-winding, core-type transformer model is presented. The model treats the leakage inductances and the coupling effects of the core in a straightforward and integrated way. The long-established positive- and zero-sequence star equivalent circuits of a three-phase three-winding transformer are derived from the original equivalent magnetic circuit of the transformer by applying duality. Formulations for determining the values of the leakage inductances and the core loss resistances from transformer open- and short-circuit test data are presented. A supporting routine is written to generate the /spl lambda/-i curves for each segment of the core and the other input data for EMTP. Since the duality-derived model consists of only RLC elements, no device-specific code to EMTP time-step code is needed. Winding capacitances are lumped to the terminals. The model is suitable for simulation of power system low-frequency transients such as inrush currents and ferroresonance, short circuits, and abnormalities including transformer winding faults.

Method and apparatus for isolated flyback regulator control and load compensation

Abstract: Control circuits for a flyback switching voltage regulator that uses magnetic flux sensing are provided. These circuits include a flyback error amplifier circuit, a logic circuit, and a load compensation circuit. The flyback error amplifier circuit allows a flyback voltage pulse from a primary transformer winding to be employed for output voltage regulation. The logic circuit provides appropriate timing and control signals for the flyback error amplifier circuit. The load compensation circuit compensates for parasitic impedance contributions to the flyback voltage pulse without altering the stability of the flyback regulator.

Analysis of buck converters used as power factor preregulators

Abstract: Buck-type converters are analyzed for application as power factor preregulators. In particular, the maximum power for which the IEC 10003-2 standards are met is calculated for different conversion ratios and modulation techniques. Two step-down converters are proposed, which comply with EMC standards thanks to an auxiliary flyback stage which uses the same switches of the main converter plus a small power switch commutated at the line frequency. With proper design, the voltage stress of the main switch remains the same as for a conventional buck topology. Simulations and experimental results are reported to validate the theoretical analysis.

Half-bridge zero-voltage-switched PWM flyback DC/DC converter

Abstract: A DC-DC ZVS PWM converter circuit which utilizes the leakage inductance of an output transformer and a three-step operation cycle so as to reduce the voltage stress on the converter power switching transistors and to reduce the EMI noise emissions of the circuit.

Actuating circuit of piezoelectric transformer and actuating method thereof

Abstract: An actuating circuit of a piezoelectric transformer which is small in thickness and size and has a wide input voltage range is developed In the actuating circuit of the piezoelectric transformer, when a sine wave outputted from a AGC circuit is input to a delta-sigma modulator, the sine wave switches output driver and switches a second output driver through an invertor with a 1-bit quantized bit signal so as to generate a pulse signal having an amplitude of power supply voltage Vdd from the GND potential Actuating waves output from the output drivers and are applied to 1 piezoelectric transformer extracting resonance frequency of a piezoelectric transformer through a filtering effect provided with an input capacitance of the piezoelectric transformer and coil converting the 1-bit quantized bit signal into a sine wave Consequently, since the piezoelectric transformer can be operated with the sine wave, the piezoelectric transformer can be actuated efficiently

Piezoelectric Transformer for Cold Cathode Fluorescent Lamp Inverter.

Abstract: A piezoelectric transformer of which the structure differs from the Rosen-type structure was investigated. According to the aim of reducing the heat generation of the piezoelectric transformer, the relationship between the heat generation and vibration velocity of the transformer was investigated. The temperature of the transformer rapidly rises when the vibration velocity of the transformer increases to above a critical value. Based on analysis of the electrical equivalent circuit of the piezoelectric transformer, the vibration velocity of the transformer is proportional to the output current and inversely proportional to the force factor of the output part. As a result, new piezoelectric transformers with a strip electrode at the output part which can minimize the heat generation of transformers have been developed. The inverters with these 3, 6 and 10 W piezoelectric transformers showed more than 85% efficiency at 60–80 kHz driving.

Adding active clamping and soft switching to boost-flyback single-stage isolated power-factor-corrected power supplies

Abstract: Single-stage isolated power-factor-corrected power supplies (SSIPP) have the attractive features of fast regulation and a single control loop. However, SSIPP circuits also have higher voltage stress and heavier loss (when compared with a normal DC-DC power converter), which severely limit their practical applications. In this paper, the authors propose to add active clamping to SSIPP to recycle the energy trapped in the leakage inductance of their transformer (to keep the switch voltage stress low) and to achieve soft switching of their electronic devices (to further reduce the loss). This arrangement significantly improves the viability of SSIPP for practical applications. The auxiliary active-clamping transistor in the proposed circuit uses the same control/driver circuit as the main switching transistor. Simulations and experimental works verifying the operation of the converter are reported.

Control algorithms and circuit designs for optimal flyback-charging of an energy-storage capacitor (e.g., for flash lamp or defibrillator)

Abstract: A flyback-type of a transformer-coupled DC/DC power converter supplies a train of current pulses to charge an energy-storage capacitor to a desired high voltage, converting input DC power obtained from a lower voltage DC source. The energy-storage capacitor is charged to a specified voltage within a specified time with minimum peak and RMS currents in the transistor, the rectifier diode, the transformer windings and the DC power source, minimizing the i/sup 2/R losses. This is done by generating: (1) energy-storage current pulses in the power transistor and the transformer primary winding in which the current increment from the beginning to the end of a pulse is only a small fraction of the final (peak) value; and (2) energy-delivery flyback current pulses in the capacitor and the transformer secondary winding in which the current decrement from the beginning to the end of a pulse is only a small fraction of the initial (peak) value. Recommended methods are: (1) hysteretic current-mode control with current sensing in both transformer windings; (2) peak-current-commanding current-mode control with switching frequency or transistor-nonconducting time varying in a prescribed way during the charging; or (3) valley-current-commanding current-mode control with switching frequency or transistor-conducting time varying in a prescribed way during the charging. Compared with one nonoptimal method, peak currents are reduced by a factor of about 2 and i/sup 2/R power losses are reduced by a factor of about 1.33.

Transformerless electroluminescent lamp driver topology

Abstract: A transformerless driver circuit for an EL device has a battery or other source of dc power, and a microcontroller that is suitably programmed with associated firmware, so that a first switch control signal appears at a first output and a second switch control signal appears at a second output. A flyback circuit is connected to the first microcontroller output and, through a diode, to a charge storage device, e.g., a capacitor. This charges the capacitor stepwise to a relatively high voltage. The flyback circuit includes an inductor having one end connected to a first terminal of the dc power source, and another end coupled to a transistor or similar switch element. The transistor is coupled to the second dc power terminal, and has a base or gate coupled to the first output of the microcomputer. A controlled discharge arrangement bridges across the charge storage device to discharge the same periodically, and create an alternating current to drive the EL device. A second transistor has its base or gate coupled to the microcontroller second output. An isolating capacitor can be positioned in series between the diode and the charge storage device to eliminate the dc offset to the EL element. In one alternative arrangement, two or more flyback circuits are gated on and off sequentially. In a power-saver arrangement, the discharge circuit returns charge back to the battery.

Application of integrated magnetics in resonant converters

Abstract: The physical size of inductors in resonant converters was examined in terms of inductor to transformer size ratio. Following the general discussion of the issue, the inductor size in a series resonant DC-DC converter is examined in detail. It is shown that the inductor to transformer size ratio is a function of the peak voltage of the inductor to the RMS voltage of the transformer and is independent of the inductance. The physical size of the inductor could be much larger than the transformer when the converter operates near resonance. Away from resonance, the inductor size becomes close to, and even smaller, than the transformer. Leakage inductance of the transformer can be used as the resonant inductance but if the leakage is associated with the secondary windings of the transformer, it will increase the peak reverse voltage of the rectifier diodes when a center-tapped rectifier topology is used. To solve this problem, an integrated transformer-inductor element with high primary leakage inductance and low secondary leakage is proposed and tested. The experimental unit was built for a power level of 1 kVA and switching frequency range 30-60 kHz.

Isolated power supply for indicator light

Abstract: A planar transformer having windings on a printed circuit board coupled by a high frequency ferrite core driven by a high frequency operational amplifier based relaxation oscillator controlling a switch for pulsing a primary winding of the transformer at a set frequency. The secondary of the transformer powers a lamp circuit which is isolated from the electrical supply, and a test input is connected in a logic OR arrangement with the electrical supply.

Novel single-stage isolated power-factor-corrected power supplies with regenerative clamping

Abstract: Single-stage isolated power-factor-corrected power supplies (SSIPP) have the attractive feature of fast regulation and single control loop. In this paper we further propose to add a very simple regenerative clamping circuit to SSIPP to reduce the voltage stress and to recycle the energy trapped in the leakage inductance of the isolation transformer, thus eliminating the need for a lossy snubber circuit. In addition, this proposed clamping circuit also provides a mechanism to reset the magnetizing current of the output transformer of SSIPP employing a forward converter as the output stage. Simulations and experimental results are reported to verify the operation and performance of the SSIPP with regenerative clamping.

Power converter for converting AC shore power to shipboard use

Abstract: A power converter for converting shore power voltage, phase, and frequency for shipboard use includes a variable inductance input transformer that can be connected to the shore power. The primary windings of the transformer have a plurality of taps, and a respective computer-controlled switch is connected between adjacent taps to selectively establish a closed circuit or an open circuit between the taps and thereby configure the primary windings as a low or high voltage "delta" or "wye", as appropriate for the shore power voltage. The output of the input transformer is sent to a variable speed drive, then to an output transformer, and thence to the distribution bus of the ship. A voltage regulator regulates the output voltage of the output transformer. If desired, a phase selector can be provided between the shore power and input transformer to establish the phase characteristics (i.e., single, two-, or three-phase) of the power signal that is output by the input transformer, depending upon the phase characteristics of the shore power that is connected to the input transformer.

New universal control methods for power factor correction and DC to DC converter applications

Abstract: Two new methods are described in implementing power factor correction. They are simple, easy to implement, cost effective and provide comparable or better performance over the existing schemes. The first method is a generalization of the nonlinear carrier control method which could be applied to all second order power converters: the buck, boost and flyback power converters with either leading-edge or trailing-edge modulation. Equations are derived for each of these six topologies, and simulation results are presented for the boost power converter with leading-edge modulation. The advantage of using leading-edge modulation is that the RHP zero is eliminated, thus broadening the power converter's bandwidth. The authors suggest that this generalized technique be called "input current modulation". The second method is similar to the average current control method employing leading-edge modulation, but sensing of the input voltage information is not required. Slope compensation is achieved by integrating the output of the error amplifier where the slope is controlled by the output level of the error amplifier. This method can be applied to all six topologies mentioned and is called the "input current shaping" technique. The authors implemented a boost power converter with leading-edge modulation on a 2 /spl mu/m BiCMOS process. Experimental results are provided to demonstrate the robustness of the latter method.

Alternating current power control device

Abstract: An alternating current power control device including a phase comparison controller for comparing a phase of an input voltage with that of a first reference voltage, a single-winding transformer for varying the input voltage, a mutual induction reactor for lowering the input voltage by a desired level in response to an output voltage from the single-winding transformer, an output voltage comparator for comparing an output voltage with a second reference voltage, an output current comparator for comparing an output current with a reference current, an OR logic controller for performing an OR operation with respect to output signals from the phase comparison controller and output current comparator, and a switch array for selectively transferring the output voltage from the single-winding transformer to the mutual induction reactor in response to output signals from the output voltage comparator and OR logic controller. According to the present invention, the mutual induction reactor is implemented on the basis of the principle of a linear transformer and has a small capacity corresponding to about 1/10 of a load power. Therefore, a proper power necessary to the saving of energy can be supplied by using the mutual induction reactor.

Design considerations and performance evaluations of synchronous rectification in flyback converters

Abstract: Design trade-offs and performance comparisons of various implementations of the flyback power converter with a synchronous rectifier are presented. Specifically, the merits and limitations of the constant-frequency (CF) continuous-conduction-mode, CF discontinuous-conduction-mode (DCM), variable-frequency DCM, and zero-voltage-switched DCM flyback power converters with synchronous rectifiers are discussed. The theoretical efficiency improvements of the discussed synchronous rectification approaches relative to Schottky diode implementations are derived. Finally, theoretical results are verified on an experimental, universal-input, offline, 15 V/36 W flyback prototype.

Low-cost, high-voltage, flyback power supply

Abstract: A low-cost, high-voltage, flyback power supply (100) comprising two switching transistors (155, 150) connected in series with the primary winding (119) of the transformer (118). Such a power supply (100) also comprises a clamping circuit (116) in parallel with the primary (119) of the transformer (100).

A novel isolated high quality rectifier with fast dynamic output response

Abstract: This paper describes an integrated boost-derived and flyback power factor corrector topology with fast regulation of the output voltage for single-phase applications. With this scheme, major power goes through a single stage to the output, while both unity power factor and tight output regulation can be achieved, and the efficiency as well as the power density can be higher than in a conventional two cascade stage scheme.

Exit sign having a pulse switching tandem flyback voltage converter and a backup battery

Abstract: This invention allows conversion from AC or DC line voltage between 70 and 424 volts to small loads between 2.5V and 18V DC for charging of batteries and operating of small loads. The invention uses a topology including two flyback stages in tandem. This invention has many uses and we are believed to be the first to apply it to battery charging and the operation of small loads. The invention is very cost effective and has feedback both from the input line voltage and output voltage to allow different loads and to allow the universal voltage input. The invention operates at high frequency and thus eliminates large transformers and uses surface mount components. All of this results in its very small size, low heat generation, and high efficiency. The invention draws very little power when connected only to a battery without the AC having been cycled. Primary applications for this invention include low powered uninterrupted power supply (UPS) devices. As disclosed herein, our first application is an emergency lighting device combined with an exit sign. However, we may use the same power supply for lighting equipment, lighting sensors, smoke detectors, burglar alarms, passive receivers, infrared detectors, ultrasonic detectors, stand-alone battery chargers, communications equipment or any other device which has a small load or requires charging with a battery from high input line voltages, such as 120V and higher.

Power flow control with rotary transformers

Abstract: A power flow controller seeks to inject a voltage V ser on a transmission path between a first electrical area and a second electrical area, in order to cause a desired power flow into the second electrical area. The power flow controller (20) includes a series transformer (40), a regulating transformer (44), a rotary phase shifting transformer network (44), and a control system (46). The rotary phase shifting transformer network (44) includes a first rotary phase shifting transformer (102 1 ) and a second rotary phase shifting transformer (102 2 ). The first rotary phase shifting transformer and the second rotary phase shifting transformer have first terminals (windings of one of either rotors or stators) connected in parallel to a regulating winding 62) of the regulation transformer. Second terminals (windings of the other of rotors or stators) are connected in series with an excited winding (52) of the series transformer. The control system applies control signals to the first rotary phase shifting transformer and the second rotary phase shifting transformer to obtain desired phase angles θ E1 , θ E2 between the rotor (110) and stator (112) of each transformer, and thereby achieve an effective phase shift θ PFC and a voltage magnitude ratio T PFC between the first electrical area and the second electrical area.

Rcc-type switching power supply

Abstract: A RCC switching power is turned on/off repeatedly by a main switching means (9) to supply a switching current to a primary winding (31) and an energy is transferred from the primary side to the secondary side by flyback operation A circuit composed of a series connection of a snubber capacitor (7) in a snubber circuit (5a to 5c) and an auxiliary switching means (3) is connected in parallel to the primary winding (31) When the auxiliary switching means (3) is closed by an auxiliary winding (4) while the main switching means (9) is opened, the auxiliary switching means (3) performs a third quadrant operation in which the snubber capacitor (7) is charged by the energy stored in the leakage inductance component of the primary winding (31) and then performs a first quadrant operation in which the snubber capacitor (7) is discharged to supply a current to the primary winding (31) By the current, the energy is transferred to the secondary winding side (32) or a smoothing capacitor (21) on the primary side is charged and the energy is transferred to a primary side rectifying/smoothing means (18) As a surge voltage is not applied to the main switching means (9) and the energy stored in the leakage inductance component is not wasted, a low noise and high efficiency RCC switching power supply (2a to 2c) is obtained

A practical approach to minimize the zero-sequence current harmonics in power distribution systems

Abstract: In this paper, a simple and practical approach to minimize the zero-sequence current harmonics in three-phase four-wire power distribution systems is proposed. The zero-sequence current harmonics are minimized by using a combination of a very low zero-sequence impedance transformer and a very high zero-sequence impedance transformer. The very low zero-sequence-impedance transformer is shunt connected to the load and the very high zero-sequence impedance transformer is series connected to the source. The series connected transformer will act as a zero-sequence current isolator between the source and load and, therefore, almost all of zero-sequence currents which are generated by the load will flow through the shunt connected transformer. Experimental results are included to verify the proposed approach.

Drive circuit supplying drive signals to a plurality of windings of a multi-phase d.c. motor

Abstract: A drive circuit for supplying drive signals to a plurality of windings of a multi-phase d.c. motor. The drive circuit comprises a multi-phase inverter which supplies the drive signals to the motor windings; a phase detector which samples the back-emf signal of a winding in order to obtain a phase-error signal; a low-pass filter which generates a control signal dependent upon the phase-error signal; and a controllable oscillator which generates a frequency signal whose phase and frequency depend on the control signal. The timing with which the multi-phase inverter supplies the drive signals to the windings is dependent on the frequency signal. The drive circuit further comprises a masking circuit for temporarily inhibiting the further processing of the phase-error signal by the low-pass filter, at least during the presence of a flyback signal in the phase-error signal, as a result of which the processing of the flyback pulses present in the phase-error signal is inhibited.

Steady-state characteristics of the push-pull piezoelectric inverter

Abstract: Steady-state characteristics of the push-pull inverter with a piezoelectric transformer are analyzed. The piezoelectric transformer operating in the 3rd-order longitudinal vibration mode is used in place of a conventional magnetic transformer to produce a high output voltage to light up a cold cathode fluorescent lamp. The circuit operation, the load characteristics, the efficiency and the ZVS conditions are analyzed using equivalent circuits, analytical results are confirmed by experiments. An example of the output current control is also shown.

Stability analysis of air-core superconducting power transformer

Abstract: The air-core superconducting power transformer is being investigated as a transformer having the function of a shunt reactor. From the results of the authors' previous analysis, the magnetic field acting on the superconducting wires of an air-core transformer under load includes the rotating component besides the alternating component. Since this rotating component has a possibility of affecting the wire stability, the influence should be clarified. In this paper, a method of stability limit analysis based on the instantaneous magnetic field calculation is proposed. Quench tests of an experimental air-core superconducting transformer are carried out, and the stability limit of the air-core superconducting transformer is analyzed by using the proposed method. From the results of the analysis, it is seen that the load factor of the superconducting wire, which is defined in this paper, is almost the same regardless of the superconducting power transformer load.

A zero voltage switching flyback converter topology

Abstract: A zero voltage switching flyback power converter topology employing an auxiliary circuit is presented in this paper. The proposed power converter has lossless switching (whatever the line and load conditions), few components and can be operated either in voltage or current mode control. A detailed analysis of the circuit is presented and the design procedure is illustrated. A 50 W 200 kHz prototype zero voltage switching flyback power converter is built which shows an efficiency improvement of approximately 7% as compared to a conventional hard switching flyback power converter.

High quality flyback power factor corrector based on a two input buck post-regulator

Abstract: The two-input buck (TIBuck) post-regulator has been proposed to improve the dynamic characteristics of conventional power factor correctors (PFCs). This post-regulator exhibits very high efficiency due to the fact that only a part of the total power undergoes a power conversion process and, therefore, the overall efficiency of the complete converter is very close to that of the first stage. In this paper, the implementation of a PFC based on a conventional flyback and a TIBuck is analyzed.

Harmonic eliminating PWM converter

Abstract: A PWM based converter including a Y-Δ, Y--Y transformer (or a Δ--Δ, Δ-Y transformer) wherein the Y-Δ portion of the transformer phase shifts input voltage by 30° with respect to the Y--Y portion of the transformer and thereby eliminates many low order supply line harmonics. The rectifier also includes two series connected PWM switching rectifiers, one rectifier receiving input voltages from the Y--Y portion of the transformer and the other rectifier receiving input voltages from the Y-Δ portion of the transformer, and a controller for controlling the first and second rectifiers so as to eliminate low order harmonics on the supply lines that are not eliminated by the transformer. A capacitive bank is required between each rectifier and the transformer.