Showing papers on "Flyback transformer published in 1994"

Utilization of an active-clamp circuit to achieve soft switching in flyback converters

Abstract: Flyback derived power convertor topologies are attractive because of their relative simplicity when compared with other topologies used in low power applications. Incorporation of active-clamp circuitry into the flyback topology serves to recycle transformer leakage energy while minimizing switch voltage stress. The addition of the active-clamp circuit also provides a mechanism for achieving zero-voltage-switching (ZVS) of both the primary and auxiliary switches. ZVS also limits the turn-off di/dt of the output rectifier, reducing rectifier switching losses, and switching noise due to diode reverse recovery. This paper analyzes the behavior of the ZVS active-clamp flyback operating with unidirectional magnetizing current and presents design equations based on this analysis. Experimental results are then given for a 500 W prototype circuit illustrating the soft-switching characteristics and improved efficiency of the power converter. Results from the application of the active-clamp circuit as a low-loss turn-off snubber for IGBT switches is also presented.

Low loss synchronous rectifier for application to clamped-mode power converters

Abstract: A synchronous rectifier for use with a clamped-mode power converter uses in one embodiment a hybrid rectifier with a MOSFET rectifying device active in one first cyclic interval of the conduction/nonconduction sequence of the power switch and a second rectifying device embodied in one illustrative embodiment as a low voltage bipolar diode rectifying device active during an alternative interval to the first conduction/nonconduction interval. The gate drive to the MOSFET device is continuous at a constant level for substantially all of the second interval which enhances efficiency of the rectifier. The bipolar rectifier device may also be embodied as a MOSFET device. The subject rectifier may be used in both forward and flyback power converters.

Synchronously rectified buck-flyback DC to DC power converter

Abstract: A synchronously rectified buck-flyback converter is described which provides multiple synchronous regulated outputs. A synchronous buck converter provides the main output and a synchronous flyback converter, utilizing the primary inductor of the buck converter, provides the secondary output. The converter utilizes a split-feedback signal, whereby each of the regulated outputs provides a component of the signal and a switch controller synchronously activates and deactivates rectification switches based on the feedback signal, required output levels and load. The switches are synchronously controlled such that a power input switch is operated in anti-phase to a control switch for each regulated output.

Third order longitudinal mode piezoelectric ceramic transformer and its application to high-voltage power inverter

Abstract: Color liquid crystal displays (LCD) require low-profile, miniaturized and highly efficient power inverters, replacing conventional electromagnetic transformers, to light up their backlights, which include cold cathode fluorescent lamps (CCFL). The object of this study is to actualize the power inverter, to which a novel multilayered piezoelectric ceramic transformer operating in the third order longitudinal mode is applied. The piezoelectric transformer has a symmetrical structure in the lengthwise direction and its output part operates in a piezoelectric stiffened mode in order to increase both energy conversion efficiency and power density. This transformer has a great advantage, in that all the electronic terminals can be connected at the vibration nodes of the transformer, which contributes to the guarantee of stable transformer performances at high power operation. In this power inverter, a separately excited oscillation circuit was adopted to drive the transformer with high efficiency, and the transformer drive frequency was controlled by detecting the backlight current in order to adjust the backlight luminance properly. Using a triple-layered piezoelectric transformer, a fabricated power inverter exhibited the overall efficiency of 92%, the output power of 4.5 W, which is enough power to light up a 9.4 inches color LCD, including the stray capacitance loss resulted from CCFL mounting. The luminance value on a light transmission plate of the color LCD was 2500 cd/m2 while the inverter dimensions are as small as 76t22t6 mm

Clamped continuous flyback power converter

Abstract: Size reduction in a clamped power converter can be achieved, and stability of the converter under no-load and transient loads can be substantially improved, by operating the converter in a continuous flyback mode.

An actively cooled 120 kW coaxial winding transformer for fast charging electric vehicles

Abstract: A 120 kW coaxial winding transformer has been built and tested to verify previous indications that a high power transformer is feasible with the key attributes of this novel design, namely: low leakage inductance, minimal effect of leakage field on core losses, low copper losses, and a convenient "nesting" structure well suited for separability of the findings. The power transfer capability is more than double that of any previously published result for coaxial winding transformers. The application chosen for the fabricated transformer was an inductive coupler for fast charging of electric vehicles. Presented are the key parametric decisions, their impact on transformer fabrication and characteristics, and the results of these design choices as observed in the experimental data. The final design has active cooling to facilitate high power density and a separable core to allow the primary and secondary windings to be coupled and uncoupled. The experimental data shows performance better than expected, with a magnetizing to leakage inductance ratio of 1000:1, efficiency well over 99% and power density of 25 kW/kg.

Uninterruptable off-line, isolated flyback topology switch-mode power supply

Abstract: An all-ranging DC output uninterruptible switched mode power supply (SMPS) of off-line flyback topology is capable of operating with an input voltage between 90 v AC and 270 v AC and an input frequency range of 40 Hz-70 Hz for operation throughout the world. Provided with a battery backup, the SMPS gives DC output without interruption even during AC power failures. The battery and the regulated AC main's supply outlet are connected through an "OR" connection comprising Shortsky rectifier diodes. A pulse width modulator whose conductive duty cycle is responsive to the condition of a voltage, Vcc, provides a reference voltage. An isolated flyback converter includes MOSFET transistor switch and power transformer. The power transformer stores energy in its primary winding when transistor is conductive and transfers energy to the secondary winding when transistor is nonconductive. The pulse width modulator controls the conduction of the transistor. A snubber circuit allows slow decay of current in the power transformer. An opto-coupler acts as a feedback or the pulse width modulator. Inductor is used for storing energy and transferring energy to the negative voltage regulator when control IC, is off, to provide -12 v at the output of negative voltage regulator.

Characterization of an active clamp flyback topology for power factor correction applications

Abstract: Flyback derived power convertor topologies have long been attractive because of their relative simplicity when compared with other topologies used in low power applications. Incorporation of active clamp circuitry provides the additional benefit of recycling transformer leakage energy while minimizing switch voltage stress. This paper presents the analysis, design, and experimental results of 500 W single stage and 600 W interleaved active clamp flybacks used for power factor correction. Several practical issues, including the application of charge control, the use of mixed power devices, and a solution to the hold-up time problem are discussed and experimentally verified. >

A BIFRED converter with a wide load range

Abstract: In this paper, the boost integrated flyback rectifier energy DC-DC (BIFRED) power converter which incorporates power factor correction, output voltage hold-up and input-to-output isolation is examined The particular problem of high bulk capacitor voltage at light loads is addressed and it is shown how this may be resolved if the boost and flyback sections of the power converter are allowed to operate discontinuously The criteria for ensuring correct operation in the discontinuous mode are investigated It is shown that operating in this mode places no restrictions on the minimum load and simplifies the control loop design >

Harmonics from SVC transformer saturation with direct current offset

Abstract: Circulation of direct current in transformer windings can cause significant transformer saturation and harmonic generation. This problem may be experienced by static VAr compensators with an anti-parallel thyristor arrangement. This paper presents a technique to analyze the harmonic distortions caused by transformer saturation with direct current offset. The technique is used to investigate the harmonic generation from the transformer of a static VAr compensator to be installed in the BC Hydro system. >

PWM converters for three phase AC power control and AC to DC conversion

Abstract: PWM converters provide buck, boost, buck-boost, flyback, and Cuk configurons for three phase AC-AC power control. In an AC-DC embodiment, only a single power conversion circuit is used in a configuration including a pair of series connected gate turn off devices which are oppositely poled and oppositely timed, are connected directly to an AC input source, and provide an output to a high frequency isolating transformer. The transformer provides an output to a rectifier, which thus provides the DC output.

Resistance forward telephone line feed circuit

Abstract: A line feed circuit employing a low-inductance transformer, and providing a major portion of the terminating impedance as line feed resistors connected between a telephone line and the transformer primary. A low impedance output amplifier drives a low resistance transformer secondary, thus reducing the need for large transformer inductances. By connecting the line feed resistors between the transformer and the telephone line, high voltage surges are absorbed by the resistors, and thus little is dissipated in the transformer. The transformer can be made physically small, because of the reduced inductance, reduced winding insulation, and reduced power requirements. The resistance forward type of line feed circuit lends itself well to simple implementation with flux cancellation and impedance synthesis circuits.

PCB based transformer for power MOSFET drive

Abstract: Power MOSFET and IGBT gate drives often face isolation and high voltage constraints. The gate drive described uses a printed circuit board based transformer combined with the memory effect of the power MOSFET input capacitance. This transformer is a bidirectional link between the ground referred control IC and the floating gate drive. It transfers energy and signal to the gate drive, provides full duty cycle range, perfect dV/dt immunity and virtually no voltage constraint. No floating auxiliary is required for the secondary circuit. If the short circuit protection is operated, an alarm signal is transmitted back to the primary through the same transformer. This circuit is perfectly suited to drive floating and/or isolated switches in motor drives, uninterruptible power supplies and AC switches. Due to the printed winding approach, cost reduction can be expected in the transformer manufacture automation. >

Power converter having regeneration circuit for reducing oscillations

Abstract: A power converter including a complementary regeneration circuit for eliminating oscillations and conserving leakage energy to increase the efficiency of a flyback power converter. The complementary regeneration circuit includes a regeneration capacitor, a regeneration switch, a diode and appropriate timing circuitry to switch the regeneration capacitor in and out of the circuit at the appropriate times. Due to the operation of the regeneration switch, the capacitance of the regeneration capacitor is much larger than a typical snubber/clamp capacitor, so that it overdamps the circuit eliminating voltage overshoot typically appearing across the primary switch. The regeneration capacitor charges with regeneration energy and drives negative current into the primary inductor, holding the voltage across the primary switch constant when the secondary current goes to zero. When the regeneration switch is turned off, the negative current in the primary inductor drains the capacitance in the primary switch, which activates the inherent diode of the primary switch causing low voltage across the primary switch when it is turned on. A simple resistor or transistor circuit may be added between the input voltage and the PWM timing circuit to change the frequency of operation to compensate the regeneration energy for changes in the input voltage. Similarly, a resistive element coupled between the PWM timing circuit and an auxiliary voltage having a voltage proportional to the output voltage changes the operating frequency to compensate the regeneration energy for changes in the output voltage.

Power converter having regeneration circuit for reducing oscillations

Abstract: A power converter including a complementary regeneration circuit for eliminating oscillations and conserving leakage energy to increase the efficiency of a flyback power converter. The complementary regeneration circuit includes a regeneration capacitor, a regeneration switch, a diode and appropriate timing circuitry to switch the regeneration capacitor in and out of the circuit at the appropriate times. Due to the operation of the regeneration switch, the capacitance of the regeneration capacitor is much larger than a typical snubber/clamp capacitor, so that it overdamps the circuit eliminating voltage overshoot typically appearing across the primary switch. The regeneration capacitor charges with regeneration energy and drives negative current into the primary inductor, holding the voltage across the primary switch constant when the secondary current goes to zero. When the regeneration switch is turned off, the negative current in the primary inductor drains the capacitance in the primary switch, which activates the inherent diode of the primary switch causing low voltage across the primary switch when it is turned on. A simple resistor or transistor circuit may be added between the input voltage and the PWM timing circuit to change the frequency of operation to compensate the regeneration energy for changes in the input voltage. Similarly, a resistive element coupled between the PWM timing circuit and an auxiliary voltage having a voltage proportional to the output voltage changes the operating frequency to compensate the regeneration energy for changes in the output voltage.

Switch mode power supply with output feedback isolation

Abstract: A switch mode power supply includes a transformer and a switching transistor for turning the primary of the transformer on and off. The secondary of the transformer is connected to a comparator which compares the output voltage to a reference voltage and provides a reverse current to the switching transistor to control the duty cycle of the switching transistor in accordance with the comparison.

Switching power supply

Abstract: A switching power supply with a high power-conversion-efficiency is obtained by further reducing a loss occurring in a transistor rectifying element A driving transistor Q3 is arranged between a base of a transistor Q2 as the rectifying element and the ground A driving signal is inputted from a connection point of the transistor Q2 and a choke coil L1 generating a flyback voltage to the base of the driving transistor Q3, and an ON ad OFF operation of the transistor Q2 is caused to synchronize with an ON ad OFF operation of the switching transistor Q1, thereby preventing a leakage of the current in direction of the base from the collector of the transistor Q2 when it turns off, reducing the loss of the transistor rectifying element and then, improving the power conversion efficiency of the switching power supply

Flyback power supply having a VCO controlled switching rate

Abstract: A DC-DC current-mode controlled flyback switching power supply provides a high efficiency of operation throughout a wide range of input voltages. An error amplifier produces an error signal from the difference between a reference voltage and an output voltage feedback signal. The error signal controls a VCO that sets a latch to enable a power switch to store power in a flyback transformer. A comparator compares the error signal against a current sense feedback signal indicating the current flowing through the power switch. The comparator resets the latch and disables the power switch to transfer the stored energy in the flyback transformer to the output of the power supply. The extended input range of operation is achieved by varying the switching frequency of the DC-DC converter through the use of the VCO to accommodate varying input voltages and loading.

Modeling magnetic devices using the gyrator re-cap core model

Abstract: This paper is an extension of the gyrator-capacitor more model introduced by D.C. Hamill (1994). This core model is simple, efficient and handles both linear and nonlinear cores. The only item lacking is an efficient core loss element for determining circuit Q and efficiency. The gyrator re-cap core model contains a core loss element that takes into account both eddy current and core hysteresis losses. This paper describes the model and then demonstrates how to use it to accurately model the following magnetic devices: inductor; transformer; flyback transformer; ferroresonant regulator; and flux gate magnetometer.

Non-contacting power feeding device for traveling object

Abstract: PURPOSE: To reduce the size and weight of a non-contacting power feeding transformer so as to prevent the production of electromagnetic noise from the transformer by connecting a series capacitor with a feeder line which is also acts as the primary winding of the transformer and creating a series resonance state with the capacitance of the capacitor, circuit inductance of the feeder, and the frequency of AC power. CONSTITUTION: A series capacitor 21 is connected with a feeder 7 and the output frequency of AC power 20 is controlled so that a series resonance state can be created with the capacitance of the capacitor 21 and the circuit inductance 5 of the feeder 7. When a non-contacting power feeding transformer is constituted in such a way, no excessive power supplying capacity is required for supplying reactive power, because the circuit inductance 5 of the feeder 7 becomes nearly zero. Therefore, the size and weight of the transformer can be reduced and the production of unpleasant electromagnetic noise from the transformer can be prevented. COPYRIGHT: (C)1995,JPO

Efficient VCCP supply with regulation for voltage control

Abstract: A highly efficient compact multiple output voltage generation circuit is designed for use in integrated circuit devices such as DRAMs which require multiple internal voltage supplies for optimum performance An oscillator is connected to a primary coil of a microtransformer The microtransformer secondary coil has multiple taps one of which is connected to ground A second transformer tap is connected to a transformer output node The oscillating transformer output signal is capacitively coupled to a voltage rectifier The input to the rectifier is biased to one diode drop below Vcc The output of the rectifier is an internal supply voltage greater than ground Another transformer tap is connected to a negative oscillation output node The negative oscillating signal is rectified to produce a negative internal supply voltage The voltage generation circuit operates effectively at low Vcc input levels where capacitor based voltage pumps often fail The circuit is compatible with CMOS manufacturing processes

Design Criteria for Transformers in High Voltage Output, High Frequency Power Converter Applications

Abstract: SummaryWhen a dc high voltage needs to be obtained from low voltage inputs (main voltage), the necessary power converter needs a high value for its transformation ratio; consequently, a large number of turns is often necessary for secondary windings and some parasitics appear (large leakage inductance and large capacitance). Thus, it is usual to design a resonant converter to include both inductance and capacitance in the power topology. However, as the parasitics are used to obtain the resonance, their value (and their spreads) are critical. The present paper proposes several criteria in order to establish an adequate method for constructing the transformer, and a new topology for transformers and a model for parasitic capacitances are also presented taking into account high voltage and high frequency problems and limitations of materials.

Deflection apparatus for raster scanned CRT displays

Abstract: Deflection apparatus for a raster scanned cathode ray tube display comprises a flyback circuit (T2,T4,Ly,Df,Cf) including a switch (T2,T4) connected in series with an inductor (Ly). The switch (T4) is responsive to a line drive signal (LINE) to alternately open and close a current path through the inductor (Ly) between a first voltage level (B+) and a second voltage level (OV) lower than the first voltage level (B+) to generate a raster scan current signal in a deflection coil of the display. The amplitude of the raster scan signal is determined as a function of the first voltage level (B+) and the frequency of the line drive signal (LINE). A feedback circuit (D2,R3,D3,C2) connected to the switch (T4) generates a feedback signal (F) as a function of current flowing out of the switch (T4). A regulator (600-630,T3,L,D1,C1) is connected to the flyback circuit (T2,T4,Ly,Df,Cf) for varying the first voltage level (B+) as a function of the feedback signal (F) to maintain a constant raster scan width despite variations in the frequency of the line drive signal (LINE).

CRT protector circuit

Abstract: A CRT protector circuit for detecting an overcurrent or an overvoltage to a CRT to protect the CRT. A detector circuit is provided for detecting the overcurrent and the overvoltage, and when such is detected an abnormality detection output from the detector circuit is supplied to a control circuit which in turn controls a horizontal output circuit. The operation of the horizontal output circuit, provided on a primary side of a flyback transformer is, instantaneously broken by the control circuit according to the abnormality detection output from the detector circuit. When the frequency of generation of the abnormality detection output becomes a predetermined value or more, the operation of the horizontal output circuit is continuously inhibited. Accordingly, when the abnormal condition is temporary, a normal high-voltage generating operation can be automatically restored.

Multi-output DC-DC convertor

Abstract: A diode, a condenser and a switching element are connected to a primary winding of a flat type transformer such as a wire type transformer. A citation energy discharged during an off-condition of the switching element, namely a reset period of the transformer, is accumulated in the condenser. An output voltage is obtained from the condenser. Two system direct current voltage output can be obtained from one transformer. Since the two system direct current voltage output can be obtained from the transformer having a pair of a primary winding and a secondary winding, the volume and the weight of the transformer can be reduced and the compact and the slim of the machine apparatus being mounted can be contributed. Making the small winding ratio of the transformer, the copper loss of the transformer can be reduced. By using MOS synchronous rectification, the loss in the circuit can be reduced. It is unnecessary to select highly the switching frequency.

Development of film transformer

Abstract: In order to realize the light and small power supplies, we propose a film shape transformer. This new transformer is constructed by chemical etching process. Experimental works show that this film transformer has about 98% coupling factor over 500 kHz and over 95% efficiency at 1.5 MHz. As an initial test, we applied our film transformer to a push-pull type DC to DC converter and succeeded in obtaining 11 W output power. >

Dual current sensing driver circuit with switching energization andflyback current paths

Abstract: A driver circuit for controllably connecting an inductive load to a source of electrical power in response to an input control signal is provided. The inductive load includes an inductive winding of a solenoid. The driver circuit controllably connects and disconnects the inductive load to and from the source in response to a first control signal and controllably provides a discharge path for a flyback current of the inductive load in response to a second control signal. The driver circuit senses both the energizing current and the flyback current and responsively provides an energization path and a flyback discharge path in a non-overlapping manner.

Capacitive transformer having a switch responsive to clock signals

Abstract: A transformer including two half capacitive transformers operating in antiphase. Each half capacitive transformer steps an input voltage down during one phase of a clock signal. Each half capacitive transformer uses a number of capacitors and switching circuitry controlled by a clock signal. According to whether the clock signal is active or inactive, the switching circuitry places the half capacitive transformer in one of two configurations. In a first embodiment, in one configuration the capacitors are coupled in parallel between the input voltage and the output port, while in the other configuration, the capacitors are coupled in series between the output port and ground. In an alternative embodiment of the half capacitive transformer, in one configuration the capacitors are coupled in series between the input voltage and the output port while in the other configuration the capacitors are coupled in parallel between the output port and ground. The step-down ratio of the transformer is related to the number of capacitors included in a half capacitive transformer and not to the values of the capacitors. The capacitive transformer may step up voltages by swapping the input and output ports.

Flyback switching power supply with bootstrapped gate drive

Abstract: Method and apparatus for providing bootstrapped gate drive voltage in a flyback switching power supply. Switching transients and ringing caused by leakage inductance and capacitance in the flyback transformer are captured and used to provide a boosted gate drive voltage for the flyback switch, resulting in lower on resistance and lower switching losses.

Transformer with reduced signal rise time

Abstract: A current transformer for monitoring a current in a conductor. The current transformer comprises a winding assembly that includes a resistive load. The transformer further comprises a compensation circuit that has an impedance selected to reduce output signal overshoot across the output terminals of the current transformer caused by the intrinsic inductance of the resistive load. The transformer also comprises a small gauge semi-rigid coaxial cable to reduce a loop pickup area formed by the conductive paths that connect the winding assembly terminals of the winding assembly and the output terminals of the current transformer. This results in output signal overshoot across the output terminals being further reduced. Additionally, the transformer comprises a transformer shield that encloses the winding assembly and has end portions that do not contact each other to define a gap that prevents the transformer shield from acting as a shorted turn. The end portions overlap each other so as to reduce penetration of stray magnetic flux through the gap and further reduce output signal overshoot. All of the transformer shield is spaced from the winding assembly and the transformer shield does not enclose another transformer shield. This reduces stray capacitances between the transformer shield and the winding assembly so that the frequency response of the current transformer is flattened and ringing in the output signal is reduced.