Showing papers on "Flyback transformer published in 2000"

A topology survey of single-stage power factor corrector with a boost type input-current-shaper

Abstract: A topological review of the single stage power factor corrected (PFC) rectifiers is presented in this paper. Most of reported single-stage PFC rectifiers cascade a boost type converter with a forward or a flyback DC-DC converter so that input current shaping, isolation, and fast output voltage regulation are performed in one single stage. The cost and performance of a single-stage PFC converters depend greatly on how its input current shaper (ICS) and the DC-DC converter are integrated together. For the cascade connected single-stage PFC rectifiers, the energy storage capacitor is found in either series or parallel path of energy flow. The second group appears to represent the main stream. Therefore, the focus of this paper is on this group. It is found that many of these topologies can be implemented by combining a 2-terminal or 3-terminal boost ICS cell with DC-DC converter along with an energy storage capacitor in between. A general rule is observed that translates a 3-terminal ICS cell to a 2-terminal ICS cell using an additional winding from the transformer and vice versa. According to the translation rule, many of reported single-stage PFC topologies can be viewed as electrically equivalent to one another. Several new PFC converters were derived from some existing topologies using the translation rule.

White light-emitting-diode lamp driver based on multiple output converter with output current mode control

Abstract: A white light-emitting-diode array driver circuit with a multiple output flyback (or forward) converter with output current mode control. The circuit comprises a power supply source and a transformer. The transformer has a primary winding coupled to, and configured to receive current from, the power supply, and a plurality of secondary windings coupled to the primary winding. The circuit also comprises a plurality of light-emitting-diode arrays, wherein each light-emitting-diode array is coupled to one of the secondary windings. A main controller is coupled to a first of the light-emitting-diode arrays and is configured to control a flow of current to the primary transformer winding. The circuit also comprises a plurality of secondary controllers, each of which are coupled to another of the light-emitting-diode arrays. In addition, each of the secondary controllers are configured to control a flow of current to its corresponding light-emitting-diode array. According to one embodiment of the invention, each of the light-emitting diodes has a resistor coupled to its cathode terminal. An output signal of each resistor is transmitted to the respective controller and is employed to determine the appropriate current flow to the light-emitting-diode array. The circuit may be configured as either a flyback converter, wherein the primary transformer winding is wound in the opposite direction of the secondary transformer windings, or as a forward converter, wherein the primary transformer winding is wound in the same direction as secondary transformer windings.

Detection of shorted turns and winding movements in large power transformers using frequency response analysis

Abstract: There are various techniques for diagnosing electrical faults in a transformer such as the DDF, tan/spl delta/, partial discharges and high voltage tests But, there are no reliable techniques to identify mechanical faults in a transformer These faults are winding movement loss of clamping pressure, disc movement etc Frequency response analysis (FRA) is a tool that can be successfully applied for reliable detection of such faults In this paper, frequency partitioned mathematical models of a large power transformer is presented and it is shown how the sensitivity of the model parameters can be correlated to inception of transformer faults Finally, some experimental results are presented

Flyback as LED driver

Abstract: The invention relates to a circuit arrangement for operating a semiconductor light source, comprising input terminals for connecting a supply voltage, input filter means, a converter provided with a switching element having a control circuit, and provided with inductive means, and output terminals for connecting the semiconductor light source. The switching element is periodically driven into conduction for a period t on . According to the invention, the converter is formed by a flyback converter, and the inductive means are formed by a transformer, and the control circuit controls the t on .

Switch mode power supply using transformer flux sensing for duty cycle control

Abstract: A switch mode power supply (200, FIG. 2; 600, FIG. 6) includes a transformer (208), a transistor (212) that drives the primary winding of the transformer, and a controller (210, 610). The controller senses whether or not the transformer is reset and applies a switching control signal to a control terminal (220) of the transistor, accordingly. The signal is produced at a switching frequency, and the signal has a duty cycle that is limited based on whether or not the transformer is reset.

Single-stage single-switch input-current-shaping technique with reduced switching loss

Abstract: In this paper, a new single-stage, single-switch input-current-shaping (S/sup 4/ICS) technique which features substantially reduced turn-on switching loss of the switch in a S/sup 4/ICS flyback topology is described. In the proposed technique, the turn-on switching loss due to the discharging of the output capacitance of the switch is reduced by turning on the switch when its voltage is minimum. To achieve the turn-on loss reduction for a wide range of line and load conditions, the flyback transformer is continuously operated at the boundary of the continuous conduction mode (CCM) and discontinuous conduction mode (DCM) by employing a variable-frequency control. The performance of the new S/sup 4/ICS flyback technique was evaluated on a 70-W (20-V/3.5-A) experimental prototype.

Synchronous rectifier flyback circuit for zero voltage switching

Abstract: The present invention relates a flyback circuit for zero voltage switching {ZVS} in continuous mode {CCM} and discontinuous mode {DCM}, which circuit minimized loss generated when electrifying parasitic diode of MOS transistor {MOSFET} that is secondary side switch of synchronous rectifier and which also enabled ZVS in whole range of discontinuous mode {DCM}. Particularly it contains a synchronous rectifier driver that delays the gate drive signal that is outputted from pulse width modulation part after which the driver compares it with reference voltage that is outputted from pulse width modulation part and then the driver amplifies result value so as to supply it as the drive signal for synchronous rectifier part, a level change device that drives the synchronous rectifier gate, changing the level of gate drive signal that is outputted from gate drive device, and an insulating transformer that transmits the drive signal that is outputted from synchronous rectifier driver, to the level change device side. Wherewith it inverts the output signal of the pulse width modulation part in driving the synchronous rectifier gate, resulting in minimization of loss occurred at time of electrification of parasitic diode of MOS transistor {MOSFET} that is secondary side switch so that it makes effect to enhance efficiency letting it perform zero voltage switching {ZVS} under fixed frequency condition in discontinuous mode {DCM}.

Switched power supply converter with a piezoelectric transformer

Abstract: the switched power supply converter comprises a piezoelectric transformer for converting a first voltage supplied from a voltage source into a second, different, stabilised voltage by means of a DC/AC converter block, followed by a second rectifier connected in cascade to a second filter. The DC/AC converter block comprises a driver block followed by the piezoelectric transformer, such that the driver block feeds the piezoelectric transformer with a pulse train (21) the frequency of which coincides with the switching frequency (F1) of switching elements included in the driver block. The switching frequency (F1) is less than a resonant frequency (FR) of the piezoelectric transformer, for example, the switching frequency is a sub-harmonic of the resonant frequency (FR).

DC-DC flyback converters in the critical conduction mode: a re-examination

Abstract: The critical conduction mode for DC-DC flyback SMPS, in which the converter is forced to operate at the boundary between continuous and discontinuous conduction modes, represents an interesting alternative to the classical constant-frequency PWM technique. In fact, such an operating mode allows for a soft turn off of the freewheeling diode, zero voltage commutations of the switch and a reduction of the generated EMI. In this paper, this operating mode is re-examined with the aim of accurately predict switching frequency variation and component stresses in those applications in which the delay inserted between the turn off of the freewheeling diode and the turn on of the switch, used to achieve zero voltage commutations, cannot be neglected. The analysis presented allows for a correct prediction of the converter behavior in all operating conditions as well as for a proper design of the feedback loop through a suitable small-signal characterization. The theoretical forecasts are verified by means of a flyback prototype built using a new smart power IC developed by ST Microelectronics in VIPower(R) M3 technology.

Power transformer monitoring using UHF sensors: installation and testing

Abstract: External UHF couplers have been fitted to a 1000 MVA autotransformer as part of a project aimed at developing new transformer monitoring techniques. The couplers will supply valuable raw data from a transformer operating under normal service conditions. UHF signals were recorded while the transformer was re-energized and returned to load. Initially, some large discharges appeared, but these were short-lived. Background signal levels were low, indicating no significant interference problems. A small intermittent discharge signal was recorded and its characteristics are described. The possibilities for UHF monitoring of transformers are discussed, together with some of the remaining challenges.

Single unit integrated transformer assembly

Abstract: A transformer unit includes a first isolation transformer, a second isolation transformer and a power transformer. A single package incorporates the first isolation transformer, the second isolation transformer and the power transformer. A plurality of connection pins provide connections to the first isolation transformer, to the second isolation transformer and to the power transformer. A process is also provided for connecting transmission lines to a network device including providing transmission lines carrying an electrical supply current, sufficient to power the network device, concurrently with a network data signal. The single unit has the first integrated isolation transformer the second integrated isolation transformer and the power transformer. Some of the transmission lines are connected to the first isolation transformer to isolate transmission signals on the sending transmission lines from a transmitter of the network device. Some other transmission lines are connected to the second isolation transformer to isolate transmission signals on the receiving transmission lines from a receiver of the device. Within the single unit each of the first isolation transformer and the second isolation transformer are connected to the power transformer. The power transformer is used to supply power to the circuit board of the network devise at a potential which is reduced compared to a potential of said transmission lines carrying the electrical supply current.

Power factor correction using merged flyback-forward converters

Abstract: A single stage isolated PFC converter is obtained merging flyback and forward topologies. Thus, the flyback section allows power transfer while the line rectified voltage is not high enough to enable the forward stage operation. By this way, optimal correction is feasible. Also, this approach allows sharing of the transformer and the power transistor.

Radio frequency dc-dc flyback converter

Abstract: An RF (radio frequency) dc-dc converter has been developed to demonstrate the possibility of using a flyback configuration at 63 MHz. The converter consists of two sections: a variable pulse width generator (PWG) and a FET switch with a transformer and a detector. The bulk of the design was concentrated on improving the efficiency of the switch, the transformer and the detector. Low capacitances of the heterostructure AlGaAs/GaAs FET (HFET), a low leakage inductance of the RF transformer, a fast Schottky diode, multilayer ceramic chip capacitors and surface mount chip resistors made it possible to achieve high efficiencies from 20 MHz to 63 MHz. The "hard switching" 1-Watt converter achieves 60 to 70 percent efficiency, while operating with a wide range of input and output voltages.

High voltage discharge lamp apparatus for vehicles

Abstract: A discharge lamp apparatus is provided having a DC power source (1) and a high voltage discharge lamp (2) comprising: a DC-DC converter comprising a transformer (41) for boosting a voltage supplied from the DC power source, a switching element (42) connected to a primary winding (41a) of the transformer in series, and a capacitor (45) connected in parallel with the transformer connected in series with the switching element, for generating the boosted voltage; a starter circuit (7) having a thyristor (76) for turning on the thyristor when the high voltage discharge lamp is started to light and for applying a high voltage pulse to the high voltage discharge lamp based on the boosted voltage generated from the DC-DC converter; and a gate circuit (11) for generating the gate signal to turn on the thyristor, wherein the switching element and the gate circuit are both formed on a hybrid IC board (100), the negative electrode side terminal of the capacitor is connected to a first wiring member (24) and then connected to the hybrid IC board by way of the first terminal (12c), wherein the cathode terminal of the thyristor is connected to a second wiring member (24) and then connected to the hybrid IC board by way of the second terminal (12m) different from the first terminal, and wherein the first terminal and the second terminal are electrically connected on the hybrid IC board.

Power factor preregulators based on combined buck-flyback topologies

Abstract: The limitation imposed on the achievable power level by the IEC 1000-3-2 standard in buck-derived power factor preregulators, is overcome by using a combined buck-flyback power stage. Two different step-down converters are proposed in this paper, which incorporate an auxiliary flyback stage. The auxiliary stage uses the same switch of the main converter, plus an additional power switch commutated at the line frequency. As compared to a simple buck rectifier, with this solution the harmonic content of the absorbed line current, at a given power level, can be reduced, thanks to the resulting increased conduction angle of the input rectifier bridge. Experimental results based on a 1 kW prototype are reported to validate the theoretical analysis of the proposed topologies.

Negative inductance and numerical instability of the Saturable Transformer Component in EMTP

Abstract: Numerical instability of the EMTP built-in model, the Saturable Transformer Component for the three-winding case, has been the topic of interest of the EMTP community for the past twenty years Through theoretical analysis and computer simulation, the source of the numerical instability of the component is identified as the use of the negative inductance in the equivalent circuit of the transformer A simple modification of the structure of the component is suggested, and the numerical instability is eliminated The modification is supported by theoretical analysis and verified by the benchmark test of the GPU line energization test of 1973 The stability of the three-winding transformer equivalent circuit with a negative inductance is discussed in detail A topology-based and duality-derived single-phase three-winding transformer model is described

Asymmetrical PWM flyback converter

Abstract: The asymmetrical PWM converter with the flyback output rectifier (asymmetrical PWM flyback converter) is proposed in this paper. The asymmetrical PWM flyback converter has the feature of zero-voltage switching (ZVS) in the active switches using resonance of the parasitic components. Moreover, the diode in the rectifier stage can commutate softly which minimizes the loss and noise during the commutation interval. The design procedure is presented, which includes the ZVS range of the active switches, and the component value satisfying the zero-current switching (ZCS) of the diode. Experimental results confirm the validity of this topology.

Method and apparatus for driving piezoelectric transformer

Abstract: It is an object of the present invention to provide a method and an apparatus for driving a piezoelectric transformer capable of always driving with maximum conversion efficiency regardless of changes in the input voltage level, load and temperature, etc. The method and apparatus for driving a piezoelectric transformer of the present invention generate a time-varying sweep voltage through a sweep circuit at predetermined regular intervals, thereby changing the frequency of a drive signal output from a voltage control oscillator, at this time detect a phase difference between the voltage and current generated on the primary side of the piezoelectric transformer by a phase difference detector, and hold the sweep voltage corresponding to the timing at which a maximum value detector detects the maximum value by a sample-and-hold circuit, thereby controlling the frequency of the drive signal so that the phase difference between the voltage and current on the primary side of the piezoelectric transformer always becomes a maximum value.

New topologies of active input current shapers to allow AC-to-DC converters to comply with the IEC-1000-3-2

Abstract: This paper deals with the analysis of four new implementations of the recently proposed active input current shaper (AICS). These new implementations of AICS can be used with DC-to-DC topologies in which the voltage across the transformer is either a symmetrical waveform (e.g. half-bridge, push-pull or full-bridge) or an asymmetrical waveform (e.g. forward, flyback, SEPIC, Cuk or Zeta). Using some of these implementations, the size of the AICS inductors can be reduced and even integrated in only one magnetic core. As in the case of other converters with AICS, the new implementations allow us to reduce the line current harmonics in order to comply with the IEC 1000-3-2 specifications, maintaining all the features of standard DC-to-DC converters (e.g. fast transient response). Finally, the proposed topologies have been experimentally tested.

Transformer test control device

Abstract: This transformer test control device permits testing of an electrical transformer as installed on a power pole without connecting any high voltage of the power distribution line to the transformer, thereby significantly enhancing the safety of the lineman during the testing procedure. A test control device for controlling the testing of an electrical transformer combines a visual indicator acting as both a power-on indicator and a fuse tester, a voltmeter, a voltage adjustment control, an operator control switch and a fuse as well as terminals for connecting both to an alternating current electrical supply and to the terminals of the primary coil of a transformer to be tested. Additionally, the test control device includes terminals for connecting the device and a secondary circuit to selected output terminals of the secondary coil of the transformer and additional terminals for receiving and retaining the contact portions of voltmeter test probes. The test control device simplifies the transformer testing and aids the lineman in testing while maintaining high standards for safety practices and, especially, during adverse weather, conditions. This device may be embodied to include a dedicated second voltmeter. The test control device may be powered boy either normal 120 volt line voltage or the output of a power inverter connected to the electrical system of a truck or other motor vehicle in those areas without readily available 120 volt AC power

On the injection transformer used in the dynamic voltage restorer

Abstract: The injection transformer used in the dynamic voltage restorer (DVR) plays a crucial role in ensuring the maximum reliability and effectiveness of the restoration scheme. The functional relationship between the transformer and the other components constituting the DVR and the external distribution system is analyzed. Based on the results of the investigation, a design guideline leading to a cost-effective voltage restoration system is then proposed.

Power supply with flux-controlled transformer

Abstract: There is provided by this invention an apparatus and method for generating voltage pulses (V) to first (A) and second (B) magnetron devices in a plasma chamber (4). An isolation transformer (8) is connected to a pulsed DC power supply (2) having a flux sensor (10), such as a Hall effect sensor, in close proximity to its air gap (12) to monitor the transformer flux (B). A control circuit is connected to the flux sensor (10) to control the duty cycle of the transformer (8) by controlling the flux (B) of the transformer (8) such that the maximum and minimum peak transformer fluxes (B) are equal in magnitude and opposite in sign to prevent saturation.

A novel high-efficiency flyback power-factor-correction circuit with regenerative clamping and soft switching

Abstract: Although most power factor correction (PFC) circuits use the boost topology, the flyback topology does have the advantages of input-output isolation, inrush current limiting and voltage step-down capability. In this paper, the problems associated with flyback PFC circuits are identified. These problems are solved by using a novel regenerative clamping circuit. The circuit topology, analysis, design considerations and experimental results of the new flyback PFC circuit are presented.

System and method for charging a capacitor using a constant frequency current waveform

Abstract: A system and method for charging a high-voltage capacitor through the application of current having magnitude that has a fixed frequency waveform During a charging sequence in which the current is applied to the capacitor, the duty cycle of the fixed frequency current waveform is dynamically controlled based on the voltage state of the capacitor to modify the energy transfer according to the efficiency with which energy can be delivered to the capacitor This optimizes the capacitor charging sequence, increasing the speed with which the high voltage capacitor is charged Generally, energy is transferred from a power source to the capacitor via a magnetic element such as a fly-back transformer A pulsed voltage supply provides voltage pulses having a constant frequency and an adjustable duty cycle to a primary winding of the transformer Initially, there is no energy stored in the transformer core As a result, the duty cycle of the initial voltage pulse is of sufficient duration to accumulate stored energy in the transformer core Once a predetermined quantity of energy is stored in the transformer, the transformer is controlled to generate a current to charge the capacitor The magnitude of the current has a fixed frequency and variable duty cycle waveform

High frequency planar transformer with helical winding structure

Abstract: A high frequency planar transformer with helical windings is proposed. This transformer combines the advantages of the planar magnetic core transformer and air core transformer. The experimental results show that the input impedance and the voltage ratio of this new transformer are much higher than its air core counterpart. The numerical result shows that the flux is evenly distributed and totally enclosed inside the planar ferrite. The electromagnetic interference (EMI), generated from the windings of transformer, is significantly reduced by using magnetic ferrite cores.

Failure analysis of dry type power transformer

Abstract: This paper provides the failure analysis of three phase, dry type, silicone resin vacuum pressure encapsulated, 750/1000 kVA, AA/FA, 34.5 kV-480 Y/277 V, delta-wye, power transformer. Transient overvoltage switching surge propagation through the transformer winding and protection margin is discussed. An arbitrary sensitivity of 10 pico-coulombs (pc) at 120% rated voltage generally used for the partial discharge tests at the factory may be inadequate for the design of the failed transformer.

Efficient, low leakage inductance, multi-tap, RF transformer and method of making same

Abstract: A low leakage inductance, versatile RF transformer with multiple input/output voltage ratios. The transformer has many applications. For example, and not by way of limitation, the transformer can be used with switching power supplies, RF induction power supplies, and RF plasma power supplies. The efficiency of the transformer is on the order of 99% to 99.7%. These efficiencies have been measured at power levels of 3 kilowatts (KW) to 10 KW.

Zero-voltage and zero-current hybrid soft-switching phase-shifted PWM DC-DC power converter for high power applications

Abstract: This paper presents a novel prototype version of zero-voltage switching (ZVS) PWM DC-DC power converter with a high frequency transformer link, which incorporates zero-current switching (ZCS) mode synchronous active power switches in series with each rectifier diode in high-frequency transformer secondary side. This converter circuit with an isolated high-frequency transformer link can achieve ZVS in transformer primary side and ZCS in transformer secondary side under the wide load variations. Using the proposed converter, switching and conduction losses of all the active power devices are reduced as well as circulating current flowing through a transformer link as compared with the previously-developed soft-switching converter with a phase-shifted PWM scheme in the high-frequency transformer primary side. The steady-state operating principle of this converter in the open loop system and voltage regulation characteristics are described and evaluated on the basis of the simulation analysis and some experimental results of 2 kW-40 kHz breadboard.

Flyback switching power source

Abstract: PROBLEM TO BE SOLVED: To provide a small-sized power source module, having a fewer number of terminals. SOLUTION: In a power source, a transformer has a primary winding, a secondary winding, a control winding, a semiconductor switch connected in series to the primary winding, a control circuit for turning the semiconductor switch on and off, a rectifying circuit connected to the secondary winding, a means for forming error signals of the output voltage of the rectifying circuit, a means for transmitting the error signals of the output voltage to the control circuit as a feedback signal for the output voltage errors, a means for regulating the output voltage by the feedback signal for the output voltage errors, a means for detecting a voltage generated in the control winding, and a means for detecting timing when radiated energy by the secondary winding becomes zero to feed energy stored in the transformer, when the semiconductor switch is in an on-state to the rectifying circuit from the secondary winding when the semiconductor switch is in an off-state. A first operation mode is changed over to a second operation mode, when the semiconductor switch is in an off-state and the voltage of the control winding is lower than a set voltage during operation in a first operation mode. The second operation mode is changed over to the first operation mode, when the semiconductor switch is in an off-state and the voltage of the control winding is the set voltage or higher during operation in the second operation mode. COPYRIGHT: (C)2002,JPO

High frequency resistance in flyback type transformers

Abstract: Interleaving techniques are usually applied to magnetic components in order to reduce the leakage inductance and resistance. However, since the behavior of flyback-type transformers is different than conventional ones, the features of these techniques in these transformers are also different. This work presents a study of the modification of the resistance in flyback-type transformers when interleaving techniques are applied, as well as the main differences compared with its application in conventional transformers. The results have been quantified using FEA techniques in order to account for geometry and frequency effects.