Showing papers on "Flyback transformer published in 1999"

Integrated high-quality rectifier-regulators

Abstract: A new family of AC-DC converters is derived 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. 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 is presented, which uses the "loss-free resistor" concept. 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.

An approach to achieve ride-through of an adjustable speed drive with flyback converter modules powered by super capacitors

Abstract: Adjustable speed drives (ASDs) under short-term power interruptions (STPIs) can interrupt a critical process. In this paper an approach to provide ride-through with flyback converter modules (FBCMs) powered by super capacitors is explored. The proposed approach is modular and facilitates additional modules to be added to suit higher voltage/power ratings. Both unidirectional and bidirectional flyback DC/DC converter topologies are examined. Simulation and experimental results are presented.

Offset resonance zero volt switching flyback converter

Abstract: A continuous mode flyback converter circuit which includes elements capable of generating a zero volt switching (ZVS) signal across the power switch. The ZVS generating elements include a switched shunt inductance coupled in parallel with active clamp components and connected across the primary winding of the power transformer. The circuit reduces the reverse recovery current through the secondary stage rectifier and the current through the active clamp switch during operation of the converter. The ZVS generating elements may also be used for flyback converters which do not utilize an active clamp.

A general technique for derivation of average current mode control laws for single-phase power-factor-correction circuits without input voltage sensing

Abstract: This paper presents a general technique to derive average current mode control (CMC) laws without input voltage sensing to achieve high power factor for single-phase topologies operating in continuous conduction mode (CCM). The control laws are derived based on the steady-state input-output voltage relationships and the CCM large-signal averaged pulsewidth modulation (PWM)-switch model. Using this methodology, average CMC laws with linear PWM waveforms are discovered for commonly used single-phase power stage topologies such as boost, flyback, SEPIC, and buck/boost. Conventional three-loop-controlled average CMC converters can now be controlled with a two-loop architecture. Hardware results for a boost power factor correction (PFC) and simulation results for flyback, SEPIC, and buck/boost topologies verify operation. The small-signal models of the current loop and voltage loop are derived for the boost topology and are used for control loop design. Input current harmonic distortion measurements demonstrate improved performance compared to the conventional three-loop control technique.

Ignition boost and rectification flame detection circuit

Abstract: A gas furnace control circuit combines an igniter circuit and a rectification flame detection circuit. Pulsating current is applied respectively to inducer and gas valve relay coils to actuate the furnace. A rectifier supplies flyback pulses from the inducer relay coil to a capacitor arrangement to accumulate flyback voltage. An ignition transformer has its secondary connected to the igniter and flame detection probe for generating an ignition arc. A hysteresis switch is coupled between the capacitor and the primary of the ignition transformer discharges current from through the primary whenever the stored flyback voltage reaches a predetermined threshold. Another capacitor is connected to the gas valve relay coil. A transistor has a signal impedance connected with its drain or power electrode to define an output terminal. A resistor network has a first resistor with one end connected to the capacitor and a its other end connected to the gate or control electrode of the transistor. A second resistor is connected between the gate and source electrodes of the transistor. The ignition transformer secondary is also connected with the first resistor, so that the igniter and flame detection probe is connected through said transformer secondary and through the first resistor to the transistor. The transistor output is in a first state if flame is present, and in a second state if flame is not present in the burner.

A zero-current-switching PWM flyback converter with a simple auxiliary switch

Abstract: A simple and effective approach of turning an isolated hard-switched converter design into a soft-switched one is presented. By adding an auxiliary winding, switch and small capacitor to the conventional pulsewidth modulation (PWM) isolated flyback converter, all switches and diodes are softly turned on and off. No extra active or passive voltage clamp circuit is needed to suppress voltage stress on the switching devices that were usually found in classical converters. A zero-current-switching (ZCS) PWM flyback converter topology with multiple outputs is analyzed and examined. The proposal inherently utilizes the leakage inductance of the "flyback" transformer to achieve ZCS of all switching devices. A complete steady-state DC analysis and the operating principle are described. The performance of an 80 W experimental converter prototype with dual-voltage outputs is included.

Performance of a 1-MVA HTS demonstration transformer

Abstract: We report on test results for a single phase, 60-Hz, 13.8 kV/6.9 kV, 1-MVA high temperature superconducting (HTS) transformer which was completed in February, 1998. This transformer models in many ways a full scale section of a 30-MVA HTS commercial transformer design. The transformer windings are cryocooled in the range of 25 K and are made with a low-cost, surface-coated BSCCO-2212 conductor. Heat leaks are reduced using a liquid nitrogen thermal ballast and reservoir. The use of high temperature superconductors can substantially reduce transformer losses, weight, size, noise and potential fire and environmental hazards. Designs promise stable operation through faults without thermal degradation, and at temperatures that allow efficient and reliable refrigeration.

Transformer monitoring using the UHF technique

Abstract: The viability of applying UHF partial discharge monitoring techniques to an in-service oil-filled power transformer is established. Discharges in oil are shown to radiate the high frequency signals necessary to allow detection. On-site pulse injection is used to test the operation of a UHF coupler fitted to the transformer. The effects of on-load tap changing operations are also investigated.

Analysis and design of an isolated single-stage converter achieving power-factor correction and fast regulation

Abstract: This paper presents the analysis and design of an isolated single-stage converter achieving high-power-factor correction and fast regulation. By using the technique suggested by Wu et al., a buck-boost converter and a flyback converter can be integrated to form the discussed converter. The buck-boost semistage working in the discontinuous conduction mode (DCM) functions as a power-factor corrector, and the flyback semistage operating in the DCM is a voltage regulator which is controlled, theoretically, to be independent of load variation. An approximated small-signal model of the converter operating in the DCM is developed. Design of a peak-current feedback loop with an optimal proportional integral controller is also presented. A prototype is implemented to verify that the analysis and design are effective and feasible.

Effects of very fast transient overvoltages on transformer

Abstract: An analytical solution is found using the Laplace transform to describe the very fast transient overvoltage (VFTO) in the gas insulated switchgear (GIS) connected directly to a transformer. The oscillation frequencies, and other properties, are explicitly given in terms of system parameters. The magnitude of VFTO at the transformer is suppressed due to the transformer capacitance, Magnitudes of the initial abrupt voltage change and oscillatory voltage are assessed. The abrupt voltage is larger, but not enough to induce a harmful voltage in the transformer. The oscillatory components may damage the winding insulation at the occurrence of resonance.

Performance evaluation of 70-W two-stage adapters for notebook computers

Abstract: The paper presents the design and performance evaluation of two-stage AC power adapters for notebook computers which deliver 70 W from the universal line. Three versions of the flyback power converter, as well as the PWM and resonant half-bridge power converter were evaluated and compared with respect to their efficiency, component stress, output filter size and complexity.

Wholly integrated switch-on control loop of a high voltage power transistor of a quasi resonant flyback converter

Abstract: A flyback DC--DC converter employs a flyback transformer for storing and transferring energy to a load having an auxiliary winding whose voltage is compared by a comparator with a threshold to detect its crossing. As a consequence, a power transistor driving the primary winding of the transformer is switched on through a control flip-flop, for a new phase of conduction and accumulation of energy, whose duration is established by a secondary control loop of the output voltage producing the switching off of the power transistor for a successive energy transfer phase toward the load of the energy stored in the transformer during the preceding conduction phase. The converter has a wholly integrated control circuit that includes a second comparator of the voltage existing on the current terminal of the power transistor connected to the primary winding of the transformer with respect to the ground potential of the circuit. Furthermore, a delay network is coupled in cascade to the output of a first comparator and has an output coupled to a second input of a logic gate, so that under steady state functioning conditions of the converter, the setting of the flip-flop is done by the second comparator rather than by the first comparator.

Simplified control technique for high-power-factor flyback Cuk and Sepic rectifiers operating in CCM

Abstract: Control techniques for high-power-factor rectifiers which do not need input voltage sensing are gaining considerable attention due to their simpler implementation and inherently superior stability, as compared to conventional average or peak current mode control. Among these, the solutions based on the integration of a current signal (switch, diode, or inductor current) provide an inherent noise immunity, which makes them further appealing. This paper proposes a simple implementation of one such control technique for high-power-factor flyback, Cuk, or Sepic rectifiers, which, while still retaining a high power factor, further reduces the control complexity, thus making the solution very attractive for smart-power integration. A 200 W flyback rectifier with the proposed control technique was implemented and tested. The achieved results are in good agreement with the expected performance.

A new flyback-current-fed push-pull DC-DC converter

Abstract: This paper introduces a new flyback-current-fed push-pull DC-DC converter whose significant advantages in comparison with the conventional one are a reduction in the number of output diodes and unified output characteristics to represent both the buck and the boost operation modes in the continuous conduction mode. Theoretical analysis, design methodology and experimental results taken from a 600 W 25 kHz laboratory prototype are presented in this paper. The circuit introduced is suitable for switching mode power supply design and power factor correction applications as well.

Design considerations of transformer DC bias of forward converter with active-clamp reset

Abstract: In the forward converter with active-clamp reset circuit, the leakage inductance of the transformer and the parasitic capacitances of the switches produce a DC bias of the magnetizing current of the transformer. The DC bias of the magnetizing current could saturate the transformer core, cause diode reverse recovery problem, and make the active clamp switch lose zero voltage turn-on if the bias is not considered in the transformer design. This paper derives the explicit equation of the DC bias of the magnetizing current for the first time and provides the transformer design procedures according to the derived equations.

Transformer for switched mode power supplies and similar applications

Abstract: A transformer for switched mode power supplies and the like comprises an input stage transformer section which is designed for very good coupling and very low primary leakage inductance, without regard for insulation above "working insulation" or for interwinding capacitance. One or more additional stage transformer sections are optimized for very low interwinding capacitance and very high dielectric isolation. The secondary of the input stage drives the primary of the next stage, so that the transformer stages are in series. Accordingly, the total interwinding capacitance from end to end is very low and the total dielectric isolation from end to end is very high. The secondary of the input stage transformer is isolated from both the input and the output, so it can be grounded as a safety ground. Because the input stage can be designed without regard for capacitance or isolation, it can be smaller, lighter, less expensive and have better thermal and high frequency characteristics, enough so that the transformer as a whole can be smaller, lighter, less expensive and have better thermal and high frequency characteristics than a single stage transformer of comparable rating.

A power transformer protection technique with stability during current transformer saturation and ratio-mismatch conditions

Abstract: Summary form only given as follows. This paper describes a digital technique for protecting power transformers. The technique uses positive- and negative-sequence models of the power system in a fault-detection algorithm. While phase voltages and currents at the transformer terminals are used to detect a fault, no information concerning parameters of the transformer and power system is required. The performance of the proposed technique was studied for a variety of operating conditions using data generated by EMTP simulations. The impact of ratio-mismatch and saturation of current transformers on the performance of the technique was also examined. Results indicate that the proposed technique is stable during these conditions.

Method and apparatus for controlling power transfer in a flyback converter by modulating the power switch off time during transient conditions

Abstract: A method of controlling a flyback DC-DC converter includes using a primary control loop to monitor an auxiliary winding of a transformer for determining the amount of energy being transferred to a load. The voltage in the auxiliary winding is induced by current flowing in the secondary winding of the transformer. The primary control loop disables and enables the turning on of a power switch for driving the primary winding of the transformer, and detects the zero-crossing. The duration that the power switch is turned on is established by a secondary control loop using the output voltage for turning off the power switch for a new off phase. The flyback DC-DC converter further includes a fixed frequency oscillator having a frequency lower than the self-oscillating frequency of the converter. The power transferred from the primary circuit to the secondary circuit of the flyback transformer is controlled by introducing a delay on the turn-on instant of the power switch. This is with respect to a turn-on command generated during a self-oscillating functioning phase regardless of the mode of control of the converter. The turn-on command is based upon a zero crossing, a fixed frequency functioning phase, a rising edge of the signal generated by the oscillator, and as a function of the input variables of the primary and secondary control loops.

Modeling of cross-regulation in multiple-output flyback converters

Abstract: In this paper, the complex operation of multiple-output flyback power converters is explained in terms of the extended cantilever magnetics model. Analytical results are derived that can accurately predict steady-state cross-regulation properties of a power converter with any number of outputs and with arbitrarily complex magnetics configuration. Two snubber configurations are considered: a passive voltage-clamp snubber; and an active-clamp snubber. Predictions of the model are verified by experiments. The analytical models are the basis for a discussion of magnetics design guidelines that can result in improved cross-regulation in multiple-output flyback power converters.

Adaptive off-time control for variable-frequency, soft-switched flyback converter at light loads

Abstract: The soft switching of a flyback converter can be achieved by operating the circuit in the critical conduction mode. However, the critical-mode operation at light loads cannot be maintained due to a very high switching frequency and the loss of the output voltage regulation. A control which regulates the output down to the zero load and maintains soft switching at light loads is proposed. The proposed control scheme was implemented in the 380 V/19 V, 65 W flyback DC/DC converter.

Analysis and design of a practical discontinuous-conduction-mode BIFRED converter

Abstract: Impending international standards on harmonic current levels drawn by single-phase mains-operated equipment have created a need for low-cost off-line power-factor-corrected switched-mode power supply topologies in the power range up to a few hundred watts. The boost integrated/flyback rectifier/energy storage/DC-DC converter (BIFRED) is one such topology which shows promise in this regard. In particular, the discontinuous-conduction-mode (DCM) BIFRED avoids the light-load high-voltage stress problem associated with the continuous-conduction-mode design, while still achieving the combined advantages of a low-cost single-stage topology with high displacement factor and low total harmonic distortion. In this paper, a practical DCM BIFRED converter with integrated low-loss snubber is investigated from both power and small-signal control perspectives. Design equations are given to ensure DCM operation under closed-loop output voltage control, in which switch duty cycle is varying. Experimental results on a prototype converter are also presented.

A high-power-factor electronic ballast using a flyback push-pull integrated converter

Abstract: This paper describes a high-power-factor electronic ballast for fluorescent lamps. The converter offers a high power factor and a high-frequency supply to the lamp using a single switch. In spite of its simplicity, an excellent performance concerning load and supply is achieved, ensuring a sinusoidal and in-phase supply current. High power factor is achieved by using a flyback converter operating in discontinuous conduction mode. Operating principle, design equations, component stress, and efficiency are presented. Experimental results have been obtained for one 40-W fluorescent lamp operating at 50-kHz switching frequency and 220-V line voltage.

Power supply system for battery operated devices

Abstract: A power supply device for a battery-operated electric tool for converting an AC input voltage into a DC output voltage and supplying the DC output voltage to a power tool (78), said power supply device comprising: a housing (76, 82); So as to be electrically connected to the AC input voltage comprises a transformer (12) formed in the housing (76, 82) that reduces a voltage level of the AC input voltage; a first thermal protection means to electrically disconnect the AC input voltage from the transformer (12) (22, 60) which is thermally connected to the transformer (12), if enabled, in response to the exceeding of a predetermined temperature through the transformer (12) ; a second thermal protection means (24) which is connected to the transformer (12) to separate the transformer (12) electrically isolated from the AC input voltage when the temperature of the transformer (12) exceeds a maximum temperature which is greater than the predetermined temperature is; a rectifier (26) electrically connected to the transformer (12) is connected to the through ...

Electronic transformer for lighting

Abstract: An electronic transformer (10) for lighting inlcudes a rectifier (13) coupled to an inverter (18, C2, C3, Q1, Q2) an output transformer (T1, T10) and a drive transformer (T2, T11). A protection mechanism (VR1, VR2) is responsively coupled to a winding of the output transformer and to a winding of the drive transformer such that the voltage across each of the windings are approximately equal and opposite during normal operation but differ substantially during a short-circuit.

Ignition circuit with piezoelectric transformer

Abstract: Circuits for use in ignition systems are disclosed which use a resonating piezoelectric transformer along with complementary circuit components, to efficiently convert a DC first voltage to a transformer-output AC second voltage. In the preferred embodiment of the invention, a High Displacement Piezoelectric (HDP) transformer converts a DC voltage into an AC voltage which is rectified into a DC signal of sufficiently high voltage to create a spark across the spark gap of a spark plug. The transformer circuit may be a "self resonating" circuit which relies on an initial pulse from turning on the DC power supply to cause the transformer to begin resonating. In a modified circuit the circuit is not "self resonating" and instead has a phase shift oscillator sub-circuit that provides small pulse signals to start the transformer resonating when the circuit is initially turned on.

Cross regulation in flyback converters: solutions

Abstract: Studies at UCI have shown that cross regulation in multiple output flyback converters can be significantly improved when the clamp voltage is lowered to slightly above the reflected output voltage In this paper, three solutions for reducing the clamp voltage are investigated In a conventional RC clamp, the clamp voltage can be reduced by decreasing its resistor value, but this leads to higher power losses A new operating condition for the nondissipative LC snubber is found to achieve the goal by setting its resonant frequency below the switching frequency In addition, a simple passive energy regenerative clamp is proposed that allows the clamp voltage to be lower than that of the RC clamp, thus improving the cross regulation without using an extra inductor as in the nondissipative LC snubber

Sub-miniature high efficiency battery charger exploiting leakage inductance of wall transformer power supply, and method therefor

Abstract: A battery charger (100) suitable for sub-miniaturization and connection to a wall transformer power supply (20) to charge a battery (30). The battery charger (100) features a switch (130) that controls flow of current from the transformer (20) either to output terminals for charging the battery (30) or to ground, a voltage regulator (120), a microprocessor (110), a current sensing resistor (150) and a Schottky diode (140). The microprocessor (110) is coupled to the switch (130) to control whether the switch is open or closed. The secondary leakage inductance of the wall transformer (20) is exploited to control charging of the battery. The microprocessor (110) is programmed to initiate a charging mode comprising oscillation between a conduction interval and a flyback interval. A charging pulse is delivered to the battery (30) during the flyback interval.

High voltage transformer and ignition transformer using the same

Abstract: A small-sized heat resisting high voltage transformer and an ignition transformer using the high voltage transformer are provided and utilize both a heat resistant casting resin and a bobbin, which contain an inorganic filler. The high voltage transformer is capable of producing an output voltage of 10-35 kV and comprises a primary coil, a secondary coil, and a magnetic core, wherein a casting resin is injected into the coil part and subsequently cured. The casting resin and bobbin material used for making the coils have heat distortion temperature of at least 130° C., and contain an inorganic filler. The surface of the bobbin may be pretreated. Thereby, adhesion between a bobbin and a casting resin is enhanced to ensure operating properly under the sever heat cycle condition and provide a small-sized heat resistant high voltage transformer.

Topology-independent synchronous rectifier commutation circuit

Abstract: The use of synchronous rectifier MOSFETs in the secondary circuit of AC/DC converters is made possible in synchronous rectifier unfriendly topologies such as flyback converters by sensing the onset of forward current in the MOSFET drain-source circuit, optionally converting that current information into logic level signals, and using the information or signals to drive the gate of the synchronous rectifier MOSFET.

A DC current transformer for large bandwidth and high common-mode rejection

Abstract: A review of known magnetic-coupled current-sensing techniques is presented, Subsequently, a novel technique is introduced, based on a configuration discussed in a previous paper. The previous technique made use of a galvanomagnetic device (Hall effect sensor) to sense the magnetization of a current transformer core, so that the sum of the Hall voltage and the voltage across the secondary shunt resistor would yield a faithful copy of the input current. The technique described in this paper makes use of the same principle to obtain a high bandwidth (from DC to 1 MHz) and very high common-mode rejection current transformer, without the need for a Hall effect probe. This is achieved by subtracting the high-frequency components, detected across the secondary shunt resistor, from the voltage across a primary shunt resistor connected in series with the primary of the current transformer. The resulting signal is an accurate image of the transformer magnetizing current, which is then transferred to the secondary side by means of a low-bandwidth isolation amplifier. The high-frequency components are subsequently added, to the amplified and filtered low-frequency components, by means of a third transformer winding, the number of turns of which is chosen to be equal to the gain of the low-frequency amplifier.