Showing papers on "Flyback transformer published in 1995"

Interleaving technique in distributed power conversion systems

Abstract: In distributed power supply systems, the parallelism of DC-DC converters is a basic architecture. In this paper, we use the time domain method to show that the amplitude of the input/output current ripple of N(/spl ges/1) parallelly interleaved modules is always less than or equal to that of the individual modules for buck, boost, flyback, Cuk, and SEPIC converters if the phase shift among the modules is 2/spl pi//N. Furthermore, the insight gained from the time domain method allows us to develop efficient numerical algorithms for predicting the net ripple amplitude in interleaved power modules,. >

Multiple output regulator with time sequencing

Abstract: A switching voltage regulator is described which provides multiple independently regulated outputs. A switch control independently monitors two or more voltage outputs and generates control signals for driving a main switch and two or more auxiliary switches to charge selective ones of the outputs which have fallen below their target voltages. Time sequencing techniques are utilized to control the switching of the auxiliary switches such that energy stored in an inductor is transferred to the appropriate voltage outputs. The switching voltage regulator may be implemented as an integrated circuit and may have various topologies, such as boost, buck, flyback or SEPIC.

Interleaved DC to DC flyback converters with reduced current and voltage stresses

Abstract: Interleaved flyback DC to DC converters are provided comprising a first and a second switching transistors controllable with 180° phase shift and a first and a second flyback transformers. A primary winding of each transformer is coupled in a series circuit with the corresponding switching transistor. A secondary winding of the first transformer is coupled with the secondary winding of the second transformer via a first catch diode and both said secondary windings are coupled to an output filter capacitor via a second and a third catch diode, correspondingly. When discharging to the output filter capacitor, the transformers interlock each other. By interlocking, non-pulsating output current is generated and voltage across switching transistors is reduced. A secondary quasi-resonant snubber network relieves voltage spikes across the switching transistors. A common magnetic core of the transformers cuts the cost and the size of the interleaved flyback converters.

Ignition system power converter and controller

Abstract: A high efficiency high power DC to DC power converter and controller system for a CD ignition system with a simple converter controller (8) for controlling a power switch (2) of a transformer (1) operated as a flyback which includes a lossless snubber (6) and simple current sensor (8a) for sensing and controlling the power converter current, and further including ignition trigger conditioner (9) and phase conditioner (10) for operating a trigger output circuit (11) based on an octal counter (67) for triggering ignition coil circuits of a preferred distributorless ignition circuit of the hybrid ignition system type.

High efficiency resonant switching converters

Abstract: Resonant DC to DC power converter topologies include a PWM-controlled flyback converter having a single transformer and a primary side resonant subcircuit that is optimally controlled to minimize reverse recovery losses. A second transformer may be added wherein the primary windings are connected in series, the first transformer having substantially greater inductance than the second transformer to more efficiently transfer energy over a wide range of output load conditions. A combined forward-flyback resonant converter utilizing a load-side buck loop for increased power delivery performance and start-up circuitry for initial power connection of the converter to a voltage source utilizing a hysteresis protection circuit are also disclosed.

Lossless snubber circuit for use in power converters

Abstract: A switching power converter employing a novel lossless zero-voltage-switching passive snubber network having a power range of up to 5 KW is presented. The passive snubber network improves efficiency, power density, and transient performance, reduces switching losses and EMI, and permits fixed frequency operation of the switching power converter. The passive snubber network also reduces and/or eliminates large peak currents and reverse recovery current spikes normally seen in conventional switching power converters. The proposed passive snubber network may be used in various switching power converter topologies such as boost, buck, balanced, and flyback power converters.

Power control circuit for improved power application and temperature control of low voltage thermoelectric devices

Abstract: A power control circuit for improved temperature control of thermoelectric devices to maintain the temperature of thermoelectric devices at a set point. The circuit includes a rectifying device to provide rectified alternating current when receiving an input from an electrical power source; a flyback power supply to supply a DC voltage to the thermoelectric device; a switching device to modulate the rectified alternating current across the primary of the flyback transformer; sensor circuitry to monitor the temperature of the thermoelectric device; and a programmable control device to receive an output from the sensor circuitry and provide a control signal to the switching device, the control signal being determined by the difference between the sensed temperature of the thermoelectric device and the desired set point to allow the DC voltage to the thermoelectric device to bring the temperature of the thermoelectric device to the set point and maintain the temperature of the thermoelectric device at the set point.

Modular battery system having a pluggable charging module

Abstract: A modular battery system for a portable device including a charging module with a retractable plug and charging circuit for converting an AC line voltage to a DC battery charging current. The charging module combines with a battery module and optional fuel gauge (if present) to form a single unit for recharging, preconditioning the battery, and connection to the portable device. The modules are releasably connected, preferably involving conductive fasteners, so that a user may connect a new battery module to an old charging module. The releasable connection serves as both the mechanical and the electrical interface between the battery module and the charging module. The conductive fasteners may be located in different positions on the modules to accommodate different connector geometries. The charging module may also combine with a battery mounting module, rather than the battery module, so that the system works with conventional battery packs. The preferred charging module incorporates a PWM charging circuit having a transformer with a primary winding, a secondary winding, and a control winding. The control winding has two purposes, it provides feedback information and it provides operating current for the continued operation of the PWM charging circuit. The transformer is designed so that the primary winding has a better magnetic coupling with the secondary winding than with the control winding so that the charging circuit will run in a safe low-power "standby" mode in the event of a short circuit in the secondary circuit. The feedback circuit from the control winding is preferably filtered through a low-pass filter to remove "flyback" transients.

Integrated backlight display system for a personal digital assistant

Abstract: A backlighting system is placed in an elongated interior space within a personal digital assistant (PDA) which normally houses a stylus used to touch a liquid crystal display (LCD) touch and display screen. A backlight driver circuit is constructed on a printed circuit board (PCB) which fits within the elongated space, and an on-off switch extends from the PCB to an exterior hole formed in the PDA housing. An on-time control turns off power to the backlight driver circuit after a predetermined time has elapsed following activation of the on-off switch, and a dimming control controls the amount of energy delivered to the electroluminescent film. A torroidal switching transformer of a high voltage power supply minimizes noise, and a switching controller switches adjustable width current pulses through the transformer to regulate the high voltage level. A flyback circuit captures and uses a portion of the back EMF energy created when the current pulses are switched through the switching transformer. A H bridge of transistors alternately connects the high voltage positively and negatively to energize the electroluminescent film.

Overvoltages in power transformers caused by no-load switching

Abstract: When an unloaded power transformer is switched on via a relatively long cable, sometimes extreme high voltages appear at the secondary side of the transformer. These overvoltages are caused by a resonant phenomenon that occurs when the resonant frequencies of the transformer and the cable match. The resonant frequency of the cable feeder is equal to the reciprocal of 4 times its travel time /spl tau/. The resonant frequency of the transformer is determined by its short-circuit inductance and the capacitance which is connected to the secondary winding. In this paper a model of this phenomenon is presented and an example of this resonant phenomenon, leading to the insulation breakdown at the secondary side of a power transformer, is given. >

Full wave buck-boost power converter with buck power converter properties

Abstract: A continuous mode full wave power converter topology which integrates the buck-boost (flyback) and buck converter properties. The voltage transfer function is M = (D/(1-D)), characteristic of the buck-boost (flyback) converter. Characteristic of the full wave buck converter, the inductor current is source continuous during the alternate D intervals, source discontinuous during the simultaneous (1-D) intervals, and load continuous during both the D and (1-D) intervals. A continuous mode full wave power converter topology which integrates the buck-boost (flyback) and buck converter properties. The voltage transfer function is Eout = Ein (D/(1-D)), characteristic of the buck-boost (flyback) converter. Characteristic of the buck converter, the inductor current is source continuous during the alternate D intervals, source discontinuous during the simultaneous (1-D) intervals, and load continuous during both the D and (1-D) intervals.

Multiple output flyback DC-to-DC converter with synchronous rectification and constant on-time current mode control

Abstract: A multiple output flyback DC-to-DC converter with synchronous rectification and constant on-time current-mode control. A controller includes a constant on-time, minimum off-time oscillator that is coupled to control a gate of a first transistor which controls a current through a primary winding of a transformer having three secondary coupled inductors. Each of the three secondaries is coupled to a capacitor which is charged by each secondary current to an output voltage level which depends, in part, upon a ratio of windings. A transistor is coupled between each secondary winding and a resistive network. The gates of these transistors are coupled to be controlled by the controller for synchronous rectification. The resistive network monitors the secondary currents by generating a voltage signal that is representative of a weighted sum of the inductor currents. A difference between an output voltage level and a reference voltage level is added to the voltage signal generated by the resistive network for controlling the oscillator. When the voltage signal generated by the resistive network reaches a first predetermined level, the off-time of the oscillator is terminated and a new on-time is started, causing additional current to flow through the primary winding. When the output voltage level decreases, the first predetermined level is decreased. If the output voltage exceeds a second predetermined level, the controller enters a discontinuous mode whereby the oscillator halts until the output voltage drops below the second predetermined level.

Flyback charging with current mode controlled flyback converter

Abstract: A flyback charger for an energy-storage capacitor has a controller for causing the energy-storage pulses of current in the transformer primary winding and the energy-delivery pulses of current in the transformer secondary winding to be nearly flat-topped. The controller includes a peak-current-commanding current-mode control or a valley-current-commanding current-mode control which controls the duration of a switching circuit on and off interval, respectively, responsive to the current flowing in the transformer primary winding and secondary winding, respectively. A feed-forward controller controls the duration of the switching circuit off and on interval, respectively, in response to the voltage provided by the secondary winding and D-C supply voltage, respectively. When using the valley-current-commanding current-mode controller, there may be a fixed duration of the switching circuit on interval.

DC and AC current sensor having a minor-loop operated current transformer

Abstract: The invention relates to a current sensor for non-contacting measurement of current in a line. Current is sensed by a circuit which provides a high frequency reversing voltage to a sensing winding on a current transformer, for driving the transformer into its linear region at least once per high frequency cycle. Current through the sensing winding is sampled while the transformer is in that linear region. Preferably, the current is sampled approximately at the instants of reversal of the voltage being applied to the sensing winding, and the sample having the lower absolute value is selected as a sample proportional to the line current.

Method and apparatus for providing isolated power sourced from bleeder current

Abstract: An isolated low power converter including a low voltage, self-oscillating power converter, which derives power through bleeder current from the relatively high-voltage, input bulk capacitors. A bleeder circuit taps a relatively low voltage current source from the bulk capacitors to supply an oscillator circuit. The bleeder circuit preferably incorporates current limit resistors typically provided according to safety specifications. The oscillator circuit is preferably implemented using the primary of a transformer. A simple regulator circuit coupled to the secondary of the transformer provides a low voltage SELV power signal for powering detection circuitry. In the preferred embodiment, the bleeder circuit includes a relatively large resistive voltage divider for supplying current to charge a capacitor. The voltage of the capacitor is regulated using a constant voltage device, such as one or more Zener diodes. The oscillator is implemented in a very simple and inexpensive manner, including a switching transistor having a current path coupled to the primary inductor of the transformer, a current limiter coupled between the current path of the transistor and primary ground, a bias circuit coupled to the control terminal of the transistor and a voltage regulating device coupled between the control terminal of the transistor and ground. The transformer preferably includes a tertiary winding coupled between the other end of the voltage divider and the current limiter for facilitating oscillation.

Voltage-follower control in zero-current-switched quasi-resonant power factor preregulators

Abstract: In this paper, we propose to study the use of several zero-current-switched (ZCS) quasi-resonant converters (QRCs) (buck-boost, flyback, SEPIC, Cuk, boost, and buck) with a half-wave switch, working as power factor preregulators (PFPs) with voltage-follower control. The analysis carried out demonstrates that these converters show excellent characteristics to obtain a high power factor (PF) without using any input-current feedback loop, and they also allow high switching frequency to operate because they integrate transformer and rectifier diode parasitics into the power topology.

Combination of a gas-filled interrupter and oil-filled transformer

Abstract: A gas-insulated switch for a distribution transformer and its associated electrical connections are located within a tank containing insulating and cooling oil for the transformer.

Power control electronics for cryogenic instrumentation

Abstract: In order to achieve a high-efficiency high-density cryogenic instrumentation system, the power processing electronics should be placed in the cold environment along with the sensors and signal-processing electronics. The typical instrumentation system requires low voltage dc usually obtained from processing line frequency ac power. Switch-mode power conversion topologies such as forward, flyback, push-pull, and half-bridge are used for high-efficiency power processing using pulse-width modulation (PWM) or resonant control. This paper presents several PWM and multiresonant power control circuits, implemented using commercially available CMOS and BiCMOS integrated circuits, and their performance at liquid-nitrogen temperature (77 K) as compared to their room temperature (300 K) performance. The operation of integrated circuits at cryogenic temperatures results in an improved performance in terms of increased speed, reduced latch-up susceptibility, reduced leakage current, and reduced thermal noise. However, the switching noise increased at 77 K compared to 300 K. The power control circuits tested in the laboratory did successfully restart at 77 K.

Hardware arrangement and method of driving a piezoelectric transformer

Abstract: An apparatus for controlling a piezoelectric transformer is disclosed. A transformer driver (12) supplies the transformer with a driving voltage the frequency of which is controlled by a frequency oscillator (18). A load current monitor (20, 22, 24, 26) observes a load current flowing through a load such as a fluorescent which is powered by said transformer. A frequency sweep controller (16) controls the frequently oscillator, when the transformer is initially energized, so as to execute a downward frequency sweep wherein the frequency of the driving voltage is swept from a predetermined upper frequency to a predetermined lower frequency. The frequency sweep controller further controls the frequency oscillator, after the transformer has been brought into stable operation, so as to execute the downward frequency sweep when the load current reduces to a second preset level lower than the first preset level.

Current ripple bounds in interleaved DC-DC power converters

Abstract: In distributed power supply systems, the parallelism of DC-DC power converters is a basic architecture. In this paper, the authors use the time domain method to show that the amplitude of the input/output current ripple of N(/spl ges/1) parallelly interleaved modules is always upper bounded by that of the individual modules for buck, boost, flyback, Cuk, and SEPIC power converters if the phase shift among the modules is 2/spl pi//N. Efficient numerical algorithms for predicting the net ripple amplitude in interleaved power modules are derived based on the insight gained from the time domain method. >

Inductance controller with load regulator

Abstract: A method for changing the inductance of a multiple-tap transformer in a circuit having a current regulator and the transformer, including the steps of comparing the current regulator's duty-cycle to a duty-cycle setpoint, increasing the turns ratio of the transformer when the duty-cycle is less than the setpoint. An apparatus for switching the taps of a multiple-tap transformer connected to a power supply and a load circuit, including a load regulator for generating a desired duty-cycle signal, and an inductance controller having a first reference signal generator, a comparator for comparing the reference signal to the desired duty-cycle, and relays connected to the transformer taps that are responsive to the comparator.

Analysis and optimisation of a flyback convertor with a nondissipative snubber

Abstract: The paper explores the optimum design of a nondissipative snubber employed in a PWM-controlled flyback power convertor. A simple but efficient transistor model was used to evaluate the switching loss. An optimum snubber capacitor value was defined, providing minimum total losses in the snubber network. Owing to the snubber, the operating frequency region of the IGBT transistor used was significantly extended. A 850 W convertor prototype for microwave heating was built and tested to verify the theoretical results.

Cold cathode tube operating apparatus with piezoelectric transformer

Abstract: An inverter apparatus of the present invention has a cold cathode tube and its operating circuit provided with a piezoelectric transformer. Specifically, for increasing the boost ratio of the piezoelectric transformer, a boost chopper is mounted in the premier stage of a semi-class E voltage resonance inverter and a power switch element is mounted operable commonly for both the inverter and the chopper so that a single voltage resonance controller IC controls the cold cathode tube at a constant current. As the operating circuit is composed of the voltage transformer, the apparatus will be minimized in the number of components and decreased in the overall size and the production cost. Also, as the operating frequency of the cold cathode tube is increased by increasing the resonance frequency of the piezoelectric frequency, the discharge efficiency will also be enhanced.

Fixed frequency forward-flyback converter with two fully regulated outputs

Abstract: Multiple output power converters are widely used in telecommunications equipment when several voltages are needed These power converters are smaller and cheaper than various individual converters However, it is very difficult to obtain multioutput power converters with high efficiency and tight regulation To overcome these difficulties, a new technique has been developed and is presented in this article This technique consists on a forward/flyback topology with active clamp where the forward output is regulated with the duty cycle of the main switch and the flyback output is regulated with the duty cycle of the auxiliary switch Experimental results for a +5 V/20 A, -5 V/125 A power converter show efficiencies at full load higher than 87% and a switching frequency of 175 kHz This solution introduces few additional components, but nevertheless the advantages versus other regulation techniques are not only in efficiency but also in volume and cost

Electrical transformer with reduced core noise

Abstract: An electrical transformer includes a housing, a transformer core and winding subassembly located in the housing, and a cooling fan subassembly. The cooling fan subassembly includes a variable speed fan located outside the housing, a temperature sensor located near the housing, and a controller having an output port connected to the variable speed fan and an input port connected to the temperature sensor. The controller reduces the fan speed (and hence the fan noise) when a lower fan speed can maintain the desired temperature as sensed by the temperature sensor. Preferably, the electrical transformer further includes an active mount subassembly and/or (when the housing includes a tank containing transformer fluid) a mechanism for varying the dynamic pressure of such transformer fluid.

Design issues of the high-power high-frequency transformer

Abstract: A completed procedure for optimum design of a high power, high frequency transformer is presented. The procedure is based on both electrical and thermal processes in the transformer and determines: (a) the power rating of ferrite cores in relation to the operating frequency, (b) the optimum flux density in the core and (c) the optimum current densities of the windings providing maximum transformer efficiency. Its analytical results can be used not only for the transformer optimisation but for the entire power supply optimisation as well. Two high power, high frequency transformers are optimally designed, built and tested. The practical results show good agreement with the theory. >

Switching power supply system

Abstract: PURPOSE: To provide a switching power supply system which is used in various kinds of electronic equipments, especially an RCC, and which operates stably even under a light load by preventing the increase in a switching frequency under a light load or rather actively lowering the frequency and thereby lessening a turn-on loss. CONSTITUTION: This system is provided with a controlling circuit 80. The controlling circuit 80 sets the minimum off-state time which would be longer as a load gets lighter based on a feedback signal from a detecting circuit 7. After the passage of the minimum off-state time, the controlling circuit 80 sees if the flyback voltage appears in a tertiary winding 23. If the controlling circuit 80 detects no flyback voltage in the tertiary winding 23, it turns a switching device 3 on and then determines the on-state time of the switching device based on the feedback signal of the detecting circuit 7 so that the output DC voltage may be stabilized. By providing such a controlling circuit in this system, a switching frequency gets lowered as a load gets lighter and then a turn-on loss can be lessened and thereby the system can operate stably even under a light load.

System and method for detecting fault conditions in a direct current motor

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

Small-signal analysis of open-loop PWM flyback dc-dc converter for CCM

Abstract: A flyback dc-dc converter is obtained from the conventional buck-boost converter by replacing the inductor with an isolation transformer. A transformer in the flyback converter is used to achieve a dc isolation between the input and the output of the converter. This paper presents dc and small-signal circuit models for the flyback converter for continuous conduction mode (CCM). The parasitic components are included in these models. The dc model is used to derive the equations for the dc voltage transfer function and the efficiency. The small-signal model is used to derive the equations for the open-loop small-signal transfer functions, such as control-to-output transfer function, input-to-output transfer function, input impedance, and output impedance. Bode plots are also given for the small-signal transfer functions.

Control process for a voltage transformer with a wide input voltage range and the application of such a process

Abstract: A control process for a voltage transformer for sine-wave line current input with a large input voltage range, includes controlling or regulating the input current of the voltage transformer as a function of a current command value. The output voltage of the voltage transformer is in the form of an actual value input quantity of a controller which supplies a control signal as a function of an output voltage command value. The above-mentioned current command value is obtained by multiplying a signal proportional to the rectified input voltage of the voltage transformer by the above-mentioned control signal, and also by a direct current voltage signal which is a reciprocal of the peak value, to the effective value or to the average value of the input voltage of the voltage transformer. Such a process is preferably used in a switched-mode voltage transformer, e.g. in an isolating transformer, a step-up transformer or a step-up/step-down transformer.