Showing papers on "Isolation transformer published in 1993"

Signal modulation across capacitors

Abstract: A method and apparatus for communicating a modulated signal across an isolation barrier using capacitors is provided. The present invention allows low distortion communication of an audio signal across an isolation barrier without the need for a large and bulky isolation transformer. The present invention may be used to provide telephone line isolation for modem applications compliant with governmental regulations. A line interface integrated circuit (IC) may be connected directly to a telephone line and powered by the telephone line. The line interface IC may include a sigma delta modulator to communicate the receive signal across a capacitor over an isolation barrier and a digital-to-analog (D/A) converter to provide an analog transmit signal from a sigma delta bit stream communicated across a capacitor over an isolation barrier. Circuitry on the opposite side of the isolation barrier includes similar components to process the transmit and receive signals.

Soft-switching converter DC-to-DC isolated with voltage bidirectional switches on the secondary side of an isolation transformer

Abstract: A soft-switching dc-to-dc converter for providing regulated voltage to a load combines the functions of loss-less soft switching at zero voltage and at a constant switching frequency on the primary side and soft switching at zero current on the secondary side of an isolation transformer for all load currents from full load to no-load and PWM output voltage regulation on the secondary side. This is made possible by using voltage bidirectional switching element in series with a low-pass filter on the secondary side and current bidirectional switching element on the primary side driven at close to 50% duty ratio with adjustable dead time between switching. The adjustable dead-time is realized by sensing voltages across paired primary side current bidirectional switching element in order to enable alternate turn ON of said pair only at zero voltage, thereby eliminating or greatly reducing switching losses under all load current conditions. The output voltage is regulated by PWM control of the voltage bidirectional switching element comprising one of the following: a bipolar transistor, or a MOSFET in series with a diode, or preferably a saturable reactor in series with a diode to form a magnetic amplifier on the secondary side.

Modem with digital isolation

Abstract: The MODEM WITH DIGITAL ISOLATION removes the relatively large heavy isolation transformer from the Data Access Arrangement and substitutes two tiny pulse transformers between the Integrated Analog and Digital Signal Processor with multiplexers and demultiplexers to eliminate analog distortion and multiple leads, and to accommodate Lap Top/Palm Top computers, while enhancing data speeds. The combination with surge protection enables both uncommon and common mode protection.

Multi-level data transmitter

Abstract: A data transmitter circuit includes a pseudoternary conversion circuit for converting a binary logic signal to a differential pseudoternary signal having symmetric rise and fall characteristics The output of the pseudoternary conversion circuit is filtered and passed to an electrically conductive medium via an isolation transformer The conversion circuit includes a symmetric arrangement of toggle circuits which respond to transitions in respective complementary binary signals constituting a differential binary input signal Voltage dividers are connected to the output terminals of the toggle circuits for providing three levels of output voltages in response to the logical states of the toggle circuits

Galvanic isolation device for direct current electrical signals or electrical signals likely to include a direct current component

Abstract: Galvanic isolation device for direct current electrical signals or electrical signals likely to include a direct current component, which includes a transformer (T), reversible switch I for chopping the incident signal applied to one wind of this transformer reversible switch I' for chopping the signal obtained at the other winding of this transformer, controlled either in phase or in phase opposition with each other and filters (F1,F2) for filtering the chopped signals respectively obtained at windings of the transformer.

Method for rejecting electrical interference from physiological measurements

Abstract: Methods and apparatus for eliminating the effects of electrosurgical interference on continuous, heat-based cardiac output measurements employing several procedures, including the steps of (1) supplying power via an isolation transformer (12) and carrier frequency to a catheter-mounted heating element (16); (2) measuring the voltage and current on the primary side (10) of the isolation transformer (12); (3) determining the voltage and current on the secondary side (14) of the transformer (12) on the basis of the measured primary side voltage and current; and (4) calculating the power delivered to and resistance of the catheter-mounted heater (16) on the basis of the secondary voltage and current. A heater power waveform generated with this process will be substantially free of electrical interference due to electrosurgical devices. Then, a system transfer function may be produced via signal processing techniques which involve cross-correlating the heater power waveform with the blood temperature waveform. The system transfer function will be uncorrupted, even if the blood temperature waveform contains moderate electrical interference, since the heater power waveform is free of any correlated electrical interference.

Current estimating circuit for switch mode power supply

Abstract: In a switch mode power supply the switch current of the power switch (901) is connected (via 911) to a low pass filter network (904) during the time interval when current is flowing through the power switch (901) The filter network (904) is disconnected from the power switch when switch current is not flowing This technique takes advantage of the fact that the average current through the power switch during its conduction interval is either equal to the output current of the power supply, or is proportional with the ratio between the average switch current and the output current being the fixed isolation transformer turns ratio

Switching power supply with electronic isolation

Abstract: A switching power supply that converts an input AC or DC voltage to a regulated output DC voltage while offering electrical isolation between the input and output stages through use of solid state switches and charge storage devices in place of isolation transformer used in traditional systems The power supply uses two series connected switching blocks that alternately charge and discharge a storage capacitor, wherein each switching block includes a pair of switches which may be turned on and off with a duty cycle adjusted by a controller The duty cycle and on time of each block is adjusted such that respective blocks are never turned on at the same time, thereby providing electrical isolation

High voltage regulator for an integrated horizontal sweep system

Abstract: A voltage regulator for a flyback-type high voltage supply having: a pulse transformer with its secondary interconnected in series with the primary of a flyback transformer; a control circuit for sensing the generation of a flyback pulse, a reference voltage, and a feedback voltage signal appearing at the output of the flyback transformer; and a switch for selectively applying energy to the primary of the pulse transformer while uniformly maintaining the flow of current through the primary of the flyback transformer.

Switching converter with open-loop primary side regulation

Abstract: The isolated, multiple output, switching converter is created with a number of unique performance characteristics. The converter operates in continuous inductor current mode (CICM) of operation for all load currents from no load to full load on all outputs despite the presence of simple rectifier diodes only on the converter secondary sides. The regulation of output voltages on all outputs against the changes of the input voltage is provided by use of a simple open-loop control circuit connected to the primary side and thus eliminating the need for isolation in the control circuit. The regulation against the load current changes in the single output case is also provided on the primary side by a load current sensing circuit. An additional benefit of the switching converter is in the elimination of the losses and voltage overshoots associated with the leakage inductance of the isolation transformer when operated as pulse width modulated (PWM) converter.

Toroidal transformer with magnetic shunt

Abstract: A transformer or inductor is made by wrapping a magnetic core material about a toroid-like structure made up of one or more electrical windings. A ferroresonant transformer may be constructed by including a slotted washer between primary and secondary windings. By shorting one of the windings, the ferroresonant transformer can be made into a gapped inductor with the gap totally enclosed within the core.

Piezoelectric transformer converter for power use

Abstract: In a piezoelectric transformer converter for power use that includes a switching circuit that generates alternating current, a power-use piezoelectric transformer, and a rectification-smoothing circuit, the alternating current output of the power-use piezoelectric transformer is directly phase-inverted and amplified by a phase inversion-amplification circuit, and by way of a driving circuit, produces self-excited oscillation. In addition, the output voltage of the rectification-smoothing circuit is compared with a reference voltage by means of an error amplifier, and based on the resulting amplified voltage difference, the output voltage is controlled by using PWM control or frequency modulation control without the need for an additional electrode for self-excited oscillation. In addition, when controlling the output voltage to be constant, stable control is enabled that is unaffected by variance in the frequency characteristics of the power-use piezoelectric transformer.

Parallel-resonant inverter-type fluorescent lamp ballast

Abstract: A push-pull inverter is supplied from an inductively current-limited DC voltage source by way of a center-tap on a transformer having significant inductance. This transformer inductance is parallel-coupled with a capacitance means. The inverter is made to self-oscillate through positive feedback provided by way of a saturable current transformer. The inverter frequency is determined by the saturation time of this current transformer, which saturation time is designed to be somewhat longer than the half-cycle period of the natural resonance frequency of the transformer inductance combined with the capacitance means. By controlling the length of this saturation time, the magnitude of the current provided to the fluorescent lamp is controlled, thereby permitting control of the light output in response to changes in the magnitude of the power line voltage.

A resonant DC-DC transformer

Abstract: The characteristics of a push-pull parallel resonant converter (PPRC) when operated as a DC-DC transformer were investigated theoretically and experimentally. In the DC-DC transformer region, the voltage transfer ratio of the PPRC was found to be practically constant and independent of the input voltage and load. In this mode, all the switching elements operate in the zero voltage switching (ZVS) condition. Another important feature of the proposed DC-DC transformer is the ability to drive it by an arbitrary switching frequency, provided that the latter is lower than the self-oscillating frequency. This permits the synchronization of the converter to a master clock. The analytical expressions for voltage and current stresses, as well as the other key parameters derived, are applied to develop design guidelines for the DC-DC transformer. The proposed topology was tested experimentally on a 100-W unit which was run in the 200-kHz frequency region. >

Transformer fault analyzer

Abstract: A transformer fault analyzer provides on site fault analysis of electrical distribution transformers, relying on patterns of parameter variation in transformer winding ratios, winding resistance and magnetizing impedance, and comparison of these parameters to predetermined values. In a preferred embodiment the analysis considers transformer ratio balance and magnetizing impedance balance. The transformer analyzer may be used with the transformer under load or no load conditions, and thus can be used to test transformers in the field as well as surplus or refurbished transformers.

Electronic ignition enhancing circuit having both fundamental and harmonic resonant circuits as well as a DC offset

Abstract: A high frequency electronic ballast (128) having a transformer (104) in which the transformer (104) has a primary winding (106) which is coupled to a secondary winding (108) via a primary flux path (1) from which flux can be diverted by a secondary flux path (2) including an air gap (114) which can be adjustable. Use of the transformer (104) permits load operation from a rectified alternating current power source which can be compensated by a high frequency power supply (192) to present a favorable power factor to the alternating current supply.

Control circuit for a switching DC-DC power converter including a controlled magnetic core flux resetting technique for output regulation

Abstract: A DC-DC power converter having a power transformer primary winding and a secondary winding producing a regulated output using a control technique and circuit to control the magnetic flux reset time of the core of the power transformer. The control circuit for the power converter provides control of the on and off time of the power transformer by controlling the magnetic flux reset voltage produced on the secondary winding, thereby controlling the duty cycle of the power transformer, and thereby regulating the output of the power transformer. Because control of the power transformer is accomplished by controlling the secondary winding reset voltage, input-to-output isolation and improved converter stability is provided. Minor variations to the input section of the DC-DC converter allows for a wide range of input voltages. Minor variations to the control circuit configuration provide the capability for short-circuit protection and inrush current limitation.

Power transformer with superconducting windings

Abstract: A 330-kVA power transformer with superconducting windings is discussed. A niobium-titanium based superconducting wire optimized for AC applications was used in the windings. The transformer worked according to its design at rated power. The total heat input to the liquid helium bath at this power was 9.4 W, of which the AC losses dissipated in the windings were about 1 W per winding. The low voltage feedthroughs which had to carry 830 A/sub rms/ at rated power worked adequately. The transformer revealed an apparent current limiting effect. This property can be utilized to limit currents in a network for time periods 10-50 ms. A quench protection device was designed and incorporated in the test circuit. >

Active power line conditioner having capability for rejection of common-mode disturbances

Abstract: The present invention provides an APLC which has improved common-mode disturbance rejection capability when compared with similarly-sized devices constructed according to current teachings. The need for an isolation transformer is, in many cases, eliminated by the invention. The invention alters the coupling transformer of the series parallel APLC or the isolation inductor of the newly-proposed inductor-parallel APLC to create a balun effect in the high and low conductors of the electrical supply network. Particularly, first and second windings are substituted for the single winding of the transformer primary or the isolation inductor. These two windings are serially-connected on the high and low conductors, respectively, with appropriate polarity such that self-inductance values of each are additive. Low pass capacitors and surge protectors may also be added to further protect the APLC and the load.

Current limiters in power utility applications

Abstract: A current limiting method and apparatus for preventing fault overload in a utility power transmission system (10) employs a high power, superconducting coil based pulse transformer (36) for saturating the core of the utility power transformer (30) thereby limiting its current carrying capacity. The utility transformer core (54) is biased to a disadvantageous portion of its B-H curve. A fault condition is detected and as a result the superconducting coil (48) is quenched thereby sending a high energy pulse of current into the utility transformer magnetic core (54). The core, while heating, does not exceed its capability to maintain a stable thermal condition while at the same time limiting the current being transformed from its input (32) to output (34) lines, until a transformer circuit breaker activates.

Power transformer switching-on current transient suppression system - pre-magnetises transformer core before switching to supply network with secondary load disconnected.

Abstract: The current transient suppression system feeds a pre-magnetisation current to a transformer drive winding (3) having a defined phase relationship to an AC supply voltage. A load (9) is disconnected from the transformer secondary winding (8), with a signal delay stage for time-delayed connection of the transformer to the supply network (6, 7), relative to the pre-magnetisation. The load is pref. connected across the transformer secondary upon the transformer primary circuit attaining the load condition. ADVANTAGE - Relatively simple circuit preventing high switching-on current transients with high network loading.

Systems and methods for transmitting pulse signals

Abstract: The invention relates to a method and system for communicating from the secondary side of an isolation transformer (6) to receiver means, the primary of said transformer being connected via a power cable to a circuit fed with a periodic voltage from a constant-current generator, said receiver means being connected to said circuit. More particularly, switch means (30) are arranged for generating communicating signals by momentarily affecting the impedance on the secondary side so as to generate one or more voltage pulses on the primary side (8) of the transformer for propagation along the cable to said receiver means.

A simulation model for transformer internal faults base for the study of protection and monitoring systems

Abstract: The study of internal faults in transformers, i.e. the calculation of the fault current and its external detection (phase currents) as a function of the location and the amplitude of the fault, is of great interest. This situation has led the authors to manufacture a special, multiple output transformer. This device, designed on the basis of a 100 kVA MV/LV transformer, has enabled them to carry out numerous turn-to-turn and turn-to-earth short-circuits. In association with these tests, they have developed a digital model of the transformer, validated by the actual measurements. This model, when applied to a HV network transformer, enables the efficiency of the usual protection devices to be examined, in particular that of the transformer differential protection.

Duplex communication coupler system

Abstract: The single transformer generally used in a duplex coupler for coupling local telecommunication equipment, such as a modem, to a telephone line may be replaced by a number of transformers or other suitable forms of DC isolation device which then enables each transformer and its associated circuit network to be specifically tailored to optimize the operation of the coupler system. The transmit output path 3 is connected to a transformer 2 having a center-tapped secondary winding 11 which is connected across the communication line 4. A second transformer 5 has its primary winding connected between the center-tap and the line 4, and its secondary winding coupled to the receive input 6. By optimizing each transformer the intermodulation products and other unwanted products are reduced. The coupler system may be miniaturized and the line matching components incorporated in or selected by a specific line cord designed to match the network characteristics.

Motor control system and apparatus for providing desired three-phase voltage therein using a main transformer energized through an autotransformer

Abstract: A motor control system and apparatus for providing a desired three-phase voltage in the motor control system include: (1) a main transformer and components that are rated for one nominal voltage input, and (2) a commonly housed input transformer that transforms a different voltage power source to provide the nominal voltage input to the main transformer.

Electrical circuit for operating a fluorescent lamp and for measuring the lamp current

Abstract: In an electrical circuit for feeding a fluorescent lamp, a serial resonant circuit is comprised of a first coil of a feedback-transformer, a resonant inductor, a coupling condenser, a first lamp cathode, a resonant condenser, and a first coil of an isolating transformer, this serial resonant circuit being connected between the output of an inverted rectifier, connected to a voltage supply source and one terminal of said voltage supply source, with a second coil of the isolating transformer being connected in parallel with the second lamp cathode. If the coils of the isolating transformer have the same number of loops, this connection of the second lamp cathode ensures that the same heating current will flow through both lamp cathodes, so that these will be heated equally. The parallel circuit of the second lamp cathode with the second coil of the isolating transformer is connected through a resistance with a terminal of the supply voltage. The lamp current flows through this resistor, thus the voltage across the resistor is proportional to the actual current of the lamp and it can therefore be transmitted to the main circuit which regulates the lamp current.

Pulse transformer circuit for isolating electrical signals

Abstract: A signal isolator circuit employing a pulse transformer overcomes the disadvantages of both prior art opto-coupler and pulse transformer signal isolator circuits by employing an active signal retrieval circuit which, in a higher accuracy configuration, repetitively performs the following steps on the electrical side of the pulse transformer where the signal information is required: 1) drives a current pulse into the pulse transformer; 2) samples or detects the voltage across the pulse transformer after it has been stabilized; 3) holds or stores the sampled voltage for a full cycle of operation; and, if necessary, 4) filters the sampled signal. On the other electrical side of the pulse transformer, the retrieval circuitry is configured such that when the pulse transformer is being driven by the current pulse, the voltage will be clamped by the source signal reset. In a lower accuracy configuration, the signal retrieval circuit of the present invention performs the same steps set forth above with the exception that, rather than sampling the voltage across the pulse transformer, the reflected impedance is detected as being either high or low, by some quantitative measure, and the detector output will be set to either a high or low voltage corresponding to the detected impedance.

Apparatus for remote ballasting of gaseous discharge lamps

Abstract: Remote ballasting apparatus adapted for insertion between a high frequency power source and one or more gaseous discharge lamps The ballasting apparatus includes an isolation transformer having a primary winding adapted for connection to the high frequency power source, a low capacitance power transmission line having an output end adapted for connection to the one or more gaseous discharge lamps, and current limiting means, such as an inductor or a capacitor or a series resonant circuit connected between the secondaries of the isolation transformer and the input end of the low capacitance power transmission line

current sensor for alternating currents.

Abstract: The present invention relates to a current sensor for the isolated measurement of alternating currents. The invention is to enable the cost of current sensors to be reduced and is to overcome geometrical and constructional constraints. This sensor comprises a primary circuit through which the entire current to be measured flows, and a secondary circuit coupled to the primary circuit via a multi-turn compensated isolation transformer. The primary circuit consists of a shunt (SH) of low ohmic value and having good thermal stability, through which more than 99% of the current to be measured flows, Im, and connected, on the one hand, to the primary winding (P1) of the compensated isolation transformer and, on the other hand, to a localised real resistance (R1) in series with the primary winding (P1), having good thermal stability but of a high ohmic value compared to that of the shunt (SH). The secondary windings of the compensated isolation transformer are connected to associated electronics (E). The secondary winding (S1) is connected in parallel to the resistor (R2), the combination being connected, on the one hand, to earth and, on the other hand, to the resistor (R3), the other lead of which is connected to the output Vs, the resistors (R2) and (R3) both having good thermal stability.

A low-cost high power factor resonant mode battery charger

Abstract: A power converter for battery charger applications, which has at the input a full wave rectifier, followed by a series resonant power converter with a clamped voltage resonant capacitor, is presented. In this converter, only two MOSFETs are employed. They control the current delivered to the battery across a high-frequency isolation transformer, and produce a high (near unity) power factor input current. The proposed topology allows the design of low cost equipment. A laboratory prototype has been built, rated at 440 W and 48 V, with measured efficiency of 0.89 and power factor of 0.96 full load. >