Showing papers on "Isolation transformer published in 1989"

Characterizing high-frequency effects in transformer windings-a guide to several significant articles

Abstract: Several papers pertaining to the design and modeling of high-frequency transformer windings are reviewed. Each paper is summarized, stressing its significant contributions and its relationship to the others. The emphases and relative merits of each are discussed, and the understandability and applicability are evaluated. >

Insulated gate bipolar transistor power module

Abstract: A power module contains IGBT die along with integrated circuit driver chips and opto isolators or isolation transformers within the same module housing. Output terminals are provided which can be interfaced directly to control logic or microprocessors for operating the module. The IGBTs may have current-sensing electrodes to simplify current measurement and control functions.

High frequency matrix transformer

Abstract: A high frequency matrix transformer comprises a plurality of interdependent magnetic elements (101) arranged and interwired to provide very low leakage inductance and very good coupling from the primary (102) to the secondary (103). The matrix transformer is particularly well adapted for high equivalent turns ratios, high frequency, high power, and high dielectric isolation. It can have parallel secondaries (103) which can source current to parallel rectifier circuits (CR1, CR2) with current sharing. It can also have parallel primary circuits (102) to balance the load between source switching circuits (Q1, Q2) to provide dual input voltage capability. The matrix transformer can be very flat, making it easy to ventilate or heat sink. The matrix transformer having push pull windings can include the primary switching means (Q1, Q2) and secondary rectifying means (CR1, CR2) within its windings, so that the transformer as a whole has direct current inputs and outputs.

Synthesis of PWM and quasi-resonant DC-to-DC power converters

Abstract: Synthesis of DC-to-DC converter topologies in the two largest families - PWM and Quasi-Resonant (QR) - is completed in this thesis In a PWM converter, two linear time-invariant networks, consisting of only capacitors and inductors, source and load, are switched at constant frequency with duty ratio D. From defining assumptions, several general properties of PWM converter networks are derived. The established general properties interrelate the number of elements, attainable DC conversion ratio M(D), and features such as continuous terminal currents or possible coupling of inductors. Based on matrix representation of the converter topology, the systematic synthesis procedure for generation of PWM converters with a given number of reactive elements is constructed. A prescribed set of requirements is the input for the procedure. The requirements may include desired DC conversion ratio, continuous terminal currents, possible coupling of inductors and a given number of switches. In particular, the number of switches implemented as transistors can be specified. Outputs of the procedure are complete classes of PWM converters that satisfy the input requirements. A number of useful PWM topologies, which have not been identified before, are uncovered. A comparison of members of the classes is included. Several extensions of PWM converters are considered, including insertion of the isolation transformer and two discontinuous operating modes for which unified DC analyses are completed. Quasi-Resonant converters are defined as two-switch PWM converter networks to which resonant elements are added. Synthesis of QR, converters is based on the recognition that there are only a finite number of topologically distinct positions for resonant elements within a two-switch PWM parent converter. If a single resonant inductor and a single resonant capacitor are added to a two-switch PWM topology, examination of all possible positions yields a total of six QR classes, which come in dual pairs. Two pairs are identified as known QR classes, namely, Zero-Current/Zero-Voltage (ZV/ZC) and Zero-Current/Zero-Voltage Quasi-Square-Wave (ZC-QSW/ZV-QSW). The remaining two classes, named Off-Resonant and On-Resonant Quasi-PWM (Q[f]-PWM/Q[n]-PWM), have not been recognized so far. The names originate from the fact that Q-PWM converters can be regarded as PWM converters operating in both discontinuous modes simultaneously. The synthesis procedure can be generalized to encompass additional resonant elements. As an example, classes of Zero-Current and Zero-Voltage Multi-Resonant (ZC-MR/ZV-MR) converters are formally defined. In contrast to square-wave switch waveforms in PWM converters, all QR topologies exhibit smooth quasi-sinusoidal waveforms and therefore reduced switching losses. Of particular interest are operating modes in which all switching transitions are at zero current or at zero voltage. A study of operating modes and a DC analysis unified with respect to all PWM parents and all topological variations are carried out for four selected classes of QR Converters - Q[n]-PWM, ZV, ZV-QSW, and ZV-MR. It is emphasized that for a QR converter, topology alone is not sufficient to derive DC conversion properties. Subject to different switch implementations and control timing, the emerging operating modes can result in vastly different behavior of the same converter topology. Two switch implementations are considered - conventional, with one controllable switch and one diode, and the one that resembles the technique of synchronous rectification - with two controllable switches. In the first case, with the exception of converters in two Q-PWM classes, only variable-frequency control is applicable. However, if both switches are controllable, constant-frequency control is restored in all QR classes, and several novel operating modes of practical interest are uncovered. Various QR classes and operating modes are compared with respect to sets of switching transitions, sensitivity to parasitic elements, available operating region, frequency range and stresses on switching devices. The role of free parameters in various design trade-offs is exposed, thus allowing a designer to select and realize the topology best suited for a particular application.

Off-line uninterruptible power supply with zero transfer time using integrated magnetics

Abstract: An offline uninterruptible power supply (UPS) or emergency power system with zero transfer time is presented. The principal application is to personal computers and systems. The power transformer, a triport-like transformer, acts as an inverter and as a voltage stabilizer with no external loading coil. It is made with commercial EI scrapless laminations. The battery charging circuit is integrated into the transformer and improves the dynamic output response during line-mode operation. The result is robust, short-circuit-proof equipment with harmonic distortion of lower than 3%, a static output stability better than 1.5%, and a very high reliability. >

A signal generating circuit for ballast control of discharge lamps

Abstract: A ballast control apparatus for an electric discharge lamp (1) comprises a first series circuit including a first winding (5) of an Ac supply voltage transformer (4), a first winding (7) of a ballast transformer (8), a lamp current sensing resistor (11) and the lamp (1). A current sensing transformer (13) has a first winding (12) parallel to the resistor (11). A second winding (16, 9, 14) of the supply voltage transformer (4), the ballast transformer (8) and the current sensing transformer (13) are connected in a second series circuit. A signal voltage proportional to lamp power is derived by adding together the voltages included in the three series-connected second windings (9, 16, 14). A second signal voltage proportional to lamp voltage is derived across the series combination of the second windings (9, 16) of the ballast trans­ former (8) and the supply voltage transformer (4). The voltage induced in the second winding (14) of the current sensing transformer (13) is proportional to lamp current. A signal voltage indicative of the condition of the lamp load can be derived across the second winding (9) of the ballast transformer (8). These three signal voltages are used to control a DC/AC inverter (2) that energizes the lamp (1) via the supply voltage transformer (4).

Integrated exciter generator and rotating transformer

Abstract: The problem of providing field power to a stationary main generator rotor is addressed such that it can be used as a synchronous or brushless dc motor. To that end, a dynamoelectric machine performs the dual-functions of an exciter generator and a rotating transformer integrated into a single unit (14). The heads (64) of the stator salient poles (60) include pole slots (68) for a primary transformer winding (34) for the rotating transformer, while the rotating armature winding (36) serves as the transformer secondary. To assist in starting the engine (10), external ac power (42) is applied to the primary transformer windings (34), coupled to armature windings (36), and rectified (44) to develop dc field power for the main generator (12).

Dual transformer device for power converters

Abstract: A dual transformer device (34) for use in a power converter (30) is provided. The dual transformer device is preferably implemented as an integrated magnetics device suitable for use in high density power converters. Two transformers, T1 and T2, have series connected primary windings (300 and 302), and secondary windings (304 and 306) connected at a common node (312). T1 and T2 have magnetizing inductances, L1 and L2, that independently store energy responsive to an AC voltage, V p . Diodes, D1 and D2, operate to rectify substantially out-of-phase secondary voltages, V S1 and V S2 and produce a rectified voltage V R . D1 and D2 cause L1 and L2 to store discharge energy such that the magnitude of an output current, I5, is always equal to the sum of magnetizing currents, I L1 and I L2 . An output filter (38) reduces current ripple in I5 and voltage ripple in V R . Another inductance, L3, supplies energy to an AC voltage supply (32) to reduce switching losses.

Highfrequency heating apparatus using frequency-converter-type power supply

Abstract: A high-frequency heating apparatus comprises a power supply including a commercial power supply or a battery, a frequency converter for converting the power of the power supply into high-frequency power, a boosting transformer for increasing the voltage of the output of the frequency converter, and a magnetron for receiving the output from the boosting transformer. The apparatus further comprises a shield member made of a non-magnetic conductive material and forming a substantially electrical open loop in the winding direction of the primary winding between the primary and secondary windings of the boosting transformer. The shield member is connected to the core or the housing of the boosting transformer thereby substantially containing a high-voltage circuit in the shield space. High safety of the high-frequency heating apparatus is thus assured without grounding the housing.

Phase-controlled reversible power conversion with equal duty cycle substantially constant amplitude square wave excitation of the power transformer

Abstract: A universal phase-controlled reversible power converter having one transformer with multiple windings couples a d.c. voltage to an associated transformer winding through a fixed port having controllable switches; and further simultaneously couples any number of a.c., d.c., combination a.c. and d.c. or stochastic voltages, each to an associated transformer winding and each through an associated variable port having a filter with an inductor and controllable switches. All couplings, transpiring in any number of relatively independent ports, are to an equal duty cycle substantially constant amplitude square wave within the transformer's windings. Any number of relatively independent open-loop transfer functions, or closed feedback control loops, may be simultaneously active (i) to control switching in variable ports so as to continuously couple power regardless of its waveform or distortion, or regardless of variations in waveform or distortion even so far as changes between a.c. and d.c., and (ii) to control switching in any of the variable ports so as to cause the port to present a controlled counter emf to a source of power, or any desired output waveform to a sink of power despite any variations in its impedance. Aggregate coupling, and conversion, efficiency ranges to 95% at kilowatt power levels.

A switch-mode power supply

Abstract: A first switching transistor Q2 is coupled to a primary winding W1 of an isolation transformer T2. A secondary winding W2 of the transformer T2, is coupled via a switching diode D3 to a capacitor C4 of a control circuit 120 for developing a DC control voltage V4 in the capacitor C4. The DC level of the control voltage V4 varies in accordance with a B+ supply voltage. A change in B+ voltage produces a corresponding greater change in the control voltage V4. The control voltage V4 is applied to the transformer T2 when the diode D3 is conducting, for producing a pulse-width modulated control signal V5. The control signal V5 is applied to a mains coupled chopper transistor Q1 for generating and regulating the B+ supply voltage in accordance with the pulse width modulation of the control signal V5. In standby operation low power operation is provided by burst mode switching operation of oscillator 110 which occurs during an interval (t10-t12, Fig 5), the oscillator being periodically triggered by half wave rectified voltage of signal V7 at mains frequency. A soft start up is provided whereby the power supply operates initially in the burst mode until started.

Forward converter type of switched power supply

Abstract: A transformer isolated switched power supply of the forward converter type which includes a clamping circuit for the switching unit of the power supply which recovers the energy stored in the transformer during each switching cycle without any need to dissipate the energy, and which also serves to reverse the flux in the power transformer during each switching cycle to restore the flux capacity of the power transformer to the same level as in other types of converter circuits.

Secondary electric power source produced by current flow through a primary a.c. power circuit

Abstract: Voltage drop developed across a transformer primary winding coupled in series with a primary a.c. power circuit including an a.c. power source and an a.c. load is utilized to provide a secondary source of a.c. power having secondary voltage level stability which is substantially independent from otherwise influential changes in primary power circuit levels. Secondary power stabilization is mainly established by constant voltage limiting of the primary winding excitation by the forward voltage drop developed across an arrangement of semiconductor junctions coupled in parallel with the primary winding. The transformer may be used to change the source level of the secondary a.c. power which is produced, and to obtain electrical isolation between the primary power circuit and any ancillary circuits coupled with the secondary a.c. power source.

Transient-filtered transformer

Abstract: A transformer comprising a primary winding and a secondary winding also includes a capacitor connected across at least a portion of the secondary winding within a housing of the transformer so that magnetically coupled voltage transients are filtered to prevent such transients from damaging a load connected to the secondary winding. An electrostatic shield is also included in the transformer to shield against capacitively coupled voltage transients. The capacitor also improves the power factor.

Ballasting system for fluorescent lamps

Abstract: A ballasting system for powering an array of flourescent lamp assemblies, as in a sun tanning apparatus, comprises an electronic frequency converter adapted to convert ordinary 60 Hz power line voltage into two non-current-limited high frequency outputs: a first output of 400 Volt/30 kHz sinusoidal voltage provided between a first pair of distribution conductors, and a second output of 50 Volt/30 kHz sinusoidal voltage provided between a second pair of distribution conductors. Each lamp assembly comprises two mutually parallel-disposed series-connected fluorescent lamps. The 50 Volt/30 kHz voltage is provided to the one end of this assembly and is used by way of an isolation transformer means to provide cathode heating power for the two lamp cathodes located near that end. The 400 Volt/30 kHz, voltage is provided to the other end of the assembly and, in addition to providing cathode heating power by way of isolation transformer means, provides a voltage of magnitude directly suitable for starting and running the two series-connected lamps by way of a simple inductive or capacitive reactance ballast. Every other lamp assembly is ballasted with an inductive reactance ballast; and every alternate other lamp assembly is ballasted with a capacitive reactance ballast. That way, the net load represented by any even number of lamp assemblies will be substantially resistive.

Electrical power supply unit

Abstract: An electrical power supply unit having at least one output has a transformer (10) to whose primary winding (11) a voltage is applied, which voltage is pulsed by means of a controllable switch (13). Two outputs (16, 17) are connected to the secondary winding (15), the transformer (10) being operated as an isolating transformer (flyback converter) for the voltage at the first output and as a forward converter for the voltage at the second output. The discharge time of the transformer (10) can be varied in order to control the isolating transformer output voltage.

Washer fluid monitor

Abstract: A washer fluid monitor comprising a pair of electrically conducting probes projecting downward into a washer fluid reservoir and incorporated into part of the positive feedback loop of a Wien bridge oscillator. One of the probes is grounded; and the Wien bridge oscillator is modified with an additional capacitor isolating the other probe from the DC supply and intermediate voltages so that it is essentially grounded at the oscillator frequency to greatly reduce or eliminate ionic currents in the washer fluid and resulting probe degradation without the need for an isolating transformer.

Power source for metal halide lamps and the like

Abstract: A power supply for a gas discharge lamp includes a current regulator for regulating the current supplied to a lamp and current steering means for steering current from the current regulator in alternating directions through an isolation transformer primary winding, the secondary winding of the transformer being connected with a lamp through an arc striking circuit. The frequency of alternating the current through the transformer is controlled as a function of the lamp voltage in order to regulate the volt-second product of the transformer through all portions of a lamp operating cycle including arc striking. This reduces saturation of the transformer and allows a much smaller transformer to be used. In a preferred embodiment, the current regulation and steering functions are performed in a bridge circuit having FET switches in each leg and in which the transformer primary spans the sides of the bridge. Pairs of FETs in diametrically opposite legs of the bridge are operated in unison, with one FET of each pair controlling lamp current by pulse-width regulation. The current is steered through the transformer primary by alternatingly operating the FET pairs at a frequency established by a voltage-controlled oscillator responsive to transformer voltage.

Magnetically controlled variable transformer

Abstract: A magnetically controlled variable transformer comprising magnetic cores and windings by which to accurately and reliably control electrical AC output power. The cores and windings act as a continuously variable turns-ratio transformer for use primarily at high power frequency applications (e.g. 400 KHz or higher), such as in aircraft and aerospace vehicles. The transformer of the present invention is implemented by coupling a 2-core variable saturable transformer to a fixed turns ratio linear transformer. By varying a DC control current to a DC control winding which is magnetically coupled to the saturable transformer, the AC output voltage at a resistive or reactive load can be varied from zero to full power, whereby the control range of the transformer can be maximized.

Synchronized switch-mode power supply

Abstract: In a switch mode power supply, a first switching transistor is coupled to a primary winding of an isolation transformer. A second switching transistor periodically applies a low impedance across a second winding of the transformer that is coupled to an oscillator for synchronizing the oscillator to the horizontal frequency. A third winding of the transformer is coupled via a switching diode to a capacitor of a control circuit for developing a DC control voltage in the capacitor that varies in accordance with a supply voltage B+. The control voltage is applied via the transformer to a pulse width modulator that is responsive to the oscillator output signal for producing a pulse-width modulated control signal. The control signal is applied to a mains coupled chopper transistor for generating and regulating the supply voltage B+ in accordance with the pulse width modulation of the control signal.

Inverter switch current sensor with shoot-through current limiting

Abstract: The problem of sensing current through inverter switches is solved by a current transformer which has windings connected with the flyback diodes to demagnetize or reset the current transformer core. Size and weight of the transformer are minimized while avoiding a buildup of flux which would saturate the core.

Apparatus and method for a quasi-resonant DC to DC bridge converter

Abstract: A DC to DC converter is described having a bridge circuit coupled to the secondary windings of a transformer, the transformer supplying power to a capacitor and a constant current load source. The circuit parameters are chosen to provide a circuit that has quasi-resonant characteristics close to the frequency of the signal providing power to the transformer, but at a higher value. Other constraints on the circuit parameters are discussed. The resulting circuit provides an efficient transfer of energy from the source power supply to the load.

Power converter with cascaded output transformers

Abstract: In a power converter having a resonant output circuit transformer coupled to a load circuit, a transformer coupling circuit comprises at least two transformers providing a coupling stage having inductively coupled windings that are in step down relationship to an input and/or output winding of the transformer coupling circuit. This enables the rate of change of voltage in the coupling stage to be reduced and thus correspondingly reduces the transmission of interference from the power converter to the load circuit.

Switching power supply.

Abstract: The switching power supply operates on the isolating transformer principle and contains a regulation circuit for the primary in which the supply voltage of the regulation module (N) is branched off from a voltage divider, having the resistors (R1, R2, R3) and located in parallel with the DC voltage source. The switching power supply is characterised by a switch-on control circuit having a first control switching transistor (ST1), whose input is coupled via a timer (C3, R4, R5) to the measurement circuit, and by a second control switching transistor (ST2), which is controlled by the first control switching transistor (ST1) and is connected in series with the first resistor (R1) of the voltage divider (R1, R2, R3).

High-reactance transformer (high-leakage-reactance transformer)

Abstract: A high-reactance transformer consists of a core, a primary coil, an air gap, and a secondary squirrel-cage winding in the form of an organic substance for the purpose of forming eddy currents in the cells and between the cells of this organic substance. This organic substance can be the body or a part of the body of a human being or an animal and is arranged in the air gap of the high-reactance transformer. In order to make possible small, handy high-reactance transformers despite large-area treatment applications, a multiplicity of high-reactance transformers is placed side by side. In order to facilitate the treatment of the human being, the high-reactance transformer or the multiplicity of small high-reactance transformers is provided in or around or over or under or behind a mattress, couch, deck chair, armchair, chair, cushion or the like, depending on the purpose of the application and the kind of treatment of the human being or of the body part of the human by means of pulsating magnetic fields to form eddy currents in and between the cells.

An advanced design of piezoelectric ceramic transformer for high voltage source

Abstract: The basic characteristics of a novel ceramic transformer are studied in detail. Because the input section consists of laminated ceramic strips and each strip can be made very thin, the input driving voltage can be very low. The output section consists of four piezoelectric ceramic columns utilizing k/sub 33/. These columns are electrically connected in series, so that the induced voltages are added up, and therefore a very high output voltage can be obtained. Experimental results show that the transformation ratio is about 200, i.e. 40 to 50 times greater than of the existing ceramic transformer. It is confirmed that this ceramic transformer is useful for a high-voltage source. >

Circuit arrangement for preventing gain from responding to frequency variation despite the presence of an isolation transformer

Abstract: By the use of a feedback arrangement, deleterious circuit effects of an isolation transformer in a terminal device for a telephone line can be eliminated. By this arrangement, a smaller, cheaper transformer may be used. A terminal device employing such arrangement can present a balanced termination to a telephone line, exhibit a known and controlled impedance to that line and provide for signals to be coupled to and from that line.

A new electric power sensor module using magnetoresistive thin film

Abstract: The authors describe an electric power sensor module using Ni-Fe magnetoresistive thin film. It is compact and microprocessor-interfaceable. The module is constructed of five components: a bridge-type magnetoresistive element used as a multiplier, a permanent magnet to provide some magnetic bias, a Permalloy case for a magnetic shield, an isolation transformer, and an amplifier. The thin-film element has good offset voltage/temperature characteristics and linearity. >

Matrix transformer having high dielectric isolation

Abstract: A matrix transformer with high dielectric having the capability of withstanding very high potentials between its primary (102) and secondary (103a, b) and is well adapted for use as a safety transformer in switch mode power supplies. It can also have the primary and the secondary physically separated from each other by an intermediary winding (606) which is at ground potential.

Characteristics of a new implantable transformer with planar shape.

Abstract: This paper describes output characteristics of a new transformer for an implantable artificial heart. The implantable transformer consists of Co-based amorphous magnetic fiber and conductive fibers. Features include (i) a thin, planar shape and (ii) high flexibility. The trial transformer made can supply electric power of 10 W. Magnetic field distribution around the transformer was measured, and leakage magnetic flux behind it could be reduced. A transformer with spiral woven structure was also discussed.