Showing papers on "Isolation transformer published in 1988"

Phase-controlled DC-AC converter with high-frequency switching

Abstract: An analysis of the phase-controlled DC-AC converter is presented. This converter has a pair of switches in each side of the primary and the secondary of the isolation transformer. The voltage conversion ratio is controlled by the phase difference between the two pairs of switches. The averaged equivalent circuit for low frequency operation is derived. The switching surge during commutation is much reduced by dividing the reactor into two parts. As a result, the transformer is miniaturized by increasing the switching frequency and the reactive energy can be easily recovered to the DC source. This DC-AC converter is especially suitable for small uninterruptible power supply systems. >

Finite element analysis of copper loss in 1-10 MHz transformers

Abstract: Issues related to the copper loss in the planar windings of 1-1 MHz power transformers are discussed. The relationship between current distribution, copper loss, and core geometry is investigated with the aid of finite-element analysis. Magnetizing current proximity effects are shown to cause excessive copper loss in a simple sandwich transformer, a structure formed by sandwiching the planar winding between two plates of magnetic material. Three alternative transformer structures that reduce this problem are compared. These alternative structures are: the cofired transformer, the slotted gapped transformer, and the slotted ungapped transformer. It is concluded that a slotted transformer design should be used if the magnetizing current is relatively large. Both a slotted gapped and a slotted ungapped design relies strongly on the exact permeability of the material and may suffer from higher core losses because all of the energy is stored in the magnetic material, rather than in an air gap. In either case, the depth of the slot should be About 40% of its width. >

D. C. to D. C. converter

Abstract: A d.c. to d.c. converter system converts a d.c. signal into a pulsating a.c. signal, which is applied to the primary of a power transformer. A transformer in which the primary and secondary windings are planar is employed to generate the output pulse signal. The planar transformer design provides the inductance required to filter the output signal and reduce the ripple therein, while simultaneously providing tight coupling between the primary and secondary windings. A single turn secondary winding is provided to reduce the number of turns in the transformer and thereby reduce the associated power loss.

Comparison of the square-wave and quasi-resonant topologies

Abstract: The waveforms of a square-wave DC-DC converter and a quasiresonant DC-DC converter are examined in detail and a comparison is made between the switching losses and conduction losses for each topology. Using data from commercially available semiconductor devices, conservative estimates are then given for the switching frequency at which the resonant approach becomes advantageous. The effect of an isolation transformer on this comparison is also addressed. >

Design of high-frequency hybrid power transformer

Abstract: Fabrication of a high-frequency power transformer/inductor using multilayer thick-film hybrid technology is presented. An experimental 6 MHz, 40 W miniature transformer is fabricated with windings printed on the ferrite substrate. Half of a conventional low-profile pot core is used to close the magnetic path. Issues related to power density, thermal management, and efficiency of this hybrid power-magnetic integrated circuit (HPMIC) are discussed. >

Capacitor switching and transformer transients

Abstract: The impact of capacitor switching on transformer transients is evaluated. Two specific transformer failure events are described. Each of these failures coincided with the switching of a capacitor bank some distance away from the transformer. The causes of these failures are evaluated, and field-test transient voltage waveforms are duplicated by computer simulations. The simulation capability is extended to determine system conditions that are susceptible to these transient voltages as well as the means to minimize them. >

Switching mode DC-to-DC power supply with improved current sensing

Abstract: A switching rectifier power supply circuit has a power MOS transistor connected in series with half of the primary of a center-tapped transformer, and has rectifiers in series with an inductive load on the secondary side. The gate of the power transistor is driven by a pulse source which is pulse-width modulated in response to the load voltage, and also controlled in response to the current through the power transistor. To prevent leading-edge current spikes due to turn-on of the power transistor from adversely affecting the pulse-width modulator, yet allow trailing-edge current spikes due to transformer saturation to be compensated for, an inhibit circuit is included in the control path responding to current through the power transformer.

High efficiency converter

Abstract: A new principle for high efficiency power conversion at high frequencies is described. The principle provides zero voltage switching by using the magnetising current of a transformer or parallel inductance to charge the switch adjunct capacitance and other capacitance during the dead time. The transformer is prevented from being loaded during the dead time. An embodiment of the invention is described where loading of the transformer during the dead time is prevented by directing the output inertial current to a capacitor instead of through the rectifiers to the secondary of the transformer. This can also be achieved by using synchronised rectification that provides pulse width modulated regulation on the output and ensures that the transformer secondary is separated from the inertial current of the output during the dead time. Voltage and current stresses on the switching devices and rectifiers are minimised. The principle may be applied to inverters where the load is resistive.

Implantable transformer for an artificial heart utilizing amorphous magnetic fibers

Abstract: It is a very serious problem for an implantable artificial heart to receive energy from outside the body. A new implantable transformer with a plain weave structure was proposed by using amorphous magnetic fibers. The transformer has the following features: (i) a thin, planar shape; (ii) high flexibility; and (iii) low waste heat in the range of several tens kHz. Appropriate conditions for the size of the transformer were shown experimentally. The transformer (70×30×1 mm3) of a trial design can supply a power of 6 W. The temperature rise of the transformer based on iron loss is considered to be negligibly small.

Ac power source device

Abstract: PURPOSE: To improve efficiency and to make a device small-sized and inexpensive by providing an LC filter by the use of the transformer leakage inductance and the capacity of the secondary winding and by regulating the slope of leading and trailing edges of the modulated trapezoidal pulse wave. CONSTITUTION: An AC power device connects a DC power source 14 between power terminals 12 and 13. The power terminal 12 is connected to the intermediate tap of the primary winding of a transformer 1. It is connected from the primary winding of the transformer to the other power terminal 13 through a pair of transistors(Tr) 2 and 3, while it connects regenerative diodes 7 and 8 to the Trs 2 and 3. High frequency pulses modulated so that the time ratio varies trapezoidal-wave-wise with respect to time are given from a pulse width control oscillator 4 to the bases of the Tr 2 and 3, which are operated to turn ON alternately. To both ends of the secondary winding of the transformer 1 a capacitor 15 is added. A resonance circuit is thereby dispensed with, so that the loss by DC resistance component and dielectric loss will extremely be reduced. COPYRIGHT: (C)1989,JPO&Japio

Telephone circuit using dc blocked transformer and negative impedance technique

Abstract: The invention provides a combination in a SLIC for telecommunication applications of ac impedance synthesis, e.g. raising the impedance of battery feed resistances by feedback techniques; in combination with real battery feed resistors and a dc block transformer. A dc blocked transformer is coupled to line current feed resistors and a feedback loop network to synthesize the desired input impedance, such that the feedback network incorporates both positive and negative feedback. A loop stabilizing resistor is used in shunt with the dc blocked transformer secondary to reduce gain peaking and phase shift. The transformer is an integral part of the feedback loop, and one of the outputs of the solid state circuitry are directly connected to the subscriber line, thereby eliminating the problem of lightning induced transients, in that the output stages of the solid-state operational amplifier circuitry of the invention are transformer isolated from the subscriber line, and are coupled to the subscriber line through high impedances providing high resistance isolation.

A complete study of the double forward-flyback converter

Abstract: A novel two-output DC-to-DC converter is studied. Using only a power transistor, both outputs have been regulated by controlling duty cycle and switching frequency. The number of power components is very low, as the use of demagnetizing components of the isolation transformer is avoided. A static and dynamic study of the converter has been carried out, and the results are verified for a prototype. >

Push-pull current-fed dc-dc converter

Abstract: A push-pull transformer of a push-pull current-fed DC-DC converter is arranged so that the inductance of the primary side of the transformer diminishes equivalently, thereby reducing a conversion loss attributable to a distributed capacitance of the transformer. To equivalently reduce the inductance of the primary side, for instance, a gap is formed in the core of the transformer and/or an inductor is connected in parallel to any one of the windings of the transformer.

Low-voltage-side current-surge phenomena in single-phase distribution transformer systems

Abstract: Lightning current surges entering the secondary windings of distribution transformers can be a cause of transformer failure. Proposed solutions have included interlacing the secondary windings and applying low-voltage arresters. Tests have been proposed to verify the ability of a transformer to withstand these surges. It is shown that the amount of current varies significantly for different sizes and designs of transformers, loads, and secondary cables. It is also shown that the entire secondary circuit must be treated as a system. Measures taken to protect the transformer generally increase the surge voltage stress on the load equipment. The source of the problem is the voltage drop along the secondary cable. Minimizing that voltage can effectively alleviate the problem of both transformer and load. These facts must be taken into consideration before developing transformer test standards to address the low-voltage-side current surge problem. >

Supply having a load invariant auxiliary power supply supplied from a main transformer and a current suppressing inductor

Abstract: Disclosed is a switching power source having a series connection composed of a main transformer, a current-suppressing inductance element, and a switching element and connected across a DC input power source, in which output windings are additionally wound on the main transformer and the inductance elements respectively and those output windings are connected in series to each other so as to form an auxiliary power source for a control circuit for driving/controlling the ON-OFF of the switching element, and a starting circuit is provided to supply power from the DC input power source to the control circuit only during the starting time of the switching power source.

Computation of current transformer transient performance

Abstract: A computer program for the calculation of the transient performance of a current transformer during short-circuit conditions is discussed. A numerical analysis that includes the dynamic hysteresis loops is used to calculate the performance, and results are compared with those of direct laboratory tests. The test methods, proposed in IEC Document 38 (Central Office) 78, are discussed. Results show the calculation can successfully replace expensive laboratory tests. >

Watthour meter with isolation transformers having a feedback loop

Abstract: A voltage transducer in a watthour meter, for sensing AC line voltage across a load, includes a current transformer having its primary winding connected in series with a current-limiting resistor across the AC source. The transformer includes a secondary coil and a tertiary coil. The current through the secondary coil represents the sensed voltage and is signal conditioned through an integrator circuit for input to a solid-state watt transducer chip. An active circuit is connected across the tertiary coil, with an output feeding a compensating current into the input of the secondary coil. The active circuit includes an RC network at the output of the tertiary coil for providing a loop stability. A first non-inverting op amp amplifies the voltage output from the RC network to provide a phase correction, adjustable by a replaceable resistor connected between the inverting node of the first op amp and an electrical ground. An intergrating op amp is connected between the output of the first op amp and the input to the tertiary coil to form a feedback circuit to reduce DC offset signals from the output of the first op amp. The primary coil of the current transformer is composed of an electric conductor wire coated with an electrically insulating layer to withstand impulse voltages of at least 6 kV.

Current density measurement system by self-sustaining magnetic oscillation

Abstract: A system for measuring parameters in an environment having a metallic body positioned in an electrolytic medium includes a current density sensing device positioned adjacent the metallic body in a non-invasive manner. The device is sufficiently sensitive to measure current density in the milliamp per square centimeter range. A housing is provided for enclosing at least a portion of the current density sensing device in an electrically and thermally non-conductive manner. A computer is used for processing the data from the current density sensing device and wiring is provided for electrically interconnecting the two. The current density sensing device, which can be used separately from the apparatus, includes a toroidal transformer and a square wave magnetically coupled oscillator which drives the transformer. A pair of multi-section low pass filters are provided for monitoring the transformer. A fixed gain differential instrumentation amplifier is utilized for processing an output of the transformer. The processed transformer output is proportional to a current sensed by the transformer.

Synchronous modulation circuit

Abstract: In pulse width modulation (PWM) power regulation and amplification circuits, separate DC rectification and filtering circuitry is eliminated by providing synchronous output switching directly from an available AC source. Output switch steering logic connected to an AC power source, such as a square wave AC signal available at the secondary of an isolation transformer, receives the PWM control signal that is developed by a conventional pulse width modulator in response to an input signal and causes an output switch stage to selectively and synchronously connect the alternating current power across the load with the proper timing and polarity. Preferably the output switching stage includes a low pass filter for filtering out the higher frequency switching transients.

Voltage resonance type switching power source apparatus

Abstract: In a voltage resonance type switching power source apparatus, which has a step-up transformer, a resonance capacitor connected in series with a primary winding of the transformer, and a transistor connected in parallel with the capacitor to cause a resonant oscillation current by the on-off operation thereof, an on signal of the transistor is produced in synchronism with a second signal, which is obtained by delaying a first signal depending on a voltage induced in a detecting winding provided in the transformer by a predetermined delay time.

RF transformer and diagnostic technique therefor

Abstract: An RF transformer employs at least three elongated conductive elements in generally parallel spaced relationship. At least a first inductive element is connected between a pair of the conductive elements to provide a desired field distribution. A diagnostic technique for determining the frequency shift of the transformer employs a perturbing object which is selectively longitudinally positioned within the transformer. The transformer has particular utility as an RF excited gas laser.

Analysis of a generator step-up transformer failure following faulty synchronization

Abstract: An analysis was carried out to investigate an out-of-phase synchronizing condition which resulted in the failure of a 725 MVA GSU (generator step-up) transformer. Using a technique described, the circuit breaker closing angle was estimated from oscillograph traces. This information was used with the Electromagnetic Transients Program (EMTP) to simulate the disturbance events and thereby produce a complete set of probable synchronizing currents and generator electrical torques experienced during the disturbance. The analysis of the simulation results, and the analysis of the failure of the GSU transformer have been viewed in light of the large number of prior system faults in the vicinity of the transformer. A review of the ANSI/IEEE standards on transformer fault withstand capabilities as related to this type of analysis is presented. >

Continuous, online monitoring of freestanding, oil-filled current transformers to predict imminent failure

Abstract: A power-factor-monitoring scheme used successfully to predict catastrophic failures of current transformers on the Tennessee Valley Authority's system is discussed. The method permits removal of the equipment from service before a failure occurs. Other monitoring and relaying schemes have also been evaluated, and the results are compared. >

Control circuit for a switching DC to DC Power converter including a multi-turn control transformer

Abstract: A control circuit for a power converter which includes a power transformer having a primary transformer winding for receiving an input voltage signal and a secondary transformer winding for generating an output signal provides control of the on and off time of the power transformer by utilizing a control transformer having a plurality of windings. A switch is provided which is coupled to the control transformer. The switch is conductive to render the power transformer on and when non-conducting renders the powder transformer off. Activacation of the switch is controlled through magnetic coupling between the windings of the control transformer to thereby render the output voltage of the power transformer constant while the switch on time remains constant and the switch off time is variable.

No-break current supply system

Abstract: A no-break current supply system working with high efficiency and high input power factor comprises a first converter (20) connected to a commercial AC mains (2) and delivering alternating current with predetermined voltage and the highest possible frequency to the input winding of a transformer (30). A second converter (40) is connected to an output winding of the transformer (30) and supplies a load (60) with alternating current having the desired voltage and frequency. The AC side of a current converter (50) is connected to a third winding of the transformer (30) which is isolated from the input winding and output winding, a back-up battery (10) being connected to the DC side of this current converter which, as required, acts as a rectifier for charging the battery or as a DC-AC converter for delivering energy from the battery to the load. Since the transformer (30) is driven at a frequency which is markedly higher than the mains frequency, the transformer can be constructed with small dimensions and low weight.

Notch gap transformer and lighting system incorporating same

Abstract: The invention is directed to a transformer having notch gaps extending partially across the flux path of the transformer core and having a total gap volume which stores sufficient magnetic energy to substantially eliminate inductive voltage spikes in a clipped sinusoidal waveform applied to the primary of the transformer. As used in a low voltage lighting system in which the intensity of a filament lamp is regulated by a dimmer control which selectively clips the voltage applied to the transformer primary winding by an ac source, the invention substantially eliminates filament ringing.

Spray-coating device

Abstract: A spray-coating device for spraying liquid or powdered coating material on articles includes a transformer for stepping up an alternating voltage and a voltage multiplier circuit for converting the output of the transformer to a high DC output for driving a charging electrode in the spray-coating device. The alternating voltage for the transformer is obtained from a controllable source of alternating voltage which produces a sinusoidal voltage whose frequency is constantly adjusted such that the voltage and current flowing through the transformer are in phase with one another. This assures that the transformer is operated at its resonant frequency.

Electrical power supply circuit, in particular for a wave generator for a pulse radar

Abstract: An electrical power supply circuit, in particular for a pulse radar wave generator, includes a chopper regulation circuit and a transformer which is fed from a low voltage source. The primary winding of the transformer of the circuit has a plurality of primary windings wound on a common transformer core. Each of the primary windings is connected to the low voltage source via an electronic power switch controlled by a voltage regulation signal at the repetition frequency of the radar pulses or at a multiple of the frequency. The transformer secondary includes a plurality of secondary circuits with their outputs connected in series between the very high voltage output terminals of the power supply circuit as a whole. Each secondary circuit includes a secondary winding wound on the common transformer core and connected in series with a rectifier connected to oppose the voltage induced by the primary current, together with a filter capacitor connected in parallel with the series circuit consituted by each secondary winding and each rectifier.

Circuit arrangement for operating a discharge lamp from a low voltage DC-voltage source

Abstract: The circuit arrangement for the radio-frequency operation of a discharge lamp (L) connected to a low-voltage DC source has a self-oscillating push-pull converter with two power transistors (T1, T2) and a drive transformer (Tr2), a series resonant circuit in parallel with the output circuit, having a resonant inductor (L1) and a resonant capacitor (C3), as well as a power transformer (Tr1) for the transmission of the radio-frequency oscillation of the push-pull converter into the series resonant circuit. The primary winding (n1) of the drive transformer (Tr2) for the push-pull converter is connected in series with the secondary winding (n3) of the power transformer (Tr1) in the series resonant circuit. The output current thus flows via the primary winding (n1) of the drive transformer (Tr2), resulting in continuous matching of the transistor control to the load conditions. In addition, a device to vary the time constants of the control circuits of the push-pull converter is provided, by means of which the lamp power is stabilised in the event of variations in the operating voltage. The device preferably consists of a transistor (T3) whose emitter-collector junction is connected in parallel with the real total resistance of the control circuits.

Method and apparatus for detecting a reduction in the input voltage to a power supply

Abstract: A scheme for detecting reduced source of voltage of a controlled switching power supply including a transformer employs the inherent insolation characteristics of the transformer to yield an isolated alarm signal indicative of a failed or inadequate source voltage.