Showing papers on "Isolation transformer published in 1981"

Electrosurgical generator safety apparatus

Abstract: Leakage cancelling apparatus suitable for use in electrosurgery apparatus to prevent electrical burns is disclosed. The apparatus comprises a transformer which is connected in the electrical circuit between the electrosurgical source and the patient. The transformer has a primary winding connected in series with the active surgical electrode and a secondary winding connected in series with the return path to the electrosurgical generator. The connections to the windings are polarized so that during normal operation the magnetic fields in the transformer core generated by current flow are almost completely cancelled. Consequently, the transformer windings present very small impedances in series with the electrosurgical circuit. If a break occurs in the return lead of the electrosurgical circuit and the patient becomes ungrounded, a condition which would normally result in a high risk of a burn, the currents in the primary and secondary windings of the transformer become unequal, the magnetic fields in the transformer core do not cancel and the transformer windings present a significant impedance to the flow of electrosurgical current which reduces the occurence of electrosurgical burns. In addition, the uncanceled inductance presented by the transformer windings during a break situation may be chosen to resonate with the leakage capacitance of the electrosurgical circuit, further reducing the current flow and preventing burns.

Lightweight electronic ballast for fluorescent lamps

Abstract: A lightweight, transistorized, inverter circuit is particularly adapted for starting and operating a screw-in compact fluorescent lamp intended for incandescent lamp replacement. Household-type AC is converted to DC with one terminal connected to the center tap of a transformer primary through a choke which constitutes a high impedance at the operating frequency. A tuned circuit capacitor is connected across the transformer primary and a current-limiting capacitor and the lamp to be operated are connected in series across the transformer primary. A pair of transistors are connected in push-pull arrangement between the end portions of the transformer primary and the other terminal of the DC source, with the base electrodes of the transistors connected to the transformer secondary winding so that the push-pull connected transistors oscillate at the tuned circuit resonant frequency which is determined by the inductance of the transformer primary winding and the total capacitance of the connected capacitor means. A potential is applied to the midpoint of the transformer secondary upon energization of the apparatus in order to initiate transistor conduction. The system operates with a high efficacy for the production of light.

Application of Superconducting Technology to Power Transformers

Abstract: We have developed a detailed conceptual design for a 1000 MVA, 500/22 kV line-to-line, 1300 BIL power transformer which uses superconducting windings. The design uses a multiple winding configuration which is current limiting under fault conditions. This conductor design and winding configuration result in an efficiency of the superconducting transformer of 99.85%. The savings in the cost of losses over the life of the transformer provide the economic-feasibility of this design approach.

No-break power supply

Abstract: An A.C. power supply conditioner uses semi-conductor diodes (D1) and (D2) and energy storage capacitors (C1) and (C2) to produce a high D.C. voltage which is inverted at (TR1) and (TR2) to provide an A.C. output (L0, N0) without use of isolating transformer. A standby battery system includes a low voltage battery 'B' a DC/AC/DC converter 'E', and a charger 'F'. The inverter may provide a high frequency square wave, pulse-width modulated to form an effective sine wave at input frequency. In the event of a fault, switch G may be automatically changed-over.

Current limiting power supply for electron discharge lamps

Abstract: A power supply including a high frequency inverter circuit coupled to an electron discharge lamp load through a special purpose transformer is disclosed The transformer is wound on a saturable ferromagnetic core structure forming a first magnetic flux path coupling the primary and secondary windings of the transformer and a second shunt magnetic path including an air gap which carries and increasing share of flux as load current increases The switching of the inverter circuit occurs in response to the partial saturation of the core Auxilliary windings serially connected with the primary winding of the transformer and wound about the shunt magnetic path enhance the current regulating properties of the supply

Self-oscillating DC to DC converter

Abstract: A self-oscillating DC to DC converter which includes either two or four transistors, three transformers (a converting transformer, a driving transformer and a current transformer) and an inductance. The operating frequency of the converter is fixed by the saturation time of the driving transformer. The base currents of the transistors are mainly supplied by the current transformer so as to be in proportion to the collector currents of the transistors. The operating frequency of the converter is kept constant in spite of load fluctuations. The inductance which is connected in series between a winding of the converting transformer and a winding of the driving transformer. The inductance prevents the two or four transistors from being `on` simultaneously.

Telephone line protection device for steep electromagnetic pulses - uses low pass LC filter with voltage dependent shunt impedances connected symmetrically in series and parallel with grounded chassis

Abstract: Two symmetrical conductors (8,9) link the input terminals (1,2) to respective inductors (14,15) and are connected by spark gaps (10,11) to the earthed screen between the two input stages (3,4). The inductors (14,15) are connected via feed-through insulators (18,19) into an output stage (6) contg. a low-pass filter (24) with 50 Hz cutoff frequency (for power line protection). The normal operating voltage (e.g. 220V) and current (100A) are passed without distortion, but perturbing pulses of higher frequency are greatly attenuated by Zener diode or voltage-dependent resistive shunts (20,21) at the filter input connections. A 10kV peak pulse with 10ns rise time is reduced to less than 100V at 1kV/microsecond at output terminals (33,34). Alternatively the two inductors are replaced by a screened 1:1 isolating transformer.

Electric insect trap power supply

Abstract: A power supply for an electric insect trap having an electrocution grid and a fluorescent lamp for attracting insects to the grid employs an inverter to generate a high frequency alternating voltage. The alternating voltage is applied across the primary winding of a first transformer having a secondary winding for development of a current-limited voltage for operating the lamp. Due to large inductance, the secondary winding functions as a constant current source to the lamp, so that lamps having different voltage characteristics may be used in the same circuit. A high voltage transformer has a primary driven by the limited lamp current to produce a high voltage for the electrocution grid across its secondary winding. Current limiting is achieved, in part, by providing a selected amount of flux leakage between the primary and secondary windings of the first transformer. Alternately, current limiting for the high voltage transformer output is achieved by providing the high voltage transformer core with a selected amount of flux leakage. A capacitor connected in parallel with one primary winding of the high voltage transformer functions to filter out harmonics of the alternating voltage frequency or to cause the transformer to operate in a ferro-resonant mode. When operating in a pseudo-ferro-resonant mode, saturable, toroidal transformers for providing drive and feedback to switching transistors in the inverter are thermally coupled with the high voltage transformer core. Those toroidal core transformers function to change the frequency of the alternating voltage applied to the high voltage transformer to offset changes in its output caused by temperature induced changes in the saturation limits of its core. A capacitor for AC coupling the high voltage to a lamp cathode causes a field to be created between the lamp and the electrocution grid to assist in starting the lamp.

Solid state off hook phone line load

Abstract: A direct connect telephone line interface which includes a solid state off hook phone line load is disclosed. The solid state off hook phone line load utilizes an active semiconductor device coupleable between the phone lines, with the control input to the active semiconductor device being coupled to a bias circuit operative from the voltage across the phone lines to bias the active semiconductor device in saturation as a result of an answer voltage on the phone lines. The bias circuit is frequency selective so that the bias point of the active semiconductor device is substantially independent of information signals on the telephone line. Thus the active semiconductor device, in combination with any impedance in series therewith to set the desired answer load on the telephone lines, provides the desired load impedance on the lines to maintain the connection, but at the same time provides a very high impedance to the AC signals (communication signals) on the line so as to not attenuate the communication signals subsequently coupled to an isolation transformer. This allows the reduction in the size of the isolation transformer normally used in such interfaces without requiring a separate, relatively large holding coil.

Effects of stray capacitances between transformer windings on the noise characteristics in switching power converters

Abstract: In switching-mode power converters, transformers are frequently used for the dc isolation between input and output terminals. The transformer has parasitic effects such as leakage inductances and stray capacitances of windings. These parasitic effects cause the complexity of noise problems in power converters. Particularly in the transformer with nonunity turns ration of windings, the description of the noise characteristics becomes more complicated due to the stray capacitances between windings. This paper presents a high-frequency equivalent circuit of the two-winding transformer with nonunity turns ration, and describes the noise transmission characteristics of a dc-to-dc converter with a transformer. Furthermore the extension of this equivalent circuit to the three-winding transformer and the cross-noise characteristics are discussed. The above discussion are followed by the experimental results.

Voltage sensing apparatus for a voltage regulating transformer

Abstract: An automatic voltage regulating transformer is provided which incorporates a potential transformer electrically disposed across its series windings, and a set of sensing windings disposed across its shunt windings to provide a voltage sensing network which is responsive to the flow of current both into and out of the transformer. The output of the potential transformer is connected in series with the sensing windings to provide a control voltage which is representative of the voltage across the shunt windings and series windings taken together. In the case of a normal voltage regulating transformer, this control voltage is proportional to the voltage across the output terminals. In the case of an inverted regulating transformer, the output voltage of the voltage sensing network is proportional to the voltage across the input terminals. In each case the same control voltage can be used to automatically operate the transformer whether or not current is flowing into or out of the input terminals of the transformer. In one embodiment the tertiary winding that is used to provide voltage to operate the tap changing mechanism of the transformer is also used to provide a voltage proportional to the voltage across the shunt windings.

DC High voltage generator for a dental X-ray photographing apparatus

Abstract: This disclosure relates to a DC high voltage generator disposed on the base which is adapted to freely move into and out of a casing and on which a high voltage transformer circuit is disposed. The transformer circuit comprises a variable magnetic leak transformer and capacitor type multiple boosting circuits disposed separately on the right and left sides of the transformer. The high voltage generator is compact, easy of maintenance and inspection and is excellent in insulating countermeasures and in efficiency.

Power supply and method utilizing applied current for increased hysteresis swing in transformer core

Abstract: Power supply and method in which the primary current to a transformer is switched on and off to maintain the output of the supply at a desired level. When the energizing current is off, an additional current is applied to the transformer to maintain the core at a level of magnetization such that the full hysteresis characteristic of the transformer is utilized during the next half cycle of operation.

Power supply housings for exterior light apparatus

Abstract: In a power supply housing having an annular flange, suspension means having a central opening therein is provided to be secured to said annular flange, and said suspension means is used to secure a power supply isolating transformer to the underside thereof such that the secondary socket of said transformer is positioned in the central opening of the suspension means for direct plug-in connection of a light source without need of a bipolar cable. An integral transformer construction is also disclosed for attachment to the suspension means as described.

Method and apparatus for providing signals from LTC transformer to electrical devices

Abstract: A method and apparatus for utilizing a load tap changing transformer as a control signal communicator.

High frequency power switching circuit

Abstract: Two power switching transistors have their emitter and collector connected together respectively. A high level DC voltage is connected across the transistors. The junction of the two transistors is connected by way of a load sensing resistor to a power bus and to the primary of an auxilary transformer. A secondary of the auxiliary transformer is coupled to the input of a transcondance limiting amplifier whose output is coupled to a drive amplifier. The output of the drive amplifier is coupled to the primary of a timing transformer. Two secondaries of the timing transformer are coupled to the two transistors respective for providing drive for the transistors. The auxiliary transformer, transconductance amplifier, drive amplifier, and timing transformer are coupled together in a positive feedback loop forming a high frequency oscillator with the two transistors for converting the DC voltage to a high frequency voltage. A symmetry control circuit is coupled from the secondary of the auxiliary transformer to the output of the transconductance amplifier. A boost transformer is provided having its primary connected across the load sensing resistor and its secondary connected in a series aiding configuration with the primary of the timing transformer.

Circuit for reducing voltage stress across a transformer

Abstract: Disclosed is a circuit for protecting a transformer from high voltages in those cases where a differential and a common mode output exist at the secondary of the transformer The differential output is a load having a relatively small voltage thereacross; the common mode output is an output terminal connected to said load and having a relatively high voltage applied thereto The present invention replaces the transformer with two or more smaller transformers cascaded together A resistor is connected between the primary and the secondary of each transformer Together the resistors form a voltage dividing network which splits the single high voltage among all of the transformers, relieving the stress on each Optional capacitors are connected in parallel across each of the resistors in the case where the interwinding capacitances of the transformers are not equal Each of the load and the output terminal can be either an ac or a dc component If the load is a dc component, a rectifier/filter is inserted between the secondary of the last transformer in the chain and the load

Low frequency converter with diode pair mixer

Abstract: A low frequency, diode pair mixer is provided in combination with simple, compact transformer circuitry. A diode mixer bridge has a pair of diodes interconnecting secondary windings of single and dual transformers. The diodes are connected in series across the secondary winding of the single transformer. The same polarity ends of the pair of secondary windings of the dual transformer are connected in common to a point between the diodes. The other ends of the pair of secondary windings are connected to respective ends of the secondary winding of the single transformer. The combination affords isolation between the signals coupled through each of the transformers. The combination may be implemented as an up converter or a down converter.

Control system for plural transformer relays

Abstract: A control system adapted to control a plurality of transformer relays. An electrical isolation network is coupled to each of a plurality of transformer relays, having a pair of common control lines and providing electrical isolation for each of the plurality of transformer relays. A switch is coupled to the electrical isolation network and is coupled in parallel to the plurality of transformer relays providing selection of state of all of the plurality of transformer relays. The electrical isolation network may also provide control, as e.g. unidirectional current flow, for selecting a state of each of the plurality of transformer relays. In a preferred embodiment the electrical isolation network includes an array of diodes.

Transformer with impedance matching means

Abstract: A transformer characterized by groups of low voltage and high voltage windings inductively related to a core member, and a shunt of magnetizable microlaminations disposed between the low and high voltage windings, whereby the shunts independently adjust the transformer impedance.

Current transformer high voltage probe utilizing copper sulfate water resistor

Abstract: A current transformer and copper sulfate water resistor are combined to provide a probe capable of measuring very fast, high voltage pulses. The resistor is connected in series with the primary winding of the current transformer and consists of an elongated plastic tube filled with an aqueous solution of copper sulfate. The series arrangement of resistor and current transformer primary winding is applied across the source of voltage to be measured and the current transformer secondary winding output is a function of the measured voltage. The current transformer secondary output is applied to and displayed on an oscilloscope.

Starting transformer for gas lamps with open secondary

Abstract: The specification discloses a starting transformer having a floating secondary. Coupling between the line and high voltage electrodes is effectuated through the distributed capacitance between the primary and secondary windings.

A programmable LF voltage ratio transformer using CMOS switches

Abstract: A programmable 12-bit voltage ratio device having a voltage rating of 0.1 times frequency and a terminal linearity error of less than 1×10-7 at 10-80 Hz is described. The compact design incorporates a 3-stage ratio transformer and it accommodates the use of solid-state switches having an ON-resistance of 100 Ω.

Direct-current arc welding apparatus with static members

Abstract: The direct-current arc welding apparatus which can be connected to the alternating-current supply network has a bridge rectifier (5), to the output of which a line having two controlled diodes (6, 7) connected in series and the primary winding (8a) of an isolating transformer (8) is connected. A further controlled diode (13) is connected in parallel with the primary winding (8a). Connected to the secondary winding (8b) of the transformer (8) is a line with a voltage rectifier (18) and voltage-smoothing means (20), at whose output the consumer connecting terminals (3a) are situated. In this line there is a resistor (3b), to the terminals (21a, 21b) of which a control circuit with pulse amplifiers and converters is connected, by means of which the switching-on and switching-off of the series-connected, controlled diodes (6, 7) and of the further diode (13) is controlled as a function of the voltage or the current at the consumer connecting terminals (3a). By a circuit of this type, the problem of achieving the following desired aim is solved: - the laying and operating costs of the electric control circuits are reduced; - the upper limit of the frequency delivered by the frequency transformer is widened; - the current losses due to the discharge of the magnetic energy are reduced.

Television receiver high frequency regulated power supply including a low voltage ferroresonant transformer coupled to a step-up high voltage transformer

Abstract: A source of high frequency alternating input voltage is coupled to the primary winding of a high frequency low voltage ferroresonant transformer of a television receiver power supply. A capacitor is coupled across the secondary output winding of the ferroresonant transformer, and generates a circulating current that magnetically saturates the secondary core portion of the transformer to regulate the alternating polarity output voltage developed across the secondary output winding. A step-up high voltage transformer includes a primary winding and a high voltage secondary winding tightly coupled to the step-up transformer primary winding. The regulated alternating polarity output voltage developed by the low voltage ferroresonant transformer is coupled to the primary winding of the step-up high voltage transformer without prior DC rectification of the ferroresonant transformer output voltage. The applied, regulated ferroresonant transformer output voltage develops a regulated high voltage across the step-up transformer high voltage secondary winding. A high voltage rectifier arrangement develops an ultor voltage from the regulated high voltage.

Parallel-Plate Windings Transformer for Pulsed Power Applications

Abstract: : Two sizes of the parallel-plate windings transformer with 10:1 step down turns ratios have been designed, tested at 10 kV, 500 kA, installed and have now been operating for several months in the ZT-40 RFP experiment at Los Alamos. The total leakage inductance for these three turn secondary transformers referred to the secondary has been measured at 9 nh for the larger transformer and 8 nh for the smaller transformer. Since these transformers were designed for use with a load having relatively high d.c. resistance, the d.c. resistance of aluminum windings was acceptable.

An electrical power supply

Abstract: A power supply circuit comprises: an input choke (30) having one end connected to one side (28) of a DC supply source connection from a bridge (20); a transformer (34); and a circuit loop connected between another end of said input choke (30) and another side (38) of said DC supply source connection. This circuit loop includes a series connection of a capacitor (36), a switching device (44) and a primary winding (32) of the transformer (34). The switching device (44) includes a controlled conduction path and a control input (49) for rendering the conduction path conductive. The capacitor (36) is arranged to be charged primarily by the DC supply source bridge (20). There is provided a resistive-capacitive trigger circuit (54, 56, 58) connected between the DC supply source bridge (20) connection and the control input (49) for repetitively rendering the switching device (44) conductive at a predetermined repetitive rate so as to repetitively discharge the capacitor (36) through the primary winding (32). The transformer (34) includes a secondary winding (64) and has a predetermined turns ratio between the secondary winding (64) and the primary winding (32). The power supply circuit further comprises output circuit means (72, 78) for rectifying and filtering the output of the secondary winding (64) to provide the output of the power supply circuit.

Minus 35kV Space-Borne Instrument Power Supply

Abstract: A -35kV power supply has been developed for a plasma experiment on the out-of-ecliptic mission. In addition, an isolation transformer has been developed to provide low voltage power at the -35kV potential. The design features incorporated to produce a spaceflight power supply housed within a 4 × 4 × 2.5 in package are discussed. The supply is powered from an unregulated spacecraft bus and provides a regulated output of -35kV ± 5 percent with less than 0.5 percent ripple over a temperature range -20°C + 60°C. The unit serves as a bias supply with an output current less than 0.5 , ?A. With the supply essentially operating unloaded, 5 percent regulation is achieved by sensing and regulating the first stage of a 12-stage Cockcroft/Walton multiplier. Control of the ac voltage input to the multiplier stack provides the regulation. The isolation transformer utilizes a ferrite u-core with the primary and secondary windings placed on opposite legs for separation. The transformer is encapsulated with the power supply.

Inductive voltage transformer and circuit therefor

Abstract: Disclosed are an inductive voltage transformer having a primary winding connected to a network line and a protective circuit therefor. In order to prevent a large thermal and mechanical stress in such a transformer, the protective circuit comprises a control unit which controls a switching device for connecting a circuit arrangement to a secondary winding of the voltage transformer. The circuit arrangement includes a current generating circuit with a charging capacitor. The protective circuit operates to generate a current causing a counter excitation in the transformer to that caused when the capacitance of the network line is discharged via the primary winding of the transformer. The voltage transformer and the protective circuit are suited particularly for connection to network lines having a large internal capacitance.