Showing papers on "Isolation transformer published in 1992"

Power conditioning device and method

Abstract: A power conditioning device protects sensitive electronics in modern electronic equipment from disruption or destruction caused by transients which can cause both induction and injection currents into the grounding system of the electronic equipment. This device nominally comprises an isolation transformer and a ground impedance between the earth ground connection from a distribution panel and the safety ground connection to the powered equipment. In addition, this device may also comprise a voltage clamping device such as an MOV and a capacitive filter to provide a complete power line conditioner. This device may be used in systems with guarded or driven grounds, or in a system with a high voltage reference to safety ground. In addition, ground conditioning can be added to a Ground Fault Circuit Interrupter (GFCI) to attenuate ground surge currents. The ground impedance may take many forms, including inductors, resistors, diodes, gas tubes, transformers, capacitors, or combinations of these or other components. The ground conditioning device may be used on power systems of different voltages and frequencies, including three phase power systems.

Novel zero-voltage-switching family of isolated converters

Abstract: An isolated zero-voltage-switching converter in which the magnetizing inductance of the isolating transformer is a resonant element and an open circuit is provided on the secondary side of the transformer during the time interval when both primary switches are off. When the secondary of the transformer is open, the magnetizing inductance is in series with the capacitances of the primary switches, thus forming a resonant circuit.

Zero voltage switching power converter

Abstract: A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch is disclosed. The power converter includes a transformer having a primary winding and a second winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch. A second switch means is connected in series with the secondary winding of the transformer and is operated to prevent the loading effects of the secondary from interrupting the creation of the zero-voltage switching condition.

Electrical protective device for electro-medical appts. - contains isolation transformer and resistive insulation monitor with safety switching

Abstract: The device for protecting against contact currents consists of an isolation transformer (TR) and an insulation monitor (IU). The protected person (P) is connected via a resistor (R3) to the centre tapping of a potential divider (R1,R2) which is connected to the transformer secondary. A current change in the three resistors caused by a single or double insulation failure triggers a warning signal and/or the switching off of the device and/or the activation of a redundant protection device. ADVANTAGE - Ensures safe operation of one or more electrical devices irrespective of local safety measures and ambient conditions.

Class E resonant low dv/dt rectifier

Abstract: A class-E resonant low dv/dt rectifier is analyzed and experimentally tested. All major parasitic reactive components are included in the rectifier topology. The diode capacitance and the leakage inductance of the isolation transformer and lead inductances are absorbed into the resonant inductance. Therefore, the rectifier is suitable for high-frequency applications such as resonant DC-to-DC converters. The rectifier is driven by a sinusoidal voltage source. Equations governing the circuit operation are derived using Fourier techniques. Experimental results are obtained at 1 MHz and an output voltage of 5 V. The design equations show good agreement with the measured circuit performance. >

2 MHz power converter with piezoelectric ceramic transformer

Abstract: A power converter with a new piezoelectric transformer is presented. The piezoelectric transformer, made of lead titanate solid solution ceramic, is operated with a thickness extensional vibration mode. This transformer can operate at high frequency, over several megahertz, with about 90% efficiency. The resonant frequency for the transformer is 2 MHz. The power converter with the transformer applies the theory for a class-E switching converter using an electromagnetic transformer. Maximum output power is obtained when the switching frequency is slightly higher than the resonant frequency. A 4.4 W output power is successfully obtained with 52% efficiency at 2.1 MHz switching frequency. >

Method and apparatus for a cardiac defibrillator high voltage charging circuit

Abstract: A variable rate defibrillator charging circuit includes a power transformer that accepts an internal battery output and the output from an AC-to-DC converter on separate primary windings. The secondary winding of the transformer is coupled through a rectifier to a storage capacitor. The transformer operates in a fly-back mode whereby energy is discharged into the storage capacitor when the power supplies discontinue charging the transformer. After energy in the transformer is discharged into the storage capacitor, the power supplies are reactivated, recharging the transformer. The separate primary windings of the transformer provide a fast, reliable, low cost means for charging the storage capacitor with multiple power supplies. The AC power source feeding the AC-to-DC converter is detachable allowing the defibrillator to be operated remotely whereby the storage capacitor is charged solely from the internal battery. The charging circuit monitors the output voltage levels of both the battery and the AC-to-DC converter and enables or disables the power supplies in accordance to their ability to charge the storage capacitor within a predetermined amount of time. The energy in the storage capacitor, which is eventually discharged into a patient, is monitored to prevent overcharging.

High efficiency floating gate driver circuit using leakage-inductance transformer.

Abstract: A gate driver for turning on and turning off a power switching device (118) having a capacitive gate control input (162) provides galvanic isolation between low-level control circuitry (122) and the power switching device by means of a transformer (104) having a controlled amount of effective secondary leakage inductance. The secondary (108) of the transformer is connected in series with the gate control input (162) and a first unidirectional conducting device (110). Driver logic on the secondary side of the transformer controls a gate switch which is connected across the gate control input. The gate driver operates in a multiplexed mode: if a voltage pulse is applied across the primary winding (106) of the transformer at a time when the power switching device is off the driver logic will turn the gate switch off, thereby enabling charging of the effective gate capacitance (116) as a means of turning the power switching device on; if a voltage pulse is applied across the primary winding of the transformer at a time when the power switching device is on the driver logic will turn the gate switch on, thereby discharging the effective gate capacitance as a means of turning the power switching device off.

Zero voltage switching power converter with secondary side regulation

Abstract: A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch and to regulate the output voltage is disclosed. The power converter includes a transformer having a primary winding and a secondary winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch. A second switch means is connected in series with the secondary winding of the transformer and is operated to prevent the loading effects of the secondary from interrupting the creation of the zero-voltage switching condition. A secondary side regulation circuit is included to both regulate the output voltage and to prevent the loading effects of the secondary circuit from interfering with zero-voltage switching in the primary circuit.

Transformer-less hybrid circuit

Abstract: An improved transformer-less electronic isolating transformer is obtained with an output subcircuit that outputs a controlled current rather than voltage. Specifically, the improved hybrid comprises an output drive subcircuit that receives an ac signal and creates a corresponding current that is passed to the line that supports two way communication. The subcircuit not only converts the applied voltage to current but includes means for effecting gain. Signals arriving to the hybrid from the line are applied directly to a near-end echo circuit that is also responsive to the signal applied to the output drive subcircuit. Both the input of the output drive subcircuit and the output of the near-end echo subcircuit are isolated with opto-isolators that employ photodiodes in their photo-voltaic mode.

Design issues for the transformer in a low-voltage power supply with high efficiency and high power density

Abstract: Circuit model, design feasibility, and design tradeoffs are investigated for the transformer in 1.5-5 V power supplies with high efficiency and high power density. The transformer is constructed from a single or a matrix of pot cores and from interleaved planar windings. It has been determined theoretically and verified experimentally that such a transformer is realizable as long as the loss constraint is not severe (e.g. less than 0.5 W transformer loss per 100 W output). The primary source of loss is the winding, not the core, in 1.5 V/turn design. Measures to reduce the transformer height tend to increase transformer loss or volume. >

Ground fault detector and associated logic for an electronic ballast

Abstract: An embodiment of the present invention is a lighting system including a sense transformer with two primaries and a secondary for receiving alternating current (AC) from a power source, a low ohmage resistor placed across the sense transformer secondary winding for preventing saturation of the core of the sense transformer, an analog comparator for detecting when ground-fault signals in the sense transformer secondary winding exceed a threshold voltage and digital counters for testing whether or not a ground-fault condition persists longer than three consecutive half-cycles of the received alternating current from the power source.

Constant frequency ZVS converter with integrated magnetics

Abstract: The author introduces a high-frequency DC-DC converter which provides zero-voltage-switching (ZVS) and allows control of the output by pulse width modulation (PWM) at constant frequency. The topology is very tolerant to leakage inductance in the isolating transformer, and it is possible to combine the transformer and filter choke into a single integrated magnetic assembly yielding several additional benefits. The converter has been operated with ZVS to reduce losses at the switching transition, and this has allowed high-frequency operation even with high frequency and high input voltage. A control scheme has been defined whereby constant frequency operation and PWM produce a linear control to output transfer function with minimal interaction of load. >

Power factor matching in an ac power meter

Abstract: A solid-state AC energy consumption meter includes an array of AC signal transducers which provide voltage and current signals to a watt transducer chip. The watt transducer chip operates on the multi-phase voltage and current signals to produce AC energy consumption data which is fed to a register for visual display. In one aspect of the invention, a calibrating resistive component is placed in series with the input to the primary coil of the potential transformer for each phase. The value of the resistive component is calibrated to produce an appropriate change in the phase angle difference between the potential transformer secondary voltage and current transformer secondary current. More particularly, the addition of the resistance of the primary of the potential transformer provides the necessary amount of phase lead to the potential transformer to account for this phase error difference.

Switching power source device

Abstract: A switching power source device includes a rectifying smoothing circuit made up of a full-wave rectifier 2 and a small-capacity capacitor 3, a resonance frequency controlled type resonance converter circuit 4 having a controlled resonance frequency, a power source regulating transformer 7 having a primary winding N 1 , a secondary winding N 2 insulated from the primary winding N 1 , and a control winding at right angles to the primary and secondary windings, a controller 9 for controlling the controlling current of the power source regulating transformer 7 and a rectifying smoothing capacitor 8 determining the ripple voltage of the dc output voltage from the power source regulating transformer 7 in conjunction with the load power. With the switching power source device, the harmonic distortion in the ac input current is diminished and the ac input voltage is improved to a sinusoidal wave.

Transformer driver having unlimited duty cycle capability by inserting narrow pulses during unlimited duty cycles

Abstract: A transformer driver having an unlimited duty cycle capability is disclosed herein. The transformer driver 10 of the present invention is coupled to an output circuit 20 and includes a transformer 32 having primary winding and secondary windings 30 and 34. The inventive driver 10 further includes a generator 26 for applying a plurality of charging pulses P1, P2 to the primary transformer winding 30 to keep the transformer from being saturated. A transistor buffer network 36 selectively electrically isolates the output circuit 20 from the transformer. In a particular embodiment the charging pulses P1, P2 serve to maintain the voltage at the control terminal 38 of a power transistor included within the output circuit.

Protective snap-together enclosure for current transformers

Abstract: There is provided an enclosure that encapsulates a current transformer by utilizing a snap together design while allowing for electrical coupling between the transformer and external wiring. Two housing members will snap together while capturing the transformer in a rigid fashion to avoid excess vibration or friction, which could fatigue the transformer's wiring.

Power factor correction circuit for ac to dc power supply

Abstract: A saturating inductor or transformer is used to shape input current flowing into an alternating current (AC) to direct current (DC) power supply to correct the power factor for the supply. If a saturable inductor is used, it is connected to feed current into the power supply and a capacitor is connected across the input of the power supply. The capacitor precharges the saturable inductor to a point just short of saturation during a preliminary portion of each sinusoidal half cycle of the input AC power. For steady state operation, this is the point at which current will start to flow into the AC to DC power supply and the inductor will saturate. Since the inductance falls in accordance with a permeance curve characteristic of material used to construct the inductor, the current will continue to flow at the same or an increasing level despite the declining voltage level of the AC input power. In the final portion of each half cycle of the input AC power, power stored in the inductor and capacitor discharges into the power supply to extend the current flow beyond its normal point of termination. If a saturable transformer is used, it is connected to feed current into the power supply through a secondary winding of the transformer with a primary winding of the transformer being connected to a common low voltage or ground of the source of AC power and the AC to DC power supply either directly or through primary current control means. For this embodiment, transformer action boosts the voltage level applied to the AC to DC power supply which also serves to precharge the secondary winding. As the current builds, the transformer nears saturation toward the peak of the input voltage waveform. Operation is similar in that current continues to flow or even increase during a portion of the declining voltage of the input power due to the reduced inductance caused by saturation of the transformer.

Apparatus for efficient remote ballasting of gaseous discharge lamps

Abstract: A ballast apparatus for starting and operating a gaseous discharge lamp which allows operation of the lamps at frequencies in excess of 10 kilohertz and at a predetermined distance from the power supply comprising a frequency adjustable high frequency power supply and suitable current limiting means connected to the primary winding of an isolation transformer comprising at least a primary winding and first and second secondary windings arranged in a center tapped secondary configuration and wound to minimize interwinding capacitance, a low capacitance power transmission cable having an input end and an output end comprising a first and second conductor with insulation means and an outer sheathing conductor surrounding said first and second conductor and insulated from both said conductors connected with the input end of said first and second conductors connected to the first and second secondary windings respectively of said isolation transformer and the sheathing conductor connected to the center tap of said isolation transformer, the output end of said power transmission cable is connected with the first conductor connected to one end of a gaseous discharge lamp and the second conductor connected to the other end of said gaseous discharge lamp.

Technique to drive transformer coupled line amplifier

Abstract: The invention relates to a circuit for driving a transformer coupled line amplifier. The present invention uses a high impedance differential negative feedback from the secondary of the transformer and uses positive feedback from the primary winding of the transformer. This enables the transformer to be smaller in size while still reducing the harmonic distortion, improving the frequency response, eliminating ringing, lowering the output impedance, improving the longitudinal balance, and also improving the overall stability and phase response of the transformer.

Circuit with nonlinear transformer allowing DC current measurements via an isolation gap

Abstract: A sensor circuit allowing the measurement of DC current via an isolation gap is investigated. The primary coil of a nonlinear transformer and an operational amplifier are connected into an RL-multivibrator circuit. The measured DC current is applied to the secondary of this transformer. The DC voltage at the inverting mode of the operational amplifier gives information on the polarity and value of the measured current. The sensor transfer characteristics are calculated using piecewise approximation of the core magnetization characteristic, and experimentally verified. >

Monitoring and control apparatus and method

Abstract: A computer network (10) using half-duplex communication to transmit digital data, including commands, addresses and responses, and power over a single MCI NETCON communication line (40). The network provides isolation to prevent a malfunctioning network device (28) from adversely affecting the system. Each device connected to the network includes an isolation transformer (58) to decouple devices with short circuit occurrences from properly functioning devices, permitting the network to continue to operate. A power-data balancing mechanism (56) reduces net dc-imbalances from the system, allowing cool and reliable operation of the transformers. Additionally, use a dynamic snubber (114) coupled to a power-data transmitter reduces inductive ringing in the network, improving power-data throughput.

On-line monitoring of electrodynamic effects on power transformers windings

Abstract: A strategy for protecting power transformers, based on the possibility of taking measurements on machines under real operating conditions, is discussed. A measurement technique for determining the online variations of stray reactance of transformers due to short-circuit events is reported. This parameter can be indicative of winding geometry; hence it makes possible the setting up a diagnostic system that provides useful indications of conductor insulation reliability. This method is suitable, with the proper choice of measuring device constants, not only for identifying core and winding losses, but also for determining the changes of short-circuit reactance of the transformer. >

Passive sensor for measuring rotation rate of vehicle wheel bearing - comprises winding with low number of turns coupled to step=up voltage transformer

Abstract: The passive sensor (15) is connected to a voltage changer, voltage transformer or voltage step-up device. The voltage transformer is arranged inside a connector which connects the measurement coil to a central supply. Alternatively, the transformer can be positioned near the measurement coil. The windings forming the measurement coil are made in the form of a printed circuit of one or more layers. USE/ADVANTAGE - For measuring the rotational speed between two relatively rotating parts, e.g. rings (10, 11) of vehicle wheel bearing. Minimal size in axial direction.

Circuit for operating a fluorescent lamp with a current measuring circuit

Abstract: of EP0589081A series-resonant circuit having a first winding of a feedback transformer (Tr1.1), having a resonance inductor (L1), having a coupling capacitor (C1), having a first lamp cathode (LK1), having a resonance capacitor (C2) and having a first winding of an isolating transformer (Tr4.1) is formed in the circuit arrangement for supplying a fluorescent lamp (LL) and is connected between the output of an invertor, which operates on a supply voltage (Ub), and one pole of the supply voltage (Ub). The second coupling of the isolating transformer (Tr4.2) is connected in parallel with the second lamp cathode (LK2). As a result of this circuitry of the second lamp cathode (LK2), the same currents Iheat flow through the two lamp cathodes (LK1, LK2) with the same number of windings of the windings of the isolating transformer (Tr4.1, Tr4.2), and in consequence the same heating of the two lamp cathodes (LK1, LK2) is achieved. The parallel circuit formed by the second lamp cathode (LK2) and the second winding of the isolating transformer (Tr4.2) is connected to one terminal of the supply voltage Ub, via a resistor (R1), at a potential. The lamp current IL flows through the resistor (R1). The voltage dropped across the resistor (R1) is thus proportional to the actual value of the lamp current Iact and can thus be supplied to the main circuit (HS), which is also provided for regulating the lamp current.

A study of push-pull parametric transformer

Abstract: The parametric transformer has voltage regulation, overload protection, and a kind of filter function for harmonic currents produced by nonlinear loads. The operating characteristics of the push-pull parametric transformer with resistive load are discussed. Furthermore, the authors demonstrate the operation of the push-pull parametric transformer with a thyristor rectifier circuit as an example of a nonlinear load. The authors propose an application of the transformer as a power supply for suppressing higher harmonic currents produced by nonlinear loads such as the thyristor rectifier circuit. >

Switched-mode converter with energy recovery

Abstract: The converter, with current isolation, includes an isolating transformer (Tr), the primary winding (1) of which is connected in series with a semiconductor switch (4). Upon opening the switch (4), the current (Ip) flowing in the primary winding charges a storage capacitor (3). A switch (6), when it is closed, makes it possible to recover the energy stored in the capacitor (C3), at the primary winding. This makes it possible to recover the energy held in the leakage inductances of the transformer.

Pulse transmission circuit with undershoot eliminating circuitry

Abstract: An undershoot eliminating circuit is provided between a pulse transformer of a pulse transmitter coupled to a transmission line and a pulse transformer driving circuit for driving the pulse transformer. The pulse transformer driving circuit has an impedance high enough to cause the pulse transmitter to be substantially isolated from the transmission line. The undershoot eliminating circuit includes a capacitor, and a switching unit. The switching unit is connected to the capacitor, and has the function of selectively connecting the capacitor to the pulse transformer driving circuit and the pulse transformer in parallel on the basis of a voltage based on a pulse wave generated by the pulse transformer driving circuit and applied across the switching unit.

Fixed-voltage thyristor convertor rolling-stock transformers to control DC traction motors

Abstract: The more recent use of power thyristors on AC railway vehicles, with their facility for controlling the DC output, has simplified the traction transformer in that it need only be of a constant ratio. However, the demands of the thyristor circuit designer can still impose some transformer design problems, particularly when a variety of different output windings are required. The mechanical arrangement of modern traction transformers demands more compact integral units, with the transformer and its accessories contained in as small an envelope as possible. As a result of experience gained both from type tests on new designs of traction transformer, as well as operating experience on older designs, it is possible to achieve greater compactness, still using conventional transformer materials.

Multi-system energy supply for train carriage - uses transformer with two primaries supplied via pulse width modulation DC-AC converter

Abstract: The energy supply has a transformer (13) with 2 primary windings coupled via a DC/AC converter (7..9, 14, 15) with controlled thyristors (14, 15) to a rectifier (6), in turn coupled to the current collector rails (ZS). The thyristors (14, 15) are each coupled to a firing and extinction device (36, 37) providing pulse width modulation control, to allow the secondary voltage provided by the transformer (13) to be held constant. - Pref. the transformer secondary voltage is supplied to main and auxiliary heating devices (21, 22).