Showing papers on "Voltage drop published in 2005"

Switched constant current driving and control circuit

Abstract: The driving and control device according to the present invention provides a desired switched current to a load including a string of one or more electronic devices, and comprises one or more voltage conversion means, one or more dimming control means, one or more feedback means and one or more sensing means. The voltage conversion means may be a DC-to-DC converter for example and based on an input control signal converts the magnitude of the voltage from the power supply to another magnitude that is desired at the high side of the load. The dimming control means may comprise a switch such as a FET, BJT, relay, or any other type of switching device, for example, and provides control for activation and deactivation of the load. The feedback means is coupled to the voltage conversion means and a current sensing means and provides a feedback signal to the voltage conversion means that is indicative of the voltage drop across the current sensing means which thus represents the current flowing through the load. The current sensing means may comprise a fixed resistor, variable resistor, inductor, or some other element which has a predictable voltage-current relationship and thus will provide a measurement of the current flowing through the load based on a collected voltage signal. Based on the feedback signal received, the voltage conversion means can subsequently adjust its output voltage such that a constant switched current is provided to the load.

Current measurement by real-time counting of single electrons

Abstract: The fact that electrical current is carried by individual charges has been known for over 100 years, yet this discreteness has not been directly observed so far. Almost all current measurements involve measuring the voltage drop across a resistor, using Ohm's law, in which the discrete nature of charge does not come into play. However, by sending a direct current through a microelectronic circuit with a chain of islands connected by small tunnel junctions, the individual electrons can be observed one by one. The quantum mechanical tunnelling of single charges in this one-dimensional array is time correlated, and consequently the detected signal has the average frequency f = I/e, where I is the current and e is the electron charge. Here we report a direct observation of these time-correlated single-electron tunnelling oscillations, and show electron counting in the range 5 fA–1 pA. This represents a fundamentally new way to measure extremely small currents, without offset or drift. Moreover, our current measurement, which is based on electron counting, is self-calibrated, as the measured frequency is related to the current only by a natural constant.

Achieving high-current carbon nanotube emitters.

Abstract: When a carbon nanotube emitter is operated at high currents (typically above 1 μA per emitter), a small voltage drop (∼few volts) along its length or at its contact generates a reverse/canceling electric field that causes a saturation-like deviation from the classical Fowler−Nordheim behavior with respect to the applied electric field. We present a correction to the Fowler−Nordheim equation to account for this effect, which is experimentally verified using field emission and contact electrical measurements on individual carbon nanotube emitters. By using rapid thermal annealing to improve both the crystallinity of the carbon nanotubes and their electrical contact to the substrate, it is possible to reduce this voltage drop, allowing very high currents of up to 100 μA to be achieved per emitter with no significant deviation from the classical Fowler−Nordheim behavior.

LED light source for backlighting with integrated electronics

Abstract: An LED backlight structure and technique for setting the voltages and currents for the LEDs are described. In one embodiment, red LEDs are connected in series between a first voltage regulator and a first controllable current source, green LEDs are connected in series between a second voltage regulator and a second controllable current source, and blue LEDs are connected in series between a third voltage regulator and a third controllable current source. The current sources may linear current regulators. After all the LEDs are mounted on a printed circuit board, each voltage regulator is controlled so that there is a minimum voltage drop across the current source to minimize energy dissipation by the current source. Also, after all the LEDs are mounted on the printed circuit board, the current sources are controlled to balance the three colors to achieve a target light output of the board using a light detection chamber. In another embodiment, a constant current source is connected to the series string of LEDs. PWM controllers control transistor switches connected in parallel across groups of LEDs, where the duty cycles set the average current through each group of LEDs. The control values used to achieve the target light characteristics are then stored in a memory on the board. With such a technique, LEDs do not need to be binned to match their efficiencies, since the controllable voltage and current sources compensate for the variety of LED efficiencies. Accordingly, all boards will have the same target light output using the particular values stored on each board. In other embodiments, not all the LEDs of a particular color are connected in series. The brightness levels of the LEDs may be further controlled by a PWM controller. The backlight may be for an LCD television or other color display.

Electrode dependence of resistance switching in polycrystalline NiO films

Abstract: We investigated resistance switching in top-electrode/NiO∕Pt structures where the top electrode was Au, Pt, Ti, or Al. For Pt∕NiO∕Pt and Au∕NiO∕Pt structures with ohmic contacts, the effective electric field inside the film was high enough to induce trapping or detrapping at defect states and thus resistance switching. For a Ti∕NiO∕Pt structure with well-defined Schottky contact at Ti∕NiO interface accompanied by an appreciable voltage drop, the effective electric field inside the NiO film was not enough to induce resistance switching. For an Al∕NiO∕Pt structure with a low Schottky barrier at the Al∕NiO interface, resistance switching could be induced at a higher voltage since the voltage drop at the Al∕NiO interface was not negligible but small.

Effect of scattering and contacts on current and electrostatics in carbon nanotubes

Abstract: We computationally study the electrostatic potential profile and current carrying capacity of carbon nanotubes as a function of length and diameter. Our study is based on solving the nonequilibrium Green’s function and Poisson equations self-consistently, including the effect of electron-phonon scattering. A transition from the ballistic to diffusive regime of electron transport with an increase of applied bias is manifested by qualitative changes in the potential profiles, differential conductance, and electric field in a nanotube. In the low-bias ballistic limit, most of the applied voltage drop occurs near the contacts. In addition, the electric field at the tube center increases proportionally with diameter. In contrast, at high biases, most of the applied voltage drops across the nanotube, and the electric field at the tube center decreases with an increase in diameter. We find that the differential conductance can increase or decrease with bias as a result of an interplay of nanotube length, diameter, and a quality factor of the contacts. From an application viewpoint, we find that the current carrying capacity of nanotubes increases with an increase in diameter. Finally, we investigate the role of inner tubes in affecting the current carried by the outermost tube of a multiwalled nanotube.

Voltage stability in weak connection wind farms

Abstract: The total operating wind power capacity in the world increases fast, and these types of generating units also bring new opportunities and problems to the utilities and customers. It becomes necessary and important to evaluate their impact on the electrical network voltage stability, especially for weak connected systems. This paper uses the detailed wind energy conversion system and the full order induction generator model to analyze the voltage stability in a weak connection wind farm. The possibility of network voltage drop and instability are investigated by the detailed electromagnetic transient simulation program. Some techniques to improve the transient response of voltage are also discussed.

Electric Power Distribution Equipment and Systems

Abstract: FUNDAMENTALS OF DISTRIBUTION SYSTEMS Primary Distribution Configurations Urban Networks Primary Voltage Levels Distribution Substations Subtransmission Systems Differences between European and North American Systems Loads The Past and the Future References OVERHEAD LINES Typical Constructions Conductor Data Line Impedances Simplified Line Impedance Calculations Line Impedance Tables Conductor Sizing Ampacities Secondaries Fault Withstand Capability Other Overhead Issues References UNDERGROUND DISTRIBUTION Applications Cables Installations and Configurations Impedances Ampacity Fault Withstand Capability Cable Reliability Cable Testing Fault Location References TRANSFORMERS Basics Distribution Transformers Single-Phase Transformers Three-Phase Transformers Loadings Losses Network Transformers Substation Transformers Special Transformers Special Problems References VOLTAGE REGULATION Voltage Standards Voltage Drop Regulation Techniques Regulators Station Regulation Line Loss and Voltage Drop Relationships References CAPACITOR APPLICATION Capacitor Ratings Released Capacity Voltage Support Reducing Line Losses Switched Banks Local Controls Automated Controls Reliability Failure Modes and Case Ruptures Fusing and Protection Grounding References INDEX

Automatic gain control technique for current monitoring in current-mode switching regulators

Abstract: A current-mode switching regulator uses adaptive current sensing to reliably monitor an inductor current in a cost-efficient and power-efficient manner. A semiconductor switch periodically turns on to conduct the inductor current. A voltage drop across the semiconductor switch is monitored when the semiconductor switch is on. A variable gain amplifier with an automatic gain control loop generates a feedback signal from the voltage drop of the semiconductor switch when conducting to provide an indication of the inductor current to a controller. The automatic gain control loop compensates for any variations in the on-resistance of the semiconductor switch.

LED driving circuit

Abstract: The utility model relates to an LED driving circuit. The utility model has the technical proposal that the LED driving circuit is characterized in that the LED driving circuit comprises a control unit, a first push-pull type driving circuit, a second push-pull type driving circuit, and an LED circuit; the control unit is used for sending out a driving control signal; the first push-pull type driving circuit is formed by the connection in series of a transistor Q1 and a transistor Q2; the second push-pull type driving circuit is connected in parallel with the first push-pull type driving circuit and is formed by the connection in series of a transistor Q3 and a transistor Q4; the LED circuit is connected between a common terminal R+ of the transistor Q1 and the transistor Q2 and the common terminal R-of the transistor Q3 and the transistor Q4 and is formed by the connection in parallel of two sets of LEDs with opposite directions, wherein under the function of the driving control signal, a circuit composed of the transistor Q1 and the transistor Q4 and a circuit composed of the transistor Q2 and the transistor Q3 are alternatively switched on to cause the LED circuit to generate voltage drop, and a set of the LEDs which are in forward connection emit light consequently. The LED driving circuit has the advantages that the number of driving circuits is reduced, the number of discrete assemblies and online is reduced, production processes and installation and debugging are simplified, the corrosion of LED lead wires and socket connectors caused by various aggressive gases is effectively avoided, reliability and maintenability are enhanced, and systematical cost is reduced largely.

Stochastic Power Grid Analysis Considering Process Variations

Abstract: In this paper, we investigate the impact of interconnect and device process variations on voltage fluctuations in power grids. We consider random variations in the power grid's electrical parameters as spatial stochastic processes and propose a new and efficient method to compute the stochastic voltage response of the power grid. Our approach provides an explicit analytical representation of the stochastic voltage response using orthogonal polynomials in a Hilbert space. The approach has been implemented in a prototype software called OPERA (Orthogonal Polynomial Expansions for Response Analysis). Use of OPERA on industrial power grids demonstrated speed-ups of up to two orders of magnitude. The results also show a significant variation of about /spl plusmn/35% in the nominal voltage drops at various nodes of the power grids and demonstrate the need for variation-aware power grid analysis.

Mitigation of voltage disturbances using adaptive perceptron-based control algorithm

Abstract: This paper presents a generalized control algorithm for voltage disturbance extraction and mitigation. The proposed mitigating device is the dynamic voltage restorer (DVR). A DVR is commonly used to mitigate the voltage sags. In this paper the proposed DVR can compensate the voltage unbalance and mitigate voltage harmonics in the time of normal operation as well as performs its basic function during the fault condition. The suggested control algorithm employs an adaptive perceptron to effectively and adaptively track and extract the most common voltage harmonics, voltage unbalance (which include negative and zero sequence voltage drops), and different types of voltage sags, which include balanced and unbalanced voltage sags. Digital simulation results are obtained using PSCAD/EMTDC to verify the effectiveness of the proposed control algorithm. Experimental results are demonstrated to prove the practicality of the mitigating device.

Integrated overcurrent protection system for class-D audio power amplifiers

Abstract: A fully integrated overcurrent protection system is presented suitable for application in integrated class-D audio power amplifiers. Accurate overcurrent detection is used based on parallel measurement of the voltage drop across the DMOS power transistors. A logic circuit enables continuous current limiting during overload situations. Actual short circuits can be distinguished from load impedance minima using a simple short-circuit discrimination method.

Method and apparatus for sensing current and voltage in circuits with voltage across an LED

Abstract: Methods and apparatuses to sense current and voltage in circuits with voltage drop. A sense circuit includes a series combination of a diode and a resistor in the path of the current to be sensed, the voltage across this series combination coupled to drive a light emitting diode (LED).

Light emitting diode display circuit with voltage drop compensation

Abstract: A light emitting display having a pixel circuit for compensating driving voltage variation between pixels due to voltage drop in the voltage supply line. The light emitting display includes pixels, data lines extending in a first direction, through which a data signal is supplied to the pixels, scan lines extending in a second direction crossing the first direction, through which a selection signal is supplied to the pixels, a first power source line supplying driving voltage to the pixels, and a second power source line along the first direction supplying a compensating voltage to the pixels. The compensating voltage compensates for the drop of driving voltage across pixels that can cause non-uniformity in brightness of the display.

Spectrometer system for optical reflectance measurements

Abstract: A spectrometer system includes a thermal light source for illuminating a sample, where the thermal light source includes a filament that emits light when heated. The system additionally includes a spectrograph for measuring a light spectrum from the sample and an electrical circuit for supplying electrical current to the filament to heat the filament and for controlling a resistance of the filament. The electrical circuit includes a power supply that supplies current to the filament, first electrical components that sense a current through the filament, second electrical components that sense a voltage drop across the filament, third electrical components that compare a ratio of the sensed voltage drop and the sensed current with a predetermined value, and fourth electrical components that control the current through the filament or the voltage drop across the filament to cause the ratio to equal substantially the predetermined value.

DV/DT related spurious gate turn-on of bidirectional switches in a high-frequency cycloconverter

Abstract: We identified a failure mode in a two stage dc/ac converter, comprising a high-frequency dc/ac inverter followed by an ac/ac cycloconverter, both operating at the same switching frequency. The failure-mode is a short-circuit condition, which is a combined effect of the reverse recovery of the MOSFET body diode and simultaneous spurious turn-on of the bidirectional switches of the cycloconverter, owing to a significantly high dv/dt (>2/spl times/10/sup 8/V/ns). A high dv/dt causes appreciable current to flow through the gate-to-drain (Miller) capacitance, thereby producing a significant amount of voltage drop across the external gate resistance. Consequently, the gate-to-source voltage of the power MOSFET may exceed the threshold voltage of the device, which turns the device on. We explain the mechanism for the dv/dt-related gate turn-on and present experimental results to validate the explanation. We also demonstrate, how a two-fold increase in the value of external gate resistance of the inverter switches (to reduce the dv/dt applied to the cycloconverter) reduces the periodicity of the short-circuit condition.

Apparatus and method for regulating white LEDs

Abstract: The present invention is an apparatus for driving white LEDs. The apparatus includes a switchable current sink, a DC-DC converter and a reference circuit. The DC-DC converter provides a driving voltage to a plurality of LEDs. The switchable current sink regulates currents through the plurality of LEDs, and the switchable current sink further provides a first reference voltage and outputs a plurality of voltage drops. The reference circuit receives the first reference voltage and the plurality of voltage drops to provide a second reference voltage to the DC-DC converter. The DC-DC converter adjusts the driving voltage provided to the plurality of LEDs according to the second reference voltage. In this way, the driving voltage is regulated to a minimum possible value and consequently the voltage drops across the switchable current sink is minimized. Hence, the LED driving system maintains higher efficiency.

A three-phase symmetrical multistage Voltage multiplier

Abstract: A three-phase symmetrical Cockcroft-Walton (CW) multistage voltage multiplier (VM) is proposed. It consists of one smoothing column and six oscillating columns. The oscillating columns are connected to three-phase power through center-tap transformers. The capacitors of the smoothing column are charged six times per cycle by six oscillating columns and are discharged six times through the load, unlike the conventional symmetrical VM in which they are charged and discharged twice per cycle. The three-phase symmetrical structure completely eliminates the first five harmonic components of load-generated voltage ripple. Theoretical analysis indicates that the proposed three-phase symmetrical CW-VM has one-third the voltage ripple and voltage drop of the conventional single-phase symmetrical CW-VM. Experimental and simulation results of the proposed three-phase symmetrical CW-VM as well as of the conventional single-phase symmetrical CW-VM are presented. A comparison shows that the three-phase symmetrical CW-VM has significantly less voltage ripple, half the voltage drop, and a fourfold increase in output power over the conventional single-phase symmetrical CW-VM.

Method and apparatus to clamp SRAM supply voltage

Abstract: An apparatus and method are provided for limiting a drop of a supply voltage in an SRAM device to retain the state of the memory during an IDLE state. The apparatus may include a memory array, a sleep device, and a clamping circuit. The clamping circuit may be configured to activate the sleep device when a voltage drop across the memory array falls below a preset voltage and the memory array is in an IDLE state.

Scaling Analysis of On-Chip Power Grid Voltage Variations in Nanometer Scale ULSI

Abstract: This paper presents a detailed scaling analysis of the power supply distribution network voltage drop in DSM technologies. The effects of chip temperature, electromigration and interconnect technology scaling (including resistivity increase of Cu interconnects due to electron surface scattering and finite barrier thickness) are taken into consideration during this analysis. It is shown that the voltage drop effect in the power/ground (P/G) distribution network increases rapidly with technology scaling, and that using well-known countermeasures such as wire-sizing and/or decoupling capacitor insertion which are typically used in the present design methodologies may be insufficient to limit the voltage fluctuations over the power grid for future technologies. It is also shown that such voltage drops on power supply lines of switching devices in a clock distribution network can introduce significant amount of skew which in turn degrades the signal integrity.

Over voltage protection scheme for synchronous buck converter

Abstract: An over voltage protection circuit for single phase and multiphase buck converters. According to one embodiment, upon the occurrence of an over voltage condition, the high side switch is turned Off and the low side switch is On. As the output voltage drops below a lower threshold, the low side switch is turned Off thereby reducing or eliminating negative spikes on the voltage output.

A resonant energy-recovery circuit for plasma display panel employing gas-discharge current compensation method

Abstract: A resonant energy-recovery circuit for a plasma display panel (PDP) employing a gas-discharge current compensation method is proposed. Its main concept is to make the resonant circuit biased by V/sub s/ and 0V instead of V/sub s//2 in charging and discharging the PDP, respectively. This operation helps the PDP to be fully charged and discharged and all main switches turned on under zero-voltage switching. Moreover, since the inductor current can compensate the large gas-discharge current, the current stresses on main power switches can be considerably reduced and all main switches have the turn-on timing margin, which ensures the no voltage drop across the PDP. Therefore, all these features could favorably provide a high energy-recovery capability, more accumulated wall charge, reduced sustaining voltage, and low electromagnetic interference. Therefore, the proposed circuit is expected to be well suited for a hang-on-the-wall PDP TV.

A voltage-based observer design for membrane water content in PEM fuel cells

Abstract: This paper presents a scheme for estimating membrane water content in polymer electrolyte membrane (PEM) fuel cells from voltage, current, temperature, and several pressure measurements. The approach is to exploit the resistive voltage drop which is closely associated with membrane water content. To distinguish this resistive drop from other voltage losses we make use of a well-developed fuel cell voltage model that characterizes each loss term, as well as the open circuit voltage. The unmeasured hydrogen and oxygen partial pressure values in the open-circuit model are estimated with a variant of the hydrogen and oxygen observers developed by M. Arcak et al. (2004). Preliminary experimental results, obtained at the Connecticut Global Fuel Cell Center, are presented and discussed.

Overmodulation in Voltage Source Inverter with Small DC-link Capacitor

Abstract: Overmodulation (OM) is used to increase the voltage output of the PWM controlled frequency converter. Full inverter voltage utilization is important because of the cost and output power improvement perspectives. The voltage source inverter (VSI) with high overmodulation performance is less sensitive to inverter DC-link voltage disturbances. DC-link voltage drop may result in unintentional entrance to the Overmodulation region. DC-link drop is often due to line voltage sag or fault conditions. When small DC-link capacitor is used, voltage drops due to full-wave rectifier bridge are present all the time. A high performance overmodulation method improves the drive performance under such conditions

Switching power supply device

Abstract: PROBLEM TO BE SOLVED: To provide a switching power supply device of a forward-coupling converter type that is used to a lighting power supply device or the like, to surely achieve reductions of ripple rate of DC load current and noise, facilitated in the constitution of the device as a circuit constitution, and that further can perform higher frequency switching SOLUTION: The FCC-type power supply device is configured, such that an AC input is rectified and inputted to a primary winding of a transformer, and a DC driven lamp load is connected to a secondary winding of the transformer via a smoothing and rectifying circuit The circuit configuration comprises an operational amplifier that amplifies the voltage drop amount generated from a current flowing to a detection resistor, by connecting the DC driven lamp load to the detection resistor in series, and a pulse-width control device circuit, that is optically coupled to the operation amplifier and controls the pulse width of the primary winding of the transformer by switching an FET element COPYRIGHT: (C)2005,JPO&NCIPI

Low voltage high speed SiO/sub 2/AlGaN/AlLaO/sub 3/TaN memory with good retention

Abstract: To improve trapping using deeper well AlGaN (chi=38eV), lower voltage drop in high-K AlLaO3 barrier (k=23 ), and smaller erase current by large DeltaEC of AlLaO3/TaN, the SiO2/AlGaN/AlLaO3/TaN devices show good 85degC memory integrity of low plusmn10V 1ms P/E, large 39V initial DeltaVth and 24V extrapolated 10-year retention A fast 100mus P/E of plusmn11V still gives 30V initial DeltaVth and 16V 10-year retention

Charge injection across a polymeric heterojunction

Abstract: The charge injection across a polymeric heterojunction of a poly-p-phenylene vinylene derivative (injecting layer) and poly (9,9-dioctylfluorene) (accepting layer) is investigated. The electric field in the accepting layer is obtained after correcting the applied voltage for the voltage drop across the injecting layer due to the buildup of space charge. At high electric fields, the current across the polymeric heterojunction exhibits only a weak dependence on the field due to the absence of image force effects, in agreement with model predictions. The strong dependence at low fields can be explained by taking the increase of the Fermi level into account, which effectively modifies the barrier for charge carriers waiting for a jump across the heterojunction.

Dimmer control system with memory

Abstract: A dimmer control system has a communication control loop that connects a master unit in series with a plurality of remote units, and it is superimposed in series on the dimmer load line so as to allow two-way communication between the master unit and remote units without affecting the operation of the load. Communications from the master to the remote units are encoded in loop current fluctuations, whereas communications from any remote to the master unit are encoded in loop voltage fluctuations. The master unit has a switched power supply, for use during normal LOAD ON operation, in tandem with a capacitive power supply, for use during LOAD OFF operation of the control units so as to minimize hum. The master unit power supply circuit provides an output rail voltage comprised of a reference voltage for the load superimposed with a control loop voltage for the voltage drop across the series-connected remote units. The master unit has a POWER OFF detection circuit and a non-volatile memory for storing system status information, so that when power is restored, the system can be restored to its former power level. The switch units are formed with a cover frame mounting a switch plate on a hinge axis allowing ON/OFF movement of an opposing side thereof. An array of LED light pipes is mounted in the switch plate aligned with the hinge axis, in order to minimize displacement of the light pipes during actuator movement.