Showing papers on "Negative impedance converter published in 1992"

Temperature compensated cmos voltage to current converter

Abstract: A voltage to current converter circuit is provided which outputs a constant current independent of temperature. The temperature coefficient of a first onchip impedance network is canceled by a threshold voltage of a transistor which has a temperature coefficient that tracks the temperature coefficient of the first impedance network. The magnitude of the output current is adjustable using the first impedance network, and does not affect the temperature coefficient. A second impedance network effectively zeros out the temperature coefficient of the circuit by adjusting an input reference voltage assumed to be constant. Furthermore, the present invention uses no bipolar transistors or diodes.

Method for incipient failure detection in electric machines

Abstract: An improved method for detecting an incipient failure in a multiphase electric motor includes the following steps: periodically measuring or continuously monitoring voltage and current values at each input to the motor; determining negative sequence voltage and current values for each periodic measured input voltage and current value; calculating an effective negative sequence impedance phasor value angle from each of the determined negative sequence voltages and current values; and comparing the calculated negative sequence impedance phasor angles and/or real and imaginary components over a plurality of periodic measurements to detect a change therein, which change is indicative of an incipient failure mode.

Synthesis of zero-impedance converter

Abstract: A method for synthesizing a system that converts a finite value of an impedance to zero, with an associated finite current and zero voltage, is presented. The synthesis method comprises positive current feedback of an exactly specified nature and value of its transfer function. The stability and dynamics of the system are controlled by an additional voltage loop. The zero-impedance converter is used to synthesize load-independent systems including (switch-mode) power converters and electric motor drive systems incorporating any kind of motor. >

Voltage-resonant DC-DC converter

Abstract: A voltage-resonant DC-DC forward converter is provided with a snubber circuit in its secondary circuit. The snubber circuit comprises a series connection of a first capacitor and a first diode connected to both ends of the secondary winding of the main transformer to make up a loop of a secondary resonance circuit which allows a secondary resonance current to flow in the forward direction of the first diode, the forward direction being so directed that the first diode blocks the secondary resonance current from flowing at least while the second winding supplies a current to the smoothing circuit through a second diode for rectifying the secondary current. The converter is further provided with a regulation circuit for regulating the output voltage of the converter. The circuit has a transistor for controlling switching of the output current which varies linearly with time. The transistor is controlled by the sum of the voltage signal indicative of the output current and of the deviation signal indicative of the deviation of the output voltage from a prescribed value. When the sum exceeds the base-emitter threshold voltage, the transistor is turned on to switch off the output current.

Bipolar voltage doubler circuit

Abstract: A charge pump circuit for providing a bipolar output that substantially doubles the unipolar voltage input by utilizing a three-phase clock signal to charge a first capacitor in response to the first phase of the three-phase clock signal, then in response to either the second or third phase of the clock signal connect the first capacitor in series between the positive voltage input terminal and positive voltage output terminal to generate an output voltage which is positive in polarity and substantially double the voltage of the input source, then in response to the other of the second and third clock phases connect, between the input terminals, the first and second capacitors in series for providing a second polarity voltage across the second capacitor which is substantially double the source voltage and during either the following first or second clock pulse connect the second capacitor with its positive electrode connected to the negative input terminal and its negative electrode connected to the negative output terminal, thereby providing an output voltage which is negative in polarity and substantially double the voltage of the input source.

Distance relay with load encroachment protection, for use with power transmission lines

Abstract: Voltage and current on a power transmission line are first obtained, filtered and converted to digital representations. The positive sequence components of the voltage and current are determined and the impedance at the relay is then calculated from those positive sequence voltages and currents. The positive sequence impedance is converted into a magnitude and phase angle representation and then compared against a load pattern which is also represented by magnitude and phase angle representations. If the calculated impedance at the relay is within the load impedance pattern, the distance relay is prevented, i.e. blocked, from sending an output signal to trip a circuit breaker protecting the transmission line.

The origins and characteristics of negative capacitance in metal–insulator–metal devices

Abstract: Impedance analysis of ZnS metal–insulator–metal structures has revealed strong negative capacitance behaviour Under low-field conditions, the devices are highly insulating with capacitance consistent with their geometry and dielectric constant However, at high fields they become conducting and the capacitance falls to zero and then becomes negative It may exceed the geometrie value by over five orders of magnitude This frequency-domain behaviour is explained in terms of the unusual time-domain behaviour of the devices The origins of negative capacitance are shown to He in the modulation of the differential conductance by the ac measurement voltage, combined with the interpretation of the response in terms of an electrical equivalent circuit The application of equivalent-circuit analysis to such systems is discussed Negative capacitance has been observed in a wide range of other systems which can now also be understood within the theoretical framework presented

Step-up voltage converter with overcurrent protection

Abstract: A step-up converter is utilized to convert a first lower input voltage to a second higher output voltage. The circuit includes a soft start capability such that ringing due to excessive voltage and current is substantially eliminated. In addition, this converter includes an overcurrent protection mechanism if a load failure or other overcurrent condition occurs.

Bias circuitry for content addressable memory cells of a floating gate nonvolatile memory

Abstract: A low power bias voltage generation circuitry for content addressable memory cells for a nonvolatile memory is described. The bias circuitry is comprised of a source follower pair and two cascaded high impedance voltage dividers. The source follower pair acts as a positive feedback loop coupling between the two high impedance voltage dividers for relatively quickly charging and settling the output node to a predetermined voltage level. The first high impedance voltage divider can relatively quickly provide an input signal to trigger the small-input-load second high impedance voltage divider. The second high impedance voltage divider comprised of two high impedance diode stacks allows most current drawing from the power supply to drive a relatively large output loading during switching. Both first and second high impedance voltage dividers help keep the DC current of the circuit to a relatively low level which helps to reduce the total power consumption of the circuit.

Active compensation of interconnection losses for multi-GHz clock distribution networks

Abstract: The authors propose an active compensation scheme for losses in heavily loaded high-speed differential clock distribution networks using Si bipolar integrated circuit technology. The compensation network consists of negative impedance converter circuitry and provides performance improvements up to multi-gigahertz frequencies. Even though the compensation technique is proposed in the context of Si bipolar multilevel current switch logic circuits, the analogous application with other high-speed technologies is possible where loading dominates the on-chip transmission line characteristics. The authors give general design guidelines and reports simulation results for a 2-GHz clock distribution example problem using parameters of state-of-the-art single-poly self-aligned Si bipolar transistors. >

Source impedance and current-control loop interaction in high-frequency power-factor correctors

Abstract: The authors introduce a model for the input port of the high-frequency power-factor corrector and determine the gain of the current control loop. Both the model and the expression for the loop gain are entirely general and can be used for analyzing the source impedance and current control loop interaction of virtually any corrector with any current control method, operating in continuous or discontinuous inductor current mode, and having any source impedance. Based on the model, the electromagnetic interference filter capacitor and the current-error amplifier can be designed to avoid instability of the current-control loop. The loop gain of a boost corrector with average current control was investigated in detail. The system was found to be unstable at low line voltage and at source inductance values frequently encountered in practical applications. A physical explanation for the instability is given together with recommendations on how to avoid the instability. Test data taken from an experimental boost corrector with average current control are in good agreement with theoretical predictions of the model. >

Diagnostic circuit protection device

Abstract: A circuit protection device for use with an electrical unit comprises driver circuitry connected to the electrical unit and connecting means electrically connecting the device to the electrical unit to provide a voltage signal indicative of a voltage associated with the electrical unit. A voltage detector is connected to the connecting means and receives the voltage signal, and provides a conditioned voltage signal output representative of the voltage signal. An analog-to-digital converter receives the conditioned voltage signal output and converts the conditioned voltage signal output to a digital value. A digital processing device receives the digital value from the analog-to-digital converter and provides an output signal to the driver circuitry to turn off power to the primary if an error is detected. The device may also include current obtaining means for providing an electrical signal indicative of a current associated with the electrical unit, and a current detector circuit connected to and receiving that electrical signal for providing an output voltage signal representative thereof. Multiplexing means may be provided for receiving the output signals from both the voltage detector and the current detector for selectively connecting only one of those signals at a time to the analog-to-digital converter. Alternatively, a second analog-to-digital converter may receive the second output voltage signal and convert it to a digital value, and the digital processing device may receive and process the digital values from both analog-to-digital converters.

Clocked comparator with offset-voltage compensation

Abstract: A clocked comparator circuit comprises an input stage and a sample-and-hold circuit and an amplifier-latch circuit coupled to the output of the input stage. The sample-and-hold circuit provides an accurate offset-voltage compensation and the amplifier-latch circuit provides a high operating speed by means of a switchable current source (S6, T11). Switches are provided so that the amplifier-latch circuit constitutes a differential load having a high positive impedance during a first state of a clock signal, a low positive impedance during a next state of the clock signal, and a negative impedance during a following state of the clock signal.

Reference current loop

Abstract: Reference current loop comprising a group of identical ICs (1, 2, 3), comprising each a first impedance (7) connected in series to the first impedance of another IC of the group. The combination of first impedances is connected to a reference current source (4). The voltage across the first impedance (7) is convened to a current (I0) by a voltage-to-current converter (8) and made available as a current (I1, I2) proportional to the reference current (Iref) of the reference current source (4) by a current mirror circuit (20, 23). The relation between the currents I1 and I2 and the reference current Iref is determined by the ratio of the impedance value of the first impedance (7) to that of the second impedance (19). This ratio is the same for all the ICs, so that the currents I1 and I2 in all the ICs are mutually equal.

Voltage control of super high-speed reluctance generator system with a PWM voltage source converter

Abstract: A voltage control system for a reluctance generator with a PWM voltage source converter is proposed. A phasor diagram of the generator is developed by introducing an iron loss conductance. A practical method for achieving optimal efficiency over the complete operating range is suggested. It is based on the optimal-efficiency current angle tracking by adjusting the voltage ratio of AC-to-DC voltage. The performance of the system is investigated by using the new phasor diagram. It is shown that a system with a PWM converter has wider operating range than one with a self-commutated six-pulse converter. The proposed control system is realized on a laboratory prototype, where control routines are mainly implemented by a 16 b single-board microcomputer. Experimental results show that 10% or more improvement compared with that of the system fed by a six-pulse converter is obtained at half full load. >

Analysis and design of series-parallel resonant power supply

Abstract: A modified series-parallel high-frequency resonant DC/DC converter configuration is proposed. A simplified steady-state analysis of the converter, including the effect of a high-frequency transformer using complex circuit analysis, is presented. Based on the analysis, a simple design procedure is given. The effect of magnetizing inductances of the high-frequency transformer on the performance of the converter is discussed. Detailed experimental results obtained from a MOSFET (metal-oxide-semiconductor field-effect-transistor)-based 1-kW converter are presented to verify the analysis. The converter presented has almost constant efficiency from full load to quarter load, and the converter has load short circuit capability. >

Output characteristics in the discontinuous reactor current mode of the zero-voltage switching DC-DC converter

Abstract: It is often observed that the switching frequency in the zero-voltage switching DC-DC converter becomes extremely low when the load current increases and/or when the input voltage decreases. This lowering deteriorates the advantage of the high frequency in designing the energy-storage elements of the DC-DC converter. The output characteristics of the zero-voltage switching DC-DC converter operating in the discontinuous reactor current mode are analyzed. It is shown that there exists a useful discontinuous mode in which the variation of the switching frequency can be restricted within +or-5% when the output voltage can be regulated for the load change from no load to full load or for +or-15% change of the input voltage. The voltage stress of the switch can be sufficiently suppressed compared with that in the continuous reactor current mode. >

Zero-current switching forward power converter operating in damped reverse boost mode

Abstract: In a zero-current switching forward converter both a unidirectional conducting device and a circuit consisting of a switch in series with a dissipative element are connected across the energy transfer capacitor in the output circuit of the converter. The switch is turned off at the beginning of an energy transfer cycle and is turned on when the voltage across the energy transfer capacitor returns to zero. At relatively high values of load, current flowing in the converter output inductor in the direction of the load will be bypassed around the energy transfer capacitor by the unidirectional conducting device and converter operation will be the same as a prior art zero-current switching forward converter. At low values of load, however, where current reversal may occur in the output inductor, the dissipative element will serve to damp the time varying response of the capacitor to the reverse flow of current in the output inductor and the variation of the voltage across the capacitor will be smooth and predictable. The value of the dissipative element is chosen so that the circuit formed by the dissipative element, capacitor and output inductor is approximately critically damped. In this way the frequency variation of the converter with variations in load is reduced, the output ripple of the converter is reduced and discontinuous operating modes are avoided.

Method and apparatus for buffering electrical signals

Abstract: A circuit and method for buffering a high output impedance voltage generator circuit to a low input impedance load circuit is described. Two emitter-follower stages are used with a load current feedback configuration so that the base to emitter voltages of all four transistors maintain a fixed relationship and therefore the output voltage presented to the load maintains a fixed relationship to the input voltage presented to the buffer amplifier circuit.

Anomalous reactance behaviour during the impedance analysis of time-varying dielectric systems

Abstract: Any real dielectric material deviates from ideal behaviour by exhibiting residual electrical conductivity, particularly at high fields and elevated temperatures. This conductivity is usually non-ohmic and often time-varying. During the a.c. impedance analysis of such a system, anomalous reactance behaviour may be observed including negative capacitance and low-frequency dispersion. We con-sider the characterization of dielectrics displaying time-varying conductivity and discuss their interpretation in terms of equivalent-circuit components. The situation is shown to be analogous to the Debye treatment of dielectric relaxation but with time-varying conductivity in place of time-varying permittivity. Quantitative relationships between the time-varying differential conductivity and the measured frequency-domain behaviour are derived and the origins of negative capacitance, low-frequency dispersion and related anomalous reactance effects are elucidated.

Method and device for protecting an electrical converter circuit against overload

Abstract: A converter circuit supplied with a pulsed current by a primary source is protected against overload by producing a first voltage representing the product of the mean pulsed current and a first duty factor and a second voltage representing the product of the maximum wanted power and a second duty factor. The first and second voltages are compared and the output power of the converter is limited if the first voltage becomes greater than the second. The invention finds a particular application in regulated voltage power supplies which must be kept within acceptable operating limits.

A high-density 1 kW resonant power converter with a transient boost function

Abstract: A series/parallel resonant DC-DC converter with secondary-side resonance and a novel input boosting feature is described. In order to greatly reduce the conduction loss (factor of 4) due to circulating currents in the resonant components, the boost circuit, which requires no additional active switches, operates only when needed during transient input voltage dips. This reduces the effective input voltage range over which the converter must operate and allows optimization at the steady-state input voltage. The converter employs highly efficient resonant inductors and novel z-folded thin flex circuit transformer windings in order to meet a density of 60 W/in/sup 3/ with an efficiency approaching 95%. The DC-DC converter is being developed for use as a 270 V to 50 V line converter for distributed power applications. >

Bipolar analog-to-digital conversion apparatus with unipolar current and voltage modes

Abstract: An integrated circuit incorporating an analog-to-digital (A/D) conversion subsystem having a current mode in which only negative analog currents are converted and a voltage mode in which only positive analog voltages are converted is adapted to produce bipolar digital current and voltage signals. An on-board microprocessor operates the A/D conversion subsystem to perform a conversion in the current mode. If the converted digital value is non-zero, this value is used as the negative digital value of analog input signal. If the result of the conversion in the current mode is zero, a second conversion is made in the voltage mode and used as digital value with a positive polarity. An input circuit having an output impedance substantially equal to the "full scale equivalent" input impedance of the IC defined as the full scale voltage of the IC divided by the full scale current, eliminates the need for special scale factors to correlate the positive and negative conversion values.

Analog voltage subtracting circuit and an A/D converter having the subtracting circuit

Abstract: An analog voltage subtracting circuit for calculating a difference between an analog input voltage and a voltage drop caused by a load includes an analog voltage generator 7 for generating an analog voltage, a load 3 having one end connected to an output of the analog voltage generator 7 and the other end connected to an output terminal 2, and a D/A converter 6 applying a positive output current Iout for generating a desired voltage drop at said the other end 4 of the load 3 and for applying a complementary output current Iout complementary to the positive output current Iout to said one end of the load 3. By this structure, a constant current of Iout+Iout flows at said one end 4 of the load 3, and therefore linear output can be provided.

Dc feedback firing control circuit for a dc/three-phase current converter

Abstract: Control circuit for semiconductor components of a converter circuit which can be switched on and off to convert direct current into three-phase current. The converter circuit is connected between a direct-current source and the stator of a synchronous machine having a cylindrical rotor. The control circuit measures rotor position and the direct current and determines from the obtained signals the value of the commutation angle μ of the phase current i in the converter at any value of the direct current I d on the basis of a model of the synchronous machine which solely takes account of the fundamental harmonic of the phase current i, the firing angle α of the semiconductor components being set between limits determined for any value of the direct current I d by the associated commutation angle μ.

Current-driven zero-voltage-switched resonant converter with capacitive output filter: analysis and experimental results

Abstract: The analysis and experimental results of a novel current-driven full-bridge zero voltage switching (CDFBZVS) DC/DC resonant power converter topology are presented. The present converter topology has a second-order tank circuit that consists of a parallel combination of a capacitor and an inductor. The converter exhibits zero voltage switching for a wide range of load conditions (from full load to open circuit). Due to the capacitive output filter, the voltage stresses in the tank circuit and the transistor switches are clamped to the output voltage. The converter is analyzed by means of a state-plane diagram from which the operational characteristics are obtained. To verify the analytical work, results from the experimental prototype are provided. >

Converter for providing boost voltage for a flash discharge lamp serving as a photographic light

Abstract: The present invention has an object to develop a converter allowing dielectric strength of a booster transformer to be reduced by half for miniaturization and security thereof. To achieve this object, the booster transformer is provided with first and second secondary coils so that, every time a switching element is turned ON, the first secondary coil generates positive voltage in reference with the negative terminal potential of a DC source while the second secondary coil generates negative voltage also in reference with the negative terminal potential of the DC source and a sum of these positive and negative voltages is output from the converter as a composite voltage.

Reducing switch=on current pulse for inductive loads - increasing effective voltage on lead when connected to AC networks, whilst measuring reactive current and until current threshold or desired voltage is reached

Abstract: A method of reducing the switch-on current pulse for an inductive load with a magnetisable core connected to an a.c. network involves increasing th effective voltage on the load whilst simultaneously measuring the reactive current in the load circuit. The voltage is increased until either a current threshold is reached and an opposing voltage applied to the load or the effective value of the voltage is raised to a desired or characteristic level. USE/ADVANTAGE - The method enables an inductive load to be connected to an a.c. network without an undesirable current pulse irrespective of the initial remanence.

Bootstrap voltage reference circuit utilizing an N-type negative resistance device

Abstract: A bootstrap voltage reference circuit having an amplifier with a positive feedback network including a non-linear device which operates as a current source. The non-linear device may be an n-type negative resistance device such as a tunnel diode. The circuit is operable for generating a predetermined reference voltage as the difference between the signal applied to the positive input and a signal generated by the negative feedback network and applied to the negative input approaches zero.