Showing papers on "Negative impedance converter published in 1985"

Steady-State Analysis of the Series Resonant Converter

Abstract: The series resonant converter is analyzed in steady state, and for constant switching frequency the output current and voltage characteristics are found to be ellipses. The converter operating point can then be easily obtained by superimposing a load line on these elliptical characteristics. Peak resonant capacitor voltage and inductor current are also plotted in the output plane and are dependent to first order only on output current. When peak voltage and current are plotted in this manner, the dependence of component stresses on operating point is clearly revealed. The output characteristics are modified to include the effect of transistor and diode voltage drops, and experimental verification is presented.

Failsafe monitoring system with input controlled switch circuits

Abstract: According to the load-driving switch circuit monitoring system of the present invention, on-off control of a switch circuit connected to in a circuit in series for driving an electric load is performed according to a fail-safe input signal Si, and conduction or non-conduction of the switch circuit is detected based on a load current in the driving circuit. An input signal converter and a load current signal converter, each of which puts out two different voltage values according to the input signal and load current detection signal and a signal of a problem of the converters per se, are arranged. A monitor signal generator is disposed to monitor only the normal correspondence relation (S) between the input signal Si and load current in the normal function state of the switch circuit among said three outputs generated by each converter. This monitor signal generator generates a high voltage output only when this normal correspondence relation (S) is detected, and when the correspondence relation is not normal or when a problem takes place in the input signal converter or the load current signal converter, the monitor signal generator generates a low voltage output, whereby malfunction of the load by the problem in the switch circuit and both the converters is monitored.

Control system for a power converter for driving induction motors

Abstract: In a control system for a power converter for driving induction motors, the control system separately controlling an exciting current component of the primary current of the induction motors contributing to generation of a magnetic flux and a torque current component of the primary current contributing to generation of a torque, a voltage detecting device detects the output voltage of the power converter, and a correcting device responds to the voltage detecting device for determining a current correction for correcting at least one of the exciting current component and the torque current component to reduce the difference of the detected voltage from a reference value of the output voltage.

Method and apparatus for the protection of a thyristor power conversion system

Abstract: Each of the three phase power source voltages coupled to a three phase (3.0.) thyristor power converter are respectively half-wave rectified to provide both positive and negative voltages. Signals representing the largest positive rectified voltage and the smallest positive rectified voltage are developed as are signals representing the largest negative rectified voltage and the smallest negative rectified voltage. Using signals from both the positive and negative rectified voltages, at least one comparison is made to determine a difference which, when in excess of a predetermined limit, effects a logic signal to provide an indication that an asymmetrical fault exists either phase to neutral or phase to phase across the power converter and the power lines connecting the converter to a polyphase alternating current (AC) source. Following a suitable delay, protective action is initiated, which action comprises either phasing back of gating to the converter thyristors and/or tripping of a circuit breaker or contactor which operates to interrupt the supply of AC power to the converter.

Theory of negative capacitance in membrane impedance measurements

Abstract: Three possible explanations of the negative capacitance seen in theChara corallina membrane impedance are critically examined. These explanations are based on: (1) voltage-dependent channel kinetics; (2) electro-osmosis; and (3) extracellular negative capacitance. It is shown that the first two can produce negative capacitance only with parameters which differ by several orders of magnitude from measured values. The last mechanism can produce a very large magnitude negative capacitance, in the appropriate frequency range. Possible experimental tests are discussed.

Negative capacitance bus terminator for improving the switching speed of a microcomputer databus

Abstract: The data transfer speed of a microcomputer bus can be improved by adding an active circuit to the bus. This active circuit amplifies the bus voltage and feeds back to the bus a current which is proportional to the time rate of change of the bus voltage. This circuit effectively adds a negative capacitance to the bus. The practical capacitance canceling capability is limited by the propagation delay time of the operational amplifier in the active circuit. The theory of microcomputer bus structures with negative capacitance including effects of amplifier delay is presented. Typically, an operational amplifier with propagation delay less than one tenth of the bus time constant is required to achieve significant (factor of 2) bus speed improvement. High performance operational amplifiers were used to construct a working model of the negative capacitance bus terminator. The experimental results agree well with the theory.

Tracking impedance measuring system

Abstract: A tracking impedance measuring system for measuring the impedance between a signal source such as a radio transmitter and a load such as an antenna includes a directional coupler that obtains a sample of the forward voltage and the reflected voltage. A first discriminator takes the forward voltage samples and the reflected voltage samples and obtains from the sample analog signals that represent the reflected voltage, the forward voltage, and the phase angle between the two voltages. The first discriminator utilizes an injection signal that is provided by a second discriminator which tracks the signal from the signal source but is offset therefrom by a selected frequency.

Battery feed circuit for a pair of subscriber lines

Abstract: Battery feed circuit for a pair of subscriber lines includes a voltage drive circuit with an operational amplifier having a predetermined output impedance determined by an alternating current terminal impedance for the pair of subscriber lines. Both voice signals and induced noise signals are terminated by the voltage drive circuit. The voltage drive circuit is connected in parallel with an electronic inductance circuit, between one of the subscriber lines and ground or a direct current voltage supply.

Switch-mode power supply having a free-running forward converter

Abstract: A switch-mode power supply has a rectifier for producing a small d.c. voltage from an input a.c. voltage, and a converter which comprises a switching transistor and a transformer. The converter arrangement is a free-running conductive converter and the switching transistor is switched on in the currentless state.

Circuit for maintaining the dc voltage on an electrically isolated telecommunication line at a reference level

Abstract: A DC reference voltage circuit (205) in a line interface circuit (103) for maintaining the DC voltage on an electrically isolated communications line at a reference level such as ground for private branch exchanges using ground start supervisory signaling. The DC reference voltage circuit comprises a low-pass filter (301), a difference amplifier (302), and two voltage-to-current sources (303, 304) each having a high output impedance. The low-pass filter passes only the voltage on the line below a predetermined frequency. The difference amplifier subtracts the passed voltage from a ground reference level to form a difference voltage. Depending on the polarity of the difference voltage, the two voltage-to-current sources provide source and sink currents to and from the line to maintain the DC voltage on the line at the reference level. A load resistor (305) also included in the feedback circuit keeps the circuit from oscillating where the phase shift of any signal through the circuit is an integer multiple of 360 degrees. The high output impedance of the two voltage-to-current sources does not effect the impedance balance on the line.

Monolithically integratable telephone circuit for generating control signals for displaying the telephone charges to a subscriber

Abstract: A telephone circuit which may be monolithically integrated for generating control signals for displaying the telephone charges to a subscriber is coupled to an AC voltage signal generator of having a predetermined amplitude and frequency which are constant over time. The circuit includes a voltage generator for generating signals which are spaced over time and have a trapezoidal pulse waveshape. A multiplier circuit calculates the product of the signals supplied from the two voltage generators and supplies a signal which is sent to the speech circuit of the subscriber's line and is added to the speech signals. The trapezoidal pulse generator has a capacitor which is charged and discharged by a voltage to current converter of a non-linear type which is driven by exchange control components. The voltage across this capacitor forms the trapezoidal signals supplied by the generator. The converter supplies a current which is proportional to the voltage supplied to its input terminals for voltage values lying between two predetermined threshold values which are opposite in sign and have an identical absolute value. For voltage values beyond the threshold values, a constant current is supplied irrespective of input voltage variations.

Negative capacitance in switching MISS devices

Abstract: The capacitance of the Al-SiO 2 ( A )-Si(n)-Si(p + ) structure has been measured at different dc bias for several frequencies. The experimental capacitance decreases sharply as reverse dc bias is increased, passes through zero, and attains a negative value. A similar behaviour is observed at low frequencies when the structure is forward biased. This unusual behaviour is explaned considering the interaction of the carriers with the interface states at the I-S interface and the influence of the electric field on the tunnelling emission rate of these states.

Digital-to-analogue converter arrangement

Abstract: A digital-to-analogue converter arrangement employs a digital-to-analog converter circuit (10) of a type producing an output voltage V(n') such that: ##EQU1## where k is a constant, E is a voltage applied to a reference voltage input, n' is a binary number applied to a binary signal input and M' is the maximum value n' can attain. The converter arrangement includes a negative feedback network (20) coupled between the output (13) of the digital-to-analogue converter circuit and the reference voltage input (14).

Effects of smoothing condenser on the stability of the push-pull current-fed dc-dc converter

Abstract: The push-pull current-fed dc-dc converter has been considered as one of the circuit configurations for the dc-dc converter. According to past studies, this converter is useful from the viewpoint of the voltage stability compared to traditional circuits. This paper considers the fact that the capacitance of the smoothing condenser can be reduced by raising the switching frequency. The relation is determined between the voltage stability and the capacitance of the smoothing condenser by analysis, considering the phase-delay element in the feedback circuit and the equivalent series resistance of the smoothing condenser. Hence, the push-pull current-fed dc-dc converter is shown to have better voltage stability than the traditional buck-type converter, even if the capacitance of the smoothing condenser is reduced, while the output voltage ripple increases with the increase of the output current, thereby limiting practical applications.

Logarithmic potentiometer circuit

Abstract: An inexpensive potentiometer circuit having an approximately logarithmic characteristic that can be accurately determined is obtained if a resistance element having a linearly adjustable ohmic resistance value is connected parallel to a negative impedance converter (1) having an output port connected to a fixed ohmic resistor (8).

An “equivalent voltage” for sinusoidal and non-sinusoidal voltage waveform

Abstract: It is well known that the frequency and waveshape of an applied voltage are important in determining the current waveform which passes through a human body, and it is the current that determines whether an individual can let-go of the energized conductor. The frequency dependence of both the body impedance and the human sensitivity to current complicate the task of determining safe voltage levels for arbitrary ac voltage waveforms. The “equivalent voltage” approach described here translates an arbitrary ac voltage waveform into an “equivalent” (from the standpoint of causing let-go) 60 Hz wave. Two different voltage waveforms with the same equivalent voltage are equally likely to produce a “can't-let-go” condition. The equivalent voltage concept proposed here permits retention of familiar 60 Hz safe voltage limits provided these limits are applied to the equivalent voltage. The equivalent voltage is the product of the peak voltage of the waveform and a weighting function. The weighting function for sinusoids is composed of two factors: the frequency-dependent impedance of the human body, and a measure of the relative sensitivity of the human let-go response to sinusoidal currents of different frequencies. Non-sinusoidal voltage waveforms are treated by appropriately summing the equivalent voltages of their sinusoidal components. Dalziel and others have demonstrated that in some cases of superimposed ac signals, the peak current is the relevant measure of the current. A generalized measure of the current waveform is introduced which is consistent with both the peak current concept and the varying sensitivity to different frequencies. The application of this concept to complex voltage waveforms is illustrated for the case of a square wave.