Showing papers on "Negative impedance converter published in 1968"

Power system protective relaying by time-coordinated sampling and calculation

Abstract: A method of controlling the operation of a breaker in a transmission line by first monitoring the current and if the current exceeds a prescribed limit, measuring a sampling of the voltage on the line when the current is at zero and dividing this value by the maximum current on the line to obtain a first quantity which is added to a second quantity obtained by measuring a sampling of the voltage when the current is at its maximum value and dividing this voltage by the maximum current. The previous calculations will provide a measure of impedance since the voltage when the current is zero is equal to Vm sin phi while the voltage when the current is at maximum is equal to Vm cosine phi and impedance in a rectangular coordinate representation is: z R jX Vm cosine phi /Im + j(Vmsin phi /Im). This apparent impedance is then compared against relay characteristics which are implemented in a programmed general purpose computer and in the event the apparent impedance lies within the relay characteristic zone, the associated breaker is tripped.

An investigation of broadband miniature antennas

Abstract: : The report considers the application of a negative impedance converter to a short monopole antenna. The theory of short antennas and an analysis of the negative impedance converter are presented. The frequency- response characteristics of the negative impedance converter are analyzed. The performance of each of various miniature antenna configurations is compared experimentally with that of a 16 foot untuned whip antenna. The nonlinear behavior of the negative impedance converter is explored experimentally. Also considered is the manner in which atmospheric noise level influences the design of antennas intended to operate in the frequency region below the VHF band.

Control circuit for a low-frequency amplifier

Abstract: A low-frequency input voltage is fed to a voltage divider consisting of a fixed resistor and a pair of diodes connected in parallel but with opposite polarity with respect to AC but series-connected with respect to DC The output voltage is derived from the DC common point of the two diodes and is thus a function of the impedance of said diodes. The impedance of the diodes is controlled as follows: A voltage proportional to the input voltage, after passing a threshold stage, is used to charge a capacitor. The capacitor circuit has a short charging time and a long discharge time. The capacitor voltage constitutes the voltage at the gate of a field effect transistor, the voltage at whose drain electrode is used to control the impedance of the diodes. A circuit for compensating for temperature effects on the impedance of the diodes by inserting a DC voltage in the diode circuit is also shown.

Constant current temperature stabilized signal converter circuit

Abstract: A DIFFERENTIAL AMPLIFIER IS DISCLOSED WHEREIN A CONSTANTCURRENT SOURCE IS PROVIDED WHICH IS REFERRED ONLY TO THE POWER-SUPPLY LEADS. FROM THE CONSTANT-CURRENT SOURCE, BIAS SIGNALS ARE DERIVED WHICH, IN TURN, PROVIDE AD CONTROL CONSTANT-CURRENT SUPPLY MEANS FOR EACH OF THE TWO LEGS OF THE DIFFERENTIAL AMPLIFIER, INDIVIDUALLY. THIS ARRANGEMENT PROVIDES A HIGHLY STABLE, HIGHLY ACCURATE AMPLIFICATION OF INPUT SIGNALS AND MINIMIZES ERRORS DUE TO AMBIENT TEMPERATURE CHANGES.

Sample and hold voltage circuit for controlling variably energized load

Abstract: 1,268,516. Automatic control of speed and voltage. WARNER & SWASEY CO. Sept. 18, 1969 [Dec.9, 1968], No.46153/69. Heading G3R. A counter-EMF producing load, such as a motor or a battery being charged, is controlled by a system which samples the counter-EMF, only when the load current is less than a predetermined value. In the circuit of Fig. 2, a motor 15a is energized by a single or polyphase A. C. source 10a through antiparallel thyristors 11a, and is connected in series with a current-sensing impedance 30. When driving current is flowing in the motor, an operational amplifier 44 receives an input from the impedance 30 which is converted into a negative output to maintain a field effect transistor 54 non-conductive. However, when the motor current falls below a certain value, the effective input to the amplifier 44 becomes a negative bias voltage 50, this voltage being inverted to give a positive output which is blocked by a diode 56 to allow the transistor 54 to conduct. A capacitor 55 is now charged to a voltage proportional to the counter-EMF of the motor, and the resulting potential is compared with a reference in a feedback circuit 35, the output of which controls the firing of the thyristors 11a to regulate the motor. A time delay circuit 70 may be included in a polyphase system to delay firing of the thyristors until the capacitor 55 has had sufficient time to charge fully.

Temperature-compensated frequency-voltage linearizing circuit

Abstract: A technique is disclosed for providing a desired nonlinear output control voltage which has a continuous first derivative from a linear input command voltage. The output control voltage maintains its curvature and orientation in the presence of ambient temperature variations. This is accomplished by provision of a first circuit impedance which produces the desired nonlinear curvature as a function of a linear input, while a second impedance negates impedance changes in the circuit semiconductor devices due to the temperature changes.

A Method for Obtaining Analog Circuits of Impedance Convertors

Abstract: The properties of three terminal positive and negative impedance convertors are defined in terms of the cofactors of the indefinite nodal admittance matrix, the special cases of the ideal transformer, power amplifier, and voltage and current inverting negative impedance convertors being considered in detail. The nodal admittance matrix of a six-node resistive network with two infinite gain amplifiers embedded in it is discussed, and element values are obtained to realize the required analog circuits with a minimum number of components. The analog circuits obtained are simple to set up and are ideal for demonstrating and testing applications of impedance convertors to filter network realizations. Of particular interest is the circuit obtained for the case of a loaded, phase-reversing, positive impedance convertor, which employs only one operational amplifier and four resistors in a bridge circuit, which is thought to be novel, and which can be extended by the introduction of a second amplifier and three resistors to produce a simple realization of a negative impedance invertor (NIV).

Circuit arrangement comprising a high-voltage transistor

Abstract: A circuit for increasing the speed of collector current reduction of a high-voltage transistor, in which an impedance is connected in series with the base to restrict variation in reverse base current. The specification discloses embodiments in which the impedance is a parallel circuit of a resistor and diode connected in the pass direction of base-emitter current, and in which the impedance is a coil.

Voltage regulator utilizing a negative feedback for stabilizing voltage over a defined band

Abstract: IN A VOLTAGE REGULATOR OF THE KIND INCLUDING A POWER TRANSISTOR IN SERIES WITH THE FIELD WINDING OF A GENERATOR, AND A CONTROL TRANSISTOR SENSITIVE TO BATTERY VOLTAGE FOR DETERMINING THE CURRENT FLOW THROUGH THE CONTROL TRANSISTOR, NEGATIVE FEEDBACK IS PROVIDED FROM THE POWER TRANSISTOR TO CONTROL TRANSISTOR TO STABILISE THE OVERALL GAIN OF THE REGULATOR, SO OVERCOMING PROBLEMS EXPERIENCED ON INSTALLATION OF THE REGULATOR IN VEHICLES.

Current converter arrangement comprising a plurality of converter elements connected in series

Abstract: An electrical converter arrangement comprises a plurality of series-connected controllable current converter elements such as thyristors which together form one and the same path for current flow. The converter elements forming this current path are not fired simultaneously but rather are fired sequentially either singly or in groups by means of a pulse generator in cooperation with delay means interposed in the circuit connections to the various converter elements, or element groups so that the proper time delays are established for ,firing. By firing the converter elements in sequence, i.e. in stages, one avoids formation of undesirable steep voltage jumps. The required sequential firing delays can be obtained by use of individual delay devices having progressively longer time delays, or a ring counter can be utilized.

Equivalent Circuits for Negative Resistance Devices

Abstract: : The report examines certain phases of the dynamic behavior of an open-circuit stable, two-terminal negative-resistance device with its specific equivalent circuit, as well as the dynamic behavior of a short-circuit stable, two-terminal negative-resistance device with its specific equivalent circuit. The equivalent circuits for these two devices are duals of each other. The static current/voltage characteristic curves for the two types of negative- resistance devices affect their dynamic equivalent circuits. It is shown that the static current/voltage characteristic curve for the negative-resistance device has a limited negative-slope region since the device possesses particular physical restrictions. The complete equivalent circuit for the current- controlled and voltage-controlled negative-resistance devices is derived by recognizing specific information about the device. The basic equivalent circuit for the negative-resistance device is obtained by assuming a cause-effect relationship between the current and voltage of the device and then by using the Taylor Series expansion on the cause. The basic equivalent circuit for the negative-resistance device is related to the static current/voltage characteristic curve when the device is operated as a trigger circuit. Expressions for the input admittance of the current-controlled negative- resistance device and the input impedance of the voltage-controlled negative- resistance device are derived from the equivalent circuit of the device.

Current Comparator Using Ferromagnetic Cores and Its Application to Analog-to-Digital Converters

Abstract: A current comparator using ferromagnetic cores with a rectangular hysteresis loop is described. Design criteria for this comparator are derived from the B-H characteristics of the core. To verify the performance of the current comparator, basic experiments and experimental A-D converters with these comparators have been made. By application of the current comparator, it would be possible to realize an A-D converter that could convert a current between a few milliamperes and a few amperes into 9- to 10-bit binary forms within an order of microseconds. The merits of an A-D converter of this type are 1) its very low input impedance, 2) its high impedance between the balanced input terminal pair and the ground, and 3) its ease of conversion of the sum/difference of two currents. Because of these features, the A-D converters can measure currents in circuits having high potential to ground without giving disturbance. The input impedance, measured at 500 kHz, of the experimental A-D converter is shown as a series connection of 0.3-ohm resistance and 0.24-?H inductance, with a stray capacitance of 7.5 pF between input terminals and ground.

Impedance controlling circuit for a load element

Abstract: 1,259,358. Transistor switching circuits; non-contact-making relays. G.T.E. LABORATORIES Inc. 18 April, 1969 [19 April, 1968], No. 20035/69. Headings H3B and H3T. [Also in Division H2] The impedance of the primary winding 11 of a transformer 10 is lowered, so that an electroluminescent device 15 is operated by an A.C. source 16 by rendering conductive a transistor 23 which then connects the junction of two diodes 20, 21 connected across the secondary winding 12 to a tapping thereon so as to short circuit the secondary. Control signals are applied at 14 to the transistor, and when it is non- conductive, the secondary is open circuited and the primary impedance is sufficiently high to prevent the operation of the device 15. The electroluminescent device 15 may have an impedance of 50 k#; the source 16 may be 90 V. at 2 kc/s.; and the extreme values of primary impedance maybe 2k# and 150k#. The device 15 may form part of a display array.

A negative impedance converter using an in-line cryotron

Abstract: A negative impedance converter using a single in-line cryotron is presented. The design requires fewer active elements than conventional circuits.