V. A. Piskarev

Sensing and measurement of DC current using a transformer and RL-multivibrator

A circuit for sensing and measurement of DC current using a transformer and RL-multivibrator is proposed. The bridge multivibrator circuit is obtained, connecting the primary coil of a nonlinear transformer to an operational amplifier. The DC current that has to be measured is applied to the secondary of the transformer. It is shown that the DC voltage measured at the inverting node of the operational amplifier gives the information on polarity and value of DC current in the secondary. The transfer characteristic of such a DC current sensor is linear for small values of the measured DC current. >

RL-multivibrator and retrieving the coil magnetization curve

A method for retrieving the magnetization curve of a nonlinear coil is described. The parameters of a piecewise-linear or a third-order polynomial approximation can be obtained. A simple bridge RL-multivibrator, which includes an operational amplifier and this coil, is used. The coil parameters are calculated observing two oscillograms of the voltage at one of the bridge branches and measuring the oscillation period. >

Circuit with nonlinear transformer provides isolation for DC measurements

A nonlinear transformer that can be used to isolate a source from the measuring device is presented. A simple RL oscillator constructed with this transformer and a comparator is discussed. The oscillator uses a 220 Hammond pulse transformer and a LF356 operational amplifier with +or-12 V power supply voltage. Using a fast comparator and a small ferrite core transformer will yield a more versatile circuit. Ultimately, the multivibrator can work at frequencies to 30-40 kHz, and an electromagnetically-coupled isolation amplifier can be developed.<<ETX>>

Design of DC polarized solid-state relays with electromagnetic coupling

Abstract An approach is described to the design of bipolar solid-state relays with electromagnetic coupling. The relay includes an RL-multivibrator with nonlinear transformer, a duty-cycle detector and an output stage. The input DC current applied to the transformer primary develops the magnetic field which modifies the cores saturation condition, which, in turn, modifies the multivibrator oscillation duty cycle. This change is detected by the duty cycle detector so that the polarity of the detectors output voltage changes with the input DC current polarity. The output stages represent the circuits designed in correspondence with required relay characteristics.

Design of electromagnetically coupled isolation operational amplifiers without input buffer

The paper describes an approach to design of isolation operational amplifiers with electromagnetic coupling. The amplifier includes an RL-multivibrator with nonlinear transformer, a duty-cycle detector and an output amplifier. The multivibrator is used as a DC current sensor. The input DC signals and the feedback signal are applied to the transformer secondaries which results in the magnetic field modifying the core saturation. The multivibrator duty cycle changes. Then the duty cycle detector output voltage changes. The output amplifier further amplifies detector output signal and provides the necessary loop gain.<<ETX>>

On design of polarized solid-state relays with electromagnetic coupling

The authors describe an approach to the design of bipolar solid-state relays with electromagnetic coupling. The relay includes a RL-multivibrator with a nonlinear transformer, a duty-cycle detector and an output stage. The input DC current applied to the transformer primary results in a magnetic field which modifies the core saturation condition. The multivibrator oscillation duty cycle changes. This is detected by the duty cycle detector where the polarity of the output voltage changes with the input DC current polarity. The output stages represent the circuits designed to correspond to required relay characteristics.<<ETX>>

A sinusoidal RC-oscillator with amplitude control by current splitting

Abstract The paper describes a method of amplitude control in a sinusoidal RC-oscillator. The oscillator includes an amplifier of current with differential output and the amplitude control is achieved by insertion of a current splitter in the positive feedback path. The current splitter is realized as a bipolar transistor differential pair with control of emitter tail current splitting from an amplitude detector. The approach is suitable for design of RC-oscillators operating with a low voltage power supply (an example of the oscillator for a 3 V power supply is given).