Circuit arrangement for determining the polarity and magnitude of the

Abstract

A circuit arrangement for determining the polarity and the magnitude of the load current in a reversible d-c controller includes a bridge circuit comprising two pairs of bridge arms connected to opposite terminals of the voltage supply bus. Each pair of bridge arms connected to the same side of the supply bus form a bypass circuit connected across the load. Two diagonally disposed bridge arms each contain a primary winding of a current transformer having two primary windings connected in opposite winding phase. Load current normally flows through either pair of diagonally disposed bridge arms, but during pauses in the load drive, circulates in one of the two bypass circuits. Electronic switches in each of the bridge arms are controlled so that the load current circulates in successive bypass periods in an alternating pattern in the two bypass circuits. When current flows in a bypass circuit, a phase sensitive voltage is induced in the single secondary of the current transformer. Signals from the electronic switches in one of the bypass circuits are fed via digital logic circuitry to a further electronic switch which causes an operational amplifier to invert pulses from that bypass circuit alone. A pulse train having a polarity corresponding to the polarity of the load current is thereby obtained. In a further embodiment, a sample-and-hold stage for determining the magnitude and polarity of the load current is provided.