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.

Abstract: In a reversible d-c controller, a current transformer having two primary windings as current measuring sensors is provided for determining the load current. The primary windings are connected with opposite winding sense into two diagonally disposed bridge arms of a controller bridge circuit. The secondary winding of the current transformer is coupled through a full wave rectifier and across a load resistor to the input of a sample-and-hold stage which is provided with an electronic sampling switch and at the output of which a signal proportional to the actual value of the load current is present. The bridge circuit comprises 4 bridge arms, each bridge arm having an electronic switch and a reverse biased diode shunted across the switch. Each pair of bridge arms connected to the same side of the power supply buss and coupled across the load form a bypass circuit.