Abstract: In a circuit arrangement for an alternating control a PI controller comprises a first operational amplifier having an output connected via a resistor to the non-inverting input of a second operational amplifier wired as an impedance transformer. The output of the second operational amplifier is fed back via an RC stage to the inverting input of the first operational amplifier. The output of a second controller is connected via a decoupling diode to a junction between the decoupling resistor and the non-inverting input of the second operational amplifier. Positive as well as negative signals can occur at the output of the first operational amplifier, and discontinuities in control during a switch over between the two controllers are avoided.

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.