Gte Laboratories Incorporated

Bent Norlund

Rob Moolenbeek

A control circuit for the current in a pair of coils, which are utilized for generating a rotating magnetic field, supplies a sinusoidal current to each coil during the normal, operate mode and a maximum DC current to the coils whenever the operate mode is initiated or stopped. Each coil is a common element in the sinusoidal and DC current supplying circuits. A transistor switch, which is open during the operate mode, is connected in series with the coil in the circuit for the DC current and is connected in parallel with the coil in the circuit for the sinusoidal current through the coil. Since the switch is open and is connected in series in the circuit for the DC current no DC current flows through the coil during the operate mode. Whenever the operate mode is initiated or stopped, the transistor switch is closed so that both the sinusoidal and DC currents flow through the switch. However, only the DC current flows through the coil, since the switch forms a shunt path around the coil for the sinusoidal current. This arrangement inhibits the sinusoidal current from simultaneously flowing through the coil and the switch, so that the switch does not distort the sinusoidal current which flows through the coil. The DC magnetic field at the beginning and end of the operate mode insures that the bubbles in the propagation path of the cylindrical domain memory do not move in an unpredictable manner when the rotating field starts or stops.

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Sudbury, MA, United States of America

Bent Norlund