US 4,243,931 AGranted

Current isolator

AssigneeRosemount Inc.

InventorMoises A. dela Cruz

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Abstract

A current isolator circuit generates an electrically isolated output current which is related to an input current. The current isolator includes a magnetically saturable transformer having a core and first, second, and third windings. The input current flows through the first winding, and the output current flows through the second winding. The third winding is driven by a periodic drive signal, which alternately drives the transformer between first and second magnetically saturated states. When a change in the input current occurs, the magnetizing current in the third winding changes, thereby causing a change in the time required to drive the transformer from the first to the second magnetically saturated state, and an opposite change in the time required to drive the transformer from the second to the first magnetically saturated state. The difference in saturation times is sensed and is used in controlling the magnitude of the output current flowing through the second winding. As a result, the output current again attains its predetermined relationship to the input current, and the current isolator is returned to a balanced condition.

Claims11

Dependent claims

A current isolator for electrically isolating a first current and a second current having a predetermined relationship, the current isolator comprising:

a transformer having a core and first, second, and third windings, the first winding having the first current flowing therethrough, the second winding having the second current flowing therethrough, and the third winding being connected to receive a periodic drive signal;
wherein the periodic drive signal alternately drives the transformer between first and second opposite magnetically saturated states;
and wherein changes in magnetizing current in the third winding cause differences between a first saturation time required to drive the transformer from the first to the second magnetically saturated state and a second saturation time required to drive the transformer from the second to the first magnetically saturated state;
means for providing a control signal as a function of changes in magnetizing current in the third winding resulting from changes in the first and second currents;
wherein the means for providing a control signal senses differences between the first and second saturation times and provides the control signal as a function of the sensed differences;
the means for providing a control signal comprising:
first and second integrating means for providing first and second integrated signals representative of the first and second saturation times, respectively;
and
comparing means for comparing the first and second integrated signals and providing the control signal as a function of the comparison;
and
means for controlling the second current as a function of the control signal.

8 more elements

A current isolator for receiving a first current and providing a second current which is electrically isolated from the first current and has a predetermined relationship to the first current, the current isolator comprising:

a transformer having a core and first, second, and third windings, the first winding having the first current flowing therethrough, and the second winding having the second current flowing therethrough;
drive means connected to the third winding for alternately driving the transformer between the first and second opposite magnetically saturated states;
means for providing a control signal as a function of differences between a first saturation time required to drive the transformer from the first to the second magnetically saturated state and a second saturation time required to drive the transformer from the second to the first magnetically saturated state, and wherein differences between the first and second saturation times are a function of the first and second currents;
and wherein the means for providing a control signal comprises:
first and second integrating means for providing first and second integrated signals representative of the first and second saturation times, respectively;
and
comparing means for comparing the first and second integrated signals and providing the control signal as a function of the comparison;
and
means for controlling the second current as a function of the control signal.

6 more elements

Dependencies are inferred from the claim text.