Drive circuit for a bidirectional flow control valve

摘要

A normal-direction mode which switches on first and fourth switches and in a mutually diagonal relationship of an H-type bridge circuit and switches off second and third switches also in a mutually diagonal relationship of the bridge circuit is executed for an on-duty time of an opening-degree command signal, and a reverse-direction mode which switches off the first and fourth switches and switches off the second and third switches is executed for an off-duty time of the opening-degree command signal. During normal operation, conduction of current to the H-type bridge circuit 70 and a coil is constantly performed irrespective of a degree of opening of a valve to be adjusted, and in a case where conduction is interrupted, it can be presumed that a broken wire has occurred in the H-type bridge circuit or coil, and determination of a broken wire can be made.