Drive circuit for a bidirectional flow control valve

摘要

A normal-direction mode which switches on first and fourth switches T1 and T4 in a mutually diagonal relationship of an H-type bridge circuit 70 and switches off second and third switches T2 and T3 in a mutually diagonal relationship 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 T1 and T4 and switches off the second and third switches T2 and T3 is executed for an off-duty time of the opening-degree command signal. When normal, conduction of current to the H-type bridge circuit 70 and a coil 61 comes to be 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 70 or coil 61, and determination of a broken wire can be made. $$