LEVEL SHIFTING CIRCUIT BETWEEN ISOLATED SYSTEMS

摘要

A level shifting circuit (20, 30) couples an input current (Iin) from one system to another, isolated, system, by driving a single load (L) via one or more current mirrors of a common type. In a first embodiment (20), two similar type (either N-type or P-type) current mirrors (M1,M2;M3,M4) provide output current (Iout1, Iout2) to a common load. Diodes (D1,D2) are used to split the input current (Iin1, Iin2) between the two current mirrors during normal, non-faulty conditions, and to turn off either one of the two current mirrors during a fault condition to permit proper operation in the presence of a fault. In a second embodiment (30), a single current mirror (M1,M2) mirrors the input current (Iin) to the output load (L), and a pair of diodes (D1,D2) selects which of the isolated systems to use as the power source in the event of a fault.