The C&C T-CDU unidirectional output dc signal converter converts a dc current or voltage into a load independent dc current or voltage signal capable of driving a number of independent instruments. Power for the unit is derived from an auxiliary supply. Input, output and auxiliary supply are all galvanically isolated from each other allowing the separation of signal circuits. The unit conforms to IEC 688. In addition it meets the insulation requirements of IEC 255-5, clauses 5, 6 and 8 as well as the high frequency disturbance test of IEC 255-22-1 for Class III test voltage.