A conversion circuit for discriminating sourcing current and sinking current utilizes a complementary switch circuit to change the serial loop connected with the output load according to ON/OFF signals, so as to correspond to a sourcing current output and a sinking current output. The conversion circuit also employs a voltage emulation circuit to shift the feedback voltage of both sourcing and sinking current to a suitable positive range, so as to omit a negative power source design. The conversion circuit utilizes a switch control logic circuit to timely blank the partial compared result of the feedback voltage of sinking current to generate correct ON/OFF signals.