drainsource

Drainsource is a term used in electronics to describe the two-terminal path of a field-effect transistor (FET) between the drain and the source terminals. In FET devices, a conductive channel forms in response to a gate voltage, enabling current to flow from drain to source in an N-channel device or from source to drain in a P-channel device when the device is on. The drain-source voltage (Vds) and the gate-source voltage (Vgs) govern the device’s operating region: in the ohmic (triode) region, the current Id increases roughly with Vds; in the saturation region, Id depends mainly on Vgs and is relatively insensitive to Vds.

In MOSFETs and JFETs, the drain-source path is the primary current channel. The intrinsic body diode in a MOSFET lies between the drain and source; with the body tied to the source, the diode conducts when the drain is driven below the source by about one diode drop. The orientation of this diode differs for P-channel devices. While drain and source are often treated as interchangeable in symmetrical devices, the body connection and diode prevent perfect interchangeability, especially in power applications where reverse blocking or conduction paths matter.

The term drainsource frequently appears in datasheets, circuit schematics, and circuit-modeling contexts to denote the FET’s drain-source path. It underpins switching, amplification, and power-management functions across a wide range of electronic systems.