onresistance

On-resistance, often abbreviated Ron or Rds(on), is the resistance between the drain and source of a transistor when it is in the on state. It is a key parameter for power switches such as MOSFETs, and to a lesser extent IGBTs, where it directly affects conduction losses and thermal design. Rds(on) is specified by manufacturers under defined conditions, typically at a chosen gate-source voltage (Vgs) and temperature.

In MOSFETs, Ron reflects how easily current flows through the channel when the device is turned on. It depends on device geometry (the channel width and length), material properties, and the quality of the gate oxide. Increasing the gate drive improves channel formation up to device limits, reducing Rds(on). Conversely, Rds(on) generally rises with temperature due to reduced carrier mobility and other temperature-related effects. Modern devices may use wide-bandgap materials to achieve very low Ron and higher-temperature operation.

Ron is a major factor in switching and conduction losses. For a given current, the power dissipated in the on state is approximately I^2 times Rds(on). Designers derate Rds(on) with temperature and use the worst-case value from the datasheet at the operating temperature. Other parasitic resistances in pins, leads, and PCB traces add to the total conduction loss and can influence thermal performance.

In IGBTs, the on-state conduction is often characterized by Vce(sat) rather than a simple resistance, so Ron is less commonly specified. The term is most closely associated with MOSFETs but can appear in broader discussions of switch performance.