I have understood all the parameters except R<sub>ds</sub> and conduction loss. Please explain them to me. I am using a lithium-ion battery pack of 36 V and its maximum voltage is 42 V to drive a motor. Motor specifications: <br/> Minimum current: 500 mA <br/> Maximum current: 15 A <br/> I<sub>pulse</sub>: 30 A **The MOSFET I am planning to use is the [Vishay SQD50N05-11L][1]** MOSFET specifications: [![MOSFET specifications part 1][2]][2] [![MOSFET specifications part 2][3]][3] So based on the above specification, I have calculated the power dissipation: Power dissipation: I<sup>2</sup> * R<sub>ds</sub> = (15 A)<sup>2</sup> * 11 mohm = 2.47 watts And the maximum power the transistor can dissipate without a heat sink: (T<sub>max</sub> - T<sub>ambient</sub>) / R(jA) = (175 °C - 25 °C) / 60 °C/W = 2.5 watt I am confused that how to check and relate the *power* dissipation with R<sub>ds</sub> and select the MOSFET based on it. Is the MOSFET that I have chosen okay, based on the above specifications or should I go for a MOSFET with a low R<sub>ds</sub>? And please explain how to select the MOSFETs based on R<sub>ds</sub>. [1]: https://www.vishay.com/docs/72168/sqd50n05-11l.pdf [2]: https://i.sstatic.net/lcFkR.png [3]: https://i.sstatic.net/BjiYB.png