Drain-source current and internal resistance are key indicators for determining the load-carrying capacity of MOS tubes.

According to the formula P=I²R, the larger the drain-source current, the smaller the internal resistance, and the stronger the load-carrying capacity of the MOS tube.

When the MOS tube is fully turned on, the on-resistance is equivalent to the "small resistance" between the drain and source (as shown in the figure), and a loop is formed by VCC→RDS(on)→RL→GND.

 Another factor to consider is the principle of resistor voltage division. The voltage division in a series circuit is proportional to the resistance value. The larger the resistance value, the more voltage is divided. By using MOS tubes in parallel, the total internal resistance can be reduced, thereby enhancing the load capacity.

The drain-source current specifies the maximum current that can be safely carried from the drain to the source during normal operation.

The larger the internal resistance, the more power the tube consumes, the easier it is for the tube to heat up, shorten its lifespan, or even burst.

The smaller the internal resistance, the more partial pressure generated by the load, and the greater the energy obtained, which means the load-carrying capacity is stronger, so MOS tubes with lower internal resistance are generally selected.

What does the internal resistance RDS(on) relate to?

Let's take an example, when the driving voltage is 10V, the on-resistance is 0.12Ω.

The on-resistance of MOS increases with the temperature. The figure below shows that the on-resistance of the MOS when the junction temperature is 130°C is twice that when the junction temperature is 20°C.

 As can be seen from the figure below, the higher the drive voltage, the actually slightly larger the on-resistance and the slightly larger the maximum on-current.

 Therefore, when selecting a MOS tube, its drain-source current, internal resistance, and the changes of these parameters with temperature and voltage should be considered. In applications with high power or high heat dissipation requirements, consider using a MOS tube with low internal resistance, and may need to be connected in parallel to enhance the load capacity.