Do you know what factors are related to the load capacity of MOSFETs?

Do you know what factors are related to the load capacity of MOSFETs?

The drain-source current and the resistance are the key indicators for determining the load capacity of MOSFET.

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

When the MOSFET is fully conductive, the conductive resistance is equivalent to "small resistance" between the drain and the source (as shown in the figure), and the VCC → RDS(on) → RL → GND forms loop.

Another factor to consider is the voltage division principle of resistors. The voltage division in a series circuit is directly proportional to the resistance value, and greater the resistance value, the more voltage it divides. By using MOSFETs in parallel, the total internal resistance can be reduced, thereby enhancing the load capacity

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

The larger the internal resistance, the more is consumed by the transistor itself, the easier it is for the transistor to heat up, the shorter its life span becomes, and even it may explode.

On other hand, the smaller the internal resistance, the more voltage is divided by the load, and the more energy is obtained, indicating a stronger load capacity. Therefore, is generally advisable to choose MOSFETs with lower internal resistance.

And what factors are related to the internal resistance RDS(on)?

Let's illustrate this with an example. When the driving voltage is 10V and the conductive resistance is 0.12Ω.

The conductive resistance of the increases with the rise in temperature. The figure below shows that the conductive resistance of this MOS is twice that at 20℃ when the junction temperature is 30℃.

As can be seen from the following figure, the higher the driving voltage, the actual conductive resistance is slightly larger, and the maximumive current is also slightly larger.

Therefore, when choosing a MOSFET, it is necessary to consider its drain-source current, internal resistance, and how parameters change with temperature and voltage. In applications with high power or high heat dissipation requirements, it is advisable to consider using MOSFETs with low internal resistance and may to use a parallel connection to enhance the load capacity.