What is a MOSFET?

When looking for ESC's you have surely read the term MOSFET - in fact they (and the controller) are the heart of every ESC - but what does it mean, and how do they work? The abbreviation  MOSFET stands for Metall Oxide Semiconductor Field Effect Transistor and is used in electronics to switch and amplify signals.

It is a more specialized version of the classical transistor. In comparison to the classical transistor a MOSFET requires very little input current to control the load current. MOSFETS come in different sizes and packages. On ESC's nowadays the small surface mounted SMT package is most commonly used - simply because it is the smallest and most light weight option. 

In context of an ESC, the job of the MOSFET is to switch the three phases of the brushless motor in order to make it spin. A brushless motor with four poles needs to be switched through all 6 different states for one full rotation.

Each phase can be positive, negative or not connected. With three phases this gives us 6 different combinations that need to be triggered with a very precise timing. A motor with more than 4 poles needs to go through this six states multiple times in order to complete a full rotation.