The ESC is usually composed of 3 parts:
-The voltage regulation
-The logic part
-The power part
The first one, voltage regulation is a BEC. Nothing more, nothing less. It is not always present in higher power ESC because there is two simple ways to lower a given voltage. First is to put a resistance in the circuit. The draw back is that the extra energy will be converted to heat. That is good if you have little difference in voltage and little current draw. The second method is switching. It turns full power on, then full power off for a given percentage of the time. That means that if you have 12v and need 5v, you need the BEC to be “on” only 41% of the time. To make sure that the logic parts work well, the switching is made REALLY fast (usually around 30k-45k times a second). The voltage is then “buffered” with capacitors. Think about it like a ***. It hold water and let it flow when full. Then, where there is missing water in the system, it uses the stored water to compensate.
The second part is the important one. The logic part takes the 5v signal from the receiver and reads it. The signal that the receiver sends to the ESC is not a PWM signal (Pulse Width Modulation, a signal that is never on for 0% and always on for 100%). It sends a signal that will be 0v most of the time, and on for a given TIME (instead of percentage), typically between 1ms and 2ms. It then acts as your hand when switching the lights on-off in your house. The exact same way that a switching BEC works, this one turns on and off at high frequencies to generate a PWM signal. But since it is powered by the regulated 5v from the BEC/regulator, it can only output 5v at 100%.
In a non-BEC ESC, this circuit uses the red wire from the receiver to know what is 100% (since the external BEC supplies the receiver, the red wire from the receiver will also power the logic part of the ESC). For that reason, most ESCs will have 3 wires from the receiver. If there is a BEC in it, it will supply the receiver (positive, negative and signal from the receiver). If there is no BEC, it will receive power from the receiver on top of the signal. The ESCs that only have two wires (black and with or yellow) use the current directly from the signal to know what is 100%.
The third part is what makes the motor turn. It is made of a MOSFET controller and an array of MOSFETs. MOSFET stands for Metal Oxide Switching Field Effect Transistor. Basically, it means that it is transistor that is made to be switched on-off and that it works on a magnetic field principle. This MOSFET is just like a wall switch. There is 3 pins on it. One is the input, one is the output and one is the switch (Source, Drain, Gate).
There is 2 types of it, just like Transistors: NPN and PNP. the first turns on when there is current applied to the Gate. The other works when there is none (0v or ground). This is important since you will need at least 4 MOSFETs, two each type, if you want to have a BRUSHED motor that turns both ways OR have a brake. For BRUSHLESS, this goes to 6.
That is because you have two wires on a brushed motor and 3 on a brushless. If you want the motor to turn both ways, you need at least two “positions” for each wire.
The controller is the part that takes the 5v signal that was decoded from the logic circuit and makes the MOSFETs work at full voltage (11.1v if you use 3 cells LiPo). It also makes sure that there is never two electrical paths that are open at the same time (causing a short). Since most MOSFETs require a Gate voltage that is above 5v (Most are CMOS parts), the controller makes sure that the 5v part stays at 5v and that the higher voltage part stay on it’s side