Two major functions of MOS tubes: Isolation (2)

By adding a diode, current can flow from A to B, but not from B to A.

 The same effect can be achieved by replacing the diode with a MOS tube. This is the isolation function of the MOS tube .

 The isolation function is to achieve unidirectional conduction of the circuit.

Why use MOS tubes instead of diodes? It all comes down to the voltage drop problem.

When the diode is turned on, a voltage drop will be generated. When the MOS tube is isolated, when it is forward-conducted, a suitable voltage is added to the control electrode to make the MOS tube saturated and turned on, and the current will hardly produce a voltage drop.

When we use a laptop, we will plug in the adapter and battery at the same time. When the power grid is out, the laptop will automatically switch to battery 12V power supply, and the adapter will no longer supply power.

 If there is no isolation of Q1 at this time, the 12V voltage will directly enter the output circuit inside the adapter and burn the adapter.

 When the MOS tube is isolated, the direction of the parasitic diode must be consistent with the unidirectional conduction direction to be achieved by the motherboard.

The above is about the isolation function of MOS tube.

Some of the above pictures are from 'Study Help'