What is the isolation function of MOS tube?

The advantage of choosing MOS tube for isolation is that no voltage drop will occur .

Essentially speaking , isolation is to achieve unidirectional conduction of the circuit, so where is its isolation function?

In fact, it is the worry that the current of the front pole will leak to the circuit behind, causing misjudgment of the power-on timing of the circuit system, the operation of the processor or logic device, and ultimately causing the system to fail to work normally.

Therefore, in practical circuit applications, isolation is very important.

Let’s take a look at the following circuit to see how isolation is achieved.

 (Laptop powered)

1. Connection adapter

2. The PQ66 here is a PMOS tube. When the adapter (19V) is connected, PQ66 is cut off, and the G pole voltage = S pole voltage = 19V.

When the adapter and the battery are connected at the same time, PQ70 is turned on and the gate voltage is 0.

 The gate of PQ6 is connected to 5V 

PQ6 is turned on, and the G pole voltage is greater than the source voltage. At this time, PQ62 and PQ66 are also turned on, and the gate voltage of PQ70 is 19V. PQ70 is turned off, and the battery no longer supplies power.

PQ70 plays an isolating role.

We know that there are three situations when laptop power supply is needed:

- Powered by adapter only

- Battery powered only

- Powered by adapter and battery at the same time

Isolation on the laptop motherboard separates the adapter and the battery to prevent them from directly connecting , but ensures that the computer can continue to be powered when either power source is unplugged, achieving seamless power switching .