The advantage of choosing MOS tubes for isolation is that there is no pressure drop.
Essentially, isolation is to realize the one-way conduction of the circuit, so where does it play a role in isolation?
In fact, it is worried that the current of the previous pole will leak to the circuit behind it, which will cause misjudgment on the power-on timing of the circuit system, the work of the processor or logic device, and eventually cause the system to fail to work normally.
Therefore, isolation is very important in practical circuit applications.
Let's take a look at the following circuit to see how the isolation effect is achieved.
(Laptop powered)
- Connect the adapter
Here PQ66 is a PMOS tube, when the adapter (19V) is connected, PQ66 cuts off, G pole voltage = S pole voltage = 19V.
Access to the adapter at the same time as the battery, PQ70 on, the gate voltage is 0.
2. The gate of PQ6 is connected to 5V
PQ6 is on, and the G-pole voltage is greater than the source voltage. At this time, PQ62 and PQ66 are also turned on, the gate voltage of PQ70 is 19V, PQ70 is cut-off, and the battery is no longer powered.
PQ70 acts as an isolating effect.
We know that there are three situations in which a laptop can be powered:
- Powered only by adapter
- Powered by batteries only
- Adapter and battery power supply at the same time
Isolation on a laptop motherboard separates the adapter from the battery so that they don't communicate directly, but it also ensures that the computer can continue to power when unplugging any of the power supplies, so that the power can be switched seamlessly.
Some of the above pictures and data come from the Internet (Chip Electronics Home)