Power on:
After the computer is powered on (not turned on), the power standby circuit works and outputs 5VSB to the mainboard, and enters the standby state.
Press the power button, the motherboard will send a signal to the power supply, the power supply receives this signal to start all, generate all output voltage, and then feedback a PG signal to the motherboard, telling the motherboard “I’m OK, you can turn on”. The motherboard will start after the PG signal.
——This is booting. The sequence of this process cannot be disordered.
Shut down:
When shutting down, the motherboard and power supply will also communicate with each other and return to standby.
What about the sudden power failure?
At this time, the motherboard cannot give a shutdown signal. The power supply detects the AC power failure, and will convert the PG signal to another signal to inform the motherboard “the power is out, quickly reset”, and the power supply should continue to output power for more than ten milliseconds at the same time. Ensure that the reset is successful. After the motherboard receives the power signal, it uses this power dispatch related hardware reset to deal with abnormal shutdowns. The most important thing is to reset the head of the mechanical hard disk (otherwise, the hard disk may die after an abnormal power failure).