How the PSON to power on the ATX and then output other dc outputs?

If we don't do anything on the PSON to keep it high, then the ATX power supply is always on standby (no other dc output, no built-in cooling fans). 

It's easy to make the PSON low. If you want to lower the green 5v, you can and can only make the green 5v short-circuit to the ground. In other words, either use a conductor (such as tweezers, wires) to short the green 5v to the pin in the output terminal (the ATX power housing is also available). Either indirectly short the PSON to the ground through the boot button on the chassis panel through the boot triode or other gate circuits when the desktop motherboard starts up normally.

Tap the PSON and the ground pin next to it with tweezers (this action will not damage the ATX power supply) and observe the state changes of the built-in cooling fan in the ATX power supply. We will find that the built-in cooling fan in the ATX power supply starts to turn at the moment the PSON is tapped into the ground pin with tweezers. The rotation of the built-in cooling fan is the most intuitive visual evidence of the ATX power being turned on.

 next, we continue to do the same and continue to sum up the dc outputs of the ATX power supply by measuring the dc voltage of each pin of the ATX power output terminal using a multimeter.

It is not difficult to find that the dc voltage of about 3.3 v can be measured on the pin of the orange cable and about 5 v of dc voltage can be measured on the pin of the red cable. About-5v dc voltage can already be measured on the pin of the white cable, about 12v dc voltage can be measured on the pin of the yellow cable, and-12v dc voltage can be measured on the pin of the blue cable.

Particularly note that at this point a dc voltage of approximately 5v can be measured on the eighth pin of the gray cable leading to the ATX power output terminal (PG, also commonly referred to as "grey 8"). Re-test PSON, because the PSON has been directly connected with the ground wire with tweezers, at this time the actual measured on the PSON is the voltage of the ground wire, 0v. The measured voltage and uncharted PSON are the same as those before the ground wire, and it is still 5v.

Then, while removing the tweezers (that is, canceling the short-circuit relationship between the PSON and the ground wire), observe the change in the state of the internal cooling fan in the ATX power supply. Notice that the fan begins to slow down and eventually stop. Repeat orange cable, red cable, white cable, yellow cable, blue cable, gray cable dc voltage, all are 0v.

 Through the tweezers before and after all the output of the ATX power supply and built-in cooling fan state changes are summarized, it is not difficult to draw the following two conclusions.

(1) the PSON is indeed a switch that controls the power supply of the ATX on and off. It's just a logical level (not a mechanical) switch. The PSON is turned off at a high PSON of 5v, and the PSON switch is on at a low PSON of 0v.

(2). The PG is close to 5v dc voltage with each group of outputs (PSON short circuit, ATX power on) and 0v in the absence of each group output (PSON floating, ATX power standby). PG is also used to indicate whether the ATX power supply has normally outputted the dc voltages of each group.

In fact, the PG changes from low to high after each dc output reaches a specific threshold, with a delay of around 300ms. This delay may be realized by the delay capacitor or by the implementation of the delay gate circuit in the chip, which requires specific analysis of the power supply.

 to sum up, when the ATX power supply is connected to the ac 220v, the first generation of 5vsb. The 5vsb then provides a 5v dc voltage to the PSON through a specific circuit. -the Dane PSON gets a 5v dc voltage, and the ATX power goes into standby, ready to power on after the PSON is pulled down. Finally, the dc voltages of + 12v, + 5v and 3.3v were output. The full timing of the input and output of the ATX power supply is as follows.

(1) access to ac power 220v

(2) generates 5vsb.

(3) to produce PSON.

(4) the PSON is artificially lowered or the motherboard is pulled down. Directly

(5) produces + 12v, + 5v, + 3.3v, etc.

(6) after the delay of 300ms, a high-level PG is emitted.

This article is from Allicdata Electronics Limited. Reprinted need to indicate the source.