# What is the PSON?

Last Update Time: 2019-03-14 11:40:34

The full text of PSON is power supply on, in which power supply refers to the ATX power supply and ON refers to the power on.

Literally, a PSON is the control switch that controls whether the ATX is turned on. In fact, this is true, but the PSON is very different from the switch in its usual sense. For example, the switch of the lamp, turn on the switch with the finger, lighten the lamp, turn off the switch with the finger, turn off the lamp.

Table lamp switch as a visible physical switch is very easy to understand. In contrast to the PSON, it is physically a pin (14 feet, with a 3~ 5 v level) that is drawn from the inside of the ATX power supply with a green cable to the ATX power output terminal. It can be seen that even if the PSON is really the switch of the ATX power supply, it is indeed a switch with a significant difference from the desk lamp switch.

Whether it is a visible mechanical switch for table lamps, or a PSON switch similar to an ATX power supply, we can first proceed from an intuitive and perceptual point of view. Imagine that all switches in the world should have something in common (regardless of their physical state). It is true that all switches in the world should have and must have (at least) two stable logical states: the switch is on and the switch is off.

It is not difficult to understand that the state of a mechanical switch, such as a visible lamp switch, is closely related to the physical position of the switch. So, when it comes to a PSON switch, what is the physical representation of its switching state?

In a digital circuit, the voltage level clearly corresponds to a different state: high level (1) is a state, low level (0) is a state. With regard to the PSON switch, can we speculate that the PSON switch is in a stable logical state (on behalf of off) when the PSON is at a high level; while the PSON is at low normal times, the PSON switch is in another stable logical state (on behalf of the open), and that is the case.