What is the basic function of ATX power supply?
As a switching power supply, the basic function of ATX power supply is to complete the power conversion of ac/dc.
Ac 220v is first converted into dc power (310v dc voltage after rectifying) through ac input and rectifying filter circuit. The voltage of the dc will flow intermittently and continuously through the primary winding of the switching transformer in the form of a pulse dc current under the control of the switch tube.
In the process of the pulse dc current flowing through the primary winding of the switching transformer, the switch tube is open. This process is the process of converting the electric energy of ac power 220 into magnetic energy and storing it in the core of the switching transformer (core charging). Next, the switching transformer should pass the magnetic field energy out of the core through its secondary coil. After rectifying, filtering and storing energy on the low-voltage side, the switching transformer should finally output to the output terminal of the ATX power supply.
Throughout the energy conversion process, there is an upper limit to the on-off time of the switch, which does not (and cannot) be unrestricted (not to mention always in the short-circuit limit) for obvious reasons. For the core of the switching transformer, after the switch tube is on, the core of the switching transformer is charged with the pulse direct current through the primary coil, but the magnetic field energy that the core can hold is also limited. Once the core's ability to store energy is exceeded, the most immediate result is that the primary coil of the switching transformer at the moment has no blocking effect on the current flowing through it (the primary coil is now equivalent to a normal straight wire). If the switch cannot be closed at this critical state (such as the switch itself short circuit), it means that the 310v dc voltage will return directly to the negative pole of the rectifier full bridge after passing through the switch tube and the primary coil of the transformer. This is equivalent to short-circuit the positive and negative output of the rectifier full bridge directly with the wire, and the consequences are self-evident. In fact, based on the actual output of the dc voltage at the output terminal of the ATX power supply (feedback), the switching tube is actively controlled for a period of time before the switch is turned off. We can call the time between the switch on and off as the "on-off time of the switch", which is recorded as ton, and the length of the "on-off time of the switch-on" must be controllable.
It is conceivable that switching-on times are different for the same ATX power supply at low and high loads. When switching from a low load to a high load, the switch should be switched on for a longer period of time so that more power can be delivered to the back-stage circuit. Otherwise, the speed of the input energy cannot keep up with the speed of the load consuming the electricity, which will cause the actual output voltage of the output terminal to decrease, and vice versa (the actual output voltage will rise.
To sum up, the switch tube in the switching power supply is actually a "turn-on, then turn-off, and then-turn-off" cycle, which starts over and over again. This mode of work is called "oscillation".
This article is from Allicdata Electronics Limited. Reprinted need to indicate the source.