What is the role of voltage transformer in the ATX power?

The voltage transformer plays a role from front to back in the ATX power supply. The electrical energy input from the primary winding is converted into magnetic energy stored in the core. The magnetic field stored in the transformer core requires a secondary winding output to the rear stage at a "suitable" time via a voltage-varying secondary winding. So, what's the right time? Let's analyze this problem through real-life examples.

1.Cases of  reservoir storage for power generation.

 After a certain amount of water is stored in the reservoir, it can start to generate electricity. At the same time, upstream incoming water can continue to flow into the reservoir and accumulate. This means that there are inputs (upstream water) at the same time as output (power generation) for reservoirs linking up and down.

2.Cases of charging and discharging of rechargeable battery

 After the rechargeable battery has run out of power, it needs to be recharged. Only after recharging, can it be installed into the device to provide the equipment with normal electrical energy.

This means that there is no output (discharge) for a rechargeable battery with input (charge) at the same time.

But why many battery-powered devices (such as laptops) can be charged at the same time?This is actually an illusion, because it is the AC 220V, not the rechargeable battery, that supplies the device with normal power at the moment.

So, is the switching transformer, like reservoir storage, able to output electricity through secondary windings at the same time as charging, or is it possible to output electrical energy through secondary windings after charging and discharging of rechargeable batteries? The answer is: yes, just avoid oversaturation of the core of the switching transformer It is referred to as "forward" (analogy to reservoir energy reserve) in the process of transformer energy conversion which outputs electrical energy through secondary windings at the same time as the primary winding is charged with energy. This is referred to as "fly back" (analogy to charging and discharging of a rechargeable battery) for a transformer that converts energy after the primary winding is charged and then outputs electricity through the secondary winding.

Visible, "forward" and "fly back" are not in fact based on the direction of energy transfer (the direction of any switching power supply is fixed, from the primary winding to the secondary winding), It's a distinction based on the transmission time of energy. Therefore, forward and fly back are essentially the concepts of time related to energy storage, transfer (release).

For "single-transistor forward" and "double-transistor forward" ATX power supplies, the primary switching transformer, while charging the primary windings, has begun to output electricity to subsequent rectified circuits through secondary windings. This is the meaning of "forward" in "single-tube forward" and "double-tube forward".

"fly back" is suitable for low power applications, while "forward" is more suitable for higher power applications. In the ATX power supply, the auxiliary power supply is small, basically uses the "fly back", and the main power supply is large, basically uses "forward". Although there is no word "forward" in the "two-tube and half-bridge" topology, it is actually a form of "forward".

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