The Transformer That Is Forbidden to Transform
The Transformer That Is Forbidden to Transform
A flyback converter looks like it contains a transformer: two windings sharing an iron core, primary and secondary, the shape everyone already knows from a wall wart or a power pole. It is not a transformer in the sense that matters. A transformer's whole purpose is simultaneity — current flowing in the primary induces current flowing in the secondary at the same instant, energy passing through the core without stopping to rest inside it. The flyback topology forbids exactly that.
During the on-state, current flows into the primary winding. The secondary diode blocks any current from leaving the secondary side at all. No energy crosses. What the primary current does instead is build a magnetic field in the shared core and leave it there, stored, doing nothing useful yet — the article's own figure names this precisely: "the output capacitor supplies energy to the output load" during this phase, because the transformer itself is not supplying anything. Only in the off-state, when the primary switch opens and primary current stops, does the secondary diode open and let the stored field discharge into the load. The article's figure states the mirror image just as plainly: "the energy is transferred from the transformer to the output load."
Two windings on one core, and at every instant exactly one of them is doing something. Never both. A component built in the unmistakable shape of a transformer, wired so that it can never do the one thing a transformer is for.
This is not a workaround or a compromise forced on the flyback by cheapness or scale — it is the entire mechanism. The core is not a bridge two windings cross together; it is a bucket one winding fills and the other later empties, and the two operations cannot overlap by the circuit's own design, not by accident of timing. Call the object a "flyback transformer" if you like — the name is conventional and the article uses it too — but what sits inside that shell is two inductors that have agreed to take turns.