The push-pull converter solves a problem flyback and forward converters can't: efficiently moving hundreds of watts through a transformer without wasting half of every cycle. Two switches alternately drive opposite ends of a center-tapped primary, so the transformer core swings symmetrically through both quadrants of its B-H loop. That doubles the usable flux swing compared to a forward converter, letting you shrink the core for the same power.

How it works: Two MOSFETs (Q1, Q2) connect the ends of the primary to ground; the center tap goes to V_in. When Q1 conducts, current flows through the top half of the primary, inducing voltage in the secondary. Q1 turns off, both switches sit idle for a dead time, then Q2 conducts and drives the bottom half — flipping the secondary polarity. A center-tapped secondary with two diodes (or synchronous FETs) rectifies both half-cycles into a continuous output through an LC filter, exactly like a buck converter's output stage.

The killer advantage: the transformer never sees DC bias because flux swings symmetrically. Compare to a forward converter, which only pushes flux in one direction and needs a reset winding or RCD clamp to demagnetize the core every cycle. Push-pull uses all of the B-H loop, so the core is roughly half the size for the same throughput.

The killer problem: flux walking. If Q1 and Q2 don't conduct for exactly equal times — mismatched gate drive delays, asymmetric R_DS(on), even slight duty cycle errors — the core accumulates DC flux each cycle and eventually saturates. Saturation drops primary inductance to nearly zero, current spikes, and the FETs explode. Modern push-pull controllers use current-mode control (peak current sensing per cycle) to force exactly equal volt-seconds on each switch and prevent walking.

Real-world example: A 48 V telecom rectifier delivering 12 V at 50 A (600 W). Push-pull at 100 kHz with a ferrite EE42 core handles this comfortably. Each FET sees 2×V_in = 96 V during its off-time (the other half-winding's voltage adds through transformer coupling), so you'd pick 150 V MOSFETs with margin.

Rule of thumb — primary turns: For a given core, N_pri = (V_in × D_max) / (4 × f_sw × B_max × A_e). With V_in = 48 V, D_max = 0.45 per switch, f_sw = 100 kHz, B_max = 0.15 T (ferrite, derated for symmetric swing), A_e = 178 mm² (EE42): N_pri ≈ (48 × 0.45) / (4 × 100k × 0.15 × 178e-6) ≈ 8 turns. Note the factor of 4 instead of 2 — symmetric drive doubles the available flux swing.

Push-pull dominates the 100 W–1 kW isolated supply range where flyback runs out of steam and full-bridge is overkill.