Work out flyback transformer instantly with clear inputs, formula shown and shareable results.
In a flyback the output voltage plus diode drop is reflected onto the primary multiplied by the turns ratio. The switch must withstand the input voltage plus that reflected voltage plus leakage spike, and the turns ratio is therefore a direct trade between switch voltage rating and rectifier rating.
Flyback voltages
Vreflected = (Vout + Vd) x N; switch stress = Vin + Vreflected + spike; D = Vr / (Vin + Vr)
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
It raises the reflected voltage and so the switch stress. A lower ratio instead raises the secondary diode's reverse voltage, so the choice balances the two.
Transformer leakage inductance and the snubber design. A 20-30% margin on top of the calculated stress is normal practice.