Flyback Converter Calculator
Compute the output voltage (Vout), duty cycle (D), or transformer turns ratio (N2/N1) of a flyback DC-DC converter with the ideal CCM model: Vout = Vin × (N2/N1) × D/(1−D). Includes CCM/DCM boundary check and MOSFET and diode stress estimates.
Advanced options (CCM/DCM boundary & component stress)
Verified examples
| Case | Input | Result |
|---|---|---|
| Find Vout | Vin = 12 V, D = 40%, N2/N1 = 2 | Vout = 16 V |
| Find duty cycle | Vin = 12 V, Vout = 16 V, N2/N1 = 2 | D = 40% |
| Find turns ratio | Vin = 12 V, Vout = 16 V, D = 40% | N2/N1 = 2.000 |
| Buck-boost mode (n = 1) | Vin = 24 V, D = 60%, N2/N1 = 1 | Vout = 36 V |
| CCM/DCM boundary | Vout = 16 V, D = 40%, n = 2, Lm = 100 µH, f = 100 kHz | Io,lim = 72 mA |
| MOSFET stress | Vin = 12 V, Vout = 16 V, n = 2, Vd = 0.7 V | VDS ≈ 20.35 V ideal (≈ 25.44 V with 25% spike margin) |
Frequently asked questions
What is the flyback converter formula?
In ideal CCM (continuous conduction mode), Vout = Vin x (N2/N1) x D/(1-D), where D is the duty cycle (0-1) and N2/N1 is the secondary-to-primary transformer turns ratio. This model ignores losses.
Flyback calculation example?
Vin = 12 V, 40% duty cycle, turns ratio N2/N1 = 2. Vout = 12 x 2 x 0.4/(1-0.4) = 9.6/0.6 = 16 V. This result is verified with high-precision calculation.
How do you find the duty cycle from a target voltage?
D = Vout / ((N2/N1) x Vin + Vout). Example: for a 16 V target from 12 V with turns ratio 2, D = 16/(2x12+16) = 16/40 = 40%.
What is the difference between flyback and buck-boost converters?
Flyback uses a transformer, so there is input-output electrical isolation and multi-output is possible; buck-boost is non-isolated. With turns ratio n = 1, flyback becomes equivalent to buck-boost: for example Vin 24 V and D 60% produce Vout 36 V.
What are CCM and DCM in a flyback?
CCM (continuous conduction mode): the transformer magnetizing current never reaches zero within one cycle, so the Vout formula above applies. DCM (discontinuous conduction mode): at light load, the core energy runs out before the cycle ends and the voltage ratio becomes load-dependent. This calculator computes the critical load current Io,lim; if your load is below it, watch out for DCM. Example: at Vout 16 V, D 40%, n 2, Lm 100 uH, f 100 kHz, the boundary is 72 mA.
What is a safe duty cycle limit?
Mathematically D must be below 1 (100%). In practice, flybacks are generally designed with D below 50-65% so the transformer core can reset each cycle and component stress stays controlled. The calculator warns when D is above 50%, and warns strongly when D reaches 90% or more.
What voltage must the MOSFET and diode withstand?
The MOSFET drain voltage is approximately Vin + (Vout+Vd)/n. Example 12 V to 16 V with n = 2 and Vd 0.7 V: about 20.35 V ideal, or about 25.44 V with a 25% leakage-inductance spike margin added. The secondary diode withstands a peak inverse voltage (PIV) of about n x Vin + Vout + Vd, 40.7 V in the example above. Always pick component ratings with margin above these values.
Does this calculator replace simulation?
No. This is an ideal model for early design estimates and learning. Conduction losses, leakage inductance, parasitic capacitance, and component tolerances make real results differ. Verify with simulation (for example SPICE) and prototype measurements before production.
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