Flyback Converter Turns Ratio

Np/Ns = Vin×D / (Vout×(1−D))

Calculator

Result
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Formula

Np/Ns = Vin × D / (Vout × (1 − D))

Description

The flyback converter is an isolated switching topology that stores energy in a coupled inductor (flyback transformer) during the switch-on time and delivers it to the secondary during the switch-off time. The turns ratio and duty cycle together determine the voltage conversion ratio. Unlike forward converters, the flyback uses the transformer magnetizing inductance for energy storage rather than transferring energy directly. Flyback converters are popular for low to medium power applications (5-150W) because they require minimal components and provide galvanic isolation.

Variables

  • Np/Ns — Primary to secondary turns ratio
  • Vin — Input voltage (V)
  • D — Duty cycle (0 to 1)
  • Vout — Output voltage (V)

Practical Notes

This ideal formula does not account for diode drops, resistive losses, or leakage inductance snubber losses. Practical duty cycles are kept below 0.45-0.5 for continuous conduction mode (CCM) operation. Multiple outputs with different voltages are easily achieved by adding secondary windings. The leakage inductance spike at turn-off requires a snubber circuit (RCD clamp or active clamp) to protect the switch.

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