Calculate the required duty cycle for a Flyback DC-DC converter in continuous conduction mode.
This calculator assumes continuous conduction mode (CCM) ideal conditions:
Real designs add 5-20% guard margin for component losses, temperature variations, and load regulation. Consult datasheets and use simulation for production designs.
A flyback converter is an isolated DC-DC topology. While the switch is on, energy is stored in the transformer's magnetizing inductance. When the switch turns off, that stored energy is delivered to the secondary winding and output capacitor.
The turns ratio changes the voltage conversion range, while duty cycle controls how long the primary stores energy during each switching period. This calculator estimates the ideal CCM duty cycle before practical losses and design margin are included.
Solving for duty cycle gives:
Enter the primary-to-secondary turns ratio as N_p / N_s. The calculator converts it internally to N_s / N_p for the formula.
Use the DC voltage available at the converter input.
Use the regulated DC output voltage required by the load.
Enter primary turns divided by secondary turns: N_p / N_s.
Use the result as an ideal starting point, then account for losses, voltage range, and controller limits.
Given: V_in = 12 V, V_out = 5 V, and N_p / N_s = 1.
Result: The ideal required duty cycle is 29.41%.
What does the turns ratio mean?
This calculator expects N_p / N_s: primary turns divided by secondary turns. A larger value means fewer secondary turns relative to the primary.
Why is this only an estimate?
The ideal formula omits diode drop, switch losses, winding resistance, leakage inductance, controller limits, and regulation margin.
What is continuous conduction mode?
In CCM, current in the magnetizing inductance does not fall to zero before the next switching cycle begins. Discontinuous mode uses a different design analysis.
Can a flyback converter step voltage up or down?
Yes. The duty cycle and transformer turns ratio allow a flyback converter to produce outputs above or below its input voltage while providing galvanic isolation.
Is a higher duty cycle always better?
No. Very high duty cycles reduce off-time available for energy transfer and can conflict with controller limits, core reset requirements, and practical efficiency goals.
What should I check before building a converter?
Check the full input-voltage range, load current, switching frequency, core saturation, winding currents, voltage stress, thermal performance, isolation, and protection requirements.
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