Flyback Converter Calculator

Use the flyback converter calculator to find the duty cycle, currents, and inductances for the primary and secondary sides of your circuit.

Duty cycle26.966%D = V_out ÷ (V_out + N·V_in) — the ideal continuous-conduction value, before switch and diode drops

Conversion ratio0.0369×stepping down

Switching period4 µs

On time1.0787 µs

Off time2.9213 µs

Output power24 W

Input power26.6667 Wat 90% efficiency

Input current82.0513 mALESS than the output current — a buck trades voltage for current, which is why it is not a linear regulator

Power dissipated2.6667 Was heat in the switch, diode and inductor

Inductor ripple current7.1834 A359.17% of the output current — 20 to 40% is the usual design target

Peak inductor current5.5917 Awhat the inductor and switch must actually be rated for — sizing on the average current undersizes them

Minimum current for continuous conduction3.5917 ABELOW this the converter runs discontinuously and the duty cycle no longer follows the simple relation

Inductance for 30% ripple562.6966 µH

At twice the switching frequencyhalf the rippleripple is inversely proportional to both frequency and inductance, which is the trade that sets converter size — faster switching allows a smaller inductor but costs switching losses

The formula

buck D = V_out/V_in; boost D = 1 − V_in/V_out

Each topology has its own relation

A buck converter's duty cycle is simply the voltage ratio; a boost converter's is one minus the inverse ratio. They are not interchangeable — applying the buck formula to a step-up conversion gives a duty cycle above 1, which is why this page refuses the combination rather than returning a meaningless number.

All these relations assume continuous conduction and ideal components. A real converter needs a somewhat larger duty cycle, because the switch and diode each drop a few tenths of a volt and the inductor has resistance. Below a critical load the inductor current reaches zero each cycle, the converter enters discontinuous mode, and the duty cycle stops following the simple formula altogether — which is why the minimum continuous-conduction current is reported.

The peak inductor current, not the average, is what sizes the inductor and the switch. With 40% ripple the peak is 20% above the output current, and a component chosen on the average figure will saturate.

Ripple is inversely proportional to both frequency and inductance, which sets the central trade in converter design: switching faster allows a physically smaller inductor, at the cost of switching losses that rise with frequency.