How this calculator works
The transformer transfers energy to the output while the primary switch is on, and an output inductor smooths current. The secondary-to-primary turns ratio scales the input before the buck-like duty relation is applied. The reset circuit must restore core flux each cycle; its allowed maximum duty cycle is an additional design constraint.
Formula
Vo = Vi (Ns/Np) D; L = [Vi (Ns/Np)-Vo]D/(fs deltaI).
Worked example
A 100 V input, 20 primary turns, 10 secondary turns and D = 0.4 give 20 V output. With 0.0001 H at 100 kHz, current ripple is 1.2 A.
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Frequently asked questions
Does this include efficiency?
No. It uses an ideal power stage. Real semiconductor drops, winding resistance and switching losses alter the required duty cycle.
What does ripple current mean?
The entered ripple is the difference between maximum and minimum inductor current within one switching cycle.
Can this model discontinuous conduction?
No. If current reaches zero for part of the cycle, conversion ratio also depends on the load. Check the conduction mode and controller limits separately.