Flyback Converter Calculator

Estimate ideal duty cycle, converter currents, and switching energy for a basic flyback power stage.

Calculate flyback converter values

This first-pass model assumes a 1:1 transformer turns ratio and continuous ideal voltage conversion.

Input voltage (V)

Output voltage (V)

Output power (W)

Efficiency (%)

Switching frequency (kHz)

About flyback converter calculations

A flyback converter stores energy in a coupled inductor while its primary switch is on, then delivers that energy to the secondary and load while the switch is off. This calculator provides useful first-pass operating values from input voltage, output voltage, output power, efficiency, and switching frequency. For the displayed ideal duty cycle it assumes equal primary and secondary turns. Under that assumption, volt-second balance gives duty cycle as output voltage divided by the sum of input and output voltage. Average output current is output power divided by output voltage. Average input current is larger than output power divided by input voltage when efficiency is below one, because the source must also supply converter losses. Input energy per switching cycle equals input power divided by switching frequency. These average quantities help establish the scale of a design, but they are not switch, diode, winding, or capacitor peak and RMS currents. Flyback waveforms are pulsed, so component stresses can be much higher than their average values. Transformer turns ratio changes the relationship between voltage and duty cycle. With a primary-to-secondary ratio other than one, the reflected output voltage must be included. Diode forward voltage, switch voltage drop, winding resistance, leakage inductance, snubber loss, dead time, and control-mode limits also move a practical converter away from the ideal result. Discontinuous and continuous conduction modes have different current waveforms and design equations. The magnetizing inductance and allowed peak current determine how much energy can actually be stored each cycle. Use these outputs to sanity-check a proposed conversion ratio, source current, load current, and per-cycle energy before detailed magnetic design. A complete design must account for the full input range, load range, transformer core area, flux density, air gap, wire current density, isolation requirements, creepage, clearance, thermal rise, electromagnetic interference, control-loop stability, and transient voltage stress. Select semiconductors and capacitors with suitable voltage, current, ripple, temperature, and safety margins. Offline and high-voltage flyback circuits can retain lethal energy; qualified design review and safe laboratory procedures are essential.

Flyback converter examples

Electrical inputs	Calculated values	Design context
12 V to 24 V, 48 W, 80%, 100 kHz	66.67% duty; 5 A input; 600 µJ	Ideal 1:1 step-up estimate
48 V to 12 V, 60 W, 90%, 200 kHz	20% duty; 1.389 A input; 333.33 µJ	Ideal 1:1 step-down estimate
24 V to 24 V, 36 W, 85%, 150 kHz	50% duty; 1.765 A input; 282.35 µJ	Equal-voltage baseline

How to estimate flyback values

Enter the operating input and desired output voltages.
Enter delivered output power and expected conversion efficiency.
Enter the switching frequency in kilohertz.
Select Calculate flyback values and review the ideal duty and average currents.
Use detailed magnetic and stress calculations before selecting components.

Frequently asked questions

What transformer ratio does this calculator assume?

The ideal duty-cycle result assumes equal primary and secondary turns. A different ratio changes the reflected voltage and therefore the required duty cycle.

Are the displayed currents peak currents?

No, they are average source and load currents based on power balance. Switch, diode, and winding peak or RMS currents require conduction-mode and magnetizing-inductance calculations.

Why does efficiency affect input current?

Input power must cover both useful output power and losses. Lower efficiency therefore requires more source current for the same input voltage and output power.

What does energy per cycle mean?

It is average input power divided by switching frequency. It indicates the energy-processing scale per cycle but does not by itself specify magnetizing inductance or peak current.

Can I use this result to build a mains converter?

No, it is only a preliminary ideal estimate. Offline converters require expert treatment of isolation, transient stress, EMI, thermal behavior, protection, and applicable safety standards.