Flyback Converter Calculator

About the Flyback Converter Calculator

The flyback converter is one of the most widely used isolated switch-mode power supply topologies, found in phone chargers, LED drivers, telecom power modules, and countless other applications below about 150 W. It stores energy in a coupled inductor (often called a flyback transformer) during the on-time and releases it to the secondary during the off-time.

Designing a flyback converter requires balancing many interdependent parameters: turns ratio, duty cycle, magnetizing inductance, peak currents, and voltage stresses on the MOSFET and output diode. Getting any of these wrong can lead to excessive losses, component failure, or audible noise from the transformer.

This Flyback Converter Calculator automates the core design equations. Enter your input voltage, desired output, load current, switching frequency, and efficiency target, and the tool computes the minimum inductance, ideal turns ratio, peak currents on both windings, voltage stresses, and a recommended output capacitor value. Use the operating mode selector to switch between continuous (CCM) and discontinuous (DCM) designs. Preset buttons provide common application profiles so you can explore trade-offs quickly.

When This Page Helps

Flyback converters are deceptively simple on paper but tricky to optimize. This calculator shortens the first-pass design work by solving the key equations together and highlighting potential stress issues before you order components.

How to Use the Inputs

1. Enter the DC input voltage (e.g., 12 V from a battery or 48 V from a bus).
2. Enter the desired regulated output voltage.
3. Enter the maximum output current your load requires.
4. Set the switching frequency — typically 100–300 kHz for flyback designs.
5. Adjust the expected efficiency (85% is a good starting point for most designs).
6. Set the diode forward voltage (0.3–0.7 V depending on Schottky or Si diode).
7. Review outputs: turns ratio, inductance, peak currents, and voltage stresses.
8. Use the table to compare primary vs secondary winding parameters.

Example Calculation

Tips & Best Practices

• Keep the duty cycle below 50% to simplify the RCD clamp design.
• Choose a Schottky diode for the output when Vout < 40 V for lower losses.
• Always derate components — choose a MOSFET rated at least 1.5× the calculated Vds.
• Use the magnetizing inductance as a minimum; going higher reduces peak current but may require a larger core.
• Check that your chosen switching frequency is above the audible range (> 20 kHz) to avoid transformer noise.

Flyback Topology Overview

A flyback converter uses a coupled inductor to store energy when the primary switch is on and deliver it to the output when the switch turns off. Unlike a forward converter, the flyback does not need a separate output inductor, which keeps the circuit compact for low- to mid-power supplies.

Selecting the Transformer Core

The core must handle the peak flux density without saturating. Ferrite cores are common because they perform well at switching frequencies in the hundreds of kilohertz. Use the magnetizing inductance and peak current from this calculator to choose a core and gap that can tolerate the intended load.

Snubber and Clamp Design

Leakage inductance creates a voltage spike when the switch turns off, so a clamp network is still required in most real designs. The MOSFET stress shown here is a design estimate, not a complete worst-case value, so leave margin for spikes and component tolerances.

Frequently Asked Questions

• What is the difference between CCM and DCM?

  In CCM the magnetizing current never reaches zero, giving lower peak currents. In DCM it drops to zero each cycle, simplifying control but increasing peak stresses.

• Why is flyback limited to about 150 W?

  Above ~150 W the peak currents and transformer size become impractical; forward, half-bridge, or full-bridge topologies are more efficient.

• What duty cycle should I target?

  For most designs 40-50% is ideal. Exceeding 50% requires a more complex clamp and increases transformer reset time.

• How does turns ratio affect component stress?

  A higher turns ratio reduces MOSFET stress but increases secondary peak current, and vice versa. The design is a trade-off.

• Why does the calculator ask for diode forward voltage?

  The output diode drop (0.3–0.7 V) directly affects duty cycle and reflected voltage calculations.

• Can I use this for multiple-output flyback designs?

  This calculator handles a single output. For multiple outputs, you would ratio the secondary turns proportionally.