Flyback Converter Calculator

Calculate duty cycle, peak currents, and inductances for flyback converter design

Calculate Flyback Converter Parameters

Input Voltage (V_in)

DC input voltage to the flyback converter

Output Voltage (V_out)

Desired DC output voltage

Rectifier Voltage (V_rect)

Voltage drop across the rectifier diode (typically 0.7-1V)

Windings Ratio (N = N_p/N_s)

Ratio of primary to secondary transformer windings

Output Current (I_out)

Load current at the output

Switching Frequency (f_s)

Switching frequency of the MOSFET

Example Calculation

12V Power Supply

Input: 95V DC (from rectified AC)

Output: 12V, 4A

Rectifier drop: 1V

Windings ratio: 5.3

Switching frequency: 70 kHz

Results

Duty cycle: D = 42.04%

Primary peak current: I_p,peak = 2.60 A

Secondary peak current: I_s,peak = 13.80 A

Primary inductance: L_p = 219.08 μH

Secondary inductance: L_s = 7.80 μH

Converter Types

Flyback

Isolated buck-boost

Energy storage in transformer

Buck

Step-down converter

V_out < V_in

↑

Boost

Step-up converter

V_out > V_in

Flyback Advantages

✓

Galvanic isolation between input and output

✓

Can step up or step down voltage

✓

Simple topology with few components

✓

Multiple outputs possible

✓

Low cost for low power applications

Understanding Flyback Converters

What is a Flyback Converter?

A flyback converter is a type of DC-DC converter that provides galvanic isolation between input and output through a transformer. It can step voltage up or down and stores energy in the transformer's magnetic field during the switch-on phase, then releases it to the output during the switch-off phase.

How It Works

The flyback converter operates in two phases: when the switch is ON, energy is stored in the transformer's primary inductance, and the secondary diode is reverse-biased. When the switch turns OFF, the stored energy is transferred to the secondary side through the forward-biased diode.

Applications

•Switch-mode power supplies (SMPS)
•Battery chargers and adapters
•LED drivers
•Auxiliary power supplies

Key Design Formulas

Duty Cycle

D = N·V_fb / (N·V_fb + V_in)

V_fb = V_out + V_rect

Secondary Side

I_s,peak = 2·I_out / (1 - D)

L_s = V_fb / (2·I_out·f_s·(1-D)²)

Primary Side

I_p,peak = I_s,peak / N

L_p = L_s · N²

Note: Flyback converters are typically used for power levels below 150W due to efficiency limitations and high voltage stress on components.