SMPS Flyback Boost Converter Calculator

This calculator tool supports a Boost Converter Flyback setup which means now the code considers:

Corrected turns ratio and primary voltage logic since the flyback works by storing energy during "ON" time and transferring to secondary during "OFF" time.

Flyback boost topology where output voltage is higher than input.

An accurate duty cycle formula for isolated flyback (especially in DCM).

How to Use This Boost Flyback Calculator

This calculator gives you a quick estimate of the primary turns, secondary turns, transformer turns ratio, and reflected voltage for a flyback transformer.

To use the calculator, just enter the following parameters:

Input Voltage (Vin): The DC supply voltage applied to the primary winding.

Output Voltage (Vout): The required DC output voltage.

Switching Frequency: The operating frequency of the flyback converter in kHz.

Core Cross-Section Area (Ae): The effective magnetic cross-sectional area of the ferrite core in mm².

Maximum Flux Density (Bmax): The maximum allowable flux density of the ferrite core in millitesla (mT). For most ferrite cores, values between 180 mT and 250 mT are commonly used.

Target Duty Cycle: The desired maximum duty cycle of the converter. A value between 40% and 50% is typically selected for flyback designs.

After entering these values, click the Calculate button. The calculator will show you the following figures:

• Primary Turns (Np)
• Secondary Turns (Ns)
• Turns Ratio (Ns/Np)
• Reflected Voltage
• Duty Cycle

The results provide a useful starting point for boost type flyback transformer design and verification.

Practical Calculation Example

Let us Assume we have the following specifications:

Vin = 12 V
Vout = 220 V
Frequency = 50 kHz
Ae = 125 mm²
Bmax = 200 mT
Duty Cycle = 45%

Step 1: Convert Units

Ae = 125 × 10⁻⁶ m²
Bmax = 200 × 10⁻³ T
      = 0.2 T

Frequency = 50 × 1000
          = 50000 Hz

Duty = 45 / 100
     = 0.45

Step 2: Calculate Primary Turns

Formula:

Np = (Vin × Duty) / (Bmax × Ae × Frequency)

Substituting the values:

Np = (12 × 0.45) / (0.2 × 125×10⁻⁶ × 50000)

Np = 5.4 / 1.25

Np = 4.32 turns

The calculator rounds this to:

Np = 4 turns

Step 3: Calculate Turns Ratio

Formula:

Turns Ratio =
((Vout + Vdiode) × (1 − Duty))
/
(Vin × Duty)

Assuming:

Vdiode = 0.7 V

Then:

Turns Ratio =
((220 + 0.7) × 0.55)
/
(12 × 0.45)

Turns Ratio =
121.385
/
5.4

Turns Ratio = 22.48

Step 4: Calculate Secondary Turns

Formula:

Ns = Np × Turns Ratio

Therefore:

Ns = 4 × 22.48

Ns = 89.9

Rounded:

Ns = 90 turns

Step 5: Calculate Reflected Voltage

Formula:

Reflected Voltage =
(Vout + Vdiode)
/
Turns Ratio

Substituting the values:

Reflected Voltage =
220.7 / 22.48

= 9.82 V

So Final Result Gives:

Duty Cycle      = 45 %
Primary Turns   = 4 turns
Turns Ratio     = 22.48
Secondary Turns = 90 turns
Reflected Voltage = 9.82 V