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

So this tool is for helping us design a flyback transformer for a boost type flyback converter, that means we are converting low DC voltage to high DC voltage, like maybe 12V to 300V, or 5V to 150V, etc. Ok?

Now follow these simple steps:

Input Voltage (Vin): Here we put the voltage from our battery or DC source. Like if we are using 12V battery, then put 12.

Output Voltage (Vout): This is the voltage we want at output after boosting. Like if we want to charge 300V capacitor or power 310V load, then write 300.

Switching Frequency (kHz): This is the frequency at which your transistor is switching ON/OFF. Mostly 50 kHz to 100 kHz is OK. You can try 65 for standard.

Core Cross Section Area (mm²): You check your ferrite core datasheet or measure it manually. Like EE25 or EE35 type core may have Ae = 60mm² to 100mm².

Max Flux Density (mT): It is the max safe limit of magnetic field inside core. You can use 200 to 300 mT, or write 220 as default.

Core Path Length (mm): This is the magnetic path length of the ferrite core. Like 50 mm is typical for medium core. Check datasheet or measure.

Core Relative Permeability (μr): This is the permeability of core material. Ferrite usually has 1500 to 3000. Use 2000 as safe value.

Then just hit the "Calculate" button.

It will give you:

• Duty Cycle in percent
• Turns ratio (Np / Ns)
• Primary winding turns (Np)
• Secondary winding turns (Ns)
• Primary Inductance in µH

Now you can wind your flyback transformer easily using those values.

Working Concept of Boost Flyback Converter

So this boost flyback converter works like this:

1. What Actually Happens:

We got a transistor (like MOSFET or BJT) and one flyback transformer. The input DC voltage is connected to primary winding. When the transistor is ON, then current flows through the primary coil and stores energy inside the core in the form of magnetic field, OK?

2. Why Flyback Is Cool:

Flyback works in a very special way. The primary and secondary never conduct together. When transistor is ON, then only primary works. When transistor turns OFF, then all that stored magnetic energy is released into the secondary and that charges the output capacitor through a diode.

3. Boosting Happens Like This:

Because we let energy build up slowly at low voltage (like 12V) in the core and dump it quickly into a high voltage winding, the output voltage becomes much higher, like 300V or more.

This boost depends on:

• How much time we keep transistor ON (that’s called duty cycle).
• How many turns we have on primary and secondary.
• How good is our core material and size.

4. Turns Ratio:

This is how we control output voltage. More secondary turns = more voltage. But we must also match it with duty cycle and frequency. So we calculate proper turns to keep flux inside safe limit (Bmax).

5. Inductance:

Primary inductance decides how much energy we can store per cycle. If L is too low, then we get too much peak current and may blow transistor. If L is too high then core saturates slowly and response becomes poor.

Example:

Let us say we want to convert 12V to 300V:

• Vin = 12
• Vout = 300
• freq = 65 kHz
• Ae = 80 mm²
• Bmax = 220 mT
• Lcore = 50 mm
• μr = 2000

Hit calculate.

You might get:

• Duty = 96%
• Turns ratio = 25
• Np = 18 turns
• Ns = 450 turns
• Lp = 120 µH

Then just wind 18 turns on primary and 450 on secondary. Use fast diode on secondary (like UF4007 or FR207) and your converter is ready.