SMPS Calculator for Toroidal Ferrite Transformers

This SMPS transformer design calculator is specially for toroidal ferrite core, so we can calculate everything from turns, inductance, core size, wire size and power handling, for high current DC-DC conversion using PWM (push-pull or forward).

Here we have added:

• Input voltage, output voltage, output current
• Frequency and duty cycle
• Core AL value (nH)
• Core window area and core cross-sectional area (optional)
• Primary and secondary turns
• Core loss estimation (approx)
• Copper fill factor check
• Recommended winding wire gauge and parallel strands
• Required ferrite core power rating estimate

How this smps transformer calculator work

So first we understand that this calculator mainly helps us to design smps transformer which is using ferrite toroid core.

We want to use it for dc to dc high current converter like push pull or forward smps. We also want that this toroid transformer give proper voltage and high amp output with minimum heating and saturation.

So this calculator takes few inputs like what is our input voltage which we give from battery or dc source, and what output voltage we want and how much current we want to draw from output.

Then we put switching frequency in kilohertz and also we put duty cycle value.

Then we put al value of the core which is in nano henry. Al value means how much inductance per turn square that core is giving.

Then we also put window area and core area of the ferrite toroid if we know it. Window area means how much winding space available inside the toroid hole. Core area means how much cross section area of the core center.

How calculation is happening inside

So after we give all values, first calculator takes our output voltage and current and calculate power. Then it divides that power by input voltage and finds input current. We assume 90 percent efficiency so that losses are also included little.

Then it calculates how much inductance we need in primary so that ripple stays under control. Here ripple taken as thirty percent of output current, just for safe operation. Then from inductance and al value, it calculates how many turns we need in primary winding. This is important because if we wind less turns then transformer saturates, and if we wind more turns then core get underutilized and also wire become long.

After getting primary turns, it again calculates what is actual inductance happening from those turns. Then it calculates how many turns we need in secondary winding by using voltage ratio and duty cycle.

Then it calculates how much ampere current we have in primary and secondary and then it find what cross sectional wire size we need in millimeter square.

We take 4 amp per mm square for safety, so wire not heat much.

Then it tries to calculate total copper area and compare with core window area. So that we know how much percentage winding space we are using. If winding space is more than hundred percent then we know wire not going to fit properly.

Then it tries to estimate how much magnetic flux we are generating in the core, based on input voltage, on time, turns and area of core. This is very important because if flux become more than 200 millitesla then core will saturate and whole thing may burn.

Finally it gives all result, including how many turns we need in primary and secondary, what wire size we need, what flux we are generating, and what core we should use based on power level.

When we should use this calculator

We should use this when we want to build high current dc dc converter using ferrite toroid transformer, but we do not know how to select turns and wire.

This helps us to decide transformer part fully. But this does not design whole smps. This only designs transformer part which is very important.

What we must take care

We must make sure that core al value is correct. We must make sure we use proper frequency. We must check if wire fitting in the core properly or not. We must test it practically also after winding. This calculator gives rough estimation but good enough for real world testing.