Simplified Calculation of pulse transformers

Simplified Calculation of pulse transformers

I want to talk about the calculation of the pulse transformers, in the network it is described many techniques, but use some incomprehensible coefficients, those numbers where they come from? No one clearly describes, if I do not understand something or if I do not spegano clearly I will never be able to replicate what they learned and if necessary adapt it to my needs.

Let's start with the fact that we want to achieve a certain device, it needs a power supply, for example, equal to 250 watt, then you must select the magnetic circuit capable of delivering this power.

For this, there is a real formula for estimating the overall input power of a magnetic element:

  • kf is the form of voltage or current: for breast = 1,11 for the rectangle = 1.
  • KLC – Factor of the geometric cross section of the magnetic filler material feromagnetica GLC = 0.6 – 0,95, and it is available in reference books on magnetic element.
  • why – filling coefficient of the magnetic conductor window with the conductor sections, Kok = 0,35.
  • n0 – coefficient showing which of the primary winding of the coil needed to n0 = 0,5 in transformers.
  • Sc – section of the magnetic circuit.
  • Many It is the section of the magnetic circuit window.
  • J – current density, with natural cooling 3500000 A / m2, forcing you can get to 6000000 A / m2
  • B – Induction of the operation of the magnetic circuit.
  • f It is the frequency of the voltage or current Hz.

And so, according to this formula, we will estimate the actual total power of the transformer and will estimate what we can squeeze from this core!


We have a transformer from a computer power supply with parameters.

The cross section of the magnetic circuit is Sc = 0,9 cm2

The cross section of the window is Sok = 2,4 cm2

Work induction B = 0,15 (indicative value)

The expected frequency of the work of our device is f = 50 kHz.

We translate all in meters, ampere, hertz, etc.

We obtain:

Then the core is sufficient to withstand 250W, go further, it is now necessary to calculate the coils and the wire section.

Wanting a lot of data of the above formula I can be assumed to be constant further simplifying the formula, leaving only variables as the physical dimensions of the transformer and the frequency.

For completeness of discussion I have not done it but nothing prevents you from doing so for your personal calculations

We begin with ii number of primary winding turns, why there is a wonderful formula:

All the data we have seen above, except U1 – This is directly the primary winding voltage.

Suppose you build a half-bridge converter, starting from the traddrizzata mains voltage En = 310V, then U1 = 155V because the primary winding will be connected through a capacitor divider, eg 310/2.

Further we assume.

The secondary winding must have a voltage of 50 V.

Given that intend to obtain a dual voltage will be 14 more 14 spire. All values ​​are rounded to the nearest whole number!

Now calculate the cross-section of the conductors of the windings.

  • Primary:

P1: the power we need in output and set at 250 W.

  • Secondary: (the losses are neglected)

In this article, I wanted to explain briefly and easily calculating a pulse transformer, explaining the basic coefficients of what we are on hand.

Furthermore, do not forget that for a more accurate calculation it is necessary to use the magnetic element reference data.

At the end, I would say that I have used this technique for several years to calculate both the low-frequency transformers to high frequency.


1 reply
  1. Avatar
    doctor says:

    Amilcare I must say that you are always in the field despite the commitments ,but the passion is beyond praise limit , go on
    I'm always struggling my Power 4Kw x2 , I decided to do it straight , I'm testing .


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