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Calculation of the transformer

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Knowing the required voltage on the secondary winding (U₂) and maximum load current (I_н), the transformer is calculated in the following sequence:

1. Determine the value of the current flowing through the secondary winding of the transformer:

I₂ = 1,5 I_н,

where: I₂ - current through the winding II of the transformer, A;
I_н - maximum load current, A.

2. Determine the power consumed by the rectifier from the secondary winding of the transformer:

P₂ = U₂ I₂,

where: P₂ - maximum power consumed from the secondary winding, W;
U₂ - voltage on the secondary winding, V;
I₂ - maximum current through the secondary winding of the transformer, A.

3. Calculate the power of the transformer:

P_mp = 1,25p₂,

where: P_mp - transformer power, W;
P₂ - maximum power consumed from the secondary winding of the transformer, W.

If the transformer must have several secondary windings, then first calculate their total power, and then the power of the transformer itself.

4. Determine the value of the current flowing in the primary winding:

I₁ = P_mp /U₁,

where: I₁ - current through the winding I, A;
Р_mp - calculated transformer power, W;
U₁ - voltage on the primary winding of the transformer (mains voltage).

5. Calculate the required cross-sectional area of ​​the core of the magnetic circuit:

S=1,3P_mp,

where: S - cross section of the core of the magnetic circuit, cm2;
Р_mp - transformer power, W.

6. Determine the number of turns of the primary (network) winding:

w₁ = 50U₁ / S,

where: w₁ - number of winding turns;
U₁ - voltage on the primary winding, V;
S - cross section of the core of the magnetic circuit, cm2.

7. Count the number of turns of the secondary winding:

w₂ = 55U₂ / S,

where: w₂ - number of turns of the secondary winding;
U₂ - voltage on the secondary winding, V;
S-section of the core of the magnetic circuit, cm2.

8. Determine the diameters of the wires of the transformer windings:

d = 0,02I,

where: d-wire diameter, mm;
I-current through the winding, mA.

The diameter of the winding wire can also be determined from the table. one.

Table 1

After that, you can proceed to the selection of suitable transformer iron and wire, the manufacture of the frame and, finally, the implementation of the windings. But W-shaped transformer plates do not have the same window area, so you need to check whether the selected plates are suitable for the transformer, that is, whether the wire will fit on the transformer frame. To do this, it is enough to multiply the previously calculated power of the transformer by 50 - you get the required window area, expressed in mm². If in the selected plates it is greater than or equal to the calculated one, the iron can be used for the transformer.

When choosing the core of the magnetic circuit, one must also take into account the fact that the ratio of the width of the core to the thickness of the set (the ratio of the sides of the core) should be within 1 ... 2.

As power transformers, radio amateurs often use unified vertical scan TV output transformers (TVK transformers). The industry produces several types of such transformers, and each of them, when working with a bridge rectifier, allows you to get quite certain voltages at the load, depending on the current it consumes. These parameters are summarized in Table. 2, which will help in choosing a TVK transformer for a particular power supply.

Table 2

Publication: radioman.ru

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