# how to design a transformer

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#### franticEB

##### Full Member level 3 Hi i would like to learn to design a transformer for a forward converter (or other application), but i don't know where to start to study.
Is there any tutorial or book on this subject that you advise me?

I would like also to simulate the behavior of the transformer: how could i do?

Thanks a lot.

#### tpetar See this material can be useful:

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• AN-4134.pdf
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#### Charming Cherish

##### Member level 1 Transformer design process consists of five steps: (1) determine the turns ratio of the sides of the original; ② determine the original secondary turns; (3) determine the winding of wire diameter; to ④ determine the winding wire Shares; ⑤ accounting window area.

(1), former deputy edge ratio
In order to improve the utilization of high-frequency transformer, reducing the current switch, reducing output rectifier diode reverse voltage, reduce losses and reduce costs, the former deputy edge of the high-frequency transformer ratio should be as large.
In order to be able to get the required voltage at any input voltage, the transformer ratio should be a minimum input voltage selection. The maximum duty cycle for the selected sub section of the minimum voltage of the secondary side can be calculated as follows: In the formula, the output voltage maximum value, the on-state voltage drop of the output rectifier diode, for filtering inductance on the DC voltage drop. The ratio of the sides of the original:

(2) to determine the number of turns of the primary and secondary side
First select the core. In order to reduce iron loss, according to the switching frequency, the reference core material sheet, and may determine the maximum working magnetic flux density, the effective permeability of the core cross-sectional area, the window area. Transformer secondary turns: According to the number of turns and the turns ratio of the secondary side, the number of turns in the primary side can be calculated as follows:

(3) determine the wire diameter of the winding
To be considered in the selection of wire diameters, conductor skin effect. The so-called skin effect, which refers to the wire AC current flows, the current distribution of the wire cross section of the unevenness, the intermediate part of the current density is small, a large current density of the edge portion, so that the effective conductive area of ​​the wire is reduced, an increase in resistance. Under the conditions of power frequency, the skin effect is less affected, while at high frequencies greater impact. Wire the reduction of the effective conductive area is generally used penetration depth to represent. The so-called depth of penetration, and refers to the current density decreased to 0.368 of the current density of the surface of the wire (i.e.: a) when the radial depth. , Wherein, as the magnetic permeability of the wire, the relative permeability of copper, namely: the copper magnetic permeability of the magnetic permeability in the vacuum, as the conductivity of the conductivity of the conductor, copper.
In order to effective use of the wire, to reduce the skin effect of the current collector, generally require less than twice the depth of penetration of the wire diameter, i.e.. Require winding diameter is greater than the maximum diameter is determined by the depth of penetration can be small diameter wire multi-strand wound or flat, wide copper wound copper thickness of less than twice the penetration depth.

(4) determine the shares of winding wire
The winding wire Shares decide on the maximum rms current and wire diameter winding flowing. Consider the skin effect to determine the wire diameter, to calculate the maximum RMS current winding flowing.
The primary winding of the number of conductor strands: transformer primary current RMS maximum, then the primary winding of the number of conductor strands (wherein, J is the current density of the wire, generally take J = 3 to 5, for each of the wires of the conductive area).
The secondary windings conductive shares: ① full-bridge: transformer only a secondary windings, according to the relationship between the secondary current of the transformer primary, secondary side current RMS maximum:; ② half-wave: transformer has two secondary windings, each load windings respectively the half cycle of the load current, and therefore the effective value of (the maximum value of the output current). Thus the wires of the secondary winding Chunghwa

(5) Accounting window area
Calculate the transformer the original secondary turns, the wire diameter and the number of shares after the window area of ​​the core can rotate about the next or whether the window is too large, must be accounted for. If the window is too small, the core is too small, to choose a bigger core; if the window is too large, the core is too much, you can choose a small number of core. Re-select the core, and then recalculate the appropriate date until the selected core basic.

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