**Subject :**Electronics Switching

## Design of Transformer

**Design of Transformer**

Unlike the inductor, the transformer does not store energy. The transformer consists of more than one winding. Also, in order to keep the magnetization current low, the transformer does not have air gap in its magnetizing circuit. Consider a transformer with a single primary and single secondary as shown in Fig.2.7. Let the specifications be

Primary: V_{1} volt; I_{1} ampere;

Secondary: V_{2} volt; I_{2} ampere;

VA Rating: V_{1} I_{1} = V_{2 }I_{2};

Frequency: f Hz

For square wave of operation, the voltage of the transformer is,

The window for the transformer accommodates both the primary and the secondary. With the same notation as for inductors,

The above equation relates the area product (A_{C}A_{W}) required for a transformer to handle a given VA rating.

**Design Steps**

For a given specification of VA, V_{1}, V_{2}, J, B_{m}, k_{w}, and f, it is desired to design a suitable transformer. The design requires,

- Size of wire and number of turns to be used for primary and secondary windings.
- Core to be used.
- Resistance of the winding.
- Magnetizing inductance of the transformer.

1. Compute the Area product (A_{C}A_{W}) of the desired core.

2. Select the smallest core from the core tables having an area product higher than obtained in step (1).

3. Find the core area (A_{C}) and window area (A_{W}) of the selected core.

4. Compute the number of turns

5. Select the nearest higher whole number to that obtained in step (4), for the primary and secondary turns.

6. Compute the wire size for secondary and primary.

7. Select from the wire tables the desired wire size.

8. Compute the length of secondary and primary turns, from the mean length per turn of the core tables.

9. Find from the wire tables, the primary and secondary resistance.

10. Compute from the core details, the reluctance of the core.