Design and Peripheral Components Selection

Once an IC is decided upon, you move on with the design process by referencing the data sheets for the IC and example applications. In this process, you need to determine constants such as the external resistance and capacitance. In the case of a switching AC-DC converter, the design of a transformer represents a critical step.

Figure 32

The design of a transformer involves the following steps. First, the size of the transformer needs to be evaluated, by taking into consideration such factors as the power supply system to be employed, the switching frequency, and output power. Secondly, you need to decide on the inductance for the main coil (primary coil) and the number of winding turns for each coil to prevent any magnetic saturation. After that, you begin the structural design process. In the structural design, you determine the wire diameter of the wire material while ensuring an adequate layer configuration by taking the required degree of coupling into account, as well as an adequate creeping distance that complies with safety standards, and by making sure that wires can be wound on the effective spool on the bobbin. An example of transformer specifications is given below for your reference.

Figure 33. Example of transformer design

Selecting parts and evaluating the design of almost any electrical devices, beyond the transformer, requires not only knowledge of electricity and electronics, but also a considerable amount of experience. Armed with such a skill set, you work on the design phase; however, there may be situations where things do not go as intended. In such a case, you need to tap into the support provided by IC and parts manufacturers so that the design task can be executed speedily and efficiently.