Firming up the Specifications


Points of this article

・Because power supply specifications are often decided upon at the last minute, high-quality design must be accomplished within a short period of time.

The first important task is firming up the required specifications. Normally, this is the first and most important task, however, since power supply specifications cannot be determined until specifications for the entire circuit board are fixed, it is not uncommon that the task of establishing power supply specifications is undertaken only when the end of allotted design time approaches. That said, because the design process cannot move forward unless something is in place, the task is started based on the required voltage and an assumed load current, as provisional specifications. Normally, the following items must be fixed at the start of a design process:

Figure 30

If we take input conditions as an example, 100 VAC would be adequate for sales in Japan. However, if a given product is to be sold overseas, universal input capabilities fit for the voltage in the destination country in which the product is offered, or any voltage across the world, must be provided. Also, in some countries the voltage may be unstable, in which case a wide latitude in tolerance must be taken into consideration. When a large number of such factors must be addressed, selection of parts changes widely. Consequently, it is important to collect as much relevant information as possible at the outset of a design effort. Strictly speaking, a design process cannot be started unless specifications are clearly defined. However, the objective being to design an appropriate power supply within a given timeframe, a flexible posture is also good thing to have.

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