Design Procedure


Points of this article

・It is often the case that at the start of a power supply design process, specifications have not completely been decided upon; nevertheless, undertake the design task by firming up the specifications as much as possible.

・In the actual power supply design process, the power supply IC represents a significant part of that which must be designed; the circuits and parts to be employed are determined by the type of IC to be used.

・In making decisions with respect to mass production feasibility, beyond the question of compliance or non-compliance with required specifications, making adjustments involving tradeoffs may also be necessary.

After understanding the design basics, the next phase would be to perform the following design procedure:

Beyond the AC-DC converters, most design tasks involve the types of design steps outlined below. The first step concerns the verification of design specifications and the selection of components necessary to implement those specifications. Since most power supply design tasks nowadays require the use of a power supply IC, the “Selecting a Power Supply Controller IC” step listed below in essence involves selection of a power supply IC and performing a design process around the IC. After that, you select the parts required for the IC and execute the design process by calculating component values and other factors. When drawings are completed, a prototype is created, and its performance is evaluated. After that, mass production and product shipment follow in the overall flow of events.

1. Firming up the Specifications

The first step involves the process of clearly defining the required specifications. This is the first and most important step, to be sure. However, it is a fact of life that power supply specifications cannot be fixed until the overall specifications for the circuit are determined. As a consequence, the design task must be performed in great hurry near the end of the overall design timeframe ? adding considerable difficulty to those of you who may be involved in the power supply design phase. That said, since nothing can move forward unless something is decided upon to begin with, in many cases the design process is undertaken based on provisional specifications.

1. Firming up the Specifications

  • Input/output: Input voltage range, output voltage/accuracy
  • Load: Current with or without transient (including sleep/wakeup)
  • Temperature: Max/Min, with/without cooling
  • Size: mounting area, height (form factor)
  • Required protection: under-voltage, over-voltage, over-heating
  • Environmental/application conditions: automotive, aerospace/communication, RF
  • Cost

Strictly speaking, there is no denying that a design task cannot be undertaken unless clear specifications are developed first.

Listed above are the principal verification items required in firming up specifications. In the case of input conditions as an example, for doing business exclusively in Japan, we only need to concern ourselves with 100VAC. For worldwide sales, however, a broader range of voltages must be accommodated, and the fact that in some countries power supply is accompanied by unstable voltages must be taken into account. The specific components to be selected can vary widely, depending upon what margin of safety needs to be provided.

Other parameters also require careful consideration in order to design a power supply unit that fulfills given specifications.

2. Selecting a power supply controller IC

The second item to be addressed is the selection of a power supply controller IC. Based upon the requirements verified in Step 1, selection of a controller IC is undertaken by making decisions on such items as: a suitable method, whether a transformer or switching method is to be adopted, whether voltage stepping-up or stepping-down, flyback or forward basis, and whether an isolator or non-isolator type is to be used, which is a critical evaluation item for AC-DC converters. Thus, the selection of a controller IC amounts to determining the specific power supply method to be employed.

2. Selecting a power supply controller IC

  • System: Transformer, Switching
  • System: Step-up, Step-down, Buck-Boost, Inverting
  • System: Linear, Flyback, Forward and others
  • Isolated/Non-isolated

In actual power supply design processes, the power supply IC represents a significant part of that which must be designed; the circuits and parts to be employed are determined by the type of IC to be used. In other words, it would not be an overstatement to say that the design of a power supply unit hinges on the specific IC being used.

3. Design and Selection of peripheral parts

Once the IC and the power supply method to be employed are decided upon, you move forward with the design task, including reviewing application examples of the IC. Including the design of a transformer, you need to determine component values of capacitors and resistors for peripheral circuits.

3. Design and Selection of peripheral parts

  • Major transformation components:Transformers, bridges, diodes, capacitors
  • Components required for the IC
  • Calculation and optimization of component values
  • Transformer design

The design task requires considerable experience under the belt, not to mention knowledge of electricity, electronics, and components. While you pursue the design process based upon such knowledge and experience, you may still run into difficulties or questions for which you need help. In such cases, you can prosecute the design task speedily without wasting much time or effort by tapping into the support provided by the manufacturers of components.

4. to 5. Prototyping, Evaluation, Mass production, Shipment

4. Prototyping & Evaluation

  • Using an evaluation board/tools
  • Board prototyping and evaluation of operations and performance under assumed conditions
  • Debugging & optimization
  • Check for compliance with required specifications & Trade-off

5. Mass production design, Evaluation, Shipment inspection

In the prototyping process, you start with the verification of basic operations. There may be situations, however, where it is difficult to determine whether or not the prototype is operating as intended. In such a situation, in many cases evaluation boards for the IC you are working on may be available from the IC manufacturer, even though those boards may not exactly match the specifications for which the power supply unit is being designed. Taking advantage of such evaluation boards may be a smart way of getting the task accomplished. By using an evaluation board that is known to operate correctly, you can perform comparison evaluations to determine whether the circuit being designed operates correctly.

When finished with the debugging and optimization processes, you need to make decisions in regard to mass production. At this point, there may be situations where the required specifications are not completely satisfied. If a given set of specifications is an essential requirement, you may need to redesign the whole power supply unit or make tradeoffs, that is, make compromises here and there to bring the whole unit closer to the overall goal, and make similar considerations.

We believe that the design process should be conducted by performing this type of procedure.

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Basic of AC-DC Conversion

Basic studies to understand AC-DC converters and to go designing.