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By John Benatti

There are several factors to consider when choosing a power supply. An important first step is to categorize the major attributes of the supply. These can be generally be summarized as Fit, Form and Function:

    Fit is the ability to interconnect, interface or become an integral component of another item.
    Form is the size, mass, weight, shape and any and all dimensions that uniquely identify a power supply.
    Function defines the performance of a power supply under a quantified criteria (environment, electrical stress, physicality etc.).

Four Important Guidelines

Priority

Every power supply has a data sheet which identifies fit, form and function. The designer should consult the manufacturer data sheet to make sure the supply meets the requirements of their application. While all specifications should be considered, different applications may find some parameters more critical than others. In some designs, fit or the ability to conform to existing footprints and connections may be the most important. Others may have a need for a special form factor, while still others may require a specific electrical function and the ability to perform under a special set of circumstances. Consider the most important factor(s) when choosing a supply and assign the appropriate priority to them.

Data Sheets

A key consideration is that one manufacturer's definition of fit, form and function may be different from other information of the same parameter.  This can be caused by differences in terms that mean the same thing. Here's an example, one manufacturer publishes the rated current as "full load" while another uses "max load". You may call it operational current or static load or something else.  Also, keep in mind that space does not allow for all data to be published, therefore some information must be extrapolated from curves or other given data. Sometimes the curves themselves are formatted differently.  Inquire to the manufacturer's technical support if you have trouble understanding the information or need information not shown on the data sheet. Manufacturers will typically furnish additional data upon request.

Lastly, keep in mind that manufacturer is only responsible for the published data, which may be subject to change without notice. If full document control is necessary, it should be discussed with the manufacturer.

Interchangeability

When looking for replacement supplies, manufacturer part numbers and data sheets are good tools for discussion In the event that an exact replacement is needed, it's advisable to present a comprehensive written specification to the manufacturer for a full technical review.  This is often done in military applications where the designer will submit a procurement document. The procurement document assures that the manufacturer will meet all requirements. Changes to the part may be allowed when it still fulfills the requirements of the procurement document.  The end customer can request full document control to scrutinize any manufacturer changes before accepting them in all revised documents.

Review

New technologies and packaging have led to many changes in  power supply forms, with multiple connection options, and electrical characteristics.

As your particular market evolves, it may be worthwhile to make a periodic review of your requirements. You may consider using a higher density supply with a smaller footprint to gain space for additional build out.  Be vigilant about any changes that may have occurred to your operating environment. Advances in thermal management can help increase your operating spectrum, making for a more robust design.

Review your power budget, it may have decreased and you're  paying for unnecessary power. Consider any special connectors or feature sets that might have changed or been eliminated. Cost savings may be realized through standardization where possible.  Stay up to date on the necessary safety approvals for your market and any updates to those approvals. Re-certifications and/or amendments are often required for  continued sale to certain markets and countries.

Once your review is finished, you're ready to choose a power supply. PSUI engineers and sales staff are ready to work with you throughout the process with over 10,000  available SKUs.  Let us help you make the right decision for all your power supply needs.