Individually, the cost for components of a power supply is high compared with buying an off-the-shelf power supply. For example, a 30-amp 5-volt commercial power supply costs about 5 times less than the cost of making the same power supply, and already-assembled power supplies may come with a 5-year warranty. Therefore, it usually makes sense to design only what you cannot buy.
However, sometimes you might need a power supply that is very unique and specialized. Many companies attempt to design their own. Some are successful but many incur large expenses and waste precious time-to-market because they simply do not know how to design power supply systems that are stable, reliable, can be manufactured in high volume, and operate over long periods of time. Often they don’t know when to design it themselves and when to buy what they need.
When to Buy
Many times, one is told to “get that 40 dollar part out of the networking system to cut the cost.” After all, it’s just a power supply and any fresh young engineer can do that….right? Often, organizations with core competencies other than power electronics do not have the proper background, people, or test equipment and are unaware of associated issues. They dive head first into an area they are ill-prepared to navigate. The mistake is assuming that power supplies are simple components and can be designed by anyone. Why are companies outsourcing manufacturing to EMSI providers? Simply put, it costs them less and they can do a better job than in-house assembly. Consider also that your customers may have more demanding clients than you. The quality, reliability, and cost have been beaten out of the process with a bigger stick and thus total cost can be reduced when purchasing pre-assembled.
When to Make
Sometimes you cannot avoid having to make your own power supply. When does it make sense to build your own power supply?
• If you can’t buy something that meets your needs commercially.
• If the requirement for designing your own supply can be handled with off-the-shelf semiconductors or power-supply-on-chip parts that are well supported by applications engineering staff and software design tools.
• You have access to proper test equipment and have the expertise and the time to do the job properly.
• There is time to do it right.
• If buying a supply is really too much cost for the application and you are going to build enough of something to make a difference.
Although excellent resources are available, the best advice on using reference designs is that you should not put the responsibility for the design on your component suppliers without some effort internally. The designer and the company with the product are ultimately responsible for the end product or system. Don’t proceed without doing 4 corner testing and evaluation of the design and make sure the design is going to work over time and temperature. Do some hands-on evaluation and/or simulation. Never rely completely on the reference design from a semiconductor supplier and go right to full volume production.
Regardless of the topology or control technology used, companies should definitely invest in the training, design tools, test equipment, and software to validate the design so it will exceed expectations in the intended application. There are very good resources available, in many cases at no cost or with minimal investment in time or resources. Suppliers can provide reference designs, evaluation boards and design software – often at no charge. In many cases they will also supply the gerber files you can drop into your own system, ready to go.
Design Considerations if you Make
There are some questions you should ask before you make your own power supply or power electronics system. First, it’s important to consider what type of power converter system you need. This dictates the level of complexity of the overall design effort, risks, and regulatory requirements. Do you have the proper test equipment? Frequency response analyzers, electronic loads, electrical safety testers and other specialized equipment are needed and many simply don’t have these items on hand. Do you have people with expertise to design power supplies with the proper skills? Consider the magnetics, PCB layout, grounding, and shielding techniques needed. The autorouter will need to be turned off and manual layout skills will be needed. Safety spacing techniques in layout need to meet leakage guidelines.
Start with asking if the design is off-line or DC-DC. Is it isolated or non-isolated? Is something available off the shelf with proven performance? Parts with integrated supplies may be available. At lower power levels the components from the semiconductor companies have become highly integrated with many even containing the inductor inside the package forming what is commonly called PSIP or power supply in a package. If your design requires isolation, do you have the expertise and equipment to perform electrical safety testing on the designs to worldwide safety specifications and regulations? Do you know how to design magnetics for clearances required by safety agencies and approvals? Consider hours of operation; is this going to be a 24×7 high reliability application? It may make sense to buy if its high power off line, isolated, and demonstrated reliability is needed out-of-the-box and volumes are not sufficient to justify a make-it-yourself effort.
The expense to obtain safety agency approvals is great and takes time. If your product will ship internationally it will require large input ranges of voltage 85-265 Vac 50-60 HZ and will require agency approvals for worldwide acceptance; are you prepared for the expense and delays? Do you have safety experts on-staff who know the regulatory requirements and how to test? Consider EMI-RFI. Switching supplies can generate lots of noise and more if they are not properly designed. Regulatory agencies have no sense of humor or sympathy for your poor switching power supply design.
Make with More Tools and Resources than Ever Before
If after considering the issues you decide to make your power supply, it is strongly recommended that you involve suppliers early and often in the definition, selection, and design process. The earlier you seek support and assistance, the more time you will have to do things in an orderly fashion with greater flexibility and more options. A project timeline loses flexibility the closer you get to the prototype and production phase.
With energy efficiency, regulations, and so forth becoming a system level consideration, considering the power electronics up front rather than towards the end of the process is critical. Don’t choose the wrong part, topology or circuit, only to have units in stock with failures mounting. Nothing has to be designed in a vacuum; there are plenty of resources available to help you implement a successful in-house design under the appropriate situations. If you are going to design your own supply, the good news is that there is more support than ever before. New developments in technology available from Mouser include products for many levels of power converter powers. There are plenty of resources available to help you implement a successful in-house design under the appropriate situations. Whether you Buy or Make, Mouser carries products from over 450 suppliers with resources available for any power level and is there to help.
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