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Power Supply Make-or-Buy Decision FAQs

Power Supply Make-or-Buy Decision FAQs

What should I consider when creating or purchasing a power supply? Sam Davis covers all of the questions you should ask yourself before doing so in this FAQ.

Many electronic systems companies are confronted with a decision on whether to design and build a power supply themselves or buy a power supply and integrate it in the system they are manufacturing.  When I worked in the Aerospace industry the company would build a system then try to get a power supply that would fit the available open space, which was usually difficult and ended up with some strange power supply shapes.  However, the system manufacturer may not know his power requirements until the system design is complete.There is a better way: make allowances for the power supply when the system is being designed, which may or may not be feasible.

These FAQs pose questions and answers to some of the decisions system manufacturers will have to make. Usually the decision boils down to time, money, and in-house capability in terms of people and facilities.

What impact does a make-buy decision have on the overall electronic system?
The decision to make or buy the power supply impacts overall power management subsystem cost and as well as cost of the entire end-item system. Therefore, equipment manufacturers are faced with the task of deciding whether to make or buy a power supply for their system that can either be bought or made by the equipment manufacturer. The make-or-buy decision for power supplies can have a major impact on the cost and time-to-market for the end item electronic equipment.

What questions should the equipment manufacturer consider before making a power supply in-house?

  • Can they make it cheaper than a purchased power supply?
  • Is time-to-market a consideration?
  • Are the necessary people and resources available to make the power supplies, including design and production facilities?
  • Does the design and production include the time, costs and fees associated getting agency certifications specific to power supplies?

What are the possible reasons for an equipment manufacturer to make the power supply in-house ?

  • They can’t install a commercial power supply because there is not enough room, such as in a battery-based portable system.
  • They must meet unique safety and EMC (electromagnetic compatibility) requirements that are not available in commercial units, such as found in military and aerospace systems.
  • They want the equipment to be proprietary.
  • They think they can make it cheaper.

Are there other factors to consider when deciding between making or buying power supplies?

  • Overall budget
  • Time-to-market for the end-item equipment
  • Finding and employing “safety critical” components for the power supply section
  • Time, costs and fees associated getting agency certifications specific to power supplies
  • Will your competitors have an advantage if they purchase a technically superior standard power supply?

What steps should the equipment manufacturer take if the decision is to buy the power supplies?

Figure 1. This allows you to list your requirements and then leave it up to power supply vendor to give you the answer
Figure 1. This allows you to list your requirements and then leave it up to power supply vendor to give you the answer

Find a manufacturer certified to meet the required reliability, safety, and EMC specifications. This usually means an investigation into the proposed manufacturer and development of the appropriate specification for the power supplies. Also, this usually requires a means for the equipment manufacturer to inspect the incoming power supply to ensure it meets its specifications. Plus, the equipment manufacturer may want to establish multiple sources to ensure delivery of enough products. In addition, the power supply manufacturer should provide documentation and technical support, if it is required. The power supply company should also be able to support the return of failed units.

Involve the power supply manufacturer early on in the design stage for architectural, product and cooling discussions. Traditionally, power supplies have been subject to the tail-pipe syndrome (i.e., remembering them when the project is nearly complete and having little time to select them).

The OEM power supply must provide the necessary output voltage, current and power. With such a broad range of standard products, you should see what type of power supply can meet your requirements. One way to start is to understand the characteristics of the available power supplies. If you can’t find a standard supply to meet your requirements, you will probably need to buy a custom-designed supply that is more expensive than a standard unit. An economic alternative to a custom power supply is the wide range of “modular power supplies” on the market today that can be tailored to your needs without the NRE and delays associated with a custom design.

One of the best ways to find the optimum power supply for your application is to fill out a form similar to that in Figure 1 (below). This allows you to list your requirements and then leave it up to power supply vendor to give you the answer. The completed form also allows you to use the same information if you are looking for a second source.

What steps should the equipment manufacturer take if the decision is to make the power supplies?
The first step is a paper design, followed by a prototype, design review, and then a decision on whether to go ahead with production. A typical design can take up to six months, depending on the availability of design engineers. Given the go-ahead, the purchasing department can order all the components, which usually includes qualified components from qualified vendors. As long as there are no long lead time components, production can start. Allow sufficient time for relevant safety agency approvals.

Are there any alternatives to the conventional make-buy decision?
There are alternatives to making and manufacturing the power supplies. For example one alternative is to subcontract the design phase. In addition, the production can also be subcontracted. Compare the cost of subcontracting with doing everything in-house.

What else has to be done with supplies built in-house?
When the first units are completed they will have to be tested for safety, EMC and reliability over the required temperature range. This depends on the appropriate standards that must be met, which might vary for some countries. If the manufacturer doesn’t have this facility in-house, the units can be sent to a testing laboratory.  
It is a good idea to select a power supply design that provides a safety margin for the future. Too often, electronic systems expand from their initial requirements and need additional current power, and sometimes even a new output voltage. A new output voltage requires an additional power supply or one with an adjustable output voltage, although most supplies can accommodate a 10% variation in output voltage.

How can a manufacturer check supply reliability?

Whether purchased or made in-house the equipment manufacturer must check the supply’s reliability. One way is to send one or two supplies to a facility that performs HALT (Highly Accelerated Life Test) or ALT (Accelerated Life Test).

  • HALT is the process of determining the reliability of a product by gradually increasing stresses until the product fails. This is usually performed on entire systems, but can be performed on individual assemblies as well.
  • ALT is the process of determining the reliability of a product in a short period of time by accelerating stresses (usually temperature) on the product. This is also good for finding dominant failure mechanisms. ALTs are usually performed on individual assemblies rather than full systems.
  • Electrolytic capacitors are a potential long term failure component. Calculate the electrolytic capacitor life using measured temperature data.
  • The equipment manufacturer may also want to check each power supply by “burning them in.” This is usually done by powering each supply for a given period, for example 24 hours, and then checking them to see if they are operating properly. Often, this is done by putting several supplies on a burn-in rack at the same time.

What OEM ac-dc power supplies can be purchased?
1. AC adapters
2. Front End power supplies for Distributed Power Architecture (DPA)
3. Centralized power supplies (single and multiple output voltages)
4. AC-DC brick power supplies
5. High Voltage power supplies

What OEM dc-dc converters can be purchased?
1. DC-DC brick dc-dc converters (single and multiple output voltages)
2. Non-brick dc-dc converters (single and multiple output voltages)
3. Encapsulated dc-dc converters (single and multiple output voltages)
4. Bus dc-dc converters
5. Point-of-Load (POL) converters (non-isolated)
6. Power Over Ethernet Power (PoE) Supplies
7. High voltage dc-dc converters

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