Benefits Of External Power Supplies In Low-Power Applications
Most companies today are directing their limited engineering resources to focus on developing their product's key attributes, rather than designing the power supply which will power their system. Typically, power requirements are not fully known until very late in the design process and as a result, power supply selection is left as the final design chore. This causes system designers to frequently encounter a number of problems, leading to design choices that are less than optimal and cause both project delays and cost increases. This document will examine this problem and describe how external power supplies can help.
PROBLEM: What Power Supply
The ASIC's have been delivered and the first board has been stuffed and all systems appear to be functioning satisfactorily. Total system power has finally been determined and the project is only three weeks late. A quick decision must be made regarding the power supply to meet a market entry that was committed months ago. Sound familiar? This scenario is played out daily throughout the Electronic OEM marketplace as designers come to grips with real problems involving power supply choices.
PROBLEM: Space
Tooling is close to completion and there are only 16 cubic inches left available for the power supply.
PROBLEM: Height
Initial review of power supplies indicates that the smallest unit available is 2.2 inches high yet the max dimension on the case is 1.8 inches.
PROBLEM: Thermal overload
Power supply is adding 6 watts into the case and there are no vents or room for a fan.
PROBLEM: Agency approvals
Safety engineer indicates that spacing changes have to be made thereby delaying FCC testing.
DESIGN CHALLENGES
In low-power applications, design engineers responsible for the latest portable/hand held products face a number of design challenges to have their products effectively compete in the global marketplace. First, the market driven objective to make the package smaller, lighter, more reliable and yet retain all the desired technical features. For the designer, this translates into downsizing the package, increasing the density of logic boards, using smaller peripheral devices and eliminating the space normally occupied by the power supply. Then there is the additional challenge of shipping product very rapidly into the global marketplace.
To accomplish such a task, this requires shortening design cycle time and effectively reducing stumbling blocks such as international safety agency approval cycles. Lastly all designers wish for the flexibility to make continuous product modifications and to add features without delivery interruption. All are challenges that require design engineering ingenuity without compromising either design or market objectives.
TIMELY SOLUTIONS
External power supplies, once considered low cost technically marginal products for toys and consumer goods are now being accepted as the primary power source for a variety of technically advanced products. The benefits of using external power supplies in low-power applications have been recognized by major OEM's. In turn, the external power supply manufacturers have responded with products that reflect the needs of the market. New designs are being rapidly introduced to keep pace with a variety of high growth emerging worldwide markets for smaller portable and hand held products.
BENEFITS OF EXTERNAL POWER SUPPLIES
The benefits of using external power supplies in low-power applications can be divided into six definable categories.
Elimination of power supply design responsibility
Move the product to market faster
Reduce size and weight
Make product changes easily
Extended product life
Market worldwide
ELIMINATION OF POWER SUPPLY DESIGN RESPONSIBILITY
From a functional standpoint, there is not a great deal of difference between internal and external power supplies. i.e.: the system or subsystem requiring a 5 volt or 12 volt output operates satisfactorily whether the voltage was derived internally or externally. But the power supply design required to generate these voltages is different for externals versus internals.
First, designers of external power supplies must take into account that:
1. Evolving technologies demand smaller packages;
ie, more watts/cubic inch.
2. Component location and heat distribution effect long term reliability.
3. Listed international safety agency approvals are required to compete in the market.
4. Class B FCC and VDE is the minimum requirement for international EMI conformance.
Alternatively, these responsibilities are typically passed to the buyer of internal power supplies. System designers must:
1. Make the unit fit into the available space.
2. Assume responsibility for thermal problems.
3. Obtain agency approvals worldwide.
4. Solve EMI problems.
The assumption of these responsibilities by the external manufacturer is a prime benefit to the system designer and allows for more productive use of engineering resources.
MOVE THE PRODUCT TO MARKET FASTER
The transfer of the power supply design from the systems designer to the external power supply manufacturer also passes the responsibility of safety agency approvals to the external power supply manufacturer. Many of the US based external manufacturers have many standard models with approvals. This is very beneficial to the system designer if the use of a standard model meets the design criteria.
The use of safety agency approved external power supplies greatly simplifies the process of obtaining system approvals worldwide. Typically, if the product is saleable internationally, it requires at least three approvals (UL, CSA and VDE/IEC). Each of these safety agencies focuses on different parameters in determining whether the power supply meets the applicable safety criteria. UL and CSA place a lot of emphasis on flammability whereas VDE/IEC considers high voltages more of a threat.
The net result is that manufacturers of external power supplies spend considerable effort and expense to ensure worldwide conformance. The time to complete the approval cycle ranges from three to six months dependent on the complexity of the power supply and the type of approval. Costs including samples, materials, engineering and test time, and agency submission fees will be in the $6000 to $10,000 range per agency. All of this being assumed by the external manufacturer benefits the OEM user in getting the product to market faster and at a lower cost.
Should the systems designer require a modified standard or a pure custom designed external power supply, the agency approval cycle and costs will be very dependent on the manufacturer’s previous agency history. All of the US external manufacturers have a lot of experience in obtaining the various agency approvals and usually cycle time and cost is below what other manufacturers would encounter.
Hence, using a pre-approved model will provide a significant time and cost benefit to the project and speed the product into the marketplace. Additional time to market is gained when new features are desired or when engineering modifications are required. Changes and alterations can be accomplished without obtaining new approvals and the shipment of product can continue as if no change had occurred.
REDUCE SIZE AND WEIGHT
Certainly, one of the more challenging aspects of the design of portable or hand held products is size reduction. This may or may not require the elimination of the power supply from the packaging effort. However, the removal of the power supply from the package and the substitution of an external power supply does provide for a number of benefits.
In addition to obtaining space, the removal of the power supply also results in the elimination of other system components that are necessary when using an internal power supply. These may include filters, brackets, fans, power connectors and cords. The removal of both the power supply and associated components results in smaller and lighter packages. There is also the additional benefit of substantial cost savings associated with removing unnecessary components.
Packaging for external power supplies is now available in a variety of shapes and sizes with units being either freestanding tabletop designs or wall plug-in configurations. Packaging configurations are offered for both the North American market and the European market.
MAKE PRODUCT CHANGES EASILY
If the external power supply is an agency listed product, design changes to the system can be implemented rapidly without concern for agency re-submittals. This is a major benefit when trying to quickly either upgrade the product or introduce a new variation.
EXTENDED PRODUCT LIFE
In the majority of systems the power supply, being an inefficient device, provides a substantial amount of heat within its enclosure. Continuous exposure to excessive temperature has a tendency to shorten the expectant life of other system components. Therefore, using an external power supply removes the primary source of heat within the enclosure and should increase the anticipated MTBF.
The latest models of external power supplies being offered in the market bear no resemblance to those used in consumer or toy applications. Both quality and reliability have improved significantly. Elpac recently publicized that its WRI Series exceeded 800,000 hours of demonstrated MTBF. This greatly surpasses most if not all internal supplies being offered today.
MARKET WORLDWIDE
It is rare to find a company engaged in designing and marketing technical products that does not have its eye cast on the European or Far Eastern market. In fact, most major OEM's are shipping a minimum of 20 percent of their products internationally. Therefore design considerations must be taken into account for the vast differences encountered from country to country. External power supply manufacturers have met this challenge head-on by designing products that not only function across all borders but also conform to the safety and emissions requirements.
For example, a number of manufacturers produce "Wide Range Input" or "Universal Input" units that function equally well in the USA or in Europe regardless of AC voltage input. To further ensure ease of use, many of the standard models available incorporate an IEC input connector to allow the use of international cord sets. This greatly benefits the OEM by limiting his power supply purchases to a single model for all shipping destinations.
External manufacturers have begun to offer more standard models in wall plug-in configurations for Europe. Again, this is in response to the needs of the market and the continuing acceptance of external power supplies for worldwide applications.
Additionally, most external power supply manufacturers have expended the resources to obtain international safety approvals. This includes UL, CSA, VDE or TUV and listing to IEC950 the specification required throughout the common market. A number of external manufacturers, including Elpac, have applied for recognition to IS09001, the European Quality Standard. This accomplishment by the external manufacturers is the primary reason for the wide acceptance of external power supplies.
Lastly, most of the external manufacturers have designed their units to meet the North American and European emissions requirements. This was a difficult challenge because of the major differences between North American and European specifications. However, it had to be accomplished if external power supplies were to satisfy the OEM and the need to ship product worldwide.
SUMMARY
External power supplies do provide measurable substantial benefits when used in low-power applications. The latest models of external power supplies reflect the specification requirements of OEM manufacturers of laptop and notebook size computers, datacomm and telecomm devices, instrumentation and medical devices.
Small lightweight slim units that function internationally with the proper safety approvals are available today. Then there is the additional requirement for external power supplies to meet the input voltage and safety requirements of not only the North American market but the European market as well. These types of units are also available. Other more intangible benefits include getting the product to market rapidly, the ability to ship the product to a global market, improved reliability and the ability to institute changes without infringing on delivery. Although these are benefits that can not be easily associated with dollars and cents, they are in fact the significant ones that ultimately contribute to the success of a product.
Practically speaking, external power supplies today offer the design engineer the most comprehensive array of power supply solutions available for low-power applications. In fact, external power supply models currently available represent the most beneficial and reliable solutions for providing the primary power to a vast range of products. The benefits of using external power supplies for these types of products exceed those for any other type of power supply currently being produced.
Externals will continue to offer a broad range of benefits to designers. Whether the objective is to shrink the package, shorten the time to market or to reduce the agency issues. However they are applied, externals are the solution of the real power supply problems of today and tomorrow.