Power supplies are sometimes considered trivial designs problems, often relegated as first projects for engineers joining industry, usually with disastrous results.
These disastrous results include schedule slips, cost overruns, and excessive field failures, with associated warranty costs. The root of the problem is usually underestimating the complexity of power supply design, especially switching-mode power supplies.
The perception that power supply design is trivial dates from the era when power supplies were usually a transformer-rectifier set and a dissipative series or shunt regulator. The perception was probably not true then and is certainly not true now -- now that most power supplies are of the switching-mode variety.
Because this perception led to inexperienced designers being assigned to the power supply, power supply related problems became severe in the 1970-80 decade. The Navy claimed that if power supplies just met their specifications there would be a 20% improvement in fleet readiness. They dictated that the procurement agency had to investigate if less than 10% of a project development budget was devoted to the power supply development -- an unprecedented action. Projects on an 18 month schedule sat on the shipping dock for another 18 months waiting for a working power supply.
Switching-mode power supplies are:
- non-linear circuits
- difficult to stabilize, often having real and complex poles in the right-half plane
- subject to chaos
- magnetically complex -- requiring consideration of proximity and eddy current effects and often requiring planar construction
- analog, digital, and power circuits, requiring knowledge of each discipline
- sources of electromagnetic interference
They are not a trivial design task.
The problem and consequences of underestimating the complexity of power supply design and application is relevant to almost all electronic systems, since virtually every electronic system requires a power supply.
Awareness is the first step in solving any problem. At first the problem was buried as being too embarrassing to talk about (after all, how could something as simple as a power supply cause so many problems), but a Navy/Industry team brought the problems solidly into the open with the 1982 publication of the first edition of Navy Power Supply Reliability - Design and Manufacturing Guidelines . With over 18,000 hard copies distributed, most of which were further copied, along with substantial press coverage -- both supportive and critical -- the lack-of-awareness issue was resolved and industry could get on with solving the problem. Although somewhat dated, reading this landmark publication should be informative for any system or power supply designer and their management. The Best Manufacturing Practices Center of Excellence website published a second edition  and then replaced it with the current design guide,  NAVSO P-3641A, More Power For The Dollar, January 1989, which is available on the World-Wide Web.
In essence the problem was and is solved by taking power supplies seriously, getting someone on the program from the beginning who understands their applications and pitfalls, getting manufacturing or the vendor on board early, allocating sufficient resources -- including schedule, knowledgeable personnel, and software and hardware tools, and by serious use of design reviews and manufacturing screens.
The solution to underestimating the complexity of power supplies is awareness. A short history lesson provides an introduction.
Throughout the 1960's and 1970's, many program managers learned the hard way (though experience) that power supplies were the critical-path item on their program, causing embarrassing schedule slips and cost overruns on an otherwise successful program. Unfortunately, people talk about their successes and not their failures, especially when it is something as embarrassingly simple as a power supply. Hence, the trouble with power supplies was one of the best kept secrets of these decades.
But the Navy was keeping score and by 1979 had determined
"Failure data suggests that fleet readiness could be improved as much as 20% if electronic power supplies simply met their specified mean times between failures in service use." P4855-1, page 1
To put it in stronger terms, if only power supplies met their allocated field reliability, it would be equivalent to adding a couple of aircraft carriers to the fleet -- complete with a full compliment of aircraft, munitions, and crew -- at no extra cost to the taxpayer.
The Navy then went on to contact 170 Navy power supply design activities, convened a panel of experts to work on solutions, and published the solutions in Navy Power Supply Reliability - Design and Manufacturing Guidelines , arguably the widest read document ever written on power supplies.
Once the problems were aired, contractors admitted they had the same problems on Air Force, Army, NASA, and commercial programs as they had on Navy programs. The problems with power supplies were widely discussed and solutions found and implemented. By 1989, the Navy could claim that power supplies were no longer the number one failure item in the fleet. But before this occurred, some remarkable things happened.
Prior to the release, and in anticipation of Navy Power Supply Reliability - Design and Manufacturing Guidelines , the Navy released NAVMAT NOTICE 3080 , which, among other things, required a Navy Program Manager's procuring activity to investigate and justify any program that did not meet certain criteria. These criteria included:
"The development schedule shall allot at least 18 months from power supply specification release to production start, including completion of qualification and reliability growth screening."
"At least 10% of the total electronic system development cost, excluding software, shall be budgeted to the power supply function."
These are remarkable requirements. To the best of my knowledge no program manager had ever been constrained before or since to allocate a specific percentage of their resources to a specific function.
There were probably few program managers who were allocating this much to power supplies or who wanted to do so -- they thought they had better use for their money.
To further make program managers aware, if the schedule was less than 12 months or the funding less than 5%, special approval had to be obtained from the Deputy Chief of Navy Material, Reliability, Maintainability, and Quality Assurance (then Mr. W. J. Willoughby, Jr.). And this was no rubber stamp approval. The program manager had to explain to people knowledgeable of the history of past problems why their program was different. If he could do that, no problem, but he had to do his homework.
The bottom line is that this established awareness at the highest program management level.
The above illustrates the steps the Navy took in making program managers and subordinates aware of serious power supply problems. After making them aware, a plan was provided, Navy Power Supply Reliability - Design and Manufacturing Guidelines , that was designed to reduce the risk of the problem to acceptable levels (power supplies meeting their allocated reliability in the field).
History often repeats itself when the members of the current generation do not have knowledge of the problems of past generations. The 1980's decade saw the recognition and solution of a serious reliability problem with power supplies. Power supplies are still a serious design and application problem. Not being aware of the potential problems and the ways to reduce risk leave any present program manager susceptible to their worst nightmares - schedule slips, cost overruns, and poor field reliability.
Disclosure: I was on the committee that wrote the first edition -- but that does not mean I agree with everything. Never-the-less, it is one of the better committee efforts concerning power supplies. If you read the document and see something that has been overtaken by events or is wrong from your viewpoint, don't reject the whole document. Much of it is still relevant.
There are lessons to be learned from two programs in two separate large corporations that got into problems by underestimating the complexity of power supplies. I learned the details about the first by talking to two engineers who were involved. I had personal experience with the second.
The first resulted in an 18 month schedule slip on a system schedule that was 18 months from go-ahead to completion of qualification testing. At the beginning of the program a buy decision was made and the power supply development was awarded to the lowest bidder. When it became apparent the design activity could not deliver, the contract was pulled and awarded to the next lowest bidder. When it became apparent that they also could not deliver, the power supply was pulled inside. However, instead of drawing on a group of designers who had strong experience in switching-mode power supply design, the company gave it to some excellent designers with strong backgrounds in communications and analog design (one of the engineers I talked with). When they ran into trouble, the corporation finally tapped their power supply design experts (the other engineer I talked with) and the job was completed. The rest of the system was completed on the original schedule up to the start of qualification testing and waited on the dock for qualification testing for 18 months before the power supplies were available. The final result was an 18 month schedule slip for underestimating the complexity of power supply design.
The second started the same, but ended up on schedule. Again a buy decision was made and the power supply development was awarded to the lowest bidder. Again, when it became apparent the design activity could not deliver, the contract was pulled. But this time work was pulled inside to give more management control over results. Also, the company informed their government customer of the problem and the government offered their expertise. That is how I got involved. The company found and gave the project to the best qualified power supply engineer in the corporation, told him the schedule was sacred and to do everything possible to keep the system on schedule using the full resources of the corporation. He and his management first selected the best corporate facility in the country to produce the power supply, which was on the west coast, and assembled a team to do the job, mostly from east coast engineers. They were placed in a hotel near the west coast plant and worked between 60 and 80 hours a week. Two of the engineers were control experts and had the best computer tools available in the corporation to work the stability issues. Another was an electromagnetic interference expert who made sure everything in this area was done right. Magnetic designers, layout and packaging experts, and manufacturing experts rounded out the team. Most of the system tests were completed using laboratory power supplies, but when qualification testing started, the final power supplies were there. The final result was a system delivered on time.
What are the lessons learned? The problems started on both of these programs by awarding the power supply contract to the lowest bidder. This invites buy-in by unqualified design activities. The Navy recognized this problem in Navy Power Supply Reliability - Design and Manufacturing Guidelines and other directives which state:
"A fundamental criterion in power supply source selection should be the bidder's stated, perceived, and demonstrated ability to comply with these guidelines." [Navy Power Supply Reliability - Design and Manufacturing Guidelines]
Lesson #1. The lowest bidder is not the primary consideration for contract selection. The primary consideration is that the bidder must be perceived as being able to do the job. The bidder usually establishes this by the experience of their designers and manufacturing personnel in the design and manufacture of similar power supplies. Also their track record in accurate bidding of the cost and schedule on similar power supplies. I once asked a successful power supply buyer what the three most important things he would recommend to other buyers. His list was:
- Vendor Selection
- Vendor Selection
- Vendor Selection
Lesson #2. When in trouble ask yourself how you can do things better, rather than repeat past mistakes. In the first example, they just repeated their first mistake -- giving the contract to the lowest, and unqualified, bidder -- then when they brought it in-house, continued to give it to an unqualified bidder, an in-house design activity with no power supply experience.
Lesson #3. Ask for help when you first get into trouble and then apply a big enough hammer to get the job done. Large corporations have many shortcomings, but one advantage they have are formidable resources they can apply to a problem. In the first example, when they finally pulled the contract in house, they gave it to the best they had locally -- who had little to no power supply experience (after all, power supply design should be no problem for experienced analog and communication designers) instead of tapping the corporate power supply experience. Eventually they tapped their in-house expertise and finally got an excellent power supply -- at an extremely high cost in terms of schedule slip and the associated cost overruns. In the second example, when program management perceived a schedule problem, they not only asked that the full resources of the corporation be applied, but also asked for any resources their customer, the government, could offer. By asking for help, and recognizing what was needed to get the job done, it got done.
This failure to ask for help is getting worse instead of better in today's environment of product teams. Teams and their management pride themselves on their ability to get the job done. But often they get in over their head because a generalist team member thinks they can do the job of a specialist. When they finally realize they can't, the program schedule is usually at risk.
On the Web
Navy Power Supply Reliability - Design and Manufacturing Guidelines
This is a digital "how-to book" on the Best Manufacturing Practices Center of Excellence website. The book is part of the KnowHow books in the Electronic Library and requires special software available through the website to run. The website states: "The main goal of BMP is to increase the quality, reliability, and maintainability of goods produced by American firms. The primary steps toward this goal are simple: identify best practices, document them, and then encourages industry, government, and academia to share information about them." There is much more of interest on this website.
First edition, replaced by the second edition below. Obsolete: Replaced by  More Power For The Dollar.
Second edition. Obsolete: Replaced by  More Power For The Dollar.
 NAVMAT NOTICE 3080, Power Supply Reliability, 16 April 1982.
The Navy document, followed by NAVMAT INSTRUCTIONS, that put the teeth into NAVMAT P-4855-1 Navy Power Supply Reliability - Design and Manufacturing Guidelines, December 1982. Obsolete.
 NAVSO P-3641A, More Power For The Dollar, January 1989
Replaces the P4855-1 documents. Available on the World Wide Web.