Underestimating Complexity of Power Supply Design

Underestimating the complexity of power supply design can
lead to schedule slips, cost overruns, and excessive field failures.

Summary

Problem -
Schedule slips, cost overruns, and excessive field failures, with associated
warranty costs, due to underestimating the complexity of power supply design,
especially switching-mode power supplies.
Relevance
- Since virtually every electronic system contains a power supply, it is almost
universally relevant.
Solvability
- Awareness, education, and allocation of adequate resources including budget,
schedule, trained design personnel, design review, and software and hardware
tools.
Solution
- Solution details.
Personal
- A personal anecdote.
On the Web -
Additional information on the Web.
References
- One to a few key papers.

Problem

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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

etc.

They are not a trivial design task.

Relevance

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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.

Solvability

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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 [1].
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
mandatory for any system or power supply designer and their management. The
Best Manufacturing Practices Center of Excellence website has the second
edition [2] (the most
current) available on the
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.

Solution

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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 [1], 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 [1],
the Navy released NAVMAT NOTICE 3080 [3],
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 [1],
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.

To keep history from repeating itself on your watch there
may still be no better way than getting a supply of Navy
Power Supply Reliability - Design and Manufacturing Guidelines and making
sure everyone associated with the project from program manager to manufacturing
foreman has a copy on their desk. They may not read it -- it was written by a
committee and is dry reading -- but try at least get them to invest the six to
ten minutes it takes to read the executive summary and skim the document. Make
sure you read it also.

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. When you see
something in the document that has been overtaken by events or is wrong from
your viewpoint, don't reject the whole document. Most of it is still
relevant.

Personal Anecdote

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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

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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 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.

References

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[1]  NAVMAT P-4855-1 Navy Power
Supply Reliability - Design and Manufacturing Guidelines, December
1982

First edition, replaced by the second edition below.

[2]  NAVMAT P-4855-1A (NAVSO P-3641),
Navy Power Supply Reliability, Design and Manufacturing Guidelines, Revised
Including High Voltage, January 1989 (Stock No. 0518-LP-204-4800).

Second edition, available
on the World-Wide Web.

[3] 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

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Original: 08 February 1999, revised 07 December 2000

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