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NAVSO
P-3641: Navy Power Supply Reliability Design & Mfg
Guidelines

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3.3 Output Power Density
- Low Voltage
Typical Levels
Today

Output power density is most often
expressed in terms of "watts per cubic inch"
where the power is rated output power and the
volume is total power supply volume, including
cooling fins or fan (if so equipped) and
integral EMI filter. Because of the
permutations of output power, prime power and
diversity of output configurations and
voltages, the parameters for this section have
been restricted to those in Table 3-2 which
describe the low-voltage baseline power supply
characteristics.

TABLE 3-2. LOW-VOLTAGE
BASELINE POWER
SUPPLY
CHARACTERISTICS

Switching-mode
conversion
Single output {5 VDC <
Output Voltage < 28 VDC}
Hold-up period: 1
millisecond
Conduction cooled
MTBF:
See Table 3-4
EMI: MIL-STD-461 except
with RE-01 and CE-01

modified
Prime Power: 270 VDC or
3-phase per
MIL-STD-704 and/or
MIL-STD-1399

Reliability is a function of many
factors including the ratio of operating to
rated stress, temperature and environment.
Typical MTBF data is presented in Table 3-3
for various environmental applications. These
MTBF figures should not be used as guides for
specifying requirements, but rather as
thresholds above which program management must
be especially attentive to the development
schedule and cost requirements (Section
3.2) and rigorous application of the
design and manufacturing guidelines (Section
4 ).

TABLE
3-3. LOW-VOLTAGE BASELINE POWER SUPPLY
MTBF

APPLICATION/
ENVIRONMENT

CALCULATED
PER
MIL-STD-756
METHOD
2005
55°C
AMBIENT

EXPECTED
WHEN
DESIGNED
AND
MANUFACTURED
PER NAVMAT

P-4855-1A

Ground
Fixed

150,000

300,000

Ground
Mobile

30,000

60,000

Naval
Sheltered

50,000

100,000

Naval
Unsheltered

25,000

50,000

Airborne
Inhabited

20,000

40,000

Airborne

Uninhabited

15,000

30,000

NOTE: Power Supply characteristics
defined in Table
3-2.

Figures 3-2 and 3-3 display the
range of power densities in watts/cubic inch
and watts/pound which are presently achievable
for power supplies with the baseline
characteristics of Table 3-3, employing
standard design and construction techniques. For
power supplies exhibiting greater complexity,
it is suggested that the worksheet in Appendix
D
be utilized to more accurately
predict the corrected power density expressed
in terms of a Power Density Index. The worksheet
in Appendix
D may be applied to a personal computer to
obtain an interactive spreadsheet. This allows
the user to make "what-if" changes in power
supply characteristics and packaging volume
which directly affect density, complexity,
reliability, maintainability and development
cost. Actual package density, reflecting
standard packaging techniques, remains
relatively constant in the range of 0.04 to
0.06 pounds per cubic inch.