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Designers Manual
Advanced Energy CoolX600 Series
t
infant
t
operation
Failure rate λ(t)
Wear out
Constant failure rate
(useful lifetime)
Infant
mortality
Time t
FFiigguurree 66‑‑3311..
Failure rate of a power supply
The failure rate comprises three stages:
• Infant mortality—immediately after production, some units fail due to defective
components or production errors.
• Constant failure rate—the useful lifetime of a product.
Power supplies rarely fail during this period.
• Wear out—units begin to fail due to wear.
As the unit approaches its end of life, the first signs of wear appear and failures
become more frequent. The lifetime of a unit is generally defined as the time when
the failure rate increases to five times the statistical rate of the flat portion of the
bathtub curve in the previous figure. The lifetime is the time after which the unit fails
due to wear appearing.
The MTBF is a measurement of how many devices fail in a period of time (that is, a
measure of reliability) before signs of wear appear. The MTBF can be calculated
mathematically as follows:
MTBF = Total×t
Failure
Where:
• Total = the total number of power supplies operated simultaneously
• t = the observation period
• Failure = the number of failures
MTBF can be established in two ways:
• By actual statistics on the hours of operation of a large population of units
Advanced Energy
®
CoolX
®
600 Modular Power Supply
57010208-00B
Installation, Setup, and Operation
6‑26
