ATX/ATX12V Power Supply Design Guide
Version 1.1
Page 32
7. Reliability
7.1. Component Derating
The following component derating guidelines are recommended:
•
Semiconductor junction temperatures shall not exceed 110 °C with an ambient of
50 °C.
•
Inductor case temperature shall not exceed safety agency requirements.
•
Capacitor case temperature shall not exceed 95% of rated temperature.
•
Component voltage and current derating shall be > 10% at 50 °C.
•
Magnetic saturation of any transformer will not be allowed under any line, load, startup,
or transient condition including 100% transients on the five main outputs or +5 VSB.
7.2. Mean Time Between Failures (MTBF)
The MTBF of the power supply can be calculated with the Part-Stress Analysis method of
MIL-HDBK-217F using the quality factors listed in MIL-HDBK-217F. A target calculated
MTBF of the power supply is greater than 100,000 hours under the following conditions:
•
Full-rated load
•
120 VAC input
•
Ground benign
•
25 °C ambient
A target calculated MTBF of the power supply is greater than 30,000 hours under the
following conditions:
•
Full-rated load
•
120 VAC input
•
Ground benign
•
50 °C ambient
