Intel ATX Power Supply Design Guide

Version 0.9

7. Reliability

7.1 Component Derating

The following component derating guidelines shall be followed:

∙Semiconductor junction temperatures shall not exceed 110 °C with an ambient of 50 °C. Any exceptions are subject to final approval.

∙Inductor case temperature shall not exceed safety agency requirements.

∙Capacitor case temperature shall not exceed 95% of rated temperature.

∙Resistor wattage derating shall be > 30%.

∙Component voltage and current derating shall be > 10% at 50 °C. Any exceptions are subject to final approval.

∙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 +5VSB.

7.2Mean Time Between Failures (MTBF)

The MTBF of the power supply shall be calculated utilizing the Part-Stress Analysis method of MIL-HDBK-217F using the quality factors listed in MIL-HDBK-217F. The calculated MTBF of the power supply shall be greater than 100,000 hours under the following conditions:

∙Full rated load

∙120 VAC input

∙Ground benign

∙25 °C ambient.

The calculated MTBF of the power supply shall be greater than 30,000 hours under the following conditions:

∙Full rated load

∙120 VAC input

∙Ground benign

∙50 °C ambient.

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