ATX12V Power Supply Design Guide
Version 2.0
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3.2.4. Power Limit / Hazardous Energy Levels
Under normal or overload conditions, no output shall continuously provide 240 VA under
any conditions of load including output short circuit, per the requirement of UL 1950/CSA
950 / EN 60950/IEC 950.
3.2.5. Efficiency
3.2.5.1. General
The power supply required minimum is 70% efficient under “Full” load, 70% under
“typical” load, and 60% in a “light” load or idle condition. The efficiency of the power
supply should be tested at nominal input voltage of 115VAC input and/or 230VAC input,
under the load conditions defined in Table 7 and Table 8, and under the temperature and
operating conditions defined in Section 5. The loading condition for testing efficiency
shown in Table 8 represents a fully loaded system, a ~50% (typical) loaded system, and a
~20% (light) loaded system.
Table 7. Minimum Efficiency Vs Load
Loading Full load Typical load Light load
Required Minimum Efficiency
70% 70% 60%
Recommended Minimum Efficiency
75% 80% 68%
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