Intel ATX Power Supply Design Guide
Version 0.9
3.3.3 Output Ripple/Noise
The following output ripple/noise requirements should be met throughout the load ranges specified in Section 3.3, and under all input voltage conditions as specified in Section 3.1.
Ripple and noise are defined as periodic or random signals over a frequency band of 10 Hz to 20 MHz. Measurements shall be made with an oscilloscope with 20 MHz bandwidth. Outputs should be bypassed at the connector with a 0.1 µF ceramic disk capacitor and a 10 µF electrolytic capacitor to simulate system loading.
Table 8: DC Output Noise/Ripple
Output
+12VDC
+5VDC
+3.3VDC
+5VSB
Max Ripple & Noise
(mVpp)
120
50
50
100
120
50
3.3.4 Output Transient Response
The +3.3VDC and +5VDC outputs will see transients up to 30% of the rated output current (e.g., for a rated +5VDC output of 18 A, the transient step would be 0.3 × 18 A = 5.4 A). The +12VDC output will see transients up to 50% of the rated output current. The transient slew rate will be 2.5 A/µs. The power supply should be stable under all transient conditions from any steady state load, and the over/undershoot should be within the regulation band stated in Section 3.2.1.
3.3.5 Capacitive Load
The power supply should be able to power up and operate normally with the following capacitances simultaneously present on the DC outputs.
Output: | +12VDC | +5VDC | +3.3VDC | +5VSB | ||
Capacitive load (μF): | 1,000 | 10,000 | 6,000 | 350 | 350 | 350 |
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3.3.6 Closed Loop Stability
The power supply shall be unconditionally stable under all line/load/transient load conditions including capacitive loads specified in Section 3.3.5. A minimum of 45 degrees phase and 10
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