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ATX12V Power Supply Design Guide 
Version 2.0  
 
21
 
3.2.7.   Output Transient Response 
Table 11 summarizes the expected output transient step sizes for each output.  The transient 
load slew rate is = 1.0 A/µs. 
Table 11.  DC Output Transient Step Sizes 
 
Output 
Max. step size 
(1)
 
Max. step size 
(amps) 
 +12 
V1DC 
40% 
 
 +12 
V2DC 
60% 
 
 +5 
VDC 
30% 
 
 +3.3 
VDC 
30% 
 
 
-12 VDC 
 
0.1 A 
 
+5 VSB 
 
0.1 A 
(1)
 For example, for a rated +5 VDC output of 18 A, the transient step would be 30% × 18 A = 5.4 A 
 
Output voltages should remain within the regulation limits of Section 3.2.1, and the power 
supply should be stable when subjected to load transients per Table 11 from any steady 
state load, including any or all of the following conditions: 
•  Simultaneous load steps on the +12 VDC, +5 VDC, and +3.3 VDC outputs 
  (all steps occurring in the same direction) 
•  Load-changing repetition rate of 50 Hz to 10 kHz 
•  AC input range per Section 3.1 
•  Capacitive loading per Table 12. 
3.2.8.   Capacitive Load 
The power supply should be able to power up and operate normally with the following 
capacitances simultaneously present on the DC outputs.  This capacitive loading should be 
used to check stability and should not be included for noise testing. 
Table 12.  Output Capacitive Loads 
Output ATX12V 
 
Capacitive load (
PF) 
+12 V1DC 
5,000 
 +12 
V2DC 
3,000 
 +5 
VDC 
6,000 
 +3.3 
VDC 
6,000 
 -12 
VDC 
350 
 +5 
VSB 
350