Testing – AC Ripple on DC Outputs
The amount of AC ripple present on the outputs was checked using an oscilloscope. This AC component may be present in the KHz range where most switching power supplies operate or it may be more prevalent at the 60 Hz line frequency. In each case, I adjusted the O-scope time base to look for AC ripple at both low and high frequencies.
40 mV P-P on the +12 VDC output of the Silencer 360 ATX
The ATX specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.
Ideally we would like to see no AC noise on the DC outputs — the cleaner the better! But in reality there will always be some present. I measured the amplitude of the AC signal (in millivolts, peak-to-peak) to see how well each power supply complied with the ATX standard. The following table lists the ripple/noise results during our 240 w load tests. The four main output voltages of interest (+3.3 V, +5.0 V, +12 V and +5 VSB) were recorded for each power supply after the 24 hr burn-in period.
.
|
AC Ripple Load Test (mV p-p) | ||||
|
Power Supply |
+3.3V |
+5V |
+12V |
+5VSB |
|
Silencer 360 watt ATX |
10 |
10 |
40 |
30 |
|
Silencer 410 watt ATX |
20 |
15 |
40 |
20 |
Both of the Silencer power supplies exhibited very good AC ripple suppression on all of the measured outputs.
