Tiny, Silent and Efficient: The picoPSU

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TEST RESULTS


The picoPSU in action.

For a fuller understanding of ATX power supplies, please read the reference article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to SPCR's PSU Test Platform V.3. The testing system is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

Because of the unique design of the picoPSU, no thermal testing was done. Not only is our standard test bench ill-equipped to test a power supply on the actual ATX header, but the levels of power are so low that not much heat is generated anyway. Unlike a conventional power supply, the picoPSU plays no role in removing heat from the system, so it would be unfair to subject it to the rigors of our standard test. By the same token, noise levels also did not need to be tested, with the exception of the fan in the larger of the two power bricks.

The picoPSU was run through two complete tests: One for each of the supplied power bricks. By necessity, the measurements reflect the combined performance of the picoPSU and the power brick. Testing them independently would have been far too impractical, and would have been of limited use in the real world anyway.

Ambient conditions during testing were 20°C and 20 dBA, 121V/60Hz.

TEST RESULTS: picoPSU from Mini-box, 80W brick
DC Output Voltage (V) + Current (A)
Power Factor
Total Output
Input
Calculated Efficiency
+12V1
+5V
+3.3V
-12V
+5VSB
12.12V
1.05A
5.03V
1.06A
3.32V
1.04A
0.0
0.0
0.83
21.5W
27.1W
79.4%
11.94
2.05
5.01
2.11
3.32
1.03
0.0
0.5
0.92
41.0
49.0
83.6%
11.73
3.03
4.99
3.11
3.32
2.98
0.0
0.8
0.98
65.0
76.6
84.8%
11.65
4.00
4.98
3.12
3.32
2.01
0.0
0.8
0.99
72.8
86.0
84.7%
11.61
3.97
4.98
3.13
3.32
4.20
0.0
1.0
0.99
80.6
95.3
84.6%
Miscellaneous Results:
  • Power Draw in Standby: 1.5W
  • Power Factor in Standby: ~0.30
  • Power Draw with no load applied: 2.5W
  • Power Factor with no load applied: ~0.36
NOTE: The current and voltage for -12V and +5VSB lines is not measured but based on switch settings of the DBS-2100 PS Loader. It is a tiny portion of the total, and potential errors arising from inaccuracies on these lines is <1W.

* * *

TEST RESULTS: picoPSU from Mini-box, 120W brick
DC Output Voltage (V) + Current (A)
Power Factor
Total Output
Input
Calculated Efficiency
+12V1
+5V
+3.3V
-12V
+5VSB
12.32V
1.07A
5.03V
1.06A
3.32V
1.05A
0.0
0.0
0.96
22.0W
28.3W
77.7%
12.18
2.11
5.01
1.05
3.32
2.04
0.0
0.5
0.98
40.2
47.0
85.6%
12.00
3.11
4.99
3.14
3.32
2.01
0.0
0.8
0.99
63.7
73.1
87.1%
11.80
5.13
4.99
3.15
3.31
3.02
0.0
1.1
0.99
91.7
105.3
87.1%
11.64
6.05
4.94
5.04
3.30
5.14
0.0
1.5
1.00
119.8
143.0
83.8%
Miscellaneous Results:
  • Power Draw in Standby: 3.7W
  • Power Factor in Standby: 0.56
  • Power Draw with no load applied: 4.7W
  • Power Factor with no load applied: 0.60
NOTE: The current and voltage for -12V and +5VSB lines is not measured but based on switch settings of the DBS-2100 PS Loader. It is a tiny portion of the total, and potential errors arising from inaccuracies on these lines is <1W.

ANALYSIS

1. VOLTAGE REGULATION

The picoPSU itself provided excellent voltage regulation, staying well within the ±1.5% specified. In fact, the +3.3V line did not appear to fluctuate at all — it stayed stuck at +3.32V throughout the test. However, the +12V line from the power bricks sagged significantly under heavy load, dropping by almost 0.5V. Even so, it always stayed within the ±5% tolerance specified by ATX12V. The voltage regulation with the 120W brick was more or less the same as with the 80W brick, with a little less sag on the 12V line at loads >60W. Perhaps because of the higher amount of power being drawn, the two lines controlled by the picoPSU did show slightly more variation when delivering >80W with the larger power brick. Even so, neither of the lower voltage lines were ever in danger of exceeding the tight ±1.5% tolerance.

Overclockers would probably be scared off by the weak voltage regulation on the +12V line, but for the rest of us the voltages are good enough. Understandably, the drop was most significant as the maximum load was approached, so the solution is simple: Either build a more efficient system, or use the larger 120W brick.

2. EFFICIENCY was excellent with both the 80W brick and the 110W brick — much higher than any other power supply we've measured at these low output power levels. Part of this is by design — the low capacity of the brick and the picoPSU mean that efficiency is optimized over a much smaller output range than conventional PSUs, which are rated well over 300W these days. However, there is more at work here. The efficiency wasn't just high for the load, it was high, period. In fact, only two other power supplies we've tested have had higher efficiency than 84.8% at any level. That the picoPSU + 80W power brick was able to maintain this through a large part of its output range is impressive.

The 87.1% peak efficiency makes the picoPSU + 120W brick the most efficient power supply we have tested by almost two percentage points. Even better, this efficiency was maintained between 65W and 90W — precisely what most minimalist AMD-based systems demand when under heavy CPU load. This will make a very real difference in power draw, as very few conventional power supplies reach even 80% at such low loads.

Ironically, even this combination would probably fail the 80 Plus certification program, which requires that a power supply be at least 80% efficient at 20%, 50% and 100% load. Ordinarily, the 20% point is the crucial one: It's the most important in real terms, and it's the hardest target to achieve, especially for lower powered PSUs. The picoPSU + 120W brick would also fail at the 20% test point; 20% of 120W is 24W, where the efficiency was ~78%.

3. POWER FACTOR

This result seems mostly dependent on the power bricks. Although EDac advertises active power factor correction for the 80W brick, it measured quite low until the output reached at least 40W. At 20W output, the power factor was 0.83 — higher than is achievable with passive power factor correction, but much less than we've seen from other forms of active power factor correction. Above 40W, the power factor was always at the expected 0.9 and above.

The 120W brick was much better. PF was well above 0.90 even at 20W, and even touched 1.00 during the last test point. In standby mode, it maintained a respectable 0.60.

4. FAN & FAN CONTROLLER

The 80W unit doesn't have a fan, so this section applies only to the 120W unit. It's the one downside to the 120W brick — the built-in cooling fan. The fan turned on promptly when we boosted the output load to 90W, and it was loud. The 36 dBA@1m that we measured was far too loud to be acceptable in a quiet system. The fan speed increased slightly when full load was reached, but by then it was already too loud to consider.

Because of the fan, the 120W brick is best treated as a 90W unit that can sustain short peaks of 120W. Any sustained load above 90W would be unacceptable to users of quiet systems.

MP3: EDac 120W power brick @ 90W output: 36 dBA@1m



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