Seventeam ST-380PAS Power Supply Review
By Gabriel Torres on June 12, 2009


Introduction

Hardware Secrets Golden Award

ST-380PAS is the latest entry-level power supply from Seventeam, featuring active PFC and a 120 mm fan on the bottom. Is it a good product? Can it deliver its labeled power? Check it out.

Seventeam is one of the few real power supply manufacturers around. They are the company behind of power supplies from XG/MGE and some models from Cooler Master.

One funny detail is the sticker in Engrish saying “Breakage Invalid” instead of “Warranty Void if Broken,” a common “feature” on all Seventeam power supplies.

Seventeam ST-380PAS power supply
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Figure 1: Seventeam ST-380PAS power supply.

Seventeam ST-380PAS power supply
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Figure 2: Seventeam ST-380PAS power supply.

ST-380-PAS is a small power supply (5 ½” or 14 cm deep).

Only the main motherboard cable use a nylon protection, which comes from inside the power supply housing, as you can see in Figure 3.

The main motherboard cable uses a 20/24-pin connector and this unit comes with two ATX12V connectors that together form one EPS12V connector.

The reviewed power supply comes with four peripheral cables: one with one six/eight-pin auxiliary power connector, one with three SATA power connectors, one with two standard peripheral power plugs and one with one standard peripheral power plug and one floppy disk drive power connector.

All wires are 18 AWG, which is the correct gauge to be used.

We think Seventeam could have added at least one extra peripheral power plug, as this power supply comes only with three of them. Even though ST-380PAS comes with three SATA power plugs, the distance between the first and the last one if of only 11 1/32” (28 cm), so you may have trouble installing a SATA optical drive and a SATA hard disk drive on this cable depending on the bays you choose to install these devices.

On the good side we have an EPS12V connector, feature usually not found on sub-400 W power supplies, and the video card power plug being a six/eight-pin connector.

The distance between the power supply housing and the first connector on each cable is of 16 17/32” (42 cm) and the distance between each connector on cables that have more than one plug is of 5 ½” (140 mm).

Seventeam ST-380PAS power supply
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Figure 3: Cables.

Now let’s take an in-depth look inside this power supply.

A Look Inside The ST-380PAS

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used.

Seventeam ST-380PAS power supply
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Figure 4: Overall look.

Seventeam ST-380PAS power supply
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Figure 5: Overall look.

Seventeam ST-380PAS power supply
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Figure 6: Overall look.

Transient Filtering Stage

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

On this power supply this stage is flawless, with two X capacitors, one X capacitor after the rectifying bridge, two Y capacitors and one ferrite coil more than needed.

Seventeam ST-380PAS power supply
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Figure 7: Transient filtering stage (part 1).

Seventeam ST-380PAS power supply
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Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the Seventeam ST-380PAS.

Primary Analysis

On this page we will take an in-depth look at the primary stage of Seventeam ST-380PAS. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1006 rectifying bridge in its primary, which can deliver up to 10 A at 100° C. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Seventeam ST-380PAS power supply
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Figure 9: Rectifying bridge.

On the active PFC circuit two 2SK3568 power MOSFET transistors are used, each one capable of delivering up to 12 A at 25° C or 48 A in pulse mode at 25° C.

Seventeam ST-380PAS power supply
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Figure 10: Active PFC transistors.

The active PFC capacitor is Samxon and labeled at 105° C. Usually manufacturers use 85° C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

In the switching section, two SPA20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode (note the difference temperature makes) or 62.1 A in pulse mode at 25° C.

Seventeam ST-380PAS power supply
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Figure 11: Switching transistors.

The primary is controlled by the popular CM6800 PFC/PWM combo controller.

Seventeam ST-380PAS power supply
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Figure 12: PFC/PWM combo controller.

Now let’s take a look at the secondary of this power supply.

Secondary Analysis

This power supply uses six Schottky rectifiers on its secondary and they are all from the same model: SBR30A60CT, each one capable of delivering up to 30 A (15 A per internal diode at 110° C). Each positive output uses two of these.

The maximum theoretical current each line can deliver is given by the formula I / (1 - D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

So the maximum theoretical current each output can deliver is of 43 A (15 A x 2 / 0.70), which translates into 514 W for +12 V, 214 W for +5 V and 141 W for +3.3 V. As you can see the secondary is highly overspec’ed, however we must remember that these are only theoretical numbers and the real limit depends on other factors, especially the coils used on the secondary.

Seventeam ST-380PAS power supply
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Figure 13: Rectifiers.

The outputs are monitored by a WT7510 integrated circuit, which supports only under voltage (UVP) and over voltage (OVP) protections. Any other protection that this unit may have is implemented outside this integrated circuit.

Seventeam ST-380PAS power supply
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Figure 14: Monitoring integrated circuit.

Electrolytic capacitors from the secondary are also manufactured by Samxon and labeled at 105° C.

Power Distribution

In Figure 15, you can see the power supply label containing all the power specs.

Seventeam ST-380PAS power supply
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Figure 15: Power supply label.

In theory this power supply has two virtual rails, distributed like this:

This is not well distributed in our opinion, as we prefer to see the ATX12V/EPS12V connector on a different rail from the video card connector. However, during our tests over current protection failed (which makes sense, as the monitoring integrated circuit does not provide this protection and Seventeam doesn’t list OCP as a feature available on this power supply), making this power supply to work like a single-rail design, so this +12V1/+12V2 separation doesn’t make sense.

Just to remember, the difference between a single-rail design and a multiple rail design lies on the over current protection circuit, where on a single-rail design it is monitoring all +12 V outputs at the same time, whereas on a multiple-rail design there is a separated OCP circuit for each group of wires (“virtual rails”).

Now let’s see if this power supply can really deliver 380 W.

Load Tests

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.

For the 100% load test we had to use two patterns. On the first one, test number five, we respected the 252 W limit for the +12 V rail that was printed on the label. In order to achieve that, we had to pull less current from +12 V than we’d like to, and more current from +5 V and +3.3 V. After this test we tried to pull 100% load from the power supply the way we like: pulling more current from +12 V and less current from +5 V and +3.3 V. This was test number six.

If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

+12V1 and +12V2 are the two independent +12V inputs from our load tester and during our tests both were connected to the single +12 V provided by this power supply.

Input

Test 1

Test 2

Test 3

Test 4

Test 5

Test 6

+12V1

2.5 A (30 W)

5.5 A (66 W)

8 A (96 W)

10.5 A (126 W)

10.5 A (126 W)

13 A (156 W)

+12V2

2.5 A (30 W)

5 A (60 W)

7 A (84 W)

10 A (120 W)

10 A (120 W)

13 A (156 W)

+5V

1 A (5 W)

2 A (10 W)

4 A (20 W)

5 A (25 W)

15 A (75 W)

6 A (30 W)

+3.3 V

1 A (3.3 W)

2 A (6.6 W)

4 A (13.2 W)

5 A (16.5 W)

14 A (46.2 W)

6 A (19.8 W)

+5VSB

1 A (5 W)

1 A (5 W)

1.5 A (7.5 W)

2 A (10 W)

2 A (10 W)

2.5 A (12.5 W)

-12 V

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

Total

80.1 W

161.1 W

228.8 W

305.3 W

387.1 W

381.0 W

% Max Load

21.1%

42.4%

60.2%

80.3%

101.9%

100.3%

Room Temp.

45.9° C

44.5° C

47.8° C

49.0° C

47.0° C

47.1° C

PSU Temp.

49.0° C

47.9° C

51.2° C

52.1° C

51.9° C

51.1° C

Voltage Stability

Pass

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Pass

Pass

AC Power (1)

94 W

182 W

261 W

351 W

462 W

449 W

Efficiency (1)

85.5%

88.5%

87.7%

87.0%

83.8%

84.9%

AC Power (2)99,1 W184,5 W271,8 W366,4 W478,8 W465,9 W
Efficiency (2)80.8%87.3%84.2%83.3%80.8%81.8%
AC Voltage113.3 V112.6 V111.3 V110.3 V109.1 V109.7 V
Power Factor0.9820.9910.9930.9940.9950.995

Final Result

Pass

Pass

Pass

Pass

Pass

Pass

Updated 06/24/2009: We re-tested this power supply using our new GWInstek GPM-8212 power meter, which is a precision instrument and provides accuracy of 0.2% and thus presenting the correct readings for AC power and efficiency (results marked as "2" on the table above; results marked as "1" were measured with our previous power meter from Brand Electronics, which isn't so precise as you can see). We also added the numbers for AC voltage during our tests, an important number as efficiency is directly proportional to AC voltage (the higher AC voltage is, the higher efficiency is). Also, manufacturers usually announce efficiency at 230 V, which usually inflates efficiency numbers. We added power factor (PF) numbers as well. These numbers measure the efficiency of the power supply active PFC circuit. This number should be as close to 1 as possible. The active PFC circuit from this power supply is excellent, as you can see (only at 20% load we saw something different than 0.99, but 0.98 is still excellent).

This power supply achieved a very high efficiency when we pulled 40% from its labeled power (152 W): 87.3%. At 60% (228 W) and at 80% (304 W) loads efficiency was also very good, at 84.2% and 83.3%, respectively. At light load (20% load, i.e., 76 W) and at full load (380 W) efficiency dropped a lot, but still above the 80% mark.

Voltage stability was another highlight from ST-380PAS, with all voltages inside 3% of their nominal values(i.e., voltages were closer to their nominal value than needed, as ATX spec allows voltages to be up to 5% from their nominal values, 10% for -12 V).

And finally we have noise and ripple, which were below the 120 mV (+12 V) and 50 mV (+5 V and +3.3 V) limits set by ATX specs, especially +12 V, which was around only ¼ of the maximum allowed. Below you can see the results for test number six.

Seventeam ST-380PAS power supply
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Figure 16: +12V1 input from load tester at 381 W (31.2 mV).

Seventeam ST-380PAS power supply
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Figure 17: +12V2 input from load tester at 381 W (31.6 mV).

Seventeam ST-380PAS power supply
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Figure 18: +5V rail with power supply delivering 381 W (30.4 mV).

Seventeam ST-380PAS power supply
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Figure 19: +3.3 V rail with power supply delivering 381 W (30.4 mV).

Now let’s see if we could pull more than 380 W from this unit.

Overload Tests

Before overloading power supplies we always test first if the over current protection (OCP) circuit is active and at what level it is configured.

In order to do that we removed the video card power connector from our load tester, so the +12V1 input would be connected to the power supply +12V1 rail and the +12V2 input would be connected to the power supply +12V2 rail. Then we configured a low current at +12V1 (1 A) and increased current on +12V2 until we saw the power supply shutting down. That never happened. So OCP is either disabled (more probable, as the monitoring circuit does not support OCP and Seventeam does not list OCP as a feature) or configured above 33 A, which is the maximum current we can configure on our load tester.

With OCP disable this means that this power supply has, in fact, a single-rail design, despite of what is written on the label.

Then starting from test five we increased currents to the maximum we could with the power supply still running inside ATX specs. The results are below. When we tried to increase one more amp at any output ripple would go to the roof, meaning that the unit stopped working correctly.

The idea behind of overload tests is to see if the power supply will burn/explode and see if the protections from the power supply are working correctly. This power supply didn’t burn and when we tried to pull far more than it could deliver it would shut down, so this unit passed on this test.

Input

Maximum

+12V1

17.5 A (210 W)

+12V2

17.5 A (210 W)

+5V

7 A (35 W)

+3.3 V

6 A (19.8 W)

+5VSB

2.5 A (12.5 W)

-12 V

0.5 A (6 W)

Total

491.4 W

% Max Load

129.3%

Room Temp.

50.0° C

PSU Temp.

51.3° C

AC Power (1)

597 W

Efficiency (2)

82.3%

AC Power (2)623 W
Efficiency (2)78.9%
AC Voltage107.9 V
Power Factor0.996

When overloaded this power supply presented efficiency below 80% (consider the results marked as "2", as they are the correct ones, measured with our precision power meter).

Main Specifications

 

Seventeam ST-380PAS power supply specs include:

Conclusions

This is a very good entry-level power supply if you are building an entry-level PC. It provides an excellent efficiency between 84% and 87% if you pull between 40% and 60% from its maximum labeled power (between 152 W and 228 W), outstanding voltage regulation, low noise and ripple levels and best of all, can deliver up to 490 W at 50° C.

The only negative aspect from this power supply is the low number of peripheral power plugs (only three). If this doesn’t bother you, this power supply won’t let you down and you will be buying a terrific and inexpensive product, a combination rarely seen together.

Originally at http://www.hardwaresecrets.com/article/Seventeam-ST-380PAS-Power-Supply-Review/734


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