Seventeam ST-620PAF Power Supply Review
By Gabriel Torres on July 20, 2009


Introduction

Hardware Secrets Silver Award

You need to pay close attention because Seventeam has two power supply series with practically the same name but using different projects: PAF and P-AF. PAF series has models with 450 W, 520 W, 580 W and 620 W capacities, while P-AF series has models with 550 W, 650 W, 750 W and 850 W capacities. As you can see these two series don’t have models with the same capacity, so it is easy to see if a particular model is from the PAF or from the P-AF series. Can ST-620PAF really deliver 620 W? Let’s see.

Seventeam ST-620PAF power supply
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Figure 1: Seventeam ST-620PAF power supply.

Seventeam ST-620PAF power supply
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Figure 2: Seventeam ST-620PAF power supply.

ST-620PAF doesn’t have a modular cabling system. It has a 120 mm fan on its bottom and active PFC circuit, of course.

It is a very small unit, being only 5 ½” (140 mm) deep. All cables have a nylon protection that comes from inside the power supply. The included cables are:

The number of cables is enough for you to build a mainstream PC, but it would be great if Seventeam had added more SATA power connectors.

All wires are 18 AWG, which is the correct gauge to be used. All cables measure 19 11/16” (50 cm) between the power supply and the first connector on the cable and 6” (15 cm) between each connector on the cable on cables that have more than one connector.

Seventeam ST-620PAF 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-620PAF

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-620PAF power supply
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Figure 4: Overall look.

Seventeam ST-620PAF power supply
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Figure 5: Overall look.

Seventeam ST-620PAF 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.

The transient filtering stage from this power supply is flawless, providing two Y capacitors, one ferrite coil and one X capacitor more than required, plus one X capacitor after the rectifying bridge. The MOV is located behind the fuse in Figure 8 and that’s why we can’t see it on this picture.

Seventeam ST-620PAF power supply
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Figure 7: Transient filtering stage (part 1).

Seventeam ST-620PAF 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-620PAF.

Primary Analysis

On this page we will take an in-depth look at the primary stage of Seventeam ST-620PAF. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBJ2506 rectifying bridge in its primary, which can deliver up to 25 A at 100° C. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 2,875 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 2,300 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.

On the active PFC circuit two SPW20N60S5 power MOSFET transistors are used, each one capable of delivering up to 20 A at 25° C or 13 A at 100° C in continuous mode (note the difference temperature makes), or up to 40 A in pulse mode at 25° C. These transistors present a resistance of 190 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

The primary electrolytic capacitor is Japanese from Chemi-Con, which is always nice to see, and labeled at 85° C.

In the switching section, another two SPW20N60S5 power MOSFET transistors are used on the traditional two-transistor forward configuration.

Seventeam ST-620PAF power supply
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Figure 9: Switching transistors, active PFC diode, active PFC transistor and rectifying bridge.

The primary is controlled by an FN4800I PFC/PWM combo controller.

Seventeam ST-620PAF power supply
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Figure 10: PFC/PWM combo controller.

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

Secondary Analysis

This power supply uses four Schottky rectifiers on its secondary.

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%.

The +12 V output is produced by two SBL3060PT (30 A, 15 A per internal diode at 95° C, voltage drop of 0.70 V) connected in parallel. This gives us a maximum theoretical current of 43 A or 514 W for the +12 V output.

By the way, we are now talking about the voltage drop presented by the rectifiers. This parameter shows how much voltage is wasted by the rectifier. The lower this number is, the better, as less voltage is wasted, increasing efficiency.

The +5 V output is produced by one SBL6040PT Schottky rectifier (60 A, 30 A per internal diode at 100° C, voltage drop of 0.55 V), giving us a maximum theoretical current of 43 A or 214 W for this output.

The +3.3 V output is produced by another SBL6040PT Schottky rectifier, giving us a maximum theoretical current of 43 A or 141 W for this output.

All these numbers are theoretical. The real amount of current/power each output can deliver is limited by other components, especially by the coils used on each output.

The -12 V is regulated by a 7912 integrated circuit.

Seventeam ST-620PAF power supply
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Figure 11: -12 V integrated circuit and rectifiers.

The outputs are monitored by a PS223 integrated circuit, which supports under voltage (UVP), over voltage (OVP), over current (OCP) and over temperature (OTP, not implemented on this power supply) protections. Any other protection that this unit may have is implemented outside this integrated circuit.

Seventeam ST-620PAF power supply
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Figure 12: Monitoring integrated circuit.

Most electrolytic capacitors from the secondary are from Samxon, a Chinese company.

Power Distribution

In Figure 13, you can see the power supply label containing all the power specs.

Seventeam ST-620PAF power supply
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Figure 13: Power supply label.

This power supply has two +12 V rails distributed like this:

In our opinion this is not a good distribution, because +12V2 will be overloaded, since the components that most pull current/power from the power supply (the CPU and the video cards) are connected to this rail, while the +12V1 rail will always work  lightly loaded, as the motherboard and peripherals don’t pull a lot of current/power.

Now let’s see if this power supply can really deliver 620 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.

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 the +12V1 input was connected to the +12V1 (main motherboard and peripheral connectors) and +12V2 (video card power connector) rails, while the +12V2 input was connected to the +12V2 (EPS12V connector) rail.

Input

Test 1

Test 2

Test 3

Test 4

Test 5

+12V1

5 A (60 W)

9 A (108 W)

14 A (168 W)

19 A (228 W)

24 A (288 W)

+12V2

4 A (48 W)

9 A (108 W)

14 A (168 W)

18 A (216 W)

23 A (276 W)

+5V

1 A (5 W)

2 A (10 W)

4 A (20 W)

5 A (25 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)

6 A (19.8 W)

+5VSB

1 A (5 W)

1 A (5 W)

1.5 A (7.5 W)

2 A (10 W)

2.5 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)

Total

128.4 W

244.8 W

382.3 W

500.4 W

628.7 W

% Max Load

20.7%

39.5%

61.7%

80.7%

101.4%

Room Temp.

44.5° C

45.6° C

48.0° C

49.5° C

45.5° C

PSU Temp.

45.5° C

46.6° C

49.9° C

52.7° C

48.4° C

Voltage Stability

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Pass

AC Power

161.6 W

295.0 W

462.8 W

619.0 W

795.0 W

Efficiency

79.5%

83.0%

82.6%

80.8%

79.1%

AC Voltage

112.6 V

110.2 V

109.7 V

107.8 V

105.3 V

Power Factor

0.977

0.99

0.995

0.996

0.996

Final Result

Pass

Pass

Pass

Pass

Pass

Before commenting our results, we must say that the first SY-620PAF sample we got burned when we tried to pull 620 W from it (test number five) and after inspecting it we found out that one of the +12 V rectifiers was the component that burned. We replaced it and the same thing happened again. We got a second sample, which worked just fine, so our first sample was defective. The results above are from this second sample.

Seventeam ST-620PAF presents decent efficiency around 83% when we pulled between 40% and 60% from its labeled power (between 248 W and 372 W). At 80% load (496 W) efficiency dropped to 80.8%, still above 80%. But at light load (20% load, i.e., 124 W) and full load (620 W) efficiency dropped below the 80% mark.

This unit is 80 Plus certified, but you have to keep in mind that they test power supplies at a room temperature of 23° C (which is impossible to be achieved inside a PC), while we test them at a room temperature at least the double. The higher the temperature, the lower efficiency is.

Voltage stability was the highlight from this product. All voltages (including -12 V) were within 3% from their nominal value, whereas the ATX specification says they must be within 5%. Translation: voltages were closer to their nominal values than needed.

Ripple and noise levels were extremely low except on -12 V output, where they were always high (from 96.0 mV during test one to 108.2 mV during test five), but still inside the maximum allowed. You can see the results for test number five below. All numbers are peak-to-peak figures and the maximum allowed is 120 mV for the +12 V outputs and 50 mV for the +3.3 V and +5 V outputs.

Seventeam ST-620PAF power supply
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Figure 14: +12V1 input from load tester at 628.7 W (40.6 mV).

Seventeam ST-620PAF power supply
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Figure 15: +12V2 input from load tester at 628.7 W (48.2 mV).

Seventeam ST-620PAF power supply
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Figure 16: +5V rail with power supply delivering 628.7 W (17.2 mV).

Seventeam ST-620PAF power supply
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Figure 17: +3.3 V rail with power supply delivering 628.7 W (16.2 mV).

Let’s see if we could pull more than 620 W from this unit.

Overload Tests

Before overloading a power supply we always test to see if over current protection (OCP) is active and at what current level it is triggered. To test this we removed the video card auxiliary power connector from our load tester (because it was connected to the +12V2 rail together with the EPS12V/ATX12V cable) and started increasing current on +12V2. We went all the way up to 33 A (the maximum our load tester can deliver) and the power supply didn’t shut down, showing that either OCP is disabled or configured at a value above 33 A.

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. If we tried to increase one amp more on any output the power supply would shut down, showing that one of the protections entered in action.

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.

As you can see Seventeam could have labeled this unit as a 650 W or even 700 W product, but they decided not to do so probably because of efficiency, which drops way below 80% if we pull more than 620 W from it.

Input

Maximum

+12V1

26 A (312 W)

+12V2

26 A (312 W)

+5V

9 A (45 W)

+3.3 V

9 A (29.7 W)

+5VSB

2.5 A (12.5 W)

-12 V

0.5 A (6 W)

Total

710.7 W

% Max Load

114.6%

Room Temp.

48.9° C

PSU Temp.

49.6° C

AC Power

915.0 W

Efficiency

77.7%

AC Voltage

105.5 V

Power Factor

0.996

Main Specifications

Seventeam ST-620PAF power supply specs include:

Conclusions

Seventeam ST-620PAF is an honest mainstream power supply. It has two disadvantages. First, efficiency, which is only decent if you pull between 40% and 60% from its labeled capacity (i.e., between 248 W and 372 W). The second drawback is the reduced number of cables: only two power cables for video cards using six-pin connectors and only four SATA power connectors.

The reviewed power supply can really deliver its labeled power at high temperatures, provide very stable voltages, very low noise and ripple levels (except on -12 V) and will shut down if you try to pull more than it is capable of delivering.

If you are aware about its drawbacks it can be a good option, however if you are really worried about getting a good efficiency with any load pattern you should pay more and go with Enermax ECO80+ 620 W.

Originally at http://www.hardwaresecrets.com/article/Seventeam-ST-620PAF-Power-Supply-Review/765


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