SilverStone Element ST75EF 750 W Power Supply Review

[nextpage title=”Introduction”]

SilverStone Element ST75EF 750 W is simply a Seventeam ST-750P-AF with a different cable configuration and a different name. Since we have already reviewed ST-750P-AF, we will be able to tell if these two units are completely identical or if there are small differences between them. It is important to know that models from SilverStone Element series can be manufactured by two distinct companies: models up to 600 W are manufactured by Enhance Electronics, while models starting at 650 W are manufactured by Seventeam. SilverStone uses a lot of different manufacturers for their power supplies. Besides Enhance and Seventeam, units from their Decathlon series are manufactured by Impervio and units from their Strider series are manufactured by FSP. Phew!

Figure 1: SilverStone Element ST75EF power supply.

Figure 2: SilverStone Element ST75EF power supply.

SilverStone Element ST75EF is a small 750 W unit, being 6 ½” (16.5 cm) deep, using a 135 mm fan (which actually measures 130-mm) on its bottom and featuring active PFC, of course.

All cables are protected by a nylon sleeving, which doesn’t come from inside the power supply housing, as you can see in Figure 2. Here we saw a small difference between ST75EF and Seventeam ST-750P-AF: on ST-750P-AF only the main motherboard cable has this nylon protection.

Cables are somewhat long, measuring 20 7/8” (53 cm) between the housing and the first connector on the cable, and 9 7/8” (25 cm) between connectors on SATA and peripheral cables – which is a lot, usually power supplies have only 5 29/32” (15 cm) between connectors – and 5 29/32” (15 cm) between the connectors from the video card cables. Here we saw another smaller difference between ST75EF and Seventeam ST-750P-AF: on the reviewed power supply the cables are a little bit (1 1/4” or 3 cm) longer from the power supply housing to the first connector on the cable and also the distance between connectors on SATA and peripheral power connectors is way bigger (9 7/8” vs. 5 29/32” or 25 cm vs. 15 cm).

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

The cables included are:

• Main motherboard cable with a 20/24-pin connector.
• One cable with two ATX12V connectors that together form an EPS12V connector.
• Two auxiliary power cables for video cards with two six-pin video card auxiliary power connectors each.
• One auxiliary power cable for video cards with one six/eight-pin connector.
• Two SATA power cables with three SATA power connectors each.
• Two peripheral power cables with three standard peripheral power plugs each and one floppy disk drive power connector on one of them.

Probably the main difference between SilverStone ST75EF and Seventeam ST-750P-AF is here. On Seventeam ST-750P-AF the main motherboard connector does not provide a 20-pin option, it comes with a cable with one EPS12V connector and one ATX12V connector (instead of two ATX12V connectors that together form one EPS12V connector) and only two six/eight-pin connectors for video cards (in separated cables).

SilverStone ST75EF has five power connectors for video cards, allowing you to install up to two very high-end cards in SLI or CrossFire mode, since each card from this class uses two power connectors. So no direct support for three-way SLI is provided. Two cables have two connectors attached, which is not the best configuration possible: it is always better to see video card power cables using individual cables.

Figure 3: Cables.

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

[nextpage title=”A Look Inside The Element ST75EF”]

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.

Figure 4: Overall look.

Figure 5: Overall look.

Figure 6: Overall look.

[nextpage title=”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.

This stage is flawless, with two Y capacitors and one coil more than the minimum required.

Figure 7: Transient filtering stage (part 1).

Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the SilverStone Element ST75EF.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of SilverStone Element ST75EF. 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 25A at 100° C  if a heatsink is used, which is the case. 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.

Figure 9: Rectifying bridge.

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.

Figure 10: Active PFC diode and transistors.

This power supply uses a Japanese capacitor from Matsushita (Panasonic) labeled at 85° C to filter the output from the active PFC circuit.

In the switching section, two SPW16N50C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 16 A at 25° C or 10 A at 100° C in continuous mode (note the difference temperature makes), or up to 48 A in pulse mode at 25° C. These transistors present a maximum RDS(on) of 280 mΩ.

Figure 11: Switching transistors.

The primary is controlled by a FAN4800I PFC/PWM combo controller.

Figure 12: PFC/PWM combo controller.

So far SilverStone Element ST75EF and Seventeam ST-750P-AF are internally identical.

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

[nextpage title=”Secondary Analysis”]

This power supply uses six 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 four of these rectifiers. Two SBR30A60CT (30 A, 15 A per internal diode at 110° C, typical voltage drop of 0.53 V) connected in parallel are in charge of the direct rectification part, while two STPS60L45CW (60 A, 30 A per internal diode at 135° C, maximum voltage drop of 0.50 V) connected in parallel are in charge of the “freewheeling” part (i.e., discharging the coil). For our math we need to consider the path with the lower current limit, which is the direct rectification one. This gives us a maximum theoretical current of 86 A or 1,029 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 KCQ60A04 Schottky rectifier (60 A, 30 A per internal diode at 83° C, maximum voltage drop of 0.58 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 KCQ60A04 Schottky rectifier, so the maximum theoretical power this output can deliver is of 141 W.

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.

Figure 13: 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.

Figure 14: Monitoring circuit.

Electrolytic capacitors from the secondary are Chinese from Samxon and labeled at 105° C.

The secondary from SilverStone Element ST75EF is also identical to the one from Seventeam ST-750P-AF, so these two power supplies are internally identical. Seventeam ST-750P-AF uses different rectifiers on the secondary but with the same specs, the main difference being only the manufacturer.[nextpage title=”Power Distribution”]

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

Figure 15: Power supply label.

This power supply has two virtual rails, distributed like this:

• +12V1 (yellow with black stripe wire): Main motherboard cable, video
  card power cables.
• +12V2 (solid yellow wire): ATX12V/EPS12V connectors, SATA and peripheral power connectors.

This distribution is perfect, as the video cards and the CPU are on different rails. This distribution is different from the one found on Seventeam ST-750P-AF

Now let’s see if this power supply can really deliver 750 W.[nextpage title=”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 power supply +12V1 and +12V2 rails and the +12V2 input was connected to the power supply +12V2 rail.

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12V1	5 A (60 W)	11 A (132 W)	16 A (192 W)	22 A (264 W)	27 A (324 W)
+12V2	5 A (60 W)	10 A (120 W)	16 A (192 W)	21 A (252 W)	27 A (324 W)
+5V	2 A (10 W)	4 A (20 W)	6 A (30 W)	8 A (40 W)	10 A (50 W)
+3.3 V	2 A (6.6 W)	4 A (13.2 W)	6 A (19.8 W)	8 A (26.4 W)	10 A (33 W)
+5VSB	1 A (5 W)	1.5 A (7.5 W)	2 A (10 W)	2.5 A (12.5 W)	3 A (15 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	149.4 W	301.4 W	452.1 W	601.5 W	749.5 W
% Max Load	19.9%	40.2%	60.3%	80.2%	99.9%
Room Temp.	45.2° C	46.5° C	47.8° C	46.5° C	47.6° C
PSU Temp.	47.4° C	49.6° C	50.8° C	52.5° C	55.0° C
Voltage Regulation	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	184.1 W	357.6 W	540.4 W	735.0 W	953.0 W
Efficiency	81.2%	84.3%	83.7%	81.8%	78.6%
AC Voltage	111.9 V	110.5 V	108.2 V	106.2 V	103.3 V
Power Factor	0.987	0.996	0.998	0.998	0.999
Final Result	Pass	Pass	Pass	Pass	Pass

This power supply burned while delivering 750 W for a while (test five). We asked a second sample to SilverStone, which worked just fine during all our tests (we re-did the whole data collection process). So we guess we got a defective sample. Examining the burned sample, the switching transistors and the +12 V rectifiers were the components that went bad.

Efficiency was relatively high between 84.3% and 83.7% when we pulled between 40% and 60% from this power supply labeled capacity (i.e., between 300 W and 450 W). Under light load (20% load, i.e., 150 W) and 80% load (i.e., 600 W) efficiency dropped to between 81% and 82%, not a bad number. Under full load (750 W), however, efficiency dropped to 78.6%.

This unit is 80 Plus Bronze certified, meaning that according to Ecos Consulting (the company behind the 80 Plus certification) it presents efficiency of at least 82% under full load. The difference between what we achieved and what they achieved can be easily explained: they collect data at a room temperature of only 23° C, a temperature that is impossible to be seen inside a PC, and efficiency decreases with temperature (click here for more information). This is not the first (and probably not the last) that we’ve seen a power supply passing the 80 Plus certification but failing to deliver high efficiency at higher temperatures. That is why we test power supplies at temperatures between 45° C and 50° C: they are more realistic.

One of the highlights from SilverStone Element ST75EF was voltage regulation: during our tests all outputs were within 3% from their nominal values, i.e., closer to their nominal values than required. This included the -12 V output, which usually doesn’t like to stay so close from its nominal value. Interesting enough on our test with Seventeam ST-750P-AF, -12 V output failed to be inside the correct range during test number five, so it seems that it was either a problem with the sample we got or that Seventeam fixed this problem.

Ripple and noise levels were below the maximum allowed, achieving lower values than Seventeam ST-750P-AF, so again it seems that it was either a problem with the sample we got or that Seventeam fixed this problem. You can see the results below for test number five. All values are peak-to-peak figures and the maximum allowed is 120 mV for the +12 V outputs and 50 mV for the +5 V and +3.3 V outputs.

Figure 16: +12V1 input from load tester at 749.5 W (58.2 mV).

Figure 17: +12V2 input from load tester at 749.5 W (88.6 mV).

Figure 18: +5V rail with power supply delivering 749.5 W (19.6 mV).

Figure 19: +3.3 V rail with power supply delivering 749.5 W (14.4 mV).

Now let’s see if we could pull more than 750 W from this unit. [nextpage title=”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 peripheral power
connectors from our load tester, making the +12V1 and +12V2 inputs from our tester to match the power supply +12V2 and +12V1 rails, respectively. Then we increased current on each rail up to 33 A (the maximum our load tester is able to go) , but the power supply would still turn on, meaning 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. 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	32 A (384 W)
+12V2	32 A (384 W)
+5V	15 A (75 W)
+3.3 V	15 A (49.5 W)
+5VSB	3 A (15 W)
-12 V	0.5 A (6 W)
Total	906.9 W
% Max Load	120.9%
Room Temp.	46.2° C
PSU Temp.	57.5° C
AC Power	1,246 W
Efficiency	72.8%
AC Voltage	96.8 V
Power Factor	0.999

[nextpage title=”Main Specifications”]

SilverStone Element ST75EF power supply specs include:

• ATX12V 2.3
• Nominal labeled power: 750 W.
• Measured maximum power: 906.9 W at 46.2° C.
• Labeled efficiency: Between 82% and 85% (80 Plus Bronze certified)
• Measured efficiency: Between 78.6% and 84.3% at 115 V (nominal, see complete results for actual voltage).
• Active PFC: Yes.
• Modular Cabling System: No.
• Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector.
• Video Card Power Connectors: Four six-pin connectors (in two cables) and one six/eight-pin connector (in a separated cable).
• SATA Power Connectors: Three in three cables.
• Peripheral Power Connectors: Three in two cables.
• Floppy Disk Drive Power Connectors: Two in two cables.
• Protections: Over voltage (OVP, not tested), over current (OCP, tested and not working), over power (OPP, not tested) and no load protection (NLO). Short-circuit protection (SCP) present and working.
• Warranty: Three years.
• Real Model: Seventeam ST-750P-AF
• More Information: https://www.silverstonetek.com
• Average price in the US*: USD 130.00 (USD 90.00 after a mail-in rebate).

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

SilverStone Element ST75EF is basically a Seventeam ST-750P-AF with a different cable configuration and rail distribution. Internally the two power supplies are identical.

Since we gave Seventeam ST-750P-AF our Golden Award seal, we don’t see why not giving it to Element ST75EF as well: it presents decent 83%-84% efficiency is you pull between 40% and 60% from its labeled capacity (i.e., between 150 W and 450 W). In fact Element ST75EF performed better than the Seventeam ST-750P-AF on voltage regulation and ripple and noise, plus it comes with more video card cables, allowing you to install two high-end video cards under SLI/CrossFire mode without the use of adapters – what doesn’t happen with the model from Seventeam.

Something really interesting is happening on the market right now. Both SilverStone Element ST75EF and Seventeam ST-750P-AF used to be sold for USD 130, however Seventeam ST-750P-AF price tag dropped to only USD 100, and Newegg.com provides a USD 40 mail-in rebate for SilverStone Element ST75EF, making this power supply from SilverStone to cost only USD 90 – which is a real bargain for a mainstream 750 W power supply.

Of course there are better products out there, but not at this terrific price tag.