Logisys PS350MA Power Supply Review
By Gabriel Torres on May 25, 2011


Introduction

The Logisys PS350MA, targeted to small form factor (SFF) computers, measures only 4.9 x 2.5 x 3.9 inches (125 x 63.5 x 100 mm) (W x H x D). This unit raises several red flags as being a really bad product. First, it uses the SFX12V form factor, but the manufacturer is not aware of that, calling it a “Micro ATX” power supply. Second, it is sold as being a 350 W unit; however, the power supply label says that 350 W is the peak wattage, and the “average output” is 250 W. And, third, the label and product specification found online says the product only works at 220 V/50 Hz, but the unit clearly has a 110 V/220 V switch. Let’s see if our suspicions hold true or if this unit will surprise us.

Logisys PS350MA power supply
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Figure 1: Logisys PS350MA power supply

Logisys PS350MA power supply
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Figure 2: Logisys PS350MA power supply

This unit uses an 80 mm fan on its bottom part.

It doesn’t have an active PFC circuit and is based on the half-bridge topology, which is an obsolete design for PC power supplies, because it offers low efficiency.

The cables are permanently attached to the power supply, and they don’t have nylon sleeves. This power supply comes with the following cables:

The cable configuration is really bad, with only one SATA power connector. Nowadays, even very low-end computers need at least two SATA power connectors, one for the hard drive and another for the optical drive.

All wires are thinner than the minimum recommended (20 AWG vs. 18 AWG).

Logisys PS350MA power supply
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Figure 3: Cables

Let’s now take an in-depth look inside this power supply.

A Look Inside the Logisys PS350MA

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.

On this page we will have an overall look, and then in the following pages we will discuss in detail the quality and ratings of the components used.

Logisys PS350MA power supply
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Figure 4: Top view

Logisys PS350MA power supply
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Figure 5: Front quarter view

Logisys PS350MA power supply
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Figure 6: Rear quarter view

Logisys PS350MA power supply
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Figure 7: The printed circuit board

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 power supply doesn’t have this stage! The place for installing the components are there, but the manufacturer, in order to cut costs, decided not to install them.

Logisys PS350MA power supply
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Figure 8: The Logisys PS350MA doesn’t have a transient filtering stage

On the next page, we will have a more detailed discussion about the components used in the Logisys PS350MA .

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Logisys PS350MA. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

As with most very low-end power supplies, the rectification bridge of the Logisys PS350MA uses four discrete diodes, instead of using a ready-made bridge. The diodes are not identical; there are two 1N5408 (3 A at 105° C) and two RL257 (2.5 A at 70° C). At 115 V, this bridge supports only up to 345 W. Here we can clearly see that it is impossible for this unit to be a 350 W product. Assuming 75% efficiency (which is a common value for very low-end power supplies), this bridge would allow the power supply to deliver only up to 258.75 W.

Logisys PS350MA power supply
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Figure 9: Rectifying bridge

The electrolytic capacitors of the voltage doubler circuit are from Fhy and labeled at 85° C.

This power supply uses two 13007 NPN power transistors in its switching section, using the half-bridge topology. Each transistor supports up to 8 A at 25° C (unfortunately, the manufacturer doesn’t say the current limit at higher temperatures).

Logisys PS350MA power supply
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Figure 10: Switching transistors

The primary is controlled by an EST7502B PWM controller, which is physically located in the secondary of the power supply.

Logisys PS350MA power supply
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Figure 11: PWM controller

Let’s now take a look at the secondary of this power supply.

Secondary Analysis

The +12 V output uses one BYW51-200 rectifier (16 A, 8 A per internal diode at 156° C, 0.97 V maximum voltage drop), giving us a maximum theoretical current of 16 A or 192 W for this output. Please note that this rectifier is a “fast” model, not a “Schottky” one, meaning lower efficiency, which can be seen on the higher voltage drop offered.

The +5 V output uses one ESAD83-004 (“D83-004”) Schottky rectifier (30 A, 15 A per internal diode at 90° C, 0.55 V maximum voltage drop), giving us a maximum theoretical current of 30 A or 150 W for this output.

The +3.3 V output uses one S20C40C Schottky rectifier (20 A, 10 A per internal diode at 100° C, 0.70 V maximum voltage drop), giving us a maximum theoretical current of 20 A or 66 W for this output.

Notice how the +5 V output is “stronger” than the +12 V output, which is a typical scenario for power supplies projected more than 10 years ago. Nowadays, the most current/power is pulled from the +12 V output (because there is where the CPU and the video cards are connected to).

Logisys PS350MA power supply
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Figure 12: The +5 V, +12 V, and +3.3 V rectifiers

The PWM controller, already shown in Figure 11, also monitors the power supply outputs, providing over voltage (OVP) and under voltage (UVP) protections.

The electrolytic capacitors available in the secondary are from BH and labeled at 105° C.

Power Distribution

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

Logisys PS350MA power supply
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Figure 13: Power supply label

There is only one +12 V rail, so there is not much to say here.

How much power can this unit really deliver? Let’s find out.

Load Tests

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

Because this is a very low-end power supply, we decided to run our tests a little differently. We tried to pull around 85 W on our first load pattern, around 100 W on our second load pattern, and from then on we increased our load pattern increments by 25 W until we discovered the maximum this unit would be able to deliver. As usual, we pulled more current/power from the +12 V outputs, as this better reflects the usage of a modern PC, since the CPU and the video cards are connected to these outputs. In the table below, we list the load patterns we used and the results for each load.

If you add all the powers listed for each test, you may find a different value than what is posted under “Total” below. Since each output can have a slight variation (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. In the “Total” row, we are using the real amount of power being delivered, as measured by our load tester.

The +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During this test, both inputs were connected to the power supply’s single +12 V rail.

Input

Test 1

Test 2

Test 3

Test 4

+12VA

3 A (36 W)

3.5 A (42 W)

4.5 A (54 W)

5.5 A (66 W)

+12VB

2.5 A (30 W)

3.25 A (39 W)

4 A (48 W)

5 A (60 W)

+5 V

1 A (5 W)

1 A (5 W)

1.5 A (7.5 W)

1.5 A (7.5 W)

+3.3 V

1 A (5 W)

1 A (5 W)

1.5 A (4.95 W)

1.5 A (4.95 W)

+5VSB

1 A (5 W)

1 A (5 W)

1 A (5 W)

1 A (5 W)

-12 V

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

Total

84.4 W

98.8 W

134.9 W

146.0 W

% Max Load

33.8%

39.5%

54.0%

58.4%

Room Temp.

42.2° C

41.8° C

41.8° C

41.9° C

PSU Temp.

41.4° C

42.9° C

44.0° C

45.0° C

Voltage Regulation

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

AC Power

109.7 W

127.3 W

172.7 W

187.5 W

Efficiency

76.9%

77.6%

78.1%

77.9%

AC Voltage

116.9 V

117.5 V

116.9 V

116.9 V

Power Factor

0.630

0.634

0.640

0.642

Final Result

Pass

Pass

Pass

Pass


Input

Test 5

Test 6

Test 7

Test 8

+12VA

6.25 A (75 W)

7.5 A (90 W)

8.25 A (99 W)

9.25 A (111 W)

+12VB

6 A (72 W)

7 A (84 W)

8 A (96 W)

9 A (108 W)

+5 V

2 A (10 W)

2 A (10 W)

2.5 A (12.5 W)

2.5 A (12.5 W)

+3.3 V

2 A (6.6 W)

2 A (6.6 W)

2.5 A (8.25 W)

2.5 A (8.25 W)

+5VSB

1 A (5 W)

1 A (5 W)

1 A (5 W)

1 A (5 W)

-12 V

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

0.5 A (6 W)

Total

169.8 W

194.1 W

220.4 W

Fail

% Max Load

67.9%

77.6%

88.2%

Fail

Room Temp.

42.1° C

44.0° C

44.5° C

Fail

PSU Temp.

45.7° C

48.5° C

49.8° C

Fail

Voltage Regulation

Pass

Pass

Fail on +12 V

Fail

Ripple and Noise

Pass

Fail on +3.3 V

Fail on +3.3 V and +5 V

Fail

AC Power

221.0 W

259.3 W

310.7 W

Fail

Efficiency

76.8%

74.9%

70.9%

Fail

AC Voltage

116.5 V

116.5 V

115.8 V

Fail

Power Factor

0.644

0.649

0.652

Fail

Final Result

Pass

Fail

Fail

Fail

The Logisys PS350MA can’t deliver 350 W or even 250 W. The maximum we could pull from it was 220 W. During our test seven, when we tried to pull around 250 W from it, the power supply exploded after a few seconds. The two switching transistors were the components that fried. To give Logisys the benefit of the doubt, we tested two different samples and got the same exact results.

Logisys PS350MA power supply
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Figure 14: Bias resistors that burned together with the transistors

Efficiency was always below the 80% mark, varying between 70.9% and 78.1%.

Voltages were inside the proper range except for the +12 V output during test six (220 W), which dropped to +11.34 V. The ATX12V specification says that positive voltages must be within 5% of their nominal values, and negative voltages must be within 10% of their nominal values.

Noise and ripple levels were high, with the +3.3 V output surpassing the maximum allowed during tests six (56.8 mV) and seven (63.4 mV). During test seven, noise level at the +5 V output was at 51.4 mV, also above the maximum allowed. During the same test, the +12 V output presented a 120 mV noise level, right at the limit. The maximum allowed is 120 mV for +12 V and -12 V outputs, and 50 mV for +5 V, +3.3 V and +5VSB outputs. All values are peak-to-peak figures.

Main Specifications

The main specifications for the Logisys PS350MA power supply include:

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

Conclusions

The Logisys PS350MA is sold as a 350 W unit, but can only deliver up to 220 W. Not being able to deliver its rated wattage isn’t the worst problem with this unit. Efficiency is really low, between 71% and 78%, and starting at 200 W the noise level at +3.3 V is above the maximum allowed. At 220 W, the noise level at +3.3 V and +5 V is above the maximum allowed, and the voltage at +12 V output is below the minimum acceptable. This power supply may, in the best-case scenario, make your computer crash randomly and, in the worst-case scenario, burn your computer components. Spending less when picking a power supply is a bad idea.

Originally at http://www.hardwaresecrets.com/article/Logisys-PS350MA-Power-Supply-Review/1293


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