Bitfenix Whisper Series 550W PSU Review

A Look Inside And Component Analysis

Parts Description

Before proceeding with this page, we strongly encourage you to a look at our PSUs 101 article, which provides valuable information about PSUs and their operation, allowing you to better understand the components we're about to discuss. Our main tools for disassembling PSUs are a Thermaltronics soldering and rework station, and a Hakko FR-300 desoldering gun.

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The whole Whisper series is based on a fresh CWT platform code-named GPU. Our sources tell us that this design has some distinctive features that won't be available in other revisions of the platform. For example, some of its heat sinks were purportedly custom-made for Bitfenix. There are also parts in there we haven't seen before, like the APFC converter's FETs, which are made by Champion (well known for its PWM and PFC controllers, and not so much for other products).

In general, the design looks nice and clean. There are no power cables restricting airflow and increasing the circuit's resistance, leading to significant power losses under high loads. On the primary side, the APFC's heat sink doesn't have any fins, while on the secondary side the +12V heat sinks don't hold any components, since the corresponding FETs are installed on the solder side of the main PCB. Strangely enough, there aren't any thermal pads on the chassis, which would allow it to help cool the secondary side. It instead seems like the heat sinks mentioned above handle cooling for the +12V FETs.

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The EMI filter starts at the AC receptacle, as usual. In this unit it consists of one X and two Y caps. It continues on the main PCB with two Y caps installed after the bridge rectifier, an additional X cap, two CM chokes, a MOV, and a CAP004DG that's installed on the solder side of the PCB. The latter component blocks current through the X capacitor discharge resistors when AC voltage is connected. Efficiency is consequently improved since no energy is wasted on the bleeding resistors.

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The single bridge rectifier is bolted to a heat sink with long fins. A GBU806 can handle up to 8A of current, leaving plenty of headroom even with as little as 100V input.

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The APFC converter uses a couple of Champion GP18S50G FETs to shape the current waveform, along with a single STMicroelectronics STTH8S06D boost diode. The bulk cap is provided by Nichicon. Although it is rated at 105°C, its capacity (390uF) is low for a 550W unit. A 470uF bulk cap should be used, at least. 

An NTC thermistor handles inrush current protection. It is supported by a bypass relay, enabling quick cool-down.

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The PFC controller is a Champion CM6502S IC, which is also supported by a CM03X Green PFC controller that helps achieve lower power consumption in standby mode.

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The primary switching FETs are two Silan Microelecronics SVF20N50Fs, arranged into a half-bridge topology. Champion's famous CM6901 LLC resonant converter is also used for lower switching losses. This part shows up in a great many high-efficiency PSUs.

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A couple of heat sinks on the secondary side aren't attached to any components, as the FETs that regulate the +12V rails are installed on the PCB's solder side. However, these sinks still play a key role in cooling the FETS, which don't come in contact with the PSU's chassis. In total, four Sinopower SM4021NAKPs handle the +12V rails.

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The filtering caps are mostly sourced by Chemi-Con, and they belong to the company's KZE and KY lines. We also spotted a Chemi-Con KMG cap and a couple of Nichicons. All electrolytic caps are rated at 105°C. In addition, a number of polymer caps help reduce ripple too. The polymers are provided by FPCAP, a Japanese company that initially belonged to Fujitsu but was later bought by Nichicon. FPCAP makes some high-quality stuff, so it's nice to see them used in this unit.

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The DC-DC converters are housed on a vertical daughterboard installed right below the modular PCB. This helps limit energy losses since power only has to travel a small distance up to the modular sockets. Both converters use two UBIQ QM3006D and two QM3004D FETs. The common PWM controller is an ANPEC APW7159C IC.

CWT uses two supervisor ICs in this unit, a Sytronix ST9S429-PG14 (OCP [2x 12V channels, OVP, UVP, PG) and a Weltrend WD7518D (OCP [2x 12V channels], SCP). Both ICs provide up to four +12V monitoring channels for OCP and the other basic protections. Of course, this PSU only has three +12V rails. Higher-capacity models in the Whisper family do have four +12V rails, though.

The 5VSB rail uses a TinySwitch-LT TNY177PN (18W peak) IC, which, according to its manufacturer, easily meets all global energy efficiency regulations.

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On the front side of the modular PCB, several FPCAP polymer caps are used for ripple filtering purposes. There are four shunt resistors on the back of the same board; these provide amperage information to the supervisor IC.

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The main PCB features good soldering quality. In addition, we didn't spot any long component leads that could create problems. We spotted a UTC LM393G dual differential comparator on this side, which is probably used by the unit's protection circuits.

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The cooling fan is made by Martech and its model number is DF1352512SEMN (135mm, 12V, 0.45A, 1500 +/-10% RPM, 62.87CFM, 30,000h @25°C). It uses a hydraulic bearing, but its rated lifetime isn't as long as higher-quality HDB and FDB fans we've seen. The fan's control circuit includes a UTC 2SA928AL transistor, which is usually used as an audio amplifier according to Unisonic.