by Oleg Artamonov
07/07/2004 | 01:09 PM
ASUS is a respected name in the PC hardware market – with ECS and Gigabyte, the company is in the world’s top three mainboard manufacturers list. Recently, ASUS also engaged into production of other components, previously not selling under the company’s brand, for example, cooling systems, system cases and – that’s what we’re going to discuss today – power-supply units.
Three PSUs from ASUS underwent rigid tests in out laboratory: A-30F, A-30G and A-30H models.
I’m not going to examine each of the PSUs separately – visual inspection reveals the fact that the three units we are about to test all have absolutely the same electronics and only differ in their cooling systems.
As you know, the classic and most widespread PSU cooling design uses an 80mm fan installed at the unit’s back panel and working to exhaust hot air to the outside. This design is simple and cheap, but, unfortunately, rather inefficient for high-wattage PSUs either because of bad cooling or because of the noise factor.
Each PSU of the ATX form-factor includes four components in need of cooling: 1) a group stabilization choke, 2) a heatsink with output diode assemblages, 3) a power transformer, 4) a heatsink with switch-type transistors and, sometimes, with a guard voltage regulator (the units are marked out in the snapshot below; the snapshot depicts a 250X1 model from Codegen, rather than any from ASUS, for illustrative purposes – that unit has a lesser component density).
The hottest components are the stabilization choke and the output rectifiers, but in the classic design they are situated aside of the main airflow created by the fan (actually, I met some rare samples of PSUs with these elements placed on the same side with the fan). Thus, a high-powered unit, generating much heat, just needs to have a better airflow for cooling down, i.e. it needs to have a better fan. Meanwhile, the increase of the power of the fan leads to more noise and this is not a factor to appeal to the user.
The junior model from ASUS, the A-30F, follows this design:
Take note of the vent holes – they are not in one side only (usually, the back or front side) as in a majority of PSUs, but are distributed among the sides so that the airflows cool the entire PSU down. There are also smaller holes for cooling the passive PFC choke.
The simplest and cheapest way to improve this cooling scheme – installation of a second fan at the back side of the PSU – is not very efficient and is only employed in inexpensive PSUs. The second fan is placed coaxially to the first one (or, better, with a slight shift to the center) and helps to blow at the power transformer and the both heatsinks as its airflow hits on these components directly. Below is an illustration of this cooling scheme – the Codegen 350X PSU:
More expensive PSUs – in newer models from Codegen as well as in the reviewed ASUS models – use different cooling schemes. First, we have the now-fashionable units with two 80mm fans, one of which is placed at the ordinary location and another is fastened to the cover of the PSU and is shifted to the center so that its airflow cooled the heatsinks as well as the group stabilization choke. The fact that the stream of cool air (well, not exactly very cool – it is taken from the computer’s case rather than from outside) is directed right at the heatsinks helps to improve their cooling considerably and, accordingly, allows using slower and quieter fans.
The more expensive model from ASUS, the A-30H, uses this scheme. Instead of the punched grill, there’s a wired one on the fans – it also helps to reduce the noise level.
The vent holes on the cover disappeared – the fan has replaced them – but they remained at the rear panel. The row of holes below of the passive PFC choke has been left intact, too.
Now, the last PSU cooling solution, also popular nowadays, although less so than the dual-fan scheme, puts a big 120mm fan on the PSU’s top, which blows at all the PSU components evenly due to its big size and creates a powerful airflow at a small rotation speed. Thus, the fan on the rear panel is not necessary anymore – there’s perforation instead of it. ASUS offers a model with one 120mm fan, too. It is the A-30G.
Of course, the back panel of the PSU is now without any holes. Otherwise, the hot air from the PSU would be exhausted back into the computer, which is definitely not what we need.
As I have mentioned above, all the three units are very much like each other, so I will only describe one of them, the A-30H, and then will point out differences from the A-30F and A-30G.
The unit has an overall air of neatness about itself. The label on the PCB indicates it actually comes from Enhance Electronics and, as far as I can judge, the ASUS A-30F corresponds to the Enhance ATX-1130F model, the A-30G to the Enhance ATX-1130G, and the A-30H to the Enhance ATX-1130H. The chip of the pulse-width modulator is also marked as Enhance 16880A.
The PSU’s LC filter with two chokes muffles the high-frequency noise from the operational pulse-width regulator. The capacitors in the high-voltage rectifier have a capacity of 680µF each, which is enough for a 300W PSU. One 3300µF capacitor is installed at the output of the +12v power rail; two 3300µF capacitors are at the output of the +3.3v rail; one 2200µF and one 3300mF are at the output of the +5v rail. All the outputs are equipped with chokes.
The heatsinks have an average thickness, about 2.5mm. This is more than in many inexpensive PSUs, but less than in models from InWin, for example. As you understand, the thickness of a heatsink affects its operation: the thinner the heatsink, the higher temperature difference is between its top and bottom. The top part of a very thin heatsink won’t work – it won’t heat up due to the insufficient heat conductivity of the material. For a small heatsink, however, 2.5mm of thickness is quite enough.
The heatsinks in the A-30H PSU are T-shaped, but a larger part of the top bar is sawed through, so that it didn’t prevent the installation of the capacitors of the high-voltage rectifier, the power transformer and the PFC choke.
Although without PFC, the A-30G PSU has the same-shaped heatsinks as the A-30H, while the single-fan A-30F uses vertical plates with “fingers” on top. The heatsinks could be made taller because of the lack of the fan on the PSU’s top; so they used cheap flat heatsinks instead of T-shaped ones, but achieved the same cooling efficiency.
All the three units can automatically control the rotational speed of the fan (or fans, like with the A-30H) using the sensor on the heatsink with the diode assemblages. This control works properly as our measurements show – see the table below (we performed the test under 21°C room temperature; after setting the load in, we “warmed up” the PSUs for 15-20 minutes).
The dual-channel A-30H turns to be the quietest unit, while the A-30G couldn’t make a worthy competitor – the blades of its 120mm fan produced a distinctly perceptible buzz combined with the noise of the air stream. Of course, the cheaper A-30F couldn’t compete with the A-30H, either, since its fan sped up to about 3000rpm.
Well, the powerful fan in the A-30G is both a shortcoming and an advantage – depends on how you view it. Its Adda AD1212MS-A71GL fan creates a 80CFM air stream at the maximum rotational speed, and that’s more than twice higher above the capabilities of the fans in the A-30F (38CFM at the maximum speed) and A-30H (31CFM for the rear fan and 22CFM for the top fan). Thus, the A-30G will not only cool down itself, but will also contribute to the cooling of the entire system case.
We examined voltage pulsations in the three units at two frequencies: the frequency of the pulse-width regulator (several tens of kilohertz) and the double frequency of the mains supply (100Hz).
+5V bus, 10uS/div
+12V bus, 10uS/div
The amplitude of oscillation at the frequency of the pulse-width regulator was small, just over 15mV. It is negligible considering the acceptable levels on the +5V and +12V power rails (50mV and 120mV, respectively).
+5V bus, 4uS/div
+12V bus, 4uS/div
The oscillations at 100Hz frequency are somewhat worse – their swing was 40-50mV on the +12V rail and 20-25mV on the +5V rail. Anyway, these numbers are much below the acceptable ceiling, so there’s no need to worry. As for the reason for that, some flaws in the design of the PCB or of the power transformer may bear blame (the third possible cause – the insufficient capacitance of the high-voltage rectifier’s capacitors – evidently is not applicable here).
We checked out the stability of the output voltages depending on the load in two steps. You see, the three reviewed models from ASUS differ from the standard 300W PSU in their higher acceptable current on the +12v rail, up to 18A. It is done because modern computers consume more power from this rail. For example, new models from Zalman indexed “B” (the ZM300B and the ZM400B) also claim to provide a maximum current of up to 18A on the +12v rail (see our 3 Zalman Power Supply Units Roundup for details). Meanwhile, a majority of older 300W PSUs have 15A at most on this rail, as the ATX standard dictates. So, in order to compare the results of the units from ASUS with previously-tested models we performed the first set of our tests using a maximum current load of 15A, and then, to estimate the PSUs’ stability under the maximum load, we performed a second session with a load of about 18A. The tables below show the averaged results of all the three units; the diagrams contain the results of the A-30H.
Load on the +12v power rail: about 15A
Load on the +12v power rail: about 18A
You may note that the PSUs perform well under the “standard” load as well as under the increased load. The voltage range on the +3.3v rail might be smaller, but this rail doesn’t have its former significance in modern computer systems anymore: many low-powered devices are equipped with their own regulators (for example, the CPU and the GPU). Moreover, notwithstanding our somewhat artificial trying to put a higher load on the units (the real computer is unlikely to meet the swings and misbalances of the load as on our testbed, and thus will have a smaller voltage dispersal ranges), none of the output voltages of the PSU exceeded the standard-regulated limits (±5% of the nominal value).
Lastly, I’d like to say that the units come with six connectors for IDE devices, with two power connectors for SATA devices, and AUX and ATX12V connectors. The AUX cable has the 16 AWG section and the other cables have the 18 AWG section, save for the FDD cables that are undemanding on the maximum currents.
The units come in a simple white box with four 1” screws for fastening them to the system case.
Our tests of power-supply units selling under the ASUS brand prove their high competitiveness due to high quality and nice characteristics. The units produced similar test results to those shown by PSUs from FSP, Zalman, InWin and other companies, much experienced in this field. All the three models we’ve tested today belong to the mid-range price niche – they don’t have those gold-plated connectors or fans highlighting or any other now-popular decorations, which anyway don’t affect their functionality or quality of service. They will suit to people who need a good PSU, but don’t want to pay more for those embellishments.
In my opinion, the ASUS A-30H is superior to the other two models. It comes with two 80mm fans and the use of high-quality blowers along with the efficient control over their rotational speeds made this PSU a very quiet one.
Unfortunately, the ASUS A-30G with its 120mm fan cannot work without making some noise, but it does the cooling most efficiently. It is for users who care more about the cooling proper than about the silence. Well, this fan can also drop its speed under small loads and become very quiet.
The ASUS A-30F has average cooling/noise parameters, but its lower price and the same electrical characteristics as of the two more expensive models may make it a successful product, too.