A Look Inside

Before reading this page we strongly suggest to take a look at this article, which will help you understand the internal components of a PSU much better.


The OEM of this unit is FSP, the 5th largest power supply vendor in the world according to info provided by them. The main PCB is densely populated and the primary and secondary heatsinks are very small, so we don't expect to see a large difference between input and output temperatures during the test sessions. The topology used to achieve Platinum efficiency is the Active Clamp Reset Forward (ACRF), the same topology used in FSP Aurum units. This topology offers high efficiency and good power handling capability but up to a certain power level it cannot compete with other topologies, like double forward, full phase shift etc. However lately we have seen high capacity units utilizing ACRF with fairly good performance results.


The transient filtering stage starts at the AC receptacle with two Y caps. On the main PCB we find two more pairs of X and Y caps, two CM chokes and an MOV. Contrary to the original FSP implementations, this unit finally has an MOV installed. Here we should note that FSP also claims that the MIA IC that this platform uses is able to absorb excess surges coming from the power grid. Regardless, we feel safer with an MOV installed.


The thermistor is responsible for protection against large inrush currents and the diode cuts the path through to the thermistor once the PSU starts and the APFC cap is charged.


The single bridge rectifier is bolted on a dedicated heatsink. Its model number is GBU15L06 and can handle up to 15A so it easily covers the requirements of this PSU.


In the APFC two IPA60R125CP along with the necessary boost diode are used to shape the current waveform and make it proportional to the mains voltage waveform. The hold up cap is provided by CapXon so it is made in mainland China. It is rated at 85°C, 420V and has 390µF capacitance. We would like to see a higher capacity, Japan made, cap here.


Moving on to the primary switching section we find the ACRF topology. Let's remind you again what is going on in this topology, briefly there are two mosfets with one playing the role of the main switcher (Q1) and the other is the reset switch (Q2) which disconnects the main capacitor while Q1 is active. Also while Q2 is open, power is transferred from the primary to the secondary side. The main advantage of ACRF is the almost lossless switch of Q1, because while it is turned off the drain voltage is very low. In this case the role of Q1 switch plays an SPA17N80C3 fet and as Q2 we find an FQPF3N80C fet. The APFC/PWM controller is an FSP 6600 IC which is soldered on the component side of the main PCB. Since this is a custom made IC by FSP, we didn't find any documentation for it on the net.


In the secondary side synchronous design is used and the generation of +12V is handled by mosfets (two IRLB3036). The mosfets responsible for the minor rails generation, four IPD031N03L, are located on the solder side of the main PCB and are cooled passively by the PCB itself. The PWM controller for the DC-DC converter of the minor rails is the propriety FSP6601 IC.


As you can see there are only two toroidal chokes present in the secondary side while for independed regulation, for each rail, there should be at least three. Apparently group regulation is used in the secondary of this unit, as it is also used in the FSP Aurum PSUs on which platform the new EarthWatts PSUs are actually based. The large choke is for 12V/5V while the smaller one is used by the 3.3V rail.


In the secondary side along with several Nippon Chemi-Con caps we find one Rubycon and one CapXon. All are rated at 105°C.


The supervisor IC is a WT7579, another custom made IC for FSP as it seems, since we couldn't find any info about it.


The solder side of the main PCB is densely populated by SMD components. Soldering quality is good but we found several long component leads. Under the +12V islands there are four current sense resistors (or shunts) matching the virtual +12V rails of the unit.


The cooling fan is provided by Yate Loon Electronics and its model number os D12BH-12. It uses ball bearings for increased lifespan and in general is fairly quiet, thanks to the relaxed fan operation profile of the control circuit.