Hardware Insights Forum

Not to bump old threads, but...

I noticed in the secondary image that two STPS2045CTs were seen at both ends of the heatsink, next to the P60NF03Ls... wouldn't the STPS2045CTs be responsible for the +5V and +3.3V rails and not the STPS20H100CTs? Do you remember if there were only two STPS2045CTs or were there others in parallel at the other side of the heatsink? I ask because you managed to pull 29.6A from the +3.3V rail and I'm not sure if you could do that with only a 20A part.

EDIT: Nevermind. I think I found my answer here - it does look like there's two more on the other side for the +5V and +3.3V rails.

If you look carefully at the back of the secondary PCB, you can see that there is only one STPS2045CT rectifier for each of the rails. We can also see that the main transformer only provides the 12V output, and so the other rails would have to come from there (which is impossible to do with only diodes).

There's only a STPS2045CT for the +3.3V rail yet they rated it at 30A and you pulled over 29A from it? (are you saying there are four STP60NF03Ls too?)

Yes, and the same goes for the 5V. There are four STP60NF03Ls in total. As I said in the review, there are two on each rail. They provide most of the current, which is why I was able to pull as much as I was from it. The STPS2045CTs are only used for freewheeling (discharging the coils).

Oh... because it uses synchronous rectification, or a synchronous, buck DC-DC converter (the MOSFETs rectify those rails and don't just regulate +12V down to a lower voltage, or do two MOSFETs rectify it and the other two regulate the +12V rail down to those voltages)?

It's a buck DC-DC converter.

c_hegge wrote:There are four STP60NF03Ls in total. As I said in the review, there are two on each rail. They provide most of the current, which is why I was able to pull as much as I was from it.

But they aren't in parallel pairs - each rail has one on the high-side, and one on the low side (along with the STPS2045CTs). And the 60A rating is with the case at 25°C.

You are right. That's interesting, though. Buck only uses one transistor. A second transistor can be either added in parallel (which doesn't appear to be the case here) or used to replace the freewheeling diode (which also doesn't seem to be the case - there are definitely diodes present). I guess it must use semi-synchronous rectification, although I haven't ever heard of that with a Buck converter before.

I'll fix it up shortly

How come they used 16V rated caps on the +3.3V and +5V outputs??? Since they are 2200µF and 10mm, they would have to be custom-made. Why didn't they just use ordinary 2200µF 6.3V caps there???