Buck converter component ID and possible circuit modification - Page 1
Forum section: electronics / projects

author: Unity_Coupled
author_rank: Newbie
timestamp: July 23, 2025, 10:49:34 pm
content: Hello- I'm hoping to get some pointers with a small project.To preface, my objective is to slightly increase the output current of the 12v buck converter on a Lenovo thinkstation mainboard such that an RTX A2000 workstation GPU will run stably in the system. The A2000 draws its power entirely from the PCIe slot, which in theory should deliver 70W per the interface standard. The problem is that while the design power of the A2000 is also 70W, the GPU has transients that reach 80W causing the thinkstation to shut down during 3D applications.I've tried adding a low-Z (Nichicon HE) 470uF cap to an unpopulated position in the 12V supply and it improved stability somewhat, but nowhere near enough to make it usable.Is it possible to increase the maximum current by changing the switching controller, inductor, and other passives? Alternatively I should be able to bypass the converter using an AG7010 module, but I prefer a solution that doesn't involve mounting a separate board.I'm curious if any of you detectives can dig up data on either the switching controller or the MOSFETs as I have been unable to. (sorry the controller is upside down...all the electrons are going to fall out!)Thanks for any advice and insight!

author: HwAoRrDk
author_rank: Super Contributor
timestamp: July 23, 2025, 11:56:33 pm
content: What makes you think the 12V is being regulated on the mainboard? PCs do not typically work like that; the 12V supplied to the PCIe slots usually comes directly from the PSU. If there is a problem with the whole system shutting off under load, then the problem probably lies with the PSU. Or maybe some kind of general thermal over-temp with the whole system.Unless this is some kind of SFF size computer that is powered by an external laptop-style power brick, which often put out 18-20V, and so would indeed require further regulation to 12V. In which case, I would suggest such a system is unsuited to running a powerful GPU.It would help if you said what exact model of ThinkStation you're talking about.

author: thm_w
author_rank: Super Contributor
timestamp: July 24, 2025, 12:51:21 am
content: You can try supplying 12V via external PSU with more power, instead of stock PSU, as mentioned above.But first I would try undervolt/underclock or reducing the power target of the A2000. Power target is easiest.MSI afterburner should be able to do it.

author: Unity_Coupled
author_rank: Newbie
timestamp: July 24, 2025, 02:07:42 am
content: Quote from: HwAoRrDk on July 23, 2025, 11:56:33 pmIt's a Thinkstation Tiny P330 which is supplied 20v from an external power brick. All voltages on the board are developed using buck converters.From what I can tell, later Thinkstation Tiny models are able to meet the power requirements for the A2000...but I'm hoping to avoid buying another unit.Quote from: thm_w on July 24, 2025, 12:51:21 amDuring experimentation I used an external lab supply to bolster the 12v, and it works fine...but I'd really like to keep everything self contained (less the system power brick). I can undervolt to the point where it doesn't shut off, however the clock speeds fluctuate a lot more and performance is nowhere near as smooth as it could be.I tossed a AG7010 in my cart since I was ordering stuff from mouser anyway. Without schematics or data on the existing components, adding the module and disabling the onboard converter is probably a better solution. ...Unless the P330 won't run without detecting that the original converter is operating.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: July 24, 2025, 12:18:05 pm
content: Quote from: Unity_Coupled on July 24, 2025, 02:07:42 amWhat's the rating of the power supply? From a quick Google, it seems these things have a variety of PSUs - 135W, 230W, 300W. Could it be that you just have one of the lower-rated PSUs that's not capable enough?Quote from: Unity_Coupled on July 24, 2025, 02:07:42 amYes, you might find that the on-board converter generates a 'power good' signal that goes elsewhere, and that if it's not operating, nothing will work because this PG signal isn't asserted. But can't really know unless you find schematics or do some serious reverse-engineering.

author: squadchannel
author_rank: Frequent Contributor
timestamp: July 24, 2025, 01:08:37 pm
content: I think it would be difficult to find a Lenovo ThinkPad model that does not have leaked schematics.PU1101 = RT8130CGQW (page 59, 12V_PCIE)

author: Unity_Coupled
author_rank: Newbie
timestamp: July 24, 2025, 07:34:47 pm
content: Quote from: HwAoRrDk on July 24, 2025, 12:18:05 pmThe power supply is 170W which should be more than sufficient. I don't believe it's the issue since the behavior is the same when I feed the system with a 400W lab supply.I suspect the PG signal from the AG7010 can be implemented without much trouble...Quote from: squadchannel on July 24, 2025, 01:08:37 pmI can't thank you enough for finding those! My searches came up empty except for laptop-schematics.com which wanted $20 for the set. For convenience I've extracted and attached the relative page below.The design parameters are a nice touch...the output capacity is only 5.5A, limited by the inductor. No wonder the system was unstable.Correct me if any of this seems wrong (I am but a simple audio guy)... Using the inductor selection formula in the controller data and a max load of 8A, I should be able to increase Iout with a 6.8uH inductor with sufficient current rating...something like this should still fit in the position and has lower DCR than the original part:https://www.digikey.com/en/products/detail/bourns-inc/SRP7050WA-6R8M/18670189.I'll add extra capacitance at the input and output as well.I'm not 100% sure if I need to change the overcurrent threshold setting resistor (Rocset) as OCP is set for 10A...I may revisit that if stability issues persist.Is there anything else I'm missing?

author: HwAoRrDk
author_rank: Super Contributor
timestamp: July 24, 2025, 09:01:28 pm
content: It seems the +12V_PCIE converter does indeed have a PGOOD output, although its unclear whether this actually goes to anything else. All I could find in the full schematic is it going to a couple of seemingly non-populated MOSFETs to drive some kind of general ALL_SYS_PWRGD signal that then goes off to some other stuff.Regardless of whether it's actually used, perhaps you take advantage of the PGOOD pin of PU1101 and 'scope it to see if the output from that regulator is indeed crapping out under high load.

author: thm_w
author_rank: Super Contributor
timestamp: July 24, 2025, 11:17:20 pm
content: 80W / 12V = 6.7ASo 10A OCP might still be fine.FETs look goodOriginal inductor:https://www.digikey.com/en/products/detail/pulse-electronics/MMD-06CZ-3R3M-V1/12182233Kind of surprised it even had an issue without even heating up?The input and output capacitance are very low (50uF and 220uF), though you said you already tried a larger output cap. And there is probably more on that +20V rail on another page of the schematic.

author: Unity_Coupled
author_rank: Newbie
timestamp: July 27, 2025, 06:18:23 pm
content: I've spent some time studying the design in earnest and it seems like 12V_PCIE should have sufficient power for a 70W gpu. Sure enough, it has no problem dumping 70W into a B&K 8500 for over a half hour with the inductor only getting mildly warm...but it craps out when presented with a transient load.I wondered if simply increasing the OCP limit would help, so I swapped the tiny 12k 0402 Rocset with a 20k, which bumps the cutout threshold up to 16A.Bingo! The A2000 is working perfectly in the P330, even without the extra 470uF output capacitance I previously added. I may end up dialing Rocset back if I can find a 15 or 18K 0402 so that the limit is below saturation, but I'm content to leave it at that.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: July 27, 2025, 07:05:33 pm
content: I wonder if the current draw from the GPU is very spiky, such that it will occasionally momentarily draw peaks of over 10A.Or... maybe they just messed up the OCP calculation and installed the wrong Rocset. I don't know what's going on with the formula stated in the schematic:QuoteNot sure where they got that from, because that's not what's in theRT8130C datasheet. That gives:QuoteWhere Iocset= 10µA, and RDS(on)= 7.5mΩ (value taken for PE534SA fromdatasheet here). By my calculations, you'd have a 7.5k resistor for 10A OCP.But then that doesn't jive with OP's statement thatincreasingthe resistor value made the OCP limit higher...

author: Unity_Coupled
author_rank: Newbie
timestamp: July 28, 2025, 02:32:30 am
content: Quote from: HwAoRrDk on July 27, 2025, 07:05:33 pmHigher-end GPUs are well known for exhibiting current spikes, but I initially figured a bus-powered workstation card would be designed to minimize that. That may actually be true and the P330 is just ultra sensitive. Newer Thinkstation tiny models seem to power the same card just fine.I'm still confused about the values they used in the formula too... Rds would have to be 1.5 mOhm which doesn't line up with the MOSFET data.In any case, the OCP threshold indeed increases in proportion with the resistor value...