Question PSU rails question and GPU leds still turned on after pc completely shut down

Jun 6, 2020
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Hello everyone, I wanted to ask a technical question about how PSUs work, my question is why my gpu's (vega 56 strix) power LEDs (the ones above the 8pin pcie connectors that tell you if the GPU is powered properly or has no power) keeps shining even after the PC is completely shut down? They always shine when the PC is turned on (and this is normal because they tells me that the energy fed to the GPU is normal without any problems; but the question is how those LEDs keeps receiving energy when the PC is turned off? I'm not expert in those technical aspects but I know that when PC is turned off, the only rail that keeps working is the 5v SB and the gpu should have NO connection to the 5v SB; so how do those LEDs keeps shining? :eek: (enabling ERP mode on bios solve the "problem" but was still curious about how does it work and if I'm missing something about this. (maybe other rails keeps staying on too or things like that) Thank you everyone and have a great day :D
 
Jun 6, 2020
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I'm pretty sure it works the same as an LED strip which would also stay on till you change the S5 sleep function in the BIOS.
Thank you for your answer,I thought it too, but than it means that the PSU is never turned off; I was curious about how the PSU works because I thought that when PC is off just the 5v SB works powering just USBs, ethernet and things like that. I even checked the PCIe slot pinout and there is no 5v, just 12/3v so if those rails don't work, how does it manage to give those LEDs the current? It would means that 5v and 12v still work even with PC turned off but I can't realize how it is possible; that's why I was asking :)
 
Jun 6, 2020
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https://forums.tomshardware.com/threads/5vsb-pc-standby-power-questions.2495150/post-16257612

Also note that this isn't something unique to PCs. It's just that PCs allow you some unique benefits to that little trickle of power.

https://en.wikipedia.org/wiki/Standby_power
Thank you for your answer; I was aware of the 5v SB but thought it was JUST the 5v SB and not even the 12v and 3v; so if the graphic card doesn't have the access to this rail from where does it takes it?
 
Thank you for your answer; I was aware of the 5v SB but thought it was JUST the 5v SB and not even the 12v and 3v; so if the graphic card doesn't have the access to this rail from where does it takes it?
From the PCI-E connection (the one in your motherboard). I believe it doesn't have a dedicated 5VSB pin but it still gets the power from 5VSB on your power supply.
 
Jun 6, 2020
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From the PCI-E connection (the one in your motherboard). I believe it doesn't have a dedicated 5VSB pin but it still gets the power from 5VSB on your power supply.
Thank you for the answer, I thought it wasn’t possible to have something like 5v output from a 12v pin (for example) but I guess is the only explanation that makes sense. (I’m sorry if I say something wrong but I’m not expert in those technical aspects) :D
 
I didn’t wait; I was working with my pc turned off from hours and than noticed them (because of case’s transparent glass); since that moment I always noticed them so they always keep shining
Ok. That's really weird. PCIe slot doesn't use +5VSB. In fact, there isn't a +5V pin either. Only +3.3V and +12V. So your motherboard is really weird and somewhere converting +5VSB to +3.3V or +12V before going through the slot.
 
Jun 6, 2020
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Ok. That's really weird. PCIe slot doesn't use +5VSB. In fact, there isn't a +5V pin either. Only +3.3V and +12V. So your motherboard is really weird and somewhere converting +5VSB to +3.3V or +12V before going through the slot.
My motherboard is a b450m mortar titanium; but reading online I have seen that is something common for this GPU model and not something that happens just to me. The only thing that I was thinking is the fact that 12v/3.3v rails still works even if the pc isn’t turned off (but honestly I neither know if this is even possible)
 
Ok. That's really weird. PCIe slot doesn't use +5VSB. In fact, there isn't a +5V pin either. Only +3.3V and +12V. So your motherboard is really weird and somewhere converting +5VSB to +3.3V or +12V before going through the slot.
It could be pin 10, it is auxillary standby power. AFAIK it's common to see DC-DC to 3.3V on motherboard these days. Maybe it's something to do with that?

My motherboard is a b450m mortar titanium; but reading online I have seen that is something common for this GPU model and not something that happens just to me. The only thing that I was thinking is the fact that 12v/3.3v rails still works even if the pc isn’t turned off (but honestly I neither know if this is even possible)
Maybe 5VSB gets converted to 3.3V auxillary somewhere in your motherboard, and maybe it's common to have that these days... Because this is the only way that I can figure out.
 
Reactions: Nottwenox
Jun 6, 2020
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It could be pin 10, it is auxillary standby power. AFAIK it's common to see DC-DC to 3.3V on motherboard these days. Maybe it's something to do with that?


Maybe 5VSB gets converted to 3.3V auxillary somewhere in your motherboard, and maybe it's common to have that these days...
Thank you; yes, that is the first thing that I've checked but as you said it is the 3.3V and it shouldn't work when PC is turned off, right? (same should be for PIN 1,2,3 that are linked to 12v); that's where my initial question came out
 

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