Jump to content

Why do PCI-e USB 3 adapters require extra power?

rado33
By rado33
in Power Supplies
 Share
Posted

Specs online says PCI-e can provide 75W through the slot itself. 

 

Many (most?) PCI-e USB 3 cards require extra power, even though the spec, at max, for 3.1 power delivery is 7.5A (I mean watts not amps sorry). Even if you had a 7 slot USB card, that's only 52W. Hell, even most of the 2 slot cards require extra power. Doesn't make sense. 

 

The only thing I can think of is that (I think) the slot only provides 3V (or 3.5 or something) while USB is obviously 5V. And it may be... cheaper not to put a DC converter on the board? 

Link to comment
Share on other sites
Link to post
Share on other sites
Posted
1 minute ago, rado33 said:

The only thing I can think of is that (I think) the slot only provides 3V (or 3.5 or something) while USB is obviously 5V. And it may be... cheaper not to put a DC converter on the board? 

congratulations, you got it right. Why bother generating a 5V from 12V in the PCIe slot when your PSU already generates 5V? That's the logic behind using a power connector instead of a buck converter. Of course manufacturing cost is also considered.

CPU: i7-2600K 4751MHz 1.44V (software) --> 1.47V at the back of the socket Motherboard: Asrock Z77 Extreme4 (BCLK: 103.3MHz) CPU Cooler: Noctua NH-D15 RAM: Adata XPG 2x8GB DDR3 (XMP: 2133MHz 10-11-11-30 CR2, custom: 2203MHz 10-11-10-26 CR1 tRFC:230 tREFI:14000) GPU: Asus GTX 1070 Dual (Super Jetstream vbios, +70(2025-2088MHz)/+400(8.8Gbps)) SSD: Samsung 840 Pro 256GB (main boot drive), Transcend SSD370 128GB PSU: Seasonic X-660 80+ Gold Case: Antec P110 Silent, 5 intakes 1 exhaust Monitor: AOC G2460PF 1080p 144Hz (150Hz max w/ DP, 121Hz max w/ HDMI) TN panel Keyboard: Logitech G610 Orion (Cherry MX Blue) with SteelSeries Apex M260 keycaps Mouse: BenQ Zowie FK1

 

Model: HP Omen 17 17-an110ca CPU: i7-8750H (0.125V core & cache, 50mV SA undervolt) GPU: GTX 1060 6GB Mobile (+80/+450, 1650MHz~1750MHz 0.78V~0.85V) RAM: 8+8GB DDR4-2400 18-17-17-39 2T Storage: HP EX920 1TB PCIe x4 M.2 SSD + Crucial MX500 1TB 2.5" SATA SSD, 128GB Toshiba PCIe x2 M.2 SSD (KBG30ZMV128G) gone cooking externally, 1TB Seagate 7200RPM 2.5" HDD (ST1000LM049-2GH172) left outside Monitor: 1080p 126Hz IPS G-sync

 

Desktop benching:

Cinebench R15 Single thread:168 Multi-thread: 833 

SuperPi (v1.5 from Techpowerup, PI value output) 16K: 0.100s 1M: 8.255s 32M: 7m 45.93s

Link to comment
Share on other sites
Link to post
Share on other sites
Posted

One nitpick is that 7.5A isn't power, it's current. Power is measured in watts (most of the time)

I WILL find your ITX build thread, and I WILL recommend the SIlverstone Sugo SG13B

 

Primary PC:

i7 8086k - EVGA Z370 Classified K - G.Skill Trident Z RGB - WD SN750 - Jedi Order Titan Xp - Hyper 212 Black (with RGB Riing flair) - EVGA G3 650W - dual booting Windows 10 and Linux - Black and green theme, Razer brainwashed me.

Draws 400 watts under max load, for reference.

 

How many watts do I need? ATX 3.0 & PCIe 5.0 spec, PSU misconceptions, protections explained, group reg is bad

Link to comment
Share on other sites
Link to post
Share on other sites
Posted
  • Author
Just now, fasauceome said:

One nitpick is that 7.5A isn't power, it's current. Power is measured in watts (most of the time)

Sorry, I meant W. 5 V at 1.5A.

Link to comment
Share on other sites
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing Power Supplies

×