Replacing the 5V USB power supply in my lamp - Page 1
Forum section: electronics / beginners

author: Genshii
author_rank: Newbie
timestamp: July 22, 2023, 08:33:49 pm
content: I bought a couple oflamps off amazonbut unfortunately the USB C ports don't really work. Most of the devices I plug into it either don't charge at all or complain that something is wrong with the connection. The USB A ports work fine so I imagine the problem is that the power supply does not support USB PD so the device isn't able to negotiate charging correctly.Here's a picture of the case of the power supply:And the power supply itself:A few questions:1. I was thinking about replacing it withthis 5V 3A power supply. Would this work to power both ports or do I need something with PD capabilities for the USB C port to work?2. Would there be any issue powering both ports with this 3A supply (compared to the 2.1A supply that was already there)?3. From the picture you can see that the single output is wired to both the USB A and C ports. Does that make a difference for what kind of power supply I can/should use? (I could of course wire them up separately but I'm trying to avoid doing so.)Any help/suggestions are greatly appreciated.

author: CountChocula
author_rank: Unknown
timestamp: July 23, 2023, 01:00:34 am
content: Hiya!Quote from: Genshii on July 22, 2023, 08:33:49 pmYou'd still have the same problem; I don't think the current rating of the power supply is what's preventing things from working the way you want. If the supply is connected straight to both ports (which it probably is, since it's just 5V), the problem is more likely to be that you're just feeding 5V to whatever you connect to both of them. A USB-C device that supports PD will try to negotiate a higher voltage, fail to do so, and be unable to charge because OG USB only provides up to 500mA (with some tricks allowing up to 2A, but still only at 5V).QuoteDon't do this!If USB-C and USB-A ports are both connected straight to the power supply and you attach a common PD-compliant supply to both, as soon as a USB-C device negotiates a voltage higher than 5V, you're going to fry anything attached to the USB-A port. If you really want PD, separate supplies (or a single supply that can provide both 5V and a separate PD-compliant output) is the way to go; the one you have is probably good enough* for the USB-A connection, and you can use a separate PD-compatible supply for the USB-C port.—CC* That looks like a pretty cheap supply… be careful!

author: Genshii
author_rank: Newbie
timestamp: July 23, 2023, 01:45:09 am
content: Thank you for the response.I guess what I'm still a bit confused about is that the device I'm trying to charge (a samsung tablet) is able to charge from a 5V/1A supply that I have lying around, so even when it fails to negotiate a higher voltage it still falls back to a much slower charging rate. When it's the only thing plugged in to the 2.1A supply in the lamp it still doesn't charge, which is why I thought replacing the supply might help.

author: CountChocula
author_rank: Unknown
timestamp: July 23, 2023, 02:27:19 am
content: Well, it might—certainly the supply that you have right now doesn't look super high quality, so replacing it probably won't hurtPrior to the advent of PD, the USB spec allows for a form of primitive signalling done through the D+ and D- that allows connected devices to determine whether they can draw more than the customary 500mA from a port. This istypically doneby either shorting the two data lines, or by using a voltage divider to cause a specific voltage to appear on them when a device connects. Perhaps you can try to implement this with the your current power supply and see what happens.—CC

author: Genshii
author_rank: Newbie
timestamp: July 23, 2023, 03:06:28 am
content: Thanks for that link. That would explain why there are some resistors on the board with the connectors (and why some of my devices are able to charge faster than 500mA).After some more reading it seems like the "correct" way (at least according to USB spec?) to enable fast charging (non-PD) is to simply short the data lines (no resistors). I think the resistors are to make Apple devices happy.I'm currently getting about 2.6V on the data lines, so maybe I can try removing the resistors and see what happens?