Benchtop Power Supply based on USB PD? - Page 1
Forum section: electronics / projects

author: T_guttata
author_rank: Regular Contributor
timestamp: December 24, 2024, 09:27:00 am
content: HiRecently I came across USB-C cables, which use USB Power Delivery (PD) to provide a certain voltage from a regular USB-C Power adapter: 5V, 9V, 12V, 15V or 20V:https://de.aliexpress.com/item/1005006095918839.html?spm=a2g0o.order_list.order_list_main.154.49995c5fbXObqm&gatewayAdapt=glo2deuI asked myself if I could build a multi channel power supply with such cables. The only thing which is missing is a constant current function.I quickly googled but could not find anything which goes in the direction of using the widely available USB-C power adapters for lab purposes.Anyone had a similar idea?Benchtop power supplies with >2 channels are quite expensive, and using USB-PD could be a much cheaper option?

author: xvr
author_rank: Frequent Contributor
timestamp: December 24, 2024, 12:37:51 pm
content: QuoteNoThis cable use USB PD to select voltage. Cable itself do not contains any voltage regulation circuitry. It just performs negotiation with PD source about voltage required.And because PD source can provide only one power source at once, you can't got different voltages from single PD PSU at once.Constant current mode also impossible - PD do not provide such mode (AFAIK)

author: fchk
author_rank: Frequent Contributor
timestamp: December 24, 2024, 12:52:46 pm
content: 100% agree.Plus:Most USB C power supplies don't provide all voltages but only a subset.12V is not a standard voltage, however there are some that can provide this voltage.No constant current modes.No overcurrent protection with cheap power supplies.Noise fugures not sufficies for sensitive analogue circuits.Summary: stupid idea. Don't do it.

author: watchmaker
author_rank: Unknown
timestamp: December 24, 2024, 01:49:08 pm
content: https://www.aliexpress.us/item/3256807428562953.html?spm=a2g0o.order_list.order_list_main.64.68a718027sW6B5&gatewayAdapt=glo2usa

author: xvr
author_rank: Frequent Contributor
timestamp: December 24, 2024, 02:01:46 pm
content: Quote from: watchmaker on December 24, 2024, 01:49:08 pmO, yes. This one definitely includes regulator, but it is definitely not an original power supply cable from OP, and costs a much more.Seems that it would easily be powered from dump transformer (with a little connection from inside)

author: T_guttata
author_rank: Regular Contributor
timestamp: December 24, 2024, 05:59:04 pm
content: You only need a USB-C power adapter with multiple USB-C ports and a bunch of XL4015 boards?

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 24, 2024, 10:19:56 pm
content: Well, a few things:- The negotiated voltage will be maximum the value that is requested, but you have no guarantee that a particular USB-PD source can deliver a given voltage. So, a "15V" cable may only give you 9V or even 5V on a particular source.- As some have said, 12V is not as common as the other voltages and has an even lower probability of being available. So, similarly, if you request 12V and the source can only do 9V, 9V you'll get.- The outputs can be relatively noisy and not extraordinarily well regulated. The spec requires +/-5 %. Not crazy accurate. The requirements for the load transients are also not top-notch.- The current limit can be negotiated, but those simple "cables" do not and will get pretty much the maximum allowed for the given output voltage that the connected source can deliver. (It's possible to negotiate a lower current limit though with an appropriate USB-PD controller.)You can do the same thing as these cables (not more, not less) yourself using a basic USB-PD controlled IC such as the CH224. It works, it's cheap, and it does this job exactly: negotiate one of the basic voltages (5V, 9V, 12V, 15V, 20V) at the max current available, nothing more. It does the job - *this* job. If you don't want to make your own PCB, there are tons of available breakout boards with this chip.With this info, it's up to you to determine if that fits your requirements in terms of "benchtop power supply". Maybe so. Probably not.There are relatively inexpensive USB-PD powered programmable supplies out there (one of them was reviewed by Dave), so that would be your fastest bet. If you still want to DIY it, then you'd pretty much have to design a power supply. Just that it would itself be powered from USB-PD, the rest would be the exact same as designing any power supply. And again, if you go that DIY route, I'd recommend using one of the USB-PD controlled ICs (such as the CH224) rather than buy a ready-made cable. And, your design must accomodate the fact that the input voltage (from USB-PD) may be less than the voltage you request, so your power supply must be able to function with as low as just 5V input (with obviously/possibly degraded capabilities).