Re: No More USB-A Ports

Dan Purgert <dan@djph.net> wrote:

On 2024-06-08, Computer Nerd Kev wrote:

The USB-PD standards are interesting. Upon first reading about them
I was keen to find/design a device to just break out the outputs
and have a mini variable power supply for general use, even battery
powered from one of those power bank devices. But as with most
things USB3/C it turns out the power supplies that are actually
available only implement the bare minimum range of voltage outputs
that the manufacturers think most people will need.

 
Mine here are all 5/9/15/20V.  I "think" they're missing only 1 or 2
voltages, but that's enough for my laptops and cell phones.  Not really
sure what'd ask for 9 or 15 volts ...

9V plugpacks are pretty common for stuff I use, it's typical for
devices that reduce that to 5V internally. Similarly 5V devices
generally use 3.3V internally. My laptop's power supply is 16V, so
15V might work.

But really what excited me were the newer PPS power supplies (USB-C
3.0 PD PPS, to use their full title). These are supposed to supply
a requested voltage in 20mV steps between 3.3V and 21V+. The idea
is to allow optimised battery charging by supplying a charge
voltage/current specific to the state of charge that the battery is
in. I just liked the idea of completely universal plugpacks, but
when I went shopping for them (and granted they're quite new to the
market in Australia) the models on offer had a much more limited
voltage/current range.

Bear in mind that it's ONE output, and you negotiate the voltage on the
wire as part of the connection handshaking (IIRC CC1/2 or maybe
something more active later on, been a bit since I read up on how PD
works)

Yes it's all rather complicated, but in theory a device to allow
manual control of the output could be quite cheap because there
are chips designed for doing that in relatively dumb USB-C-powered
devices. However I found a project online from someone who'd tried
making a bench power supply adapter from a wide-range USB-PD PPS
power supply and they found the outputs were so far off what was
requested that they ended up setting it to a fixed output and used
another regulator for the final output. So not using the voltage
programming ability of the USB power supply after all. I realised
then that I was probably wasting my time - it's a standard for a
perfect power supply, which might only be used to make
barely-good-enough-to-sell power supplies. I shouldn't really have
been surprised.

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