• Re: USB-A to USB-C

    From Brian Gregory@void-invalid-dead-dontuse@email.invalid to uk.telecom.mobile on Tue May 27 22:46:31 2025
    From Newsgroup: uk.telecom.mobile

    On 22/05/2025 17:05, Tweed wrote:
    ThatrCOs a bit chicken and egg. If the equipment, eg phone, has a discharged battery it canrCOt enter into PD negotiations unless the charger provides it with some power.
    No. Part of the PD spec is that just placing certain resistors on the
    two pins that carry the PD negotiation in the USB-C connector will make
    the source output 5V power.
    --
    Brian Gregory (in England).
    --- Synchronet 3.21a-Linux NewsLink 1.2
  • From Tweed@usenet.tweed@gmail.com to uk.telecom.mobile on Wed May 28 05:59:30 2025
    From Newsgroup: uk.telecom.mobile

    Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
    On 22/05/2025 17:05, Tweed wrote:
    ThatrCOs a bit chicken and egg. If the equipment, eg phone, has a discharged >> battery it canrCOt enter into PD negotiations unless the charger provides it >> with some power.
    No. Part of the PD spec is that just placing certain resistors on the
    two pins that carry the PD negotiation in the USB-C connector will make
    the source output 5V power.


    My understanding is that those resistors are to allow higher currents at 5V
    to be requested. Without them 5V at 500mA should be provided, as per the earliest version of USB.

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  • From Chris Green@cl@isbd.net to uk.telecom.mobile on Wed May 28 08:26:10 2025
    From Newsgroup: uk.telecom.mobile

    Tweed <usenet.tweed@gmail.com> wrote:
    Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
    On 22/05/2025 17:05, Tweed wrote:
    ThatrCOs a bit chicken and egg. If the equipment, eg phone, has a discharged
    battery it canrCOt enter into PD negotiations unless the charger provides it
    with some power.
    No. Part of the PD spec is that just placing certain resistors on the
    two pins that carry the PD negotiation in the USB-C connector will make the source output 5V power.


    My understanding is that those resistors are to allow higher currents at 5V to be requested. Without them 5V at 500mA should be provided, as per the earliest version of USB.

    It's very difficult to 'provide' a specific current at a given
    voltage, it needs a 'consumer' to take more than 500mA if it's
    available. A source can limit the current to a maximum but it can't
    really provide more unless the consuming device increases its
    consumption.

    So the current might be limited to 500mA at 5v **unless** those
    resistors are present but it's down to the consuming device to take
    more than 500mA if it's available.

    In reality I doubt if the resistors change the current availability,
    they almost certainly negotiate different voltages.
    --
    Chris Green
    -+
    --- Synchronet 3.21a-Linux NewsLink 1.2
  • From Theo@theom+news@chiark.greenend.org.uk to uk.telecom.mobile on Wed May 28 09:15:31 2025
    From Newsgroup: uk.telecom.mobile

    Chris Green <cl@isbd.net> wrote:
    It's very difficult to 'provide' a specific current at a given
    voltage, it needs a 'consumer' to take more than 500mA if it's
    available. A source can limit the current to a maximum but it can't
    really provide more unless the consuming device increases its
    consumption.

    So the current might be limited to 500mA at 5v **unless** those
    resistors are present but it's down to the consuming device to take
    more than 500mA if it's available.

    In reality I doubt if the resistors change the current availability,
    they almost certainly negotiate different voltages.

    It's slightly more complicated than that. The resistors can disable power output completely, as initial versions of the Raspberry Pi 4 showed (they
    fixed it in the next revision):

    https://www.scorpia.co.uk/2019/06/28/pi4-not-working-with-some-chargers-or-why-you-need-two-cc-resistors/
    --- Synchronet 3.21a-Linux NewsLink 1.2
  • From Scott@newsgroups@gefion.myzen.co.uk to uk.telecom.mobile on Fri May 30 21:17:56 2025
    From Newsgroup: uk.telecom.mobile

    On 11 May 2025 10:35:45 +0100 (BST), Theo
    <theom+news@chiark.greenend.org.uk> wrote:

    Scott <newsgroups@gefion.myzen.co.uk> wrote:
    Thank for this helpful advice. The charger is said to be genuine Apple
    (removed from the boxes of US imports). As an added precaution, I'll
    take it into the Apple Store and ask them to check.

    I'm not sure they're able to tell you whether a third party product is >genuine or not (they are not skilled in the arts of telling whether the >writing that's supposed to be dark grey is in fact black, and similar sorts >of things used to tell them apart). For one thing they wouldn't want the >liability if they called it the wrong way.

    They were fine. He looked at it carefully and said it was genuine,
    adding that it was however for the US market. I said I was taking it
    to Canada and he said that was fine. He seemed pretty confident.
    --- Synchronet 3.21a-Linux NewsLink 1.2
  • From Brian Gregory@void-invalid-dead-dontuse@email.invalid to uk.telecom.mobile on Sat May 31 17:30:07 2025
    From Newsgroup: uk.telecom.mobile

    On 28/05/2025 06:59, Tweed wrote:
    Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
    On 22/05/2025 17:05, Tweed wrote:
    ThatrCOs a bit chicken and egg. If the equipment, eg phone, has a discharged
    battery it canrCOt enter into PD negotiations unless the charger provides it
    with some power.
    No. Part of the PD spec is that just placing certain resistors on the
    two pins that carry the PD negotiation in the USB-C connector will make
    the source output 5V power.


    My understanding is that those resistors are to allow higher currents at 5V to be requested. Without them 5V at 500mA should be provided, as per the earliest version of USB.

    That's not my understanding of how it works, at least in some cases,
    with USB-C.

    I don't think the pins in question even existed on earlier versions of USB.
    --
    Brian Gregory (in England).
    --- Synchronet 3.21a-Linux NewsLink 1.2
  • From Tweed@usenet.tweed@gmail.com to uk.telecom.mobile on Sat May 31 17:04:58 2025
    From Newsgroup: uk.telecom.mobile

    Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
    On 28/05/2025 06:59, Tweed wrote:
    Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
    On 22/05/2025 17:05, Tweed wrote:
    ThatrCOs a bit chicken and egg. If the equipment, eg phone, has a discharged
    battery it canrCOt enter into PD negotiations unless the charger provides it
    with some power.
    No. Part of the PD spec is that just placing certain resistors on the
    two pins that carry the PD negotiation in the USB-C connector will make
    the source output 5V power.


    My understanding is that those resistors are to allow higher currents at 5V >> to be requested. Without them 5V at 500mA should be provided, as per the
    earliest version of USB.

    That's not my understanding of how it works, at least in some cases,
    with USB-C.

    I don't think the pins in question even existed on earlier versions of USB.


    You are quite correct. It a function of the USB-C to USB-A adapter cable to turn on the USB-C supply.

    https://electronics.stackexchange.com/questions/323128/wiring-diagram-for-usb-c-to-usb-a-cable
    Note 1 is the important point.

    Engaging my brain gives the obvious rationale why a USB-C charger must initially present no output - it is a bi directional bus and either end can deliver power. Eg a USB-C ipad connected to a USB-C iPhone can cause
    charging to occur in either direction, depending on which device has the
    most depleted battery.
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  • From Brian Gregory@void-invalid-dead-dontuse@email.invalid to uk.telecom.mobile on Fri Jun 6 23:47:44 2025
    From Newsgroup: uk.telecom.mobile

    On 11/05/2025 10:28, Tweed wrote:
    Jason H <jason_hindle@yahoo.com> wrote:

    I tend to assume that if it's sourced from a responsible retailer, and has >> Anker or Ugreen written on it, then it will be fine.

    --
    A PICKER OF UNCONSIDERED TRIFLES


    The trouble is those brands are only sold via Amazon as far as I know.


    https://uk.ugreen.com/
    --
    Brian Gregory (in England).
    --- Synchronet 3.21a-Linux NewsLink 1.2