Compatibility Samsung fast phone chargers as 5V supply?

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gdhospers
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Posted by gdhospers: Mon. May 31, 2021 - 10:43 AM
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I got a new phone with a brick "Samsung Adaptive Fast Charging (AFC)".  The Samsung AFC chargers support up to 15W (5V/2A, 9V/1.67A).

 

 

The picture comes from https://switchchargers.com/what-... with some more information.

Previously I used a 5V brick to supply power to all kinds of evaluations boards with microUSB.

As both chargers have the same USB-A it is possible to use the fast charger with old microUSB cable that was intended for 5V.

 

 

My question is: is it safe to use this fastcharger for 5V boards?

If yes, how does it work? How is guaranteed that the 5V board is not oversupplied with 9V? Or is 9V supply in stead of 5V "considered not harmfull"?

 

 

 

Addition:

https://www.cnet.com/news/usb-ty...

"an Orzly cable that used a 10k ohm resistor instead of the 56k ohm resistor that the USB spec demands. (These resistors don't actually meter the flow of electricity, they just tell the phone how much energy is safe to pull."

I would like to see some explanation of this resistor. May be there is something to think about if we design a board with "5V" USB supply?

 

 

 

 

Tags:

Tools, Evaluation and Development Kits (AVR-related), Cypress Semiconductor, LoadSlammer, USB
Last Edited: Mon. May 31, 2021 - 11:29 AM
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Gold Markclawson
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Posted by clawson: Mon. May 31, 2021 - 11:24 AM
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USB is 5V. I don't see where your 9V fears come from? Also remember current sucks not blows. A connected device will only sink as much current as it requires (and without negotiation USB will only supply 100mA anyway). The only danger is if your powered device has a short and tries to pull too much current but then the 100mA limit should provide some protection. 

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Brian Fairchild
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Posted by Brian Fairchild: Mon. May 31, 2021 - 11:26 AM
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gdhospers wrote:

The Samsung AFC chargers support up to 15W (5V/2A, 9V/1.67A)...If yes, how does it work? How is guaranteed that the 5V board is not oversupplied with 9V? Or is 9V supply in stead of 5V "considered not harmfull"?

 

I'd guess that somehow the a Samsung phone which needs 9V will signal to the charger and ask it to supply 9V. Would I trust such a device to run anything tat will only run on 5V? No! Proper 5V supplies are cheap and it's not worth the risk.

 

Feeding 5V logic with 9V is most definitely not a good idea.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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gdhospers
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Posted by gdhospers: Mon. May 31, 2021 - 01:32 PM
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I will follow Brian's advice: better not take the (I think: small) risk.

I have gathered some more info how it works. Although I do not deeply understand it yet. I think you can instruct a capable USB-A (the fast charger) to deliver a higher voltage then 5V. A "normal" USB-A port won't understand or ignore the instructiins. A capable USB-A needs instructions. Hopefully it gets the right ones and/or has the right built in safety procedures.

For the specialists (not me) it is all in the USB-C specs. EDIT: version may 2021   https://usb.org/sites/default/fi...

 

This was usefull for me (some info about resistors that provide current capacity information):

https://www.allaboutcircuits.com...

http://ww1.microchip.com/downloa...

Last Edited: Mon. May 31, 2021 - 03:17 PM
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gchapman
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Posted by gchapman: Mon. May 31, 2021 - 01:52 PM (Reply to #2)
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clawson wrote:
USB is 5V.
up to 20V for USB Type-C PD (Power Delivery)

clawson wrote:
Also remember current sucks not blows.
Current sources and sinks (Kirchhoff's Current Law)

clawson wrote:
A connected device will only sink as much current as it requires
Crowbars can sink a lot of current; likewise with some step loads.

clawson wrote:
(and without negotiation USB will only supply 100mA anyway).
One reason why Raspberry Pi 4 went USB Type-C.

clawson wrote:
The only danger is ...
USB VBUS can exceed the upper voltage limit due to EOS (pass transistor short, sensor ('431) short or open, isolator gain reduction, PMIC malfunction, ESD damage is cumulative, lightning)

 

EZ-PD™ Barrel Connector Replacement (BCR) (Cypress Semiconductor) due to https://www.avrfreaks.net/search/site/%22EZ-PD%22

 

Kirchhoff's Laws - Kirchhoff's Current and Kirchhoff's Voltage Law - Solved Example

 

Home | LoadSlammer

 

Power (VBUS) | USB in a NutShell - Chapter 2 - Hardware

 

"Dare to be naïve." - Buckminster Fuller

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gchapman
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Posted by gchapman: Mon. May 31, 2021 - 01:57 PM (Reply to #3)
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Brian Fairchild wrote:
Proper 5V supplies are cheap ...
inexpensive (may you pardon a pedantic)

Cheap wall warts are a personal bane.

 

"Dare to be naïve." - Buckminster Fuller

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Brian Fairchild
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Posted by Brian Fairchild: Mon. May 31, 2021 - 02:13 PM
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gchapman wrote:

Brian Fairchild wrote:
Proper 5V supplies are cheap ...
inexpensive (may you pardon a pedantic)

 

I've consulted Professor Trask and he suggests I choose a different word to avoid any ambiguity. So...

 

Proper 5V supplies are readily available at a sensible price.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

Last Edited: Mon. May 31, 2021 - 02:18 PM
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ki0bk
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Posted by ki0bk: Mon. May 31, 2021 - 08:20 PM
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Don’t confuse devices made for battery charging with power supplies, they are not always interchangeable.

You maybe able to charge a battery with a power supply, although that will depend on battery chemistry, but you can seldom use a charger as a project power source, at least not with out some way to regulate the voltage, current or both, so use the the proper device for project.  5v power sources are abundant, you should not have any trouble finding somethig to fit your needs in your price range.

jim

 

FF = PI > S.E.T

 

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