12 Volt USB Adapters - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

GMB · 23rd Jun 2020, 10:20 am

Yes, it seems there is a later spec. for crude power on USB connectors that came along after I stopped designing USB hosts!

Looking at the spec. which to me is quite hard to follow and appears to have been cooked up after some manufacturers had already started doing their own thing, if your thing shorts the data pins together then it is declaring itself to be a "Dedicated Charging Port".

Given that then I think I would expect it to be able to supply 4.75V at 500mA. Over that it seems to get a bit complicated as there seems to be an assumption that you are charging a battery so the voltage only needs to be enough for that, which could mean as little as 2V at 1.5A.

So what are you finding the voltage to be as you load them up beyond 250mA? (And I presume you are just using a resistive load as they might legally go into a current-limit state if the inrush is high).

Superscope · 23rd Jun 2020, 11:04 am

Once you go past 200mA (With a 12 volt input) the Voltage starts to drop significantly.

The maximum current I got out of it was about 450mA but the Voltage had fallen below 2 Volts.

Yes, I was using a resistive Load.

From the reading I have done since yesterday, it has been suggested that joining Pins 2 and 3
together simply tells the Device plugged in (or is supposed to tell the device)
that the Host can provide up to 1 A.
I have no idea if this is indeed correct, but it was mentioned in several places.

So, in short (excuse the Pun), there is no communication from the Device to the Host.
The communication is only from the Host, simply telling the Device what it can handle. That can be Resistance references between the D pins & 0v or 5v or a Short between the Two D pins.

This is only relevant to universal USB Hosts like the one I am discussing.
Manufacturers like Samsung and Apple could be doing anything within their own products.

I have found quite a few Teardowns on Youtube with these Universal Adapters, and even one
with a £1 Adapter from the Poundshop.
Most actually seem to work.
Just obviously not cheap ubiquitous one I had clearly.

But on the plus side, I have been pointed in a better direction with those other
more profession DC to DC converters and in Hindsight, these will clearly be a safer option anyway.

Ian

trsomian · 23rd Jun 2020, 11:17 am

I think that the circuit diagram provided by Terry in #18 is missing a link from pin 4 to 0V

Terry_VK5TM · 23rd Jun 2020, 12:19 pm

Checked the datasheet and yes, pin 4 should go to ground in this case (there are other configurations where it is connected to the v-out line).

PJL · 25th Jun 2020, 6:14 pm

The 12v USB supply I ordered looks like it will run OK down to 7V and maybe below. It is for powering a USB bluetooth adaptor so a schottky diode off the 6.3V and a capacitor will have it working although I will be adding a little amplifier as the volume is very low. It will end up as a string of chinese made bits.

jamesperrett · 26th Jun 2020, 12:38 am

For the times when I've needed a more efficient version of a 78xx regulator I've found the Traco TSR-1 series to work well. Not as cheap but they always seemed reliable.

23rd Jun 2020, 10:20 am	#21
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: 12 Volt USB Adapters Yes, it seems there is a later spec. for crude power on USB connectors that came along after I stopped designing USB hosts! Looking at the spec. which to me is quite hard to follow and appears to have been cooked up after some manufacturers had already started doing their own thing, if your thing shorts the data pins together then it is declaring itself to be a "Dedicated Charging Port". Given that then I think I would expect it to be able to supply 4.75V at 500mA. Over that it seems to get a bit complicated as there seems to be an assumption that you are charging a battery so the voltage only needs to be enough for that, which could mean as little as 2V at 1.5A. So what are you finding the voltage to be as you load them up beyond 250mA? (And I presume you are just using a resistive load as they might legally go into a current-limit state if the inrush is high).

23rd Jun 2020, 11:04 am	#22
Superscope Octode Join Date: May 2017 Location: St Austell, Cornwall, UK. Posts: 1,018	Re: 12 Volt USB Adapters Once you go past 200mA (With a 12 volt input) the Voltage starts to drop significantly. The maximum current I got out of it was about 450mA but the Voltage had fallen below 2 Volts. Yes, I was using a resistive Load. From the reading I have done since yesterday, it has been suggested that joining Pins 2 and 3 together simply tells the Device plugged in (or is supposed to tell the device) that the Host can provide up to 1 A. I have no idea if this is indeed correct, but it was mentioned in several places. So, in short (excuse the Pun), there is no communication from the Device to the Host. The communication is only from the Host, simply telling the Device what it can handle. That can be Resistance references between the D pins & 0v or 5v or a Short between the Two D pins. This is only relevant to universal USB Hosts like the one I am discussing. Manufacturers like Samsung and Apple could be doing anything within their own products. I have found quite a few Teardowns on Youtube with these Universal Adapters, and even one with a £1 Adapter from the Poundshop. Most actually seem to work. Just obviously not cheap ubiquitous one I had clearly. But on the plus side, I have been pointed in a better direction with those other more profession DC to DC converters and in Hindsight, these will clearly be a safer option anyway. Ian

23rd Jun 2020, 11:17 am	#23
trsomian Hexode Join Date: Oct 2010 Location: Box End, Beds. UK. Posts: 271	Re: 12 Volt USB Adapters I think that the circuit diagram provided by Terry in #18 is missing a link from pin 4 to 0V

23rd Jun 2020, 12:19 pm	#24
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,340	Re: 12 Volt USB Adapters Checked the datasheet and yes, pin 4 should go to ground in this case (there are other configurations where it is connected to the v-out line). __________________ Terry VK5TM https://www.vk5tm.com/

25th Jun 2020, 6:14 pm	#25
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 12 Volt USB Adapters The 12v USB supply I ordered looks like it will run OK down to 7V and maybe below. It is for powering a USB bluetooth adaptor so a schottky diode off the 6.3V and a capacitor will have it working although I will be adding a little amplifier as the volume is very low. It will end up as a string of chinese made bits.

26th Jun 2020, 12:38 am	#26
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,875	Re: 12 Volt USB Adapters For the times when I've needed a more efficient version of a 78xx regulator I've found the Traco TSR-1 series to work well. Not as cheap but they always seemed reliable.