I would like to make an universal USB charger. I have a 5V, 2A max generator and I can not find any electronic assembly to create a Dedicated Charging Port able to charge Samsung, Apple and other devices.

I read the entire USB Battery Charging Specification and in my case, I need to meet Dedicated Charging Port tests.

It means:

a) Have a 200 ohms resistance between D+ and D- 
b) Have a leakage current from D+/D- ≤ 300 Kohms tied to a voltage between 0 & 3.6V 
c) Have a capacitance from D+/D- of 1nF 
d) Have VBUS discharge functionality 

But It appears that most things do not even met these specification as shown in this other topic: USB downstream port examples.

So which one to choose?

  • \$\begingroup\$ This would be a better question if it focussed on one point. Right now you're asking for an entire circuit. \$\endgroup\$
    – David
    May 12, 2015 at 17:46
  • \$\begingroup\$ I would monitor the charge current while enabling different combinations of pull-ups and pull-downs. \$\endgroup\$
    – Matt Young
    May 12, 2015 at 17:51

1 Answer 1


Am I missing something here, but if you've got a power supply (assuming it's voltage regulated) that produces 5 volts at up to 2 Amps, all you do is cable up a USB connector don't you? Then connect the USB connector into a USB charge cable with a micro USB connector on the other end and plug into the device you want to charge. The mobile phone or gadget will take whatever current it needs up to the maximumm of 2 amps.

Is this question actually more complicated than that? Whilst different phones may have different charging algorithms to suit their particular batteries, don't they all just take in a nice steady 5V DC input as their charging source?

  • 2
    \$\begingroup\$ It is a lot more complicated than that. Most things will only charge quite slowly, and Apple things not at all. Search a bit for the USB charging specifications. It's about to get much more complicated too, with bi-directional power flow. \$\endgroup\$
    – tomnexus
    May 12, 2015 at 18:31
  • \$\begingroup\$ I've found the USB Battery Charging Specification, to be honest it looks a bit of a mess. I thought it might be a serial datastream from the charger to the mobile device, but it isn't, it's far more complicated than that, with analogue levels, pull-up resistors on various lines. There are many different scenarios described. Probably the easiest approach is find a chip that will conform to the USB Battery Charging Specification 1.2 and use that in a design. \$\endgroup\$
    – Dean
    May 12, 2015 at 19:01
  • 2
    \$\begingroup\$ @Dean1 I agree it's a mess! And Apple invents something new each generation, there are long blog posts about reverse engineering them... \$\endgroup\$
    – tomnexus
    May 12, 2015 at 20:59

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