1. Home
  2. Electronics Design
  3. USB DC Converter

USB DC Converter

I'm very inexperience with electronics so these might be simple questions. I want to make a converter so I can use a USB port to charge my phone (I'm around USB ports a lot). A USB port should be

5V--500mA and my phone needs (according to the wall charger) 4.8V--350mA.

I was looking for solutions and I'm guessing I need a voltage divider? Messing with the numbers it's hard to get the current and voltage exactly right. Is it worse to be over or under those numbers (voltage & current)? Also, which is more important to get exactly right?

Reply to
TastyWheat
Loading thread data ...

What kind of connector does your phone use for the power/charging?

Reply to
a7yvm109gf5d1

Reply to
TastyWheat

You can buy one of these things from 3rd party suppliers for around $10-20 including a bunch of adapters for the phone side. I suspect these particular ones are nothing more than a cable.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

Except that the USB port only supplies 100mA by default and one has to ASK before drawing 500mA. Some hubs/operating systems even shutdown the port if a device draws more than it has been allowed to.

Reply to
OBones

USB ports will only supply 100mA unles the device negotiates for more. This requires an IC in the device to do the negotiation.

The voltage divider would only work if the current drawn by the phone was constant. It won't be (that 350mA is a maximum, not a constant value), so when your phone drew a lot of current the voltage would be too low and when it drew little current it would be too high. You'd need to use a voltage regulator, one with extremely low dropout.

Finding the right parts and putting them together would be hard work. I suspect the USB IC would be surface-mount only, for example. USB phone chargers are cheap, less than the price of the parts in small quantities to make a one-off. Buy one. Buy two and take one apart if you're interested, but it's really not something worth making yourself.

Tim

Reply to
Tim Auton

Indeed, and *every* USB-powered device ever produced conforms 100% to that specification.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

formatting link

Reply to
Homer J Simpson

Usually when I search I come up with a plain USB cable which doesn't charge the phone (although they may say it does). I did see this one though, which has a USB port on one side and the cylinder plug on the other:

formatting link

I'm totally happy with NOT building one, but I assumed they didn't make them.

Reply to
TastyWheat

Well, if you look at the picture of the charger it looks like it goes straight from the USB port to the phone. Do you think they have any resistors or capacitors or whatever in that little thing?

Reply to
TastyWheat

Possibly.

--

++++++++++++++++++++++++++++++++++++++++++++++++++++
  • Required crap appended to avoid restrictions imposed by brain +
  • damaged idiots.
+
  • Server Response: '441 Posting Failed (Rejected by POST filter)', +
  • Port: 119, Secure(SSL): No, Server Error: 441,
+
  • Error Number: 0x800CCCA9
+ ++++++++++++++++++++++++++++++++++++++++++++++++++++
Reply to
Homer J Simpson

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.