first time here. I've been working on developing a 3-port USB charging circuit coming out of a 120VAC wall outlet. Here is a basic schematic of what I'm following.

Charging Schematic

I've been having some trouble with finding a a transformer that allows enough amperage for my system (5V @ 2A through each USB) as well as understanding if all I need is a transformer and a rectifier or if I need some sort of controller chip. Here is a schematic of the TI chip I will be using for each USB port. I don't quite understand where the FB connects to at the converter.

TI Chip Schematic

Any feedback or advice is much appreciated!

  • \$\begingroup\$ Your first problem is that you've only specified a 1A fuse! In addition, you'll fry the voltage regulator - why use a 12V transformer when you only want 5V out? \$\endgroup\$ – Simon B May 17 '16 at 15:49
  • \$\begingroup\$ "FB" is "feedback" - the DC converter in the example uses a feedback input to sense the voltage at the TPS2511 and compensate for losses in the wiring between the regulator and the TPS2511. Your simple 7805 doesn't have a feedback input. \$\endgroup\$ – JRE May 17 '16 at 15:54
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    \$\begingroup\$ Today's solutions for this using switching power supplies, not the linear supply topology you have drawn, especially if you want 2 amps out. Trying to do this with a linear circuit is not recommended - as you are finding, common transformers won't provide that, and neither will a 7805. \$\endgroup\$ – Chris Stratton May 17 '16 at 22:21

Honestly it looks like you're just slapdashing circuits together that you found on the web.

Look at the AC supply section. You're getting something like 17V peak out of that transformer-rectifier-cap combo. Feeding that into a resistive voltage regulator that must drop 12V at 6A draw, so you'll be dissipating 72W. Gonna have water cooling on that 7805?

You are better off simply buying an off-the-shelf 120V to 5V power supply (you can even get multi-voltage ones that use switching power supplies, in fact, a PC power supply is basically that). And then put the circuit from the lower diagram on that.


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