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My phone charger (Male wall adapter to female USB) says it outputs 5V @ 2A on the back. I want to use it to plug a Male USB into.

I guess my question is; is that 2A always being output? Or is it a maximum of 2A?

I have a homemade project, that is simply 10 RGB LEDs with 5V going to the common anodes (parallel), and only the R and B are going to 200 ohm resistors going to ground to show purple light.

I tested this with the USB cable in my computer, but I want to make sure it's safe to use with this phone adapter before I plug it in. Thanks!

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Current is dependant on voltage. If you have a small load it will draw a lot of current, if you have a large load it will draw small current. The 5V @ 2A indicates that it's rated to handle up to 2A at 5V. The other day I took an old phone wall charger (similar idea), made sure that the RGB LED's didn't go over their rated voltage and plugged it in! If you think 5V is too much you can always add a resistor in series with your LED's. Hope that helps! Josh

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  • \$\begingroup\$ In normal usage, you would say that a large load would draw more current. I've not seen your usage where you are using the load's relative resistance to describe the "size of a load". \$\endgroup\$
    – DoxyLover
    Jul 7 '15 at 1:54
  • \$\begingroup\$ Yeah I thought of that after I posted. I was referring to a large impedance load. But I do understand the confusion. \$\endgroup\$
    – Josh Jobin
    Jul 7 '15 at 1:58
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The current rating on a power supply is the maximum current that it is designed to supply.

Any load you connect to the supply will only draw the current that it (the load) requires. The supply does not force its full rated current through the load.

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Josh is right and to expand on his answer. The 2A is the maximum current draw allowed by your wall wart. Your PC will allow probably 0.5A or 0.9A depending on the USB version. So this implies your RGB project is working fine with under 1A therefore it will be ok with the wall wart. To work it out properly you should use Ohms law I=V/R Where I is the current in amps, V is the voltage and R is the resistance in Ohms. Not exactly sure how your circuit is laid out so if you want to supply a Schematic diagram we can help you calculate the exact current required.

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5 volts constant at 2 amperes is maximum rating. You may have a load that consumes less current.

5 x 2 = 10 watts = rate of change of Energy (the more is it, the more powerful is the device)

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