# Arduino uno voltage regulator

Hi “arduinonians” , how much current can the arduino uno voltage regulator handle ? I just bought a dc power supply rated 9v, 1A and I want to use it to power up a project with the uno that will draw up to 700mA. Can I use the power supply I bought ?

Assuming you are drawing the current from the 5v line (which is the o/p of the linear regulator) you'll probably shutdown the regulator due to heat.

9v - 5v = 4V drop @ 700mA = 2.8 Watts....
The regulator would get too hot and shutdown - it needs to be around 1watt max for safety...

.. Ken

You will almost certainly need a separate voltage regulator if you want lots of current at 5V.

If the main load can work at 9V then run it from 9V, it will simplify things.

Thanks for the response. So what you guys are saying is that even if I power up the uno externally with a 9V, 1A supply, I can not draw up to 700mA from the board. Then what is the maximum current that I can draw from the board safely if I power it up with the 9V power adapter ?

malgwi, you'll want to try to keep the power to no more than 1 watt...

Max Current You Can Draw = 1(watt) / (Supply Voltage - 5v)

So, 1w / (9v-5v) = 1w / 4v = 250mA

You might want to look at a DC-DC (Buck) Converter - this would be more efficient than the built in linear converter and allow you to draw more current.

.. Ken

Thanks Ken, I now get it.

Hi! This is quite old posting but one question came to my mind.

What if using 7 V as a power supply, wouldn't it then be possible to get 500 mA instead 250 mA because

P = U * I
P = (7-5 V) * 0,5 A
P = 1 Wat (still safe, regulator wouldn't heat too much!)

So 2 V voltage drop would make it possible to get 500 mA (and with 1 V voltage drop even 1 A). What am I missing here?