user76022: I've need to control some leds which draw 300mA with an arduino (actually an atmega) and after some searching I think the following is the circuit I need, but I'm not really sure if the power source for the LEDs can be the same as for the arduino.
R1 = 1k

user76035: If the power supply has sufficient power and voltage stability, you can use it to power the LED and Arduino. However, the circuit is not entirely correct on the LED side, a current limiting resistor should be used in series with the LED. I would also recommend using a more powerful bipolar transistor or field effect transistor.

76022: <p>I've need to control some leds which draw 300mA with an arduino (actually an atmega) and after some searching I think the following is the circuit I need, but I'm not really sure if the power source for the LEDs can be the same as for the arduino.<a href="https://i.stack.imgur.com/PaQyn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PaQyn.png" alt="enter image description here" /></a></p>
<p>R1 = 1k</p>
 76035: <p>If the power supply has sufficient power and voltage stability, you can use it to power the LED and Arduino. However, the circuit is not entirely correct on the LED side, a current limiting resistor should be used in series with the LED. I would also recommend using a more powerful bipolar transistor or field effect transistor.</p>
