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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.enter image description here

R1 = 1k

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    Yes, it can, as long as it can provide the needed current. And be sure to not let the LED current through the Arduino. Connect the led circuit directly to your power supply
    – chrisl
    Apr 9 at 19:08
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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.

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  • Thank you, yes, the leds have a resistor connected I just didn't draw it, didn't realize it could be confusing for someone seeing it. Thanks for the tip on the transtor, what would be the problem with this one?
    – SantiMar
    Apr 9 at 21:08
  • This transistor will dissipate about 0.2 W of power and may be slightly warm.
    – Boffin
    Apr 9 at 21:26
  • can you use a npn transistor high side like that from the MCU? IT would seem to be a voltage follower, 0.6v below Vcc. Much better to switch on the low side...
    – dandavis
    Apr 10 at 18:43

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