Sascha Krüger

Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

11 years, 8 months ago.

how high is the max current on DigitalOut?

hey guys,

i will 4 Led´s connected on PIN17, 18 19 and 20 as DigitalOut.

one LED had 20mA. is that possible? or i need a mosfet?

thanks for your answers

2 Answers

Kyle Cassar
11 years, 8 months ago.

40mA each digital out. You will have no problems without a FET. You need to limit the current through the led.

Vs-Vdrop/ 16 mA will work your resistor value out.

All you need to know can be found here https://mbed.org/handbook/mbed-NXP-LPC1768 (assuming you are using 1768)

posted by Kyle Cassar 08 Apr 2013
Gert van der Knokke
11 years, 8 months ago.

From the handbook:

Quote:

Digital IO pins are 3.3v, 4mA each, 400mA max total

The 40 mA (at high level -45 mA) is the 'short circuit' current and not the constant current. You might stretch it a bit, I have done 20 mA on the I2S output without problems but no guarantees.. Better put a FET in.

Thanks for pointing out my mistake......listen to Gert! :-)

posted by Kyle Cassar 09 Apr 2013