brightness of the led connected to the stm ic pin reduces.

[Amal Babu]

Hai I have a simple design.I am using STM32F051R4T6TR.I just connected a led such that the led sinks the 20mA current when the led turns on.i happen to notice that each time i switch on my board the brightness of my led is getting reduced.this happened to me many times.The Led turns on with full brightness at first but later on after multiple turn on's the brightness is gradually decreasing and finally thebrightnessis too di, which would ultimately led to changing of the led.What would be the possible reason behind this? Can Anyone suggest me a reason behind this?Will this issue be cleared if i drive an led by sourcing from the pin rather than sinking?

[T J]

I dont like to drive too hard from the processor pin, it does affect the A/Ds in some configurations,

however with super bright LEDs, you can get down to 2mA and still see the led easily...

@20mA I guess the LED is getting hot, it will die one day..

[T J]

best to use a transistor like BC817 then you can drive 100mA..

[Tesla DeLorean]

How exactly do you have them wired? Do you have a series resistor to limit current?

[Amal Babu]

yes i have placed a series resistance

[T J]

1K ohm is 1mA per volt, less the LED forward voltage drop , 1-2mA... good enough for super brights