I want to drive an 20mA rated LED directly from an IMP001 pin (configured as PWM) without using a current limiting / voltage dropping resistor in series with the LED. Default LED state will be off and PWM will be used to ramp it on and then ramp it off again.
From a practical viewpoint, will this damage the imp, or will the imp limit the current to 4mA?
The imp will try to drive harder. You really should add a resistor in there.
thanks for your reply. I’d like to not add a resistor if possible just to keep the component count down and had hoped that by choosing the PWM duty cycle carefully it would be possible that the average LED current would be no more than the 4mA. If lack of a resistor does drive the the pin harder, is it likely to damage the pin/imp?
LEDs are really not like bulbs; it’s not so much on the average current, it’s on the peak current. Remember people modulate LEDs at very high frequency.
I’d strongly advise the LED. Without it, your current is being limited by the current from the imp pin, which could exceed 20mA, damaging both the LED and possibly the imp.
Thanks Hugo. That’s clear now. The last thing I want to do is damage the imp. I thought I was hoping for too much when I was asking the question. But it was worth asking just in case.