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Topic: Can I use a smaller resistor to make a PWM LED brighter (Read 136 times) previous topic - next topic

sparkie2u

I'm making a little gizmo that uses an arduino UNO to produce a 6.25kHz pulse that lasts for .165 seconds and repeats every 1.3 seconds. I installed an LED to indicate that the pulse pattern is working. My problem is that the LED is maybe half as bright as it should be and I assume that's because the pulse is emulating what a PWM does to control electric motors. If I'm right, my question is can I use a lower value resistor for the LED to allow more current to flow thus making the LED brighter? If so, how would I go about calculating the proper resistor value? The LED is not powered from the UNO, but from a separate 5v source.

Grumpy_Mike

You need to see what the maximum LED current is for your LED. Contrary to popular belief you should not exceed the maximum continuous current rating on a pulsed LED unless the data sheet has a pulsed current rating.

To calculate a resistor take the supply voltage and subtract the LED's forward voltage from it. Use the resulting voltage and divide it by the required current to get the resistor value.

You can always get an ultra bright LED if things are not bright enough for you. White LEDs are especially bright on very little current

Paul__B

So you think asking a question without giving any details is clever?

  • Circuit schematic.
  • Specification of all parts.
  • Specifically, the resistor value in question.

sparkie2u

Thank you Grumpy_Mike. Your answer to my simple question that I shouldn't exceed an LED's rated current even when pulsed was exactly what I needed to know. And thanks for your suggestion of using white LED's, I will give that a try.

sparkie2u

Paul__B - No sir, I was not trying to be 'clever' as you put it. Perhaps I should have worded my question differently, as it was basically if I could use a lower value resistor to increase current to a pulsed LED. I felt the question was fairly generic and didn't require a specific schematic since a pulsed LED could be used in many different applications. I apologize for my stupidity and will certainly provide all the information you suggested in any future posts.

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