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Topic: Does an IR LED on PWM need a Resistor? (Read 717 times) previous topic - next topic

Ardalan

Hi there, I am  using an TX IR LED on Arduino Uno digital pin 3 PWM.

​Does the IR LED on PWM need a Resistor?​

I am looking for max range

Paul_KD7HB

Hi there, I am  using an TX IR LED on Arduino Uno digital pin 3 PWM.

​Does the IR LED on PWM need a Resistor?​

I am looking for max range
Any LED is a current driven device. The junction temperature goes up as the current increases and the internal resistance goes down, so It draws more current and quickly dies. The series resistor limits the current to the LED so the run away does not happen.

If you want max range, work on the receiving end.

Paul

TonyWilk

Does the IR LED on PWM need a Resistor?
Yes.
On an Arduino UNO the minimum resistor value will be approx 82 Ohms giving around 40mA to drive the LED.

( 5V - 1.5VLED) /0.04 Apin max = 82 Ohms (nearest resistor value)


Yours,
 TonyWilk

Ardalan


INTP

Why starve the LED with 40mA when it can handle 1000mA?

TonyWilk

Why starve the LED with 40mA when it can handle 1000mA?
Maybe because until you tell the OP which LED to use, the conditions under which it can handle 1A and a failsafe driver circuit to build, they are stuck with driving it directly from a pin.

Yours,
  TonyWilk

Wawa

Two IR LEDs in series, with e.g. a 47ohm CL resistor, might give you some more range.
Leo..

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