Why I should us a transistor to drive an IR LED?

I see many schematics which use the following circuitry:

enter image description here

If I connect the IR LED directly to an Arduino digital pin, it works. But with the transistor circuit, it works better.

Why is that?

(my value of R2 is just for show)

  • 3
    \$\begingroup\$ Works, but better? In what way? \$\endgroup\$
    – Finbarr
    Apr 30 '19 at 22:48
  • \$\begingroup\$ Do you understand how a transistor behaves? Please try to ask a more specific question. \$\endgroup\$ Apr 30 '19 at 23:07
  • \$\begingroup\$ Do you the Vol/Iol=R? from specs of the Arduino ( ~25 Ohms ) and the transistor Vol/Iol=Rce ? It seems you want 100mA but don't know how to get it from Ohm's Law with Ic/Ib=10 \$\endgroup\$ Apr 30 '19 at 23:46
  • \$\begingroup\$ With transistor, it has better range - I can control TV/radio with IR waves from more length than with - just LED. Why is that? \$\endgroup\$ May 1 '19 at 11:32

The quick answer is that a transistor can provide more current than an arduino pin. This makes the LED emit more light.

There are complexities, however. Take a look other questions here and here for examples of the necessary considerations and calculations.

  • \$\begingroup\$ Hi, I try this schematic without resistor behind LED. Is it a problem? \$\endgroup\$ May 21 '19 at 22:18

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