Constant current IR LED circuit

[AnalysIR]

First thing to check is if you have the x1 and x10 setting correct on your scope & pobes????

[Remax79]

First thing to check is if you have the x1 and x10 setting correct on your scope & pobes Regroupement de prêt immo ????

You're right

[AnalysIR]

Thanks for the update!

[nibbler]

Hello to AnalysIR,

I rebuild your "one LED version" circuit (thanks for this work and inspiration!) but as a electronic clumsy I was wondering what the point of the R2 actually could be. I am currently driving this one with an ESP32, so available current that can be drawn is limited but at which point this could be risky for the MC? A 500 Ohm or lower resistor increases the range drastically. How can I calculate how low I can go without damaging anything?

br
n.

[AnalysIR]

I rebuild your "one LED version" circuit (thanks for this work and inspiration!) but as a electronic clumsy I was wondering what the point of the R2 actually could be. I am currently driving this one with an ESP32, so available current that can be drawn is limited but at which point this could be risky for the MC? A 500 Ohm or lower resistor increases the range drastically. How can I calculate how low I can go without damaging anything?

Difficult to say without seeing your exact schematic and components used. However I would guess that 300R would be OK for the base resistor..

If you use the dual IR LED emitters you essentially get double the IR output for free!

[nibbler]

I used a TIP120 as transistor, apart from that just like your circuit and a LD 274-3 IR diode.

Double the output? Couldn´t I get more power to each LED in a parallel circuit?

[AnalysIR]

I used a TIP120 as transistor, apart from that just like your circuit and a LD 274-3 IR diode.

Double the output? Couldn´t I get more power to each LED in a parallel circuit?

If the leds are in series and connected to 5V, then the same current goes thru both. If you only have 1 LED in series there is more voltage drop across the transistor which is dissipated in the form of heat.

If you cant provide a schematic. then just draw it by hand and post a photo of it and a photo of your wiring..

[nibbler]

Okay good to know. So as long as the power source can provide the amperage I could add even more LED?
Schematic attached...

[AnalysIR]

Okay good to know. So as long as the power source can provide the amperage I could add even more LED?

IN this circuit it is also about voltage drop. With a Vcc of 5V you can easily put 2 IR LEDs in series (a 3rd might be an issue).

regarding your schematic....

You should have a resistor on the emitter as in the original circuit. You can play around with resistor values to suit.

Regarding the base resistor: Vgpio = 3.3V, Vbase = 1.2. Assume max GPIO current for ESP32 = 12mA (0.012A)

so your base resistor = (3.3 - 1.2) / 0.012 = 175R (minimum value)

As above, I usually use 300R as the base resistor. 220R would also be OK.

You can measure the IR current by the voltage of the emitter resistor (using ohms law). Then by adjusting the value of this resistor you can alter the IR current. In the circuit using 2 IR LEDs in series has no material penalty and gets you double the IR output.

[nibbler]

Thanks alot, I´ll alter the circuit according to that.