Constant current IR LED circuit

An area for more general discussion by the user community for topics not covered elsewhere
User avatar
AnalysIR
Site Admin
Posts: 742
Joined: Sat Aug 31, 2013 3:51 pm
Location: Dublin, Ireland
Contact:

Re: Constant current IR LED circuit

Post by AnalysIR »

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

Remax79
Posts: 1
Joined: Sat Jan 23, 2021 10:41 am

Re: Constant current IR LED circuit

Post by Remax79 »

AnalysIR wrote:
Sun Jan 10, 2021 4:48 pm
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


nibbler
Posts: 4
Joined: Sat Jul 23, 2022 9:39 am

Re: Constant current IR LED circuit

Post by 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.

User avatar
AnalysIR
Site Admin
Posts: 742
Joined: Sat Aug 31, 2013 3:51 pm
Location: Dublin, Ireland
Contact:

Re: Constant current IR LED circuit

Post by AnalysIR »

nibbler wrote:
Sat Jul 23, 2022 9:50 am
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
Posts: 4
Joined: Sat Jul 23, 2022 9:39 am

Re: Constant current IR LED circuit

Post by 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?

User avatar
AnalysIR
Site Admin
Posts: 742
Joined: Sat Aug 31, 2013 3:51 pm
Location: Dublin, Ireland
Contact:

Re: Constant current IR LED circuit

Post by AnalysIR »

nibbler wrote:
Sat Jul 23, 2022 6:04 pm
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
Posts: 4
Joined: Sat Jul 23, 2022 9:39 am

Re: Constant current IR LED circuit

Post by nibbler »

Okay good to know. So as long as the power source can provide the amperage I could add even more LED?
Schematic attached...
You do not have the required permissions to view the files attached to this post.

User avatar
AnalysIR
Site Admin
Posts: 742
Joined: Sat Aug 31, 2013 3:51 pm
Location: Dublin, Ireland
Contact:

Re: Constant current IR LED circuit

Post by AnalysIR »

nibbler wrote:
Mon Jul 25, 2022 8:36 am
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
Posts: 4
Joined: Sat Jul 23, 2022 9:39 am

Re: Constant current IR LED circuit

Post by nibbler »

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

Post Reply