High power IR transmitter

Other Hardware LEDs and Multiplexing
1

I want to build a high power IR transmitter with 3 TSAL6100 LED, as transistor I want to use PN2222TA (I also have 2N3904).

I want to drive LEDs at 100mA (or 150mA -> the specification says that max peak current is 200mA). There is no constant lighting, because this would be a remote controller.

Based on this article I calculated resistors and draw this circuit:

What do you think about it? It is calculated correctly? Also it is ok to connect LEDs in series, or I would benefit more from connecting LEDs parallely?

I am not an electric engineer, just trying to build this thing to control my IR devices. :slight_smile:

irccircuit.jpg
irccircuit.jpg1035×582 71 KB

2

No it is not calculated correctly.
The three LEDs up in seriese do not take three times 100mA but just 100mA.
The base current calculation is totally wrong just use a 470R resistor.

3

Thanks for the answer. Could you please help me with the calculation? I want to calculate for various scenes LED @ 100, 150, 200mA.

If 3 LED does not take 300mA, then R1 should be:

R1=0.95V/0.100=9.5Ohm

If base resistor calculation was totally wrong, how do I calculate correctly? The formula is wrong?

4

100ma goes through the leds which are in series.
Use 100ma not 300ma.

I would urge you to use 1 resistor for each led then put these 3 strings in parallel.

.

5

If 3 LED does not take 300mA, then R1 should be:

R1=0.95V/0.100=9.5Ohm

Well yes and no. From a strictly arithmetical point of view yes.
But 9R5 is too low to act as a current regulator in the face of an unstable forward voltage that the diodes presents. That voltage will change with age, temperature and from LED to LED, so your calculations are vastly over simplified. That will result in under driving or over driving of the LEDs and maybe both as the system warms up.
Solutions:-

  1. Follow LarryD's advice
  2. Have a voltage than 5V drive it
  3. Get a constant current circuit to drive it.

If base resistor calculation was totally wrong, how do I calculate correctly?

Look in the data sheet and find the base current that will "saturate" that transistor.
Then use R = (5.0 - 0.7)/Isat

6

Thanks for the help. I built the circuit on LarryD's advice and works well. Excep that it must be directly pointed to the receiver (AC unit), I think I must find LED with wider beam. Could you recommend any LED like this?