I’m planning to use the IR barrier on a 13 V supply.
Apparently, the current flowing through the IR LED’s of the emitter are the only point of attention (LM324 of the receiver can easily function under 13V, and note that I will use the output of IC1C connected to a transistor switching 5V to a schmitt trigger input of a microcontroller instead of the original buzzer)
Could someone at Velleman please tell me which type of IR LED’s are used in this minikit, so that I can find the maximum allowed current they can withstand ? (So that I can determine if I have to change the value of the series resistor R6 or not).
So, for a drop of 0.5 V between C and E of the transistor, a power supply of 13 V (= 12.5 V after D1), a UF of 1.2 V for each LED, I’ve got 9.6 V on R6.
So R6 should be 470 ohms to limit the current to approx. 20mA. Right ?
But apparently, with the original design of the transmitter (R6 = 82 ohms, supply= 9V, or 8.5 V after D1), I’ve got a max current of more than 60 mA, which exceeds by far maximum allowed current for the LED’s… :shock: Am I wrong ? If so, my 470 ohms resistance could also be less ?
(Note that in my application, the transmitter would be on 24 hours a day, and distance between Tx and Rx will be exactly 1 meter, in a place were no direct sunlight could interfere, and with tiny reflectors on both IR LED’s and photo-transistor; so I’d prefer to play it safe with the LED current…)
Datasheet always mentions continuous current. Pulsed current can be a lot higher, sometimes up to 1A with a very small duty cycle. Keep the current as low as possible, to optimise energy consumption, while still achieving correct operation under all circumstances.